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Old 24th December 2020, 09:22 AM   #1281
SDG
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Originally Posted by Robin View Post
I don't know that it is all that interesting. We don't expect the observer to see a frequency that is constant over time and we also know that if the last of the beam has been reflected off the mirror at t'=2 then it must reach the platform observer at t'=15.211, or t=7.606.

And it can't be 1/3.5 seconds duration for the above reason and also, although you have shown 7 waves in 2 seconds, you have not shown 7 waves observed in 2 seconds.

The max/min values are based on the longitudinal Doppler effect:






When the velocity changes direction then we have







Anything diagonal has to be between min/max.
What is your 7.606 value exactly?
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Old 28th December 2020, 06:13 PM   #1282
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Originally Posted by SDG View Post
Anything diagonal has to be between min/max.
Not sure what you are getting at. Are you saying that 1/3.606 Hz falls outside that range?
Quote:
What is your 7.606 value exactly?
Just what I said it was:

The train observer as in your scenario turns on the beam at 0 seconds train and platform time

He switches it off at 1 second train time.

The platform observer first sees the reflected beam at 4 seconds platform time

The platform observer last sees the reflected beam at 7.606 seconds platform time.

That makes a 3.606 duration that the platform observer sees the reflected beam.

The train observer has emitted 1 full wavelength in 1 second

The platform observer has received 1 full wavelength in 3.606 seconds.

This equates to the average frequency observed on the platform over that 1 second as being 1/3.606 Hz which is consistent with the frequency for that one second period arrived at using the Relativistic Doppler Effect equation.
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Last edited by Robin; 28th December 2020 at 06:23 PM.
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Old 30th December 2020, 04:21 PM   #1283
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Yes, OK for the post above.
I have no issue with the relativistic Doppler effect.
I am talking about the invariance of the space time interval.
So I will try to ask differently.
The train observer releases one photon per one second of the train time.
When the grid of the platform observers sees the first photon to come back in 4s of the platform time.
How many photons are in 'flight'?
How big space gap there would be between two photons, release with 1s' train time interval?
How many photons were released by the front train observer in the meantime and not yet absorbed by the back platform observer?
Is the number of released photons supposed to be agreed upon between the train and the platform observers?

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Old 30th December 2020, 08:52 PM   #1284
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Originally Posted by SDG View Post
Yes, OK for the post above.
I have no issue with the relativistic Doppler effect.
I am talking about the invariance of the space time interval.
I didn't calculate that using the Relativistic Doppler Effect. I only pointed out at the end that it was consistent with the Relativistic Doppler Effect.
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Old 30th December 2020, 09:51 PM   #1285
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Originally Posted by SDG View Post
So I will try to ask differently.
The train observer releases one photon per one second of the train time.
When the grid of the platform observers sees the first photon to come back in 4s of the platform time.
How many photons are in 'flight'?
How big space gap there would be between two photons, release with 1s' train time interval?
How many photons were released by the front train observer in the meantime and not yet absorbed by the back platform observer?
It depends upon which frame you are talking about
Quote:
Is the number of released photons supposed to be agreed upon between the train and the platform observers?
The number of photons released is agreed, but the number of photons released before the absorption of the first photon isn't agreed because of the relativity of simultaneity.

Let us suppose the train observer releases 8 photons at 1 second intervals. The first photon reaches the platform observer at 8 seconds, by which time he has release 7 more.

But from the platform observer's frame he has only released one more by the time the first photon is absorbed.

To see this I graph the intersection of the mirror light cone for each time it reflects a photon with the x/t plane for both frames. The intersection of the light cone with the x/t plane forms a hyperbola and the intersection of the hyperbola with the time axis for the platform observer is the time the platform observer absorbs the photon. Time on the vertical axis, x on the horizontal:

The first two photons in three dimensions:

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Last edited by Robin; 30th December 2020 at 10:55 PM.
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Old 30th December 2020, 11:21 PM   #1286
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So how far away is the next photon from the platform observer in the platform frame when the first photon is absorbed?

Well it is just being reflected from the mirror which is 3.465 light seconds away in the x direction and 1 light second away in the y direction, so the second photon is 3.606 light seconds away from the platform observer at 4 seconds when the first photon is absorbed.
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Last edited by Robin; 30th December 2020 at 11:49 PM.
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Old 4th January 2021, 11:58 AM   #1287
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Robin,
very good posts.

Here is what is happening along your space time diagrams.









P1 is photon one and P2 is photon two.
Two photons emitted by the train observer.
The problem is with y axis.
How many photons are in flight when photon P1 is at y=y'=0?




P1 is at 1-1/7cs=1-1/7cs' on the y=y' axis after t'=2s' based on the train observer.
P1 is supposed to be at 0cs=0cs' on y=y' axis after t'=2s' observed by the platform grid of observers looking at/observing x'=0cs' origin.
Only 2 photons were released at 0s' and 1s' as observed by the platform grid.
Two inertial observers do not agree on simultaneity. This is not all.
Two inertial observers do not agree on many more things.
They do not agree on angles, they do not agree on y, y' position, they do not agree on energy delta.
The disagreement on energy delta is essentially disagreement on physics.

Edit: Energy delta being each individual photon released.

Last edited by SDG; 4th January 2021 at 01:58 PM.
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Old 4th January 2021, 02:11 PM   #1288
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The fourth image in the post above should have P1 label as this one.


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Old 4th January 2021, 02:13 PM   #1289
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Originally Posted by SDG View Post
Robin,
very good posts.

Here is what is happening along your space time diagrams.
You seem to be confused about how light propagates. The way you're drawing it might make some sense if the wave front of light oscillated as it propagated. But that's not how it works. The oscillation is only visible if the light is passing by you. That means the oscillation of light depends on both the position AND the time of the observer, and as any student of relativity should know, BOTH those quantities can change as you change reference frames, not just one or the other.

If you just follow the wave front as it travels at c, that front doesn't change. So if we follow the wave front, there's no oscillation in it from one event to another. In order to see a wavelength or a frequency, you've got to emit and detect over time, which means even looking at this from one frame, you will need four events (start and stop of emission, start and stop of detection), not two. And because you need four events and not two, changing reference frames becomes even more complicated.

In other words, your drawing is fundamentally wrong. It doesn't actually make sense.
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Old 4th January 2021, 07:15 PM   #1290
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Originally Posted by Ziggurat View Post
You seem to be confused about how light propagates. The way you're drawing it might make some sense if the wave front of light oscillated as it propagated. But that's not how it works. The oscillation is only visible if the light is passing by you. That means the oscillation of light depends on both the position AND the time of the observer, and as any student of relativity should know, BOTH those quantities can change as you change reference frames, not just one or the other.

If you just follow the wave front as it travels at c, that front doesn't change. So if we follow the wave front, there's no oscillation in it from one event to another. In order to see a wavelength or a frequency, you've got to emit and detect over time, which means even looking at this from one frame, you will need four events (start and stop of emission, start and stop of detection), not two. And because you need four events and not two, changing reference frames becomes even more complicated.

In other words, your drawing is fundamentally wrong. It doesn't actually make sense.
I know, it is better to show a wave packet:




Having said that, there are many drawings like this as well.



So my dot is an end of a polarized E field arrow of the second diagram.
Both observers agree on this position in the first leg of the light roundtrip.
... but the second leg is the problem.

How many photons/wave packets were emitted by the train observer in 2s'?
In order for the photon to get to y=y'=0 on the second leg there are supposed to be 7 photons/wave packets emitted to fill up the invariant space time interval of the train frame.

Last edited by SDG; 4th January 2021 at 07:28 PM.
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Old 4th January 2021, 11:23 PM   #1291
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Originally Posted by SDG View Post
I know, it is better to show a wave packet:
The problem is not the distinction between wave packets and standing waves. The problem is that you're mixing up the difference between space and time.

Quote:
Having said that, there are many drawings like this as well.
That diagram works as a snapshot in time. It is not a trajectory, which is what your earlier diagram purports to be but is not because, as I said, you are mixing up space and time.

Quote:
How many photons/wave packets were emitted by the train observer in 2s'?
In order for the photon to get to y=y'=0 on the second leg there are supposed to be 7 photons/wave packets emitted to fill up the invariant space time interval of the train frame.
Wow. This is a deeply profound misunderstanding of what a photon is.

Photons are not the peaks in a wave. That isn't how they work. Nothing about your diagram gives any indication of how many photons are involved. That simply isn't relevant to the problem. Changing the number of photons involved can simply change the strength of the field because photons can sit on top of each other, but since there's no scale on any of the diagrams, the number of photons is simply irrelevant to the problem.
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Old 5th January 2021, 01:02 AM   #1292
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Originally Posted by Ziggurat View Post
The problem is not the distinction between wave packets and standing waves. The problem is that you're mixing up the difference between space and time.



That diagram works as a snapshot in time. It is not a trajectory, which is what your earlier diagram purports to be but is not because, as I said, you are mixing up space and time.



Wow. This is a deeply profound misunderstanding of what a photon is.

Photons are not the peaks in a wave. That isn't how they work. Nothing about your diagram gives any indication of how many photons are involved. That simply isn't relevant to the problem. Changing the number of photons involved can simply change the strength of the field because photons can sit on top of each other, but since there's no scale on any of the diagrams, the number of photons is simply irrelevant to the problem.
Post #1283

'The train observer releases one photon per one second of the train time.'
The question stands.
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Old 12th January 2021, 01:38 PM   #1293
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Exclamation Usual abysmal ignorance or lies from SDG about textbook physics.

Originally Posted by SDG View Post
...
How many photons/wave packets were emitted by the train observer in 2s'?
In order for the photon to get to y=y'=0 on the second leg there are supposed to be 7 photons/wave packets emitted to fill up the invariant space time interval of the train frame.
Usual abysmal ignorance or lies from SDG about textbook physics.
If there is 1 photon in the scenario then there is supposed to be 1 photon always in the scenario. There will be perfect mirrors reflecting it. There is nothing magically creating photons as SDG imagines.
This is a photon. A photon has a frequency. It is that which changes.
This is a wave packet. The wave packet has a width related to frequency. Photons do not expand to fill up an "invariant space time interval". The 1 photon in the scenario SDG is spamming the thread with, is measured to change frequency. The photon as a wave packet will change its width correspondingly.

Last edited by Reality Check; 12th January 2021 at 01:40 PM.
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Old 12th January 2021, 04:08 PM   #1294
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Originally Posted by Reality Check View Post
Usual abysmal ignorance or lies from SDG about textbook physics.
If there is 1 photon in the scenario then there is supposed to be 1 photon always in the scenario. There will be perfect mirrors reflecting it. There is nothing magically creating photons as SDG imagines.
This is a photon. A photon has a frequency. It is that which changes.
This is a wave packet. The wave packet has a width related to frequency. Photons do not expand to fill up an "invariant space time interval". The 1 photon in the scenario SDG is spamming the thread with, is measured to change frequency. The photon as a wave packet will change its width correspondingly.
Reality Check, are you lost?
It appears, you do not understand the reality and meaning of the inertial observers disagreement on the y-positions of the photons as explained in the previous posts.
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Old 12th January 2021, 06:09 PM   #1295
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Originally Posted by SDG View Post
Reality Check, are you lost?...
My post was about his "7 photons/wave packets emitted to fill up the invariant space time interval of the train frame" photon fantasy as based on his stupid cartoons (my mistake!).
It should be
SDG wrote idiocy about Robin's post where it is stated that the train observer emits 8 photons a second. So in the train frame we have
  • A stupid "How many photons/wave packets were emitted by the train observer in 2s'?" question when the train observer emits 8 photons a second. 2 * 8 = 16!
  • The first photon reaches the platform observer in a second. There are 7 more inflight for the simple reason that the train observer emitted them. If the platform observer did not exist the train observer would still have emitted 7 more photons within that second. There is none of SDG's "to fill up the invariant space time interval of the train frame" idiocy.
The numbers differ for the platform frame.

SDG idiotically amended his scenario from a beam of light to "one photon per one second" from the train observer. One photon a second being emitted is a very weak beam of light . SDG asked irrelevant questions about the photons when it is SDG who is trying to debunk special relativity and so has to do the work.

Robin answered with textbook physics:
Originally Posted by Robin View Post
It depends upon which frame you are talking about

The number of photons released is agreed, but the number of photons released before the absorption of the first photon isn't agreed because of the relativity of simultaneity.

Let us suppose the train observer releases 8 photons at 1 second intervals. The first photon reaches the platform observer at 8 seconds, by which time he has release 7 more.

But from the platform observer's frame he has only released one more by the time the first photon is absorbed.
SDG replied with nonsensical cartoons, lies and more questions that it is up to SDG to answer because SDG is the one trying to debunk special relativity.
  • A fantasy that his cartoons are about Robin's spacetime diagrams.
    Robin ploted 2 graphs for the train and platform frames and the first 2 photons based on textbook physics. What SDG imagines he is doing is unknown! It is certainly not physics.
  • A lie that "Two inertial observers do not agree on simultaneity" is a problem for relativity when it is textbook and tested physics.
  • A lie that "Two inertial observers do not agree on many more things." is a problem for relativity when it is textbook and tested physics.
  • A probable "The problem is with y axis." lie.

Last edited by Reality Check; 12th January 2021 at 06:55 PM.
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