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Would Different Laws Of Physics Affect Gravity?

  1. Mar 22, 2005 #1
    For example if our universe had different laws would gravity as we know it now still be the same with different laws?
     
  2. jcsd
  3. Mar 22, 2005 #2
    Depends. The law of gravity is one of those laws but (so far I believe) it stands isolated from the other laws of physics?
    One could imagine a universe where the laws governing electrostatic force, the strong and weak force were all different from the ones we know, and yet gravity would remain the same. Obviously if you change the law of gravity then gravity would not be as we know it now (but I don't need to be a genius to see that :smile: )
     
  4. Mar 22, 2005 #3
    All of them

    but in the brane-theory they say that gravity would not get changed, is that true?
     
  5. Mar 23, 2005 #4
    Interesting. My understanding is that in the Ekpyrotic model the collision of two branes was the precursor to the Big Bang, and that the four forces (that we know of) subsequently condensed out in a form of spontaneous symmetry-breaking.... as far as I am aware the symmetry-breaking is supposed to have been completely arbitrary and there is no causal relationship between the branes and the precise properties of subsequent forces we observe - including gravity.
    Therefore, run the universe again and you would likely end up with completely different force laws.
    I may be wrong (and welcome any corrections), but that's my understanding of the theory. :smile:
     
  6. Mar 23, 2005 #5
    I dont know...maybe you are right
     
  7. Mar 23, 2005 #6
    I think that this would make more sense
     
  8. Mar 24, 2005 #7

    ohwilleke

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    While I think your real intent has been addressed by the other posters, your question itself seems a bit absurd. If the universe had different laws, gravity would be the same, unless it was one of the laws that was different.
     
  9. Mar 24, 2005 #8

    marcus

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    ohwilleke maybe there is a deep question hiding here

    let's say that a theory of gravity is a theory of spacetime itself, and suppose for the sake of argument that matter fields are built on spacetime as a kind of foundation.

    so then gravity looks more basic.
    like you can change the house without changing the foundation just by remodeling the superstructure
    but if you alter the foundation it necessarily affects the house that can be built on it.

    this is not an attempt to be rigorous

    maybe Goldbar's question can be interpreted as asking whether the model of gravity can be viewed as MORE BASIC than the other stuff, because it treats the context within which, or upon which, the other fields are defined.

    maybe the question can be phrased this way: Could you change the overlay of particle theory without that automatically changing the basic workings of gravity---or more precisely of spacetime geometry.
     
  10. Mar 24, 2005 #9
    Yeah I was trying to ask that but didnt know how to put it into words, sorry
     
  11. Mar 24, 2005 #10

    marcus

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    then congratulations, you DID put it into words and I got the meaning.
    not to worry. I actually dont know if there is a "correct" way to ask that

    to speculate a little, i would guess that if you could ask this question to Carlo Rovelli, whose book Quantum Gravity just came out, he would answer Yes, the gravitational field is somehow more basic than the other fields.

    for him, everything is fields but the other fields "ride on" the gravitational field.
    this may be typical of how relativists (specialists in general theory of relativity) think, as contrasted with people who picture there being a kind of rigid absolute space with a predetermined geometry in which all the fields (whether called particles or forces, and gravity included) are defined.

    relativists think of the gravitational field as the dynamic changeable geometry of the space within which other fields are defined. and they see the gravitational field as responding to matter as it moves around.

    so there is no fixed predetermined geometric framework, for the relativists,in an image rovelli has in his book, everything is animals (i.e. fields) but the other animals are riding on the whale's back
     
  12. Mar 26, 2005 #11
    I guess I'll need to read the book, but I'm not sure I see why gravitation needs to be any more fundamental than the other forces. The curvature of space depends on the masses within that space, and the properties of those masses depend on the symmetry breaking that is supposed to have occured way back when. Space did not exist prior to there being any objects within that space. What you are suggesting is that the geometrical properties of 3D space (at least the gravitational properties) were somehow pre-defined before the number of dimensions was determined and before space, matter or time existed. Rovelli is entitled to his opinion, but I don't see that this necessarily follows. The whole thing seems interconnected to me.

    Maybe it's not other animals riding on the back of a whale but (to paraphrase another great book) it's turtles all the way down?

    MF
     
  13. Mar 26, 2005 #12
    Gold Barz, you mentioned brane theory. What does that theory basically say?
     
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