Posted on 05/04/2006 12:02:17 PM PDT by PatrickHenry
Big bounces may make the Universe able to support stars and life.
A bouncing universe that expands and then shrinks every trillion years or so could explain one of the most puzzling problems in cosmology: how we can exist at all.
If this explanation, proposed in Science1 by Paul Steinhardt at Princeton University, New Jersey, and Neil Turok at the University of Cambridge, UK, seems slightly preposterous, that can't really be held against it. Astronomical observations over the past decade have shown that "we live in a preposterous universe", says cosmologist Sean Carroll of the University of Chicago. "It's our job to make sense of it," he says.
In Steinhardt and Turok's cyclic model of the Universe, it expands and contracts repeatedly over timescales that make the 13.7 billion years that have passed since the Big Bang seem a mere blink. This makes the Universe vastly old. And that in turn means that the mysterious 'cosmological constant', which describes how empty space appears to repel itself, has had time to shrink into the strangely small number that we observe today.
Cosmic disagreement
In 1996, it was discovered that the universe is not only expanding but is also speeding up. The cosmological constant was used to describe a force of repulsion that might cause this acceleration. But physicists were baffled as to why the cosmological constant was so small.
Quantum theory suggests that 'empty' space is in fact buzzing with subatomic particles that constantly pop in and out of existence. This produces a 'vacuum energy', which makes space repel itself, providing a physical explanation for the cosmological constant.
But the theoretically calculated value of vacuum energy is enormous, making space far too repulsive for particles to come together and form atoms, stars, planets, or life. The observed vacuum energy, in contrast, is smaller by a factor of 10120 - 1 followed by 120 zeros. "It is a huge problem why the vacuum energy is so much smaller than its natural value," says Carroll.
You're special
One of the favoured explanations is the 'anthropic principle'. This suggests that in the apparently infinite Universe, the cosmological constant varies from place to place, taking on all possible values. So there's bound to be at least one region where it has the right size for galaxies and life to exist - and that's just where we are, puzzling over why our observable Universe seems so 'special'.
But this runs against the grain for physicists, who prefer to be able to explain our Universe in one shot. "Relying on the anthropic principle is like stepping on quicksand," Steinhardt and Turok write. They think they have a more satisfying explanation.
They have seized on an idea first proposed by physicist Larry Abbott in 1985: that maybe the vacuum energy was once big but has declined to ever smaller values. Abbott showed that this decay of the vacuum energy would proceed through a series of jumps, with each jump taking exponentially longer than the last. Over time, the Universe would spend far longer in states with a vacuum energy close to zero than with a high vacuum energy.
A long, long time ago
The problem was that Abbott's calculations implied that by the time the vacuum energy decayed to very small values, the expansion of space would have diluted all the matter within it so much that it would effectively be empty.
The cyclic universe gets around this problem, say Steinhardt and Turok. With cycles of growth and collapse taking a trillion years or so, and no limit to how many such cycles have preceded ours, there is plenty of time for the vacuum energy to have decayed almost to zero. And each cycle would concentrate matter during the collapse phase, making sure that the Universe doesn't end up empty.
Steinhardt and Turok say that their idea is testable. The cyclic model predicts that the Big Bang induces gravity waves in space, which physicists are now hunting for. And the decay of the vacuum energy predicts new types of fundamental particles called axions, which may also be detectable.
"It's an interesting idea," says Carroll. He confesses that he has other worries about the cyclic-universe model that temper his enthusiasm. But the wackiness of it doesn't bother him. "Any explanation is quite likely to be extreme," he says, "because all the non-extreme possibilities have already been thoroughly explored."
Ah, doesn't rule out _moldy_ Swiss cheese now, does it?
Maybe I shouldn't have invested in this.
Don't let me forget. I will take a look thru my library tonight.
Hawkings' "A Brief History of Time" ain't too confusing.
most of this cosmology stuff makes my brain hurt, honestly.
Microsoft Excel sometimes makes my brain hurt, so I may be at a slight disadvantage....
'physics for dummies' is most likely as accurate for the lay person as anything else you could read.........Spanish for dummies was pretty darn good - we need one ASAP called English for dummies........
--and--
I lack the Ph.D level mathematics skill needed to understand modern theories about cosmology in any real way. Any language short of high-level mathematics is going to have trouble expressing the basis for these concepts.
Well, I have an advanced degree in math (not Phd yet), but I think understanding and accepting these concepts has more to do with intuition than anything.
MicroSquish products OFTEN make my brain hurt - not that they are particularly difficult to use -when they work- but that they are particularly annoying when they fail to work (and fail to let you know why the f[beep!] they have failed)
The term "Green" cheese is not in reference to the color green, but to "unripened" cheese which is pale white and has not taken on it final colors.........
Nature abhors a vacuum?
Preaching to the choir :)
Any theory of cosmology that doesn't predict the the magic number Nv = 72, (where Nv = number of Allah's virgins), is incomplete.
Basically, this question comes down to whether or not there is enough mass in the universe for gravity to reverse the expansion ofg the big bang.
And decades of experiments and observations have vindicated his convictions to a very high degree of certainty.
The 'devil is in the details', so they say. This particular cosmological variant requires much more investigation before one can say there's truth to it or not - but theories have to start somewhere.
Trying to figure out the origins of the universe is like sweeping a dirt floor.
So how does this theory relate to or refute Membrane theory where our big bang was caused by the collision of 2 rippling universes/membranes? Or is that theory just super old and cast away now. I really like that theory, it's elegant and with string theory one can imagine that our reality is a beautiful song or word spoken/sung by GOD
Just trying to be a little humorous. A little cheesey, even, perhaps.
Not gouda, I guess.
There used to be the Strong Anthropic Principle and the Weak Anthropic Principle.
The Strong Anthropic Principle said that the universe appeared to be designed for life because it was designed.
The Weak Anthropic Principle said that the universe appeared appeared to be designed for life because it was the only way that life could have appeared.
There used to be a reason that the one was named 'Strong' and the other 'Weak'.
Now however, the revisionists have dropped the 'Strong' principle and only the 'Weak' principle remains, without the 'weak', of course.
That's so you won't think outside the box you are given so quickly (The Weak Anthropic Principle).
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