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Aelfric
Turkey1496 Posts
On October 27 2014 19:37 Teoita wrote: Completely misleading title, plus none here actually knows anything about cosmology Cool article though. What do you think the proper title should be? | ||
Teoita
Italy12246 Posts
This article is really interesting, but not that groundbreaking in my opinion (then again im an astrophysicist, not a theoretical physicist, so i dont understand every detail of that article). I'll try to explain some basic cosmology so you guys can get an idea of what's up with this, but this is essentially me trying to condense at least an entire master's degree class into a single post, so this will probably be a little confusing. Essentially, the most accepted cosmological model for the behavior of the universe in large scales, called the lambda-cold dark matter model, predicts among other things that the universe MUST have had to go through a period of extremely accelerated expansion in its early stages. The reason for this is the existance of three very basic problems im lambda-cdm models that do not include inflation. These are called the flatness problem, the horizon event problem, and the magnetic monopole problem. In order: 1) Flatness: we know from empirical observation that the structure of space-time is flat. Ideally, it could be any kind of 4-dimensional surface with positive, negative or null curvature (just to picture things, in 3 dimensions a sphere has positive curvature while a plane is flat). Not only is the universe flat, but it can be shown easily that the further back in time you go, the more flat the universe gets. This is seriously bizarre; why the hell would the universe be absolutely perfectly flat at its start, when it can assume any possible value for its curvature while still following the same exact physical rules? It's an amazing coincidence, and it's extremely unlikely to just so happen by chance. 2) Horizon distance: this is even wierder. Basically, most photons existing in the universe are part of what is called CMB, or cosmic microwave background. These photons were emitted together billions of years ago, when the universe was still extremely hot. In fact, it was so hot that photons kept interacting with matter, keeping atoms from forming, bouncing from one nucleus to the other instead of being free to go their own way. As soon as the universe cooled enough, the photons suddenly stopped interacting with matter so strongly, and were free to go their own way. This radiation permeates the entire universe. By studying the CMB you can easily see that it was emitted at the same exact temperature at every point in the sky. On paper this makes sense, but if you look at things more carefully, you realize that light (and therefore, information) at the time of the CMB emission did not have time to travel through the entire sky as we see it. In fact, you can divide the sky in roughly 20000 patches of equal size; each of those would be able to transmit information within itself, but not to its neighbours. If these patches can not transmit any information to each other (ie, they can not reach the same temperature), why the fuck are they at that temperature? 3) Magnetic monopoles: this comes from more complex quantum mechanics stuff so i won't go in detail about it. Essentially, some quantum mechanics models predict that magnetic monopoles should exist, and their presence should be easily detectable. So why do we not see them? Is it possible that the universe evolved in a way that made them disappear? Inflation theories solve all these problems. Inflation essentially states that there was a period in the early history of the universe, during which the expansion of the universe was INSANELY fast. This solves the 3 problems of traditional lambda cdm models: 1) Even if you start with a very curved universe, if you stretch it immensly it ends up being very very flat. 2) If the universe expands extremely fast for a while, then before it expanded it was extremely tiny, to the point where it could exchange information with every part of it, reaching the same temperature easily. 3) Slightly more complex, but ideally even if magnetic monopoles exist, the expansions "stretches" them so much that they become insanely rare, almost non existant. How here's the problem: well shit if everything becomes perfectly uniform, how come the universe we see isn't uniform? Why do we see stars, globular clusters, galaxies, galaxy clusters and superclusters? So far, you'd think that inflation would make everything perfectly homogeneous. However, what does happen is that when you first start with your tiny, small universe before inflation, it isn't perfectly homogeneous because of quantum mechanics. At a very very tiny scale the universe isn't empty: particles are constantly destroyed and created, according to Heisenberg's uncertainty principle: E*t>h, where E is the energy, t is the time, h is planck's constant. As long as a pair of particles of energy E exist for a time shorter than t, in order to respect the uncertainty principle, they are free to be born out of nothing, and return to nothing shortly after. This phenomenon is called vacuum energy. The way it ties into inflation is simply that these fluctuations are blown to huge sizes when infllation starts, and are what forms the large scales structures like galaxy superclusters that we see today. Inflation was first formulated in 1981, so again, the idea of quantum fluctuations being the origin of the structures currently observed in the universe isn't new. | ||
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Teoita
Italy12246 Posts
In the article, the authors are demonstrating that one way to generate the really fast expansion i was talking about in the previous post is to assume there is some kind of force, or potential, at work. Again, nothing new, this has been done forever. The interesting thing about it is that they show that this force/potential/field (they are all the same essentially) MUST be treated with quantum mechanics. It is possible to write very very simple inflation models that use classical mechanics instead; this article shows that those models aren't accurate and you need to use quantum mechanics (which is where unfortunately my knowledge falls short) to treat inflation correctly. Given certain hypothesis, they also find a way to avoid the singularity problem - ie, everything going to either zero or infinity at the exact time of the creation of the universe as we know it. This is generally extremely hard to do, because our knowledge of advanced quantum field theory, like grand unification theory or quantum gravity, is still extremely limited (or well, almost non existant). The whole point of having a correct inflation model is, of course, to find some sort prediction that can be confirmed by an experiment. This hasn't happened so far for inflation, because it's really complex shit. Math proofs alone do not prove anything. It's extremely easy for a good theoretical physicist to construct a model of generally complex stuff (say, quantum gravity), that is prefectly fine mathematically and is internally consistent. It's much, much harder to find some way of actually demonstrating that same model in a lab, and until then, no theory can be considered "proved" or "confirmed". | ||
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Teoita
Italy12246 Posts
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lichter
1001 YEARS KESPAJAIL22272 Posts
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Targe
United Kingdom14103 Posts
On October 27 2014 20:14 lichter wrote: lol that title all of the bait | ||
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skinnyQueen
11 Posts
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Aelfric
Turkey1496 Posts
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Aelfric
Turkey1496 Posts
On October 27 2014 20:51 skinnyQueen wrote: Any paper published on arXiv.org is worthless. It literally means that the paper got rejected by all other peer reviewed journals. That is such a bold statement and simply not true. | ||
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NPF
Canada1635 Posts
On October 27 2014 20:57 Aelfric wrote: That is such a bold statement and simply not true. Indeed, you can send your paper there in pre-print so other people can see your work earlier and critique it. Also it allows people to see your work for free. Some people have links in there Arxiv papers to it's journal entry so you can quote their work. On October 27 2014 19:06 Cynry wrote: Could someone point to a document explaining or explain himself what is a false/true/whatever vacuum ? First look at this little conceptual image I made : ![[image loading]](http://i.imgur.com/V2q3IvH.jpg) A false vacuum is a state which a system is at a localized minimum energy but not the extremum minimum energy. So a system in a false vacuum giving enough energy can fall into it's true vacuum state. It's like having a large round boulder on a small dip on a bigger hill. You have to push the rock a bit before it starts speeding down the rest of the hill. So in the article in the conclusion they mention a quantum vacuum fluctuation of the false vacuum to the true vacuum they mean a fluctuation in energy allowed from the uncertainty principle Energy*time>h/4*pi. The uncertainty principle as stated is for real particle, for virtual ones (or quantum fluctuations) we write Energy*time<h/4*pi and if the Energy end up being bigger then the hill we can "fall" from a false vacuum to the real one. Equally I support what Teoita said with my limited knowledge of Astrophysics since I'm studying theoretical physics. We can get into a debate of his definition of vacuum energy is another time but he said the important part quantum fluctuations are allowed by the uncertainty principle. | ||
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quirinus
Croatia2489 Posts
On October 27 2014 19:37 Teoita wrote: Completely misleading title, plus none here actually knows anything about cosmology Cool article though. generalizing much without actually knowing? I'm not working in that field and I'm far from an expert or even decent, but I have read a few books (not popular science books, real books) about it and I know the basic and some "advanced" equations, principles etc. On October 27 2014 20:51 skinnyQueen wrote: Any paper published on arXiv.org is worthless. It literally means that the paper got rejected by all other peer reviewed journals. lol what? There have been plenty of papers (even high profile) there that have been published in peer reviewed journals, because the author(s) wanted it to be publicly available or for other reasons. On October 27 2014 19:06 Cynry wrote: Could someone point to a document explaining or explain himself what is a false/true/whatever vacuum ? uhm, here's something to get you started (although I don't like linking to Wikipedia for this, but I guess it can give you some idea): http://en.wikipedia.org/wiki/False_vacuum google shows up some more. Basically, false vacuum is a state of the field that's a local minimum, but not a global minimum. That means that it's "trapped" in a higher energy state, and can go to a lower state (another false vacuum that's lower, or even true vacuum) by some process (eg. creating particles). | ||
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Teoita
Italy12246 Posts
On October 27 2014 20:51 skinnyQueen wrote: Any paper published on arXiv.org is worthless. It literally means that the paper got rejected by all other peer reviewed journals. lolno at poster above me: it doesnt have to be a minimum. As long as the potential isn't very inclined, you can assume you are in a false vacuum state. For example, commonly used potentials in inflation look like this: ![[image loading]](http://universeinproblems.com/images/thumb/4/4d/Inflation_3_2_1.jpg/300px-Inflation_3_2_1.jpg) If your scalar field is close to V0 you are in a false vacuum state, if you are where the minimum is you are in a true vacuum state. | ||
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kubiks
France1328 Posts
On October 27 2014 20:51 skinnyQueen wrote: Any paper published on arXiv.org is worthless. It literally means that the paper got rejected by all other peer reviewed journals. That's not really true. There are many reason to publish something on arXiv, and "it's worthless" is not the only one. There's a lot of good research published on arXiv, it's just that you can find some trashy one (and you can find trashy research in bad journals anyway). You can try to look for the author of a paper, and if he is legit (like he have some papers accepted in good conferences and is in a lab), the paper itself is probably legit. Btw I was surprised the paper was that short. Is it normal in this field ? | ||
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skinnyQueen
11 Posts
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Teoita
Italy12246 Posts
Care to explain why this particular paper would be wrong other than "because yes"? I'm not being sarcastic, im actually interested in this stuff | ||
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Squat
Sweden7978 Posts
On October 27 2014 18:14 SoSexy wrote: Why so hostile? I'm not draggin religion in it, I am simply stating the point of views involved in the contemporary debate about the beginning of the universe. You linked William Lain Craig, a known charlatan whose entire career is based on misrepresenting science and inappropriate use of scientific language. He has about as much credibility as Chopra or some other new age fraud. On topic; Lawrence Krauss has spoken about this many times, and I've listened to several fascinating lectures on the topic from him. I recommend them to anyone who is interested in the subject. Suffice to say, I now know enough about quantum theory to understand that I know nothing about quantum theory. | ||
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Aelfric
Turkey1496 Posts
On October 27 2014 21:26 skinnyQueen wrote: You're all right. Not every paper on arXiv is trash, but this one certainly is. Why do you think that way? | ||
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Squat
Sweden7978 Posts
On October 27 2014 21:26 skinnyQueen wrote: You're all right. Not every paper on arXiv is trash, but this one certainly is. Please elaborate on why. Toeita's very informative posts seem to suggest that there is a lot of intriguing information in the article. Math proofs alone do not prove anything. It's extremely easy for a good theoretical physicist to construct a model of generally complex stuff (say, quantum gravity), that is prefectly fine mathematically and is internally consistent. It's much, much harder to find some way of actually demonstrating that same model in a lab, and until then, no theory can be considered "proved" or "confirmed". Outside of mathematical models, what methods exist by which to demonstrate quantum theories to be true or false? Do we currently even possess any? I am not aware of any method that is both falsifiable and demonstrable, but I fully concede I don't know anywhere near enough on the subject. I suppose something like CERN or similar projects could be used, but given the costs and committment involved, it may not be very practical. | ||
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Jockmcplop
United Kingdom9338 Posts
Bunch of people on forum argue about assumptions that were never made. Surprise me TL go on. | ||
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Teoita
Italy12246 Posts
On October 27 2014 22:01 Squat wrote: Please elaborate on why. Toita's very informative posts seem to suggest that there is a lot of intriguing information in the article. Just clarifying, i also know fuck all about quantum field theory, hence why i was curious. edit: Outside of mathematical models, what methods exist by which to demonstrate quantum theories to be true or false? Do we currently even possess any? I am not aware of any method that is both falsifiable and demonstrable, but I fully concede I don't know anywhere near enough on the subject. I suppose something like CERN or similar projects could be used, but given the costs and committment involved, it may not be very practical. I'm not really sure tbh. Current particle accelerators are most definitely not enough to study inflation, as they don't reach energies high enough. The only study regarding experimental proofs of inflation that i'm aware of is the study of the polarization of the CMB photons, which in some way i don't understand very well is tied to inflation. In fact, about one year ago a research team working with an experiment called BICEP2 claimed to have found evidence that confirmed inflation in the CMB, but that claim was later refuted; most people now believe it was a mistake in their handling of data coming from another experiment. Just check out wikipedia: http://en.wikipedia.org/wiki/Cosmic_microwave_background#Polarization The big problem with studying stuff that happened before the emission of the CMB is, essentially, that photons from that time do not arrive to us. The universe was "opaque" to photons until the CMB was emitted: as i wrote earlier, no photon was free before that time, so we can't (currently) see any kind of information about it. It's like looking at a wall and trying to guess what is in the room behind it. If the wall isn't transparent, you'll never see anything. In the future (next 50+ years i guess) we will have astrophysical data not just from photons, but also from neutrinos and gravitational waves, which should allows to study eras farther back in time than the CMB emission. For now, we don't really have any way of proving a theory like inflation because of technological limits. Quantum field theories in general...well, there's two issues here. Quantum field theory is what was used to write the standard model of particle physics for example, which so far has held up extremely well over the years (in fact, annoyingly too well lol). We know that at the very basics, the fields that moderate particle interactions are in fact quantized, so -some- quantum field theories are in fact correct. The recent discovery of the Higgs boson was a huge step forward in that sense. We also know that our current theories (ie the standard model) aren't entirely correct, since a) we can't quantize gravity and b) on a lot of predictions, general relativity disagrees with quantum field theories (ie particle physics). Regarding moving forward and finding (and proving) the existance of grand unified theories (essentially, a theory that unifies the strong, weak and electromagnetic interaction in a single force) and, further on, quantum gravity (or, finding some theory that makes general relativity and quantum mechanics agree, while also describing gravity as a quantized field), we currently do not have means to test that in a lab, which is why these theories are so varied. In fact, this stuff is so complex that for many of these theories (string theory for example), the math needed to write them fully doesn't exist yet. I hope that made sense. | ||
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