how do we know nothing can move faster than light ?

Answer 1

You think you have a headache now, just wait.

For a second forget time dilation, taychons, and other interesting, but irrelevant subjects.

Let's just look at mass.

As an objects speed inceases it's mass increased at the rate of M’ = M/sqr(1-v²/c²). As you can see, the faster you go, the more mass you have. Of course since c² is such a large number, you have to be traveling very fast for you to even notice the effect however as you approach light-speed the effect becomes more and more noticable.

Now, the more mass you have, the more energy it will take to accelerate you so the faster you go, the more energy will be needed to make you go faster until as you approach light speed, your mass become close to infinity so it would take an infinite amount of energy to increase your speed. That is why ltraveling faster than then speed of light is impossible, there is no way to get the energy necessary to go faster.

Taychons.

Taychons are interesting little buggers. First theorized about in 1962 by Olexa-Myron Bilaniky and Ennackal Chandy George Sudarshan, they wondered about the properties of an particle at superluminal velocity.

As you can see by the formula M’ = M/sqr(1-v²/c²), if you are traveling at faster than light-speed (1-v²/c²) becomes less than 0. In order to have the square root of a negative number you have to use i, or thesquare root of -1. This is an imaginary number, so you would have an imaginary mass.

An interesting thing about that is the more energy you have (ie, temperture) the slower you would travel. the exact opposite of what you expect with real mass.

I could go on and on about this, but I don't want to bore you,I think you have enough information to see why you can't travel faster than light.

PS: e=mc² does not, in itself say that you can't travel faster than light, but since it is derived from the formula M’ = M/sqr(1-v²/c²), I'll just assume that the person who said that did the math themselves and also derived that formula from the FitzGerald equations.

Answer 2

Special relativity is built on two axioms - that all motion is relative, and that everyone gets the same result for the speed of light. Both of these axioms were supported by experiment at the time.

A logical conclusion from these axioms is that to accelerate a mass to the speed of light will take infinite energy - hence is impossible.

We know the theory to be true because its other predictions have been very well tested. And the axioms have never been found to be false. Hence we know the speed of light cannot be attained by a mass travelling below the speed of light.

But of course, one experiment could prove all this wrong - however, it would also bring down the whole of the rest of the theory, so its very unlikely.

Relativity says nothing about particles that have always travelled above the speed of light. Such particles have been theorised - they are called tachyons (there could be many different types of tachyon - its a family name). They would have the strange property that their energy would decrease as they speeded up. However, they have never been observed and so remain a mathematical quirk.

Answer 3

As everyone else has said, we don't really. But all of Einstein's theories in this area do appear to be bourne out by experiments.

The famous E=MC 2 explains very neatly why it should not be possible to travel faster than light. The faster an object travels the more of it's mass it needs to convert to energy. As it approaches the speed of light, it requires an infinite amount of energy to remain in motion - and since there are no infinite amounts of energy, this would be impossible.

It does seem quite likely that there are things that can travel FTL - but they can't deccelerate past it. In other words, if you are slower than the speed of light, you cannot go faster - and if you are faster, you cannot go slower.

Why? - no blinkin' idea. But Relativity, as brilliant as it is, is still only a theory, like Big Bang and everything else. So we'll never know for sure, although we can still strongly suspect - which we currently do.

Answer 4

The words "faster than light" are much easier that the actual concept. Our common experience of light is that it is instant. It's only when we get into astronomical distances that we find it's not.

When we start dealing with millions of miles, concepts of speed and faster are rather different. We can no longer rely on our experience that running is faster than walking etc. We therefore have to rely on mathematical models such as the various theories of relativity. That gives very different ideas of space and time. If something travels at very high speed, the space time continuum tends to change around it, effectively giving a finite limit. Matter travelling at that limit would be infinitely compressed. Not even light can travel at that speed, and the speed of light in a vaccuum is very slightly less than that limit.

Answer 5

Nice answer WMan.
Well, nothing moving faster than light, tricky but funnily enough that's what I think is the only thing that can move FTL, nothing of any mass that is. The question is energy moving FTL and there is something that moves FTL.
We now know as far as I know that what happens to a particle on the edge of space is 'known' by all particles instantly everywhere in space, that's FTL as far as I see it.
Now whether this is due to Higgs-Bosun fields or parallel world super highways I have no idea being a total layman but something is going on......

Answer 6

It's not so much moving faster than light that's the problem, it's accelerating to light-speed. The faster you go, the heavier you get (according to Einstein) and it therefore takes more energy to get faster. The theory shows that you would need infinite energy to accelerate to light speed.

It's quite possible that there are particles which already travel at light speed or faster, because they don't need to accelerate. But for us slowcoaches, it seems there's no way to get there.

Answer 7

E=MC^2 says that in order to go faster than the speed of light would require infinate energy. Either Einstein was wrong or nothing can move faster than the speed of light. I tend to think that Einstein wasn't wrong - so I'll just assume nothing can move faster than light.

Answer 8

Hi,

It is not that nothing can travel faster than light, theoretical tachyon particles are supposed to travel faster than light since unusually they lose energy as the accelerate. Rather the consequence of relativity is that nothing can accelerate to light velocity since the faster it goes the more mass it gets and so needs more energy to accelerate it. Approaching light speed this energy would approach the infinite.

Answer 9

When we say faster than light what is really meant is faster than energy .
If it were discovered there were particles moving at more than 186 000mps then the speed that the newly discovered particles were moving at would be the speed of light .

Answer 10

We believe that nothing traveling slower than light can accelerate to light speed or beyond, no matter how hard you try.

If something physical (mass/energy) could be made to travel faster than light, causality could be broken. Science is very fond of cause and effect, so not considered likely.