On Sat, Feb 22, 2014 at 3:03 PM, Edgar L. Owen <[email protected]> wrote:
> Jesse, > > I think the basic problem in our discussion, which seems intractable from > you answers below, is your basic belief that time doesn't doesn't flow, > that there is no such thing as a now in which you or the twins actually > exist. From your answers it seems clear that you can't even bring yourself > to agree that you are actually some particular age right now, or were at > any time in the past. If you don't even believe that I can't see any hope > of agreement or having a meaningful discussion. > If "right now" is taken to presume there is a UNIQUE now, then you are simply assuming what you seemed to be trying to prove. On the other hand, if "right now" is understood to be an "indexical" term (see http://plato.stanford.edu/entries/indexicals/ ) whose meaning depends on who's saying it, like "here" or "mine", then of course I have a definite age "right now". It's just that in this case "I" must be understood to refer to a particular observer-moment among many, the one having the experience of saying the sentence. So the fact that I have a definite age right now does not imply the nonexistence of other Jesse-observer-moments at different ages who could be just as real as I am, and who would mean something different by "right now", any more than the sentence "I am here in Rhode Island" implies the nonexistence of other people at different locations who would mean something different if they used the word "here". This is not to say that those other Jesse-observer-moments MUST be just as real as I am, just that the fact I can say "I have a definite age right now" doesn't prove anything one way or another about whether other Jesse-observer-moments with different "nows" exist or not. > > It's quite clear from all the numerous examples I gave that it is possible > to determine a 1:1 correlation between the twin's actual ages in terms of > their own clock time readings (what you call their proper times). > You have never given any *general* rule for determining this, you just gave two rules for specific cases: 1) the rule saying that if observers are at rest relative to one another far from gravity, the ages that are simultaneous in their inertial rest frame are also simultaneous in p-time, and 2) the rules saying that if observers start at a common location with clocks synchronized and then travel away from that location inertially, identical subsequent readings on their clocks will be simultaneous in p-time (again assuming no gravity). This doesn't tell us how to determine the 1:1 correlation if one of the observers accelerates during his journey, or if they are in a gravitational field. What's more, you didn't really give any rational *justification* for these rules, you just asserted that they were true. Even a fellow believer in presentism might disagree with these rules (for example, many presentists believe in a preferred reference frame, such that only events that were simultaneous in that frame *truly* happened "at the same time")--do you think they should just take your pronouncements on faith? Finally, there is the small matter that rule 1) leads to a paradox where two different points on the same person's worldline would end up being simultaneous in p-time, assuming p-time simultaneity is transitive and that events at the same point in spacetime in relativity also happen at the same p-time. Your only response to my bringing up this paradox (the one with four observers Alice, Bob, Arlene and Bart in https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/pxg0VAAHJRQJ ) was to deny that events at the same point in spacetime happen at the same p-time, but some of your comments made me think you were misunderstanding the meaning of "same point in spacetime", so I repeatedly asked you to address some simple questions that would clarify if you were understanding the meaning the same way that I do. But you have been incredibly evasive, continually ignoring my requests to answer my questions on the subject, even when I narrowed it down to a single question at the end of my last post to you at https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/LF0Xcds_qtQJ I would think that if an intellectually honest person is told there is a contradiction in something they've proposed, they would want to explore the argument for a contradiction, either showing that it doesn't work or admitting the contradiction is genuine and revising their position. Repeatedly ducking the issue doesn't seem to be the response of someone who is interested in open-minded intellectual exploration, as opposed to paying attention only to arguments that support their current beliefs. > This is their 'true actual age' because both twins agree on both actual > ages and how their clock times correlate. They do this not by OBSERVING the > other's age, but by calculating it from knowledge of how relativity works > in both their frames. > I don't see how relativity supports either of your premises 1) or 2) above, and you have never given any attempt to derive them from basic agreed-upon equations of SR like the time dilation equation or the Lorentz transformation. > > But since you can't even bring yourself to admit the twins were actually > alive with a particular actual age at every point on their world lines I > see no useful way to continue the discussion. > Again, if "particular actual age" is understood as an indexical term, then of course I "admit that"--each point on their world-line has a specific actual age (proper time between that point and their birth), it's just that there's no basis in relativity for thinking that there must be a *unique* point on their worldline that represents their age "now" in some universal present. > Thus the basic disagreement is not really about whether p-time is > incompatible with relativity (it isn't) but that p-time is incompatible > with block time, which for you seems a matter of faith which you are unable > to set aside. > As I have said a million times, although I personally think block time makes sense, I have never assumed block time as a basic premise in my arguments with you, I'm just trying to argue that there is nothing in relativity that requires that p-time is true and block time is false, as you seem to suggest. If you say that you can't have a meaningful discussion with me because, in your words, "you can't even bring yourself to agree that you are actually some particular age right now", *and* you mean "right now" in an absolute way (an absolute present) rather than an indexical way (each point on my worldline means something different by "right now", just like people in different countries mean something different by "here"), then you are saying you can't have a meaningful discussion with someone who doesn't share your presentist beliefs from the start--THAT would be treating presentism as a "matter of faith", like a religious believer who refuses to even have a discussion with someone who doesn't believe in God. Jesse > > > On Wednesday, February 19, 2014 1:30:11 AM UTC-5, jessem wrote: >> >> >> >> On Sun, Feb 16, 2014 at 9:40 AM, Edgar L. Owen <[email protected]> wrote: >> >>> Jesse, >>> >>> OK, I'm back... >>> >>> Let me back up a minute and ask you a couple of general questions with >>> respect to establishing which past clock times of different observers were >>> simultaneous in p-time.... >>> >>> The only clocks in this example are the real actual ages of two twins.... >>> >>> >>> 1. Do you agree that each twin always has a real actual age defined as >>> how old he actually is (to himself)? >>> >>> Yes or no? >>> >> >> Yes, in the sense that at each point on his worldline he has an "actual >> age" at that point, which is just the proper time between his birth and >> that point. But if you're suggesting a unique "true" actual age, as opposed >> to just each point having its own actual age, then I would have to change >> my answer to no. >> >> >> >> >>> >>> 2. Do you agree that this real actual age corresponds by definition to >>> the moment of his actually being alive, to his actual current point in >>> time? (As a block universe believer you can just take this as perception or >>> perspective rather than actuality if you wish - it won't affect the >>> discussion). >>> >> >> >>> >>> Yes or no? >>> >> >> >> If by "perspective" you mean that each point on his worldline takes his >> experiences at that point (including his age) to be the "current point in >> time", then yes. >> >> >> >>> >>> >>> Now assume a relativistic trip that separates the twins.... >>> >>> 3. Do you agree that IF, for every point of the trip, we can always >>> determine what ACTUAL age of one twin corresponds to the ACTUAL age of the >>> other twin, and always in a way that both twins AGREE upon (that is frame >>> independent), that those 1:1 correspondences in actual ages, whatever they >>> are, must occur at the same actual times? That this would give us a method >>> to determine what (possibly different) actual ages occur at the same actual >>> p-time moment in which the twins are actually alive with those (possibly >>> different) actual ages? >>> >>> Yes or no? >>> >> >> IF we had a method to determine a unique 1:1 correspondence in ages for >> separated twins, then yes, that could reasonably be interpreted as a >> demonstration of absolute simultaneity, telling us which ages "occur at the >> same actual times". But I don't believe you can find any such method for >> determining a unique frame-independent 1:1 correspondence in relativity. >> >> Since I am answering your questions, are you willing to answer mine? In >> the post that you are responding to I requested that you respond to my >> questions at https://groups.google.com/d/msg/everything-list/jFX-wTm_ >> E_Q/xtjSyxxi4awJ , especially the part at the end about the meaning of >> "same point in spacetime" (i.e. whether two events happening at the same >> space and time coordinates in a single coordinate system automatically >> implies that they satisfy the operational definitions of "same point in >> spacetime" I had given, and whether you'd agree that this means they must >> have happened at the same moment in p-time). You ignored that request in >> your response. I'll even narrow it down to a single question I asked in >> that post: >> >> 'If we have some coordinate system where relativity predicts the event of >> Alice's clock reading 30 happens at exactly the same space and time >> coordinates as the event of Bob's clock reading 40, do you agree or >> disagree that this means relativity automatically predicts these two events >> would satisfy the various operational meanings of "same point in spacetime" >> I gave at https://groups.google.com/d/msg/everything-list/jFX-wTm_ >> E_Q/AZOhnG04__AJ , regardless of whether Alice and Bob had synchronized >> their clocks in the past or not? Please give me a clear agree/disagree >> answer to this question' >> >> For example, say that in some particular coordinate system Alice's >> coordinate position x as a function of coordinate time t is x(t)=80, i.e. >> she is at rest at position coordinate x=80, and her age T (proper time >> since birth) as a function of coordinate time t is T(t)=t+10. Meanwhile >> Bob's coordinate position as a function of coordinate time is >> x(t)=68+(0.6c)*t, i.e. at t=0 he is at x=68 and he is moving in the >> positive x-direction at 0.6c, and his age T' as a function of coordinate >> time t is T'(t)=24+0.8*t. Then at t=20 in this coordinate system, they will >> both be at position x=80, and Alice's age will be T=20+10=30 while Bob's >> will be T'=24+0.8*20=24+16=40. So the question above is asking whether, in >> an example like this one, you'd agree that their reaching these ages at the >> same space and time coordinates implies they must actually meet at the >> "same point in spacetime" when Alice is 30 and Bob is 40, according to the >> operational definitions I gave earlier (like the one involving bouncing >> light signals back and forth and noting when the time for them to bounce >> back approaches zero). >> >> Jesse >> > -- > 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. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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