# Relativity of Simultaneity Gendankin

Discussion in 'Physics & Math' started by MacM, Feb 3, 2006.

1. ### PeteIt's not rocket surgeryRegistered Senior Member

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Looks like a case of both "Ignore X until X ceases to be true", and "Assert Y until Y is true".

Beautiful

3. ### DaleSpamTANSTAAFLRegistered Senior Member

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This is apparently the best you can do against my proof.

If you can't address the logic then at least consult a thesaurus for your flaccid invective. That way your ignorance won't show quite as clearly.

-Dale

5. ### 2inquisitiveThe Devil is in the detailsRegistered Senior Member

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Sorry, Pete, I did not mean to ignore you. I'm not sure how you specify 'frame dependent'. Do you think our vector of travel affects the rotational speed of a pulsar? If we travel straight toward the pulsar, does the rotational speed of the pulsar increase when we change our vector of travel 90 degrees to the left?

7. ### PeteIt's not rocket surgeryRegistered Senior Member

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Are you interested in the actual beat rate relative to the observer, or the perceived beat rate? Usually I'd assume you mean the actual beat rate, but I think that if you want to use the pulsar as a timer then the perceived beat rate is more relevant.

I think that the perceived beat rate of the pulsar is affected by our direction of travel... this is true with or without relativity.

I think that according to special relativity, the actual beat rate of the pulsar depends only on our speed relative to the pulsar, not our direction, as long as we maintain constant direction. If we change direction without changing speed, the beat rate of the pulsar will be different during the change.

Last edited: Feb 24, 2006
8. ### 2inquisitiveThe Devil is in the detailsRegistered Senior Member

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by Pete:
"I think that the perceived beat rate of the pulsar is affected by our direction of travel... this is true with or without relativity.

I think that according to special relativity, the actual beat rate of the pulsar depends only on our speed relative to the pulsar, not our direction, as long as we maintain constant direction."
===============================================================

I am speaking of actual beat rate. Can you tell me the difference? I assume you are thinking of global inertial frames as used in Special Theory. In General Relativity, an inertial frame is a LOCAL inertial frame, pertaining to the vicinity of space near the observer's location. Now, think of what you said in the last sentence I pasted above. Our velocity relative to the pulsar IS dependent on our vector of travel. Heading straight towards the pulsar, we can have a relativistic velocity if our velocity, or the pulsar's velocity, is great enough. If we, or the pulsar, are travelling 90 degrees orthogonal wrt each other, the relative velocity between us and the pulsar can be essentially zero. So, by changing direction of travel, does the pulsar's beat rate change?

9. ### PeteIt's not rocket surgeryRegistered Senior Member

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Well, the perceived beat rate would be how often you detect a new beat.
The actual beat rate (relative to you) would be how often the pulsar completes a revolution in your reference frame.

I'm not sure how you expect to synchronize a clock to how often the pulsar spins, rather than how often you actually perceive it to spin, but anyway...

Of course... velocity is a vector, yeah?
You seem to be referring to the rate of change in the distance between us and the pulsar. That is not our velocity relative to the pulsar, and it is not what I meant by our speed relative to the pulsar in the relevant sentence.

By "speed relative to the pulsar", I meant "magnitude of our velocity relative to the pulsar".

According to special relativity, the actual beat rate of the pulsar (relative to us) depends only on the magnitude of our velocity relative to the pulsar, not our direction, as long as we maintain constant direction. If we change direction without changing the magnitude of our velocity relative to the pulsar, the beat rate of the pulsar (relative to us) will be different during the change.

So:
The pulsar's beat rate (relative to us) while we travel straight toward the pulsar is the same as it is (relative to us) after we turn 90 degrees to the left... but it is different (relative to us) while we're turning.

10. ### 2inquisitiveThe Devil is in the detailsRegistered Senior Member

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So, a Doppler shift of the pulsar's light will be affected by the change of direction, and the DISTANCE to the pulsar will be affected by a change of direction, but not the pulsar's beat (time). Distance contraction and time dilation are separate effects. How do we measure the magnitude of our velocity with only ourselves and the pulsar in the picture? I though velocity relative to the pulsar was all there was in Special Theory. Of course, quadraphonics is on Earth, isn't he. But again, if I left Earth headed straight for the pulsar, then turned 90 degrees to the right, my velocity relative to the Earth and the pulsar will decrease, won't it? Don't forget, most pulsars are thousands to billions of light years away. The pulsar will change apparent location from my front to my side, but will hardly move once it is at my side due to its great distance.

11. ### Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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Yes. I was keeping it as simple as possible for 2inqusitive - trying to get him to understand that the observed rate of the pulsar's pulses, which is the observed rate of its rotation, will change with motion towards of away from it,even if only classical physics is considered. He thinks it is a constant that all frames can use to sychronize their clocks with. A totally wrong concept. I.e. I was following the KISS rule.

Last edited by a moderator: Feb 24, 2006
12. ### MacMRegistered Senior Member

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It is not a wrong concept. The red/blue shift is a basis upon which to compensate each observers motion relative to the pulsar so as to standardize data.

It would be fairly easy in fact, even today, to design equipment which would automatically adjust such readings so that a given pulsar could be a timing beacon much like the current atomic clock timing signal which is available to standardize clocks in our frame.

13. ### funkstarratsknufValued Senior Member

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The fact that you obviously don't understand his proof makes it so much more embarrassing. Eight thousand posts on relativity, and still the absolute basics elude you.

14. ### MacMRegistered Senior Member

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The embarassment is on the other side of the isle.

15. ### funkstarratsknufValued Senior Member

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Riiight.

Tell me where his proof is wrong, then.

16. ### Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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Yes if you "fly" an arc at constant distance from the pulsar, you can kill the Doppler effect. Then you will need to consider the relativity effects to undestand why sychronization of all clocks in two differnt frame is not possible (it they are to keep time correctly) - Basically because time is passing at different rates in frames with relative motion.

Also note that pulsars pulse because the continuous narrow polar beam sweeps by your location once each rotation, but most pulsar polar beams never sweep by any particular point in space. I.e. you and your friend must be in the same "sweep plane" to even see the pulses of the same pulsar.

17. ### Billy TUse Sugar Cane Alcohol car FuelValued Senior Member

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Without knowing your velocity wrt the pulsar, how do you know how to correct the observed pulse rates? If you do know the relative velocity, why not just compute his clock rate with SRT equations?
No one is saying tht you can not know the rate of advance of his clocks, only stating that they can not both be telling correct time for him and sychronized with yours. It is entirely possible (as I think GPS does) to make all of his "clocks" sychronize with yours, but then they are not really clocks as the do not record/measure the passage of proper time.

The "total wrong concept," even with only classical physics considered, was that the observed rotation rate of the pulsar would be a universal constant.

Last edited by a moderator: Feb 24, 2006
18. ### chrootCrackpot killerRegistered Senior Member

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You know he's a lunatic, right? You can't reason with a man who knows no reason.

- Warren

19. ### 2inquisitiveThe Devil is in the detailsRegistered Senior Member

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Billy T, of course I know that Doppler effects allow one to calculate relative velocity between their frame and the source of the light. You were attempting to imply they are analogous to time dilation. Untrue.

You say it is not possible to synchronize clocks in two different frames and have them keep time properly. Why not? Is 'time' not relative in Special Theory? Let me ask you a question about the 'precieved' clock rate of the pulsar. There are three points of interest. I am in a spaceship moving away from Earth and toward the pulsar at a high relative velocity. quadraphonics is on Earth where he can 'see' both my clock and the pulsar's clock. According to quadraphonics, he 'sees' my clock beating slower than the plusar's, as my speed has increased since leaving Earth. According to Special Theory, I should see both quadraphonic's Earth clock and the pulsar's clock both beat too slowly. I need to SLOW the beat of my clock so it is synchronized with the two other clocks from my reference frame. My clock was beating faster than the other clocks. When I return to Earth and meet quadraphonics, we will discover that my clock recorded the same number of beats of the pulsar as the Earth clock, since both of our clocks recorded one beat for each beat of the pulsar. But quadraphonics 'saw' my clock beating too slow to begin with and when I slowed the beat, it should have recorded a total of far too few ticks. That didn't happen. My clock ticked in harmony with the pulsar's beat.

OK, now the same scenario with a different twist. This time let quadraphonics dictate the clock synchronization from his point of view. He 'sees' my clock beating beating slower than both his clock and the pulsar's beat. He tells me to INCREASE the beat rate of my clock to match his clock rate and the pulsar's. My clock is adjusted to synchronize with what quadraphonics sees. According to quadraphonics, who is watching my clock and the pulsar the whole period, my clock should match his clock and the pulsar's total beat count. But when I return, we discover the pulsar beat fewer times than my clock counted off ticks. My clock was adjusted to beat too fast when following quadraphonics instructions. My clock was not synchronized with the pulsar in my reference frame and did not count the same total number of ticks. My CLOCK recorded a shorter trip time because it was beating too fast, but the pulsar MUST rotate the same TOTAL number of times in both frames. quadraphonics 'saw' things incorrectly.

Now, assume I can't 'see' quadraphonics clock and he can't 'see' my clock. However, we can both see the blinking pulsar! Assume I don't have to do any adjustment to my clock to make it match the pulsar's beat rate. My clock will tick one time for each beat of the pulsar, quadraphonics clock will tick one time for each beat of the pulsar and both clocks will record the same total number of beats for the pulsar during my trip.

Now, Billy T, which of these scenarios provide 'correct time'? And don't forget, if we approach a rotating spiral galaxy, the light from it will be Doppler shifted to the blue spectrum. For that galaxy to 'appear' to rotate slower, the light from one side of the galaxy MUST blue shift LESS than light from the other side, light that has been travelling for thousands of years when we detect it. Even if the galaxy DID rotate more slowly in our new reference frame, we wouldn't know it for thousands of years until the light finally reached us.

20. ### PeteIt's not rocket surgeryRegistered Senior Member

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I'm not going to say that the beat time is not affected by the change, because it is - during the change the beat time may be extremely different.
The beat time will be the same before and after the change.

I'm not sure what you're getting at here.
No. The Earth's distance from the Sun remains roughly the same, but that does not mean that Earth's velocity relative to the Sun is zero.

21. ### PeteIt's not rocket surgeryRegistered Senior Member

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I'm assuming that:
• Your clock was synchronised to the pulsar before you let Earth.
• Quadrophonic's clock was synchronised to the pulsar before you let Earth.
• THe Pulsar is at rest with respect to Earth.
Is that right?
Are you talking about the perceived beat rate of the pulsar? It will be beating faster than your clock. You will detect more than one pulsar beat for each tick of your clock.
Doppler, right?

Which it will. According to you on your ship, Quadrophonic's instructions make your clock beat too slow on the way out and too fast on the way back.

Last edited: Feb 24, 2006
22. ### DaleSpamTANSTAAFLRegistered Senior Member

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2inquisitive

According to SR the pulsar will only really keep time in its proper frame. In any other frame there will be time dilation that will make it's signal redder than what would be predicted by the classical Doppler effect. Even if you account for the Doppler effect you would find that it is running slow in frames other than its proper frame.

Now, you certainly can say, "To hell with it, we can still use it as a clock that everyone will at least agree on the number of beats." That is fine and could certainly be done, but the problem is that different reference frames would then have different sets of physics in terms of this measure of time. Atomic absorption and emission spectra would be shifted, half lives would be different, etc. In short, according to SR, while such a pulsar clock might be excellent for arranging interstellar train schedules it would not do well for determining the results of physics experiments.

-Dale

Last edited: Feb 24, 2006
23. ### 2inquisitiveThe Devil is in the detailsRegistered Senior Member

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If the pulsar's rotation rate does not change in different reference frames, the physics in those frames do not change. I claim relative velocity does not actually dilate time in other reference frames. Special Theory claims it does. My gedankens are to support my view. Are you claiming that light from the left side of a rotating galaxy viewed edge-on will be Doppler shifted by a different amount than light from the right side, if the distant observer changes his relative velocity? I claim that if the galaxy actually did SLOW DOWN its rotational velocity because we are approaching it at a high relative velocity, THEN the laws of physics would be violated. It would collapse because gravity would overcome the slower orbital velocity of the individual stars. Or does Special Theory claim that gravity is an inverse square effect in only one reference frame? Oh, of course, we have to NEGELECT gravity in STR, don't we? How convenient.

By the way, you do understand that pulsars are collapsed stars that are spinning very fast, emitting a jet (the beam) off axis wrt its spin axis. The blink we see is due to the rotation of the pulsar, doesn't matter one whit if the Hydrogen alpha line is Doppler shifted or not due to our velocity. With an accurate spectrograph, a ship could detect a Doppler shift in the light from a lighthouse indicating their relative velocity. That doesn't make the lighthouse beam rotate faster. Are you claiming the relativistic Doppler formula indicates a slower rotational velocity of the lighthouse beam? How do you detect a transverse velocity component of the emitted light? Detecting an decreased frequency of the 'beat' of the rotating beam is not a Doppler shift, just an indication the beam is rotating slower. I do not believe that effect has ever been measured. Do you have any references?