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If the sun suddenly dissapeared.

  1. Dec 16, 2009 #1
    I have a question about this known hypothetical situation. Einstein asserts that once the sun vanishes we would still receive light for 8 min. Then at almost/same time when the sky goes dark, the gravitational wave hits earth and we would fall out of the earlier orbit around the sun.

    Some questions about the situation above.

    Have any experiments of this type been done? Confirming that a smaller object would not move, until the light from the bigger object had dissapeared?

    And would it be possible that once the sun disappeared the Earth could move, even though the gravitational wave did not reach the Earth?
     
    Last edited: Dec 16, 2009
  2. jcsd
  3. Dec 16, 2009 #2
    The Sun can't just "disappear". Conservation of energy and momentum prevents that. We can't even move it "out of the way" fast enough, it would have to be accelerated close to the speed of light, we don't know how to do that.
     
  4. Dec 16, 2009 #3

    bcrowell

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    Some relevant material here: http://www.lightandmatter.com/html_books/genrel/ch08/ch08.html#Section8.1 [Broken]

    The basic answer is that we have excellent evidence that gravitational waves exist, and that they carry energy, but we don't have any direct, model-independent evidence that disturbances in the gravitational field travel at c.
     
    Last edited by a moderator: May 4, 2017
  5. Dec 16, 2009 #4
    It's a hypothetical situation or a thought experiment if you will.
    I believe they do exist. But what I have in mind is if there are any other force holding the Earth with the Sun? If there is another force, then it would be noticable in such a situation.
     
    Last edited: Dec 16, 2009
  6. Dec 16, 2009 #5

    bcrowell

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    No, the only significant force on the Earth is gravity.
     
  7. Dec 16, 2009 #6

    DaveC426913

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    Well, you did ask if any experiments had been done...

    I'm almost afraid to ask but what makes you think there might be another force than gravity?
     
  8. Dec 16, 2009 #7
    My quote:
    "This type" in my lingo means something similar, something like the Gravity Probe B experiment. But I think it should be better be called a "thought experiment". Since such a situation is not possible.


    I don't know. I'm not good at sci-fi at the moment.
     
    Last edited: Dec 16, 2009
  9. Dec 16, 2009 #8

    DaveC426913

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    but something made you ask the question.

    Anyway, no. There are no other attractive forces known or hypothesized (though there are some repulsive ones, such as the solar wind).
     
  10. Dec 16, 2009 #9
    I don't know if I should be concentrating on the micro world with this logic or in the macro. But if it can be shown that a planet would move(even the smallest movement), then that could be a stepping stone for some further explanation between the difference of laws governing the micro and macro scale.
     
  11. Dec 16, 2009 #10

    DaveC426913

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    I completely don't follow.

    I'm not sure what micro vs. macro has to do with anything, but more importantly, it sounds like you're trying to invent a phenomenon out of whole cloth.

    Since there are no attractive forces acting between Sun and Earth other than gravity, nor is there any reason to think so, nor is there any reason to think the Earth does or would move ...

    ... what is the origin of the question?


    In the same sense (taken to a slightly more absurd level):
    Q: It is possible that Neptune is a unicorn? If it were, it should have a horn. Has anyone looked to see if it has a horn? Because of it did, that would be evidence that it was a unicorn.

    A: Um, why do you think Nepture might be a unicorn in the first place?
     
  12. Dec 16, 2009 #11

    DaveC426913

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    Wait. In re-reading your post, I realize that the whole Earth-Sun thing is not the crux of your question. This is the crux of your question:
    You're trying to sort out the quantum world versus the marco world.


    There's no real difference. Quantum effects (such as wavefunction frequency) manifest as inversely proportional to the size/mass of the object. A 100kg human has a wavefunction just like a proton does, it's just that the frequency is so high as to be irrelevant at the macro scale.

    A human can tunnel through a wall "just" like an electron can, but the probability is inversely proportional to the number of particles in the human.
     
  13. Dec 16, 2009 #12
    Ok, so I will try in other words. If I drop a pebble into the water, I will see waves forming. If I am in the water and a pebble falls. I can hear the sound of the pebble falling into the water sooner than the waves reach me, furthermore because I am in the water the pebble minimally affected me. Because there was a displacement of water.
     
  14. Dec 16, 2009 #13
    No, I think it would be wrong to say that the pebble directly affects me while in the water. I think the pebble might affect the space-time around me. Though I do think if it can somehow indirectly have an influence on me.
     
  15. Dec 17, 2009 #14

    Yes, I think you are right. But I don't know where now.
     
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