Why is faster-than-light travel 'impossible'?

[Quick_Nick]

Wrong. The speed addition at those speeds is different. You don't add them, but you use a weird formula. Basically you could have a train speeding at 99.99 % of the speed of light and another one going at 99.99 % too. If they both head towards each other, when they go next to each other they won't move at almost 2 c, but at a speed a little smaller than c (but greater than 99.99 % of c)

Right http://en.wikipedia.org/wiki/Relativity_of_simultaneity

 

[Stoat]

Right http://en.wikipedia.org/wiki/Relativity_of_simultaneity

Note the mention of the aether. Then we have the mention of Lorentz and Poincare, there should also be a mention of Riemann. This period, of a major crisis in physics, is popularly called the aether wars. It didn't end an outright victory for Einstein's relativity but as something akin to the situation in Korea.

It did get rather ugly at thee time, and it got uglier still with the rise of the Nazi party in Germany.

People had to make the choice between two relativistic theories. Einstein's theories seemed less bizarre than than an idea of an aether, so were chosen. if the solar system, the galaxy, group of galaxies, are moving through a stationary aether, then this aether has to have strange properties. Light travels through at light speed. it therefore has to be trillions of times denser than steel. yet a flea can walk through it, without any drag.

In its favour, we have a prefered frame of reference, there's no reciprocity. No ladder paradox. Time and space are absolutes, and time is not another spacial dimension at right angles to x,y, and z. (The ladder paradox is, that a ten foot ladder fired at near the speed of light should fit into a six foot barn but the barn also shrinks, so it can't)

So, now let's take a particle, an electron say, and accelerate it up to near the speed of light. Virtual particle pairs should form in its path. One of the pair can find itself on the wrong side of an event horizon. The upshot is that mass is created by this particle becoming "real" rather than "virtual."

It gets stranger yet. We are now making materials which have negative refractive index. In these metamaterials we can do odd stuff, we can stop light, we can have negative light and we can produce phonons; sound particles that travel at near the speed of light.

In short the aether is back in vogue but nobody is going to call it that. it's not stationary, and the idea that it was ever that is something of a straw man. All matter particles have their own "atmosphere" of aether particles, call that zpe or Higgs, suit yourself.

Gravity acts instantaneously, or nearly so. This is so in both Lorentzian an Einsteinian relativity. Let's take a lump of gravitational "space" and a lump of electromagnetic "space" and pop them into a blender. The grav space is informationally the same "size" as the e.m. space, yet it's volume is huge. it's energy appears very small therefore. lend this stuff up and we end up with a viscoelastic material, rather like mayonnaise. But mayo with a difference i.e. it has negative refractive index. you can run across at speed. You can walk though it. Walking through a swimming pool full of mayo is going to be hard work, the mayo finds it hard to get out of your way. With negative mayo however, the particles get out of your way and go round to you back and push.

One thing to stress with that, these would not be reverse time particles, or tachyons, They would simply be phase change particles.

 

[Fizyk]

(The ladder paradox is, that a ten foot ladder fired at near the speed of light should fit into a six foot barn but the barn also shrinks, so it can't)

The ladder paradox is, like a twin paradox, the effect of a naive interpretation of special relativity. It also shows nicely the problems that arise in relativity with rigid bodies.

[ame="http://en.wikipedia.org/wiki/Ladder_paradox"]Ladder paradox - Wikipedia, the free encyclopedia[/ame]

The point is, what is simultaneous in the barn's frame of reference (closing both doors), is not simultaneous in the ladder's frame of reference.

Gravity acts instantaneously, or nearly so. This is so in both Lorentzian an Einsteinian relativity.

Gravity in general relativity propagates at the speed of light.

 

[ZombiezuRFER]

Perhaps, if we ever find anything with "negative" mass, we have the key to FTL, unless we find that dang exotic matter to power our Alcubierre drives.

 

[Stoat]

Nah, gravity acts instantly. The centripetal acceleration of Jupiter is towards the solar system barycentre, as it is, and not where it was fifty odd minutes ago. The infamous space time rubber sheet presupposes what it claims to explain.

I totally fail to understand this obsession with the absolute nature of the speed of light. It's the king's new clothes. Here's an electron, get it up to th speed of light. Righto, electromagnetic field have the group velocity of the wave faster than light, that'll move it up to light speed, jolly good. Hang on the wave moves faster than light? Yeah but it can't carry information. Suppose though that something could travel faster than light, then it can carry information.

Maxwell unified electricity and magnetism, well maybe not quite but I'm happy with that. Einstein unified gravity and geometry. Am I happy with that, not quite. Non simultaneity I think is hokum. Likewise is reciprocity of micro events.

Here's the thing, the blue eyed boys and girls at CERN are talking about Lorentz, Poincare, and Riemann, did we back the wrong relativistic horse? But suppose that we can't go faster than light, we cannot go faster than sound after all. Wouldn't that be a shocking waste of space?

 

[Fizyk]

Nah, gravity acts instantly.

No, no it doesn't.

The centripetal acceleration of Jupiter is towards the solar system barycentre, as it is, and not where it was fifty odd minutes ago.

Actually it's the opposite.

I totally fail to understand this obsession with the absolute nature of the speed of light.

It's an experimental fact, you can't argue with facts (or maybe you can, but you can't make sense at the same time).

Suppose though that something could travel faster than light, then it can carry information.

Then causality is broken, as I've shown in my first post in this thread.

Einstein unified gravity and geometry. Am I happy with that, not quite. Non simultaneity I think is hokum.

Unfortunately what you think about it is quite irrelevant. Relativity is a tested theory, in fact there are some things, like GPS, that wouldn't work without taking relativistic effects into account.

Also, the force acting on a moving charged particle in a magnetic field (called the Lorentz force) can be viewed as a purely relativistic effect too, which surprised me when I first heard about it

 

[Stoat]

I think we'll have to agree to disagree.

 

[ZombiezuRFER]

if gravity acts at the speed of light, does that support the graviton? and Also, if gravity works at the speed of light, how come black holes have the gravity to stop light? Or is it when a photon enters the event horizon it enters orbit of the hole?

 

[Fizyk]

I think we'll have to agree to disagree.

What I present is, to my knowledge, the current understanding of relativity, which has been proven by numerous experiment. If you want to disregard that and stick to your own opinions, which have no support in experimental data (and some of which have even been disproven), fine - I can't forbid you that. I just want to point out that it's not very rational.

if gravity acts at the speed of light, does that support the graviton? and Also, if gravity works at the speed of light, how come black holes have the gravity to stop light? Or is it when a photon enters the event horizon it enters orbit of the hole?

1. The graviton is supposed to be going at the speed of light.
2. I have no idea how current quantum gravity theories work, so I have no idea how is a black hole able to interact via gravitons.
3. When a photon enters the black hole, it just falls to the singularity, like everything else.

 

[Hielor]

I think we'll have to agree to disagree.

Do you have any facts or experiments to back up your claims? The scientific community seems to disagree with you: [ame="http://en.wikipedia.org/wiki/Speed_of_gravity"]Speed of gravity - Wikipedia, the free encyclopedia[/ame]

"Agreeing to disagree" is all fine and dandy when you're dealing with opinions, not scientific facts.

 

[Linguofreak]

2. I have no idea how current quantum gravity theories work, so I have no idea how is a black hole able to interact via gravitons.

As I understand it, this is taken care of by the fact that nothing falling into a black hole, as seen by an external observer, ever passes the event horizon. You're just "seeing" the flattened, redshifted, gravitational "afterimage" of everything that ever went in, just as you'd see the flattened, redshifted, electromagnetic afterimage of everything that ever went in in electromagnetic observations.

 

[Keatah]

Well why not just spin the ladder up at high-speed, like a cat chasing its tail? Would the barn then take on an hourglass shape from the ladder's perspective..?

 

[ZombiezuRFER]

As I understand it, this is taken care of by the fact that nothing falling into a black hole, as seen by an external observer, ever passes the even horizon. You're just "seeing" the flattened, redshifted, gravitational "afterimage" of everything that ever went in, just as you'd see the flattened, redshifted, electromagnetic afterimage of everything that ever went in in electromagnetic observations.

And How does that happen that you can see it if light does not escape the hole?

 

[Linguofreak]

And How does that happen that you can see it if light does not escape the hole?

Because the light that you see never was in the hole in the first place. The closer it was emitted to the event horizon, the longer it takes to reach you, so that even many years after the object fell crossed the event horizon, you're still seeing an image from a split second before it did.