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."

Comments

no to big-bang-centricity !

[polar red]

no to big-bang-centricity ! your universe is not the center of the multiverse !

Expansion

[Altesse]

I don't understand. I thought the consensus between scientists was that the universe is expanding indefinitely, and that there won't be a big crunch ?

Re:Expansion

[boristhespider]

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.

UNfortunately like most BBC documentaries now..

[Viol8]

... 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.

Re:New?

[boristhespider]

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...

Re:Pretty old theory

[140Mandak262Jamuna]

You need to brush up on summation of geometric series. More people are alive today than all humans who have ever died. 75000 years ago we were down to 5000 people, just 1000-1500 breeding pairs. The growth was very slow, not that many people died in the prehistory.

World population passed the 4, 5, 6 and now 7 billion mark in our lifetime. Population of India was just 300 milliom in 1920s (Poem by Barathi referring to Mother India with 300 million faces comes to my mind). Population of USA was just 85 million during WWII.

Yes more people are alive today than all the dead combined. Seven eighths of scientists are still alive. Dont feel bad. Human mind is not evolved to comprehend exponential growth and geometric series well.

Re:New?

[node 3]

That's like saying it's absurd to study black holes because we can't fully model them. We don't have to, because viewing them gives us enough information to understand quite a bit about them and use that to adjust our models. For the big bang, we can't tell mathematically what happened before it, but observation can yield data to form more seemingly accurate models.

All done through science, no religion required.

logic

[t2t10]

Buddhist cosmology isn't really "religious"; whether it is true or not has little bearing on whether you're a Buddhist. The cyclic model in Buddhist cosmology simply makes sense and avoids issues of first causes and the end of time.

In contrast, Christian cosmology is used to justify Christianity: if Christian cosmology is wrong, the whole theological edifice of Christianity comes crashing down. Christian cosmology also fails to address the question of where God comes from.

Re:Turok and Steinhardt also postulate this

[boristhespider]

Yeah, these "Eastern systems" have been *superb* at predicting the anisotropies on the CMB. Why, I even once saw an ancient Hindu text that gave a beautiful B-mode polarisation map with the foregrounds cleaned out, proving both the existence of primordial magnetic fields from a coupling of the inflaton with the electromagnetic field, *and* confirming the nature of the inflaton itself! Some of the concrete, testable predictions of these religions are well beyond the best our supercomputers can come out with! I'm currently working on a proposal for the Euclid satellite and I'm basing a lot of my statistical predictions on old Buddhist texts. Those ancient dudes sure knew how to model the baryon acoustic peaks in different cosmologies and how to observe them without having to build in assumptions from a particular cosmology!

Re:Turok and Steinhardt also postulate this

[boristhespider]

Thank you. Your permission means a lot to me. From my side, please continue to walk around talking shit about ancient religions having anything pertinent to say on physical cosmology. When you can get out a prediction for the CMB sky please get back to me.

Caveat: don't misunderstand me, I couldn't care the slightest about ancient cosmological models one way or the other; they're absolutely fine by me. People can have any religion they want and that's also fine by me. I know some superb cosmologists, much better than I am, who are devoutly religious. But pretending that you can get a feasible cosmological model out of a religion is sheer delusion. A cosmological model is about predictive power -- basically, it involves numbers. No religion and particularly not ancient religions, are built on that premise. They're not about physics. Pretty obviously, they're about religion. And that's a good thing and quite how it should be. Physics killed my own belief in religion but that's my problem. Basically, physics is about how the world behaves and *nothing more*. It's algorithms. Set up a scenario, run your algorithm, and get out a prediction. That's not at all what religions are set up to do. I can sit there and dig in religious texts and support an argument if I like, but attempting to pin any scientific meaning to it is both missing the point and is, in all reality, grossly offensive to the believers of that religion while at the same time saying nothing of value to science.

You might not like that answer, but science is just about numbers. Religion has nothing to say about that. I'm a cosmologist, meaning ultimately I care about the CMB and the distribution of galaxy clusters. Until your vaunted Buddhist cosmology can give me a concrete prediction about the CMB and galaxy clusters I'm going to (rightly) dismiss it, because it has zero predictive power and zero use as a physical model.

In return, I am *not* pretending to say anything about the nature of humanity. Why would I? I deal with numbers, physical laws, and how the universe seems to behave. I draw conclusions from that, postulate a model, and test it against other bits of the universe. Metaphysics, by its very nature, is a bit outside of my domain of expertise. Likewise, physical cosmology is totally outside the domain of expertise of metaphysicists, philosophers, theologists, and random internet nerds with a hard-on for anything from the ancient East.

Re:Pretty old theory

[140Mandak262Jamuna]

Thanks for the correction. Looks like I was wrong.

Re:Old hat

[Ecuador]

Yeah, all that is the same, across universes. What is different is facial hair fashion.

Re:Old hat

[realityimpaired]

And the truth is, whoever can actually answer that question will be collecting a Nobel prize for it.

It's a question philosophers, scientists, religious types, and basically everybody has been trying to answer since humans first became sentient, and at this point, if you ask any 5 people why it all came into existence, you'll get 10 answers.

Re:Old hat

[TapeCutter]

"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.