Results 1 to 11 of 11

Thread: Universe likely to end before Sol leaves Main Sequence?

  1. #1
    Join Date
    May 2004
    Posts
    1,848

    Universe likely to end before Sol leaves Main Sequence?

    And I was so looking forward to seeing the Sun's planetary nebula :-)
    http://www.technologyreview.com/blog/arxiv/25807/

  2. #2
    Join Date
    Oct 2005
    Posts
    26,636
    From that site:
    The only way out of this conundrum is to hypothesise some kind of catastrophe that brings an end to the universe. Then all the probabilities make sense again and the laws of physics regain their power.
    Now, science explains what we see, and we tend to see what it explains, but what we can see, explain, and understand never get together to decide what is-- that's placing the cart before the horse. It seems like people outside of science often fail to understand what science even is-- yet here we have people at the center of basic science, and I've never in all my life seen a more obvious example of that problem than the above quote. What horrendous science-- for distinguished scientists to make such a rookie mistake is appalling! The universe has to be built so that we can understand it? Which scientific principle is that?
    Last edited by Ken G; 2010-Dec-30 at 07:03 AM.

  3. #3
    Join Date
    Apr 2006
    Posts
    1,643
    Reading the paper it looks more like an argument against eternal inflation than for an end of time.

  4. #4
    Join Date
    Oct 2005
    Posts
    26,636
    Perhaps then it should be framed as "why we cannot take this particular model too seriously" rather than "why we know the future of our universe without looking." It sounds like you are saying the error may be with the science writer moreso than the authors. That could certainly be, I was taking the article at face value-- a dangerous thing to do.

  5. #5
    Join Date
    Apr 2006
    Posts
    1,643
    Actually the writer seems to have done a fairly good job of explaining what the authors were saying and even pointed out the crux of the matter:-
    The imminent end of time is a little unsettling but the argument is by no means water tight. Among other things it depends crucially on an important assumption about the laws of physics: that we ought to be able to understand why they work, not just observe that they do work. And that's a philosophical point of view rather than a physical argument.
    The authors have a point, probabilities are only rigidly defined when there are a finite amount of outcomes so having a spacetime expand eternally is a problem for theories based on statistical distributions, like quantum theory. It means the theory can't be applied consistently to cosmological observations. To rescue cosmological QT (as it stands) from eternal inflation requires a finite temporal extent along with either a geometrical or causal cut-off of some kind.

    Personally I think it the paper is saying more about the limitations of QT than about the limits of the universe. It will all get fixed when QG comes along!

  6. #6
    Join Date
    Oct 2005
    Posts
    26,636
    I think that quote says it well-- which raises the question of why the philosophical stance of a few physicists is science news! Let them publish their idea in a philosophy journal instead-- and watch what happens when they try to support their view to the standards of a philosophy argument, rather than rest on their scientific laurels as justification for holding any view they want.

  7. #7
    Join Date
    May 2004
    Posts
    1,848
    Well, I emotionally prefer the idea of everything happening an infinite number of times to the universe ending in the astronomically near future, but then the cosmos was never obligued to please me!

  8. #8
    Join Date
    Oct 2005
    Posts
    26,636
    The idea that the exact same thing can happen more than once is already philosophically questionable. If it's exactly the same thing, how can it be said to be happening "again", instead of just "happening"? In other words, how could we say that we do or do not relive today a billion times before moving on to tomorrow-- if "today" is exactly the same, right down to every memory that is in our minds when the day begins? If a certain concept is never used to make a prediction about what we will experience, then science has nothing to say about it.

  9. #9
    Join Date
    Nov 2005
    Posts
    3,464
    Eternally is a long time. Observed phenomenon typically start out fast expansion and decelerate. A mechanism is needed to cause acceleration to increase after the initial start. Assuming a mechanism is causing the acceleration, it = the mechanism is stretched thin after a few orders of magnitude of expansion = the acceleration becomes negligible. Mechanisms decelerating the expansion are really tiny, but in a google years, likely sooner, they will overwhelm the accelerating expansion = not eternal. Where am I thinking wrong?
    Worse: Consensus seems to be that our local group of galaxies is not expanding. If so, it will still be here in a google years, even if the average density of the universe is reduced by a trillion trillion times = 10E24 times. The presently negligible effect that the Universe has on our local group will become even more negligible as the universe expands to negligible average density. We have nothing to fear from the expansion of the universe even if it persists forever. Neil

  10. #10
    Join Date
    Oct 2005
    Posts
    26,636
    Quote Originally Posted by neilzero View Post
    Observed phenomenon typically start out fast expansion and decelerate.
    That has not been the observed history of our universe.
    A mechanism is needed to cause acceleration to increase after the initial start. Assuming a mechanism is causing the acceleration, it = the mechanism is stretched thin after a few orders of magnitude of expansion = the acceleration becomes negligible.
    Not so for the mechanism thought to be responsible for the acceleration of the universe: the antigravity properties of vacuum. In that case, the more vacuum you have, the more it wants to accelerate the expansion.

  11. #11
    Join Date
    May 2005
    Posts
    1,810
    From the article:
    When there are an infinite number of instances of every possible observation, it becomes impossible to determine the probabilities of any of these events occurring.
    This does not logically follow.

    There are an infinite number of both even and odd integers. The probability of a randomly selected integer being even or odd is known precisely.

Similar Threads

  1. When the Sun leaves the main sequence how far out will the HZ shift?
    By PinkishDinosaur in forum Space/Astronomy Questions and Answers
    Replies: 4
    Last Post: 2011-Sep-11, 12:18 AM
  2. Crossing main sequence
    By chornedsnorkack in forum Space/Astronomy Questions and Answers
    Replies: 10
    Last Post: 2011-Jun-10, 01:28 AM
  3. Gravitational Redshifts: Main Sequence vs. Giants
    By Fraser in forum Universe Today
    Replies: 5
    Last Post: 2010-Nov-30, 09:43 PM
  4. Main Sequence Question
    By torque of the town in forum Space/Astronomy Questions and Answers
    Replies: 4
    Last Post: 2008-Oct-11, 03:39 PM
  5. A Mass And Main Sequence Question
    By BigDon in forum Space/Astronomy Questions and Answers
    Replies: 16
    Last Post: 2008-Apr-06, 01:23 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •