Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Could the expansion of space tear us apart?

  1. Mar 7, 2015 #1
    Is it possible that the forces behind the expansion of space could at some point overcome the fundamental forces holding our molecules together?
     
  2. jcsd
  3. Mar 7, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    That idea is known as big rip. Possible, but it does not look likely.
     
  4. Mar 7, 2015 #3

    Chalnoth

    User Avatar
    Science Advisor

    I think that may be overstating the situation a bit.

    The big rip scenario requires a violation of some of the energy conditions of General Relativity. I'm not sure it's possible to write a sensible theory of gravity if those energy conditions are violated.

    So we can't say for sure that it's impossible, but it's probably impossible.
     
  5. Mar 7, 2015 #4

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    Sure it is. Dark energy violates energy conditions, but we have perfectly sensible models in GR that include dark energy. Solutions that violate one or more of the energy conditions don't have certain "nice" properties, but they're still valid solutions.
     
  6. Mar 8, 2015 #5

    bapowell

    User Avatar
    Science Advisor

    The negative kinetic energy of phantom fluids makes them unstable. It's all a matter of decay timescales: http://arxiv.org/abs/astro-ph/0301273
     
  7. Mar 9, 2015 #6

    Chalnoth

    User Avatar
    Science Advisor

    Dark energy only violates the strong energy condition (a condition that is violated in other contexts as well), the "big rip" scenario violates them all. In particular, it violates the weak energy condition which requires that the observed mass density be non-negative for all observers. Negative mass can lead to all sorts of nasty consequences.
     
  8. Mar 9, 2015 #7

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    Yes, agreed. Solutions that violate all of the energy conditions are most likely unphysical. But solutions that only violate some (like ordinary dark energy) can be physically reasonable. In post #3 you said "some", which was why I commented. :wink:
     
  9. Mar 13, 2015 #8
    if my understanding is correct, the big rip hypothesis says that if the ratio between dark energy pressure and it's density is > -1 then the universe will eventually be pulled apart and that an instant before the end atoms will be destroyed
     
  10. Mar 13, 2015 #9

    Chalnoth

    User Avatar
    Science Advisor

    Yes, essentially. In the model, the cosmological horizon is constantly decreasing in size. Eventually the horizon will get so small that it will be impossible for atoms and even atomic nuclei to hold together.
     
  11. Mar 14, 2015 #10

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Specifically, to judge for yourself how unlikely, look at the latest Planck results. The equation of state number w is measured to be WITHIN 5% of the value -1 which it has in the standard LambdaCDM model (cosmological curvature constant Lambda, no big rip)
    The standard cosmic model has an INCREASING horizon distance that goes to an asymptotic value of 17.3 billion LY.
    Not a DECREASING horizon distance that gets down to atom size. Huge difference.

    Successive measurements keep nailing w down closer and closer to -1. So google [planck 2015 cosmological parameters] to get the report:

    http://arxiv.org/abs/1502.01589
    Planck 2015 results. XIII. Cosmological parameters
    Planck Collaboration: ...
    (Submitted on 5 Feb 2015...)
    ==abstract==
    We present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. ...
    ...
    ...The equation of state of dark energy is constrained to w = -1.006 +/- 0.045. Standard big bang nucleosynthesis predictions for the Planck LCDM cosmology are in excellent agreement with observations. We investigate annihilating dark matter and deviations from standard recombination, finding no evidence for new physics. The Planck results for base LCDM are in agreement with BAO data and with the JLA SNe sample. However the amplitude of the fluctuations is found to be higher than inferred from rich cluster counts and weak gravitational lensing. Apart from these tensions, the base LCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.
    ==endquote==
     
    Last edited: Mar 14, 2015
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Could the expansion of space tear us apart?
  1. Expansion of space (Replies: 28)

  2. Expansion of Space (Replies: 54)

Loading...