Dolorosa wrote:

So what's your point, besides trolling? Why can't you just be honest about your intentions here?

Allow me to assist you with the answer to that

CUE ARROW

Longloadr wrote:

Sunny-Smile wrote: So Longloadr, please tell me in your own words, what you think is the difference between the "traditional" Big Bang Theory and "new" versions of it. Saying "bye bye big bang" is more than exaggerating. Saying BYE BYE certainly got under a few peoples skin didn't it? haha Yes, perhaps exaggerating, but just a wee bit. As to your question about "traditional"..... Scientific American will answer you. Was the big bang really the beginning of time? Or did the universe exist before then? Such a question seemed almost blasphemous only a decade ago. Most cosmologists insisted that it simply made no sense--that to contemplate a time before the big bang was like asking for directions to a place north of the North Pole. But developments in theoretical physics, especially the rise of string theory, have changed their perspective. The pre-bang universe has become the latest frontier of cosmology. The new willingness to consider what might have happened before the bang is the latest swing of an intellectual pendulum that has rocked back and forth for millennia

So you admit to over exaggerating to get under peoples skin on purpose? I'd hope the mods take note of that...

Longloadr wrote:

I think it was Ari (not positive... it may even have been you?) who helped me out with this once, and he listed several problems with BBT.

If you mean problems like the monopole problem, horizon problem, flatness problem, baryon asymmetry, density perturbations and initial expansion they are all quite nicely explained when we introduce inflation. Not only does inflation solve these issues it also makes predictions (in observations of the density power spectrum for example) and thus gains even more validity as a proposed mechanism in the early evolution of the Universe.

CarlosFandangos wrote:

Longloadr wrote: I think it was Ari (not positive... it may even have been you?) who helped me out with this once, and he listed several problems with BBT. If you mean problems like the monopole problem, horizon problem, flatness problem, baryon asymmetry, density perturbations and initial expansion they are all quite nicely explained when we introduce inflation. Not only does inflation solve these issues it also makes predictions (in observations of the density power spectrum for example) and thus gains even more validity as a proposed mechanism in the early evolution of the Universe.

Yeah -- if you accept inflation. There are good reasons to do so, as you mentioned, but it's also very ad hoc; there is no natural inflation mechanism, for one. Neil Turok (who, by the way, taught me a course on general relativity ), doesn't like inflation very much, and he has proposed a cyclic universe model that has at least some of the successes of inflation, if not all; I haven't read the paper yet, though, so I don't know much about it. His current research is on colliding branes causing the Big Bang, which reeks of string theory, so I don't really know what to expect. In the end Turok does believe in the Big Bang, but he is very skeptical about inflation.

I don't know exactly what Lee Smolin thinks of Big Bang; he concentrates more on other problems, such as quantum gravity (I haven't had that much interaction with him). I doubt he disbelieves the standard Big Bang, though.

And by the way, baryon asymmetry (BA) isn't solved by inflation. I don't think it has an accepted solution, actually: The Standard Model of particle physics can't generate the observed BA. The matter-antimatter asymmetry (i.e. CP-violation) is too small, and apparently the Sakharov condition of out-of-equilibrium dynamics isn't quite met. You have to extend the Standard Model somehow to explain the BA -- but then again we have to extend the Standard Model in any case if we want to explain neutrino oscillations, dark matter, possibly inflation, and ultimately we have to extend it to quantum gravity.

While there is no accepted solution to BA, it's not because we lack possible solutions. Two Higgs model and minimal supersymmetry are apparently attractive candidates, and LHC can probe those theories (or so I've read). Grand Unified Theories can possibly do it, though they suffer from the stability of the proton and sphalerons. Leptogenesis can do it, and it just requires addition of right-handed neutrinos to Standard Model, which we have to do in any case if we want to explain neutrino oscillations -- and it can possibly explain dark matter, too.

My opinion is that the Big Bang is a solid theory, and that there is no better alternative at the moment. We can speculate about the causes of Big Bang, what happened before it, the validity of inflation or eternal inflation and so on, but at the very least we have to accept that something like a Big Bang happened sometime in the past. Observations just fit too well to that hypothesis.

Welcome back Ari! Thanks for your comments.

Ari you lucky fella being taught general relativity by Neil Turok. I had to make do with self learning pretty much with The Open University's teaching model, would have loved to have been taught by someone of Neil's experience I haven't read about his cyclical model in depth but am interested now. Although any mention of strings put me off big time

I've had a brief look at the ekpyrotic Universe model before and it sounds very interesting and importantly makes testable predictions (as well as dealing with the 'problems'). It'd be just as exciting to find there was no inflation, either way we are advancing our understanding of the Universe

Apologies, I shouldn't have lumped BA in there with the others as its not one of the key problems inflation attempts to solve. There are indeed many proposed mechanisms to explain BA.

I guess we have to wait until we can probe higher energies in labs and experiments like ACTPol start returning results before we begin to understand it all a little more. Exciting time we live in if you ask me! So many questions to ask, so many answers to search for

CarlosFandangos wrote:

Ari you lucky fella being taught general relativity by Neil Turok. I had to make do with self learning pretty much with The Open University's teaching model, would have loved to have been taught by someone of Neil's experience

It was a three week course, so it was pretty hectic. If you're interested, the lectures should be available on the web -- pretty much everything PI offers is, so no doubt you'll find something interesting.

CarlosFandangos wrote:

Although any mention of strings put me off big time Razz

I had a very nice course on string theory, and I think at least the techniques I learned there were useful. It's true that string theory hasn't been very successful in cosmology or particle physics (I think Lee Smolin called string theory the theory of anything ), but apparently you can apply it to difficult condensed matter problems via the AdS/CFT correspondence. People here are very excited about it.

CarlosFandangos wrote:

I've had a brief look at the ekpyrotic Universe model before and it sounds very interesting and importantly makes testable predictions (as well as dealing with the 'problems'). It'd be just as exciting to find there was no inflation, either way we are advancing our understanding of the Universe

Yup; inflation sometimes seems to be a bit overdoing it (my personal opinion), but it has a very interesting host of associated models (eternal inflation, say).

CarlosFandangos wrote:

Apologies, I shouldn't have lumped BA in there with the others as its not one of the key problems inflation attempts to solve. There are indeed many proposed mechanisms to explain BA.

I'm just complaining because I just finished writing an essay about leptogenesis in one possible scenario.

CarlosFandangos wrote:

I guess we have to wait until we can probe higher energies in labs and experiments like ACTPol start returning results before we begin to understand it all a little more. Exciting time we live in if you ask me! So many questions to ask, so many answers to search for

Definitely.