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    I just had some inspiration to start this thread, which I am now starting to think was horrible misguided, lol... Yet, here we are!

    Which theory do you personally find more plausible, and why?

    I will say in simplistic terms, so as not to embarass myself; that I feel there will be a big crunch. This is based on no real maths, or facts. I think that inside, I like the idea that the universe exists in a cyclical mode. I would like to imagine that there is big bang, crunch, rinse and repeat. The whole idea of perpetual conservation of all physical quanitities is somehow appealing to me.
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    Depends on the exact amount of matter in the universe (whether it exceeds the critical density) so I think either is equally plausible.

    There is also the colliding brane theory, which I don't really know much about which would make the big crunch (or the perpetual cycle of universe creation/destruction) more likely.
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    the only thing we can do is guess....... as it all depends on the amount of matter.... and it isnt exactly easy to measure whether there is enough to casue a big crunch........
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    (Original post by [_Z_])
    the only thing we can do is guess....... as it all depends on the amount of matter.... and it isnt exactly easy to measure whether there is enough to casue a big crunch........
    An accurate, but BORING answer... Meh, I should have asked the philosophers
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    I've just started to learn those harsh theories myself since I passed grade 10(one year ago). But I've made little progress in getting into them. Man are trying to find out what controls the whole universe even our thoughts. I myself rather suspect that if we finally find the head law, how sure we are that the law is true because the law itself manipulates our thoughts so that it can make us misunderstand.

    In my opinion, simple laws like Newton's or Maxwell's ,useful for every day life, are the most important. They can pull lives up from poverty or hardship.

    However,I am really interested in those mysterious events happend in an early universe. It makes me feel good whenever I try to understand.
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    I think the critical value is density (well i guess that's equal to mass in fixed amount of the universe at this time). Check ou scientific american earlier issue this year; they claimed the universe existed before the big bang! So in my opinion all hints point to a cyclical life. Doesn't this make us feel so insignificant :'( like drops in the ocean!!!

    O well I leave you with that bitter taste in your mouth Cyaz
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    (Original post by Wagamuffin)
    I think the critical value is density (well i guess that's equal to mass in fixed amount of the universe at this time).
    Yeah, it's density. The whole "fate of the universe" thing is usually talked about in terms of Ω (the ratio of the density of the universe to the critical density) though.
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    Hiya! Was it RobbieC who started this thread? One thing - it sounds like an extremely interesting thread, but the trouble is, half the people probably won't be able to even reply to this thread cus they don't do physics! And some others are the ones who aren't interested - which really does cut down the amount of replies you're gonna get! I'd love to know more about all this big bang, crunch, quantum theory (in one word, physics) stuff - but care to explain the details and new theories that will enable one to understand the thread and therefore reply? Cus so far all I can say is "depends on the density blah blah blah" - there isn't anything more interesting being commented.

    But I'd love to know the details, despite the fact that I probably won't understand half of it! (haven't done physics in a year and at GCSE level you really don't do interesting stuff like this.)
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    It's impossible to say, either there will be enough mass to generate enough gravity for the big crunch, not enough mass and so it will continue forever, always expanding; or it will be equal to the outward force and stay in a steady state.

    No one of those is more likely than the others, but I have a feeling deep down inside me that we will crunch one day, does anybody else wake up with that crunchey feeling sometimes?
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    (Original post by irisng)
    Hiya! Was it RobbieC who started this thread? One thing - it sounds like an extremely interesting thread, but the trouble is, half the people probably won't be able to even reply to this thread cus they don't do physics! And some others are the ones who aren't interested - which really does cut down the amount of replies you're gonna get! I'd love to know more about all this big bang, crunch, quantum theory (in one word, physics) stuff - but care to explain the details and new theories that will enable one to understand the thread and therefore reply? Cus so far all I can say is "depends on the density blah blah blah" - there isn't anything more interesting being commented.

    But I'd love to know the details, despite the fact that I probably won't understand half of it! (haven't done physics in a year and at GCSE level you really don't do interesting stuff like this.)
    I'm doing physics but so far have only done it at GCSE, so sorry but I don't know all the complicated facts.
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    (Original post by irisng)
    Hiya! Was it RobbieC who started this thread? One thing - it sounds like an extremely interesting thread, but the trouble is, half the people probably won't be able to even reply to this thread cus they don't do physics! And some others are the ones who aren't interested - which really does cut down the amount of replies you're gonna get! I'd love to know more about all this big bang, crunch, quantum theory (in one word, physics) stuff - but care to explain the details and new theories that will enable one to understand the thread and therefore reply? Cus so far all I can say is "depends on the density blah blah blah" - there isn't anything more interesting being commented.

    But I'd love to know the details, despite the fact that I probably won't understand half of it! (haven't done physics in a year and at GCSE level you really don't do interesting stuff like this.)
    Here's the story... and soneone will probably correct me on it, but oh well.

    Gravity pulls things together. Because of it, masses and energy are attracted. So we'd expect the force on the things in the universe to make them come inwards.

    In the early 20th century Hubble discovered that galaxies' redshifts were proportional to their distances - as redshift is a measure of velocity, so this basically means the further away a galaxy is from the Earth, the faster away it is travelling. Picture this in your head and wind back time... the most sensible argument is that everything began in a bang going outwards from the Earth's point.

    But then why are we so special to be in that point? We aren't... in truth we think that wherever we would stand in the universe, we would still see the same thing - everything moving away from us. The most common analogy is the balloon - stand on the surface of a giant balloon and when someone blows it up, you'll see everyone else move away faster. The main drawback is that this is a 2d example... only a 2d coordinate system is needed to give any position on the surface of the balloon. This is a good model of the big bang.

    Anyway, in the 1990s I think, some scientists analysed the velocities of distant galaxies and founf that the universe was actually expanding faster! So you'd think, if anything, after the big bang, because of gravity, the universe would either stop expanding and collapse, tend to a point where expansion was zero, or forever expand at a slower and slower rate. But these scientists found that since about 7 billions years after the big bang, (the universe is about 13.7 bn years old atm), the universe began expanding again.

    So now the question is why? There is believed to be repulsive gravity at work, like there was in the big bang. Yeah this is a suprise... gravity usually attracts things. But in special cases it is believed to cause things to repel. This is the belief of inflationary cosmology, a theory of the big bang.

    That's where dark energy comes in - currently the universe as we know it has 5% of the critical mass needed to experience the expansion we are seeing - scientists think another 25% is dark matter - matter that we cannot see that is spread throughout the universe, but there's the other 70%?

    That's the sroty as far as I understand. I skipped stuff about redshift and measuring the expansion because that would go off topic a bit but I'll say if it you want.

    And of course Eplaw or other university physicists.. please correct me if I'm wrong

    edit - after re-reading that's really sketchy, next time I try to recall the history of the universe I won't take breaks to play medal of honour. :confused:
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    In einsteins theory of relativity, he included a term called lamda, or the cosmological constant. Because at the time they thought the universe was static, but einstein knew that gravity would pull the universe together, so he included this term to account for that, basically it is the tendency for the universe to resist the pull of gravity.

    Einstein later called it the biggest mistake of his life when he discovered that the universe was expanding, there was no need for the cosmological constant.
    But recently scientists have started considering it as a viable part of the theory, because there does seem to be something causing the universe to expand faster, rather than slow down and collapse.
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    The most respected physical theory of all time must be the second law of thermodynamics. The overal entropy of the universe increases on average. Therefore, I find a big crunch, where the entire universe is smashed into a tiny sphere rather easily described by a mathematical formula to be much more unlikely than a vast homogenous mixture of particles and radiation.
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    (Original post by Jonatan)
    The most respected physical theory of all time must be the second law of thermodynamics. The overal entropy of the universe increases on average. Therefore, I find a big crunch, where the entire universe is smashed into a tiny sphere rather easily described by a mathematical formula to be much more unlikely than a vast homogenous mixture of particles and radiation.
    Remeber that the second law of thermodynamics is an empirical law and is not absolutely neccesarily true. There may be places in the universe where energy is being created.
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    That's a good point, I never thought of that

    except if there was a big crunch, there would be so much energy radiated that the overall entropy might still rise
 
 
 
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