astronomers use a cluster of galaxies as a giant lens

that's the basic conclusion, that there will be no contraction, no "critical" point that will reproduce the big bang. we've been seeing the universe as accelerating in its expansion for a while, which can only mean 1. the universe is accelerating in its expansion indefinitely 2. the universe is accelerating in its expansion temporarily (unlikely but not impossible) 3. we're not measuring it properly, or we're off in our mathematical definitions of gravity/time/dark energy

3 is the most likely imo

To be honest the idea of eternal entropy makes me sad. I very much prefer the big bang/big crunch cyclical thing.

To be honest we don't know enough about the so-called dark energy to make any predictions at all. We don't know any of its properties or how it will act in different situations, we don't even know if it exists or if there is something else causing the accelerated expansion. We only assume it's some kind of energy that repels everything.

what's amusing is einstein introduced something called the cosmological constant into his later work to explain the way that gravity seemed to strangely be repulsive rather than attractive at great distances, something he later called 'the greatest mistake of my career'. we now seem to be at a point where dark matter/energy seem to fulfil almost the exact role which einstein assigned to the cosmological constant.

  On 8/25/2010 at 5:37 PM, kaini said:

what's amusing is einstein introduced something called the cosmological constant into his later work to explain the way that gravity seemed to strangely be repulsive rather than attractive at great distances,

I think you'll find he introduced it because he didn't like the idea that the universe would be expanding or contracting, as predicted by the theory with no cosmological constant (this was before Hubble's discovery that the universe was expanding, obviously).

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something he later called 'the greatest mistake of my career'. we now seem to be at a point where dark matter/energy seem to fulfil almost the exact role which einstein assigned to the cosmological constant.

Dark matter has nothing to do with the cosmological constant AFAIK - rather it's necessary to explain why the gravity necessary to explain the behaviour of large-scale objects like galaxies is too big to be caused by the mass we can actually see (although we may have "seen" dark matter recently, via gravitational lensing either side of a cloud of dust which was created when two smaller clouds collided).

The current consensus is that the cosmological constant is small but non-zero.

  On 8/25/2010 at 6:50 PM, Rotwang said:

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something he later called 'the greatest mistake of my career'. we now seem to be at a point where dark matter/energy seem to fulfil almost the exact role which einstein assigned to the cosmological constant.

 

Dark matter has nothing to do with the cosmological constant AFAIK - rather it's necessary to explain why the gravity necessary to explain the behaviour of large-scale objects like galaxies is too big to be caused by the mass we can actually see (although we may have "seen" dark matter recently, via gravitational lensing either side of a cloud of dust which was created when two smaller clouds collided).

 

The current consensus is that the cosmological constant is small but non-zero.

my point is it fulfils the same role; it may be slowing expansion in a physical sense in a manner similar to the cosmological constant in einstein's equations. it's kind of ironic.