Jesse, Let me ask you one simple question.
In the symmetric case where the twins part and then meet up again with the exact same real actual ages isn't it completely logical to conclude they must also have been the exact same real actual ages all during the trip? If, as you claim, the same exact proper accelerations do NOT result in the exact same actual ages all during the trip then how in hell can the twins actually have the exact same actual ages when they meet up? What is the mysterious mechanism you propose that causes twins that do not have the same actual ages during the trip to just happen to end up with the exact same actual ages when they meet? Edgar On Saturday, March 1, 2014 11:42:18 AM UTC-5, jessem wrote: > > > > On Sat, Mar 1, 2014 at 9:55 AM, Edgar L. Owen <edga...@att.net<javascript:> > > wrote: > > Jesse, > > Of course there is a rational justification for selecting one frame over > another in many cases. All frames are NOT equal when it comes to > representing ACTUAL physical facts. > > E.g. we can choose various frames to make someone's age pretty much any > number we like but nevertheless they are still actually the age they think > they are. If Alice is really 30 we can choose a frame in which she is all > sorts of different ages > > > I've already told you that proper time at an event on Alice's worldline is > frame-independent, did you forget already? If one frame says Alice is 30 at > a particular event in her worldline, like the event of her passing a > particular object or observer (or her age when she reunites with her twin), > then ALL frames say this, there is no need to use her comoving frame to get > the correct answer. Different frames may disagree about simultaneity--what > Alice's age is at the "same moment" that Bob turns 40, at a distant spatial > location--but this is precisely why physicists don't believe there is any > "actual physical fact" about simultaneity in relativity (this doesn't rule > out presentism since there could still be a "metaphysical fact" about > simultaneity, but no physical experiment would be able to determine it if > there was, unless relativity turns out to be incorrect in its physical > predictions). > > > > > but she is still actually 30. Different VIEWS of her age don't change her > actual age. Isn't that obvious, and don't you agree with this? > > > "Don't change her actual age" WHEN? Doesn't change her age at some > specific event on her worldline, or doesn't change what her age is "now" at > the same moment that some distant observer like Bob reaches a particular > age, say 40? If the first I agree that she has an actual age at any given > event on her wrodline, but there ARE no different "views" of this since all > frames agree on her proper age at any specific event on her worldline. If > the latter I don't agree there is any physical basis for saying she has a > unique "actual age" when Bob is 40, since relativity doesn't give any > physical basis for a preferred definition of simultaneity. > > > > Your expertise in relativity is clear but you don't seem to understand > that all frames are NOT equal when it comes to representing actual physical > fact. You don't understand the fundamental notion in relativity that some > frames represent actual physical fact, but others represent only HOW OTHER > OBSERVERS VIEW those physical facts. > > > Not a physicist in the world would agree with you that there is a > "fundamental notion in relativity that some frames represent actual > physical facts", you appear to be completely confused about the difference > between your own p-time views and mainstream relativity. In special > relativity there can NEVER be a basis for considering one inertial frame > more "correct" than any other. There are only two kinds of facts in > relativity: > > 1. Facts about frame-independent matters like the proper time of an > observer at a particular event on their worldline; all frames agree in > their predictions about these, so they don't give any reason to prefer one > frame over another. > > 2. Facts about frame-dependent matters like the coordinate velocity of an > object at a particular event on its worldline, or the question of which > point on worldline B is simultaneous with a particular point on worldline > A; different frames disagree on these matters, and in relativity NO FRAME'S > STATEMENTS ABOUT FRAME-DEPENDENT MATTERS ARE CONSIDERED MORE VALID THAN ANY > OTHER FRAME'S. > > If you don't believe me that it's a basic principle of relativity that all > frames are considered equally valid and none are preferred over others, > here are some quotes from books written by physicists that I found on > google books: > > "If one reference frame moves uniformly relative to another, then the two > are equally good frames for observing nature, and two identical experiments > performed in the two frames will give identical results." > > --From "Relativity for the Questioning Mind" by Daniel Styer, at > http://books.google.com/books?id=Ebr7YhJcUd0C&lpg=PP1&pg=PA13 > > "The descriptions of the two sets of observers are equally real and > equally valid, each within their own frame of reference. Since no preferred > frame exists, there is no objective basis for ascribing any more reality to > one description than the other." > > --From "Understanding Relativity: A Simplified Approach to Einstein's > Theories" by Leo Sartori, at > http://books.google.com/books?id=gV6kgxrZjL8C&lpg=PP1&pg=PA173 > > "If Albert and Betty clap nearly simultaneously, one observer may report > that Albert clapped first, whereas a second observer, in motion with > respect to the first, may report that Betty clapped first. It makes no > sense to ask, 'Who really clapped first?' The question assumes that one > viewpoint, one reference frame, is valid or 'real' and the other is not. > But time is not absolute; it is a property of a particular frame of > reference. Both observers' viewpoints are equally valid." > > --From "The Theory of Almost Everything: The Standard Model, the Unsung > Triumph of Modern Physics" by Robert Oerter, at > http://books.google.com/books?id=KAMlsa8jjt4C&lpg=PP1&pg=PT35 > > General relativity goes even further and says that the laws of GR hold > equally well in *all* smooth coordinate systems, here is Einstein himself > on the subject, from "Fundamental Considerations of the Postulate of > Relativity": > > "there is nothing for it but to regard all imaginable systems of > co-ordinates, on principle, as equally suitable for the description of > nature" > > You can see this quote at > http://b<http://books.google.com/books?id=QE-fMnpR8hAC&lpg=PR1&pg=PA39> > ... -- 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. 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