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Einstein's SR a description of observations or a description of realit

  1. Sep 20, 2013 #1
    Is Einstein's SR a description of observations or a description of reality (or both)?
    It seems tome the distinction is important.
  2. jcsd
  3. Sep 20, 2013 #2


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    is newtonian relativity a description of observations or a description of reality (or both)? :wink:

    (and is the distinction important?)
  4. Sep 20, 2013 #3
    What's the difference?
  5. Sep 20, 2013 #4


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    What is the difference? How are we supposed to learn about reality other than through observing it?

    More explicitly, is there an experiment which could tell the difference between a description of observations or a description of reality? If not, then the question is not scientific.
  6. Sep 20, 2013 #5
    Perhaps you are alluding to Newton's theory, which contains a description (postulate) of hidden reality and a related description of observations (laws of motion). But only the description of observations can be tested, and most textbooks only mention the laws of motion. Is that what you are thinking of perhaps?

    If so, then Einstein's SR is a description of observations. That is implicit in the definitions here which are -on purpose- completely free of metaphysics, starting form §1: http://www.fourmilab.ch/etexts/einstein/specrel/www/

    Also the "speed of light in empty space" is purely operationally defined. The one-way speed even depends on one's free choice of clock synchronization. He phrased that more explicitly two years later as follows:

    We now assume that the clocks can be adjusted in such a way that the propagation velocity of every light ray in vacuum - measured by means of these clocks - becomes everywhere equal to a universal constant c, provided that the coordinate system is not accelerated.

    [addendum] As SR doesn't contain metaphysics, different people fill it in with different philosophical interpretations about "reality". And this forum is not the place for long elaborations about opinions that cannot be tested by experiment. Nevertheless, the distinction that you seem to make can be important for a precise understanding of what the theory entails. Indeed, the theory limits itself to predictions of observations.
    Last edited: Sep 20, 2013
  7. Sep 20, 2013 #6
    i was just interested in the fact that the reality of one observer is different than the reality of a different observer. Just interested in your thoughts. Thanks.
  8. Sep 20, 2013 #7
    Your "fact" is not true. You're confusing objects with terms of description. According to special relativity all the spatio-temporal relations between events are absolute objective facts, and do not differ from one observer to another. However, different observers may certainly use different terms to describe things.

    Think about describing things on a flat plane surface in terms of a Cartesian coordinate system x,y, and then think about describing those same things in terms of a different Cartesian coordinate system X,Y. The descriptions will differ to the extent that the range of x values occupied by a certain object may be different than the range of X values occupied by that object. But this doesn't imply that the "realities" of the objects are different for observers who use those two different coordinate systems. Yes, the terms of description are different (and of course the relations between the objects and each observer may be different), but the things being described are not different. This isn't unique to special relativity. The same applies to everyday life, so it shouldn't be hard to understand.

    People get confused when they first hear about special relativity because they have never previously thought about where our "natural" terms of spatio-temporal description (usually inertial coordinate systems) come from, how they are defined, and what they actually represent, especially when it comes to the time coordinates of events.
  9. Sep 20, 2013 #8
    As an object enter the event horizon of a black hole the observer sees the "entrant" slow down and even stop but the entrant enters, i think.

    The children pull the frog's legs off in fun but the frog's legs come off in earnest.
  10. Sep 20, 2013 #9


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    no, he never sees it stop :redface:

    he only sees it slow down … so what?

    (and this has nothing to do with SR anyway)​
  11. Sep 20, 2013 #10
    It seems to me that the observation doesn't coincide with the reality the entrant experiences.
  12. Sep 20, 2013 #11


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    Light pulses sent by the infalling observer to an external static observer take an infinite time to actually travel to said static observer, in the limit as the infalling observer reaches the event horizon. So there is no contradiction, it's just that the external observer's communication ties with the infalling observer are cutoff in the limit as ##r\rightarrow 2M##.
  13. Sep 20, 2013 #12


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    I was watching an airplane flying through the sky this afternoon. At one point it disappeared behind a cloud, and a few minutes later a very similar-looking airplane emerged from behind the other side of the cloud. I haven't asked the people on the airplane, but if I did I expect that they'd tell me that not only did their airplane not disappear, but that I was the one who disappeared behind a cloud as they were looking down at the ground.

    In this case there's no great mystery. We both agree that we experienced the same reality, that that reality involved a cloud that came became us, and that although our very different observations do not even slightly coincide with what the other experienced, they are consistent with that reality.

    It's the same thing with the relativity examples, both the SR phenomena you started this thread with and the black hole entrance example you introduced later. The only difference is that the phenomena are less familiar to us, so we cannot unconsciously fall back on our intuitive sense of what to expect from reality. A lifetime of past experience makes it easy for me to believe that the airplane that emerges from behind the cloud is the same one that disappeared behind it a moment before; I don't have the same lifetime of experience with (for example) the relativity of simultaneity.
    Last edited: Sep 20, 2013
  14. Sep 20, 2013 #13
    Do the light pulses from the "entrant" eventually dim and then disappear?
  15. Sep 20, 2013 #14


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    Nonsense. Do you similarly think that the Doppler shift of a cars engine causes multiple realities? Or that different time zones make different realities. This is just silly.

    The thread is closed. If you want to start another thread you will need to post a peer reviewed scientific paper with a definition of "reality" to discuss. Not just go around making stuff up at a whim.
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