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Thread: Big crunch again (Last time I swear!)

  1. #1 Big crunch again (Last time I swear!) 
    Forum Ph.D. Raziell's Avatar
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    http://i.imgur.com/HBj7E.jpg

    L
    ooking from that picture there is no saying how much bigger it gets. The last picture there could be a grain of sand in sahara, and even that could be a vast understatement beyond our understanding.

    Physicists tend to shoot down the idea of the big crunch theory with what I consider a very, very poor argument. That things isnt "moving/going that way" as we can observe.

    Consider if the universe was a lake and our milkyway is just a small bacterial colony on the surface in the middle. If one drop of rain hits near us, and we can observe that "The ripple is moving outwards" it doesent mean ANYTHING on a bigger scale.

    What we observe might aswell be some small local force in a machinery way to big for us to grasp. So again, please help me understand why this argument can be held in such a "Tight grip".

    Im sorry for bringing this up for the 74th time. Its not that Im trying to defend the big crunch theory as much as Im trying to understand why scientists seem to exclude it as probable.


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    I'm only an "armchair physicst", but I exclude it because gravity didn't stop the universe expanding when it was smaller and denser. The whole thing with gravity is that it alters the motion of things through space. Despite what you might hear about black holes and the waterfall analogy, it doesn't suck space in. And the expanding universe concerns the expansion of space. Gravity isn't making the galaxies move closer together, and even if it did all you'd end up with is a big universe with something like a black hole in the middle, still expanding. Not a small universe.

    If you've ever read anything about general relativity you'll notice that Einstein talked about stress-energy. Stress is like pressure only it's directionless, they're both measured in Pascals. So in a nutshell I'd say space expands because it's got an innate pressure. I don't know why Einstein didn't work this out, but think of the universe as expanding something like a stress-ball when you open your fist. Gravity affects the motion of waves through the stress-ball, but it doesn't make it contract back down again. There isn't anything that will do this, so I'm afraid the Big Crunch is reduced to little more than hypothetical woo peddled by wannabee celebrities with a book to plug.


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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by Raziell View Post
    Im sorry for bringing this up for the 74th time. Its not that Im trying to defend the big crunch theory as much as Im trying to understand why scientists seem to exclude it as probable.
    My understanding is that it is simply because the information we have is that the (observable) universe is expanding and that expansion is now accelerating.

    This is, as you say, purely based on the part of the universe wee can observe. One of the underlying assumptions of cosmology is the cosmological principle; basically that we are not in a special part of the universe and it is generally the same everywhere. We can only draw conclusions from the evidence we have.

    It is possible that outside the part of the universe we can observe, conditions are very different and the (larger) universe is collapsing. But we have no evidence to suggest that.

    It might be that outside the observable universe, everything is made of chocolate. But we have no evidence to suggest that.
    ei incumbit probatio qui dicit, non qui negat
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    Brassica oleracea Strange's Avatar
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    By the way, this question caused me to go and check the "anthropic principle" as well. I came across the lovely word "unbeheld". So thanks for that.

    only in a universe capable of eventually supporting life will there be living beings capable of observing any such fine tuning, while a universe less compatible with life will go unbeheld
    Anthropic principle - Wikipedia, the free encyclopedia
    ei incumbit probatio qui dicit, non qui negat
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    Oh no, not the anthropic principle! I don't know your views on that Strange and maybe it's a bit off-topic, but if it's something you're attracted to have a look at John Webb's site along with papers such as Indications of a spatial variation of the fine structure constant. The universe isn't necessarily the same everywhere.

    Also check out the criticisms section of the wiki article on the anthropic principle. Then look at NIST where you can read this about the fine-structure constant:

    "Thus α depends upon the energy at which it is measured, increasing with increasing energy, and is considered an effective or running coupling constant. Indeed, due to e+e- and other vacuum polarization processes, at an energy corresponding to the mass of the W boson (approximately 81 GeV, equivalent to a distance of approximately 2 x 10^-18 m), α(mW) is approximately 1/128 compared with its zero-energy value of approximately 1/137. Thus the famous number 1/137 is not unique or especially fundamental."

    It's a "running" constant. Which means it isn't constant. And it's the ratio of strong-force coupling to electromagnetic coupling. The guys at NIST and plenty of serious physicists and cosmologists have evidence that it varies, but the celebrity woo-mongers with a book to push ignore that. Take a look at the wiki fine-tuned universe article which says this:

    "If, for example, the strong nuclear force were 2% stronger than it is (i.e., if the coupling constant representing its strength were 2% larger), while the other constants were left unchanged] diprotons would be stable and hydrogen would fuse into them instead of deuterium and helium. This would drastically alter the physics of stars, and presumably preclude the existence of life similar to what we observe on Earth."

    Try squaring that with an α = eČ/2ε0hc that isn't actually some "Goldilocks" fine-tuned absolute constant. It just doesn't square. I'm afraid the anthropic principle is woo too. There's a lot of it about.
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by Farsight View Post
    I'm afraid the anthropic principle is woo too.
    It seems to me that the worst criticism that can be levelled against the anthropic principle in the sentence I quoted is that it is a truism; so obviously true as to be uninteresting. As such, the only reason I mentioned it was because of the use of the word "unbeheld".
    ei incumbit probatio qui dicit, non qui negat
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