Actual mechanics behind gravity

  1. This isn't a question but more of a request of opinion. How do you think gravity actually works, whether with gravitons, waves, or space-time bending to physically interact with matter etc. Not just what the theory says gravity does but what you think actually causes the effect.
     
  2. jcsd
  3. atyy

    atyy 10,065
    Science Advisor

    In the theory of general relativity there are two sorts of visualizations. First, gravity can be imagined as the curvature of space; secondly it can be imagined as something that causes rulers to bend and clocks to run slow. General relativity is presumably wrong at some level, so a lot of people are working on a new theories with a new pictures (strings, string nets etc). We don't know which, if any, of the new theories give experimentally correct predictions yet. You could look at discussions about this in the "Beyond the Standard Model" forum.

    Claus Kiefer, Quantum Gravity: General Introduction and Recent Developments, http://arxiv.org/abs/gr-qc/0508120
     
  4. I will not answer your question because it exposes how dopey we people are!!!!

    Most of physics is incomplete at some level (lot's of opportunities left) and that may be why we usually need several explanations, several different viewpoints, to understand phenomena. Or maybe it's because our senses and intuitions are based on inaccurate superficial impressions often far removed from what "really" goes on.

    As if that were not enough to cause complications in explaining phenomena, mathematics itself (while a great tool) offers many solutions that have no basis in physical reality, as well other solutions that do match reality in this universe, and even those solutions that do are often subject to different physical interpretations.... Add uncertanty on small scales : no matter what we try to understand about how stuff "really works" it appears nature will not let us make simultaneous perfect readings on stuff like energy/time, position/momentum ...and on large scales: nobody can see everything...the universe is observer dependent because it's too big...Each observer, in general, sees a different piece of the pie.
     
  5. Hurkyl

    Hurkyl 16,090
    Staff Emeritus
    Science Advisor
    Gold Member

    Matter follows geodesics, and curves the space around it, of course.

    Er... "what the theory says" represents the culmination of all of our collective knowledge and experience regarding the universe, and has been very well-tested by observation. For the most part, wouldn't you think it incredibly arrogant for anyone to think they know better?
     
  6. Jonathan Scott

    Jonathan Scott 1,342
    Gold Member

    At present, General Relativity is the most successful theory we have, and it is typically summed up in John Wheeler's words "Matter tells space how to curve, and space tells matter how to move". We don't really even known what matter is, let alone how it curves space.

    Any ideas for explanations would therefore be new theories; if someone had a good one which really worked and remained consistent with the known GR experimental results, I think we would probably get to hear about it.

    I have some personal models which I use to visualise various aspects of gravity theory. For example, to visualise the relationship between "action at a distance" descriptions and "local field" descriptions, I imagine that anything containing energy emits spherical complex scalar waves expanding at c with the frequency associated with that energy (which is vaguely related to the sort of things that are assumed to happen in quantum theory). In that case, the divergence of the gradient (the Laplacian) of the total phase of that combined wave at any point is a scalar quantity which is equal to the sum of the energy of each source divided by its distance. Multiplied by G/c^2, that sum gives the total Newtonian gravitational potential, and the gradient of that potential is then the Newtonian field.

    Although I like to use that sort of model to help understand how things might work, I can also usually find ways in which the model does not work, or find completely different models for the same theory. This doesn't mean I need to throw the model away, but does mean I have to be cautious about its limitations, just as when using Newtonian theory as an approximation to GR.
     
  7. Jonathan has the best working model with Wheeler's quote...

    But as he notes that explains what happens not really why. Who's the "boss"?

    Another piece of the puzzle may be revealed when gravity is united with the other three forces (strong, weak, electromagnetic) that is, when general relativity and quantum mechanics are unified....there appear to be missing pieces at the moment, most evident at or near singularities like the big bang and black holes...meantime we do pretty well in most situations...
     
  8. LURCH

    LURCH 2,512
    Science Advisor

    Since the mechanics behind gravity are not known, any answer to this question would have to be speculative. Therefore, I speculate:

    In string theory, it is believed that all physical phenomena can be explained by multidimensional strings. As humans, our observations and subjective experiences of these phenomena are limited to the three dimensions with which we are most familiar. Perhaps gravity is the curvature of space-time that results when these hyper dimensional strings poke through our three-dimensional universe, bending its surface like a thread passing through the two-dimensional surface of a pan of water.

    Again, that was pure speculation. One field of science that attempts to actually described how gravity functions is "loop quantum gravity" (LQG). If you do a search for that here in the Forums, there are several discussions.
     
  9. jtbell

    Staff: Mentor

    If we ever find out How Gravity Really Works, how will we know that we have done it? :confused:
     
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?