Is it true? Is the universe flat?

Discussion in 'Physics & Math' started by camilus, Dec 6, 2010.

  1. ULTRA Realistically Surreal Registered Senior Member

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    Forgive me, I haven't read all the posts, but isn't the universe more kinda conical?
     
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  3. arfa brane call me arf Valued Senior Member

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    Perhaps you can point out why taking the CMB to be "at rest" and syncronising clocks against a CMB frame of reference is stupid.

    Note that GR says there are always (choices of) coordinate systems that allow for two spacelike-related events to be "simultaneous", but perhaps you can point out why this is a problem, or why choosing a frame of reference is "stupid".
     
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  5. RJBeery Natural Philosopher Valued Senior Member

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    Dude, there are two causes for apparent c violation: acceleration (as in Sagnac) or path length change. You claim that GPS is not under acceleration and the path length does not change. Please explain GPS errors without either of the above...and by "explain", I mean YOU please explain it; don't google "ummm +linear +sagnac +physics" and then link to the results, which is exactly what I think you've been doing.

    Also, in your explanation, please include an answer to the following which you did not address:
    Thanks, and good luck.

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  7. AlexG Like nailing Jello to a tree Valued Senior Member

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    Both the receiver and the emitter are undergoing acceleration, so neither is an inertial frame, and the accelerations are always different.
     
  8. James R Just this guy, you know? Staff Member

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    Moderator note: chinglu is taking 3 days off from sciforums.

    Let's hope he uses this time to develop some intellectual honesty.
     
  9. AlphaNumeric Fully ionized Moderator

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    No, I didn't claim they are the same. I was talking about two distinct situation, the issue of two people at different places comparing their motions versus one person at one place setting their motion relative to other physical objects.

    At each point in space the CMB defines a particular frame via its dipole. My comment about it being the same as setting yourself by any other object was a way of saying the frame isn't more 'absolute' or special than any other frame, in contrast to what Farsight said.

    You've repeatedly ignored corrections, simply repeating your already retorted claims about my posts. You claim I don't know the difference between SR and GR, when I have both education and teaching experience in them. You claim I said SR and GR are equivalent, when I did nothing of the sort.

    Besides, I think it laughable you whine about my posts when you, in the thread over in pseudo, claim special relativity is false and time dilation doesn't exist. Time dilation is an experimental reality and whether or not SR is the exact model of that doesn't negate the fact you're denying reality.

    Now that is stupid and a failure.
     
  10. chinglu Valued Senior Member

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    Uh, because you are accelerating when at rest with CMB.

    I hate being honest with the mainstream reasoning.
     
  11. chinglu Valued Senior Member

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    OK, Maybe I am wrong.

    Please provide links to support your proposal that sagnac is only an acceleration issue. Please show the math that path length is not relevant.

    Thanks.
     
  12. chinglu Valued Senior Member

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    You claimed setting yourself at rest with CMB is no different from setting yourself with an SR inertial frame.

    That is false.

    You fail to admit your error.
     
  13. chinglu Valued Senior Member

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    I guess time dilation is a fact.

    If I am at rest with the GPS satellite clock, the earth based clocks are moving. Using a blind SR, those clocks must be time dilated. But they are not.

    Can you explain that?
     
  14. kurros Registered Senior Member

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    You're not explaining why it is false. The CMB is just a bunch of photons, to most observers it looks doppler shifted in various ways, but it so happens there is a frame that makes it look nice and uniform in energy. Similarly to the Earth is just a bunch of matter that looks to be flying about at all sorts of velocities to different observers, but there happens to be one frame in which it is nice and stationary, at least for a moment.
     
  15. RJBeery Natural Philosopher Valued Senior Member

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    From Wiki on Sagnac...
    "Loop geometries" means that the ends are connected, whether it's a circle, square or pentagram...agreed? Now, does Sagnac occur with a loop if it is not rotating? No, because this is the only way to "change path lengths". This means that Sagnac necessitates rotation.

    Rotation necessitates acceleration. I cannot help the fact that you don't appear to accept that centripetal acceleration exists even when tangential acceleration is absent. I've mentioned this probably a half-dozen times, what else would you have me do?

    Your mention of "linear Sagnac" is just another way of altering path lengths that does not involve a loop geometry. Although most people would object to calling this phenomena a "Sagnac effect", there is only one way to do this; guess what it involves..? Linear acceleration! This is why I said apparent c violation occurs with either Sagnac or path length change...they are both require acceleration. No acceleration, no Sagnac.
     
  16. Pete It's not rocket surgery Moderator

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    The GPS satellite rest frame is not inertial in SR, so SR doesn't necessarily say that the ground clocks are time dilated. In fact, for this particular case SR says that the ground clocks run faster than the GPS clock in the GPS clock's rotating rest frame.
     
  17. AlexG Like nailing Jello to a tree Valued Senior Member

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    Why is it so difficult to distinguish between an inertial frame and an accelerated frame?

    If a frame is in any orbit, it is an accelerated frame. Any frame following a path which is not a geodesic is undergoing acceleration.

    If the frame is undergoing acceleration, SR does not apply. GR does.
     
  18. AlphaNumeric Fully ionized Moderator

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    At a single point in space-time the CMB defines a single reference frame via its dipole. At the same point in space-time the Earth's motion defines a specific frame via its instantaneous velocity. Likewise the Sun, the Moon, Sirius, Andromeda's centre of mass, any well defined specific object, they all define a particular frame via their instantaneous velocity. Choosing to set your coordinates to match the velocity vector which removes the CMB dipole is no different to matching to the velocity vector of any other physical object.

    This is only true for an instant because the expansion of the universe will then alter the view you have of the various objects I just listed, something which special relativity cannot account for.

    If you disagree or don't understand anything I've said say precisely where and why. If you just reply with another "Wrong!" but without explaining yourself I'll take it to mean you admit you can't justify your position. Notice how I explain myself? Try it.

    Yes, experiments prove it. Whether or not special relativity is the correct description is irrelevant, relative motion results in different clocks measuring different amounts of time.

    I think you need to learn about the way GR describes GPS systems. Your ignorance is not my responsibility to correct.
     
  19. chinglu Valued Senior Member

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    I am not taking CMB at rest. AN was. Do you read?
     
  20. chinglu Valued Senior Member

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    GPS does not use GR for sagnac. It uses path length and v.

    http://relativity.livingreviews.org/Articles/lrr-2003-1/

    You failed.
     
  21. chinglu Valued Senior Member

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    You are uneducated.

    Time to learn you are wrong.

    http://relativity.livingreviews.org/Articles/lrr-2003-1/

    Let's take this up when you at at least minimal on GPS.
     
  22. chinglu Valued Senior Member

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    Yet another uneducated soul.

    http://relativity.livingreviews.org/Articles/lrr-2003-1/

    If I am wrong, you can use this link to prove it.
    But, you will find you are not even educated on GPS.
     
  23. chinglu Valued Senior Member

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    Your problem is you cannot face the fact in front of others that you totally failed.

    You said being at rest with CMB is no different from being at rest with anything else.

    It is time to face your failure. You are completely wrong. Why do you not face the facts?
     

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