On Wed, Feb 26, 2014 at 2:31 PM, Edgar L. Owen <edgaro...@att.net> wrote:
> Jesse, > > You continue to quibble over terminology to avoid engaging the real > issues. Of course by 'view' I DO mean the actual equations in terms of a > coordinate system with origin at a particular observer. There is OF COURSE > a single set of equations that describes that view. > There are a single set of equations for any particular coordinate system, but my point is that for non-inertial observers or observers in curved spacetime, talking about an observer's "view" is ill-defined because there is no convention about which coordinate system to label as the "view" of a given observer. Even if you specify that you want a "coordinate system with origin at a particular observer", there are an infinite number of DIFFERENT non-inertial coordinate systems you could come up with that would have the property that the observer is always at the origin, each with a different set of equations. I asked about this issue specifically in the second question from my last post, which you didn't answer: '--If you don't disagree with the statement above, do you disagree with my statement that there's no specific coordinate system that is understood by physicists to represent a particular observer's "view" or "perspective" in general relativity, so that if you just talk about equations "used by" observer A without specifying a coordinate system, physicists wouldn't know what you were talking about?' Could you please just just quote my questions and answer them specifically in turn, as I always do with yours, rather than just sort of summarizing what you think my main points are and addressing them in a broad manner? > Answers to your next question: > > Yes, of course the OBSERVABLES are based on some coordinate system, but > you can't seem to get it through your head that any observer A who observes > another observer B can also know the equations governing how that observer > B observes A himself. > I'm not sure which question you are responding to here, you say "next question" but it seems like this is actually a response to my FIRST question (with no response given to any of the others), namely: '--Do you disagree that equations that observer A uses to "calculate the observables of any other observer B" are always based on A using some particular coordinate system? (if so, can you give an example of an equation that could be used to make such a calculation which would not depend on any specific coordinate system, but which would still be observer-dependent in some sense, so it would still be meaningful to identify this equation specifically with observer A?) ' You didn't really respond to any of the subsequent three questions with dashes before them, as far as I can see, although you did respond to the question in my last paragraph. Can you please go back and respond to the middle 3 questions? > > Do you deny that? > I deny that there is any single set of "equations governing how observer B observes A himself", if B is not an inertial observer in flat spacetime. If he's not, then as I said, there's no convention in relativity that says that any particular coordinate system should be interpreted as "belonging" to B. If you specify in detail what coordinate systems you want A and B to use to perform calculations (or if both of them are inertial in flat spacetime, so it's taken as read that they each use their own rest frame), then of course A can figure out what B would calculate and B could figure out what A would calculate. Also, do you understand that even for inertial observers, the idea that an observer's own rest frame can be labeled "his view" or taken to describe "his observations" is PURELY A MATTER OF CONVENTION, not something that is forced on us by the laws of nature? Physicists just don't want to have to write out "in the observer's comoving inertial frame" all the time, so they just adopt a linguistic convention that lets them write simpler things like "from this observer's perspective" or "in his frame" as a shorthand for the observer's comoving inertial frame. Physically there is no reason an observer can't assign coordinates to events using rulers and clocks that are moving relative to himself though, lots of real-world experiments involve measuring-instruments that move relative to the people carrying out the experiment. > > I'll skip now to the point you make in your last paragraph responding to > my symmetric trip case: > > Your comments here are true (more standard relativity) but irrelevant. > Why, because the point of the symmetric trip argument is TO ESTABLISH a 1:1 > correlation ONLY BETWEEN THE PROPER TIMES OF A and B, not any of the "any > other coordinate systems" you attempt to drag into the discussion to > obfuscate things. > It isn't a 1:1 correlation between the proper times of A and B without qualification, it's a 1:1 correlation between the proper times of A and B RELATIVE TO THEIR REST FRAME. If you use a different frame, there is a different 1:1 correlation between the proper times of A and B, RELATIVE TO THAT OTHER FRAME. Nothing in the phrase "1:1 correlation between the proper times of A and B" by itself tells us what frame to use. > > Do you agree in the symmetric trip case we can establish a 1:1 correlation > between the proper times of just A and B MEANING IN ONLY THE VIEWS FROM > THEIR TWO COORDINATE SYSTEMS? > If you drop the word "meaning", then I agree, but if you think the phrase "a 1:1 correlation between the proper time of just A and B" already somehow itself "means" that we must use their rest frame, then you are defining your terms in a way different from all physicists. And if you say that it is somehow true in absolute, non-frame-dependent terms that the proper times of A and B are "correlated" in this particular way (that certain pairs of ages for each are simultaneous in some absolute sense), then this goes beyond linguistic conventions into a physical claim about frame-independent truths that physicists would definitely disagree with. > I know you will find some reason to refuse to agree to this no matter how > true and obvious it is, but it is logically inescapable. And this 1:1 > relationship is transitive between all observers, and it does establish a > p-time plane of simultaneity between all observers in terms of their proper > times, and since the current proper time of any observer is the present > moment of his p-time, this does demonstrate a current universe present > moment. > If you make good on your promise to get back to my questions on the other line of discussion about "same point in spacetime" at https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/dM2tcGYspfMJ , then once we have come to agreement the physical meaning of two events sharing the same space and time coordinates in some inertial frame, I can show you that your "logically inescapable" claim about absolute simultaneity leads to a contradiction (the Alice/Bob/Arlene/Bart example from https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/pxg0VAAHJRQJwhich you have never really addressed, other than your original objection to my claim in the example that "same point in spacetime" should imply same point in p-time). > > I've demonstrated this over and over with all sorts of examples. If you > can't understand it, or can't bring yourself to accept it, so be it, but it > is a demonstrable truth. > You have asserted this over and over, but in none of your posts does it seem to me you made any attempt to "demonstrate" it. In other words, nowhere have you used mainstream relativity to DERIVE the claim that events which are simultaneous in the frame of two inertial observers in SR who are mutually at rest must also be simultaneous in some absolute, frame-independent sense akin to taking place at the same p-time. And even aside from a strict physics derivation, I can't even see where you've made anything like a conceptual or quasi-philosophical argument for why this should be true. Jesse On Tuesday, February 25, 2014 5:16:52 PM UTC-5, jessem wrote: > > > On Tue, Feb 25, 2014 at 4:02 PM, Edgar L. Owen <edga...@att.net> wrote: > > Jesse, > > So we agree on my first two points. And yes, I agree you can have as many > arbitrary coordinate systems as you like but that adds nothing to the > discussion. > > I accept your criticism of my third point which was not worded tightly > enough. I'll reword it... > > What I mean here is that all observers can know how relativity works both > for them, and for all other observers. In other words they can know exactly > what equations any observer A uses to calculate the observables of any > other observer B, in particular the equation A uses to calculate the clock > time of B relative to A's own proper time clock. This is standard > relativity theory assumed in all relativity examples. it follows for any > observer who knows relativity theory. > > With that revision do you now agree? > > > > No, you still seem to be laboring under the misconception that there is > some single set of equations that define the "view" of a given observer, > which they use to calculate observables for distant clocks. But all > relativistic calculations depend on the use of a COORDINATE SYSTEM, and > only with inertial observers in flat SR spacetime is there a standard > linguistic convention which treats the "view" of a given observer as > shorthand for a specific coordinate system, his inertial rest frame. > > Please answer these questions: > > --Do you disagree that equations that observer A uses to "calculate the > observables of any other observer B" are always based on A using some > particular coordinate system? (if so, can you give an example of an > equation that could be used to make such a calculation which would not > depend on any specific coordinate system, but which would still be > observer-dependent in some sense, so it would still be meaningful to > identify this equation specifically with observer A?) > > --If you don't disagree with the statement above, do you disagree with my > statement that there's no specific coordinate system that is understood by > physicists to represent a particular observer's "view" or "perspective" in > general relativity, so that if you just talk about equations "used by" > observer A without specifying a coordinate system, physicists wouldn't know > what you were talking about? > > > > > > You inconveniently snipped the examples where I made clear what I meant by > this and did not respond. Here they are again: > > > I did respond, I said it was wrong, because that there is no basis in > relativity for an agreement between observers about "rates". > > > > Thus it is possible for all observers to know the RATES of all proper > clocks in this system, and all observers will agree on all those proper > clock RATES. Note I'm talking here only of RATES, not of proper TIME clock > readings. We will get to that. > > E.g. IF THEY UNDERSTAND RELATIVITY, then all observers would agree that > the PROPER clock in a certain gravity would be running at 1/2 the rate as > PROPER clocks in no gravity. > > > Nope, this is just a misconception that is obviously based on an incorrect > intuitive understanding, not any detailed understanding of particular > equations used in relativity (if it was, you would write out the equations > rather than making vague statements like "if they understand relativity"). > My point was that there are only two ways to compare "rates" of clocks at > different points in space in general relativity: > > 1. Pick a coordinate system, and look at the rate each clock is ticking > relative to coordinate time at a pair of points on each clock's worldline > (or an interval on each clock's worldline, if you want to talk about > average rates over an extended period rather than instantaneous rates) > > 2. Restrict yourself to talking about visual rates a given observer sees > using light signals > > And as I said, in NEITHER case will you get universal agreement--for 1), > if two different observers use two different coordinate systems they can > disagree about the rates, and for 2), two different observers each looking > at one another can disagree about the ratio of the other clock and their > won clock in terms of visual speeds. > > If you disagree, please actually address this ARGUMENT rather than just > accusing me of not having read you closely enough and repeating something > I've already told you I don't agree is true. Specifically, please answer > these questions: > > --Do you disagree that 1) and 2) are the only methods *in relativity* of > comparing rates of clocks that are separated in space? Yes or no? (if you > do disagree, please be specific and give the equations and/or technical > term for a third > ... -- 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. -- 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 firstname.lastname@example.org. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.