Jesse, I gave you a clear easy to follow and understand procedure that I believe works in every case to determine if any two clock time labeled events occurred in the same p-time moment or not.
I'm sorry if you don't see how it works. I don't see how I can make it much clearer. It's just applying standard relativity calculations. You don't have to do them backwards BTW. If you start with A and B in the same frame, they will automatically be in the same p-time present moment so you can do the math forward from there to establish the same p-times for all different clock time of A and B when one starts to travel. That's simple standard relativistic calculations. I don't have time to start doing calculations for you but the procedures I gave you are standard relativistic calculations that should enable you to determine which clock time labeled events occurred at the same p-times if you want. Edgar On Saturday, February 8, 2014 5:28:08 PM UTC-5, jessem wrote: > > > > > On Sat, Feb 8, 2014 at 4:01 PM, Edgar L. Owen <[email protected]<javascript:> > > wrote: > > Jesse, > > Yes, I think there is always a way to determine if any two events happen > at the same point in p-time or not, provided you know everything about > their relativistic conditions. > > You do this by essentially computing their relativistic cases BACKWARDS to > determine which point in each of their worldlines occurred at the same > p-time. > > Take 2 observers, A and B. > > 1. If there is no relative motion or gravitational/acceleration > differences you know that every point t in A's CLOCK time was in the same > present moment as every point t' in B's CLOCK TIME when t=t'. > > > And what if there *are* gravitational differences, if there are sources of > gravity nearby and they are at different points in space? Gravity is dealt > with using general relativity, and in general relativity there is no > coordinate-indepedent way to define the "relative motion" of observers at > different points in space (see discussion at > http://math.ucr.edu/home/baez/einstein/node2.html for details). And the > only coordinate-independent definition of "acceleration" is proper > acceleration (what an observer would measure with an accelerometer that > shows the G-forces they are experiencing), but all observers in freefall > have zero proper acceleration, so if you think there is a > "gravitational/acceleration difference" between an observer orbiting far > from a black hole and one falling towards it close to the event horizon, > you can't quantify it using proper time. > > > > > 3. In the case of twins DURING the trip in relative motion we can always > back calculate the relativistic effects to make a statement of the form > "the twins were in the same current moment of p-time when A read his own > clock as A-t and B's clock as B-t, AND B read his own clock as B-t' and > read A's clock as A-t'. In this case A-t will NOT = A-t', and B-t will NOT > = B-t', but they will have specific back calculable t values for every > current p-time during the trip. Thus if we have all the details of that > trip's motion we should always be able to back calculate to determine which > clock times of any two observers occurred in the same current p-time > SIMULTANEITY even when those observers cannot agree on CLOCK time > simultaneity among themselves. > > > HOW would you "back calculate" it though? Even if we set aside my > questions about gravity above and just look at a case involving flat SR > spacetime, your answer gives no details. If you have any procedure in mind, > could you apply it to a simple example? Let's say Alice is sent on a ship > that moves away from Bob on Earth on the day they are both born, and the > ship moves with speed of 0.8c relative to the Earth, towards a planet 12 > light-years away in the Earth's frame. Alice arrives at that planet when > she is 9 years old, and at that point the ship immediately turns around and > heads back towards Earth with a relative speed of 0.6c. Alice experiences > the return journey to take 16 more years, so when she returns to Earth she > is 25 years old, but Bob is 35 years old when they meet. Can you show me > how to back-calculate how old Bob was when he was in the same moment of > p-time as Alice turning 9 and her ship reaching the planet and turning > around? > > > > So since p-time has no metric itself you can't just compare p-time t > values because there are none. You have to back calculate clock times to > determine in what current p-times they occurred. > > So that's how we determine whether any two events occurred a the same > p-times or not. You should always be able to determine that even though you > can assign a p-time t value because there are none because p-time doesn't > have a metric. > > > I have never asked you for a p-time "value", I'm only interested in the > question of which events are simultaneous in p-time. I don't think your > answers so far have made it clear that you have any well-defined procedure > for determining this, see my questions above. > > Jesse > > > > > Edgar > > > > On Friday, February 7, 2014 12:51:32 PM UTC-5, jessem wrote: > > > > > On Fri, Feb 7, 2014 at 12:27 PM, Edgar L. Owen <[email protected]> wrote: > > Jesse, > > Well you just avoid most of my points and logic. > > > Can you itemize the specific points you think I'm avoiding? > > > > But yes, I agree with your operational definition analysis. That is > EXACTLY my point. That what our agreed operational definitions define is a > COMMON PRESENT MOMENT, and NOT a same point in spacetime, because the logic > of it does not support it being in the same point in space, only in the > same point of time > > > Huh? Even if one accepts p-time, that "operational definition" still must > be seen as a merely *approximate* way of defining the same point of p-time, > not exact, just like with "same point in space" or "same point in > spacetime". If I bounce some light off you, surely you agree that the event > of it reflecting off you occurred at a slightly earlier point in p-time > that the event of reaching my eyes (or instruments)? Likewise if I feel our > palms meet in a handshake, I don't actually begin to feel it until a > slightly later moment of p-time than the moment our palms first made > physical contact, and likewise for any shift or movement you might make > with your hands. If you want to talk in a non-approximate way, all our > experiences are slightly delayed impressions of events that occured in the > past, regardless of whether we're talking about p-time or coordinate time. > > On this subject, could you address the question I asked in another post > about whether you think there's any empirical way to determine whether two > events in the past occurred at the same p-time, or whether the assumption > of p-time simultaneity is a purely metaphysical one and that there's no way > of knowing whether a specific pair of events we have records of actually > happened simultaneously in p-time? > > > > and that same point in time is obviously not anything that relativity > predicts, because no matter what set of coordinates you choose, relativity > always gives 2 different real answers for the ages of the twins. > > > > I don't know what part of this you're not understanding, "same point in > time" in relativity just MEANS that two events are assigned the same time > coordinate, relativity doesn't deal with any absolute notion of > simultaneity of distant events whatsoever. And relativity definitely does > predict situations where clocks show different readings at the same > coordinate time--do you deny this? > > Like I said earlier, there is a direct spatial analogy here that makes > perfect sense if you don't assume p-time from the start. If two different > measuring tapes cross, and the point where they cross is at the 30 cm mark > on one tape and the 40 cm mark on the other, and there's a Cartesian > coordinate grid on the surface under them which says this point has an > x-coordinate of 50, wouldn't you say that the measuring tapes DO cross at > the "same point in space"? Would the fact that the tapes themselves show > two different readings at that point negate this? > > As for your last paragraph you seem to agree that both our operational > definitions DO support the notion of a same present moment, just not that > time flows. > > > How do you figure? My last paragraph was just clarifying what I meant by > arguments "dependent on conscious experience" vs. arguments defined in > terms of straightforward experiments whose results we can all observe and > agree on. Nowhere did I say anything in support of an absolute "same > present moment". > > > Jesse > > > > On Friday, February 7, 2014 8:49:32 AM UTC-5, jessem wrote: > > > On Fri, Feb 7, 2014 at 7:57 AM, Edgar L. Owen <[email protected]> wrote: > > Jesse, > > OK, here's the detailed analysis of how I see the current state of this > issue that I promised: > > > A few points: > > 1. Since you asked let me repeat my 'operational definition' of the > present moment that I used before. The twins meet, shake hands and compare > watches. That is the operation definition. > > That is essentially the same as your reflected light operational > definition with which I have no problem. > > 2. However it is important to note that that works not just for the twins > together, but for every single twin by himself. Because any twin or > observer can shake his own hand, look at his own watch, or note that the > light reflected from a mirror in his hand takes minimal time to return. > > Therefore what is true for the twins together is also true for each twin > separately, and is true for every observer in the universe as well. < > > ... -- 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. For more options, visit https://groups.google.com/groups/opt_out.
