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Author Topic: How do we know nothing is faster than light?  (Read 4859 times)

Offline thedoc

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How do we know nothing is faster than light?
« on: 01/04/2012 10:04:01 »
Roger Kujawa  asked the Naked Scientists:
   Hi Chris and all:

Thanks for the show. I really enjoy listening. I have a question about light. From what I gather nothing can go faster than light. How do we know?

Secondly, I think I heard that light has no mass and you can't find enough power to push something with mass to the speed of light. If this is so, how come light can be bent by gravity or not escape from black holes? It would seem to be contradictory.

Thanks again,

Roger
Morton, IL. USA

What do you think?
« Last Edit: 01/04/2012 10:04:01 by _system »


 

Offline Ęthelwulf

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Re: How do we know nothing is faster than light?
« Reply #1 on: 01/04/2012 13:04:28 »
Roger Kujawa  asked the Naked Scientists:
   Hi Chris and all:

Thanks for the show. I really enjoy listening. I have a question about light. From what I gather nothing can go faster than light. How do we know?

Secondly, I think I heard that light has no mass and you can't find enough power to push something with mass to the speed of light. If this is so, how come light can be bent by gravity or not escape from black holes? It would seem to be contradictory.

Thanks again,

Roger
Morton, IL. USA

What do you think?

Actually, that's incorrect.

I remember when all this fuss came about of the faster than light neutrino's. Many were saying it would have been the end of relativity - even prominent physicists, which worried me because that was a load of hoolah!

Relativity actually permits superluminal particles. So long as these speedy particles began their journey over the speed of light and did not accelerate past it. The arguement which is correct, is that no such particle can accelerate up to and exceed the speed of celeritas, which is denoted by c, the speed of light. Perhaps of some interest, some string theories actually require superluminal particles, but I am not too fond of string theory.
 

Offline Ęthelwulf

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Re: How do we know nothing is faster than light?
« Reply #2 on: 01/04/2012 13:06:22 »
And the reason why light cannot escape black holes, is because the speed required to escape the gravitational pull of the body is over the speed of light, or more accurately put, the escape velocity is over the speed of light, so light particles become trapped under it's influences since their speeds match that of lightspeed of course.
 

Offline Pmb

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Re: How do we know nothing is faster than light?
« Reply #3 on: 01/04/2012 14:08:42 »
Responses like these are what make this forum great. Great responses folks!

Pete
 

Offline yor_on

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Re: How do we know nothing is faster than light?
« Reply #4 on: 03/04/2012 09:27:10 »
Light doesn't have a mass if we're talking about the invariant kind, also called rest mass (matter). But it have a 'energy' as you know from going out in the sun. That energy does the trick. Einstein thought of boring a hole in the wall of a elevator, and then send a light beam into a accelerating elevator to see the equivalence between light and its 'relative mass', as it also can be named. That was also the reasoning behind the equivalence between his geometrical definitions of 'gravity' and accelerations.

It's all goes back to a principle of least 'energy' expenditure as I see it. That photon 'bends' as you observe it because SpaceTime 'bends' to gravity. In reality the photon is taking the path of least resistance, or no resistance may be a better world here. If it didn't it would lose 'energy' 'propagating' and that would mean that a lot of light never would reach us.
 

Offline yor_on

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Re: How do we know nothing is faster than light?
« Reply #5 on: 03/04/2012 09:33:42 »
It's also called a 'straight path' because it's the straightest path it can take inside SpaceTime. But I like my idea better :)
Because we have no proofs for 'photons propagating', of the direct observable kind. If you're interested you can look at geodesics to see the different definitions. Geodesics in GR.
 

Offline yor_on

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Re: How do we know nothing is faster than light?
« Reply #6 on: 03/04/2012 09:54:05 »
And no, if the neutrinos would have been FTL (superluminous) they would also have needed to be of  a 'imaginary mass' which they aren't, as far as I know? We have proofs for them having a very slight rest mass, which should mean that they also have a acceleration, in contrast to 'bosons' as light which does not accelerate at all. So it would have destroyed relativity as I see it, if true.

As for how Einstein defined Lights speed he firstly used Maxwell's equations in SR which can be shown to be a 'constant'. There are other ways nowadays but that was his beginning as I seen it. some folks drag in a lot of stuff and assumptions in that and want it to be anything but Maxwell but Einstein himself states it. And you got to remember that this theory is now over a hundred years old and a lot of people expect QM to supersede it somehow, although Relativity firstly is a 'macroscopic' model of 'reality' whereas QM is a 'microscopic'. But I'm getting quite tired of those wanting Einstein to lose his reputation, it, to be perfectly honest, sux. And it comes from people that don't have the brains to make their own ideas.
 

Offline Ęthelwulf

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Re: How do we know nothing is faster than light?
« Reply #7 on: 03/04/2012 12:45:08 »
And no, if the neutrinos would have been FTL (superluminous) they would also have needed to be of  a 'imaginary mass' which they aren't, as far as I know? We have proofs for them having a very slight rest mass, which should mean that they also have a acceleration, in contrast to 'bosons' as light which does not accelerate at all. So it would have destroyed relativity as I see it, if true.

As for how Einstein defined Lights speed he firstly used Maxwell's equations in SR which can be shown to be a 'constant'. There are other ways nowadays but that was his beginning as I seen it. some folks drag in a lot of stuff and assumptions in that and want it to be anything but Maxwell but Einstein himself states it. And you got to remember that this theory is now over a hundred years old and a lot of people expect QM to supersede it somehow, although Relativity firstly is a 'macroscopic' model of 'reality' whereas QM is a 'microscopic'. But I'm getting quite tired of those wanting Einstein to lose his reputation, it, to be perfectly honest, sux. And it comes from people that don't have the brains to make their own ideas.

Actually, Most physicists who are well-educated in this area, believe an imaginary mass would behave probably just the same as ordinary mass.

And there are also reinterpretation rules and mathematical processes you can use to escape the notation of imaginary mass. So that generally cannot be used as an explanation.
 

Offline yor_on

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Re: How do we know nothing is faster than light?
« Reply #8 on: 03/04/2012 13:42:01 »
Possibly, can you source it for me?

This is how I think of imaginary mass. Still, what can be said is that a neutrino is expected to have a 'rest mass', and so be inside our arrow (The ability of a single neutrino to shift identity over the course of its travels) and that makes it unlikely for me. And tachyons etc don't exist in our arrow, well, as far as I know.
=

Or SpaceTime, if you find that more suitable than a arrow?
« Last Edit: 03/04/2012 13:44:23 by yor_on »
 

Offline Ęthelwulf

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Re: How do we know nothing is faster than light?
« Reply #9 on: 03/04/2012 13:50:14 »
Possibly, can you source it for me?

This is how I think of imaginary mass. Still, what can be said is that a neutrino is expected to have a 'rest mass', and so be inside our arrow (The ability of a single neutrino to shift identity over the course of its travels) and that makes it unlikely for me. And tachyons etc don't exist in our arrow, well, as far as I know.
=

Or SpaceTime, if you find that more suitable than a arrow?

I can try and find some links, I am not promising I will find anything though. I will tell you though, that Tsao Chang has made a number of papers on superluminal neutrino's, modelling them with strictly a positive mass within a Dirac Theory.
 

Offline krool1969

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Re: How do we know nothing is faster than light?
« Reply #10 on: 05/04/2012 01:29:59 »
The best explanation of time dilation I've ever heard was this: Time is actually a spacial dimension, just like the three we normally think of. We normally move through time at the speed of light, so if you and I are sitting next to each other we are moving through time at the same speed. If I stand up to go get us some beer from the fridge I need to use some of my motion through time to move through space. So as I walk away I'll be moving through time just a bit slower than you are.

To move through space at the speed of light I'd need to use ALL my speed through time. And because that speed is the speed of light I won't be able to go any faster.
 

Offline MikeS

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Re: How do we know nothing is faster than light?
« Reply #11 on: 05/04/2012 07:37:12 »
krool1969

Nice explanation.
 

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Re: How do we know nothing is faster than light?
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