Jesse, Frankly the utility of this approach seems opaque to me. I don't see how it differs from just being able to calculate the actual clock time differences the twins will have when they meet in 'a same present moment'. Because you say we already have to previously define what the same present moment they meet in is (means) and do that independently of this coordinate time calculation. You first must define, rather than calculate, what a same point in spacetime means by the reflected light method which is fine for establishing two twins are at the same point in spacetime WHEN they are at the same place in space but not otherwise.
You say that (using coordinate time calculations) "For the twins, if you know the coordinates they departed Earth and their coordinate speeds when they departed, and you know the coordinates of any subsequent accelerations (or forces causing those accelerations), you can predict the different coordinates where they will reunite, and what proper time their clocks will show then." But that's exactly what the standard equations of relativity give you isn't it? Assuming that by the "proper time their clocks will show then (when they meet)" is just the t values their clocks read. So I fail to see what we get out of this approach that standard relativity calculations don't give us. Don't they give us the exact same results of two different times in a "same point in spacetime" that we've already defined independently of the calculations? If so I repeat my assertion that there is no calculation from coordinate time, or relativity in any form, that gives the twins having the exact same coordinate time reading on some cryptic clock that proves they are the same time as well as the same place when they meet. So again I repeat my assertion that the present moment is locally DEFINABLE (via reflected light) but NOT CALCULABLE by a coordinate time or any other approach. Therefore the present moment is a completely independent kind of time since it is not a calculable result of relativity. That's what I've always said, but I thought you were telling me that same points in spacetime were CALCULABLE with coordinate time, that there was some mysterious coordinate time calculation that made the twins' clocks come out the same t readings when they met proving that the meeting was at the same point in spacetime. Edgar On Wednesday, February 5, 2014 7:29:22 PM UTC-5, jessem wrote: > > > On Wed, Feb 5, 2014 at 6:27 PM, Edgar L. Owen <[email protected]<javascript:> > > wrote: > > Jesse, > > Again, if I understand you, this is just a way to define 'same points in > spacetime'. > > > No, it's a way to physically define coordinate position and coordinate > time in terms of actual physical clocks and rulers. The definition > presupposes that you *already* have an operational definition of when > events happen at the "same point in spacetime", like the operational > description I described earlier that you seemed to be happy to accept--I > said in > https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/PBeMO1PpJmsJthat > the "same point in spacetime" could be "defined operationally in terms > of them being able to send light to the other one and get the reflected > light back in a negligible amount of their own clock time, with the light > coming back showing the clock time of the other one", and you replied in > https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/DarNEwAiOp0Jthat > "Re your last paragraph, then we DO agree (and your note that that is > measurable and confirmable by the zero light distance between them is a > good one)" > > My explanation of the physical meaning of coordinate systems said, for > example, that if you say the event of twin A turning 30 happened at > x=10,y=15,z=5,t=50, what that means is that if you consider the physical > clock in the lattice at ruler-markings x=10,y=15,z=5, and we call this > "clock C", then the event of A turning 30 happens AT THE SAME POINT IN > SPACETIME as the event of clock c reading a time of 50. Obviously this > explanation is meaningless if you don't already have a way of deciding if > two events happened "at the same point in spacetime!" But if you accept the > operational definition above, then this tells you what it means physically > to say that the event of A turning 30 happened at time-coordinate t=50 in > some frame. > > > > > Again there is no calculation that tells us the twins will meet at a new > same point in spacetime from the original same point in spacetime. > > > > Did you want such a calculation? You asked 'what is that 'WHEN'? It is not > A's clock time and it is not B's clock time', which seemed to be a question > about the physical meaning of coordinate time. > > The usefulness of defining inertial coordinate systems of the type I > described is that there is a set of known equations that make correct > predictions in *all* such inertial coordinate systems. For example, they > allow you to predict that if a clock is moving inertially (no forces acting > on it), and you know that it passed by the x=10 mark when it read a proper > time T=0 and the coordinate clock there read t=0, and it passed by the x=8 > mark when the coordinate clock there read t=10, then from its coordinate > speed of 0.8c you can predict it must have read a proper time of T=6 as it > was passing that second coordinate clock at x=8, and you can also predict, > for example, that it will pass the x=16 mark when it reads T=12 and the > coordinate clock there reads t=20. For the twins, if you know the > coordinates they departed Earth and their coordinate speeds when they > departed, and you know the coordinates of any subsequent accelerations (or > forces causing those accelerations), you can predict the different > coordinates where they will reunite, and what proper time their clocks will > show then. > > > > > Or are you claiming that every point in this lattice is somehow a 'same > point in spacetime'? > > > > Not sure what you mean by this, obviously x=10,t=12 is not the same point > in spacetime as x=15,t=8. But you could certainly have one event which > happens at the same point in spacetime as the clock at x=10 reading t=12, > and a distinct event which happens at the same point in spacetime as the > clock at x=15 reading t=8. In my usage "same point in spacetime" only has > meaning as a relative phrase joining two or more events, I don't know what > it would mean to say a given event "is" a "same point in spacetime" without > specifying another event it's at the same point AS. In this sense it is no > different from a spatial phrase like "same longitude as", you might say "my > foot is at the same longitude as this knot in the floor I'm standing on" > but you would never say a given point on the globe "is a same longitude". > > Jesse > > > > On Wednesday, February 5, 2014 4:00:43 PM UTC-5, jessem wrote: > > > > On Wed, Feb 5, 2014 at 3:10 PM, Edgar L. Owen <[email protected]> wrote: > > Jesse, > > No, what the equations of relativity say, and the only thing they compute, > is that WHEN the twins meet up again at the same point in space, that they > will have different clock times. > > But what is that 'WHEN'? It is not A's clock time and it is not B's clock > time. > > > > It is the coordinate time, and as I've mentioned to you several times, it > is ideally defined in terms of local readings on a lattice of coordinate > clocks and rulers filling up the area of space that the coordinate system > is intended to cover, as illustrated at http://www.upscale. > utoronto.ca/GeneralInterest/Harrison/SpecRel/SpecRel.html#Exploring > > The idea is to imagine a lattice of physical rulers, with some parallel to > the direction we call the x-axis and marked with x-coordinates, some > parallel to the direction we call the y-axis and marked with y-coordinates, > and some parallel to the direction we call the z-axis and marked with > z-coordinates. At each point where 3 such rulers oriented in different > directions meet, there is a clock attached. All the clocks at all points in > this lattice have been mutually "synchronized" using what's known as the > Einstein synchronization convention, which involves the assumption that > light should be measured to have the same coordinate speed in all > directions in the rest frame of the lattice, so for example if you set off > a flash of midpoint along a line between two clocks, they should be set in > such a way that they both read the same time at the moment the light hits > them. > > So for example, say some frame says "A turned 30 and B turned 40 at the > same coordinates of x=10 light-years, y=15 light-years, z=5 light-years and > t=50 years". Now imagine looking at the clock that's attached to the > unique intersection point between three rulers where the marking "10 > light-years" appears on the x-ruler, the marking "15 light-years" appears > on the y-ruler, and the marking "5 light-years" on the y ruler. Let's > label this "clock C". Then the meaning of the statement above about A and B > is that these THREE events all happened at the same point in spacetime > (which again can be defined in the operational way I discussed): > > 1. "A's life clock shows a time of 30 years" > 2. "B's life clock shows a time of 40 years" > 3. "clock C shows a time of 50 years". > > In practice of course physicists don't actually build networks of clocks > of this sort, but the point is that once you have deduced how to write the > equations of the laws of physics expressed in terms of coordinates defined > by such a lattice, it's often easy in practice to figure out what local > coordinate-clock readings *would* coincide with various events if such a > lattice were in place, without actually needing to construct one in > reality. For example, you can use optical methods to deduce the distance to > events in your frame without actually needing a ruler stretching from your > location to the location of the distant event, and if you know an event > occurred X light-years away, you can just subtract X years off the time the > light from the event reached your position in order to determine the time > coordinate of the event, which should be no different from what a > synchronized clock would have read if it was right next to the event when > it happened. > > But in principle, using such local readings on a set of clocks and rulers > is probably the best way to define the meaning of position and time > coordinates in a particular frame, the definition that will lead to the > least conceptual confusion about the meaning of these coordinates. In > particular, you can see that coordinate time is just a third type of clock > time. These coordinate clocks are particularly *useful* because they allow > you to express the laws of physics using a neat set of equations that > doesn't depend on the velocity of the coordinate clocks relative to > anything else (for example, if a light flash is emitted from a coordinate > clock when that clock reads t1, and received by another coordinate clock > when that clock reads t2, and the distance along the ruler between them is > d, then it's guaranteed that (t2 - t1)/d = c, meaning light always has a > velocity of c in these coordinates). But other than that they are no > different than any other type of clock. > > Jesse > > > > Thus it is a completely necessary but UNSTATED assumption of a completely > different common point in time different from and outside of the 2 clock > times, in which the 2 clock times differ and that can be agreed on by both > twins. > > Thus relativity itself implicitly and cryptically assumes a common present > moment in which the results of spaceCLOCKtime calculations are compared and > make sense. > > I'll ask you again: What is the choice of frame in relativity that > computes the fact that the twins meet in the agreed SAME POINT of spacetime > with different clock times? I don't think there is any.... > > Of course you can always avoid this question by noting that they are at > the same point of spacetime when they are. That's an oxymoron. But what's > the calculation that predicts that from beginning to end? There simply > isn't any.... > > Edgar > > On Wednesday, February 5, 2014 2:54:39 PM UTC-5, jessem wrote: > > > > On Wed, Feb 5, 2014 at 2:35 PM, Edgar L. Owen <[email protected]> wrote: > > Jesse, > > Let me ask you this simple question. You agree that there is "a same point > in spacetime" that both twin meet at and in which their clock times are > different. > > How does your theory, or relativity, account for or predict this same > point with different clock times starting from when the one twin leaves on > his journey? > > Is there any choice of frames which computes this result in relativity > theory? If so what? > > > > Yes, all of them predict it. In the context of any allowable choice of > coordinate system, if two events occur at exactly the same position and > time coordinates, then that leads to the conclusion that they must have > occured at the "same point in spacetime" in a coordinate-independent sense > (understood either in terms of spacetime geometry or in terms of the > operation definition I mentioned). So if any given frame assigns the same > space and time coordinates to a pair of clock-readings for each twin, like > "twin A turns 30" and "twin B turns 40", that implies these events happened > at the same point in spacetime, and it always works out that other frames > assign this pair of events identical coordinates too. > > Jesse > > > > > If not then we must assume a separate kind of time in which it is true. > That is p-time. > > I think this question gets to the crux of the disagreement.... > > Edgar > > On Wednesday, February 5, 2014 1:40:41 PM UTC-5, jessem wrote: > > > > On Wed, Feb 5, 2014 at 10:53 AM, Edgar L. Owen <[email protected]> wrote: > > Jesse, > > A couple of points in response: > > 1. Even WITHOUT my present moment, the well established fact of a 4-d > universe does NOT imply block time nor require it. Clock time still flows > just fine in SR and GR. > > > I would agree that the 4D mathematics of relativity theory doesn't require > the ontology of block time, though I don't see any alternative to block > time besides some sort of "metaphysically preferred" definition of > simultaneity (which wouldn't contradict relativity as long as long as this > definition wasn't "preferred" by the measurable laws of physics). I don't > know what you mean by "clock time still flows" in SR and GR--it only > "flows" in the sense that its value is different at different points along > a worldline, the same sense in which we could say that "distance from the > end of the wire" flows along a piece of wire (i.e. the value of "distance > from the end of the wire" is different at different points along the wire). > > > > > No clock time simultaneity of distant (relativistic is a better > descriptor) events does NOT imply time is not flowing at those events. This > is quite clear. It's a fundamental assumption of relativity that time flows. > > > What mathematical element of relativity corresponds to your notion of > "flow"? > > > > In fact relativity itself conclusively falsifies block time as it requires > everything to be at one and only one point in clock time due to the fact > that everything always travels at the speed of light through spacetime. I > find it baffling that so many can't grasp this simple fact. > > > Huh? "Everything moves at the speed of light through spacetime" is not how > most physicists would describe relativity, and those few who do are just > speaking in a colorful way about the magnitude of the 4-velocity always > being equal to c. And the 4-velocity is just defined as a vector whose > components give you the rate of change of the spacetime coordinates t,x,y,z > relative to proper time. > > Nothing about this notion is contrary to the notion of block time--as an > analogy, if we have a piece of wire embedded in a block of ice and forming > some type of curved shape, and we use an x,y,z coordinate system to > describe different points within the block and on the wire, then at every > point along the wire we can define a vector whose components give the rate > of change of x, y, z coordinates relative to "proper length" at each point > (where "proper length" refers to the distance between that point and the > end of the wire--or some point along the wire marked "0"--as measured along > the the wire itself). And in fact it's not hard to show (I can give you the > derivation if you like) that using these purely spatial definitions, the > magnitude of *this* vector must always be 1 at every point on the wire, > regardless of the shape of the wire. Would you describe this situation by > saying "every wire-point moves at the same speed through the block of ice", > even though we are talking about wires that from our point of view are > completely static, frozen in a particular shape within the block? > > > > > > > 2. You complain about me not answering a few of your questions. As I've > explained before I have limited time to post here because running my > business keeps me very busy. > > And please note that a lot of my posts have received NO answers at all > either, e.g. > > a. Several major posts, some as new topics, on my theory of how spacetime > emerges from quantum events. Apparently this has just sailed over > everyone's heads with not a single meaningful comment, not even any > negative ones which is pretty surprising among this crowd! Apparently no > one is interested in understanding the nature of time at the quantum level? > > b. My post on a solution to Newton's Bucket. Also no relevant responses. > > c. Several thought experiments lending very strong support to my present > moment theory, posted just a couple days ago. Again zero response. And > weren't those directed to YOU? > > d. Several thought experiments designed to dig into the fine points of > various aspects of time dilation. Again only a vague comment or two on > 'asymmetry' but zero actual analysis of the points I raised. > > e. Several other new topics on basic issues of science and epistemology. > Again no relevant responses. > > > Those posts were not part of an ongoing discussion with *me*, though. I'm > not asking you to respond to every argument I make, just to respond to > posts that are part of ongoing discussions with you, in which I raise > serious difficulties with arguments you have presented to me. And I don't > mind if you take your time in getting back to me, but it is rather > suspicious when > > ... -- 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.
