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TheArsenal
2011-12-04, 05:50 PM
By leaving notes into the past telling to go to the past and give yourself a note to do the above to your past self in the future?

Lord Raziere
2011-12-04, 05:51 PM
Depends. Can you fall up? Can you reverse entropy? Can you disarm a bomb by setting it on fire so that its triggering mechanism is safely burned away?

Mewtarthio
2011-12-04, 06:00 PM
A paradox isn't something that gets "fixed." It's something that logically cannot exist in the first place.

Arrghus
2011-12-04, 06:11 PM
A paradox isn't something that gets "fixed." It's something that logically cannot exist in the first place.
Going by real-world logic and science, yes.

Going by your typical media logic, the OP's suggestion's a pretty cool way to keep the time monkeys off your lawn, whether your universe works by Gargoyles-style predestination or Back to the Future/Doctor Who-esque semicoherent nonsense.

That is to say, it can certainly be worked into a story and allow for cool and interesting plot developments given a setting with sufficient incentive to keep time travel in neat, stable/semi-stable loops. Like evil time monkeys from space.

Kindablue
2011-12-04, 06:13 PM
A paradox isn't something that gets "fixed." It's something that logically cannot exist in the first place.

But that situation isn't really paradoxical (if I'm reading it correctly), so it can't be fixed because it wasn't broken in the first place.

Nerd-o-rama
2011-12-04, 06:17 PM
If you can "fix" it, it was/will/is never be a paradox in the first place.

Jade Dragon
2011-12-04, 06:21 PM
It's like in book 3 of Harry Potter, where Harry gets hit in the back of his head by a rock while in Hagrid's hut, then when they use the time turner, Hermione does some quick thinking and throws a rock at Harry when he's in the hut, and how later Harry saves himself.

So the events didn't change from what happened before they had time traveled, they just changed from if they hadn't.

Kindablue
2011-12-04, 06:21 PM
If you can "fix" it, it was/will/is never be a paradox in the first place.

Exactly, assuming that the universe makes sense in the first place.

Cespenar
2011-12-04, 06:23 PM
People really need to stop thinking about messing with time. It's getting a bit... old.

Triscuitable
2011-12-04, 06:26 PM
People really need to stop thinking about messing with time. It's getting a bit... old.

http://images3.wikia.nocookie.net/__cb20090805053044/tardis/images/a/a3/Timey-wimey.png

Never will it be considered "old".

chiasaur11
2011-12-04, 06:29 PM
It all depends on if there's a madman in tweed and a bow tie around to set things right.

warty goblin
2011-12-04, 06:48 PM
A paradox isn't something that gets "fixed." It's something that logically cannot exist in the first place.

Although Godel demonstrated that for any system complex enough to be particularly interesting, logical consistency is a faith statement - the only systems that can prove their own consistency are in fact inconsistent.

Thus the question reduces to whether or not you believe paradoxes (in the sense of A and not A being true) are impossible or not. Logic can't answer the question except by assumption.

Forum Explorer
2011-12-04, 07:02 PM
By leaving notes into the past telling to go to the past and give yourself a note to do the above to your past self in the future?

Yes and This is how you do it. (http://xkcd.com/716/)

Anderlith
2011-12-04, 07:07 PM
Logically, you cannot change the past. If you step on a butterfly, then that butterfly was supposed to be stepped on.

Weezer
2011-12-04, 07:08 PM
Logically, you cannot change the past. If you step on a butterfly, then that butterfly was supposed to be stepped on.

That only holds true if you think the universe is deterministic and absent of free will.

Orzel
2011-12-04, 07:09 PM
Yes, a time paradox be fixed.

You just need supernatural powers.

Good luck getting those.

Raddish
2011-12-04, 07:37 PM
I find most time paradoxes are fixed with super glue, just apply to both edges and hold together for 30 seconds and it should be securely fastened. Jus make sure not to stick yourself to the paradox, it can be difficult to get your fingers/arms/tongue free.

Traab
2011-12-04, 08:21 PM
That only holds true if you think the universe is deterministic and absent of free will.

Just because the universe knows what the choices will be doesnt mean you lack the free will to make them. Good old rock (http://www.youtube.com/watch?v=NMxzU6hxrNA) Does bart have no free will just because lisa knows what he is going to choose?

Tiki Snakes
2011-12-04, 08:26 PM
Just because the universe knows what the choices will be doesnt mean you lack the free will to make them. Good old rock (http://www.youtube.com/watch?v=NMxzU6hxrNA) Does bart have no free will just because lisa knows what he is going to choose?

But if she does know and tells him, then he might not. If he cannot even with extra evidence to work with change his actions, then does he really have free will?

Weezer
2011-12-04, 08:40 PM
Just because the universe knows what the choices will be doesnt mean you lack the free will to make them. Good old rock (http://www.youtube.com/watch?v=NMxzU6hxrNA) Does bart have no free will just because lisa knows what he is going to choose?

I'm aware of that, it's just that Anderlith's point requires both a deterministic universe (so that the butterfly is 'supposed' to be stepped on) and a lack of free will (it's impossible to change). If free will was present then it would be possible to choose not to step on the butterfly, which in his view of time travel it is not possible to do.

Traab
2011-12-04, 08:47 PM
But if she does know and tells him, then he might not. If he cannot even with extra evidence to work with change his actions, then does he really have free will?

And if everything leading up to it had happened differently, maybe something different would have happened as well. That was just an example of how a deterministic universe doesnt necessarily mean free will doesnt exist. Knowing what the choice will be doesnt deny him the chance to make it.

The simpsons example was just grossly simplified. If the universe really is under such rigid control that it has already determined how everything everywhere will happen, then it has also determined how to make the outcomes that it has determined will happen, happen. Just like how, by keeping her trap shut, lisa was able to determine exactly what barts choice was going to be in a game of rock paper scissors.

nolispe
2011-12-04, 08:59 PM
I'm aware of that, it's just that Anderlith's point requires both a deterministic universe (so that the butterfly is 'supposed' to be stepped on) and a lack of free will (it's impossible to change). If free will was present then it would be possible to choose not to step on the butterfly, which in his view of time travel it is not possible to do.

Well, in his defense, Free Will is a dodgy concept - usually we need to invoke religion to defend it, because otherwise it's simply evidenceless. So actually a deterministic universe is a completely legitimate point to take.
So I would have to agree with his version of time travel, although I do agree that if you take Free Will as an axiom you can't accept it.

And /\: Actually, a deterministic universe does wipe out Free Will, because it kills the "free" part. Also, we don't live in a deterministic universe, thank you quantum uncertainty (although this doesn't imply that Free Will is compatible with this time travel system...)

Weezer
2011-12-04, 09:12 PM
Well, in his defense, Free Will is a dodgy concept - usually we need to invoke religion to defend it, because otherwise it's simply evidenceless. So actually a deterministic universe is a completely legitimate point to take.
So I would have to agree with his version of time travel, although I do agree that if you take Free Will as an axiom you can't accept it.

And /\: Actually, a deterministic universe does wipe out Free Will, because it kills the "free" part. Also, we don't live in a deterministic universe, thank you quantum uncertainty (although this doesn't imply that Free Will is compatible with this time travel system...)

Oh, I personally agree that Free Will is a dodgy concept (though I would say we need to invoke metaphysics to defend it rather than religion, plenty of metaphysical yet non-religious defenses of free will, Sartre is a good example of it), I have just gotten in the habit of arguing based on other people's beliefs, so I termed it based on his arguments. Picked it up arguing philosophy where it works a lot better than on a forum.

Quantum uncertainty doesn't break the deterministic system where it applies to the brain and thus free will. Nothing in the brain is on a scale where quantum effects would actually make any difference. And even if you do hold that it makes the universe non-deterministic, that isn't enough for free will.

Anderlith
2011-12-04, 10:16 PM
That only holds true if you think the universe is deterministic and absent of free will.

No, see you have the free will to make what ever decisions you want, but I can & will predict them, if I am all knowing. Think about this. I throw a handful of marble on to the floor. At first this looks like chaos, but chaos is an illusion. If you need the speed, velocity, angle, density, mass, etc. of the marbles you could predict where they go.

Weezer
2011-12-04, 10:23 PM
No, see you have the free will to make what ever decisions you want, but I can & will predict them if I am all knowing.

Except then I don't have the free will to make whatever choice I want, I can only make the choices you have previously determined I make. This is one of the classic critiques of compatibalism (the idea that free will and a deterministic universe aren't mutually exclusive), that what compatibalists call free will isn't free enough. In my opinion you need to have the actual ability to choose any of our possible options to have free will and in your view we don't have that ability, we merely have the possiblity. I make a difference between having choice in potentia and having choice in actuality. Your system gives you only the first one and not the second, which is not true free will. Of course we have the illusion of free will and must act as if we have free will, but that doesn't

Jade Dragon
2011-12-04, 10:27 PM
Except then I don't have the free will to make whatever choice I want, I can only make the choices you have previously determined I make. This is one of the classic critiques of compatibalism (the idea that free will and a deterministic universe aren't mutually exclusive), that what compatibalists call free will isn't free enough. In my opinion you need to have the actual ability to choose any of our possible options to have free will and in your view we don't have that ability, we merely have the possiblity. I make a difference between having choice in potentia and having choice in actuality. Your system gives you only the first one and not the second, which is not true free will. Of course we have the illusion of free will and must act as if we have free will, but that doesn't

No, you make the choices you want to make, but the people in charge can see all the actions you'll ever take. They don't interfere, they just weave it into the tapestry.

Soras Teva Gee
2011-12-04, 10:31 PM
That only holds true if you think the universe is deterministic and absent of free will.

Actually they are completely unrelated matters. Non-linear causality is around freewill but determined by to it. Afterall if you make a decision in ignorance your freewill is still influenced by any number of factors. The problem is confusing free will (a human factor) with a law of physics. Not being omnipotent we do not have an unlimited ability to realize choices in the first place. Earth takes 365 days to orbit Sol, the sun will one day run out of hydrogen fuel, mass cannot accelerate to lightspeed.

The only trap of a deteministic universe is if you have absolutely perfect knowledge of the future not matched with the absolute omnipotence. Even then its debatable because to have perfect knowledge of the future would imply to me to know the why of a choice and thus would not do things simply because "you always did them"

With less then perfect knowledge you can choose to reject what your foreknowledge shows and attempt to prevent it. Whether or not that successful prevention is possible does not change that you still made a choice in how to deal with a situation. Which at many levels is all the choice you EVER have.

Anderlith
2011-12-04, 10:34 PM
Except then I don't have the free will to make whatever choice I want, I can only make the choices you have previously determined I make. This is one of the classic critiques of compatibalism (the idea that free will and a deterministic universe aren't mutually exclusive), that what compatibalists call free will isn't free enough. In my opinion you need to have the actual ability to choose any of our possible options to have free will and in your view we don't have that ability, we merely have the possiblity. I make a difference between having choice in potentia and having choice in actuality. Your system gives you only the first one and not the second, which is not true free will. Of course we have the illusion of free will and must act as if we have free will, but that doesn't

I'm not forcing you to do anything.

Say you looove chocolate. Say I know you love chocolate. So when you step into a candy store I know you are going to pick chocolate. Even if you had a reason not to choose chocolate, I would know why & therefore predict the new choice. In no way do I force you to do anything. I am an observer.

rpgZenMaster
2011-12-04, 10:41 PM
I'm inclined to agree with Mewtarthio, despite Godel.

Answer this: if it can't work, how does it work?

Forum Explorer
2011-12-04, 10:41 PM
Except then I don't have the free will to make whatever choice I want, I can only make the choices you have previously determined I make. This is one of the classic critiques of compatibalism (the idea that free will and a deterministic universe aren't mutually exclusive), that what compatibalists call free will isn't free enough. In my opinion you need to have the actual ability to choose any of our possible options to have free will and in your view we don't have that ability, we merely have the possiblity. I make a difference between having choice in potentia and having choice in actuality. Your system gives you only the first one and not the second, which is not true free will. Of course we have the illusion of free will and must act as if we have free will, but that doesn't

Yes you do. For example if I know you like pizza but hate spaghetti and I offer you pizza or spaghetti I pretty much know that you will choose pizza over spaghetti but you are still making that choice.

The idea is that with infinite knowledge of an individual and of every other thing that the individual interacts with then you should be able to predict the individual's choices with an accuracy that is close to if not 100%.

EDIT: Ninja'd!

Tiki Snakes
2011-12-04, 10:43 PM
I'm not forcing you to do anything.

Say you looove chocolate. Say I know you love chocolate. So when you step into a candy store I know you are going to pick chocolate. Even if you had a reason not to choose chocolate, I would know why & therefore predict the new choice. In no way do I force you to do anything. I am an observer.

If, however, you know that I will choose chocolate because you left yourself a note from the future, telling your past self that I chose chocolate, and I you mention it to me, I might decide Vanilla is good too.

But if events can only ever happen as they have always happened, then you have a paradox unless I don't actually have the free will required to make a choice.

[edit] Essentially, Deterministic universes as I understand them only really work if time travel doesn't, or if you can only travel forward, perhaps.

Anderlith
2011-12-04, 10:52 PM
If, however, you know that I will choose chocolate because you left yourself a note from the future, telling your past self that I chose chocolate, and I you mention it to me, I might decide Vanilla is good too.

But if events can only ever happen as they have always happened, then you have a paradox unless I don't actually have the free will required to make a choice.

[edit] Essentially, Deterministic universes as I understand them only really work if time travel doesn't, or if you can only travel forward, perhaps.

Exactly. You can only travel forward, but with manipulation of gravity, you can control the speed.

If time travel was even remotely possible, we would have met future people already

Soras Teva Gee
2011-12-04, 10:55 PM
[edit] Essentially, Deterministic universes as I understand them only really work if time travel doesn't, or if you can only travel forward, perhaps.

You can time travel forward right now, relativity.

And time travel from my thinking at the moment is only resolvable in a deterministic universe. Consider, if there is not a "predetermined" future then where exactly is a time traveler supposed to come from?



If time travel was even remotely possible, we would have met future people already

Not if they have the good sense to conceal their presence.

Also there the closest thing to a scientific basis for time travel (relativistic travel of wormholes) would only allow travel back to the creation of the phenomena.

HalfTangible
2011-12-04, 11:08 PM
By leaving notes into the past telling to go to the past and give yourself a note to do the above to your past self in the future?

As i understand it, Time Paradoxes are impossible in the first place

There are several ways to interpret how your actions can affect the past:

1) The back-to-the-future route, where an alternate reality is created with each action you undertake. If something existed in the original reality but couldn't exist in the new one it would fade from existence or change to suit the new reality.

2) The Artemis Fowl route, where anything that occurs when you go back already occurred in the timeline you're from. Under this model, for instance, leaving notes to yourself would mean that you lost your memory of the note or never read it.

3) The Apocalypse Lane route, where any major change (paradoxical or not) creates a black hole.

4) Casuality itself breaks down, thereby destroying all reason as we know it.

5) The (book about a dinosaur hunt whose name i can't remember) route. You can go back and make changes, but you come back in a changed reality. This one's pretty similar to #1 except nothing is destroyed, you just notice all the changes.

Traab
2011-12-04, 11:18 PM
As i understand it, Time Paradoxes are impossible in the first place

There are several ways to interpret how your actions can affect the past:

1) The back-to-the-future route, where an alternate reality is created with each action you undertake. If something existed in the original reality but couldn't exist in the new one it would fade from existence or change to suit the new reality.

2) The Artemis Fowl route, where anything that occurs when you go back already occurred in the timeline you're from. Under this model, for instance, leaving notes to yourself would mean that you lost your memory of the note or never read it.

3) The Apocalypse Lane route, where any major change (paradoxical or not) creates a black hole.

4) Casuality itself breaks down, thereby destroying all reason as we know it.

5) The (book about a dinosaur hunt whose name i can't remember) route. You can go back and make changes, but you come back in a changed reality. This one's pretty similar to #1 except nothing is destroyed, you just notice all the changes.

Or a paradox is caused and the universe rejects it, obliterating the cause and resetting the events back to their original form. Think of it as hitting a combination of the delete and reset buttons on your computer. Or altering a computer program in such a way that it crashes, then removing that change. Paradoxes may be happening all the time, they just get deleted from reality and events reset whenever they do, so we would never notice them.

For all we know, 100 years from now, there will be an immense effort into developing time travel. The only problem is, just by virtue of going back in time, due to chaos theory, they alter the future which causes a paradox and obliterates them from existence, so all the researchers know is, everyone who tries to time travel never returns. So its possible, but its a death sentence.

Marillion
2011-12-05, 12:33 AM
5) The (book about a dinosaur hunt whose name i can't remember) route.

Ray Bradbury - A Sound of Thunder

warty goblin
2011-12-05, 12:51 AM
I'm inclined to agree with Mewtarthio, despite Godel.

Answer this: if it can't work, how does it work?

It can't obey traditional logic of course, because standard logical systems don't allow contradiction. But logic is itself a set of assumptions, which may not in fact perfectly encapsulate the actual reality of the universe, and which are not (quite) universally agreed upon. For instance in general False implies anything is taken as true, but there are logical systems where A -> B, with A False is taken as having undefined truth value.

Anderlith
2011-12-05, 09:08 AM
It can't obey traditional logic of course, because standard logical systems don't allow contradiction. But logic is itself a set of assumptions, which may not in fact perfectly encapsulate the actual reality of the universe, and which are not (quite) universally agreed upon. For instance in general False implies anything is taken as true, but there are logical systems where A -> B, with A False is taken as having undefined truth value.

To deny logic is to deny reason.


You are still treating the problem logically, you are just adding a veil of chaos to the solution

Ravens_cry
2011-12-05, 09:28 AM
If time travel was even remotely possible, we would have met future people already
Maybe, maybe not.
One, maybe this is the first "time" we have gone through this. In a multiple parallels (I hesitate to use the word universe given its literal meaning) with quantumly brittle splits world, when anyone goes back in time, they go back to a different parallel "created" when they appear as their presence means a different future. Which means if this is the first "time" time travel has been invented, we won't see any backwards time travellers appear in this time line.

Two, even if this isn't the "first" this splitting means you can never go home. Oh, you might go home if you go forward again, or maybe not depending on the Butterfly effect, but unless you have a means of jumping the tracks, of moving sideways to other parallels, your original friends and family won't ever see you again, ever.

Three, maybe humans just never invent backwards time travel? Maybe by the time it is invented, humans are extinct and forgotten?
Less morosely, maybe our culture just isn't that interesting to whatever future invents time travel?

Weezer
2011-12-05, 09:41 AM
To deny logic is to deny reason.


You are still treating the problem logically, you are just adding a veil of chaos to the solution

To deny logic is to deny an unprovable, constructed system based on axioms chosen by man. Logic is a useful tool in some circumstances, but it is nothing more than a tool, don't confuse it for something more fundamental.

Traab
2011-12-05, 09:53 AM
To deny logic is to deny an unprovable, constructed system based on axioms chosen by man. Logic is a useful tool in some circumstances, but it is nothing more than a tool, don't confuse it for something more fundamental.

But if we cannot work from logic then there is no way to even approach an answer that is anything but random. Without using logic I could make the claim that the answer to the question of whether paradoxes can be fixed is ecru. Or toast. Perhaps 42. And those answers would be equally as valid as any other that you might come up with.

Lord Raziere
2011-12-05, 10:00 AM
To deny logic is to deny an unprovable, constructed system based on axioms chosen by man. Logic is a useful tool in some circumstances, but it is nothing more than a tool, don't confuse it for something more fundamental.

Agreed. Came from a forum who practically worshipped logic as the be-all, end-all solution to everything. Never going back, those jerks.

warty goblin
2011-12-05, 10:21 AM
To deny logic is to deny reason.


You are still treating the problem logically, you are just adding a veil of chaos to the solution

Of course I'm still treating the problem logically, that's all anybody can do. However, logically, one must also acknowledge the limitations of the system in which one operates. In this particular case that means recognizing that one cannot prove the universe free of contradictions, one must assume there aren't any.

Ravens_cry
2011-12-05, 10:23 AM
Logic is only as good as what you base your assumptions on.
False assumptions will lead to absurdity, completely logical absurdity.

Weezer
2011-12-05, 11:53 AM
But if we cannot work from logic then there is no way to even approach an answer that is anything but random. Without using logic I could make the claim that the answer to the question of whether paradoxes can be fixed is ecru. Or toast. Perhaps 42. And those answers would be equally as valid as any other that you might come up with.

You need to remember that there isn't one "logic", there are innumerable logical languages and systems that have been created by humans as an effort to model either our thinking or as tools to use in a more practical manner. Logic is a model, and if you run up against something that breaks that model (aka time travel and most traditional systems of logic) the correct answer is not to stick your fingers in your ear and ignore the fact that your logic has failed, instead you need to change your logical construction to deal with the new facts. Logic is not some objective system that is never changing and always correct, it is nothing more than a formal linguistic representation of the consequences of chosen axioms.


Also logic and reasoning are not synonymous, logic tries to represent human reason in a formal manner, but does a really, really bad job at it. Humans do not actually think using any logic yet developed, and the logicians I've talked to think that no formal system will be developed to accurately represent human thought. We aren't purely rational beings, we jump to conclusions, ignore evidence and make assumptions, in some ways our thought process is far closer to random output than it is to sentential logic.


EDIT: One thing to remember, logic is just a tool. It can be a very good tool, but it is not a universal tool, sometimes you need a hammer instead of a screwdriver and it's important to recognize which situation is which.

Ravens_cry
2011-12-05, 12:09 PM
Technically, logic and human reasoning have different goals.
Human reasoning is about survival, more specifically surviving in the pre-historical savannah we did most of our biological evolving in.
Our cultural evolution and divergences have a quite significant effect, but human nature hasn't changed all that much.

Anderlith
2011-12-05, 09:14 PM
A fact is immutable. Our perception of the fact may be flawed & we may perceive false facts, but a fact is immutable. Logic is built on a foundation of facts, Reason is the architecture.

A false Fact cannot exist. It can be perceived to exist but it doesn't. This creates a flaw in your Logic, this corrupts your Reason.

To think a paradox can/will/does exists creates a false fact.

Traab
2011-12-05, 10:36 PM
A fact is immutable. Our perception of the fact may be flawed & we may perceive false facts, but a fact is immutable. Logic is built on a foundation of facts, Reason is the architecture.

A false Fact cannot exist. It can be perceived to exist but it doesn't. This creates a flaw in your Logic, this corrupts your Reason.

To think a paradox can/will/does exists creates a false fact.

Unless its not a false fact. /whistles innocently. Honestly, the idea of fixing paradoxes is theory based off of theories we have on time travel theories and the theories on how it might work. This question is about 5 degrees removed from scientific knowledge and deep into the realm of pure guess work.

Sgt. Cookie
2011-12-06, 05:23 AM
Everyone, stay... stay right where they are. I'm going to go look for a temporal physicist.

[/silliness]


Honestly, the idea of fixing paradoxes is theory based off of theories we have on time travel theories and the theories on how it might work. This question is about 5 degrees removed from scientific knowledge and deep into the realm of pure guess work.

I agree, without knowledge of what time travel even is, we can't decide what a paradox could even be. Right now, all we have are thought experiments and possibilities. To my knowledge there isn't even an agreed definition as to what a time paradox even is.

Once a global definition of what a paradox is has been agreed on, then we can get round to discussing causes and fixes. That is, if this agreed thing even allows for such things.

Right now, all we are saying is "Chocolate is great" but failing to mention if we are talking about milk, white or dark.

TheArsenal
2011-12-06, 06:13 AM
This was just for fun!

Adanedhel
2011-12-06, 06:55 AM
Quantum-mechanics, relativity and time-travel, seems like my kind of discussion :)

I am aware of 2 ways to be able to travel in time, the first, as mentioned by Soras Teva Gee, only allows timetravel back to point of creation of time machine.

To explain, objects moving at high speed (velocity is the vector, I want the lenght of the vector, so speed does just fin) perceive time to be slower, the idea is as following. All objects move at lightspeed, it's just that part of the velocity is aimed in 4th dimension (time thus) rather then the 3 classical dimensions, this is a quick and dirty explanation, but it should suffice, if you want a better explanation PM me, it's not really relevant here. In every case, by having more velocity in space, you go slower in time, so if you would take a tunnel, where you could move the one end far faster then the other end, you'd be able to travel back from one end to another, this basically is the idea of wormhole time travel.

Second method is even worse from a practical point of view, you'd need an infinite cilinder of infite mass, have fun finding that :)

So yeah, getting back to see the dinosaurs might give a few practical problems :)

Now, let's try to compare quantum mechanics with classical mechanics.

to go from the classical equations of motions in the picture of Hamilton equations, is pretty easy, replace physical variables with operators, then replace poisson brackets with commutators (commutators are equal to poisson brackets if and only if h/2pi =0, and this is the way to get classical mechanics out of quantum mechanics, just as classical mechanics follows from relativity if one approximates c with infinity).

Practically speaking, you'll want to use Ehrenfest equations.

Funny thing about them they're very similar to the classical equations, you just need to use the classical equations on the uncertainties as well.

On chaos, entropy (S) is a physical propery of a system, which is used to be able to say something about a lot of particels without needing to calculate position or momentum of any single one of them, it's pretty handy, for example in the idea of throwing a jar of marbles on the table, because calculating all marbles is a mess and very unpratical (which is a massive understatement), and this gets even worse if you get ârticles you cannot easily discern. (ever tried to watch 2 protons, look away, and try to see which was which, it is indeed impossible). Entropy is important, cause it give us a chance to get knowledge without knowing everything to the details.

If this wouldn't be in place, you should try to imagine a universe where you can't learn anything without knowing the fundamental principles, for example F=m*g which all of you learned at school as first approximation of graity, would be impossible to find without knowing general relativity, have fun being a scientist there ^^

jseah
2011-12-06, 02:52 PM
http://www.giantitp.com/forums/showthread.php?t=223621

I'm exploring consistent (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle)-only time travel in that thread.


There have been theoretical physics papers that calculate time travelling billiard balls and such "thought experiments".
While none of them have shown that paradoxes are possible (they have always found a solution), they have not been able to prove that paradoxes are impossible.

So the consistency principle is still just an assumption. An assumption that I would consider likely to be true, given that people more intelligent than I am have not been able to find a paradox-causing situation.

Killer Angel
2011-12-07, 03:08 AM
http://www.giantitp.com/forums/showthread.php?t=223621

I'm exploring consistent (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle)-only time travel in that thread.


I'm currently reading a short book that's about time travels and paradoxes: "Palimpsest (http://www.amazon.com/Palimpsest-Charles-Stross/dp/1596064218)", by Charles Stross, winner of Hugo Awards 2010.
Seems interesting and it's certainly on topic.

Felix Fiveblade
2011-12-07, 03:42 AM
You fix a paradox by asking yourself if you were to ask yourself if you should kill yourself, if the answer to this question would be the same as the answer to that one, then not killing yourself after you answer.

jseah
2011-12-07, 03:50 PM
I'm currently reading a short book that's about time travels and paradoxes: "Palimpsest (http://www.amazon.com/Palimpsest-Charles-Stross/dp/1596064218)", by Charles Stross, winner of Hugo Awards 2010.
Seems interesting and it's certainly on topic.
Just looked at the link. It doesn't appear to be consistent-only time travel though.

Then again, its incredibly hard to write stories for, unless you restrict yourself to a short but complicated story. Which would require the reader to understand all the principles, instead of introducing them one at a time.

The main reason why I'm drawn to consistent-only time travel is due to the conceptual challenge.

It's very hard to understand why anything happened (and why other things couldn't have happened) in that time travel scheme. Working that out is like working out an interesting puzzle or trying to visualize non-euclidean geometries (I still can't do a 3D equivalent of a klien bottle).

Parallel timeline or no-changing-past-by-fiat is an exercise in stamp-collection in comparison.

irenicObserver
2011-12-07, 04:16 PM
That only holds true if you think the universe is deterministic and absent of free will.

I think the universe would likely work in a sort, A does this, B does that when they interact C happens sort of thing. Only multiply that by A, B and C where A is any given thing B is any other given thing that can be measured separately from A (A=a rock B= a percentage of its atoms) and C is outcome of A and B relevant or not to A+B. Although if you're talking about time travel it's usually flexible or predetermined (ontological paradoxes and such), like: I sent a note back to change my present, my present is suddenly a different set that only exists because it's gained something (I would say information but let's generalize it to energy) from the set it was in before I sent the note back. This opens the possibility for all kinds of time shenanigans making time inconsistent because you can observe an entirely new set at any point all the time. It reality is predetermined that's because you locked the current set into place by sending the energy back in the first place, proving the set.


This is most likely a thing that doesn't make sense, I'd reword it but time-travel is an absurd.
This was just for fun!

I'm just laughing my butt off at the thought of you checking back on this thread and finding this highly involved argument of logic and time-travel. XD

Weezer
2011-12-07, 04:20 PM
I think the universe would likely work in a sort, A does this, B does that when they interact C happens sort of thing. Only multiply that by A, B and C where A is any given thing B is any other given thing that can be measured separately from A (A=a rock B= a percentage of its atoms) and C is outcome of A and B relevant or not to A+B. Although if you're talking about time travel it's usually flexible or predetermined (ontological paradoxes and such), like: I sent a note back to change my present, my present is suddenly a different set that only exists because it's gained something (I would say information but let's generalize it to energy) from the set it was in before I sent the note back. This opens the possibility for all kinds of quantum shenanigans making time inconsistent because you can observe an entirely new set at any point all the time. It reality is predetermined that's because you locked the current set into place by sending the energy back in the first place, proving the set.

I'm pretty sure quantum mechanics doesn't work like that. It seems like you just went "I sent something back, thus quantum mechanics", could you expand more on why you think quantum effects would start determining things on a macro scale?

irenicObserver
2011-12-07, 04:33 PM
Because quantum does everything. Ignore the quantum snippet that's just me being an idiot. I was just trying to model the idea of time travel. Consistency between timelines and stuff like that, i don't know. Time travel is an absurd, it's extremely complicated and highly involved with the cause and effects muddied by all the steps.

I think of it like this, there are a limited number of options I can take at this very moment and what those options lead to are limited as well, what's unlimited is the length of options to take as I go along the path. I file this under probability as this is the closest thing I can compare to it. With time travel you can retreat elements and put others in, not necessarily in that order and not always together. So you get to send energy back (which IMO would inevitably result in a black hole if infinite energy could be sent back) to jump the path to a different line leading it down another path. And...that's the best can do right now it's too much for me. *retreats to th corner, waits for scorn*

jseah
2011-12-07, 04:34 PM
I'm pretty sure quantum mechanics doesn't work like that. It seems like you just went "I sent something back, thus quantum mechanics", could you expand more on why you think quantum effects would start determining things on a macro scale?
Chaos theory would indicate that small changes to complex systems with feedback loops result in large differences (exponentially larger differences over time)

Also related is the Schrodinger's Cat thought experiment. Now, Schrodinger's time traveller.

irenicObserver:
Consistent-only time travel isn't absurd. It's just an assertion of "no new physics" (apart from the time travel itself).

No parallel time lines, no alternate paths. There's only what is.

irenicObserver
2011-12-07, 04:41 PM
Chaos theory would indicate that small changes to complex systems with feedback loops result in large differences (exponentially larger differences over time)

Also related is the Schrodinger's Cat thought experiment. Now, Schrodinger's time traveller.

irenicObserver:
Consistent-only time travel isn't absurd. It's just an assertion of "no new physics" (apart from the time travel itself).

No parallel time lines, no alternate paths. There's only what is.

About the first part, this is what I got from my brief skimming of transfinite, that it makes little energy now but that energy is constantly produced and while you can't get a lot in a short amount of time, over time it'll be an ocean from a faucet. That's the only way time travel can be considered really, effectively meaning changes to time are erasing whatever the original timeline was.

jseah
2011-12-07, 05:00 PM
irenicObserver:
I don't understand you.

Its not possible to get something from nothing (break 1st law of thermodynamics) with consistent-only time travel.
With certain setups (eg. time teleportation), its possible to break 2nd law of thermodynamics.

But in all cases, you cannot make energy with consistent-only time travel.

EDIT:
and pretty much by definition, you can't make changes with consistent-only time travel.

irenicObserver
2011-12-08, 10:21 AM
Forget what I said then and i'll just stop talking :U

Soras Teva Gee
2011-12-08, 03:34 PM
irenicObserver:
I don't understand you.

Its not possible to get something from nothing (break 1st law of thermodynamics) with consistent-only time travel.
With certain setups (eg. time teleportation), its possible to break 2nd law of thermodynamics.

But in all cases, you cannot make energy with consistent-only time travel.

EDIT:
and pretty much by definition, you can't make changes with consistent-only time travel.

I'd be very interested under what terms you think time travel could be used to violate entropy locally. Are you referring to certain ontological paradoxes still possible within an otherwise stable time loop?

TheArsenal
2011-12-08, 03:39 PM
Talk about a joke concept and attract nuclear physicists.

Sounds about right.

Anderlith
2011-12-08, 03:48 PM
Talk about a joke concept and attract nuclear physicists.

Sounds about right.

Well, if you ask it they shall come.

Kato
2011-12-08, 04:06 PM
Well, if you ask it they shall come.

Are normal physicists sufficient? :smalltongue:

One of the reasons time travel is believed to be impossible is because it is way too easy to break a whole bunch of laws with it.

Like go back in time with something that contains a whole lot of energy/negative entropy and voilà you basically created energy/reversed entropy. Kind of a failsafe in the universe. On the other hand it might be you need to create a certain amount of entropy/lose energy when traveling to balance this out... Well, I for my part don't think it works but that's really just me.


As for the initial question... what nerd said: If it can be fixed t is no paradox.

jseah
2011-12-08, 05:19 PM
I'd be very interested under what terms you think time travel could be used to violate entropy locally. Are you referring to certain ontological paradoxes still possible within an otherwise stable time loop?
Well, specifically, if you can time teleport small objects for free (or for small entropic cost), it would not be too hard to set up conditions under which the thing arriving from the future causes objects to be sorted.


Basically, it is conceivable that you might set up a situation whose only consistent solution results in objects getting sorted.
Something arrives from the future, and butterfly effects its way to sorting everything.


After all, entropy is a matter of the 2nd law of thermodynamics, which assumes that heat in objects approximates random motion.
Well, by constraining what appears from the future to those that would result in a consistent time loop, you can force it to be less-than-random.


Eg.
You have two time machines. One cannot time travel due to a small section of wire being broken. It's still a computer, and still working.

You place a small amount of iron powder onto the broken portion.

Aim the other time machine at the pile of powder. Anything arriving or leaving can only happen at that patch.

Program the working time machine to attempt to send some metal back in time. Make it attempt time loop logic on the problem it receives from the other machine. (aka. try to solve the received problem)

Program the non-time travelling machine. It starts with a problem that cannot be solved and attempts to receive some data from the future (but cannot due to the wire being broken). It will modify the problem in accordance to the data received from itself in the future.
After modification (or none in the case where nothing comes back), it will output the problem to the other machine to solve. Then it sends the data it received to itself at the point it received that data.

Diagram (http://dl.dropbox.com/u/10120644/Time%20Travel%20two%20machines.png)

This uses the same notation as the diagrams I linked (http://dl.dropbox.com/u/10120644/Time%20Travel%20ontological%20loops.png) in the other thread. I expanded the colours to convey more about what's happening.
Green lines indicate the flow of information.
Red lines indicate dependency. The event pointed to can only occur if the event pointing to it also occurs.
Black lines indicate inconsistency. The event pointed to cannot occur if the event pointing to it occurs.
Any line that goes downwards must start in a time travel event (green thing)
Events stacked directly above each other must either all happen or none.

Depicted solution in words:
Time machine 1 receives a piece of metal from the future causes the wire in TM2 to be fixed.
TM2 now receives some data that modifies the problem into a solvable one. It sends itself that received data.

TM1 receives the problem and applies time loop logic. It solves the problem.
After solving the problem, TM1 sends a piece of metal back in time to when it was received.

That piece of metal will have the exact configuration of motion in its atoms to cause rearrangment of the atoms in the pile of iron that ends up fixing TM2 and allowing the bit that TM1 will time teleport back to have the original configuration.


This is basically applying time loop logic to physical systems, not just information.

Soras Teva Gee
2011-12-08, 06:46 PM
@jseah:

I honestly cannot completely follow your scenario or see the problem, but if I've gathered this properly you are basically using two time machines to fix one of them with material from their future.

If we are talking stable time loops then transporting matter back from the future is not a problem. Material can loop through time and as long as it doesn't loop back into being itself (the ontological paradox) there is no problem. It would experience entropy according to its local/subjective time line. A piece of iron would keep oxidizing for example.

Talking about information, a solution only being known because of information received from the future is not a problem. Information in this context has no existence of relevance, it can loop back on itself. Yes only knowing the answer because it was the answer found is screwy but not a problem for a stable time loop, its what makes a stable time loop. And because information is essentially non-existent it has nothing to do with thermodynamics. (Yes information requires a medium but that would be material transmission again)

Otherwise I can only guesstimate you are ascribing other properties to time travel that do no hold water. I suspect this (but as I said just plain can't follow your thinking) from a few things you wrote: time teleportation got me zero results different from time travel, I've never heard entropy parsed in your terms, you're ascribing AI computing to your machines when technically that would only be the controller not the time machine itself seemingly an unnecessary specification, a broken time machine is strictly not a time machine, etc.

Also the energy costs of using a time machine are not relevant to the problems time travel raises. The machine would either have zero impact on the objects it transmits, or addition and subtraction would just be handled normally. A bullet fired through a time machine effect would come out the othertime faster/slower/the-same accordingly. Though one could possibly play some frame of reference games with this, one could not use it for say a perpetual motion device across time. If this is not the case then I'd argue you are adding other properties to time travel to make this happen.

(Also whatever its logical basis time travel we can infer though not prove time travel will require high energy situations since the only things creating singularity type effects require that. We might conclude time travel is possible but not even an anti-matter reactor could be made that could do it)

And finally for the ontological paradox: classically Kirk selling a pair of glasses that in the future McCoy acquires and gives to Kirk who sells them in the past. Where did the glasses come from? Still "possible" in a stable time loop but being a paradox would suggest it could never come to be. Ergo because such a condition could not exist (since the glasses would experience infinite entropy and break down) it simply never can exist because the closed loop has no way to enter it preventing this from ever occuring "in the first place" as it were. Attempting to will result in failure much like killing Hitler in 1933 will result in failure under the idea of a stable time loop.

jseah
2011-12-08, 07:09 PM
Actually, the thing about the glasses is a much simpler way to explain what I'm doing with the abuse of time loop logic.

Yes, as you say, Kirk's glasses will have aged a non-zero amount each time loop and therefore it cannot be the *same* glasses as the one that started out. This is inconsistent.
Glasses != Older glasses


However, this is based on the assumption that aging glasses do not have the same state as before.
As long as the glasses that travels back is the same as the glasses that arrives, there is no paradox.
The "age" doesn't matter. Just that for a certain length of the time loop (beyond a few femtoseconds), it is overwhelmingly unlikely that the glasses will be in the exact same state. And it really has to be the exact same state, even one atom out of place is a paradox. (you can shuffle equivalent atoms around though)

The probabilities involved pretty much ensure that if there is a consistent solution that increases entropy, that entropy-increasing consistent solution will be so much more likely to happen that it pretty much does all the time.


Sure, 2nd law of thermodynamics ensures this is incredibly unlikely. But not, technically, impossible.

If you set up a condition that nothing except the extremely unlikely reversal of entropy will result in a consistent solution, then this ensures that entropy will reverse.
Failure to reverse entropy results in paradox.

Extremely unlikely is not zero. Probability of entropy reversal is non-zero and thus greater than probability of paradox.


I did think about this a bit. You can send one atom around on a time loop and it'd be fine. Physics is time-symmetric.

You can even do this for a radioactive atom. It just happens to not decay during that time it existed in the time loop. Radioactivity is a random process, not one that has "history".

warty goblin
2011-12-08, 07:12 PM
@jseah:

I honestly cannot completely follow your scenario or see the problem, but if I've gathered this properly you are basically using two time machines to fix one of them with material from their future.

If we are talking stable time loops then transporting matter back from the future is not a problem. Material can loop through time and as long as it doesn't loop back into being itself (the ontological paradox) there is no problem. It would experience entropy according to its local/subjective time line. A piece of iron would keep oxidizing for example.

Which means that you added energy to the past. There's more there than there was before, which violates both conservation of matter/energy and thermodynamics.


Talking about information, a solution only being known because of information received from the future is not a problem. Information in this context has no existence of relevance, it can loop back on itself. Yes only knowing the answer because it was the answer found is screwy but not a problem for a stable time loop, its what makes a stable time loop. And because information is essentially non-existent it has nothing to do with thermodynamics. (Yes information requires a medium but that would be material transmission again)
According to what the various people I know who pay attention tell me, information is perhaps at least as fundamental as mass and energy.


Also the energy costs of using a time machine are not relevant to the problems time travel raises. The machine would either have zero impact on the objects it transmits, or addition and subtraction would just be handled normally. A bullet fired through a time machine effect would come out the othertime faster/slower/the-same accordingly. Though one could possibly play some frame of reference games with this, one could not use it for say a perpetual motion device across time. If this is not the case then I'd argue you are adding other properties to time travel to make this happen.
Again, you're adding energy to the past, which is sort of a no-no. You are also removing it from the present, which again is not really something that one can do.

jseah
2011-12-08, 07:18 PM
Which means that you added energy to the past. There's more there than there was before, which violates both conservation of matter/energy and thermodynamics.
Nah, energy and matter quantities are locally conserved.

They are not *globally* conserved at all times, but time travel implies that anyway.
They are conserved before and after though.


The total amount of energy/matter before the loop starts and after the loop ends is the exact same.

This is true for any loop under consistent time travel. The only way to increase the energy/matter totals outside the time loops is inconsistency.
In fact, that is sufficient to indicate paradox. (although not necessary)

Soras Teva Gee
2011-12-08, 10:30 PM
Actually, the thing about the glasses is a much simpler way to explain what I'm doing with the abuse of time loop logic.

Yes, as you say, Kirk's glasses will have aged a non-zero amount each time loop and therefore it cannot be the *same* glasses as the one that started out. This is inconsistent.
Glasses != Older glasses

If that is what you were getting at then I'm inclined to say you are in general over-thinking things and adding unnecessary elements. As noted there is a resolution to the problem. Namely it can never come to pass much like changes to the past cannot come to pass.

For the glasses in the intervening time Kirk would inevitably be wrong about the course of his property, and was "always" wrong. You'd at best have the Spectacles of Theseus where every piece has been replaced in the intervening time.



However, this is based on the assumption that aging glasses do not have the same state as before.
As long as the glasses that travels back is the same as the glasses that arrives, there is no paradox.

The glasses are not the same. That is the result anyways, as to be put into a loop they had to have been out of a loop at one point. Essentially you cannot engineer an closed object loop because you there is no material that can create one.

Its being the 'sameness' that creates the problem. Mind you if there was somehow the non-entroying material then you would have some kind of issue, but even here its factual existence would suggest something like a maddening exception to conservation and entropy which would be limited to the material in question... and to interact with anything else in the universe it would have to exhibit entropy to balance out the final conservation perspective.

The more I talk about this the more support I think I find for a closed object loop being increasingly impossible.



The "age" doesn't matter. Just that for a certain length of the time loop (beyond a few femtoseconds), it is overwhelmingly unlikely that the glasses will be in the exact same state. And it really has to be the exact same state, even one atom out of place is a paradox. (you can shuffle equivalent atoms around though)

The probabilities involved pretty much ensure that if there is a consistent solution that increases entropy, that entropy-increasing consistent solution will be so much more likely to happen that it pretty much does all the time.

I smell quantum mechanics. And time travel has more to do with relativity (given that relativistically treated wormholes are the only basis for time travel known) which would mean so anything involving quantum mechanics would first need a Unified Field Theory to resolve the two, and whatever that is must be consistent with the macro scale... so frankly I'm not seeing how this would matter or you are adding some kind of other principle I'm not understanding.

(I've given thought for example as any form of time travel would at some level involve sub-atomic particles existing in two places at once, and interesting issue if it has any meaning beyond "lol two places at once" because that would imply a certain quantum level "identity" that literally everything is unique.)


You can even do this for a radioactive atom. It just happens to not decay during that time it existed in the time loop. Radioactivity is a random process, not one that has "history".

While of course depending on the subjective duration of the trip that might be true in varying probabilities as noted its random, so an atom might do so but any quantity of a radioactive element would decay along its own subjective timeline as much as one would expect in a purely linear trip. And whether it did our not isn't particularly meaningful because its only an atoms subjective experience of time.

As long as the amount of loops are finite then it really makes no difference whether a particular radioactive atom decays or not in its multiple trips.

The point of stable time loop deterministic time travel is that it creates no greater problems within physics since this methods problems are only supposing some sort of enforced frame of reference we have reason to doubt already


Which means that you added energy to the past. There's more there than there was before, which violates both conservation of matter/energy and thermodynamics.

Again, you're adding energy to the past, which is sort of a no-no. You are also removing it from the present, which again is not really something that one can do.

I moved these together because they have the same resolution, as long as they are locally conserved its not a problem. We already know from relativity that only the local experience is important. Because we have already established that objects in different frames of reference do not experience the same subjective time.

That's time dilation. If you put take two accurate enough clocks synchronize themm and put one on a jet plane to fly around the world, they flying clock will come back showing less time elapsed then the stationary clock. Mind you still within fractions of a second but there and measurable. It was done to test Einstein. This implies there is no need for a universal balance as far as time elapsed.

So as long as it has an origin and an end matter and energy can loop through time without a problem for conservation. Likewise as long as the material making the loop decays it is displaying inertia. A piece of Uranium would decay according to its half-life for example so any loops would give you less unranium.

(As long as its an open loop through time, closed ones are different because you'd have infinite loops in a closed amount of time, along with infinite entropy so matter could not survive at even the sub-atomic levels if proton decay is to be believed)



According to what the various people I know who pay attention tell me, information is perhaps at least as fundamental as mass and energy.

Context is everything.

While mind you I don't understand it all myself, when someone like Stephen Hawking talks about say 'information surviving in black holes' he's not really talking about say the words in a book which are too macro-scale. Its more like the pattern of a radio signal or even deeper levels then that.

So this would go under material (matter and energy) transmission. To wit if you opened a hole in time and sent a laser signal through the hole... whomever recieved it would not then preserve that exact same signal to then transmit "back" to the past (its not possible engineering wise at the least) they'd receive the laser signal from the future go out of the loop just like any signal received from a present frame of reference.

Anderlith
2011-12-09, 02:26 AM
I can solve this debate really easily. All you need to do is take a TARDIS & cannibalize it's energies into itself. Viola! Paradox machine

jseah
2011-12-09, 04:49 AM
The more I talk about this the more support I think I find for a closed object loop being increasingly impossible.
I would not say impossible.

If you start out with a box of atoms (macroscale) that are arranged in neat rows and then let time run for a bit, the atoms will get jumbled up. Reverse time for the same bit and the atoms will "magically" line back up again.

This is the essence of determinism. Which, by the way, is assumed in consistent time travel.


Since reversing the time direction doesn't actually change physics, this implies there exists an arrangement of atoms in a box that will "magically" line up at some future point in time.


In the same way, there exists a consistent solution that involves "magically" lining everything up in a such a way that entropy is decreased and yet no micro-scale physical laws are broken.

The only problem is that consistent solutions NOT involving this exact arrangements are overwhelmingly more likely to happen simply because there are so very many more of them.

In order to reverse entropy with consistent time travel, you will need to rule out ALL entropy increasing solutions.



As long as the amount of loops are finite then it really makes no difference whether a particular radioactive atom decays or not in its multiple trips.
Um, I'm referring to a closed object loop. The object in question is one single radioactive atom.

pffh
2011-12-09, 04:56 AM
What about the good old stable time loop: I need a key to open a door so I opne a drawer and use the key in there to open the door. Later I travel back in time before I need to open the door and place the key in the drawer. Where did the key come from?

jseah
2011-12-09, 05:08 AM
What about the good old stable time loop: I need a key to open a door so I opne a drawer and use the key in there to open the door. Later I travel back in time before I need to open the door and place the key in the drawer. Where did the key come from?
It's an object loop.
As unlikely to happen as all the atoms in your room suddenly deciding to squeeze into one corner.

Gaius Marius
2011-12-09, 09:19 AM
Agreed. Came from a forum who practically worshipped logic as the be-all, end-all solution to everything. Never going back, those jerks.

Captain Archer, is that you?


I for one hardly buy into the "send a message to yourself in the past so you do the actions you are meant to do" idea. It's what I call the Inception paradox, which is brushed upon in Realm of Sorcery (WFRP referece book, 2nd edition).

In the book, the Magister Lord of the College of Magic specializing in foretelling is anguishing over a fact: he became the Lord Magister because everybody (himself included), foretold that he would be the next to hold the position.

Thing is, he didn't actually achieved anything. The prophecy was the only motivation for anyone to elect him to this position. It became a fully self-fulfilling prophecy in the most literal sense of the term. Nobody actually made a decision, there was no Idea Inception.

The concept can be applied to time-travel as well. If you go back in time because your future self told you, so you can tell yourself to go back in time to tell you to go back in time....

The idea of going back in time effectively comes from nothing. You might call it a stable time-loop, but I call it a CLOSED time loop. The loop lacks a start, therefore can't exist.

If you happen to travel in time, and accidently do something to indirectly help you achieve time-travel, without any transfer of foreknowledge instruction, then the idea originates from your future self, which makes it a stable, but still open, time loop.


Do I make sense or I just rambling?

irenicObserver
2011-12-09, 10:33 AM
Are normal physicists sufficient? :smalltongue:

One of the reasons time travel is believed to be impossible is because it is way too easy to break a whole bunch of laws with it.

Like go back in time with something that contains a whole lot of energy/negative entropy and voilà you basically created energy/reversed entropy. Kind of a failsafe in the universe. On the other hand it might be you need to create a certain amount of entropy/lose energy when traveling to balance this out... Well, I for my part don't think it works but that's really just me.


As for the initial question... what nerd said: If it can be fixed t is no paradox.

Such things as achieving infinite everything to send energy back before it was created, stuff like that. Like the comic strip where all the time travelers threw a party and all the guests generated infinite matter and created a black hole that destroyed the universe. If you can send energy back, that increases the sum mass of the universe and breaks the law of conservation. It makes as much sense as Maxwell's demon, actually I believe his demon would be very useful in time travel endeavors.

jseah
2011-12-09, 11:00 AM
The idea of going back in time effectively comes from nothing. You might call it a stable time-loop, but I call it a CLOSED time loop. The loop lacks a start, therefore can't exist.
<...>
Do I make sense or I just rambling?
All of what you mention is possible under consistent time travel.

The only thing is that your assumption of "it lacks a start, therefore can't exist" doesn't apply.

In consistent time travel, things that lack a 'start' can exist and is key to maintaining consistency in certain conditions. (eg. time loop logic and closed loops involving matter/energy)

Gaius Marius
2011-12-09, 11:09 AM
Can you please define "consistent time-travel"?

jseah
2011-12-09, 11:15 AM
Can you please define "consistent time-travel"?
Consistent (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle) time travel.


the Novikov consistency principle asserts that if an event exists that would give rise to a paradox, or to any "change" to the past whatsoever, then the probability of that event is zero. In short, it says that it's impossible to create time paradoxes.

If you travel to the past, then future you has already arrived before present you traveled. If you 'change' the past, the past is already changed.


In essence, the principle of self-consistency is a principle of no new physics. If one is inclined from the outset to ignore or discount the possibility of new physics, then one will regard self-consistency as a trivial principle.

Gaius Marius
2011-12-09, 11:27 AM
I get that part. It's the time-travel theory I subscribe to. You cannot change the past because it already happened. If you try to go back and kill your grandfather, you will fail or maybe you will discover your grandfather wasnt the man you though he was (the patsy did the nasty!)

I don't get how a closed-time loop of either an idea, an information, a piece of matter or energy can be acceptable under that theory.

Specially an object. Basic degradation theory says the item ages everytime it goes back the loop. Therefore, it is not thensame object that can be transferred from one loop to the next, since it's a different one.

And even if you accept the very impossible concept of nil-degradation. In a closed item-related time loop, what decided of the item's property? It's shape? It's color? It's base material? I guess the only way it would make sense to gain any property without having been created would be that it needs these property to properly fullfill it's role in the closed time loop.

But it's grasping at a weak entropic theory.

An item can't just "be" in a closed time loop.

Soras Teva Gee
2011-12-09, 01:05 PM
I would not say impossible.

If you start out with a box of atoms (macroscale) that are arranged in neat rows and then let time run for a bit, the atoms will get jumbled up. Reverse time for the same bit and the atoms will "magically" line back up again.

This is the essence of determinism. Which, by the way, is assumed in consistent time travel.

In a deterministic timeline such an event would be impossible to observe or otherwise separate from the flow of events because the items would have to be their earlier selves (as opposed to later selves in a different location with open looping) so you actually couldn't have them anywhere but where they always were. And reversing their own entropy would be reversing the effects of everything they interact with, even you leaving a note from the future would be meaningless because you would simply see the piece of matter you had anyways. It can't be observed, can't have an effect or otherwise interact, it can't exist/happen in anyway meaningful in a deterministic system.

Time reversal is completely different then time travel, because it looses local conservation and entropy. It is the exact polar opposite of entropy and by extension physics in any way we conceive of it. Now mind you entropy is more of a principle then a hard rule but we have no conceptual basis for how we might negate it other then "lol imagine we did" which is not the case for time travel generally seen as a peculiar warping of spacetime itself known to be fluid.

You could possibly run a thought experiment or two but in the end this is about as meaningful as if magically the values a universal constant changed.


In the same way, there exists a consistent solution that involves "magically" lining everything up in a such a way that entropy is decreased and yet no micro-scale physical laws are broken.

Its less consistent then utterly meaningless.

This is the old yarn about a tree falling in the woods when no one is around, the difference is only philosophical since it has no meaningful way to exist. Because it could only happen in an unobserved state with the same net result as if it had been observed. A tree could fall in a forest and not make a sound a trillion times as long as it was "magically" back in place for when an observer shows up and it falls once and makes a sound.


Um, I'm referring to a closed object loop. The object in question is one single radioactive atom.

And I'm saying that closed object loops are even more impossible then time travel itself, even paradox inducing time travel as there are other conceptual resolutions to time travel that simply involve more "extra stuff" to the physics.


The concept can be applied to time-travel as well. If you go back in time because your future self told you, so you can tell yourself to go back in time to tell you to go back in time....

The idea of going back in time effectively comes from nothing. You might call it a stable time-loop, but I call it a CLOSED time loop. The loop lacks a start, therefore can't exist.

To put it simply:

1. There is no conservation of ideas, they can loop and come ex nihilo because they are not a matter of physics.

2. This is a single loop presuming the future self that informs the past self then goes on to other things.


Such things as achieving infinite everything to send energy back before it was created, stuff like that. Like the comic strip where all the time travelers threw a party and all the guests generated infinite matter and created a black hole that destroyed the universe. If you can send energy back, that increases the sum mass of the universe and breaks the law of conservation. It makes as much sense as Maxwell's demon, actually I believe his demon would be very useful in time travel endeavors.

The principle of a stable time loop is that because nothing ever comes to pass that prevents events, nothing happens to prevent events. A sort of self-censorship like how we can infer that either time travel is non-existant (ever) or its negative effects are localized in some manner. You can tell in the words of Bob the Skull.... by how we all keep existing.

Now time travel automatically implies changes to the sum universal mass/energy of between scope of the time jump's past arrival and future departure. However though as long as local conservation and entropy are conserved there's no real reason it should matter.

Mind you this is time travel only, so you would never have cases of infinite energy/mass for example unless such a case already exists. Which science believes is not the case ergo time travel has nothing to steal it from. If we have some more exotic means of getting infinite energy and mass then its not from time travel.

Mind you time travel might only be practical (since we obviously can't do it) with those preconditions as a consequence but not a cause in and of itself

jseah
2011-12-09, 01:56 PM
And reversing their own entropy would be reversing the effects of everything they interact with<...>
No.

Reversing their own entropy would only be reversing the effects *on themselves* that everything else causes on them.


Its less consistent then utterly meaningless.
But you see, since all physical laws (and not statistical principles like entropy) are time symmetric, for any system you imagine running backwards in time, you cannot tell whether time is running backwards or not.

To the atoms, individually, whether they are part of a cup breaking (increasing entropy) or a cup spontaneously reforming (decreasing entropy) makes absolutely no difference.

and if you have the atoms moving in just the right way, you CAN have a cup spontaneously reforming while time is moving forwards.

And this system of air/cup/floor is a physical system obeying all the same rules as the atoms moving in a normal cup-breaking-event.
Which includes being able to time travel.


If such a reforming cup can time travel, pieces of a cup that will reassemble during the loop (taking into account all effects from the environment) can arrive from the future. (provided the pieces are sent, and indeed, consistency demands that those pieces arriving and reforming must somehow contribute to getting themselves sent!)


You can think of it like this:
1. There exists a specific arrangement of atoms and forces of the universe that will organize themselves at some future point in time, providing nothing arrives from the future
1b. The universe's current arrangement does not allow this (we don't know this for sure, but we are very highly confident that this doesn't happen)

2. If something arrives from the future, it adds to this arrangement in the universe
2b. The changes to the universe-state that can occur can put the universe into a state that will organize itself

3. This very specific change (or set of changes) to the universe state is the only set that will result in a consistent time loop (this is the condition you have to set up)
3b. Therefore, such an object will arrive from the future


Basically, the absolute requirement of consistent time loops trumps the statistical principle of entropy.

jseah
2011-12-09, 03:21 PM
I don't get how a closed-time loop of either an idea, an information, a piece of matter or energy can be acceptable under that theory.
<...>
An item can't just "be" in a closed time loop.
That theory only requires that no inconsistencies exist. If the arrival of an object or information is paired with the sending of the identical object or information in the future, then no inconsistency exists and such a loop is allowed.

As to the details of the object, it just needs to satisfy the requirement of no-inconsistency.

Multiple consistent "solutions" exist. Each of which will have a certain probability of occuring. Thus, the one most likely to occur is the one with the largest amount of minor variation allowed (aka. highest entropy), although only one particular variant will actually happen.

Soras Teva Gee
2011-12-09, 03:43 PM
No.

Reversing their own entropy would only be reversing the effects *on themselves* that everything else causes on them.

Their own entropy would have inevitable effects upon other materials. To be isolated sufficiently that they would be having zero effect on other parts of the universe would also mean the cup was invisible/undetectable/uninteractable since all our means of observation have a minute effect on the subject they are observing. To reverse their entropy causes causality violations or can't be said to happen at all since it must act as if it never happened.

This is just even mechanical uncertainty whatever one takes out of it for quantum mechanics fundamental uncertainty.



But you see, since all physical laws (and not statistical principles like entropy) are time symmetric, for any system you imagine running backwards in time, you cannot tell whether time is running backwards or not.

Which I'm cautiously going to label as being more philosophical then material in nature and going to how at the end of the day physics equations are approximations used because they work based upon observed cases. Which all happen forward in time. And that while time is used as a number it doesn't nessecarily match with the basis of numbers because it is always a positive number

Put another way, it doesn't matter unless we can observe a chain of events happening upwards in the passage of time we've no reason so assume time can run backwards.

Also this is not actually relevant to time travel because time travel observes local passage of time for those doing it. The time travel itself doesn't interact with anything between its past arrival and future departure. If you aren't from Gallifrey and you time travel for your own subjective seventy years you are either old or dead of old age.

This is why I said time travel and time reversal are not the same thing and you seem to continue equating them. If a person travelled via time reversal and against their own entropy they would wind up their younger self, and that's ignoring the problems of their needed interactions with all the rest of the universe.



To the atoms, individually, whether they are part of a cup breaking (increasing entropy) or a cup spontaneously reforming (decreasing entropy) makes absolutely no difference.

and if you have the atoms moving in just the right way, you CAN have a cup spontaneously reforming while time is moving forwards.

I'd argue whether this is so much a case of entropy reversing so much as spontaneous recycling and repair. As they can't actually apply quantum effects (the only thing even loosely allowing such an event as I understand it) to the macro scale of a cup we will have to wait upon Unified Field Theory to actually evaluate this in terms of whether this was done with energy loss to the greater universe, I think.

And again don't see what it has to do with time travel as opposed to reversal.


If such a reforming cup can time travel, pieces of a cup that will reassemble during the loop (taking into account all effects from the environment) can arrive from the future. (provided the pieces are sent, and indeed, consistency demands that those pieces arriving and reforming must somehow contribute to getting themselves sent!)

If you are talking about sending a time reversing object (cup anti-entropying itself) through time, its a time reversal problem not a time travel one.

Or the reforming cup is exhibiting entropy in some other way that isn't causing it to anti-entropy but rather provides an exact opposite force nessecary to put all the pieces back together. Which would also be not time reversing.

To be clear time travel is a relative movement back in time but anything time traveling still a single direction of time experience. Probably most easily expressed by imagining time as a line drawn on paper with two points and bending the paper so the points touch momentarily.

Time reversal is the universe (or I suppose part there of) hitting a rewind button.

(Mind you the means to create time travel itself might require any amount of new physics to actually occur but this isn't relevant to time travel as presented in everything)

jseah
2011-12-09, 04:12 PM
Ah, you do make a good point. All our physics, we know from forwards moving time.

That is true. And we won't know what new physics we might encounter if we could somehow reverse time for a section of the universe.

However, we are already assuming "no new physics" with this whole consistent time travel. Besides, I am just using it to point out how entropy reversing does not violate any physical laws.


Since you do agree that a cup spontaneously un-breaking is possible, then its certainly possible that such a specific arrangement of pieces might arrive from the future to self-assemble in a way that reduces entropy.


As for this:

Their own entropy would have inevitable effects upon other materials.
Not true. Entropy isn't a thing that has effects.

It isn't even the "history" of an object. Objects with longer histories do not necessarily have higher entropy. The entropy of an object solely depends on its current state.

...

Why do I get the feeling that we understand different things by the word entropy?


Entropy is a description of the state of an object. The entropy of an object does not affect how physical laws operate on it nor how it interacts with other objects/energy.

Its not a value that exists in some physical form like gravitational energy or velocity.

All entropy means is "the number of ways an object can be arranged and still be, functionally, the same object".

An object at a certain point in time will only ever have one arrangement. But the number of equivalent arrangements can be used to compute the entropy of an object.


the concept of entropy evolved in order to explain why some processes (permitted by conservation laws) occur spontaneously while their time reversals (also permitted by conservation laws) do not; systems tend to progress in the direction of increasing entropy.
<...>
In statistical mechanics, entropy is a measure of the number of ways in which a system may be arranged, often taken to be a measure of "disorder" (the higher the entropy, the higher the disorder). This definition describes the entropy as being proportional to the logarithm of the number of possible microscopic configurations of the individual atoms and molecules of the system (microstates) which could give rise to the observed macroscopic state (macrostate) of the system.

With time travel, the "microstates" can be forced to reverse entropy for the duration of the time loop, provided that is the most likely to happen consistent solution.

Which you will only get if you rule out all the entropy increasing solutions, since those, pretty much by definition, exist in vastly higher number if not controlled.

Soras Teva Gee
2011-12-09, 05:16 PM
Ah, you do make a good point. All our physics, we know from forwards moving time.

That is true. And we won't know what new physics we might encounter if we could somehow reverse time for a section of the universe.

I have trouble even conceptualizing an incomplete reversal myself, even putting aside say the heck photons do in case like this?


Since you do agree that a cup spontaneously un-breaking is possible, then its certainly possible that such a specific arrangement of pieces might arrive from the future to self-assemble in a way that reduces entropy.

I don't have a good reason to declare it zero because I have heard but do not have the basis to confirm things like that happening in quantum mechanics. My unanswered question would be about the energy involved in this which I suspect is one of the problems quantum mechanics has with the macro scale, things don't happen randomly/statistically or at the least I'm not aware of any macro scale observations of this. But I'm not a physicist and so lacking a reason why not leave open possibilities.

Even aside from that it should be a non-zero probability since the cups existence says it was possible so a loosely possible (if astronomically improbable) array of counter-circumstances might cause it to reform exactly as before. Spontaneously being almost besides the point because at the universal scale without restorting to mystic explanations the universe and laws of physics have to spontaneously exist. So that a cup is possible suggest the probablity of it reforming perfectly identical to itself is greater then zero.

My final answer on entropy would rest I believe on some unsettled physics


Why do I get the feeling that we understand different things by the word entropy?

Because we are.

I'm more concerned about cosmic scale entropy. At some point above a photon everything in existence can be said to have a higher state of order acting against entropy. A cup is made for example. However this is also an illusion as while we trade energy for work it is not perfectly efficient. The earth looses energy as heat to surrounding space. Its not a problem because the sun looses many orders of magnitude more energy, a portion of which keeps Earth freshly supplied. However over a long enough time its all lost to the void of space.

As I understand it many theories in physics have it that even protons should decay. Not to mention black holes evaporating and assuming dark energy continues in the manner it has we (or rather our constituent parts in other forms) are heading for a Big Rip were even spacetime comes apart. And before that the Heat Death where everything has been so spread out there simply isn't a source of energy to do anything.

So to bring it back to the cup I'm less concerned about the state of the cup then about how it goes getting back and forth between those states. It can be perfectly solid or shattered as long as its transformations do still somewhere involve a loss to that great inevitable void.

jseah
2011-12-09, 05:41 PM
Even aside from that it should be a non-zero probability since the cups existence says it was possible so a loosely possible (if astronomically improbable) array of counter-circumstances might cause it to reform exactly as before.
<...>
So that a cup is possible suggest the probablity of it reforming perfectly identical to itself is greater then zero.
So you DO get my point.

My point is that if you make everything that increases entropy inconsistent, then all those have a probability of zero.

Therefore, the tiny but non-zero probability of time travelling pieces of a cup causing the exact and torturously long stretch of coincidences required to reform the cup becomes significantly likely to happen.
(it becomes large once you renormalize since everything else is either zero or smaller than it)


But yes, that is so incredibly unlikely that if you missed anything at all, any solution that would increase entropy, that would be the most likely solution possible.


Because we are.

I'm more concerned about cosmic scale entropy.
But there isn't a cosmic scale entropy. Entropy is just a description of a system! Entropy of the universe can be broken down into entropy of various bits, and the entropy of their smaller bits and so on until you get too small to apply statistics to.

And if you can reverse entropy locally, you can do it globally.

Reversing entropy of the whole universe just going to be stuck at theoretically possible since you'll need to build a time machine that can send significant portions of the universe back in time. Or send a piece of material back far enough to have significant portions of the universe in its lightcone. (and a big enough object to allow for the amount of microscopic influence required)


RE proton decay:
Many people have looked at giant tanks of water deep underground, trying to see protons decaying. They haven't seen one yet.

Even if they do, its likely to be a random process and thus an object loop could simply have its protons just "happen to not decay". Similar to an object loop of a single radioactive atom.

Soras Teva Gee
2011-12-09, 08:30 PM
So you DO get my point.

My point is that if you make everything that increases entropy inconsistent, then all those have a probability of zero.

Therefore, the tiny but non-zero probability of time travelling pieces of a cup causing the exact and torturously long stretch of coincidences required to reform the cup becomes significantly likely to happen.
(it becomes large once you renormalize since everything else is either zero or smaller than it)

If we are talking anything Einstein or Newtonian in description then the point is that if a cup was reassembled by an extremely unlikely confluence of incidents then there would still be entropy in that something in that unlikely equation acted at less then perfect efficiency.

So you would have say the same cup being some amount colder in temperature, or something else colder as a result of loosing energy to perfectly reassemble the cup. Ergo repair not reversals of events. That I can't categorically rule the possibility of being zero does not mean we'd be ignoring cause and effect or general entropy.

When talking quantum mechanics then I don't know how its loosest bad summary of "lol everything is everywhere get dice rolling to find out where lol" I've heard allow situations like this (with astronomically low possibilities, like you could live the age of the universe a few times and never see it) but they haven't been explained to me in terms of thermodynamics and how energy works within their systems and as as soon as quantum mechanics starts talking into above atomic levels it rapidly disappears.

And when I poke around this using entropy as the second law of thermodynamics as the arrow of time compared to quantum mechanics it is listed as an unresolved problem of physics.


But there isn't a cosmic scale entropy. Entropy is just a description of a system! Entropy of the universe can be broken down into entropy of various bits, and the entropy of their smaller bits and so on until you get too small to apply statistics to.

Except there is everywhere. Entropy is directly related to the Second Law of Thermodynamics and is the closest thing to a scienifitic basis for time. It is observable in for example all the heavier atomic elements only created in supernova explosions. That is cosmic entropy, while more complex systems are created there is energy lost to do so, gradually warming up the vastly more prevalent empty void of space.


RE proton decay:
Many people have looked at giant tanks of water deep underground, trying to see protons decaying. They haven't seen one yet.

Even if they do, its likely to be a random process and thus an object loop could simply have its protons just "happen to not decay". Similar to an object loop of a single radioactive atom.

They haven't seen a lot of things. Science is probably on the verge of another iceberg (with dark energy, dark matter, exotic matter, etc) and the quantum mechanics and relativity of today may be the aether theory of tomorrow. However the basis of thermodynamics continues to be nice an observable so we aren't going to trick out entropy.

And no it matter whether the proton decayed or not in its trip, if it made enough of them it would decay all the sooner because of its increased subjective time. Where you go from there to cooking up time reversal is still rather dense to me.

Soras Teva Gee
2011-12-09, 08:31 PM
So you DO get my point.

My point is that if you make everything that increases entropy inconsistent, then all those have a probability of zero.

Therefore, the tiny but non-zero probability of time travelling pieces of a cup causing the exact and torturously long stretch of coincidences required to reform the cup becomes significantly likely to happen.
(it becomes large once you renormalize since everything else is either zero or smaller than it)

If we are talking anything Einstein or Newtonian in description then the point is that if a cup was reassembled by an extremely unlikely confluence of incidents then there would still be entropy in that something in that unlikely equation acted at less then perfect efficiency.

So you would have say the same cup being some amount colder in temperature, or something else colder as a result of loosing energy to perfectly reassemble the cup. Ergo repair not reversals of events. That I can't categorically rule the possibility of being zero does not mean we'd be ignoring cause and effect or general entropy.

When talking quantum mechanics then I don't know how its loosest bad summary of "lol everything is everywhere get dice rolling to find out where lol" I've heard allow situations like this (with astronomically low possibilities, like you could live the age of the universe a few times and never see it) but they haven't been explained to me in terms of thermodynamics and how energy works within their systems and as as soon as quantum mechanics starts talking into above atomic levels it rapidly disappears.

And when I poke around this using entropy as the second law of thermodynamics as the arrow of time compared to quantum mechanics it is listed as an unresolved problem of physics.


But there isn't a cosmic scale entropy. Entropy is just a description of a system! Entropy of the universe can be broken down into entropy of various bits, and the entropy of their smaller bits and so on until you get too small to apply statistics to.

Except there is everywhere. Entropy is directly related to the Second Law of Thermodynamics and is the closest thing to a scienifitic basis for time. It is observable in for example all the heavier atomic elements only created in supernova explosions. That is cosmic entropy, while more complex systems are created there is energy lost to do so, gradually warming up the vastly more prevalent empty void of space.


RE proton decay:
Many people have looked at giant tanks of water deep underground, trying to see protons decaying. They haven't seen one yet.

Even if they do, its likely to be a random process and thus an object loop could simply have its protons just "happen to not decay". Similar to an object loop of a single radioactive atom.

They haven't seen a lot of things. Science is probably on the verge of another iceberg (with dark energy, dark matter, exotic matter, etc) and the quantum mechanics and relativity of today may be the aether theory of tomorrow. However the basis of thermodynamics continues to be nice an observable so we aren't going to trick out entropy.

And no it matter whether the proton decayed or not in its trip, if it made enough of them it would decay all the sooner because of its increased subjective time. Where you go from there to cooking up time reversal is still rather dense to me.

jseah
2011-12-09, 09:20 PM
So you would have say the same cup being some amount colder in temperature, or something else colder as a result of loosing energy to perfectly reassemble the cup. Ergo repair not reversals of events.
Well, you only need to cool it down if the assembled cup has higher energy than the disassembled one.

Not all events have entropy and energy going in the same direction (See spontaneous endothermic reactions in chemistry).

If by energy you mean the Gibb's Free Energy, then no. You can gain Free Energy by reversing entropy.


Except there is everywhere. Entropy is directly related to the Second Law of Thermodynamics and is the closest thing to a scienifitic basis for time.
Yes, and that second law is a statistical thing. It's not a "this can't happen, ever" law. Entropy CAN decrease.

It's just so incredibly unlikely to happen that anything else will completely swamp it out.
(your mention about it being so unlikely over the period of several universe lifetimes is missing the un-likelyness of a reassembling cup by... well, let's just say that to express the magnitude of difference would be unwieldy even with scientific notation)

A H3O+ ion can, by a chain of coincidences, move UP a potential gradient. It is much much more likely to move down that gradient.

In macroscale, the many more H3O+ ions going down swamp out the one going up. Hence, entropy increases.


All I am trying to do with the time travel is cause those chain of coincidences. And no physical law is violated when I do create it, which can be forced to happen with careful use of consistent time travel.


However the basis of thermodynamics continues to be nice an observable so we aren't going to trick out entropy.
But you see, entropy decreases in spontaneous reactions (chemistry) or in normal spreading of heat.

You CAN arrange a bunch of billard balls and knock one in just such a way that they bounce around and end up back in the original triangle configuration.

Entropy can be reversed. Its use as an "arrow of time" is only what we describe the statistics as. Just a matter of chance, with a very loaded die.


And no it matter whether the proton decayed or not in its trip, if it made enough of them it would decay all the sooner because of its increased subjective time. Where you go from there to cooking up time reversal is still rather dense to me.
Let's use radioactive decay, since we don't know how proton decay is supposed to work.

You are supposing that any specific atom "remembers" how long it has existed for and thus whether it should decay. Or alternatively, it knows how long it has left before it decays.

This is a local "hidden" variable theory.

Which the Bell Test Experiments (http://en.wikipedia.org/wiki/Bell_test_experiments) have disproved, although not without some loopholes.

Radioactive half-life is just how long a radioactive atom must exist to have a 50% chance of decaying.
If a radioactive atom is on a closed time loop, the atom does not exist for an infinite period of time. It exists for exactly the length of the time loop.

During that time, there is a certain chance that atom will decay. Plainly, for the loop to be consistent, it must not. The chance is non-zero, therefore it can happen and such a loop is possible.


The time reversal was just an idea I had to try and explain what I was thinking of. You can discard the idea if you wish, I'll just use "coincidental arrangements" to refer to setups where things are going to reverse entropy.

Wikipedia mentions of time reversal on the article of Entropy (arrow of time) (http://en.wikipedia.org/wiki/Entropy_(arrow_of_time)#Correlations):

For example, whenever dealing with a gas of particles, it is always assumed that its initial conditions are such that there is no correlation between the states of different particles (i.e. the speeds and locations of the different particles are completely random
notes that this is NOT true in the case of time travelling particles in consistent time travel...

Take for example (experiment A) a closed box which is, at the beginning, half-filled with ideal gas. As time passes, the gas obviously expands to fill the whole box, so that the final state will be a box full of gas. This is an irreversible process, since if the box is full at the beginning (experiment B), it will not become only half-full later, except for the most unlikely situation where the gas particles have very special locations and speeds.
Emphasis mine.

But this is precisely because we always assume that the initial conditions are such that the particles have random locations and speeds. <...>
This can be understood if we look at experiment A backwards in time, which we'll call experiment C: now we begin with a box full of gas, but the particles do not have random locations and speeds; rather, their locations and speeds are so particular, that after some time they all move to one half of the box, which is the final state of the system (this is the initial state of experiment A, because now we're looking at the same experiment backwards!).
Which is exactly what I have been saying...

In fact, if all the microscopic physical processes are reversible (see discussion below), then the Second Law of Thermodynamics can be proven for any isolated system of particles with initial conditions in which the particles states are uncorrelated.
Which they are not. The particle states of the arriving bunch of particles from the future is constrained by the need to generate a consistent time loop.

They CAN (can, not will) be arranged with "very special locations and speeds".
They WILL if that is what it takes to satisfy the consistency requirement.

Soras Teva Gee
2011-12-10, 12:01 AM
Well, you only need to cool it down if the assembled cup has higher energy than the disassembled one.

Not all events have entropy and energy going in the same direction (See spontaneous endothermic reactions in chemistry).

You'd have a cooler something because you cannot do work with complete efficiency so some energy has to get expelled and will inevitably (though one could slow it with various means) be lost to the great void of space


If by energy you mean the Gibb's Free Energy, then no. You can gain Free Energy by reversing entropy.

On this I think we might agree for different reason, presuming magical localized reversal of entropy one would have to violate conservation of energy to wind up with more of it, because entropy is about energy travelling away from any one system.


Yes, and that second law is a statistical thing. It's not a "this can't happen, ever" law. Entropy CAN decrease.

Treating as a statistic turns Thermodynamics #2 from "You will loose every single time" to "You will loose XX% of the time greater then 50%" or it would be outright repeal of thermodynamics and entropy which is inconsistent with the observed development of the universe. Which is getting bigger, colder, and less dense.

And by the very nature of being a fundamentally uncertain occurrence means that small percentage of not loosing cannot be replicated/cultivated or there wouldn't be a fundamental uncertainty to the matter. So you would still loose in any kind of net result, just less in scientific notationally small amounts.

And given how they talk about the large scale mechanics being incompatible with the small scale it suggests that even those long odds aren't being reached or have as simple a resolution of waiting until its observed



All I am trying to do with the time travel is cause those chain of coincidences. And no physical law is violated when I do create it, which can be forced to happen with careful use of consistent time travel.

And I would say part of stable-time-loop/no-new-physics would be you can't get a result like that not achievable through purely linear means since everything is still going through its own subjective time.

There's nothing about time travel that would effect the internal probabilities of the material on the subjective course through it. So you would still have a loss just a level of probablity versus complete certainty.

Though one could perhaps relatively speaking "hurry along" that rarest of rare chances where you win you would still have in a statistical treatment of entropy with the net loss as you are just cheating the time scale by compressing it. You can't cultivate those odds to being actually higher which is what you need to act again entropy.


You CAN arrange a bunch of billard balls and knock one in just such a way that they bounce around and end up back in the original triangle configuration.

Which would result in a loss of energy due to friction with the surface and is where the entropy comes in. You would loose the energy you put into the system to the table, and a bit of wear and tear of the balls.


Radioactive half-life is just how long a radioactive atom must exist to have a 50% chance of decaying.
If a radioactive atom is on a closed time loop, the atom does not exist for an infinite period of time. It exists for exactly the length of the time loop.

Closed loops are infinite because they are by definition their very own origin. Or its not a closed loop. And therefore cannot gain or loose energy because they have an infinite time frame

Therefore a particle can't interact with anything even a photon. And therefore can only have zero effect on anything to the point of not meaningfully existing since its completely unverifiable. It cannot change because then it cannot complete its infinite loops. And if it doesn't have infinite loops it cannot be its own origin anymore.

Or you have magical ex nihilo particles that come from oblivion and add energy to the universe from nothing. At which point its not even relevant if its cycling through time or not.

It by definition could not be radioactive since that would be adding energy to the universe at the cost of itself.

SiuiS
2011-12-10, 12:14 AM
By leaving notes into the past telling to go to the past and give yourself a note to do the above to your past self in the future?

Yes, this would work. Creating a closed cycle means once you've done it, it's done. You are a singularity; your consciouscness isn't goig in circles. It isn't a groundhog day event, so it becomes past history and you're fine.


Depends. Can you fall up? Can you reverse entropy? Can you disarm a bomb by setting it on fire so that its triggering mechanism is safely burned away?

Yes, yes and yes.

jseah
2011-12-10, 05:39 AM
You'd have a cooler something because you cannot do work with complete efficiency so some energy has to get expelled and will inevitably (though one could slow it with various means) be lost to the great void of space
What I'm claiming here is that time travel will let you set up a system that does work with higher than 100% efficiency.

I make this claim based on the way consistent time travel has a strict requirement of consistency and it is possible to make a setup that free energy is gained to satisfy this requirement.

This is because the requirement of consistency is a both macro and micro scale requirement.


On this I think we might agree for different reason, presuming magical localized reversal of entropy one would have to violate conservation of energy to wind up with more of it, because entropy is about energy travelling away from any one system.
What? No, it isn't. Entropy is about a system getting more disordered. Energy travelling away as heat is only one way to increase the entropy of the universe.

A system can gain or lose energy and entropy can go up or down. Gaining heat means the system gains entropy. Losing electrical energy but gaining back a smaller portion of it as heat = net loss of energy, entropy STILL increases.
Water in your freezer loses heat to your freezer, entropy is *decreased* (but your freezer's entropy increases more)

If a system has lots of chemical energy (eg. gasoline) and you burn it in a closed system (gas + air), it has turned chemical energy into heat. No energy lost or gained. Entropy has increased.

Free Energy is the amount of useful work that can be gotten out of a system. NOT the quantity of "energy" that physics might ascribe to things like velocity, heat and light.


And by the very nature of being a fundamentally uncertain occurrence means that small percentage of not loosing cannot be replicated/cultivated or there wouldn't be a fundamental uncertainty to the matter.
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And I would say part of stable-time-loop/no-new-physics would be you can't get a result like that not achievable through purely linear means since everything is still going through its own subjective time.
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You can't cultivate those odds to being actually higher which is what you need to act again entropy.
The "no new physics" assumption of consistent time travel refers to the micro-scale physics. You can certainly have new macro-scale behaviours.

Key new macroscale behaviour is how time loop logic can create information out of nowhere. (btw, this is creating information. For 'free')

And yes, while everything is going through its own subjective time, things do not have 'history'. How much time passes for an atom makes no difference to that atom, except for marking lengths between interacting with other things.

The reason why you CAN change those odds is because the requirement for consistency allows you to make the probability of "objects not arranged in a way that results in decreasing entropy" arriving from the future to be zero.
The whole idea about consistent time travel is that certain setups affect what can or cannot arrive, independent of whether they could actually be sent if put into the time machine.
You DON'T get a randomly ordered object coming out. You get *precisely* the object that would result in itself being sent.

If that requires that entropy be reversed (through a precise chain of coincidences that the precisely ordered object sets in motion), that's what you get.


Closed loops are infinite because they are by definition their very own origin. Or its not a closed loop. And therefore cannot gain or loose energy because they have an infinite time frame
Uh, a closed loop for an atom can coexist with an open loop for the energy.

A flourescent atom in excited state arrives from the future. It flouresces and emits light. Now its in the non-excited state. It can't be sent back now since it has a lower energy than it had when it arrived.
Later, a different photon hits it and sends it to the excited state and the atom time travels back.

The ATOM is in a closed loop. The *energy* is in an open loop.

No inconsistency here.


Or you have magical ex nihilo particles that come from oblivion and add energy to the universe from nothing.
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It by definition could not be radioactive since that would be adding energy to the universe at the cost of itself.
They can add energy to the universe. That just means they will have to take up the exact amount of energy again before they leave.
But not necessarily the same packet (if you tracked it along where it went).

In fact, if a macro-scale object arrives (eg. a key), part of the object can be on an open loop. Some of the atoms might be exchanged for equivalent atoms in the universe. Some of them (say deep inside the center) might be on closed loops and only exchange heat energy.

As long as the final state of the object when its sent is the same as the one that arrives, no inconsistency occurs. This ensures you cannot add energy/matter permanently. Only for the duration of the loop.

Also, a radioactive atom that doesn't decay doesn't lose energy.

Morph Bark
2011-12-10, 05:55 AM
People really need to stop thinking about messing with time. It's getting a bit... old.

Getting? Boy, time was old before anything else existed beyond the tiniest of particles.

SoC175
2011-12-10, 04:54 PM
Maybe we are living in an altered future that was created by a time traveler just a second ago and all our memories of past years were also created one second ago

Xondoure
2011-12-10, 11:22 PM
Maybe we are living in an altered future that was created by a time traveler just a second ago and all our memories of past years were also created one second ago

But see if that were true than from the second that time traveler changed time the entire future was rewritten and we still did live all of our memories, we just wouldn't have if he had not changed the universe.

Personally if time travel is possible I subscribe to a deterministic universe with multiple timelines that are created whenever someone uses time travel. The very act of going back in time allows different events to take place so the future won't be the same, but since people are still defined by their experiences/genetics all the variables in place is all there ever will be… if that makes any sense.

Physics wise time travel is still fairly theoretical and not having a degree in the subject I don't even really know where to begin speculating on how it would work.

warty goblin
2011-12-11, 12:01 AM
Maybe we are living in an altered future that was created by a time traveler just a second ago and all our memories of past years were also created one second ago

That's one of those untestable hypotheses without any noticeable consequences whether it's true or false, which is to say irrelevant.