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Author Topic: Why is light so slow?  (Read 13999 times)

Offline Bill S

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Why is light so slow?
« Reply #25 on: 13/12/2011 16:36:31 »
Quote from: imatfaal
we just cannot say that time is frozen or stopped for photons.

Presumably, by the same token, we cannot say that something travelling faster than light would travel backwards through time.
 

Offline imatfaal

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Why is light so slow?
« Reply #26 on: 13/12/2011 17:31:18 »
Quote from: imatfaal
we just cannot say that time is frozen or stopped for photons.

Presumably, by the same token, we cannot say that something travelling faster than light would travel backwards through time.

If SR holds then something travelling faster than light will seem to contradict causality - where you go from there is anyone's guess.  massive particles cannot travel at light speed or greater, information cannot be transmitted at light speed or greater, and the minimum time between cause at A and effect at B is the distance over light speed .  boring and unimaginative ...
 

Offline yor_on

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Why is light so slow?
« Reply #27 on: 15/12/2011 09:39:09 »
No, although I fully agree on your conclusion, I don't think it's entirely true to say that SR forbids it Imatfaal, even though FTL creates all kind of weird implausibilities. I mean, you and me both doubt it, especially if formulated as a way to travel 'backward' in time, to meet/shoot 'yourself', etc.

Special relativity uses a constant 'c'. That's what defines us living here, but it doesn't say anything about what's on the other 'side' of 'c'. This 'warp space' some dreams of may, probably even, exist, but a translation from its 'reality' to ours 'reality' I very much doubt to exist.

To me it's like a quantum computer 'inferring' answers to questions that may not even have been stated, according to some interpretations. It might be possible but, I think not.

"When Einstein wrote down his postulates for special relativity, he did not include the statement that you cannot travel faster than light.  There is a misconception that it is possible to derive it as a consequence of the postulates he did give.  Incidentally, it was Henri Poincare who said "Perhaps we must construct a new mechanics [...] in which the speed of light would become an impassable limit."  That was in an address to the International Congress of Arts and Science in 1904óbefore Einstein announced special relativity in 1905.

It is a consequence of relativity that the energy of a particle of rest mass m moving with speed v is given by

          E = mc2/sqrt(1 - v2/c2)

As the speed approaches the speed of light, the particle's energy approaches infinity.  Hence it should be impossible to accelerate an object with rest mass to the speed of light; also, particles with zero rest mass must always move at exactly the speed of light, since otherwise they would have no energy.  This is sometimes called the "light speed barrier", but it is very different from the "sound speed barrier".  As an aircraft approaches the speed of sound it starts to feel pressure waves which indicate that it is moving close to the speed of sound, and before the existence and effects of these waves were well understood, they destroyed several aircraft in the mid 20th century; hence the old name of sound "barrier".  In fact, with more thrust and the right aerodynamics, an aircraft can certainly pass through the sound barrier.

The situation is different for light.  As the light speed barrier is approached (in a perfect vacuum) there are no such waves according to relativity (destructive or otherwise).  Moving at 0.999c is just like standing still with everything rushing past you at −0.999c.  Particles are routinely pushed to these speeds and beyond in accelerators, so the theory is well established.  Trying to attain the speed of light in this way is a matter of chasing something that is forever just out of your reach.

This explains why it is not possible to exceed the speed of light by ordinary mechanical means.  However, it does not in itself rule out FTL travel.  It is really just one way in which things cannot be made to go faster than light, rather than a proof that there is no way to do so.  Particles are known to decay instantly into other particles which fly off at high speed.  It is not necessary to think in terms of the particles' having been accelerated, so how could we say that they could not go faster than light?  What about the possibility of particles that might always have been moving faster than light, and which might be used to send information if they can be detected without ever slowing down to less than the speed of light?  Even if such "tachyons" don't exist (and we don't believe that they do exist), there may be ways of moving matter from A to B faster than light is able to travel from A to B by the usual route, but without anything having to go at a FTL speed locally." From Is Faster-Than-Light Travel or Communication Possible?

It's the translation between 'reality's' I doubt. Because if that's possible, then the next step is Lorentz transformations assuming to translate into a 'same global reality' for all of SpaceTime. Then we will have only locality left, with a new question becoming what the he* that will mean in understanding how we ever can percieve a same 'arrow of time'. But I have my own reasoning there of course.
 

Offline yor_on

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Why is light so slow?
« Reply #28 on: 15/12/2011 09:53:25 »
Hmm rereading, are you stating SR to be boring and unimaginative? Then we might be of two minds here :) I find it the most imaginative approach existing myself, that and GR is the most impressive framework existing still, a hundred years after its formulation.
 

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Why is light so slow?
« Reply #28 on: 15/12/2011 09:53:25 »

 

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