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Q: Relativistic frames of reference ( Answered ,   6 Comments )
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 Subject: Relativistic frames of reference Category: Science > Physics Asked by: quoll-ga List Price: \$20.00 Posted: 14 Jan 2006 21:04 PST Expires: 13 Feb 2006 21:04 PST Question ID: 433561
 ```I have a question about a thought experiment. Suppose I have an inertial frame of reference, labelled A. I'll consider this my "stationary" perspective. Passing by A is frame of reference called B, where B is travelling at c. Any observations made from A will see objects in B flattened. My understanding is that an entire universe could be in B. Observations from A would see B containing enourmous area, but with no thickness. My question then relates to another frame of reference which I'll call B'. This frame of reference is also travelling at c, and in the same direction as B. However, B' is some distance behind B. Both B and B' can be seen from A, and they both appear flattened. However, they both contain an entire universe, and should be incapable of seeing each other. Flipping the perspective around... imagine that WE are in B. Then there is some frame of reference called A which is travelling at c, and that frame of reference sees us as a flat universe. That same frame of reference can also see another flat universe, called B', travelling along behind us, but completely inaccessible to us. In fact, when viewing the current universe from a passing frame of reference at velocity c, there would be an infinite number of flat universes, all parallel to this one. It can be seen here that the frame A does not need any occupants for this to hold. It simply provides the perspective for identifying B and B', and any other frames parallel to them. Is this conjecture sound? Where can I go to see a discussion on this please?``` Request for Question Clarification by hedgie-ga on 17 Jan 2006 16:06 PST ```Most of the reasoning and terminology makes sense, but "entire universe could be in B" sounds like B is a box. It is not a box and there is only one universe, per definition. Let's say you mean some big structure, like a galaxy. (They used to call them 'island universes' in the olden times). So you have big object at center of B and another at center of B', and they look like two pancakes to an observer at A. Object B is at rest relative to B' and and I see no reason for saying that object at B is completely inaccessible to observers at B'. Objects B and B' look like pancake to observer at A, just as Milky Way and Andromeda look like two thin pancakes to a hypotetical observer living near to what we consider 'event horizon', in a galaxy moving with near speed of the light relative to us. Sp what is that conjecture again?``` Clarification of Question by quoll-ga on 18 Jan 2006 15:58 PST ```You said that the two boxes look like two pancakes to an observer in A. But the boxes are boxes in space, and they are separated by space, so there is a third larger box which contains those two boxes. Wouldn't this larger box also get compressed down to a pancake? By induction, that would mean an entire universe would compress down to a pancake. (Unless the rules change in some way for intergalactic distances?) My point is that no matter how large a box you consider, it always ends up in the one "pancake" to an observer in A (I call that pancake "B"). But this observer would be capable of seeing another pancake (B') that is separate from the first. Since every part of space can be compressed into B (as above), then the contents of B' must be separated from the contents of B by something other than 3D space. (I'm guessing that the dimension is time, and I have reason to suggest that, but Google asks that we keep the scope of individual questions down). Reading my earlier question, a conjecture wasn't defined, sorry. The conjecture is that relativity can be used to show an infinite number of parallel universes, with the separation between the universes being a dimension other than space. Is there a flaw in the reasoning (and hence my understanding of relativity)? Are there areas on the net where this sort of thing is discussed. (My area of expertise is quantum physics, not relativity, and I'd like to learn more about GR)```
 Subject: Re: Relativistic frames of reference Answered By: hedgie-ga on 18 Jan 2006 23:07 PST Rated:
 ```quoll-ga Regarding "Are there areas on the net where this sort of thing is discussed?" These should be useful: To discuss: http://groups.google.com/group/sci.physics.research?lnk=li These are expert debates, so I suggest you do not use fuzzy concept like 'parrallel universe' out of context of the Everett Interpretation of QM, without defining it first. To learn more: http://relativity.livingreviews.org/ Regarding: "Is there a flaw in The conjecture is that relativity can be used to show an infinite number of parallel universes, with the separation between the universes being a dimension other than space" Yes. 1) Separation in Relativity is not 'in space' or 'time' but is measured by Minkowski Metrics: http://mathworld.wolfram.com/MinkowskiMetric.html http://www.theory.caltech.edu/people/patricia/grela.html 2) It is necessary to differentiated between 'B looks like a pancake' (to A but not to B) and 'is a pancake' . The 'is' is reserved for invariant concepts (such as Minkowski distance, see 1) In summary: There are events E1 E2.. which are 'out of the light cone' of other events F1, F2, and so not acessible to them. Reference to Light Coness: " That is to say, "all observers will universally agree on the Light Cones at each event..". http://www.phy.syr.edu/courses/modules/LIGHTCONE/minkowski.html So, there are parts of our universe which we 'cannot see' or communicate with. These are not called 'parallel or separate universes' in GTR. One can speculate on topology of this universe, (seen as a curved surface in n-dimensional space, connected or not) http://www.answers.com/topic/connected-space and such speculation becomes interesting when connected to or related to some experimental data. The possibility of 'complex topology' of universe http://en.wikipedia.org/wiki/Topology_of_the_universe is already present in GTR and Riemann Space http://en.wikipedia.org/wiki/Differential_topology http://mathworld.wolfram.com/RiemannSpace.html Hedgie```
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 Subject: Re: Relativistic frames of reference From: kottekoe-ga on 14 Jan 2006 21:35 PST
 ```This would be sound, were it not for the fact that if this "universe" contained anything, it would have mass and thus could not be traveling at the speed of light relative to frame A. Only objects with zero rest mass (like the photon) can travel at the speed of light.```
 Subject: Re: Relativistic frames of reference From: quoll-ga on 15 Jan 2006 00:27 PST
 ```Note that I was careful not to mention the frame of reference for A containing anything. Since I suggest putting "us" into frame B, then A necessarily can't contain anything. However, I believe that it is still possible to look at B and B' from a frame like A, which is travelling at c relative to them. As I suggested, frame A gives us a way of looking at both B and B', even though there is no way for B and B' to see each other. Maybe it's not possible to look at the "mass-filled" B from A, since any energy calculations done from that frame of reference give infinite values. But I don't *think* it invalidates anything I've mentioned, so my question still stands.```
 Subject: Re: Relativistic frames of reference From: kottekoe-ga on 15 Jan 2006 08:00 PST
 ```Quoll, I don't see any flaws in your argument, it just seems more elaborate than it needs to be. You are certainly free to postulate that another universe follows ours infinitely removed in time, but completely disconnected from us. You can do this with or without the theory of relativity, although it might get more interesting if you through in General Relativity. Keep thinking about it. Einstein's original insights about relativity came from thinking about what it would look like if you could travel with a light wave.```
 Subject: Re: Relativistic frames of reference From: kottekoe-ga on 15 Jan 2006 08:00 PST
 `typeo: through -> throw`
 Subject: Re: Relativistic frames of reference From: kottekoe-ga on 15 Jan 2006 08:01 PST
 ```typo: typeo -> typo (I'd better quit editing now)```
 Subject: Re: Relativistic frames of reference From: manuka-ga on 16 Jan 2006 01:30 PST
 ```Hi quoll, It's an interesting situation to think about, but I think some aspects of your conjecture are incorrect, or at least not well defined. I think the main point of confusion is that you may have missed the point that just because B and B' are both travelling at c with respect to A doesn't mean we know anything about how B and B' appear to each other. For example, B and B' could be stationary with respect to each other, in which case they'd certainly appear to be the same to A but would not be separated. But a little contemplation of the relativistic velocity addition formula should point out to you that exactly the same thing will be true if B' is moving relative to B at any velocity short of c - it is a well known result that if one component velocity is c and the other is not -c, the result is c. So the mere condition that B and B' both have velocity c with respect to A doesn't tell us anything about their relative velocities. In addition, I'm not really sure how valid it is to actually define a pair of reference frames with relative velocity c. All the transformation equations develop singularities if you do that, so I don't think you can really say exactly what would happen - just because at successively higher speeds the other object will look more and more squashed does not imply that "at c" the object will look infinitely squashed. In particular, I don't think you can consider one frame to be inertial when looking from the other. A final note - I don't think it's a good idea to think of this in terms of separate universes. Instead, think of separate slices of our own universe. This is more accurate. Remember that every photon that hits your eyes is travelling at velocity c relative to you, and if you look at two photons from the same source you will have a situation much like what you proposed. How do the photons appear to each other? I don't think you can answer that question, because neither can ever see the other. Does that mean they are not in the same universe? Certainly not as far as we're concerned. Don't let me discourage you, though. It is an interesting scenario to think about. It's just that I don't think we can say much sensibly about it, because the theory basically doesn't say anything about what happens when your target frame is moving at c with respect to your source frame.```