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Was There Only One Big Bang?
goldaryn writes "Physorg.com is running an interesting story about the work of Oxford-based theoretical physicist Roger Penrose. Penrose has been studying CWB radiation and believes it's possible that space and time did not come into being at the Big Bang but that our universe in fact continually cycles through a series of 'aeons.' He believes that he has found evidence supporting his theory that the universe infinitely cycles."
... it was rather dumbed down with lots of silly graphics and other dicking about from the guy in the editing suite, shots of people walking backwards and forwards and a narrator asking loads of questions that the program didn't really give the interviewees enough time to answer properly. And when they did it was obvious they'd been told to keep it simple. Which was a shame , it had great potential but there seems to be a line of thought in British TV at the moment , not just the BBC, that people just can't handle difficult science in more than 30 second dollops before the viewing needs a break. Thank heavens for TED.
That's not really so much "consensus" as "the result of the model we're currently using". No-one *likes* the standard model of cosmology; it's obviously just phenomenology, but it happens to fit all the data at least as well as any alternative. The standard model of cosmology is "lambda CDM", the lambda being a cosmological constant which drives an accelerating expansion in the current universe, and the CDM being cold dark matter which was responsible for the clustering of matter and the formation of galaxies and so forth.
The problem is that if it *is* just a cosmological constant then it will grow to dominate the universe and things will, indeed, expand forever.
But it's probably not a cosmological constant. The "best" prediction from quantum field theory -- and it's not really a prediction so much as the only way of estimating the size of the constant -- comes from evaluating the vacuum energy. Doing this suggests that it should be about 10^120 times bigger than we see in reality. That's a pretty big difference. Weinberg described it as the most embarrassing mismatch between theory and observation in the history of science, and he's got a point. The conclusion is that there's probably some mechanism (coming from trans-Planckian physics, maybe, or something else) that cancels the cosmological constant. If that's true, then it's almost certain to cancel it perfectly because the fine-tuning necessary to produce the *observed* constant is horrific, whereas a symmetry principle could wipe the whole thing much more easily.
That leaves you open to more general dark energy models to explain the accelerating expansion and that's where you have more fun. There are plenty of ways to get an observed acceleration. Some of them lead to big rips, which is where eventually the universal expansion will tear galaxies, then solar systems, then stars, planets and eventually even atoms and nuclei apart. Others lead to the decay of whatever field is responsible for acceleration -- like if you couple a scalar field into dark matter you can tune it such that the scalar field grows to dominate and then starts transferring its energy into dark matter, which would cause the universe to reclump again (and then probably the dark matter would dump energy back into the scalar field causing more acceleration). Those models are horribly contrived and unrealistic, but at least they're alternatives.
And the cosmological constant is pretty contrived and unrealistic in the first place...
Anyway. Before I got side-tracked my point was that there isn't really a consensus so much as a model that fits observations and predicts eternal expansion, but that it's not the only model and it's not even the best motivated model, merely the simplest. Other models can still lead to crunches while fitting pretty much all the data as well. And others can lead to cyclic universes, which is ultimately what Penrose is talking about in one form or another.
Disclaimer: I am a cosmologist but I've not actually read the article. This is Slashdot, after all.
I'd try and defend my profession but I won't because you're quite right. We can happily build models for pre-big bang theories but until we've got a good reason to believe in a way to go with high-energy physics, it's all just phenomenology -- a mathematical way of waving your hands, basically. No-one's actually denying this; if you read the papers on this kind of model they'll tend to wave their hands madly and talk about modifications arising from M theory and low-energy effective field theories. All that is just gloss, motivations for your own model which you'll never seriously pretend is fundamental.
What I would say though is that putting the bounds on your effective theory at least gives you a handle on your inaccuracies. Not many religions do that...
Thanks for the correction. Looks like I was wrong.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
Yeah, all that is the same, across universes. What is different is facial hair fashion.
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"Penrose works on a lot of whacky far-out ideas, none of which so far have panned out."
Yes he does, many of his early "wacky ideas" did indeed "pan out", such as the proof that black holes could form and the concept of cosmic censorship.
"I can generate whacky ideas without evidence just as fast as him"
Maybe, but I doubt you have the mathematical skill of Penrose to back it up.
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