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Stretched piece of spacetime example appropriate for student

  1. Sep 15, 2015 #1
    I would like to hear different examples of presenting the difference that general theory of relativity relates between a stretched piece of spacetime around a planet and a not stretched one far away from any kind of mass or energy distortions...these examples i would like to be written in a language that could be understood from students of high school....so it should be like 1 m of stretched space and 1m of not stretched one would have this kind of difference etc....i ask this because i believe that through the exchange of knowledge we can always improve our understanding and simplify them for us and for our students...thanks in advance!
  2. jcsd
  3. Sep 15, 2015 #2


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    One meter is going to be hard to do, because the effects are so small at that scale (Consider, for example, that the force of gravity at the earth's surface is essentially indistinguishable from the force one meter higher - and that's with the entire mass of the earth contributing to the curvature between those two points).

    However, there are three examples that you may find helpful in explaining GR at a high-school level:
    - Search this forum for the excellent video put together by our member @A.T. (who will probably point you at it if he's listening).
    - Google for "Flamm's paraboloid". Be sure that read and understand the mathematical description of what it is - it's easy t misunderstand it if you just look at the picture.
    - Google for what John Wheeler called the "ouch radius", the conditions under which the curvature is great enough that to be felt across the one-meter or two-meter scale of the human body.
  4. Sep 15, 2015 #3
    i know that the effects are too small for the scale of 1 m...sometimes we use not actual measures of the quantities that we deal, just to show the basic meaning....so i dont want an accurate quantitive example....also the flamm's paraboloid and black wholes images dont think that always reveal to the viewer the exact phenomenon that happens there.....for example....could we say that it could like that if someone travels 1 m in an unstretched area of spacetime with a specific velocity and he will do time t1...and someone else travels 1 m in a stretched area of spacetime with the same velocity then he will do time t2....and despite the classical image of t1=t2....the actual phenomenon is t1<t2 ? would it be accurate to present the general image with such an example?...
  5. Sep 15, 2015 #4


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    I think the way the question is asked doesn't show a correct conceptualization what's going on, so any example based on that is going to be an incorrect example.

    It's just not true that gravity is a stretching of space.
  6. Sep 15, 2015 #5
    but general relativity isnt that what it presents? that gravity is a stretching effect of the spacetime?...of course there other theories about gravity...but i just try to present general relativity (only) with the most simple way to students of high school....
  7. Sep 15, 2015 #6


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    No, that isn't what general relativity says. (And you're now referring to stretching spacetime, which is different from your original discussion of stretching space.)

    It's possible to present general relativity without a lot of mathematics, but that's different from getting it wrong.

    A better place to start this discussion might be by talking about what your own background is and where you've gotten your previous information about GR. We might then be able to point you to, e.g., a book at the right level for you to read.
  8. Sep 16, 2015 #7
    background: Bsc Mathematician, Msc Computational Logic, Phd Non relativistic Quantum Mechanics....
    when i refer to space, of course i refer to spacetime....
    i wish that someone could be clear of what it is the proper elementary (level of practical mathematics) example for general relativity, and not just to declare what it is not...:)...
    If i wanted to search by myself i wouldnt have asked you for a straight answer :)....
    thanks anyway for your time!...
  9. Sep 16, 2015 #8
    I don't know what you mean with "stretched"... Anyway, it was rather well explained by Einstein in 1916 when discussing the weak field approximation in his scientific overview of GR, and you can read it for yourself on p.197, 198 of the English translation, here: http://web.archive.org/web/20060829045130/http://www.alberteinstein.info/gallery/gtext3.html
    His explanation of rods and clocks (leaving out the derivations) is very suitable for high school students.
  10. Sep 16, 2015 #9


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    You can look at the articles here, starting from the bottom:

    Try to get this book:
    Relativity Visualized by Lewis Carroll Epstein

    Some videos:

  11. Sep 16, 2015 #10
    thanks everyone of you!....
  12. Sep 16, 2015 #11


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    If you have a PhD in physics, then you should be able to follow a standard text on general relativity. Why do ask for an elementary example?
  13. Sep 16, 2015 #12
    because my friend i dont have time at all to search at this moment cause i have to present my phd thesis....i was expecting that someone would offer me just a simple elementary example of general relativity to promote it to a student of mine...if i had time for sure i wouldnt ask noone from her...thanks anyway for the interest!
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