On Wednesday, December 13, 2017 at 12:08:35 AM UTC, John Clark wrote: > > > On Mon, Dec 11, 2017 at 5:11 PM, <[email protected] <javascript:>> > wrote: > > > >> >>> The Equivalence Principle says if >>> you >>> ignore tidal effects and you're in a windowless elevator cab there is >>> no way to know if you're sitting on the Earth in a gravitational field or >>> in deep intergalactic space being accelerated by a rocket upward at 1G. If >>> you feel zero G and fire a Laser pointer from one wall >>> to the other >>> it will go in a straight line and hit the exact opposite side on the >>> other wall. But if you were being accelerated upward the elevator cab will >>> move >>> slightly >>> upward in the time it takes for the light to go from one wall to the >>> other so the spot the laser makes on the other wall will be slightly lower >>> than it was when you were in zero G, you see the laser beam follow a curve. >>> >> >> > >> At rest on Earth is not a situation of zero G; it's 1G. Or, say, if you >> want a straight beam, one can assume an inertial frame, >> > > The surface of the Earth is in a gravitational field and so it is *NOT* a > inertial frame, and so light from a Laser pointer does curve, although not > by a lot. The interior of an > elevator in which the cable has been cut would be a inertial frame, until > it hit the ground. > > > >> >>> A curved line from one wall to the other is longer than a straight line >>> , >>> and yet when you measure the time it takes for light to do this with >>> your very accurate clock you notice its exactly the same. You already know >>> the measured speed of light never changes so >>> if something is moving at the same speed and moves a greater distance >>> in the same number of clock ticks then >>> you'd have to conclude that being accelerated makes your clock run slow. >>> >> Since a clock in the gravity field measures less elapsed time, the number of ticks in your example cannot be identical in those two cases. Moreover, I can't convince myself that the measured time in the two scenarios is identical. AG
> >> > >> I think most of last paragraph incorrect. In experiments with GPS clocks, >> the ground clock, in the stronger gravity field, runs slower than an >> orbiting clock. >> > > > T > he > GPS > satellite is moving very fast so due to Special Relativity the > satellite's clock will LOSE 7210 nanoseconds a day, but the satellite's > clock is in a weaker gravitational field than the clock > on the ground > because it is further from the Earth's center, so due to GENERAL > RELATIVITY the clock will GAIN 45850 nanoseconds a day. Taking these 2 > factors into account the satellite's clocks gains 45850 −7210 = 38,640 > nanoseconds a day relative to > a > clock > on the ground. If this were not taken into account the GPS system would > drift off by 6 miles a day. > > There's a problem applying SR in this situation because neither the ground or orbiting clock is an inertial frame.AG > > >> > >> Fewer ticks in ground clock >> > > Yes, a clock on the ground in a 1G gravitational field > > or a clock in deep space being accelerated by a rocket at 1G will record > fewer ticks than a non-accelerating clock in no gravitational field. > > > >> In your elevator example, where zero G can be interpreted as being in an >> inertial frame, you claim the elapsed time duration using ticks, is >> identical for both beams. > > > I'm not sure which 2 beams you're talking about. The interior of the > elevator sitting on the ground > > and the elevator in deep space being accelerated by a rocket are > identical. > Agreed. IIRC, I was thinking of the orbiting clock being so far removed, that it would effectively be in an inertial frame. AG > The elevator with the broken cable near the earth and the elevator with > no rocket in deep space are identical. > > 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 https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
