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Space is expanding?

  1. Oct 10, 2004 #1
    If all space is expanding, does this include the space between the Earth and the Sun and perhaps. the space between a nucleus and an electron.
  2. jcsd
  3. Oct 10, 2004 #2
    Yes, some even think that eventually there will come a "big rip" - that the acceleration in expansion will continue to the point where even atoms and subatomic particles are ripped apart due to the expansion of space. But if the expansion or cosmological constant is dependent on the other things such as the amount of mass in the universe, then perhaps the acceleration will slow at some point in the future.
  4. Oct 10, 2004 #3
    No, systems which are bound together have become decoupled from the general expansion of the universe.

    Mike2, don't confuse expansion with acceleration in expansion.

    Also, if there is acceleration in expansion, i.e. a positive cosmological constant, then we would assume that it have a local effect. However, this won't cause the distance of the earth from the sun to increase, the orbit will just be different from what would have otherwise been the case.

    The big rip requires increasing acceleration in expansion.
  5. Oct 10, 2004 #4
    The reason I ask is I was wondering if space was not expanding would the Earth actually spiral towards the Sun
  6. Oct 10, 2004 #5
    Are you not indirectly agreeing with Mike2 when you say that accelerated expansion in the universe can have a local effect within the solar system?
  7. Oct 10, 2004 #6


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    The expansion force is trivial, even compared to gravity [which is a real weakling compared to the other three]. Expansion only occurs on a cosmological scale.
  8. Oct 11, 2004 #7
    Indirectly perhaps, but the point I was making was that it wouldn't cause the earth-sun distance to increase over time. Likewise if it were removed, then if wouldn't mean that the Earth would spiral into the sun.
  9. Oct 11, 2004 #8


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    As Chronos said, the expansion force is overcome by atomic forces, gravity forces within a galaxy, etc....so the expansion only becomes significant over vast, intergalactic distances.
  10. Oct 20, 2004 #9


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    Before good observations of distant supernovae (and later, considerably more detailed views of the angular power structure of the CMBR), the rate of expansion of the universe was thought to be declining ... the Hubble constant becoming smaller over time (not counting the very early 'inflationary era' of course!). As observations keep coming in, what may have been just a statistical fluke, or effects of an entirely different nature, is looking more and more like an acceleration of the expansion rate (there are, it should be noted, still alternative views, and the data is perhaps 10 years from being truly compelling).

    But what is the nature of this acceleration? Is it, as one poster noted, a big rip? While modest today, will it get stronger and stronger, overwhelming first gravity, then EM (which holds molecules together), and finally even the strong force?

    Might it simply be Einstein's cosmological constant? Or Dark Energy of a quite different kind, quintescence perhaps?

    All very good questions ... FWIW, it seems to be more like a constant, or varying only very slowly with time (a few % per billion years?). A great time to be doing astronomy! :smile: :approve: Too bad research funds are so tight :cry:
  11. Oct 20, 2004 #10
    What would you call the theory that we are simply loosing touch with the gravitational field of those galaxies that are disappearing behind the cosmological horizon so that the pull of gravity is getting weaker and so the universal expansion seems to be accelerating?
  12. Oct 20, 2004 #11


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    Inconsistent with observation. If distant masses are disappearing behind a cosmological horizon, wouldn't you lose the gravitational assistance they provide to expansion from our reference frame?
  13. Oct 20, 2004 #12
    Well, let's see, roughly speaking E=K+U, the total energy of a system is equal to the sum of the kinetic energy and the potential energy. And generally this is conserved. I know that in GR that they do not speak of potential energy since gravitational potential would propagate through spacetime like a wave and takes time to get there. But I assume after a long enough time that gravitation potential will average out and at least appear Newtonian.

    Now imagine reducing the mass in the system, U will become less and K will speed up.
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