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What Qm Might Say About Sr

Quantum mechanics Special relativity

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#18 exchemist

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Posted 06 January 2018 - 09:31 AM

So try to repeat the train thought experiment by considering only the observable/detectable events.

I'm not sure what you mean by that. The thought experiment consists of observed events, surely, observed by different observers, which are moving relative to one another.

 

The only assumption, it seems to me, is that light moves at c, in both reference frames, in between the events observed.

 

What is it you think QM says that conflicts with this?  

 

Or are you saying there is another assumption I have overlooked that is contradicted by QM?



#19 Vmedvil

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Posted 06 January 2018 - 11:00 PM

Here is the Train thought experiment in a void. 

 

https://www.physicsf...tionary.828562/



#20 JulianM

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Posted 07 January 2018 - 05:01 PM

I'm not sure why you say the movement of light between events is unknowable, according to QM. QM does not deny that photons move with a velocity of c. This velocity is the only property of light that you need for your scenario.


You are correct about QM, but SR only permits the velocity of light to be c in one's own frame of reference. It "concludes" that in any other frame I can detect it as either (c + v) or (c - v) i.e. never = c
This is because SR examines the movement of light, not the observable events.

#21 Vmedvil

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Posted 08 January 2018 - 01:02 AM

You are correct about QM, but SR only permits the velocity of light to be c in one's own frame of reference. It "concludes" that in any other frame I can detect it as either (c + v) or (c - v) i.e. never = c
This is because SR examines the movement of light, not the observable events.

Yes, there is something odd that happens in SR @ C everyone knows this as you get (1- (299,792,4582/299,792,4582))1/2  which says 0 length size or infinite density or Infinite Time duration, this is because this is the reference frame Einstein used to generate it, all Black hole's exist in this state. 


Edited by Vmedvil, 08 January 2018 - 01:11 AM.


#22 exchemist

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Posted 08 January 2018 - 03:39 AM

You are correct about QM, but SR only permits the velocity of light to be c in one's own frame of reference. It "concludes" that in any other frame I can detect it as either (c + v) or (c - v) i.e. never = c
This is because SR examines the movement of light, not the observable events.

I don't think it is true to say that SR "examines the movement" of light. If you read explanations of SR, it is all about what observers detect or perceive, not about anything happening in between.  

 

The way I have understood it, the only way to reconcile observations that light moves at c in any reference frame is if length and time alter with relative velocity between frames, to preserve c. 



#23 Vmedvil

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Posted 08 January 2018 - 05:44 AM

I don't think it is true to say that SR "examines the movement" of light. If you read explanations of SR, it is all about what observers detect or perceive, not about anything happening in between.  

 

The way I have understood it, the only way to reconcile observations that light moves at c in any reference frame is if length and time alter with relative velocity between frames, to preserve c. 

Well, yes but Einstein did use C as the limit to his medium in SR, so it is fair to say, SR judges us based on our speed relative to light.



#24 exchemist

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Posted 08 January 2018 - 05:52 AM

Well, yes but Einstein did use C as the limit to his medium in SR, so it is fair to say, SR judges us based on our speed relative to light.

What do you mean by "the limit to his medium"? A medium does not have a limit. And light does not require a medium.



#25 JulianM

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Posted 08 January 2018 - 06:16 AM

I’d like to keep this as simple as possible, for my sake as much as for others. Let's go back to my original post with a train of length L passing a platform also of length L.

There is a passenger in the middle of the train and a station master in the middle of the platform. As they pass each other (saying nothing about which is moving) a flash of light occurs.

Simple so far, yes?

We agree on the lengths, timing of the flash and the speed of light being constant at c.

We can't see light moving away from us at speed c, so what do we see?

Both participants see objects which are illuminated by the flash and these are a) the rear of the train and B) the end of the platform and these are dictated by length (L), and speed of light ©
Anyone disagree so far?

The station master sees the rear of the train illuminated at (L/2)/c as he knows the length of the train and the speed of light.
He also sees the rear of the platform illuminated and can perform the same calculation. What he sees is the rear of the train illuminated first.
Do we still agree?

The station master, knowing the position of the rear of the train in his own frame of reference, that the time difference between the two is simply calculated from d/v. The evidence is that both events took place at the same time (preserving simultaneity off time), light travelled at the same speed for both © and that the distance travelled had to be the same so there can be no time dilation or length shortening in this example.

The only thing we can conclude is that if two events take place at the same time I will see the one closest to me first.

#26 exchemist

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Posted 08 January 2018 - 08:45 AM

I’d like to keep this as simple as possible, for my sake as much as for others. Let's go back to my original post with a train of length L passing a platform also of length L.

There is a passenger in the middle of the train and a station master in the middle of the platform. As they pass each other (saying nothing about which is moving) a flash of light occurs.

Simple so far, yes?

We agree on the lengths, timing of the flash and the speed of light being constant at c.

We can't see light moving away from us at speed c, so what do we see?

Both participants see objects which are illuminated by the flash and these are a) the rear of the train and :cool: the end of the platform and these are dictated by length (L), and speed of light ©
Anyone disagree so far?

The station master sees the rear of the train illuminated at (L/2)/c as he knows the length of the train and the speed of light.
He also sees the rear of the platform illuminated and can perform the same calculation. What he sees is the rear of the train illuminated first.
Do we still agree?

The station master, knowing the position of the rear of the train in his own frame of reference, that the time difference between the two is simply calculated from d/v. The evidence is that both events took place at the same time (preserving simultaneity off time), light travelled at the same speed for both © and that the distance travelled had to be the same so there can be no time dilation or length shortening in this example.

The only thing we can conclude is that if two events take place at the same time I will see the one closest to me first.

No. The light has to get to the end of the train or platform and back to each observer before it can be seen.

 

If the train is stationary, the time taken for the light to get there and back, to and from the end of the platform and to and from the end of the train, will not be (L/2)/c, it will be 2 x (L/2)/c  = L/c. So that is the time that would elapse before the stationmaster would see the light arriving. 

 

If the train is moving relative to the platform, by the time the light reflects off the end of the train, the end of the train will have moved forward towards the stationmaster, reducing the distance the light has to travel, both there and back to him. So the time taken will be shorter than to the end of the platform and back. The stationmaster sees 2 returning pulses, the one from the train arriving first, as you say. 

 

But I still do not see what any of this has to do with quantum theory. 


Edited by exchemist, 08 January 2018 - 08:45 AM.


#27 JulianM

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Posted 08 January 2018 - 09:33 AM

Yes, the time to come back is the time it takes for the image of the illumination to reach (for example) the station master. I have fully taken that in to account if you read carefully.

And yes, the station master will see the illumination event in the train first, because, as we agree it is closer in his frame of reference.

So far we agree.

The next step is - did the events take place at the same time (simultaneity) or not. Do the lengths need to change for this to happen and is this consistent with light speed = c.

Do you agree with that, or do you think the events take place at different times and because the times are different the lengths must be different.

As to QM - I have several times said that QM (and commonsense too) tells us that you cannot know what happens to the light between events. Nothing deeper than that, period. Agree? Or do you believe you can see something travelling away from you at the speed of light.

#28 exchemist

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Posted 08 January 2018 - 10:18 AM

Yes, the time to come back is the time it takes for the image of the illumination to reach (for example) the station master. I have fully taken that in to account if you read carefully.

And yes, the station master will see the illumination event in the train first, because, as we agree it is closer in his frame of reference.

So far we agree.

The next step is - did the events take place at the same time (simultaneity) or not. Do the lengths need to change for this to happen and is this consistent with light speed = c.

Do you agree with that, or do you think the events take place at different times and because the times are different the lengths must be different.

As to QM - I have several times said that QM (and commonsense too) tells us that you cannot know what happens to the light between events. Nothing deeper than that, period. Agree? Or do you believe you can see something travelling away from you at the speed of light.

Well you cannot detect light without absorbing some of it, I agree.

 

But you can model what happens to it en route. Both classical and quantum optics do this routinely, when modelling what happens to a light beam in various circumstances.  



#29 JulianM

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Posted 08 January 2018 - 03:08 PM

So I think here is where we diverge. QM fundamentally says you cannot know what a particle/wave is doing until you measure it and SR theorizes something which is unseeable (visualizing light travelling away from you).

So what can we do? We can observe more events.

Let's place a mirror on the back of the train and reflect the light back towards the passenger. At some time the passenger becomes illuminated and this is easily determined from the speed of light and half the length of the train.
A simillar mirror on the platform reflects light back to the station master.
The station master sees the reflection from from the platform illuminated his position and the light reflected in the train illuminated the passenger. They are at different times but the illumination of the passenger occurs at a position in the platform frame which, knowing the distance, calculates to exactly the same time as the illumination at his position.
The time is simultaneous, the lengths haven't changed and the speed of light is c.

#30 exchemist

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Posted 09 January 2018 - 04:38 AM

So I think here is where we diverge. QM fundamentally says you cannot know what a particle/wave is doing until you measure it and SR theorizes something which is unseeable (visualizing light travelling away from you).

So what can we do? We can observe more events.

Let's place a mirror on the back of the train and reflect the light back towards the passenger. At some time the passenger becomes illuminated and this is easily determined from the speed of light and half the length of the train.
A simillar mirror on the platform reflects light back to the station master.
The station master sees the reflection from from the platform illuminated his position and the light reflected in the train illuminated the passenger. They are at different times but the illumination of the passenger occurs at a position in the platform frame which, knowing the distance, calculates to exactly the same time as the illumination at his position.
The time is simultaneous, the lengths haven't changed and the speed of light is c.

I have to say I think you are quite wrong about this. Both your initial statements are in my view false. 

 

I am not aware that anything in QM precludes having any information about a QM entity in between observations of it. We know perfectly well "what an electron is doing" in a hydrogen atom for instance, without needing to measure it.  All QM says is that there are certain limits to how exactly its properties are defined, due to the wavelike nature of matter at the atomic scale (or to non-commuting operators if you want to be more mathematical). 

 

And SR does not "theorise something unseeable". SR relies on only one thing, which is an observed, universal, property of light, namely that its speed is not frame-dependent. That is all.   

 

If you disagree I would like to see some references to where you get your information from.


Edited by exchemist, 09 January 2018 - 04:41 AM.


#31 Vmedvil

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Posted 09 January 2018 - 05:25 AM

What do you mean by "the limit to his medium"? A medium does not have a limit. And light does not require a medium.

The Medium Space-Time you know that fabric of the cosmos that is often spoken about? That is the medium of all of Einstein's Equations and models. The Time-space Aether which is "Free space's Medium", It is a common misconception that there is no medium in "Free Space".

 

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In any case, the Limit of Max Velocity through Time-space or Space-Time is C precluding a wormhole or Warp Drive but naturally due to V2/C the limit of this medium is C2 or just C as Mass becomes infinite @ V = C.

 

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Edited by Vmedvil, 09 January 2018 - 05:50 AM.


#32 exchemist

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Posted 09 January 2018 - 05:58 AM

The Medium Space-Time you know that fabric of the cosmos that is often spoken about? That is the medium of all of Einstein's Equations and models. The Time-space Aether which is "Free space's Medium"

 

 

 

 

 

In any case, the Limit of Max Velocity through Time-space or Space-Time is C precluding a wormhole or Warp Drive but naturally due to V2/C the limit of this medium is C2 or just C as Mass becomes infinite @ V = C.

 

 

 

This does not seem to make much sense. Spacetime is not a medium in the sense of a substance whose oscillations enable the propagation of waves. EM waves don't need a medium.

 

By "limit", perhaps you mean "speed limit"? If you do, then you need to qualify what you mean, because certain phenomena are not precluded from moving faster than c, for example the phase velocity of light under certain circumstances. 



#33 Vmedvil

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Posted 09 January 2018 - 06:07 AM

This does not seem to make much sense. Spacetime is not a medium in the sense of a substance whose oscillations enable the propagation of waves. EM waves don't need a medium.

 

By "limit", perhaps you mean "speed limit"? If you do, then you need to qualify what you mean, because certain phenomena are not precluded from moving faster than c, for example the phase velocity of light under certain circumstances. 

Yes, this is why both of you are wrong about this, you haven't taken in account the Energy-mass curvature of time-space or gravity of either of these objects, Yes, it is a medium that effects all of this stuff otherwise, why are black-hole's black if light was not attracted via Time-space Curvature or "Gravity" they would not be black. Yes, it makes a huge difference. In all of this.

 

spacetimelightcurves.jpg

 

This is the same reason, I called http://www.sciencefo.../86228-strange/ literally retarded for not getting this concept and having the same misconception.

 

This is going to use a shitty Newtonian Gravity Equation, so you will understand it, but is still valid. 

 

M'Train = MTrain rest/(1-(VTrain2/C2))1/2  

 

L' Train= LTrain rest(1-(VTrain2/C2))1/2   , 

 

Δt'Train = ΔtTrain Rest/(1-(VTrain2/C2))1/2 

 

Vgravity Train = (GM'Train/L'Train2)Δt'Train  

 

Vgravity platform = (GMplatform rest/LPlatform rest2)Δtplatform rest

 

Vtrain = Cphoton + Vgravity Train - Vgravity Platform  - VTrain    

 

Vplatform Cphoton - Vgravity Train + Vgravity platform

 

Then the train moving so   

 

VTrain Δt'Train = ΔxTrain  

 

Then the platform is at rest so   

 

 Vplatform Δtplatform rest = Δxplatform


Edited by Vmedvil, 10 January 2018 - 01:18 PM.


#34 exchemist

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Posted 09 January 2018 - 06:58 AM

Yes, this is why both of you are wrong about this, you haven't taken in account the Energy-mass curvature of time-space or gravity of either of these objects, Yes, it is a medium that effects all of this stuff otherwise, why are black-hole's black if light was not attracted via Time-space Curvature or "Gravity" they would not be black. Yes, it makes a huge difference. In all of this.

 

 

 

 

 

This was not posed as a problem in GR and it is quite irrelevant to drag GR into it.