Do photons have inertia?

AlphaNumeric,

I will explain to you as simple as possible.

Special Relativistic time dilation and length contraction derived


There are two frame of reference the "BLUE's frame of reference" and the "Green's frame of reference".

In the case of light in vacuum, where we assume the invariance of speed of light is true, the speed of light is the same ( c = 299 792 458 m / s), in both frame of reference (in the "BLUE's frame of reference" and in the "Green's frame of reference").

Now we consider the experiment occurs in a medium as like ethyl alcohol (ethanol), which has refractive index n = 1.361.
the speed of light in ethanol c' =c/n= 299 792 458 /1.361 m / s=220 273 664 m/s.

Now we have two possibilities: the invariance of speed of light in ethanol is true (1) and the invariance of speed of light in ethanol is false (2).

Case (1) the invariance of speed of light in ethanol is true.
There are time dilation and length contraction, with a transfer factor \(\gamma' = \frac{1}{\sqrt{1 - (v/c')^2}} \)
As this number can not be irrational, require the expression under the radical to be greater or equal to zero.
This condition is satisfied for a speed v that can not exceed the speed of light in ethanol c'=220 273 664 m/s.

Case (2) the invariance of speed of light in ethanol is false.
If in the "BLUE's frame of reference" the speed of light in ethanol is c ', then in the "Green's frame of reference" the speed of light in ethanol is c '+v or c'-v , where v is the speed between the "BLUE's frame of reference" and the "Green's frame of reference" and there arenot time dilation and length contraction.

Did you understand and have you something to comment on this reasoning?

If you have remarks as moderator please do it explicitly.
I ask the question to you as moderator.
if I do not reveal my identity (that is if you ask for a link on my performance), is considered as trolling?

 

Log in or Sign up to hide all adverts.

Again, you don't provide any evidence you understand the material at hand. I know JamesR has posted that, I saw you post it before. It doesn't negate what I said. The speed of light in a medium being slower than the speed of light in a vacuum is NOT inconsistent with special relativity. Quoting JamesR again and again doesn't support your assertion.

And I never asked you to reveal your identity. I frankly couldn't care less what your name is, your favourite colour or whether you can play the guitar. I asked you to provide a link to a post of yours, on this forum, where you show you have a working grasp of this sort of material. Where, on this forum, have you ever shown a working understanding of this sort of material?

If you prefer we can start a new thread and I can give you a few questions on special relativity from a course I used to be involved in teaching, so we can see if you can actually do this stuff. I've shown plenty of times on this forum I have a working grasp of plenty of areas of mathematics, I have evidence your claims about me are false. I want to see evidence my claims about you are false, as yet you have failed to provide.

 

Log in or Sign up to hide all adverts.

Emil, I think you are trying to apply the invariant speed of light in vacuum, directly, or in an equivalent way, to the fluid medium. The problem is that a fluid and vacuum are not equivalent mediums.

Fizeau, proved long before even the Michelson & Morley experiment that the velocity of light through a moving transparent medium, was in fact additive.., the velocity of light in the medium at rest and the velocity of the medium. This does not contradict SR, in any way. Neither does the fact that a particle with mass can move through a transparent medium at a velcity grater than light does. Neither exceeding the velocity of light in vacuum c.

Vacuum and all other transparent mediums are not equivalent mediums for the propagation of light. And the velocity of light through any transparent medium, relative to that medium is fixed and constant, as long as the medium's refractive index is fixed and constant. The fact that a liquid medium can have a velocity relative to an observer, is a whole separate issue. The vacuum has no velocity relative to anything.., except perhaps the speed of light and even that delves into a debate far beyond this discussion.

 

Log in or Sign up to hide all adverts.

As you noticed, I posted a specific question based on a mathematical demonstration of James R and completed with a question. What happens with that mathematical demonstration, if the experiment is not in vacuum?
So you can focus on this? ( I don't let you to get involved me in a different discussion.)

 

OnlyMe, please read carefully my post that you quoted.
I said that there are only two options in the case of a medium. Please choose one you think is correct.
If you think there is the third version, please submit it.

 

If you are not in a vacuum then you have to take into account interactions between photons and the medium the light is moving through. The background space-time will still obey the rules of relativity but now the photon isn't moving in isolation, it is being affected by the particles in the medium. As such the post of JamesR that you keep posting again and again is not addressing the right things. You would need to calculate things like scattering cross sections between photons and the particles which make up the medium (or some effective model thereof).

This illustrates how you don't understand what you're posting, you're just hoping that what James said is relevant and correct and that it'll be accepted. Sorry, no dice.

Originally our little disagreement was on how p=mv and \(KE = \frac{1}{2}mv^{2}\) are now universally valid. Here I laid out the background mathematical formalism. Here I specifically told you to read my post. Funny how you decided to ignore that and then accuse me of not knowing high school mathematics. The mathematics in that post is 2nd year university material. But then you'd know that if you'd covered the material yourself. Here I then outline why it's important to consider things beyond the simplest models. You're now repeating that error. But rather than respond to that post properly or admit your mistake you instead post this, which does nothing to negate what I corrected you on.

So it is in fact you who has changed the course of our conversation. You have jumped from making claims about momentum and kinetic energy to light speed in a medium.

Can you at least admit you were mistaken about p=mv, that in fact it is not a universally true relation?

And my request you provide a post where you demonstrate a working understanding of special relativity is on topic because there is no reason for me to provide any mathematics in response to your questions if you do not possess the knowledge to understand the mathematics. You've already shown you are unfamiliar with basic principles in relativity, such as p=mv not always being true, so I have no reason to think you understand the mathematics of special relativity. Therefore I see no reason to think you would understand someone doing relativistic mechanics in a fluid.

You have yet to answer any of my questions/requests, so you're hardly in a position to be demanding things of me. You can't request for me to stick to the topic at hand when you have failed to do so. You can't request for me to provide you with things when you won't answer my questions. You can't expect anyone to think you understand any of this when you fail to provide evidence.

It is clear you do not understand the post of James which you keep posting. Anyone who has studied special relativity knows about experiments which tested and verified special relativity's predictions. You don't realise that JamesR's post being accurate doesn't mean your interpretation of it is. Special relativity never said anything about light speed in a medium being invariant but that doesn't mean a medium disproves special relativity. As I've said several times now, when you use special relativity and quantum mechanics to describe light in a medium you get correct predictions. The fact light going through ethanol is slower than light in a vacuum is entirely consistent with quantum field theory, which includes special relativity. Special relativity alone, in the absence of any description of matter particle interactions, is insufficient to properly model light going through a medium but that is not a sign special relativity is false.

 

Hi guys!

Please Register or Log in to view the hidden image!

Just curious. AlphaNumeric, from what you have pointed out about the additional factors to light behaviour in media, I was wondering if, in the case where the universe was filled with Emil's example media, whether or not the SR basics can be derived once all those other factors you mentioned are allowed for? If you get my drift? In other words, given Emil's media scenario, can SR be recovered by mathematical and modeling treatments 'cancelling out' the various other factors due to medium, and SR for vacuum be extractable from all those other complicating interactions you mentioned?

I'd be very interested in both your(and anyone else's) respective opinions/takes on that. Or has it been done already?

Please Register or Log in to view the hidden image!

Cheers!

.

 

Emil, I do not believe that I was adding anything. I could not access the last link, but as I remember it James had discussed the situation, in vacuum. The blue and green frames are thus not applicable when you attempt to frame the example in a liquid medium.

I raised the Fizeau reference as it demonstrates at least one reason. A liquid can have a velocity, which can be additive to the speed of light through that liquid. Vacuum has no similar velocity.

As far as SR is involved the speed of light in vacuum is measured to be the same for all inertial observers. the same is not true when light travels through a liquid, which is itself in motion. In the case of a liquid, as long as all observers know the liquid's velocity they will agree on the speed of light relative to the loquid's at rest frame. They will not agree on the speed of light relative to their own frame, where c' (the speed of light through the liquid) and the liuid's velocity relative to the observer are additive.

There is no similar additive condition, as far as SR is concerned, in vacuum.

You cannot take James' example and explanation and replace the vacuum with any transparent medium. As I said earlier a transparent medium and vacuum are not equivalent where the propagation of light is concerned.

 

There are those who's have tried. But then you are dealing with some variation of an ether medium. There are some attractive aspects, but so far as I am aware there has been no success, in duplicating the success of SR and GR, within the context of an ether model.

The closest I think you could get is one of the incarnations of quantum gravity. I think I can just start to get a grasp on the implications of inertia as a quantum phenomena. Quantum gravity is way beyond me.

 

Yes, I have serious doubts about your ability to understand (not on your ability to reproduce)
There is no such a thing as "Newtonian model". You prove you do not understand what a model.
I've said I do not comment on subatomic particle models.
But when you expand the properties of subatomic particles of the model, over the physical bodies then we have a problem.(Especially since you make such statement :"It all fits nicely together, provided you realise that you should forget all the 'usual' expressions you get told in school.")
All laws or definitions of science which are composed of distance, length, size and time are valid, despite your attempt to overthrow them because the "time dilation and length contraction"
You understand or not, is fine, but for the SR to be true, must necessarily postulates to be true.
In a medium where the second postulate is not satisfied there is no SR.

 

Come on OnlyMe, there are two cars. What stops me to use two cars in any demonstration ?
I quote James R demonstration, because I appreciate it and have thought it was understandable.
Enough only this: where the second postulate is not satisfied, there is no SR.

 

Special relativity is a set of statements about the properties of space-time. If you have to describe the properties of matter within the space-time then you have to add something else into the mix, like quantum mechanics to give quantum field theory.

Special relativity tells you how to transform vectors, spinors and other mathematical quantities with vector-like structures under certain reformulations. Matter fields, like say the photon vector field or electron spinor field will then transform under those rules. This is what is seen in quantum field theory, as it's constructed in such a manner to have that property.

Yes, it is possible to reconstruct the behaviour of light in a vacuum from observing the behaviour of light when it interacts with things, that's precisely what science did, since we have to interact with light in order to detect and study it.

Complicated quantum interactions can mean it's possible for oscillations in say the photon field to move slower than light, despite each individual photon moving at light speed. What Emil fails to grasp is that there is no contradiction there, special relativity still holds and governs how you reformulate your point of view when doing things like boosting into a new frame.

Special relativity plays a role in physics much much deeper than "Light always moves at c in a vacuum". The use of Lorentz transforms greatly simplifies and restricts behaviour of systems and calculations, allowing otherwise intractable calculations to be done with ease. These predictions can then be tested, allowing us to test whether or not the transforms SR provides are valid.

Accelerator physics does this all the time. You can do calculations in any frame you like but if you're colliding say a positron and electron from opposite beams you have 2 obvious choices for your frame, the one where one particle is fixed, the other is when the system's centre of mass is fixed. The CoM frame is considerably nicer. Calculations involving such transformations are standard homework problems to anyone doing QED.

The assumption of using Lorentz transforms is tested more manifestly when doing heavy ion collision. You strap a heavy element into a detector, holding it still, and then smash a lighter element into it. In this case the CoM frame isn't stationary relative to the detector so our calculations in the CoM frame must be Lorentz transformed to give predictions about what the detector will see. If the detector sees something different then you have a problem somewhere, perhaps SR isn't valid? Except our predictions are born out, validating the predictions of special relativity (as well as the relevant quantum models). Emil is either deliberately ignoring or deliberately ignorant of these tests of special relativity, as illustrated when he demanded to be provided with examples of validations of special relativity.

Wow, the hypocrisy is so thick you could cut it with a knife!

Thus proving you are the one with no knowledge. Newtonian gravity ring a bell? Newtonian mechanics? A model is a formal description of a system which makes quantitative statements about it. Newtonian gravity, ie the implications of \(F = -\frac{Gm_{1}m_{2}}{r^{2}}\), is a quantitative description of gravity put forth by Newton. Thus it is a Newtonian model. The Newtonian description of mechanics involves the definitions of momentum and kinetic energy I explained to you. Other models, which generalise Newton's work, such as relativity, alter the definitions to make them more general and accurate.

You seem to have a comprehension problem as what I said doesn't imply that.

Besides, if you knew any relativity you'd know how it extends the expressions you're taught in school, which are only crude approximations to the true behaviour of systems. p=mv and \(KE = \frac{1}{2}mv^{2}\) are not universally true. This isn't me just saying "This model is correct because I say so!", there's real experimental evidence to prove p=mv isn't universally true. Accelerators show it every single day!

The second postulate is about being in a VACUUM. You're making a straw man, addressing things no one has said. You quoted James talking about transformations in a VACUUM. I have repeatedly explained how special relativity can still be valid even when light moves slower than c when moving through a medium. You aren't providing justification for your position, you're repeatedly ignoring direct questions, repeating irrelevant things, failing to show any working understanding, accusing others of not knowing things they demonstrably do, unwilling to look up information yourself and professing to have a knowledge you clearly do not have.

Since this thread has now degenerated into an "Everyone tells Emil he doesn't know anything" 'discussion', rather than a proper physics discussion, I'm going to close it. If someone wants to discuss some topic raised then start a new thread on it. As for you Emil, refrain from putting forth your 'alternative theories'. You've shown you're unwilling to find out information yourself and have no working experience with any relevant area of physics. If you want to whine about your lack of understanding of SR and make claims you cannot back up then go to the pseudo forum in future, as you offer no constructive discussion here.