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Observers/observations according to SR

  1. Aug 26, 2012 #1
    I would be thrilled reading your points of view on following:

    Special Relativity. (With that I mean: SR, not kind of an ether or LET interpretaion):
    In a frame two events are observed simultaneous because they are simultaneous in that frame, even if not observed. And those two events are non-simultaneous in another frame because they are non-simultaneous in that frame, even not observed.
    To make sure you understand what I mean please have a look at the sketch:

    154652[/ATTACH]"] spacetime3.jpg

    Sketch A.

    Top of sketch represents standard 3D space.
    The house numbers are bolted to the house. They are part of the house. So are the colors.
    Nobody will ever say that the blue house has numer 5, or yellow tower has number 2, etc
    Two obsevers look at the landscape around them.
    1/ Green observer and red observer can only look through a 2-dimensional telescope.
    2/ Because they do not direct their telescope in the same direction (because they are rotated relative to the ground), both observers see a different house. Red observer sees the yellow tower (house number 8). Green observer sees the blue house (house with number 2).
    3/ Is the tower (the image of the tower) an 'observer dependent' observation? Yes, because only the red observer sees the yellow tower. In the same context you may say that the house with number 2 is an 'observer dependent' observation: only green observer observes blue house number 2.
    4/ Nevertheless we may also say, -we HAVE to say, based on both observers' observations, that both yellow tower and blue house coexist as an 'observer INdependent' construction: part of 3D landscape space that's out there to be observed or not.
    If you do not accept that, then you do not believe there are houses in the street if you do not look at them.
    5/ For the red observer the yellow tower is in front of him, EVEN BEFORE he looks through his telescope. The fact of looking through his telescope will not change the house, nor the number, nor the color in front of him. As long as the observer does not look through his telescope (wait for the light to reach him) red observer does not know what type of house, color and number are in front of him, but he can find out by looking at it (and he will find out when the light from the tower reaches his telescope).

    You might counterargue by saying; "Wait a minute, maybe for red observer the yellow tower is brown and has number 9 instead of number 8, and he (red observer) does not know it until he observes it...". Well, that's impossible because the red observer sees a yellow tower with number 8, not a brown tower with numer 9. That's an experimental fact of the observation exercise as it turned out te be.
    What if red sees a football stadium? Well, change tower into a football stadium and start over again.
    What if there is out there a football stadium instead of a yellow tower? Well replace tower by football stadium and start over again.
    You want the tower brown? Well change the yellow into brown and we start all over again, now with a brown tower.

    ------------
    Sketch B.

    Similar scenario is applicable to Special Relativity: spacetime diagram.
    Tom is sick; his color changes every second.
    Tom turns blue (like a belgian smurf) when the pointers of the clock on his face point toward the mumer 2.
    When the pointers of the clock on his face point toward the mumer 8 he is yellow (like a ... ?).
    The time figure is a physical real time indication on the clock held in front of Tom's face.
    Nobody will say that Tom is blue when the hands of his clock point toward number 4, or 1, whatever. That's impossible.

    Green and red observer move relative to each other.

    1/ Green and red observer can only look with their 3-dimensional telescopes.
    2/ Because the two observer move relative to each other, they see light coming from diferent events.
    Red observer sees a Tom with clock indication on 8. Green observer sees Tom when the clock indication is at 2 (iow. 'Tom is not yet 8 seconds old'...). These are real observations. No illusions.
    3/ Is Tom with his clock indication 8 an 'observer dependent' event? Yes, because only the red observer sees Tom with clock indication 8. In the same context you may say that Tom with clock at 2 is an 'observer dependent' event : only green observer sees Tom with clock pointers at 2.
    4/ Nevertheless we may also say -we HAVE to say, based on both travelers' observations- that Tom with clock indication 2 and Tom with clock indication 8 coexist as an observer INdependent construction, part of 4D Spacetime Block Universe in which 'past, present and future' of Tom exist permanently, observer INdependent.
    If you do not accept that, then you do not believe there are Tom events if you do not look at them.
    (You might get away with a denial /refutation of an observer INdependent world in a QM context with microscale particles, but that's off topic here).

    You might counterargue by saying "Wait a minute, maybe for red observer the yellow tower has number 9 instead of number 8, and he (red observer) does not know it until he observes it...". No, my example shows the facts as they were reported in the observation experiment. In that observation element red observer saw yellow Tom, green observer a blue Tom. Period. And why did they see that and only that? Because the events are 'observer INdependent' out there, part of 4D Spacetime to be observed. For red observer event 'yellow-Tom-with-clock-at-8' has always been simultaneous with event E, even if he didn't make an observation during his traveling. For red observer event 'Blue-Tom-with-clock-at-2' has always been non simultaneous with event E. even if he didn't make an observation during his traveling. Etc.
    Simply because total 4D spacetime has organised the events that way. Just like the buildings are what they are, and where they are -and no place else- in 3D landscape Space of sketch A.

    In a frame two events are observed simultaneous because they are really simultaneous in that frame, even if not observed. And those two events are non-simultaneous in another frame because they are really non-simultaneous in that frame, even not observed.

    There is no other scenario unless it all gets philosophical or mathematical abstraction/illusion.
     

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  3. Aug 26, 2012 #2

    PeterDonis

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    What does "observed simultaneous" mean? I assume that you mean "assigned the same time coordinate in the given frame"; but can you clarify how, exactly, you envision this assignment of time coordinates being made based on actual observations, i.e., light signals being received from the different events? If the two events are not equidistant, in the given frame, from the observer, the light signals from those events will arrive at the observer at different times, so something about the distance from the observer to the events has to come into it, and you haven't said anything about how that is done. Not that I think this is a difficult point; I just would like to see something explicit about it.

    Given an answer to that issue, it looks to me like much of what you are saying is obvious: saying a particular event exists is not the same as saying that some particular observer observes the event. The former can be true without the latter being true. Okay. So what?
     
  4. Aug 26, 2012 #3

    ghwellsjr

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    Sketch A has no bearing on the topic you are discussing. It serves only to provide a misleading understanding of Sketch B.

    B1/ There's no such thing as a 3-D telescope.

    B2/ If two relatively moving observers are colocated, as Sketch B depicts, they will see the same light coming from all events. If one observer sees Tom at 8, so will the other one. If you think otherwise, it must be because of your magic 3-D telescope.

    B3/ If they are colocated as you have drawn them, they both see Tom with the same number on him, whatever that is. There is no way that one of them can receive an image of Tom at 2 and the other one receive an image of Tom at 8 if they are colocated.

    B4/ Your argument is flawed, mixed up, and screwy so your conclusions are also flawed, mixed up, and screwy.
     
    Last edited: Aug 26, 2012
  5. Aug 26, 2012 #4

    PeterDonis

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    To respond to my own question in my last post, I suppose the "so what" is this:

    This implied analogy with the 3-D case is not valid. In your diagram A, the two lines going to the observer from two different houses are actual sight lines--the spatial paths of light rays. Obviously both light paths can coexist in the same 3-D space, because light can be traveling along both paths continuously and arriving at the observer continuously at the same time as each other. For example, a single observer at the point where the two lines cross could use a setup with refracting lenses to see the images of both houses together.

    In your diagram B, however, the two lines, which you are claiming are analogous to those in diagram A, are *not* the paths of light rays; they are lines of simultaneity. Nothing physical actually travels along those lines. Light rays from the two events along Tom's worldline do *not* reach any observer at the same time; that's not possible. No observer can possibly see images of both Tom events at the same time, the way the observer above in the 3-D case could see images of both houses at the same time. So your analogy fails.

    You could, of course, claim that the two lines you have drawn are perfectly valid geometric objects in a 4-D geometric space, even if nothing physical travels along them. But that simply assumes what you're supposed to be proving: that there *is* a 4-D geometric space, all existing "at once", for those lines to be geometric objects in. And you have not *proved* that; you have not shown that SR *requires* that interpretation. Of course it is *consistent* with SR to interpret things this way; but you are making a much stronger claim than simple consistency.
     
  6. Aug 26, 2012 #5
    I thought my analogy between sketches A and B might work but apparently it's a screw up.

    I see that you get mixed up with light paths and lines of simultaneous events. You got a point there. Let me see wheter I can fix the text.
     
  7. Aug 26, 2012 #6
    Text is O.K.
    But sketches A and B show the situation at the moment the lights start at tower and house.
    What observers will later litterally see is only a confirmation of what's out there.
    The dotted lines are simultaneity lines.
    In 4D space an observer in his 3D space looks through a 3dimensional telescope.
    That's not what I had in mind, taking into account my extra comment above.
    See my extra comment above
    Ineresting comment.


    I hope that my extra comment above might help to see things differently.
    Relativity of simultaneity is enough prove.
    I did. What other interpretation would you give? Abstract mathematical coordinate illusions like Lorentz did?
    I probably miss subtility in enlish language to fully understand your point here.
     
  8. Aug 26, 2012 #7

    PeterDonis

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    To say that SR is consistent with the block universe interpretation just means that the block universe is one possible interpretation of SR, but not necessarily the only one.

    You are making a much stronger claim; you are claiming that the block universe is the *only* possible interpretation of SR. You have advanced two arguments for that claim:

    (1) The block universe interpretation is required because spacetime is a 4-D geometric object that exists "all at once";

    (2) The block universe interpretation is required because it's the only one you can think of.

    Argument #1 is invalid because it amounts to assuming what you are supposed to be proving, as I said before. Argument #2 is invalid because it isn't a deductive proof; it's just an assertion that you, personally, can't think of another interpretation. That's not a proof; it's an assertion about your state of knowledge, which doesn't prove anything other than the fact that that's your state of knowledge.

    You do ask a valid question:

    My interpretation of SR is that SR is a tool for constructing models of reality. The models it constructs are not exactly correct, for two reasons: (1) SR models spacetime as flat, but the actual spacetime we live in is curved, not flat; (2) SR models physics as classical, but the actual physics of the world we live in is quantum. Since SR's models are not exactly correct, SR is not a good foundation on which to base claims about "the nature of reality".

    That's sufficient to answer your question, but I also want to repeat comments I made in post #31 in the earlier thread, to which you never responded. If you want to claim that the entire 4-D spacetime of our universe has to exist "all at once", GR provides a much stronger foundation for that kind of claim than SR does, because GR includes dynamics as well as kinematics, and GR is a fully deterministic theory. But GR is also not exactly right, for two reasons: (1) it's not quantum; (2) it predicts singularities where the spacetime curvature is infinite, which is not physically reasonable.

    Most people seem to believe that a quantum theory of gravity, which would fix #1, would also fix #2 by changing the physics to avoid the singularities; that's my belief, but of course we won't know for sure until we have an experimentally verified quantum theory of gravity. But in any case, the fact remains that GR isn't exactly right; so the same interpretation I gave for SR also works for GR: it is a tool for building models of reality, and its models are not exactly correct, so it's not a good foundation on which to base claims about "the nature of reality".
     
    Last edited: Aug 26, 2012
  9. Aug 26, 2012 #8
    Ntuml

    object.... Give me a definiton of 'object'...
    But your point is wroing. Block universe exist because of relativity of simultaneity. That was also my very first post on this forum.
    That's a good one.
    In fact yes it's the only one I can think of that works for SR. That's correct. Weel, to be honnest, I didn't 'think' of block universe when I studied SR. relativity of simultaneity automatically leads to block universe. Unles, I told you more than once, you want to stick to mathemativcal abstractions, illusions, ether and so on. i.o.w. old stuff or philosophy.
    Macro world of trains getting shorter is SR, not QM. I know that your 'the event doesn't exists as long as it is not observed' comes from your QM course. Well, keep it there. Don't infect the SR forum with it.
    I'm not interested in GR and QM in SR discussions. I stick to Einstein's 1905 paper.

    Peter. I stop arguing with you. It's not the first time I say this, and after a while I give it a second chance, but I only fool myself. I consider this discussion closed. I'm tired of this. And you are probably fed up with me as well. So that's it. We better avoid each other on this forum. Good luck.
     
  10. Aug 26, 2012 #9

    PeterDonis

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    "Thing" would do as well. Does that help?

    And you didn't give a valid argument then, either; at least, not for the claim that the block universe is the *only* possible interpretation of the relativity of simultaneity.

    First of all, I have never claimed that "the event doesn't exist as long as it is not observed". If you want to say, for example, that there is some real event happening on Alpha Centauri *right now*, go ahead; I've never objected to that. What you say is perfectly consistent with any possible observation that either of us can make, so I have no problem with it. But you are trying to say *more* than that; you are trying to say that SR *forces* everyone to use your interpretation only.

    Second, your claim about the block universe, as I understand it, is a claim about "reality". "Reality" includes QM as well as SR. If they say different, incompatible things, at least one of them must be wrong. "Reality" doesn't separate itself into neat little categories to fit our theories.

    Then stop making claims about "reality" in SR discussions, and then objecting when other people bring in knowledge that's relevant, even if it's from outside SR. If you want to talk about "reality", you have to be willing to talk about *everything* we know about it, since it's all interconnected. There is only one "reality"; there is not an "SR reality" separate from a "GR reality" or a "QM reality".

    If you want to talk about SR as a scientific theory, which is very well confirmed within its domain of validity, that's fine. As far as I can see, you understand SR, as a theory, very well. But the theory is one thing, and interpretations of what it says about "reality" are something else. It's only the latter that is causing problems, not the former.

    That will be fine if you are willing to do as I suggest above. But it's not the first time someone has made that kind of suggestion to you, and so far you haven't done so.

    [Edit: I suppose I should add that if you think avoiding me on this forum will be sufficient by itself for you to avoid problems, you are most likely mistaken. I am not the only one who has objected to the position you are taking. It's your insistence that the block universe is the *only* possible interpretation of SR that is causing problems. I have probably spent more time than others raising particular objections to that position, but that doesn't mean I'm the only one who disagrees with it, or who will object to it if you raise it again.

    Also, as I said above, I think you understand SR, as a theory, very well, and I have seen you use spacetime diagrams, in particular, to clarify points in a number of other threads. So it's not your posts in general, but only the particular ones where you have taken the position I object to, that have caused problems.]
     
    Last edited: Aug 26, 2012
  11. Aug 27, 2012 #10

    ghwellsjr

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    Vandam, I have had a hard time trying to figure out how your sketches lead to your conclusion regarding a block universe but your repeated statement in your last post that "relativity of simultaneity leads to the block universe" got me to thinking about maybe what you are saying. Tell me if this is right:

    Pick any two simultaneous events in any inertial frame. For simplicity, let's put one of them at the origin and the other one somewhere else along the positive x-axis. That makes both of their time components zero and one of the x-components zero with the other one a positive number. Now we can pick any other inertial frame moving along the x-axis with respect to the first one and we can get any time component we want for the second event. In fact, as we repeatedly select a speed for the second frame from just under -c to just under +c, we will sweep through every time from almost +∞ to almost -∞. Since Special Relativity says that no frame is preferred, we really have to accept all of them as valid, which means that any two simultaneous events proves that all other times also exist--which is what the block universe is.
     
  12. Aug 27, 2012 #11
    The whole point of Einstein's first paper was that the Lorentz transformations could be deduced from observations without a (metaphysical) model. SR as defined by Einstein restricts itself to observations ("physical phenomena"), which makes it different from interpretations of SR - be it "LET", "block universe", or whatever.
     
  13. Aug 27, 2012 #12

    Dale

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    You may not like LET, for a variety of good reasons, but it is a valid interpretation of SR that matches all experimental predictions and does not require the block universe. LET is sufficient to show that the math of SR does not imply a block universe.
     
  14. Aug 27, 2012 #13
    A little critical side note to an otherwise excellent commentary:
    SR also includes dynamics (just consider "On the electrodynamics of moving bodies" and the prediction there about accelerating electrons); and do you suggest that SR is less deterministic?
     
  15. Aug 27, 2012 #14

    PeterDonis

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    The predictions about accelerating electrons require some dynamical equation, in that particular case the Lorentz force equation IIRC, to be *added* to the kinematic structure that SR provides. SR itself does not tell you *which* dynamical equation to use; it only sets some constraints on what form the dynamical equation must take. The Lorentz force equation is certainly not the only dynamical equation that is consistent with the SR constraints.

    GR, by contrast, includes a dynamical equation--the EFE--as an integral part of the theory. If you are not using the EFE, you are not using GR. You can add additional dynamics on top of it--such as Maxwell's Equations, for example in deriving the Reissner-Nordstrom solution to the EFE--but those are always in addition to the EFE, not in place of it. Also, in such cases, the dynamics of spacetime and whatever else is present interact; that doesn't happen in SR.

    (I suppose one could view SR as implicitly including some "dynamics" in itself, by viewing it as a specialization of GR for working with one particular solution to the EFE, flat Minkowski spacetime. On that view, the difference between SR and GR would be that GR does not restrict you to one particular "dynamics". To me that amounts to the same thing, since the "dynamics" of Minkowski spacetime is basically that "there is no dynamics" as far as spacetime is concerned; it's a fixed thing that doesn't interact with anything else.)

    No, of course not. But showing that SR is deterministic is not the same as showing that "reality" is deterministic.
     
  16. Aug 27, 2012 #15
    What a nice clear way to explain the block universe concept. Good job. Thanks. I know that most of the response to your presentation focused on the inability to establish this as the final word on accounting for SR itself. As long as LET is seen as a logically alternate explanation for those same SR effects accounted for by the block universe, the question cannot be settled. I'll dig into the LET stuff, but at this point DaleSpam and others are making a valid point. Of course they have not (and haven't claimed to) established that the block universe is not the correct description for reality.

    I appreciate your fervor in pursuit of reality and I share your conviction that pursuit of foundational physics includes researching the block universe concept--I certainly would not entrust such an edeavor to the philosophers. Stick to your guns.
     

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  17. Aug 27, 2012 #16
    The philosopher Petkov does a reasonable job of presenting the case for the block universe:

    http://www.spacetimesociety.org/VPetkov.html

    He makes effective use of the twin paradox in dealing with attempts at a general relativising of 3-D objects. His problem is the same one that I had in my post which presented a case for the block universe. He makes no mention of the Lorentz Ether Theory. And it was clear to me that LET could not be included among the 3-D presentism concepts he was refuting. It's not clear whether he has just never encountered LET. In any case it has been made clear on this forum that LET must be dealt with if a case for block universe as the description for physical reality is to be made.

    I'm on your side in these post exchanges, Vandam, and I admire your sticking to your guns. But, I'll have to find a chink in the LET armor before I can be useful as a block universe team member.

    I would admonish some of the PF folks to use more restraint while taking the advisarial approach in these debates. Vandam is fairly new to the forum and has not always received the kind of polite response that should be characteristic of even handed dialog. I would hate to lose a voice like his. I've been very impressed by his posts.
     
    Last edited: Aug 27, 2012
  18. Aug 27, 2012 #17

    PeterDonis

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    LET and block universe are not the only possible interpretations. You didn't respond to my post #31 in the other thread; I restated some of what I said in that post in post #7 of this thread. Do you have any comment on what I said there?
     
  19. Aug 27, 2012 #18
    I think that you have here clearly and succinctly illustrated the rationale for the block universe in it's simplest form.
    But I am surprised at your conclusion, as you have previously, unequivocally expressed the thought that spatially separate events cannot have any definite determination regarding simultaneity. Unless I misunderstood you.
    Here you seem to be applying an interpretation of actual simultaneity to the clocks in the initial frame. That is of course the crux of the question and making that assumption is equivalent to assuming block time itself.
    Be that as it may. If we assume a negative proper time on a particular frames clock of almost -∞ and assign any actual temporal significance to this reading it would imply that this clock was contemporaneous with the big bang and before. While the clock in that frame at x=0 was contemporaneous with the initial frame. Since it is nonsense to assume that the observer at -∞ is seeing the universe as it was then, it makes it clear that any such interpretation of actual temporality attached to the time reading is without meaning or validity.
    It just occurred to me that you may have intended this whole post as a reductio ad absurdem argument in which case I think it is brilliant.
     
  20. Aug 28, 2012 #19
    The text is also wrong. The real observations that they make are the receptions of independent signals with the information "Tom is 2 seconds old" and "Tom is 8 seconds old" - thus they must conclude that at the respective times of light emission these facts indeed occurred - no illusion there.

    However, it is not at all a "real observation" that "Green observer sees Tom when the clock indication is at 2".
    In fact, Green observer sees Tom after the clock indication is at 2 (or, with different meaning, he sees Tom when the clock indication was at 2). He can then choose whatever inertial reference system he likes, and as function of this free choice he calculates a certain time of signal transfer (assumptions about light speed and angle). Based on that he then assigns a certain local time to distant Tom when he sees the clock indication at 2.

    In other words, Tom only "appears" to coexist with different clock indications (there you have it again! :wink:) as a result of such different choices - it's an extremely observer dependent construction.

    The words "observer" and "observation" as often used in SR are a bit misleading. Usually such "observations" are hypothetical readings (that could be made real in principle though) of instruments that have been set according to the free choice of the observer.
     
    Last edited: Aug 28, 2012
  21. Aug 28, 2012 #20
    I'm interested to learn how the following can be countered. I assume that the following claim is correct: The "block universe" interpretation implies that past, present and future' of Tom co-exist permanently.

    This conclusion was drawn from the interpretation that "Tom with clock indication [t1] and Tom with [different] clock indication [t2] coexist".

    As I mentioned in my last post, these different distant times t1 and t2 relate to disagreeing assumptions about the speeds of individual light rays relative to the observers (I'm talking about "closing speeds"). And while Vandam's example doesn't show it, these assumptions even imply disagreement about the speed of the light ray relative to Mr Red. And if according to the interpretation these contradictory "observations" are physical reality, then the same light ray really has different speeds relative to Mr Red. :bugeye:

    So, here's my question: how can the block universe interpretation not result in thinking that "it's all a mathematical abstraction/illusion?"
     
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