On 28 December 2013 12:57, Edgar L. Owen <edgaro...@att.net> wrote: > All, > > I haven't made any progress getting the idea of a common universal present > moment across so here's another approach with a thought experiment.... >
Au contraire, the idea is really simple, and I imagine everyone understands what you are getting at. It just appears to contradict our best understanding of how the universe works. A Common Universal Present is how Newton envisaged time, and presumably how he would have envisaged it even if he'd known that light has a finite speed, and that nothing can move as fast as light. In a Newtonian universe, one could correctly say that there is a C.U.P. and that all the problems with finite communication speed don't change this. > > To start consider two observers standing next to each other. Do they share > the same common present moment? Yes, of course. Any disagreement? > They are spacelike separated, so they can only communicate by signals travelling at or slower than light, which means that they are out of synch by maybe a few nanoseconds. (This sort of difference is actually important in the stock market, where shares are bought and sold by computers, and their distance from the stock exchange can significantly affect their ability to respond to changes.) Whether one considers objects which are spacelike separated to share a common present moment seems like a matter of preference, or maybe of definition. They can't communicate instantaneously, so neither is able to influence the other except (say) 5 nanoseconds in their own future. However, the plane of simultaneity that one can construct for them by "foliating" space-time is their common rest frame, so one *could* say that they are in a common present moment. However some observers moving relative to them will disagree about the order in which they do things, which argues against a CPM. > > Now consider those two observers, one in New York, one in San Francisco. > Do they share the same common present moment? In other words is the one in > San Fran doing something (doesn't matter what) at the exact same time the > one in New is doing something? Yes, of course they do share the same > present moment. Any disagreement? > I'm not sure what this means in a relativistic universe. They are moving at different velocities, and separated in space-time. Some observers will see them doing things in one order, some in another. I don't see how one can construct a unique present moment for them in any sense, in this case. > > Now consider an observer on earth and an observer in some far away galaxy. > But with the condition that they share the exact same relativistic frame in > the sense that there is zero relative motion and the gravities of their > planets are exactly the same so that clock time is passing at the exact > same rate on both their clocks. > > Now are these two observers sharing the exact same present moment as well? > Note that we just extended the exact same relativistic circumstances of the > previous two examples so there can be no relativistic considerations. Do > these two observers also share the exact same present moment as well? Yes, > of course they do. Not only do they share the exact same present moment but > they also share the exact same clock time t value. Any disagreement? > See above. Spacelike separated observers in the same inertial frame may be said to share a common present moment by definition, but they are still subject to the relativity of simultaneity. > > OK, if you agree then you have to take a partial step towards accepting my > thesis of a common universal present moment. You now must agree that there > is at least a common universal present moment across the universe for all > observers in the same relativistic frame. > > Agreed? > No. If you can come up with a convincing refutation of the relativity of simultaneity, I may do so, although it seems to me that you are just saying one particular reference frame is prviileged (maybe some argument could be made to privilege the "comoving volume frame" or whatever it's called - the one that "goes with the cosmic flow" (man! :) But it will take a lot of convincing to overcome the equivalence principle etc. -- 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to email@example.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.