Universe is at rest?

Discussion in 'Physics & Math' started by hansda, May 6, 2017.

  1. hansda Valued Senior Member

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    We know that a particle is always in motion and never at rest. Rest is a relative concept.

    When two particles are moving at same velocity, the relative velocity between them is zero and it can be said that the particles are at rest relative to each other. If the motion of a particle is also compared with itself, the particle can be consider at rest with relative to itself.

    We know that our universe is expanding. But if we compare the expansion of our universe, with relative to our universe itself; can we say that, our universe is at rest?
     
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  3. karenmansker HSIRI Registered Senior Member

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    Hansda: IMO, one could apply your suggestion (universe at rest) on a local scale, but since (we observe that) more distant parts of the universe 'appear' to be moving more rapidly, some sort of 'sliding' comparative measuremnt (observational) scale might be applicable to resolve more-distant apparent relative motions with one's own (at rest) FOR (Frame of Reference). Perhaps such a 'sliding scale' derives from GR? . . . . and apparent FOR differences actually are - at rest relative to each other. . . . . thus the apparent observational illusion . . . . . (HAHA!)
     
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  5. The God Valued Senior Member

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  7. danshawen Valued Senior Member

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    Good question.

    Photons are created and move at a relative velocity of c RELATIVE TO A REST FRAME that is the same rest frame as the paired electrical charges which provided the acceleration necessary to produce the photons.

    You could also go the "matching velocities" route, but this is the only example or definition you will ever need about a rest frame. Rest frames are not unique or preferred for matter or antimatter. Any inertial reference frame is a suitable rest frame, except for one whose relative velocity with respect to any of the other inertial frames in which matter or antimatter exists, =c.

    Absolutely, and also with respect to the Big Bang, or whatever it was, assuming it was the center of the expansion.

    This would also be true if it were rotating, which we can't really determine without reference to something outside of it that does not share the same angular momentum. As the universe as a whole expands, it's angular velocity nearest the outside decreases. Even more difficult to determine out there, because at cosmological distance, even the speed of light requires an eternity to rotate even by an arc second, from out point of view.
     
  8. karenmansker HSIRI Registered Senior Member

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    " . . . . As the universe as a whole expands, it's angular velocity nearest the outside decreases. . . . . ."

    danshawen: Can you provide a factual evidence resource for this statement? Has this actually been "observed", or is it merely spectulation?
     
  9. danshawen Valued Senior Member

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    http://hyperphysics.phy-astr.gsu.edu/hbase/rotq.html

    omega = v / radius

    As the radius increases (constant linear velocity, assume = c), omega (angular velocity) decreases
     
  10. karenmansker HSIRI Registered Senior Member

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    Thanks for the link on rotation . . . . . . thought above posts designated the universe as expanding, but not rotating.
     
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  11. danshawen Valued Senior Member

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    Yes, if omega = zero to begin with (no rotational velocity at all from the Big Bang forward), then all expansion would be radial and not rotating.

    And where else in nature do we find no rotation at all, even on large scales? About as often as meteors or asteroids fall directly into something else, which is not very often. Just because we haven't observed rotation on the largest scales doesn't necessarily mean it isn't there. I have suggested why this might be the case.
     
  12. hansda Valued Senior Member

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    Our Universe is expanding. That is true. But this does not imply that our universe is in motion. To decide about the motion of our universe, ideally we should have a reference point(FoR) outside the universe. But this is not possible. Any reference point(FoR) has to be considered, within our universe. This is the only possible case. Our universe has to be considered at rest, with relative to this reference point.

    For example consider a tree being planted at some location on the earth. With the gradual passage of time, the tree will grow and expand. But the tree will still remain at the same location on the earth. With relative to the earth, the tree is at rest.
     
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  13. karenmansker HSIRI Registered Senior Member

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    BTW: "Just because we haven't observed it, doesn't mean it isn't there" (paraphrased from Danshawen's recent post regarding Universe rotation on the Sciforums thread: Universe at Rest).

    "Science historically has employed the Scientific Method to examine and observe otherwise unexplainable phenomena, and via the Method to determine and explain the underlying causes of such phenomena. But phenomena are seemingly not finite in number. Newly recognized or observed phenomena will require application of the Method to determine new causalities that are perhaps yet unrecognized."
     
    Last edited: May 8, 2017
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  14. danshawen Valued Senior Member

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