joigus

But inflation corresponds to slow-roll down the hill, so that's previous to reheating, and thereby previous to plasma epoch, baryogenesis, radiation-dominated epoch and everything else. The super-stretching is always previous to big-bang cosmology. And the inflaton looks nothing like a Higgs potential (Mexican hat). It's a completely different animal: Although there are other models. But the parts of the graph that has received good confirmation is the part with a gentle slope and the steep fall. The breaking of the symmetry that we commonly associate with the acquisition of mass came much later. After re-heating. V(phi) is the potential and phi is the inflaton. The V(phi) for the Higgs is very different: Online lectures that I found very useful to understand how the inflaton is very different from other scalar fields are (Lenny Susskind, Stanford): https://www.youtube.com/watch?v=gdFldkitkJA&list=PLvh0vlLitZ7c8Avsn6gUaWX05uD5cedO-&index=8 1h 15' 12'' to the end And then: https://www.youtube.com/watch?v=gdFldkitkJA&list=PLvh0vlLitZ7c8Avsn6gUaWX05uD5cedO-&index=8 The Higgs potential is a static situation. The inflaton dynamics, on the other hand, is analogous to the dynamics of a body falling under viscous drag. And the Hubble parameter plays the role of the friction.

Sure, but you have to provide the energy. That's what's happening when you hit a proton with an energetic particle. You put in the required energy for some of these virtual particles to persist. In the inflationary theory it's the inflaton field that provides that energy. But my next question would be: What's the status of the inflaton field? Is itself a quantized field, with quanta? Why wasn't it in a superposition of states when all that transition happened? I think there are possible answers to that. For example, superselection rules, which are strict prohibitions for superpositions of different quantum numbers to exist. But the whole thing becomes more and more contrived... The inflaton field is acting like the physical element that defines the fate of these fluctuations. It's kind of jerry-built. Successful, useful, very impressive to be sure, but it doesn't give you anything like this feeling of inevitability that you normally demand of fundamental theories. Like something remains to be understood.

This is actually, IMO, an outstanding question, because I haven't the faintest idea how you would apply the principles of the quantum theory of measurement to the vacuum. I don't suppose you can do that. Certainly, as there were no real particles, only those ephemeral virtual states, how did something actually happen? Nothing would qualify as an observer or as an apparatus. Decoherence is not it, IMO, because I don't know of any instance in which the vacuum can be argued to bring about decoherence and thereby qualifying as producing a measurement. This is a part of the quantum theory of measurement that's slipped into oblivion: the problem of the pointer positions. What physical tag says that something, and not something else, has actually happened? What tips the arrow? If anybody knows of any answer to that I would be the first to thank them, because I've longed to know for more than 20 years. It was very frequently referred to in the old papers and books about measurement, but no longer is. Old papers and books: https://press.princeton.edu/books/hardcover/9780691641027/quantum-theory-and-measurement

I no longer think a quantum theory of gravity is likely to happen. Not the canonical way, and not with Feynman diagrams and renormalization the traditional way. Maybe a more topological language for QFT/gravitation has to be developed. I do believe that the holographic principle partially grasps something very surprising about gravitation. My own intuition guided by comments, lectures, reflections and papers of other physicists is that something very fundamentally different happens at Planck's scales that must be interpreted in some new way, maybe that the interior of a very small region of space-time no longer makes sense. Or maybe the distinction interior/exterior becomes fuzzy at that scale... But I'm old enough and battered by experience enough to accept whatever proves to be a better solution. If it just so happened that discreteness for space-time works better, so be it. I hope it's within my lifetime.

I suppose I agree with this, in some way, and I also think it goes deep. +1 My phrasing of it would be, "there's always something."

Oh, the Greek humanity!!!

Ok, but suppose that the naive idea of this "nothing" approached by mentally picturing the removal of things that happen to be there into nonexistence does not ultimately make sense. It's not about getting hold of these things (a planet here, a giant star there) and taking them somewhere else; it's more like snapping your fingers and decreeing that they never were. That's not an operation that you can do, or even think of doing. I think you guys know me by now. I'm very mathematically minded. I always try to write the equations we know to work and have them tell me something, suggest something to me. Not because I think I'm good at maths, but because I trust the equation more than my words or concepts. At some time in the past I read a book by George Gamow that quoted Dirac as saying "the equation knows best". I think that's one of the most brilliant thoughts in physics that's ever been formulated. Whenever you find conflict, you must stick to the equation and try to make sense of it. Right now, what the equations seem to suggest is that there is no simple formulation of "nothing". So, "what's the next best thing?", my question would go. And the most plausible next thing is either the remote-past "nothing" (quantum vacuum confined to a Planckian-size bubble, rolling down a hill, with no real particles) or huge extensions of interstellar space, devoid of matter, in the remote future, if the picture of the accelerated expansion of the universe is correct. Right there you've got two different pictures of "nothing". How can that be? So my conclusion would be: I'm puzzled by the fact that we can so easily conceive this nothingness (or we think we can: close your eyes and think of nothing), and yet the universe doesn't let us even get closer to it, or make sense of it. Different versions of nothingness or incremental approaches to it just doesn't add up in my mind. I also like the idea of ridding ourselves of the background. I'm sorry I'm not all that familiar with LQG. Although some of the ideas are attractive to me. It's the discretization of ST that I don't like.

Sorry, 50 e-foldings, not e50, meaning the universe multiplied its size by e (=2.718...) 50 times (at least). https://arxiv.org/pdf/1405.5538.pdf

Yes, you're right. But I do have lots of problems with the concept of nothing, because whenever I try to think about it, it's from some kind of somethingness. Following the current cosmological models, this quantum vacuum had to go through the slope of the inflaton field, and it had to have cooled before re-heating for billions upon billions of "years" (e50 plus e-foldings) so... Is the inflaton nothing? And the quantum vacuum? I don't know. I wouldn't even know how to get started trying to answer that kind of question. None of that seems like nothing to me. It's so similar to something that only someone who's an real expert about the something/nothing characterisation would be able to tell the difference.

Good point. The best explanation I can think of comes from classical relativistic mechanics, and it foreshadows the need for a quantum field theory, including "messenger particles" and vacuum polarization. 1) Classically, you cannot have a massive particle emit a photon 2) Classically, you cannot have a pair of particles appear from the vacuum Proof: 1) Particle at rest goes to particle + photon From conservation of momentum: \[\left(m,0,0,0\right)=\left(E,p,0,0\right)+\left(p,-p,0,0\right)\] \[m=E+p\] From Einstein's energy-momentum relation: \[\Rightarrow E^{2}-p^{2}=E^{2}+p^{2}+2Ep\Rightarrow\] So that, \[p^{2}=-Ep\Rightarrow\] So either, \[p=0\] (the particle does not decay) or else, \[p=-E\] Impossible, as we've assumed p>0 2) Particle-antiparticle pairs (from the vacuum) \[\left(0,0,0,0\right)=\left(E,p,0,0\right)+\left(E,-p,0,0\right)\] \[2E=0\] So E is zero, which is again impossible. --------------- There are more examples, but they all go to prove that particles that are produced at one point and annihilated at another are a mathematical impossibility from the classical POV. In the case of the massive particle sending a photon out, you need another charged particle coming nearby and absorbing that photon so that the uncertainty principle allows the intermediate particle go unnoticed. The closer both charged particles are, the more efficient this exchanging mechanism is, so that the force must decrease with the distance. If you think about it, it makes sense that it be an inverse square law. In the case of vacuum polarization, it is required that the pair disappears soon enough that the UP allows you to, again, get away with it (UP). These particles that appear at one point and disappear at another are what in quantum field theory corresponds to so-called "internal legs" of the Feynman diagrams. You can and must use them, they appear in the space-time picture as intermediate steps in the evolution of the overall quantum states, but they are ephemeral presences, doomed to be turned back into the vacuum or absorbed by real particles sooner rather than later.

I wish to clarify first that the animation is not mine. Also correct my grammatical mistakes: The first occurrence that I know of in the history of physics that something like the concept of changing physical laws appeared in physics was due to Dirac. He made the observation that different ratios of the most natural physical parameters in the universe (number of protons, size of cosmic horizons, number of photons, leptons, fundamental constants, like Newton-Cavendish' famous G, etc.) were very simple powers of a number the order of 1040. So Dirac thought something like "maybe all these constants are not really constants, but are related to the age of the universe by some simple power law and they are changing with cosmic time". Then the idea fell out of favour and something like that kind of reasoning has seen a re-birth, mainly possibly spurred by Alan Guth and followers. The question of meta-laws (using words I've heard to Lee Smolin) I think is a very interesting one. It is not inconceivable that Planck's constant may have been nearly zero at the starting point, or GNewton had assumed a much bigger value in the past, etc. Who knows. Guth's inflationary idea, when you think about it, is a kind of revival of something very similar in a perhaps more tractable version. In that case it's the vacuum in quantum field theory that plays the role of changing parameter, monitoring most everything else, in particular the Hubble expansion parameter. My feeling is that Guth has captured something quite right about how it all must have started to give rise to the big bang of which we're seeing the remnants in the sky. In particular, quantum fluctuations must have played a very important role, being essential to the seeding of inhomogeneities that gave rise to cluster, supercluster, and galaxy formation. So I generally agree with what Eise has explained about uncertainty and I think it complements very well the points I have let loose. It's the uncertainty principle in combination with the choice of a convenient vacuum that gave rise to the structure. Until a better idea is found, it seems to work pretty well. The problem of the "when", that Studiot has brought up, is something that worries me particularly (the "where" worries me a little bit less), because you always seem to need a parameter to deploy all the physics as a sequence of events. When we're assuming Planckian scales in the spacial sections of space time, does it really make sense to talk about eternal inflation or slow roll? That's why the question of emerging time is so important. The only way I can think of that something like this could be achieved is by deriving time from a metric in field space, which is what I tried to suggest in the thread "What is time?" @Markus Hanke didn't seem to agree with me or see very clearly what I meant. And I tend to take Markus' disagreement very seriously. But that's another story and belongs in other thread. ------- PD.: I kind of have an idea of what this timeless scenario (from which a time can be derived that could make mathematical sense) may be derived from, but it's embryonic and very mathematical, and this is probably not the right medium for it. I will also have to pass on the fine philosophical/mathematical points that Studiot suggests, for the time being (and important though they may be) as I don't feel qualified to talk about them. The idea of constructing something from nothing still boggles my mind. I'll try and think more about it. I suppose everything depends on what is nothing and what is something.

Which actually goes to prove that you mustn't take anything literally.

As to what concerns the OP's question, I totally agree with this. +1 The question of planarity of the observable universe, for all I know, is about spatial flatness and has nothing to do with the rate of expansion. Preprint is here: https://arxiv.org/abs/1911.02087 I think a wildly-varying curvature would have noticeable effects in the aberration of light. I'm not sure I understand your onion picture but, wouldn't that have problems with isotropy/homogeneity at large scale? Although I agree that not even in a spherical universe would you necessarily move in periodic orbits. Only if you followed geodesics you would.

NEW* "theory". Here's a list of concepts of common usage that's immediately obvious you don't understand: dimension, light, velocity, phenomenon, explanation (or "explantation"), understand, consider. *Not Even Wrong. (Knowing full well how much these words have been abused in the recent past.)

Yes, that's true. The theory has changed since then, but not substantially, and the original motivations are probably introduced better by the original author.

Good question, but very difficult to answer. Part of the key to that could be related to the observation that Eise has introduced and you so cleverly have caught on to: This sets the stage for the famous question of meta-laws: Were the laws of physics already there before the big bang, or did they appear along with everything else? Answering that or setting the question properly (if we can ever do it) will probably get us closer to trying to answer your question. So far, what we've got is this kind of parametrisation of the problem (the inflationary model). One should also ask what "there" and "then" or "before" really mean, as space-time is supposed to have appeared along with matter. The misleading aspect of the picture that I linked to before is that it seems to suggest an extended background (especially in time). It should be conceived of as something of Planckian dimensions (very, very small). And what about time? I don't know. There are several things about inflation I can't quite wrap my head around. To me, overall, it all looks a little bit contrived to be entirely satisfactory. Another major concern of modern theoretical physics is the emergence of time. The potential energy "down which the vacuum fell" does not live in space-time, but in the inflaton-field configuration space. But physicists that work on inflationary models do use a pre-big-bang time as a background for it. Somehow, you must be able to define a sequence of events. Sorry, my word "sea" was not very fortunate. It would be better described as a Planckian-small bundle of fields, I suppose. Well, there are models, all under the name of "inflationary model" something or other; not to explain, but at least to model what must have happened. Basically you put quantum field theory (this theory of particle-antiparticle formation and annihilation) on the background of a field of potential energy. If you set the curve correctly*, you can model much of what must have happened to give rise to the universe as we know it. Inflationary models seem to be particularly good at explaining the seeds of inhomogeneity that gave rise to clusters and superclusters that today are galaxies and clusters and superclusters of galaxies. I must warn you that some very no-nonsense physicists are not completely happy about inflationary ideas. One notable example is Neil Turok. The best source for learning about these things that I know of is Leonard Susskind's online lectures (Stanford). There's also Lawrence Krauss, that Eise suggested. ------------------------------------ In answer to: It depends a little bit on how familiar you are with differential calculus, vectors, power series, things like that. There are many confusing aspects, I know. I'm leaving many questions unanswered. I'm not sure I've done a good job of making it more understandable. *"Model the curve correctly" means it must look something like this (take a look at the graph): At the bottom down of the curve is where the big bang is supposed to have started. "Previous" to that, there is a very prolonged phase of "slow roll", as it's called.

Hi. Welcome. Very old question, but very difficult to answer nonetheless. So I'm going to get hold of some visual aids found on the web. Nothingness is quite easy to picture in your mind. Maybe we get that picture from our hours of sleeping without dreams. I don't know. But, The picture of the closest thing to nothingness that we can build from physics is not a featureless scenario. It's more like this: Or, more diagramatically, like this: A perpetual struggle of opposites annihilating each other. It just isn't just nothing. What it suggests is that what we call "nothing" is more like this ephemeral tug of war between ephemeral somethingnesses (virtual particle-antiparticle pairs). Nothing (in a poetic picture derived from serious physics) is a struggle between opposites in which nobody wins. At some point in the past, somebody won (why that was so is still an enigma; I don't like the word "mystery".) The status of the theory so far is that something like this sea of opposites annihilating each other must have fell downhill some kind of modulating field (inflaton field) 13 point something billion years ago, generating real particles and filling the universe with structure. That's called inflationary model of the universe. I hope that helps, but it's been a long time since Leibniz set that question to nowadays. So the story has become more involved.

Thousands of hours thinking about a physical problem without taking much input from experts' and known facts normally end up being thousands of hours down the drain. It's actually a very bad symptom. You're trying to re-write hundreds of years of progress in science. Be careful with how much time you spend thinking on your own. The best physicists spend thousand upon thousands of hours studying (or using) physics they can claim no authorship of, and only tens of hours thinking of new ideas. Most physicists spend their lives skillfully using other people's theories. That's how it works. So it's the other way around. Thousands of hours of study culminate in tens of hours of inspiration at best. Something like that. Again, I'm trying to be helpful.

I for one apologise for having been facetious, but you really should write down these things and consider what dimensions they have in terms of mass, length, and time. Then be aware that modern physics has all of them reduced to length, so the questions turns to writing down all your magnitudes in terms of length (or any other in the Plank scale). You can't build all of physics from scratch. It's like ordering the demolition of the Taj Mahal because you've come up with a good idea for a bungalow summer resort there. And believe me, I'm trying to be helpful. You're going to find strong opposition for very good reasons.

I don't know whether this is lateral, collateral or perpendicular to what's being discussed, but I've noticed that in modern democracies, it's become increasingly irrelevant what comes out of the mouths of people in Government or, in this case, the First Lady. This suggests to me that, to a high degree, decisions are taken by Gov. officials and technocrats, and high-profile politicians are there just to not lose face, and respond to people's pet peeves, manias and prejudices (mainly in press conference before a camera or mic), so they (the people) get the feel that their whining is being responded to.

https://en.wikipedia.org/wiki/Preon Is it? Though yours are "braided." Preons, in a nutshell, are sub-quark/lepton structures. The L's are the characteristic dimensions of the braids, if I understood Vitaly correctly. At GUT unification scale the braids' dimensions become comparable Lx,Ly,Lz. This unification scale is given by the mass of the GUT monopole. Another question: If you're disposing of SS, how do you deal with vacuum energy? And scalar-field renormalisation? In a nutshell, please.

It is defined in Principia Mathematica, by Russell & Whitehead, if I'm not mistaken (see footnote on mentioned page.) But it seems to refer to an abstract recursion or rule, not necessarily numerical.

And we don't know anything about many more things than those we know something about. And then there are things we don't know if we don't know. And things we don't know if we could know. And maybe things we think we know, but we don't. Makes you wonder.

Well, the identity is not considered to be an interesting symmetry transformation, because everything is symmetric under it. It does play a role in the theories that involve symmetry (mostly in group theory as far as I know). Example: Consider three numbers, i, j, k. And a function alpha: \[\alpha\left(i,j,k\right)=ij+jk+ki\] And the transformation, \[\pi\left(i\right)=j\] \[\pi\left(j\right)=k\] \[\pi\left(k\right)=i\] Then we say alpha is symmetric under pi.