Is There A Universal Now?

Discussion in 'Physics & Math' started by Cyperium, Jun 14, 2022.

  1. phyti Registered Senior Member

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    680
    Michael 345;

    Note, a 1 second cycle is measured with an extremely smaller cycle.
    (wave length)=c/frequency
    The total length of 9 billion+ wave lengths is 1 light second, 186,000 miles or
    3(10)^8 meters.

    I agree with you that measurements use arbitrary units. We could shoot an arrow a distance d into a distant tree, place a mirror on the tree, and reflect a light pulse over a distance 2d. Then define a new um for light transit time t as d/c. The tree would be 1 arrow distant.
    It's always what is simple and convenient.
     
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  3. phyti Registered Senior Member

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  5. Mike_Fontenot Registered Senior Member

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    Nope.
     
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  7. Neddy Bate Valued Senior Member

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    "Universal Now" is the same thing as "Now at a distance". It's just the same as synchronising clocks which are separated by distance..
     
  8. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    One way to consider Universal NOW is to think about the ONLY moment in existence is NOW

    No PAST is in existence NOW
    No FUTURE is in existence NOW

    PAST was, FUTURE will be, currently ONLY NOW exist. A situation which has existed since the universe popped into existence

    Since ONLY now exist, and said NOW encompasses the totality of the Universe said NOW is the Universal NOW by default, no other contender

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  9. Mike_Fontenot Registered Senior Member

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    To me, "Universal Now" implies that it's a "NOW" that EVERY inertial observer agrees about ... i.e., two inertial observers who are moving relative to each other and currently momentarily co-located would agree about the current age of the same distant person. That is definitely NOT special relativity ... it is Newtonian physics.
     
  10. phyti Registered Senior Member

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    680
    Mike;

    You are on Earth, your 'now' is 12:00.
    Your helper Biff is close enough to Venus to observe a clock on its surface.
    Biff's clock is synchronized with your clock, so his 'now' is 12:00.
    How does Biff inform you of the reading of the Venusian clock?
     
  11. Write4U Valued Senior Member

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    18,777
    If the universe is a set of stacked 2dimensional planes then every now in time is shared by the entire brane, no?

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  12. Mike_Fontenot Registered Senior Member

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    He sends me a message (via a light signal) that tells me, much later, what the clock on Venus read when Biff's and my clocks read 12:00.
     
  13. Mike_Fontenot Registered Senior Member

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    It sounds like you are referring to the "loaf of bread" image that Brian Greene used in his NOVA alien example. If so, the angle of the slice wrt the long axis of the loaf varies, depending on the relative velocity of the alien and the human. In Brian's example, the alien is alternately riding a bike toward and away from the human, and so the alien concludes that the current age of the human is varying by +-200 years for each of the alien's biking cycles, because of the HUGE distance between them that Brian has chosen.
     
  14. Write4U Valued Senior Member

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    18,777
    No, my example has no human subjective interpretation at all.

    I am referring to now existing on a single 2D slice of bread (brane). Each slice has a different now from all other slices, but each slice (brane) has its own timeline in toto.

    If I have a balloon and blow it up, does its circumference inflate at a different rate and one end of the balloon becomes older than the other end?

    This is the same equation as placing a drop of water in one end of a lake and saying that this part of the lake has more water than the other side?

    Can you explain this? I am really interested!
     
    Last edited: Aug 22, 2022
  15. Mike_Fontenot Registered Senior Member

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    I'm still convinced that your example is nothing but Brian Greene's example restricted to the case of zero relative velocity between the alien and the human (which is a completely uninteresting case).
     
  16. Beaconator Valued Senior Member

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    I think there is an equation for circumference to surface area.

    it’s possible to set the speed of light as a circumference and use that to establish time. Set the surface area as the surface area of the universe and come up with a number.
     
  17. LaurieAG Registered Senior Member

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  18. Beaconator Valued Senior Member

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  19. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    My thoughts

    Since NOW is the ONLY moment in existence by default it's THE Universal NOW

    Talking about stuff happening at another location (at a distance away) does not, to my way of thinking, exclude it happening at the same NOW

    The DISTANCE between every single event DOES obviously exclude all events or combinations of events being KNOWN about at any single location but NOT exclude occuring at the single instance of the only NOW in existence

    Big Bang occurred at a single instance and all the component parts of the Universe have kept lock step since

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  20. phyti Registered Senior Member

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    Mike;

    If Earth and Venus are on the same side of the sun, light transit time from sun to Earth is < 8 min. Lets say Biff's signal takes 3 min transit time.
    You don't know the time on Venus at 12:00.
    "Now' at 12:03, you know what the clock time WAS on Venus at 12:00, but
    you still don't know the time on Venus NOW at 12:03. (You agree in red.)
    If you had been observing Venus with instruments capable of capturing images or detecting electronic encoded time signals, you could receive them without Biff.

    As the example shows, you can't know the current age of a distant person simultaneously with your 'now' because light speed is finite. Newton never revised his physics to include that revelation. People believed many things that were false prior to Special Relativity.
     
  21. phyti Registered Senior Member

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    680
    Michael 345;

    Line 1 is a contradiction of terms (past and present tense).
    For you, the past is events you are aware of.
    Tomorrow your past will increase with new observations, especially if you are an astronomer.
    The future is unknown, and prediction is speculation.
     
  22. phyti Registered Senior Member

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    680
    Write4u;

    Yes. The pdf 'perception space' explains.
    The effect depends on spatial extent, insignificant for objects with dimensions a few meters, but prominent for the radius of the universe. The most distant stars appear as the youngest.
     

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  23. Write4U Valued Senior Member

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    18,777
    The OP asks an uninteresting question. The answer is a "yes", the universe in toto has a single NOW at all times.

    You can try and make it more interesting by introducing irrelevant relativity issues to the question, but that will not change the original answer which is the objectively correct one specific to the OP question.
     
    Last edited: Aug 23, 2022

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