Special Relativity

[Sythe]

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.http://en.wikipedia.org/wiki/Special_relativity#cite_note-electro-0

• 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?

 

[ioioio175]

welllll...I think i see what you are getting at here but isnt space a vacuum? and we can see stars sooo wouldnt that be definite proof that lighte travels through a vacuum. oh and if i misunderstood you please tell =]

 

[Sythe]

welllll...I think i see what you are getting at here but isnt space a vacuum? and we can see stars sooo wouldnt that be definite proof that lighte travels through a vacuum. oh and if i misunderstood you please tell =]

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

 

[FreedomFight]

How far down does the rabbit hole go? Theory of special relativity is used and reinforced by several real life applications. GPS synchronization requires extremely accurate time measurements, but the relative speed of the satellite is high enough to actually distort time. To compensate, this time must actually be calculated into the process.

Einstein's initial proof of general relativity (yes, it's an off-tangent) came from a solar eclipse with accurate predictions of "bent light".

If we established the two above to be true, I'm assuming you find deeper incoherence?

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

Well what, in one sense your right in that "perfect vacuums" are pretty much impossible to create. It's proof by induction. This particular instance is an interesting topic for me. I'm currently working as an intern for a company that produces ultra-fast pulse lasers with various applications. At the upper ends of these applications, vacuums are essential to prevent distortion because the laser will turn the molecules into plasma. I suppose the propagation of light through this vacuum is enough proof for me(yes, I realize the imperfect nature of some experimental conditions).

 

[Sythe]

How far down does the rabbit hole go? Theory of special relativity is used and reinforced by several real life applications. GPS synchronization requires extremely accurate time measurements, but the relative speed of the satellite is high enough to actually distort time. To compensate, this time must actually be calculated into the process.

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.

Einstein's initial proof of general relativity (yes, it's an off-tangent) came from a solar eclipse with accurate predictions of "bent light".

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.

If we established the two above to be true, I'm assuming you find deeper incoherence?

Well what, in one sense your right in that "perfect vacuums" are pretty much impossible to create. It's proof by induction. This particular instance is an interesting topic for me. I'm currently working as an intern for a company that produces ultra-fast pulse lasers with various applications. At the upper ends of these applications, vacuums are essential to prevent distortion because the laser will turn the molecules into plasma. I suppose the propagation of light through this vacuum is enough proof for me(yes, I realize the imperfect nature of some experimental conditions).

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?

 

[FreedomFight]

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.

Taken by Hubble Space Telescope. See explanation below:
http://en.wikipedia.org/wiki/Gravitational_lens

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

Either way, we have established some strange phenomena. The theories presented seem to accurately account for them. Based on this, I see four possibly disputes on the theory:

1. The evidence presented has questionable validity.
2. The evidence has poor correlation to the phenomenom or theories explained.
3. The theory is a product of bad induction or over generalization.
4. The theory itself is unfalsifiable.

Which of these are we talking about?

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:

Yes, also an extremely useful property in polarized lenses (which coincidentally is the focus of my current project).

Let's establish a few things:
1. "Only in a vacuum is the speed of light a constant independent of the motions of the source and the observer."

2. The speed of the light wave is constant in between the space of atoms.

3. When light hits a material, energy is absorbed. When it hits a transparent/semi-transparent material, it is effectively absorbed and re-radiated throughout each respective atom. This causes two things: loss of energy, and a slight delay between each absorption and re-radiation. The larger the refractive index, the larger the delay, and the slower the light travels through the object.

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.

I'm a little confused about how special relativity applies to this situation. For one, physics at sub-relativistic speeds produce poor and incomplete models as things approach the speed of light(thus why special relativity was developed). Secondly, because all three people are traveling at the same speed, there is no effect of relativity between the observer and the people shouting.

its speed is dependent on its medium

It's important to make a distinction between the refractive properties of a medium and the constant speed of light.

 

[5th Dimension Being]

Waves need a medium to travel through correct?
But light is both a particle and a wave and is infact unique that way.

We used to think it was impossible to completely stop light but we have done it for a incredibly breif moment before. I'm pretty sure that there is nothing that can completely stop light by itself, except maybe a black hole.

And when Sythe asked about the plane and yelling I think he meant how does the sound of their voices (which are really only vibrations that our brain interprets) keep up with them at that speed.

It probably has something to do with a pressurized cabin which they sit but I'm not sure at the moment because I cannot think straight tonight to form a reasonable hypothesis :/

 

[Sythe]

Taken by Hubble Space Telescope. See explanation below:
http://en.wikipedia.org/wiki/Gravitational_lens

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?

Either way, we have established some strange phenomena. The theories presented seem to accurately account for them. Based on this, I see four possibly disputes on the theory:

1. The evidence presented has questionable validity.
2. The evidence has poor correlation to the phenomenom or theories explained.
3. The theory is a product of bad induction or over generalization.
4. The theory itself is unfalsifiable.

Which of these are we talking about?

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.

Let's establish a few things:
1. "Only in a vacuum is the speed of light a constant independent of the motions of the source and the observer."

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.)

I'm a little confused about how special relativity applies to this situation. For one, physics at sub-relativistic speeds produce poor and incomplete models as things approach the speed of light(thus why special relativity was developed). Secondly, because all three people are traveling at the same speed, there is no effect of relativity between the observer and the people shouting.

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?
​

2. The speed of the light wave is constant in between the space of atoms.

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.

3. When light hits a material, energy is absorbed. When it hits a transparent/semi-transparent material, it is effectively absorbed and re-radiated throughout each respective atom. This causes two things: loss of energy, and a slight delay between each absorption and re-radiation. The larger the refractive index, the larger the delay, and the slower the light travels through the object.

Correct as far as I am aware.

It's important to make a distinction between the refractive properties of a medium and the constant speed of light.

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?

 

[Sythe]

Waves need a medium to travel through correct?

Yes. And the universe is full of matter.

But light is both a particle and a wave and is infact unique that way.

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.

 

[FreedomFight]

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.

http://en.wikipedia.org/wiki/Twin_QSO
This is the most concrete evidence I could find.

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?.

I suppose I place a general trust in the mechnisms used by the scientists involved to differentiate the phenomenom. I'm sure that you are not the first to propose this idea.

If the conclusions are derived by wrong means but still map to reality then this would just be a co-incidence.

Fair enough.

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 vast majority of space is a vacuum. Considering the widely accepted belief of 1atom/CM^3 in space, the size of that atom composes only a fraction of the space available.

Sound requires a critical density of particles because it depends on atomic collisions.

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

It's induction. Light actually travels better at these low pressures.

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.

I'm just confused by where the relativity is. Does special relativity predict something else? You've just introduced a closed situation where all objects are moving at the same relative speed.

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.

Well it has to. The best analogy I can think of is:

You're in a car. You drive at a constant speed of X mph, but have to stop at each red light for Y seconds. The red light in this analogy would represent the process of absorption and re-radiation.

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.

I disagree. The standard here is the speed of light only. http://nvl.nist.gov/pub/nistpubs/sp958-lide/191-193.pdf

The refraction index is a tool to compensate for the absorption and re-radiation factor of some materials.

If we reject the paradox of wave-particle duality then we are left with a problem.

Well, yes of course. That's why I don't consider the theory a paradox at all, although I realize the properties cannot be simultaneosly viewed.

I don't really know much quantam physics but the http://en.wikipedia.org/wiki/Copenhagen_interpretation seems to provide the most valid explanation for me.

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?

The best vacuum we have to work with is space itself. I feel like you have overestimated the density of space by a huge magnitude. There is no decay of transimission (unlike sound, which can be easily attributed to density of atoms).

 

[Sythe]

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.

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 vast majority of space is a vacuum. Considering the widely accepted belief of 1atom/CM^3 in space, the size of that atom composes only a fraction of the space available.

Sound requires a critical density of particles because it depends on atomic collisions.


It's induction. Light actually travels better at these low pressures.

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.

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.

I'm just confused by where the relativity is. Does special relativity predict something else? You've just introduced a closed situation where all objects are moving at the same relative speed.

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?

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.

Well it has to. The best analogy I can think of is:

You're in a car. You drive at a constant speed of X mph, but have to stop at each red light for Y seconds. The red light in this analogy would represent the process of absorption and re-radiation.

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.

The best vacuum we have to work with is space itself. I feel like you have overestimated the density of space by a huge magnitude.

Yes that may well be the case.

There is no decay of transimission (unlike sound, which can be easily attributed to density of atoms).

I definitely wouldn't assert that without testing.

 

[Bring Me The Horizon]

Please don't infract me for this but - Is Special Relativity basically, in the lowest terms saying "Nothing is ever at a stand still it's ALWAYS moving?

 

[Sythe]

Please don't infract me for this but - Is Special Relativity basically, in the lowest terms saying "Nothing is ever at a stand still it's ALWAYS moving?

No .

 

[FreedomFight]

Sorry for the late response, my first was lost when the site went down.

1. List of SR-related experiments:

http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#3.%20Tests%20of%20Einstein's%20tw o%20postulates

2. Light + Electricity are non-comparable. It's well established that free-space is actually a pretty good electical insulator.

3. So why is the constant speed of light profound? The theory of relativity would have you believe that if you travel at .8c, and you observe a light beam passing you, it'll still appear to pass you at speed c. In order to compensate for this discrepancy, speed, which is a function of d/t, must have either d or t change.

4. Space is a pretty hard vacuum I assure you. See experiments listed above to find more tests. It's important to note that the constant speed of light is a postulate of SR (not an 100% proven assumption).

 

[Sythe]

Sorry for the late response, my first was lost when the site went down.

1. List of SR-related experiments:

http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#3.%20Tests%20of%20Einstein's%20tw o%20postulates

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

2. Light + Electricity are non-comparable. It's well established that free-space is actually a pretty good electical insulator.

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.

3. So why is the constant speed of light profound? The theory of relativity would have you believe that if you travel at .8c, and you observe a light beam passing you, it'll still appear to pass you at speed c. In order to compensate for this discrepancy, speed, which is a function of d/t, must have either d or t change.

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?

4. Space is a pretty hard vacuum I assure you. See experiments listed above to find more tests.

Definitely will check out. Thanks.

 

[Imagine]

Although I realize this is a gravedig - This is one of my current interests, and instead of making a new thread, I used the search function

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

Well, light can not travel through a complete vacuum, because as soon as photons enter the vacuum, it wouldn't really be a vacuum. Although you can argue that photons possess Wave Particle-Duality, and that they are mass-less, they do still have volume (of about half a Fermi), which takes up "space", thus making it impossible to have a truly empty space in which light shines through.