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B If spacetime can be bent can it be broken?

  1. Aug 24, 2017 #1
    A planet or star can bend space time around it.The greater the mass the greater the gravitational well.Could a black hole actually be such an enormous mass as to pierce space time and create a worm hole to another dimension?Also could the effects of the other dimension explain the weird effects on gravity in our galaxies?
     
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  3. Aug 24, 2017 #2

    Drakkith

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    No, to the best of our knowledge there is no evidence for other dimensions and no known way to "bridge the gap" between them. The details of how spacetime behaves in and around a black hole are governed by General Relativity and GR has nothing in it about other dimensions.

    There are no valid theories that use this method to explain the unknown behavior of galaxies and other matter. The closest idea that I can think of is the extra dimensions of string theory, but those are very, very different than what you're proposing.
     
  4. Aug 24, 2017 #3
    If space time is a pliable material as Einstein correctly describes.It stands to reason that under sufficient pressure it can be pierced.
     
  5. Aug 24, 2017 #4

    Drakkith

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    Spacetime is not a pliable material. It is not a material at all. It is geometry and that's it. Just geometry.
     
  6. Aug 24, 2017 #5
    Material was obviously the wrong word.pliable geometry then.
     
  7. Aug 24, 2017 #6
    And what does "pliable geometry" suppose to mean? Geometry is geometry, I think that you are misguided by rubber sheet analogy. Geometry cannot be pierced, wormholes you mentioned are still part of the geometry.
     
  8. Aug 24, 2017 #7
    Ok let's forget material and pliable geometry.We are getting tripped up on my wording.spacetime is pliable! So it stands to reason it can be pierced like a rubber glove.Thats how my mind works.Please explain to me in lay mans terms why that's not so.
     
  9. Aug 24, 2017 #8

    jbriggs444

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    Substances can be pliable. Spacetime is not a substance. Spacetime is not pliable.
     
  10. Aug 24, 2017 #9
    Spacetime is not pliable.so it doesn't bend under a mass such as a planet or star to create a gravitational well?
     
  11. Aug 24, 2017 #10

    jbriggs444

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    No, it does not.
     
  12. Aug 24, 2017 #11

    Drakkith

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    No it does not. The concept of "pliability" cannot be applied to spacetime. Pliability is a property of objects, not of spacetime or geometry. Pliability and stiffness (the opposite of pliability) are quantifiable properties that depend upon the specific structure and type of matter making up the object. Since neither spacetime nor geometry is an object, pliability does not apply to them.

    Or you could make the slightest effort to understand what we're saying and not berate us for trying to correctly explain an extremely complicated subject to you.

    No, not in the sense of an object bending. What happens is that the geometry of spacetime is changed. This is NOT "bending", "stretching", or any of the commonly used descriptions you often hear and read about. Those are just the closest non-technical words we have to describe it.
     
  13. Aug 24, 2017 #12
    Ok thanks I think I understand better now.so there are no ripples in space time.no gravitational waves and absolutely no bending! A gravitational well doesn't exist except in an imperfect description.
     
  14. Aug 24, 2017 #13

    jbriggs444

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    There are features that we refer to as gravitational waves and potential wells. But describing those as being caused by spacetime "bending" "under" a "mass" is not correct.

    Or at least not correct enough to use as a basis for reasoning by analogy that something which can "bend" must necessarily be able to "break". The analogy is not close enough to reason with like that.
     
  15. Aug 24, 2017 #14

    Drakkith

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    No, that is not what we said. Gravitational waves exist. These waves are in the "metric" of spacetime, and a metric is a particular mathematical way of describing something. If you were to ask, "what is waving?", then we'd need to get into the nitty gritty details of General Relativity, which is beyond my ability to explain. Suffice it to say, gravitational waves are described and explained perfectly well by GR.

    "Ripples" in spacetime refer to gravitational waves, so they are just another term to use that unfortunately adds confusion.

    Gravitational wells also fit perfectly fine in GR. It's just necessary to recognize that these wells aren't "dents" in spacetime like you commonly see in diagrams. Again, we'd need to get into the details of the physics and math to adequately explain it all. The simple analogy is that a gravitational well is sort of like a water well. It takes energy to lift the water bucket up and out of a water well. This energy is stored as potential energy and is turned into kinetic energy if you let the water bucket fall back down the well. Similarly, an object in a gravitational well will require energy to move it away from the source of the well, and letting the object fall towards the source of the gravity well will convert the potential energy into kinetic energy.
     
  16. Aug 24, 2017 #15

    phinds

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    @Wallsy, this "bending" of space-time is the result of pop-science applying our normal framework of Euclidean Geometry to a construct (space-time) to which it does not actually apply. Euclidean works great a local levels such as the Earth but on cosmological scales you have situations such as a light beam traveling past a planet or a sun or a galaxy. The light beam goes in a straight line but it is a straight line (more properly called a geodesic) in pseudo-Riemann geometry, which in the framework of Euclidean geometry is a curved line.

    As for space-time "stretching" that's just nonsense plain and simple --- it is exactly what you will hear most of the time in pop-sci presentations but not in serious physics discussions. I recommend the link in my signature.
     
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