moving at multiple times light speed

[Traab]

Is there even a theory for this since light speed itself is supposed to be impossible to truly reach? Meaning what would happen if you manage to reach light speed and say, double it. Or is it just rank imagination land of scif i writers trying to come up with a way for traveling the galaxy to be anything other than a generational quest? I know there are some things like different orders of infinity out there, so maybe that gets covered under those headings?

[factotum]

The problem is, as you've already stated, it's impossible to reach lightspeed with any object with mass-it would require infinite energy to get it there. The only real "proper" physics dealing with FTL is in the area of tachyons, theoretical particles that can *only* travel faster than light--however, such a particle would needs have imaginary mass in order for the equations to work out, so they're generally not considered to be something that can realistically exist.

This is probably why almost all SF that involves FTL handwaves it by having the ship travelling through something other than real space when it's at FTL velocities, because that way you don't need to worry about the complications of what happens to an object at those speeds.

[Yora]

That's where relatively comes in to ruin your day.

In our normal everyday life at very slow velocities, we think that "speed = distance / time". Enter any number of distance and time and you can get any value for speed. But that's not how this actually works.

When we are talking of very high speeds, it's generally best to just forget about the humble little photon, because all of this does not really have anything to do with light.

What this is all about is "c", which is the constant for the propagation of causality. c is not variable, it always has a fixed value of about 300,000 km/s.

The photon is a curious case. The acceleration of any object depends on its mass and the energy that accelerates it. Higher mass needs more energy to accelerate to the same speed as lower mass. And for a given mass, more energy will lead to a higher acceleration and smaller energy will lead to lower acceleration. The weird thing about the photon is that it has a mass of 0, which means any possible amount of energy should accelerate it to infinite speed. Make the mass infinitely small, then the speed should be infinitely high.

But in practice light does not have infinite speed, but instead always has a constant speed of about 300,000 km/s. This is not simply a speed limit. We assume in everyday life that 1 meter is a fixed constant and that 1 second is a fixed constant. But they are not. c is a fixed constant. Distance and time are variables that change that no matter under what circumstances you measure the speed of a particle with no mass, the result will always be 300,000 km/s. When you go faster, distances contract and time moves slower.

As far as the universe is understood today, any speed greater than c makes no sense and is completely impossible. 300,000 km/s is 100% speed. Any hypothetical form of faster than light travel is basically teleportation and completely disconnected from "speed = distance / time".

[Khedrac]

The main issue with moving at (or faster than) the speed of light is that relativity means that the mass of the object (with a rest mass) increases and would obtain infinite mass at the speed of light, and that is impossible. (That and the time-travel effects dealt with in other threads in this forum.)

Photons don't have a rest mass, which is how they can travel at the speed of light (so one answer to infinity times zero is the mass of a photon).

The way to get round this is to do the travelling out of the conventional universe, and this is not just the realm of science fiction.

Method one is using a wormhole as a shortcut. Stephen Hawking used to believe that something would prevent this, but in later life he changed his opinion to that it is possible if you can make a wormhole, something we have no idea how to do and something that probably requires "exotic matter" whatever that is.

Option two is to travel "elsewhere", this is usually thought of as the realm of science fiction's hyperspace, but it is also what quantum tunnelling particles do - and they achieve an "effective speed" of about 1.3 times the speed of light!
Side note: it has been stated that it is impossible to transmit information by quantum tunnelling because it would be ftl, however a standard qt experiment has been hooked up to a record player and amplifier and the output was recognisable as Mozart, if a little scratchy; what I don't think was checked was if the music travelled ftl as distinct from the particles carrying it...

So, according to current science, so long as you don't do the travelling in the relativistic universe, it is possible to travel faster than light, but the effects are not fully known (aside from probable time travel effects) - since we count as information, the likely bar on passing information might scramble us at a sub-atomic level.

[Radar]

Method one is using a wormhole as a shortcut. Stephen Hawking used to believe that something would prevent this, but in later life he changed his opinion to that it is possible if you can make a wormhole, something we have no idea how to do and something that probably requires "exotic matter" whatever that is.

Specifically matter that has negative gravitational mass. It is assumed that Casimir effect can be used to create the needed effect.

Option two is to travel "elsewhere", this is usually thought of as the realm of science fiction's hyperspace, but it is also what quantum tunnelling particles do - and they achieve an "effective speed" of about 1.3 times the speed of light!

Not quite to be honest.

One should also be aware that there are materials in which phase speed (speed of a monochrome, constant amplitude wave) of EM waves is greater then c. However, the group speed (a speed of a pulse, which is the one important for sending any messeges) never ever exceeds c.

Essentially the only still not ruled out way to move faster then light is to cheat by taking some shortcut through a wormhole or bending the spacetime in some other ways like for example in the Alcubierre drive concept and its later fascinating improvements which actually bring the energy requirements down to reasonable levels.

[Bohandas]

The problem is, as you've already stated, it's impossible to reach lightspeed with any object with mass-it would require infinite energy to get it there.

What if there were some way to briefly remove the higgs field over a small area of space? I don't know if this is possible even in theory, but if it could be done wouldn't all matter in the area not only drop to zero mass but also immediately jump to lightspeed?

And as a more controversial followup, would it be possible to then somehow arrange for its velocity when its mass reappears to be above c. My understanding has always been that the problems lay in getting to c and in changing the velocity of an object that is currently at c. Removing the higgs field would do the first and reapplying it would do the second.

[factotum]

What if there were some way to briefly remove the higgs field over a small area of space?

As soon as you start asking questions like that you might as well be saying "What if there was some way to create a magical flying pig that can travel instantaneously across the universe because I want it to?". It has about the same level of probability.

[Yora]

What if there were some way to briefly remove the higgs field over a small area of space? I don't know if this is possible even in theory, but if it could be done wouldn't all matter in the area not only drop to zero mass but also immediately jump to lightspeed?

My very vague understanding is that nothing would keep the particles of the spacecraft together and they would fly off in random directions at lightspeed. Everything inside the area would be instantly annihilated in a flash of either elementary particles, or pure energy if the particles themselves are ripped apart.

My understanding has always been that the problems lay in getting to c and in changing the velocity of an object that is currently at c.

No. The fact that it would take infinite energy to get an object with mass to c is a common explanation for why it is i possible to go faster because its relatively easy to explain and understand. At this point you already don't have to bother looking any deeper in the realm of acceleration and relativity.

But the whole problem does go much deeper. Within the current understanding of space time, speeds greater than c make no sense. c is not randomly 300,000 m/s, but is 100%.
Saying that something is traveling at 110% of c is like saying a box is 110% full. A 1000 ccm container can not contain 1100 ccm of stuff.

Another thing: It is not just the photon that travels at c, but also the electromagnetic force and gravity, and I also assume the strong force. If atoms would travel faster than c, they would move faster than the forces that bind them together. They would no longer be able to interact with each other. Atoms can't stick to other atoms; protons, neutrons, and electrons that make up atoms can't stick together, and the quarks inside protons and neutrons can't stick together. Anything faster than c could only exis as individual elemental particles at the most.

[Bohandas]

As soon as you start asking questions like that you might as well be saying "What if there was some way to create a magical flying pig that can travel instantaneously across the universe because I want it to?". It has about the same level of probability.

Well, as I said (or attempted to say) I don't know enough about the higgs field to know whether it's theoretically possible to manipulate. I take it from your response that current theories probably say it can't be manipulated.

But the whole problem does go much deeper. Within the current understanding of space time, speeds greater than c make no sense. c is not randomly 300,000 m/s, but is 100%.
Saying that something is traveling at 110% of c is like saying a box is 110% full. A 1000 ccm container can not contain 1100 ccm of stuff.

Wouldn't it be more correct to say that celerity is 100% when speed is equal to c. Celerity has an infinite value and thus can't get any higher (barring some sort of weirdness with aleph values, and/or the explanation that if it were possible you would arrive before you left) and as a result speed can't increase either

[Radar]

Another thing: It is not just the photon that travels at c, but also the electromagnetic force and gravity, and I also assume the strong force. If atoms would travel faster than c, they would move faster than the forces that bind them together. They would no longer be able to interact with each other. Atoms can't stick to other atoms; protons, neutrons, and electrons that make up atoms can't stick together, and the quarks inside protons and neutrons can't stick together. Anything faster than c could only exis as individual elemental particles at the most.

I do not think it is the best way to look at it. After all, velocity is relative, so within the traveling objects, things should work as normal in accordance to local proper time. The crazines comes from the fact that one of the directions of space and the direction of time are switching places, when you do a Lorentz transform with speed larger then c - this is basically what the imaginary result means. By literal interpretation we would get situation that both future and past of some object can lie in, for example, causal past (or future) of the FTL traveller. His when would be our where.

Even if it would be theoretically possible (which I very much doubt due to the problems with mass and by extension any interaction with the rest of the universe), just trying to imagine, how things could look like from such a perspective is way harder then Miegakure will ever be (I so wish this game were already available).

[Anymage]

Well, as I said (or attempted to say) I don't know enough about the higgs field to know whether it's theoretically possible to manipulate. I take it from your response that current theories probably say it can't be manipulated.

"Manipulate" and "remove" are two very different things. I can trivially change the strength of the gravitational or electromagnetic field in an area (a heavy, strong magnet does both), but shutting off gravity/electromagnetism or creating a photon-free zone is pure fantasy. And while I'm sure someone could work out how the other fields would interact if one magically vanished, it would be a lot of work for very little point. (Beyond a general "existence as we know it would be thoroughly boned".)

Otherwise your question did boil down to "if we could magic the mass of a particle from a positive value down to zero, could we cause it to have an imaginary value after the magic stopped?" In which case we could justify imaginary and/or negative values because magic, but the fact that no real signs of such things have been seen in our universe says that they're about as likely here as magic is.

Incidentally, though, we're highly confident that objects going faster than light exist. Horizons, both particle and event, are defined as the point where spacetime is moving away so fast that light cannot reach us. Spacetime itself is moving FTL, and carrying anything in and beyond those regions with it. However, since anything past a horizon is by definition uninteractable, that's not really meaningful or useful as anything other than trivia.

[Yora]

I do not think it is the best way to look at it. After all, velocity is relative, so within the traveling objects, things should work as normal in accordance to local proper time.

That's what causes time dilation. When speed goes up, time slows down, so fundamental forces work as they always do, with light traveling at 300,000 m/s.
And at 100% c, time dilation reduces the passing of time to 0% and time stops.

I guess that's where the idea comes from that at faster than light, you go backwards in time, but I think that's just a result of "garbage in = garbage out". Invalid input into the equation gives you a nonsensical ourput.

[halfeye]

Incidentally, though, we're highly confident that objects going faster than light exist. Horizons, both particle and event, are defined as the point where spacetime is moving away so fast that light cannot reach us. Spacetime itself is moving FTL, and carrying anything in and beyond those regions with it. However, since anything past a horizon is by definition uninteractable, that's not really meaningful or useful as anything other than trivia.

Surely horizons move as speed changes? if something here was moving toward a horizon at a significant fraction of the speed of light, it's horizons ought to be different than ours (counting us as being stationary, though relatively speaking, we're going as fast as them and they're stationary from their p.o.v.)

[Yora]

Horizons depend on location. I think speed doesn't really factor into it.

Though since your observation horizon always expands, your speed would factor into that expansion.

[halfeye]

Horizons depend on location. I think speed doesn't really factor into it.

Though since your observation horizon always expands, your speed would factor into that expansion.

Always expands? in what sense?

I am thinking that as movement occurs, the horizon will move too. Maybe it's the distance not the speed that makes the difference?

[gomipile]

Incidentally, though, we're highly confident that objects going faster than light exist. Horizons, both particle and event, are defined as the point where spacetime is moving away so fast that light cannot reach us. Spacetime itself is moving FTL, and carrying anything in and beyond those regions with it. However, since anything past a horizon is by definition uninteractable, that's not really meaningful or useful as anything other than trivia.

I wouldn't call some horizons objects. They're loci of points in spacetime, but they aren't necessarily made of matter or energy themselves. A Rindler horizon, for example, isn't created by mass or a specific amount of energy, it's just a locus of points relative to a particular accelerating reference frame.

I can make a shadow or a dot of laser light race across the surface of the moon faster than light can travel along that surface, but I haven't created a superluminal object. It's a locus of points, but there is no matter or energy remaining a part of that locus for it's duration.

[Yora]

Always expands? in what sense?

I am thinking that as movement occurs, the horizon will move too. Maybe it's the distance not the speed that makes the difference?

When the universe was 2 billion years old, you could see objects up to 2 billion lightyears away*. You could not see objects 2.1 billion lightyears away, because light from those objects did not have time to reach you yet. When the universe was 10 billion years old, you then could see objects 10 billion lightyears away. That horizon is always expanding just as time is passing.

Let's assume you and I are 0.0001 lightseconds away from each other (completely arbitray number I just made up.) This means the horizon of my observable universe is 0.0001 lightseconds shifted to one direction from your observable universe.
If you were to move at the speed of light, light coming from behind you could never reach you, so the horizon to your back is just right behind you. In contrast, you are racing towards any light that comes to you from your front, so your horizon in that direction is not just expanding away from you at the speed of light, but twice the speed of light.

*Since the universe itself is expanding, this number is not actually correct. Objects that were 2 billion lightyears away 2 billion lightyears ago are now a much further distance away from us. So the horizon of the observable universe is not 13.8 billion lightyears away but considerably farther. We're not actually seeing things, but just receive photons that were emitted at some place in the universe at some point in the past. While the photon was travelling through space, both its source and Earth have done a lot of traveling around.

[Jay R]

Either it’s impossible, or the knowledge of how to do it, and what would happen, is beyond our understanding.

If all the mass and energy in the universe except for one neutrino were converted into energy and used to propel that one neutrino at top speed, it would move at just under the speed of light.

Moving mass at the speed of light requires infinite energy. Moving faster takes more.

There are theories about how to do it, but each such theory requires violating the laws of the universe as we know them.

Therefore we cannot use the laws of the universe as we know them to answer your question.

Either it’s impossible, or the knowledge of how to do it, and what would happen, is beyond our understanding.

[Arcane_Secrets]

The way to get round this is to do the travelling out of the conventional universe, and this is not just the realm of science fiction.

Method one is using a wormhole as a shortcut. Stephen Hawking used to believe that something would prevent this, but in later life he changed his opinion to that it is possible if you can make a wormhole, something we have no idea how to do and something that probably requires "exotic matter" whatever that is.

Realizing that I'm asking a question where I might not understand the answer, if wormholes are possible and could be made, how would the location for the endpoint of the wormhole be controllable?

[Anymage]

Realizing that I'm asking a question where I might not understand the answer, if wormholes are possible and could be made, how would the location for the endpoint of the wormhole be controllable?

I might be wrong here, but I think you need to have control over both endpoints. Making them close to each other, like in the same lab, would be the easiest way to start.

However, because space isn't just the static backdrop on which stuff happens, these wormholes also aren't static points in static space. You can keep one in your lab while coaxing the other to move somewhere else. Not only does this let you have instant transit to some faraway place, you can also have one end start moving really fast while the other stays in place. Since time will be passing differently at both ends, you can then bring the other one back and use them to directly travel through time.

[Lord Torath]

Realizing that I'm asking a question where I might not understand the answer, if wormholes are possible and could be made, how would the location for the endpoint of the wormhole be controllable?

That would be the trillion-dollar (or euro if you prefer) question, wouldn't it. I am not aware of any theories for actually how to control the end(s) of a wormhole.

[Yora]

Realizing that I'm asking a question where I might not understand the answer, if wormholes are possible and could be made, how would the location for the endpoint of the wormhole be controllable?

With wishful thinking.

[Misery Esquire]

A sort of side-along question about this idea has come to me in the past, so;

A lot of people ask about what happens to you when you move faster than light - but isn't a more curious question be what happens when you go faster than light? Would there be a... Light boom? What would the consequences of that be? Would it be like a sonic boom where only the leading edge is "the boom"? …Any guess what happens to the temporarily-faster light that was forced out of the way?

More humorously; Is there a shape best suited to moving through light, and would we call it photodynamic?

[Bucky]

The "light boom" is called "Cherenkov radiation" or "Askaryan radiation" depending on whether the faster-than-light particle has an electric charge.

[Anymage]

If a particle goes through a medium faster than light goes through that medium, see Bucky's answer. Like, light goes slower through water than through air, and slower than air than through a vacuum. Going faster than light goes through glass is quite possible.

If you're talking about the speed of light in a vacuum, that's considered the fastest anything can move through space. (Some people have thought up hacks that involve warping the fabric of spacetime itself, but don't expect to see anything close to real applications any time soon.) If you could magic yourself up to light speed as just normal movement through space, though, you would destroy the universe. As a massive object you need more and more energy to go faster as you get closer to c, and to actually reach c you'd need infinite energy. E=MC², infinite energy equals infinite mass, and infinite mass would exert infinite gravity. You'd become the mother of all black holes, and everything would get sucked in by your infinite gravity.

[factotum]

You'd become the mother of all black holes, and everything would get sucked in by your infinite gravity.

Although, since nothing else in the universe can travel FTL, and you're travelling at lightspeed, nothing would actually be able to catch up with you and get "sucked in". Moot point, of course, because absent some infinite source of energy nothing with mass is going to achieve lightspeed anyway.

[Traab]

Although, since nothing else in the universe can travel FTL, and you're travelling at lightspeed, nothing would actually be able to catch up with you and get "sucked in". Moot point, of course, because absent some infinite source of energy nothing with mass is going to achieve lightspeed anyway.

Just because it cant actually match your speed doesnt mean it wouldnt be torn apart atom by atom in your wake trying, like dragging your hand through a pool of water and watching the eddies swirl everything around as you pass, only, you know, infinitely more deadly. Hmm, I wonder if it would create a sort of current in space as the obliteration of everything in your way and the things around you getting dragged in has some sort of effect on regular space. Imagine it, the path the ftl traveler took leaves a trail behind them sort of like a riptide in space.

[factotum]

I'm not sure it would have that effect, because we're talking infinite gravity, which would presumably have infinite effects at all distances--so there'd be no tidal forces, for instance, because that requires a gravitational gradient that wouldn't exist here. Since all particles in the universe are being equally attracted by the infinite mass, it shouldn't tear anything apart unless you're close enough for the different direction of the attraction to be significant.

[Lvl 2 Expert]

Just because it cant actually match your speed doesnt mean it wouldnt be torn apart atom by atom in your wake trying, like dragging your hand through a pool of water and watching the eddies swirl everything around as you pass, only, you know, infinitely more deadly. Hmm, I wonder if it would create a sort of current in space as the obliteration of everything in your way and the things around you getting dragged in has some sort of effect on regular space. Imagine it, the path the ftl traveler took leaves a trail behind them sort of like a riptide in space.

Yeah, if traveling leaves a semi-magic riptide through space.

In the scenario where a ship traveling at light speed becomes a black hole and starts sucking stuff in the universe is pretty safe.

A black hole after all only creates the same gravity field as anything else of the same mass. Yeah, sure, they have an event horizon, but that's because they're smaller than anything else the same mass. If you'd suddenly turn the Earth into a black hole somehow we would all fall in, but the moon would just keep spinning where it does.

On top of that, gravity causes acceleration. Acceleration by gravity has to be pretty steep for it to cause damage. Yeah, you can die in a car crash where you decelerate from 50km/h to 0 within the space of a meter, but that's because the force is unevenly applied. The whole blow goes to the front of your body hitting the dashboard and goes in like a shockwave from there. If you were decelerated from 50 to 0 within the span of a meter by a large mass suddenly appearing behing you (and disappearing just as sudden ones you hit 0, for the sake of this scenario) that wouldn't be deadly, because the force is pulling on every atom in your body at the same time. So if the spaceship-black hole passes really close by, like say it flies right through you like a small mass black hole like one made out of a spaceship can, you might get a jolt, but it wouldn't be very damaging.

More to the point, the black hole would not pull you in, even though it passed right through you. That's because it is traveling at the speed of light, and the only way the atoms in your body are going to get absorbed into the black hole is if they can catch up with it. And they can't, because the black hole will accelerate them a little bit, but it can't accelerate them to match its own speed, because that would take infinite energy. It can't slow itself down either, because that would take infinite energy as well. So even quite a large black hole speeding by you would throw you around a bit, definitely a risk of throwing up, but it would leave just as fast as it arrived, and you're not going with it.

EDIT: Oh, you were talking about a black hole with infinite mass. I guess I don't know enough about physics. Would say an electron also become an infinite mass black hole if it traveled at light speed? That's silly. We just used an infinite amount of energy accelerating it and now we need to add another infinite amount of energy to make it infinitely heavy. Universe, start being reasonable.

[factotum]

Would say an electron also become an infinite mass black hole if it traveled at light speed? That's silly. We just used an infinite amount of energy accelerating it and now we need to add another infinite amount of energy to make it infinitely heavy. Universe, start being reasonable.

The infinite amount of kinetic energy you've given the particle to accelerate it to lightspeed is enough to give it infinite mass, you don't need a mysterious second infinite amount of energy.