# What Qm Might Say About Sr

Quantum mechanics Special relativity

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### #1 JulianM

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Posted 03 January 2018 - 10:43 AM

It seems to me that QM and SR would treat light beams in different ways.

SR indicates that a light pulse acts like a ball in classical mechanics, for example a light clock where a particle motion in someone else's reference frame is measured in my reference frame. We get a bouncing ball moving in diagonals.

Surely QM would say that you cannot see, or even know, what is happening to the "bouncing ball" when it is travelling between the mirrors. All we can see is the events as it strikes the mirror.

Now let's take a simple example of a moving train. A flash of light occurs in the middle of the train and adjacent platform.

The events then are
1. The (left, for example) end of the platform is illuminated at a specific point in time

2. The left end of the train is also illuminated at some time.

Because light travels at the same speed in each frame the time is (L/2)/c

Now on the platform we can easily determine what happened. For the platform observer the illumination of the rear of the train happens earlier and this can be determined by t = (L/2)/c - vt

Now since in my frame the event occurred in a different location, and earlier, I can back calculate what time these events took place in my time frame.

The difference in distance was simply vt, therefore, by exclusively considering observed events in my frame of reference then both occurred simultaneously (which is not what SR says)

Now I have light travelling at speed = c in both frames, distance = L/2 in both frames and the same event determined as simultaneous in both frames. The difference is that we see the event at different locations.

What does this mean?

### #2 exchemist

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Posted 03 January 2018 - 11:58 AM

It seems to me that QM and SR would treat light beams in different ways.

SR indicates that a light pulse acts like a ball in classical mechanics, for example a light clock where a particle motion in someone else's reference frame is measured in my reference frame. We get a bouncing ball moving in diagonals.

Surely QM would say that you cannot see, or even know, what is happening to the "bouncing ball" when it is travelling between the mirrors. All we can see is the events as it strikes the mirror.

Now let's take a simple example of a moving train. A flash of light occurs in the middle of the train and adjacent platform.

The events then are
1. The (left, for example) end of the platform is illuminated at a specific point in time

2. The left end of the train is also illuminated at some time.

Because light travels at the same speed in each frame the time is (L/2)/c

Now on the platform we can easily determine what happened. For the platform observer the illumination of the rear of the train happens earlier and this can be determined by t = (L/2)/c - vt

Now since in my frame the event occurred in a different location, and earlier, I can back calculate what time these events took place in my time frame.

The difference in distance was simply vt, therefore, by exclusively considering observed events in my frame of reference then both occurred simultaneously (which is not what SR says)

Now I have light travelling at speed = c in both frames, distance = L/2 in both frames and the same event determined as simultaneous in both frames. The difference is that we see the event at different locations.

What does this mean?

Where does QM come into any of this stuff?

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### #3 JulianM

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Posted 03 January 2018 - 12:08 PM

QM says that you know nothing about the path of the particle between events, i.e you cannot say it is a "bouncing ball" as SR does.

QM says you call only know what happens when the event occurs.

### #4 exchemist

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Posted 03 January 2018 - 12:20 PM

QM says that you know nothing about the path of the particle between events, i.e you cannot say it is a "bouncing ball" as SR does.

QM says you call only know what happens when the event occurs.

But it is the events you are noting in this thought experiment so where is the issue?

### #5 JulianM

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Posted 03 January 2018 - 01:30 PM

The issue is that simultaneity of time is preserved and SR is based on lack of simultaneity.

### #6 exchemist

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Posted 03 January 2018 - 02:58 PM

The issue is that simultaneity of time is preserved and SR is based on lack of simultaneity.

QM is a model for what happens at the atomic scale. It seems to me it has nothing whatever to say about the scenario you describe, which is self-evidently a macroscopic one.

What is the point of trying to use a spanner to turn a screw?

### #7 JulianM

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Posted 03 January 2018 - 09:08 PM

QM is a model for what happens at the atomic scale. It seems to me it has nothing whatever to say about the scenario you describe, which is self-evidently a macroscopic one.

What is the point of trying to use a spanner to turn a screw?

You don't think that light photons are on the atomic scale?

### #8 Vmedvil

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Posted 04 January 2018 - 03:49 AM

It is simple SR treats them as Photons the particle version of the wave-particle, QM on the other-hand treats it as a wave being light, QFT is the version of QM that uses SR,which is in the particle form.

Particle form will give you an exact location in causality, the wave form takes all pathways in causality or like a particle taking all possible paths to the location.

So, the Particle form views causality as Linear and the Wave form as causality non linear.

Which on the large scale causality is given a particle state by your choices, until the time of choice it is in wave form your exact future is not certain with many possible states being the wave form. You are constructed of Wave-Particles why would you not display this trait too?

If it is the case, where you behave as a wave form for a period of time before a choice like electrons and photons then there is a moment before a choice is made where there are many possible Earth futures based on your choice, which is where Parallel Universes come into play what if we took all those possible pathways as "Real" possibilities that are happening at the same-time. The Photons and Electrons do this, so why would it not happen on larger scales as you are constructed of wave-particles?

Note: look at the final sentence of the last two paragraphs, why where they in the form they are and not opposite my choice! Which said the same thing in two different ways, in another universe parallel to ours they were reversed, In others I said nothing as a reply to this post!

Edited by Vmedvil, 04 January 2018 - 04:40 AM.

### #9 JulianM

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Posted 04 January 2018 - 07:19 AM

Thanks! Very helpful.

So my understanding from your explanation is that SR is based on particle behavior, but QM is based on wave behavior.

From what I understand the multiple universes theory is still debated, but that topic is beyond where I am at,

I will go away and read some more, particularly on Quantum Field Theory, but first let me check with you - are you saying that QFT assumes SR or is it that QFT is an outcome of SR. I am not sure which leads to which.

### #10 Vmedvil

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Posted 04 January 2018 - 09:12 AM

Thanks! Very helpful.

So my understanding from your explanation is that SR is based on particle behavior, but QM is based on wave behavior.

From what I understand the multiple universes theory is still debated, but that topic is beyond where I am at,

I will go away and read some more, particularly on Quantum Field Theory, but first let me check with you - are you saying that QFT assumes SR or is it that QFT is an outcome of SR. I am not sure which leads to which.

QFT applies the math of SR to QM being in particle form where SR works and not in wave form where it gives nonsense answers.

Edited by Vmedvil, 04 January 2018 - 09:25 AM.

### #11 exchemist

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Posted 04 January 2018 - 03:41 PM

You don't think that light photons are on the atomic scale?

A photon is, sure. A light beam, travelling macroscopic distances, is not.

Just as an atom is on the atomic scale but a tennis ball is not, even though it is composed of atoms.

QM does not help address the scenario you are postulating. It is the wrong tool for the job. Just as Newtonian mechanics is the wrong tool, too.

Newtonian mechanics is highly successful for macroscopic dynamics of bodies that do not move relative to one another at close to c.

QM is successful at atomic scale phenomena in which the value of h, Planck's Constant, is significant compared to the scale of the phenomena.  But this is not the case for your proposed scenario.

Edited by exchemist, 04 January 2018 - 04:29 PM.

### #12 JulianM

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Posted 05 January 2018 - 05:26 AM

An interesting point, but I don't think it addresses the issue I am describing. Most certainly SR is envisioned by a light pulse, which can be as small as a single photon, in fact as soon as you start to describe macroscopic objects such as a tennis ball then we cannot discuss the properties of light.

SR commonly uses the idea of a light clock, a single photon bouncing between mirrors. A tennis ball cannot be used to construct such a clock.

Now I am not suggesting that we use the mathematics of QM in this scenario. All I am really saying is that, since we know from QM that the movement of light between events is basically unknowable why don't we base our math on observable events rather than the mental image of a beam of tennis balls streaming away from the observer at a relative speed of (c + v)

### #13 exchemist

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Posted 05 January 2018 - 10:18 AM

An interesting point, but I don't think it addresses the issue I am describing. Most certainly SR is envisioned by a light pulse, which can be as small as a single photon, in fact as soon as you start to describe macroscopic objects such as a tennis ball then we cannot discuss the properties of light.

SR commonly uses the idea of a light clock, a single photon bouncing between mirrors. A tennis ball cannot be used to construct such a clock.

Now I am not suggesting that we use the mathematics of QM in this scenario. All I am really saying is that, since we know from QM that the movement of light between events is basically unknowable why don't we base our math on observable events rather than the mental image of a beam of tennis balls streaming away from the observer at a relative speed of (c + v)

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.

### #14 JulianM

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Posted 05 January 2018 - 04:25 PM

I guess you missed the point.

### #15 exchemist

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Posted 05 January 2018 - 04:49 PM

I guess you missed the point.

Apparently so. I do not see your point, certainly.

It is true that regular QM does not take relativity into account, since it gives perfectly good results in most of its intended applications without this extra complexity. But in QM, photons move at c, or rather their group or signal velocity does. (Their phase velocity may not, depending on whether the photons are travelling in empty space or though a transparent medium, e.g. water, glass etc.)

### #16 JulianM

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Posted 06 January 2018 - 07:49 AM

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

### #17 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?