On Thu, May 29, 2014 at 12:08 PM, John Ross <[email protected]> wrote:
> I believe that if we try to measure how fast time is passing in a > reference that is moving very fast with respect to our reference frame, we > will get a different answer than someone measuring how fast time is passing > in the fast moving reference frame. > True. > > we could measure how much time has passed since the Big Bang, we would > all get the same answer. > True. > I read somewhere that the Big Bang occurred 13.72 billion years ago and > that the number was accurate to 4 decimal places. > Basically true although the new revised figure from the Planck satellite is 13.82 billion years ago. > I understand some galaxies are moving away from us very fast maybe at > speeds close to the speed of light. > Yes, and although we can never see them there is every reason to believe that some galaxies, perhaps an infinite number of them, are moving FASTER than the speed of light. This is not in violation of Einstein because Einstein was talking about how fast things could move in space, not how fast space itself can expand or contract. The difference may seem subtle but it's crucial and has measurable consequences. For a short time I thought I'd figured out how you could theoretically get work out of a universe that is not only expanding but accelerating; suppose you had a spool of string on a axle and you extended the string to cosmological distances and tied a weight on the end of the string. I thought there would be torque on the spool, so the axle would rotate. The axle could then be connected to an electric generator and it seemed to me you'd get useful work out of it. Of course you'd have to constantly add more mass-energy in the form of more string to keep it operating, but the amount of mass per unit length of string would remain constant, but because the universe is accelerating the amount of energy per unit length of string you'd get out of it would not remain constant but would increase asymptotically to infinity. Then I realized my brainstorm wouldn't work, there would be no torque on the spool because the weight on the end of the string was not moving through space with respect to the spool, instead space itself was moving. It's as if I grabbed the string with my left hand 4 feet from the spool and I grabbed the string with my right hand 1 foot from the spool and pulled my hands in opposite directions I would create tension in the string between my hands but I'm doing no work and producing no torque on the spool, and the same would be true of Dark Energy. If I pulled hard enough the string would break and if Dark Energy got strong enough every atom in the string would pull apart from every other atom in it, that's what happens when space expands, but there would still be no torque on the spool and no useful work could be extracted from the spacial expansion. > Would the people in those galaxies make the same estimate as we do? > Yes. Distant observers would see different galaxies than we do but just like us all the galaxies they could see would seem to be racing away from them and at a accelerating rate; and just like us when they worked backward they would calculate that 13.82 billion years ago all the stars and galaxies and everything else must have occupied just one point. > If so that would indicate to me that the passage of time is the same > everywhere in our Universe. > We know that during the Big Bang some particles must have been created that were moving very very close to the speed of light. Unlike the distant galaxies you were talking about which were not moving through space but more space was being created between then and us, these ultra high speed particles were actually moving through space and so Einstein's rules come into play. To these fast moving particles the Big Bang happened MUCH less than 13.82 billion years ago. > > my understanding is that atomic clocks are based on the frequency of > light emitted from certain atomic transitions. > Yes. > Maybe the frequency changes at very high relative speeds or at different > gravitational forces or different radial acceleration > There is no maybe about it, that is exactly why atomic clocks run slower when they are moving fast, and run faster when they are in a shallower gravitational well than we are. Atoms have internal clocks that tell them how many times per second to change the electromagnetic field, in other words what color of light to emit. In a lab on the Earth we note that when Helium gets hot it emits light at a very particular frequency, but when we look at Helium on a white dwarf star like Sirius B that is in a much deeper gravitational well than we are in on Earth the internal clocks of Helium seem to be running slow and thus the light it emits has a lower frequency, in other words it's red-shifted. Of course to observers on Sirius B their clocks would seem to be running just fine and it's our clocks that are off speed. One observers clock is not more authoritative than another and time is what clocks measure so there is no absolute time. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. 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