Could you travel faster than the speed of light?

[makinyashikino]

Say you were in a glass box travelling .99999999999999999c, and you were standing at the rear of the box. If you were to run to the front of the box, would you be going at or faster than the speed of light?

[lajoswinkler]

No, because relativistic velocities are being added by a different formula.

http://en.wikipedia.org/wiki/Velocity-addition_formula

[Camacha]

Say you were in a glass box travelling .99999999999999999c, and you were standing at the rear of the box. If you were to run to the front of the box, would you be going at or faster than the speed of light?

No. This is exactly the point of relativity. I think this question has been answered a number of times here, in ways that surpass anything I can muster. Just a quick forum or Google search will give you your answer and much more.

[PM_ME_URANUS]

No. Relative to the box you are not moving. And the box being made of glass has no influence at all. It doesn't matter if you can or cannot see outside of it.

[jfull]

Its funny, you'd think you could, but at those speeds the effects of time dilation would be extreme.

If you try to go faster, the rate that time is passing for you would be slowed so that you could never actually pass the speed of light.

Relativity is strange that way, but that really is how it works.

Edited September 3, 2014 by jfull

[Felsmak]

Why settle for running? Accelerate to lightspeed again! Relative to the box!

[WinkAllKerb'']

Could you dark the light faster than it could speed. but anyway who said they are not the same thing ? human ? are thoose guy thrustable ? ...

Hello newton. Need another apple ?

[Mazon Del]

In short to your real question about "can you go FTL" the answer you are going to get is that we don't know for certain. There is currently math that oppposes this, and currently math that supports this. So all you are going to get is "Nobody knows." but in relatively short order, this thread is quite likely to fill up with people that will violently argue back and forth on the topic until it gets locked...like usual.

[Kasuha]

Technically speaking, you can move faster than speed of light in a certain sense. It is 27,000 light years to the center of the Milky Way, yet assuming you can withstand and generate really, really excessive accelerations, you can travel that distance in a week of your subjective time. Does that feel faster than light? It sure does. Of course you'll not be actually faster than light, any light sent from Earth at together with you will be there sooner and 27,000 years will pass on Earth before you get there. But Earth will be pretty far away and you'll be just one week older.

[No one]

Not with your method.

Various other similar thought experiments:

You are stationary. You see a spaceship pass by at .8c, and you see a spaceship pass going the other way also at .8c. Thus, relative to the first spaceship, the second is going at 1.6c.

You are in a rocket going at .9c with .2c of delta-v. You burn. Now you are going at 1.1c.

(Your example) You are in a racecar on a train. The racecar goes at .2c relative to the train. The train goes at .9c relative to the ground. Thus you are going at 1.1c relative to the ground.

All of the above are wrong.

When dealing with non-relativistic relative velocities, you add them together. For example, if I see a car drive by one way at 30 m/s and I see a car drive by the other way at 30 m/s the cars are going at 60 m/s relative to each other.

If you are in a rocket going at .9km/s with .2km/s of delta-v and burn you are going at 1.1km/s

If you are in a racecar on a train, the racecar goes at 20m/s relative to the train and the train goes at 90m/s relative to the ground, you are going at 110m/s relative to the ground.

That is, if you are going at v in the same direction as another object which is going at u, your velocity relative to the other object is v+u.

When dealing with relativistic velocities on the other hand, you have to use a different formula: (v+u)/(1+(vu)/(c^2))

When v and u are really small, the difference is negligible.

When v and u are sufficiently large, the difference matters.

[Everten P.]

Warp could do it... If had been proven already and wasn't theoretical/experimental. But warp works by shortening TIME and SPACE ahead of you and expanding it behind you causing you not to move faster but there is much more to it... http://en.wikipedia.org/wiki/Alcubierre_drive I know it is Wikipedia

[rkman]

From a practical 'travelers point of view' you can in fact cover a distance of x light years in considerably less than x years, just make sure you're going very fast.

Looking at it as one would usually look at traveling, in terms of distance and time:

Per as usual the traveler uses his/her own clock to keep time.

Take note of the distance you are about to travel.

Take note of your time of departure (for the sake of this experiment the travelers' clock is synchronized to local clocks).

When you get to the destination take note of the time of arrival (and compare to local clocks).

There's one peculiar thing though: after the voyage the traveler's clock will be way behind on clocks that did not travel (local clocks).

All that happens every time something changes velocity relative to something else, but in every day life the effect is so small we don't notice.

[jfull]

All that happens every time something changes velocity relative to something else, but in every day life the effect is so small we don't notice.

There are a handful of comparatively mundane situations where you need to account for relativity.

Clocks on satellites need to compensate for a very tiny amount of time dilation in order to stay synchronized with clocks on earth.

[Kasuha]

There's one peculiar thing though: after the voyage the traveler's clock will be way behind on clocks that did not travel (local clocks).

This is true if you travel at high speed in circles and you have very precise clock (e.g. if you're a GPS satellite). But if it is about traveling to a distant place, there's no real option of comparing your clock with someone else that was perhaps traveling there significantly slower. Clock of each colonist in that place would be different based on how fast and which way did he travel there, and most likely they'd in the end agree on their own timebase, completely unrelated on Earth. There would be nothing to compare your clock to.

There is no universal time in universe. Your clock depends on how fast you are moving through it and each galaxy, even each star has its own clock, some running slightly faster, some slightly slower. In a sense, your time passes together with the direction in which you're moving. If you change direction, the direction of your time changes as well.

[rkman]

Clock of each colonist in that place would be different based on how fast and which way did he travel there,

I did specify that "local clocks" did not travel, and although I did not mention other colonists, if there are any they have long since agreed on a common time, which is referenced to Earth time. It is close enough to Earth and relative velocity is low enough that they can be considered to be in the same frame of reference. I suppose i should have specified that.

There is no universal time in universe.

I think we can get close enough in the case of a neighboring solar system.

Edited September 5, 2014 by rkman

[StrandedonEarth]

From what I recall of relativity way back in Grade 12 Physics, the math does support moving faster than light. It's getting through lightspeed that is the problem. As you approach c, time and distance dilate and mass increases. At c, the equations explode into a divide by zero error, meaning infinite mass and I suppose time would stand still. It would take infinite energy to accelerate infinite mass past lightspeed, and something already moving faster than light (Star Trek loved to mention tachyons, the hypothetical FTL particle) would not be able drop below lightspeed. IIRC (big IF), tachyons would have "imaginary" mass, due to the equations taking the square root of a negative number.

[Brotoro]

[K^2]

There would be nothing to compare your clock to.

It'd be quite trivial, for any foreseeable mode of travel, to simply use signals from a chosen distant pulsar to keep track of "universal" time. Naturally, moving closer to the pulsar would advance time, and vice versa. But we can either correct for that knowing the distance, or simply deal with it like we do with time zones.

[problemecium]

Well as long as the thread hasn't been locked, my thoughts.

While I lack the worldly knowledge to bowl over anyone's argument conclusively in either direction (being a mere human), I would like to point out that Mother Nature does not care about our silly human math and its "divide by zero errors." A well-known case is the black hole: an object that by conventional laws of physics should have an infinite density and obliterate the universe through its sheer existence, but in the real world seems to be fairly common and surprisingly harmless (just don't touch it). Many other examples exist.

So I have a hunch the light barrier will one day be broken the same way the sound barrier was (in its time, it too was believed impassable, at least inside our atmosphere). Obviously a "light boom" would be many times more noisy and dangerous than a sonic boom, but I don't see us blowing up the universe or getting facepunched by The Kraken any more than we did when we made black holes in the Large Hadron Collider (in case nobody noticed, the universe appears to be quite intact).

[K^2]

It's not so much that Universe "doesn't care" about our math problems. It's more the case that our math problems usually indicate that things aren't as simple.

For example, elementary particles are also point objects. They also have infinite density, and should result in all the same problems. But, fortunately, they don't obey laws of classical mechanics, but rather these of quantum field theory.

Same goes for black holes. There are a number of "divide by zero" problems with both singularity itself and the event horizon. And everything we've learned so far points to these problems being resolved in proper quantum gravity model. Shame we don't have one in which we can actually compute anything useful at these scales. But maybe some day.

[cantab]

Even if you could reach the speed of light - and the simple in principle though probably impossible method of reducing your mass to zero springs to mind - the biggest problem is that the next thing you would experience is crashing into something. For an outsider time stops for a thing moving at the speed of light, while from the point of view of the moving thing the entire universe compresses into a two-dimensional plane perpendicular to your motion.

[rkman]

A well-known case is the black hole: an object that by conventional laws of physics should have an infinite density and obliterate the universe through its sheer existence

A black hole should obliterate the universe? I'm sure no scientists has ever said that.

Maybe you think infinite density means infinite gravity? The force of gravity (outside the event horizon of a black hole) depends on mass, not density.

[N_las]

So I have a hunch the light barrier will one day be broken the same way the sound barrier was (in its time, it too was believed impassable, at least inside our atmosphere).

Nobody ever thought that it was physical impossible to go faster than sound. The only question was, if we could overcome the engineering problems to do so. Bullets and the tips of whips broke the sound barrier long before we even thought about airplanes. It is fundamentally different than the speed of light.

Obviously a "light boom" would be many times more noisy and dangerous than a sonic boom.

Well, obviously! Who could deny that.

*sarcasm off

[cantab]

Well in a medium a particle moving faster than the speed of light in that medium (but slower than c) produces Cherenkov radiation, which is essentially a "light boom".

[WestAir]

If quanta of space and quanta of time are actual things, and the smallest of spacial quanta is described, it is possible to go AT the speed of light without breaking relativity.*

Let's pretend a meter is the smallest quanta of space, and no particle or energy can be made to move distances smaller. Let's also pretend that a photon created during the big bang has finally traveled 13 billion light years and one meter. Let's pretend that you've existed since the big bang and have been chasing that photon, and since the big bang you've only fallen 1 quanta (1 meter) behind that photon. Because space and time go hand in hand, if we took the measurement yesterday (before you fell behind 1 quanta), you and the photon would have traveled the same distance, despite the fact that you're going slower.

It's a math game with quantization of reality. I could say you are traveling "1 quanta per 14 billion years slower than light", and if 14 billion years have yet to pass, you're neck and neck until it does. And if that's the case and quantization of space-time is possible, there must also be a finite amount of energy that would be required to make you reach the speed of light (at least until a finite amount of time passes to where you lose ground on a photon). Said energy would probably be equivalent to the mass of a Galaxy or something, but I digress.

*The following is subject to scrutiny by those who know more than me. AKA, anyone else here.