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Will the expanding universe really end up cold and empty?

  1. Aug 13, 2012 #1
    If you take it to its extremes and space continues to expand at an accelerated rate, what happens when?

    1) space is expanding so fast that virtual particles cannot annihilate.
    2) if the space between quarks ends up expanding then the energy needed to pull them apart will spawn new quarks.

    As I see it it should end with a sea of quarks that end up multiplying at an enormous rate.
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  3. Aug 13, 2012 #2


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    This is the standard result of the current big bang model --- everything end up cold and dark and every galaxy has it's own observable universe with nothing else in it.

    this is the "big rip" scenario and is speculative

    I don't know about that even in the big rip.
  4. Aug 13, 2012 #3
    Hope this explains better.

    If space expands fast enough then virtual particles created by the vacuum are drawn away from each other so fast they cannot annihilate, therefore they become real.

    The weak force that binds quarks together gets stronger with distance, if you try to pull two quarks apart you have so much energy in such a small space that it spontaneously creates a new quark.

    Therefore if the expansion of space continues to accelerate then eventually it will try and tear the quarks apart, but nature wont let you do that. Quarks would be generated at an exponential rate and I can't imagine this event being cold :)
  5. Aug 13, 2012 #4


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    According to the standard model, which gives a pretty good fit to the data, the acceleration is not as you imagine it.

    People get fooled by the word "acceleration".

    If you pick a definite length, like a million lightyears, the speed distances of that length are destined to grow is supposed to DECLINE.

    In the future, any given length will be growing MORE SLOWLY than it is today.

    Nothing will be pulled apart, a "sea of quarks" will not be created. I'm talking about the standard LambdaCDM cosmic model that cosmologists use. There are some wild scenarios that people used to write more about in the early 2000s. But they write less about that now. Fewer researchers are interested. The data continues to confirm that Lambda the cosmological constant is, well, constant :biggrin:

    So our experience of expansion will only get milder rather than more severe. No "big rip".

    When astronomers talk about "acceleration" of distance growth they mean something different. It's like money in a savings account where the bank pays you a rate of interest that slowly declines over time say down to some basic floor rate. If the decline is slow, your account can still grow almost exponentially because each year the PRINCIPAL is bigger, so you get more interest on you account (even though the percentage rate may have declined slightly).

    So if you watch a particular distance between two observers at rest relative to background, that distance will grow like a bank account with a slowly declining rate of interest and it will therefore accelerate.

    Even though the interest paid on some definite amount, like $100, declines over time.

    Sizes of ordinary things, like books, stars, or galaxies are not affected in any significant way by this expansion. However INTERGALACTIC distances, if they are large enough, and span between objects essentially at rest wrt background, are effected according to the standard expansion pattern. So far in the future our galaxy will have very few neighbors!

    You could say that this makes the place cold and lonely. But the main trouble with the longterm future, I think, is that stars eventually burn out.

    If it weren't for that, the future would look pretty much like the present (except you wouldn't see galaxies thru a telescope---astronomy wouldn;t be as much fun.)
    Last edited: Aug 13, 2012
  6. Aug 13, 2012 #5
    I thought the energy of space kind of grows over time, because there is more space!

    As I understood it the other galaxies will eventually end up at distances where they effectively vanish because space is expanding so fast that signals cannot reach us from them and that gravitationally bound systems will eventually be torn apart and then trillions of years later the atoms too.

    I've heard the description many times I'm just adding something that seems to have been left out regarding the properties of quarks, they cannot be isolated in space they have to be in pairs.
  7. Aug 13, 2012 #6


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    Exciting scenario isn't it? People used to talk about that scenario more 10 years ago, or even 5 years ago. But it requires special assumptions that so far people have not found any supporting evidence for. So in professional research now much less heard about it.
    As a verbal scenario it is exciting and appeals to lay audience, so may still be part of the schtick used by popularizers. Stimulates the imagination.

    I would suggest you first learn the standard cosmic model LambdaCDM and use that as your homebase. then if your taste runs to dramatic speculative scenarios you can branch out from there. Start at mainstream homebase with the model used by almost all working cosmologists (that you'd learn in a standard college intro course) and then if you want to, try varying parameters, equations of state etc, to get spectacular effects.
  8. Aug 14, 2012 #7

    I've listened to loads of cosmologists describe the so called death of the universe and they all describe a point in time when the runaway expansion of space eventually tears atoms apart. Where is the evidence that at some point in the future the accelerated expansion of space is going to slow down?

    I searched google for "LambdaCDM" and found a wiki page.

    But this also seems to be describing an accelerating expanding universe with no predicted slowing down in the future.
  9. Aug 14, 2012 #8


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    Here's what I said. I don't think you understood. I'm glad you went and found the Wikipedia article on LambdaCDM, but it does not say the model forecasts big rip (you need an extension e.g. involving "quintessence" but that's not talked about much any more---the constant in that case is not a constant :biggrin:) The plain LCDM without quintessence is what I'm talking about here.
    Basically LCDM says that Hubble rate is now 70.4 km/s per Mpc and is declining and in distant future will be 60.1 km/s per Mpc.

    That means if you look at a Mpc length now (distance between stationary observers) it is growing 70.4 km/s
    And in the future if you take distance that same Mpc (megaparsec) length it will be growing only 60.1 km/s.
    This does not contradict what astronomers mean when they say accelerating expansion.
    The LCDM model has accelerating expansion, just very mild.
    Eventually distances will be growing at a constant percentage rate of 1/163 of a percent per million years. This involves acceleration like a savings account grows more rapidly as the principal increases.
    But the percentage rate is actually lower than what we have today.

    Perhaps someone else will be able to help you understand that the standard LCDM DOES have accelerating expansion, at a declining percentage rate, and DOES NOT predict a big rip. I've done the best I can to explain it it to you.
  10. Aug 14, 2012 #9
    Aaaaaaaaaaaah now I get it, I've never heard that before. Now I understand why the big rip thing won't happen. Everything I've seen on the television describes an accelerating expansion that's exponential with time.

    This is the universes way of annoying me for daring to try and look at it :biggrin:
  11. Aug 14, 2012 #10


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    Welcome to the club :biggrin:
    Mass-audience telly can be treacherous, and it's true that nature herself can be a bit of a tease (however not basically malicious, it has been said.)
  12. Aug 19, 2012 #11
    If not you leave Earth, and travel towards any direction with a high velocity, and suddenly new galaxies will appear :wink: !
    Even though this scenario was practically full of problems to overcome as I and marcus did discuss a few weeks ago - but imagination is important!
  13. Aug 19, 2012 #12

  14. Aug 20, 2012 #13
    I did a bit of work on the big rip as a grad. student, and the answer to this (as can be expected) is that it depends on how the big rip is approached. If the dark energy equation of state parameter w stays relatively constant leading up to the big rip, then the scale factor goes like a power law expansion. In this scenario, for realistic values of w, dark energy wins; particle production stays negligible until well after the curvature reaches the Planck scale. (Edit: I should note that there is some disagreement in the literature about this, but I disagree with the disagreement.)

    If you allow w to time vary, then you can probably generate any amount of particle production that you wish.
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