Thread: Is time universal? NO (and its proof)

  1. #341
    Aer:

    But Pete believes there is some kind of pseudo-frames or something (I don't recall) that you can apply to GR that gives you a different explanation for time dilation than given by SR. This, I do not agree with and was what I was refering to.
    Pete's right about that.

    Take a moving spaceship which accelerates while watching a clock on the Earth's surface.

    One way to explain what the spaceship sees is to consider the spaceship as changing inertial references frames (passing through many "infinitessimal" inertial frames) as it accelerates. That's an SR picture.

    Another way to explain the same thing is to consider the spaceship as being in a single non-inertial reference for the whole accelerating period. This is the GR picture. In such a frame, there is a gravitational field in the spaceship's frame which accounts for the observed time dilation of the Earth clock.

    Both methods produce the same results if you do the quantitative calculations correctly.

  2. #342
    Registered Senior Member
    Posts
    2,250
    Quote Originally Posted by James R
    Take a moving spaceship which accelerates while watching a clock on the Earth's surface.

    One way to explain what the spaceship sees is to consider the spaceship as changing inertial references frames (passing through many "infinitessimal" inertial frames) as it accelerates. That's an SR picture.

    Another way to explain the same thing is to consider the spaceship as being in a single non-inertial reference for the whole accelerating period. This is the GR picture. In such a frame, there is a gravitational field in the spaceship's frame which accounts for the observed time dilation of the Earth clock.
    That is probably the pseudo-gravity field. I've seen references on this stating it is an outdated concept and not really "correct". Perhaps you can provide a source that says otherwise.

  3. #343
    Pete:

    Four clocks.

    The Surface clock is on the surface of the Earth, and moving with the surface as the Earth rotates.
    The Satellite clock is on the satellite.
    The Surface-stationary clock is on the surface of the Earth in the path of the Surface clock, and stationary in the Earth-Center clock's frame.
    The Satellite-stationary clock is in the satellite's orbit path, and stationary in the Earth-Center clock's frame.
    I'm assuming you mean that the satellite-stationary clock (for example) is at the same height as the satellite but not orbiting the Earth.

    1. Do you agree that the Surface-stationary and Satellite-stationary clocks are synchronized?
    In which frame? And are we including gravity or not?

    Once you answer that, I'll move on to the following questions.

  4. #344
    Aer:

    That is probably the pseudo-gravity field. I've seen references on this stating it is an outdated concept and not really "correct".
    Tell me what the difference is between a "true gravity field" and a "pseudo-gravity field", and then I might be able to tell you whether or not I agree with your reference sources.

  5. #345
    Registered Senior Member
    Posts
    2,250
    Quote Originally Posted by James R
    Tell me what the difference is between a "true gravity field" and a "pseudo-gravity field", and then I might be able to tell you whether or not I agree with your reference sources.
    They weren't my sources, they were Pete's own sources.

  6. #346
    Hi James,
    I'm assuming you mean that the satellite-stationary clock (for example) is at the same height as the satellite but not orbiting the Earth.
    Yes, that's right. Originally I had five clocks including a non-rotating Earth-Centre clock. I removed it because it wasn't necessary, but I forgot that I'd used it in the description of the other clocks.

    In which frame?
    In the non-rotating Earth rest frame.

    And are we including gravity or not?
    No, we're examining the situation with special relativity only.

  7. #347
    Quote Originally Posted by Aer
    And you think that I need to some sorting out... You are seriously asking me which is the inertial frame? Oh my.
    Ah - It seems you answered the question in the context of the problem, when I'd slipped in a more general question. I then interpreted "the inertial frame" to be a reference to some one-and-only-absolute-inertial-frame. Sorry about that.

    Let's define a comparison.

    How much definition does it need?
    When the clocks meet, record the reading on each clock.
    Compare those readings.
    Do you agree that the readings are the same in all frames?

  8. #348
    Quote Originally Posted by Aer
    After the "remeet" assume the satellite becomes inertial and shoots off in a straight line. Which clock is dilated, the satellite clock or the satellite stationary clock? Both frames are now inertial.
    The dilation is frame dependent. Your point??

  9. #349
    Registered Senior Member
    Posts
    2,250
    Quote Originally Posted by Pete

    How much definition does it need?
    When the clocks meet, record the reading on each clock.
    Compare those readings.
    Do you agree that the readings are the same in all frames?
    What is meant by reading? Sorry, but these questions become necessary because of relativity. If you are talking about "another" frame, it stands to reason that this frame's point of reference is not the meeting place of the two satellites (although it doesn't have to be). As such when each satellite takes a reading is not necessarily simultaneous in another frame.

  10. #350
    Registered Senior Member
    Posts
    2,250
    Quote Originally Posted by Pete
    The dilation is frame dependent. Your point??
    My point is at the end of your sentence above (before the question) (also, looks like a dot).

  11. #351
    Registered Senior Member MacM's Avatar
    Posts
    10,104
    Quote Originally Posted by Pete
    Since you missed the most important part, the part that's actually directly relevant to the discussion, I'll repeat it for you.

    I need to know whether you agree to the physical predictions. It's not terribly important if we disagree on the causes of these predictions, but it is important that we agree on the physical predictions themselves:

    Do you agree that SR predicts that less time elapses on the Satellite clock than the Satellite-Stationary clock between each meeting in all frames?

    Do you agree that SR predicts that less time elapses on the Surface clock than the Surface-Stationary clock between each meeting in all frames?


    Note that these questions are identical to asking whether less time elapses on the travelling twin's clock than the stay-home twin's clock in all frames.

    You might also want to think more on the other post you ignored. I know it burns you up inside when you know that someone's wrong, but you just can't find where their mistake is... but can you try to work past it and just consider the possibility that perhaps I might actually be talking sense?
    Who was this post directed to?

  12. #352
    Pete:

    Ok, ignoring GR effects (i.e. pretending the Earth has no mass for the moment):

    The Surface clock is on the surface of the Earth, and moving with the surface as the Earth rotates.
    The Satellite clock is on the satellite.
    The Surface-stationary clock is on the surface of the Earth in the path of the Surface clock, and stationary in the Earth-Center clock's frame.
    The Satellite-stationary clock is in the satellite's orbit path, and stationary in the Earth-Center clock's frame.

    1. Do you agree that the Surface-stationary and Satellite-stationary clocks are synchronized?
    In the Earth-centre frame, let's assume they are.

    2. Do you agree that in all frames, the Satellite-stationary clock is ticking faster than the Satellite clock by the same ratio? (Think twin paradox if you're not sure about this one.)
    No. In the Earth-centre frame that is true. In the satellite-stationary frame (which is the same) that is true. But in the satellite frame the satellite-stationary clock ticks slower than the satellite clock.

    (What "ratio" are you talking about?)

    3. Do you agree that in all frames, the Surface-stationary clock is ticking faster than the Surface clock by the same ratio? (twin paradox again).
    No. My answer is similar to my answer to my answer to (2).

  13. #353
    Registered Senior Member MacM's Avatar
    Posts
    10,104
    Quote Originally Posted by James R
    No. In the Earth-centre frame that is true. In the satellite-stationary frame (which is the same) that is true. But in the satellite frame the satellite-stationary clock ticks slower than the satellite clock.
    And this gentlemen is the same old unsupported rhetoric of SRT reciprocity.

    THINK. It is UNSUPPORTED. It presents a physical IMPOSSIBILITY.

    Are you going to contiinue to say with a straight face that a physical clock ticks not only at its proper rest rate but also ticks slower than another clock that is ticking slower than itself!

    My god you are hopless.

  14. #354
    I'm talking to Pete, MacM. I'm not interested in re-hashing this with you yet again. Go away.

  15. #355
    Quote Originally Posted by James R
    No. In the Earth-centre frame that is true. In the satellite-stationary frame (which is the same) that is true. But in the satellite frame the satellite-stationary clock ticks slower than the satellite clock.
    Consider a single orbit.
    Isn't this just like the twin paradox? The Satellite clock is the travelling twin, the Satellite-Stationary clock is the stay-home twin.

    Start the two clocks as they pass each other, stop them when they pass each other again.
    Which clock shows the larger elapsed time?

    What "ratio" are you talking about?)
    Ignore that bit - it's not necessary.

  16. #356
    Quote Originally Posted by Aer
    What is meant by reading? Sorry, but these questions become necessary because of relativity. If you are talking about "another" frame, it stands to reason that this frame's point of reference is not the meeting place of the two satellites (although it doesn't have to be). As such when each satellite takes a reading is not necessarily simultaneous in another frame.
    OK, picture this.
    The Satellite clock and Satellite-Stationary clock both have notepads attached.
    As they pass each other, each clock stamps its current time onto both notepads.

    Do you agree that the writing on the notepads is an unambiguous record of the readings of the clocks each time they pass each other?

  17. #357
    Consider a single orbit.
    Isn't this just like the twin paradox? The Satellite clock is the travelling twin, the Satellite-Stationary clock is the stay-home twin.

    Start the two clocks as they pass each other, stop them when they pass each other again.
    Which clock shows the larger elapsed time?
    If the satellite clock moves in a circle to come back to its starting point, then it has accelerated, while the stationary-satellite clock did not. My first thought is that I would expect its clock to display less elapsed time than the stationary clock, after the entire trip. This effect would not be symmetrical, since the stationary clock is in an inertial reference frame the whole time while the satellite is not.

    This probably means I need to revise my previous statement, doesn't it?

    BUT... hang on a minute. This is difficult, because if I think of the problem from a GR perspective the "gravitational field" experienced by the satellite constantly changes direction relative to the stationary-satellite clock, and I'm not sure if or how this affects the timing.

    I suspect an easier analysis would involve the Sagnac effect, but I'm not an expert on that...

    This is why this GPS stuff is harder than it seems at first glance. MacM thinks he has it all figured out. I think he doesn't realise all the complicating factors. Certainly the GPS literature says you need to include things like the Sagnac effect to make the system work.

    So, where do we go from here?

  18. #358
    Registered Senior Member MacM's Avatar
    Posts
    10,104
    Quote Originally Posted by James R
    I'm talking to Pete, MacM. I'm not interested in re-hashing this with you yet again. Go away.
    What you really mean is "Embarrassing questions go away"

  19. #359
    Registered Senior Member MacM's Avatar
    Posts
    10,104
    Quote Originally Posted by James R
    This is why this GPS stuff is harder than it seems at first glance. MacM thinks he has it all figured out. I think he doesn't realise all the complicating factors. Certainly the GPS literature says you need to include things like the Sagnac effect to make the system work.
    Seems to me when I first began discussions about GPS and these issues, you knew nothing about GPS. Seems also you are learning. Funny I do believe I mentioned Sagnac and all three primary frames used months ago.

    The simple fact is MacM is not confused or misinformed. Don't try to make your past and current mistakes go away by pointing your finger in other directions.

    You have said orbit is inertial since it is in freefall and now you want to claim GR affects because it is in acceleration. Which is it. Or do you simply cross the isle when you need to to defend your arguement hoping people don't recall your different positions.?

  20. #360
    MacM:

    What you really mean is "Embarrassing questions go away"
    No. What I mean is "Questions I have answered before in considerable detail go away." I have no interest in having a discussion in which I have no chance of learning anything, or of teaching anything.

    Seems to me when I first began discussions about GPS and these issues, you knew nothing about GPS. Seems also you are learning.
    I started off knowing little other than that GPS had to make relativistic corrections, and the general nature of the corrections needed. I have learnt a little more about the system - most of it from my own reading on the web, a little from 2inquisitive's posts, and, as far as I can tell, nothing at all from you.

    Funny I do believe I mentioned Sagnac and all three primary frames used months ago.
    Probably you did. I'm sure you didn't explain any of it. In fact, I'm sure you can't give a good description of the Sagnac effect now, either. (And I think it's relevant to the discussion I'm having with Pete.)

    The simple fact is MacM is not confused or misinformed.
    I don't need to argue this. The evidence is all over the forum for all to see.

    You have said orbit is inertial since it is in freefall and now you want to claim GR affects because it is in acceleration.
    I'm talking to Pete about a situation with no gravity. A real orbit is inertial. This orbit is not, because gravity is not the cause of the orbit we're discussing. We're talking about a flat-space problem here. Since this is probably beyond you, why don't you stay out of the conversation?

    Which is it. Or do you simply cross the isle when you need to to defend your arguement hoping people don't recall your different positions.?
    The only reason you think I am inconsistent, MacM, is that you don't understand my posts. I am careful to explain clearly what I mean. I sometimes make mistakes, and I'm happy to admit it when I am wrong. But I do not deliberately lie about things, as you claim. And in your particular case, your accusations that I change from one view to another as is convenient stem from your inability to appreciate subtle differences between different situations, or perhaps just a laziness on your part. You simply look for any opportunity to attack me. Instead of reading the entire argument and getting up to speed, you pick on a single point in a single post, make an unwarranted assumption, and fire away. That's why I don't engage with you any more.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •