Special Relativity

I want to open a debate on this topic.

Firstly if you don't know what STR is you can read about it here:
http://en.wikipedia.org/wiki/Special_relativity

So the theory has two core premises:

• The Principle of Relativity -- that physical laws are invariant between frames of reference.

• The Principle of Invariant Light Speed – "... light is always propagated in empty space with a definite velocity [speed] c which is independent of the state of motion of the emitting body." (from the preface). That is, light in vacuum propagates with the speed c (a fixed constant, independent of direction) in at least one system of inertial coordinates (the "stationary system"), regardless of the state of motion of the light source.

So I'll start the ball rolling.

What evidence is there to suggest that light travels at all in a vacuum?

 

I work it out to be about three billion molecules per cubic meter in deep space.

 

It is true that there appears to be an interesting phenomenon known as time dilation, however I am not convinced that it necessarily follows from special relativity. That is to say: if, logically, special relativity can be shown to be false, then this phenomenon will still exist, but in an unexplained state. -- I'm concerned primarily with the logical validity of the theory of SR; the degree to which its conclusions are accurately derived from its premises, and the degree to which its premises are correct.

I have thought about that also. If you look at the math they use to derive the gravitational lens effect (so called) it's the same as normal refraction of light through an atmosphere. The sun's atmosphere is called the heliosphere, and the earth sits in it.

http://www.informaworld.com/smpp/content~db=all~content=a793097812

So, while a very interesting phenomenon, I am not sure that 'curvature of space-time' logically follows here.

Ah most excellent.

Well here's some of my reasoning and maybe you can help me understand how it's faulty.

So the first thing to establish is that light travels more slowly and more weakly the denser the medium. Light travels about 1.5 times slower through glass than it does through air, and so on. And this holds right down to speeds visible to the human eye:

http://www.sciencedirect.com/scienc...serid=10&md5=0405c7c5fcb135c9e21e9b0fc8267ae7

The second thing to establish is that the velocity of light is isotropic within an even medium. And this is the same as all waves that we know of. Sound being the simplest example.

On to special relativity:
If I am sitting in the center of an airplane traveling in excess of the speed of sound, and there are two people at opposite ends of the plane, and they both yell something to me at once, then I will both be able to hear them despite the fact that overall we are traveling faster than the speed of sound, and I will hear their calls at the same time -- maintaining simultaneity at least from my (and their) perspective.

And this experiment will, I believe, hold exactly true if both people have laser pointers instead of voices, and if we are traveling at 0.5 C.

So my question is this:
Given that light exhibits this same behaviour that sound does -- that is: its speed is dependent on its medium, but independent of the passage or rate of passage of its medium through space -- and, given that we need no SR theory to explain the passage of sound in these analogous closed systems, then why does SR follow at all from these premises?

 

I can't see any obvious lens effect. I don't have (and can't get) two angles of the same thing, so it is impossible to tell.

But even assuming that there were, how do you know it's not caused by a huge cloud of gas or something between us and them?

Well right now I am questioning the premises. As for the phenomena which constitute empirical evidence in support of the theory, I view those with interest, but keep in mind that if the premises or reasoning of a theory is wrong then its conclusions are also wrong. If the conclusions are derived by wrong means but still map to reality then this would just be a co-incidence.

Like for example, you could have had some lengthy argument 2000 years ago about the creation of the earth in theology, and conclude that the earth must be round because this is how god did X. Your conclusions would still be wrong, even though it is also the fact that the earth is round.

Do you mean that "the speed of light is a constant independent of the motions of the source and the observer" in rarefied gas?

The closest you could come up with based on observation is "low pressures cause light to have these following properties: X, Y, Z".

The speed of light within a closed medium should be independent of the observer and source, dependent only on the type of matter it is being transmitted through, just like sound. To an observer outside the system the light may be traveling faster than light. Just as the soundwaves in a jet cabin are traveling faster than sound outside it.

(I've repositioned the following quote from below, since it's immediately relevant here.)

Ok, but lets speed it up. Say you are going 0.9 C in a spaceship. The two people have laser pointers. The cabin is pressurized. You are no longer accelerating. Both shine their lasers at you at the same time.

Are you saying this experiment won't have the same result as the shouters in the plane?
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I couldn't verify this. If you have evidence of the mechanism of light transfer between atoms I'd definately be interested to see it. I only know that the speed of light is constant through atoms of the same density, pressure and temperature in a closed system.

Correct as far as I am aware.

This is a mixed definition I believe. The refractive index of a material is defined in terms of the "speed of light in a vacuum". So this would be begging the question to quite a degree.

What we can say instead is that the speed of light in one medium can be compared against the speed of light in another medium, all other things being equal. And it is useful in terms of the mathematics to settle on one particular medium as the standard against which all other mediums are tested. I believe this is where the refractive index comes from.

As for the refractive properties. My main query is to what degree does vacuum even carry light on its own? Reasoning from first principles we can determine that energy is an attribute of matter. If we reject the paradox of wave-particle duality then we are left with a problem. Mainly that light should not travel through a pure vacuum, in the same way electricity should not. So one must then ask, how close to a pure vacuum have we actually come, and is there some decay in the transmission of light as one approaches pure vacuum?

 

Yes. And the universe is full of matter.

No, this is a theory only. In truth light is still treated as a wave, with useful abstractions derived from its tendency to be transmitted in discrete wave packets.

 

Hi FreedomFight,

First let me thank you for taking the time to have this discussion with me. I'm finding it most enlightening.

I'm going to try reference my previous quotes inside your responses where necessary, so we don't get too muddled up. And also, please excuse me if I cut tangents off to save time; If you think there was something I cut off which was important, please reintroduce it.

This is a graph of the conductivity of electricity through rarefied gas. As the hardness of the vacuum increases (toward the left) the capacity for electrical flow decreases.

One of my key proposals here is the possibility that light isn't different to other waves in this manner. But we haven't achieved a hard enough vacuum to see the dip at the end.

A few thoughts on this proposal: If light becomes attenuated in very hard vacuum then this may explain why most matter is opaque (something that isn't well understood as far as I am aware). If there is perfect vacuum between the atoms in solids then this would explain why light does not pass between and around the atoms.

Another thought is that cosmological redshift may be a consequence of attenuated light. And the hard vacuum pockets in space may cause the loss of visibility we associate with certain regions of space.

Of course none of this has any sway over the validity of the theory, they are just interesting side notes.

No, it has nothing to do with relativity, only with the second premise of SR:
"The Principle of Invariant Light Speed in a vacuum."

If people outside the spaceship saw the laser beams that were transmitted inside the spaceship, wouldn't they see them long after the ship had passed? In the same way if you were outside a silent jet you would hear the passage of the jet through the air after it had passed, and the sounds of the voices inside, in the sound analogy.

Ignoring the doppler effect, wouldn't the waves pass from the contained medium inside the ship, to the contained medium outside the ship, undergo a velocity downgrade (relative to the observer outside the ship) and continue to their normal destination?

In other-words: why is the constancy of the velocity of light in a medium anything profound?

Sure but my point here is, how do you know there is any travel between the red-lights at all?

If you have a line of magnets facing equal poles away from eachother and you push the first one, the wave will travel down the magnets, without any magnet touching another magnet. In orderwords the passage of energy might simply be the deformation and subsequent reformation and restablization of certain fields surrounding matter, in a chain reaction.

Certainly this appears to be the case with a phenomenon such as electricity -- which travels at almost C, but through copper wires.

Yes that may well be the case.

I definitely wouldn't assert that without testing.

 

No .

 

Really good find. I intend to go through them and test their experimental results / conclusions against my hypothesis.

Right I agree. Part of my proposal is that very hard vacuum is a 'light insulator', in the same way relatively soft vacuum is an electrical insulator.

This is in a vacuum right? I mean I can go plenty faster than the speed of light in a medium.
http://en.wikipedia.org/wiki/Slow_light

And if the medium is flowing in the opposite direction .. as in a fluid, then I can watch the light pass me at a very casual rate. Say cm/second.

So just to clarify: the theory asserts that the speed of light is C, in any frame of reference, for any observer, in a vacuum?

Definitely will check out. Thanks.