Questions about Multiverse and beyond

Somewhere I read Stephen Hawking’s words: there is 98% chance that another Big Bang could happen and create another universe. (meaning only) This makes the multiverse possible.When there is one, there is another one, naturally there should have unlimited number of universes exist and there should have number of neighbouring universes around our ones.Our universe is expanding now. Ultimately our universe would start shrinking or contracting. I imagine that the neighbouring universes are doing the same either expanding or shrinking right now. (I can not imagine that they are doing nothing at the moment).To make something to expand or shrink there must have some kind of energy or force to drive it.My Questions are:1. What is the force to drive the universe to expand?2. Is gravity the only force to make universe to contract?3. How could the gravity, as a very weak force, to make the Big Crunch to start, where it has only 1-2% of the mass in the universe?4. Where do the force(s) come from and what kind of characters this or these force(s) would have if they do exist?5. Why does not the universe expand with a uniform speed?6. Is there anything to do with its neighbouring universes while an universe is expanding or contracting? If there is, why and how?

Thread moved here from the Proposed New Topics forum.

Before I start answering your questions, I would like to point out that I think this statement is nonsense. On what does Hawking base this number? Why would they be neighbouring us? They could just as well exist nowhere "near" our universe, if one could even look at it that way. No. The current understanding is that it will expand "forever" until there is heat death. And what you can imagine is irrelevant. They COULD be doing nothing. But since we have absolutely no way of knowing how ANY universe other then ours behaves, this is all speculation.Alright, on to the questions. I believe this is called dark enery. As far as I know, yes. But like I said before, current understanding (the expansion is accelerating) says the universe will not contract. Like I said, it can't according to current understanding. This question makes no sense to me. I think because of dark energy, but I'm not entirely sure. Since we don't even know if there are any "neighbouring" universes, we have no way of determining this.

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I hunt for the truth

Hi youngkiwi,I'm no expert in this area of science so I will try to answer only what I do know. Currently, there is no evidence that the expansion is slowing down, let alone, eventually, contracting. In fact, it's quite the opposite, the universe is expanding at an accelerated rate and shows no signs of stopping.This hypothesis is known as The Big Rip:

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The Big Rip is a cosmological hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of universe, from stars and galaxies to atoms and subatomic particles, are progressively torn apart by the expansion of the universe at a certain time in the future. Theoretically, the scale factor of the universe becomes infinite at a finite time in the future.

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The hypothesis relies crucially on the type of dark energy in the universe. The key value is the equation of state w, the ratio between the dark energy pressure and its energy density. At w < −1, the universe will eventually be pulled apart. Such energy is called phantom energy, a more extreme form of quintessence.

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In a phantom energy-dominated universe, the "fabric" of the universe expands at an ever-increasing rate. However, this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point gets ever closer. When the size of the observable universe is smaller than any particular structure, then no interaction between the farthest parts of the structure can occur, neither gravitational nor electromagnetic (nor weak or strong), and they will be ripped apart.

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First, the galaxies would be separated from each other. About 60 million years before the end, gravity would be too weak to hold the Milky Way and other individual galaxies together. Approximately three months before the end, the Solar system will be gravitationally unbound. In the last minutes, stars and planets will be torn apart, and an instant before the end, atoms will be destroyed.

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The authors of this hypothesis, led by Robert Caldwell of Dartmouth College, calculate that the end of the universe as we now know it would be in approximately 50 billion years.

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Dark EnergyThat I'm aware of, yes. Forces, such as gravity, don't "come from anywhere". Gravity, for exapmle, is the result of mass curving spacetime. The electromagnetic force is the force that the electromagnetic field exerts on electrically charged particles. And so on...The forces are the result of this type of universe with these specific "laws".----------------------------------------------------------Ok, that's as much I'd be willing to answer with some confidence. There are others on this site with much more knowledge of this.Hope this helped.- Oni

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"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks"I never knew there was another option other than to question everything"--Noam Chomsky

Hi Huntard (if I may call you this way:Thanks for your answers.Please note that thoses questions are about multiverse. If you do not believe that the multiverse is existed your answers may not helpEdited by youngkiwi, : Add name

Of course. Whether I believe in a multiverse or not is irrelevant, we CAN'T know anything about what's "outside" this universe (if there even is such a thing). So ANYTHING we say about it will be pure speculation. Even if there are other universes out there, we don't know they exist, we have no way of measuring them, we have no way of telling what their effects are on our universe, in short, we don't know anything about them.

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I hunt for the truth

I think you may have mis-read what Stephen was saying, or he was being mis-quoted - but anyway, there are a wide variety of possible "multiverse" scenarios, and I strongly suspect that several of these scenarios are very close to our reality - in other words, there are multiple "multiverses" You're asking questions at a level where the concept of "force" is a bit too vague and "Mickey-Mouse". 4d Space-time simply shapes itself to the mass/energy distribution in 4d space-time, and the positions of the masses in the space-time are naturally carried by this shaping. From our 3d perspective, we see this as attraction between masses, orbits, and on the large-scale, expansion. "Gravity" is simply our term for the affects of space-time shaping when it appears to create "attractive" type behaviour. Universe wide positive energy densities (most mass and energy types) will cause space-time to close up, which we see as contraction or slowing expansion, and negative energy densities (dark energy, inflaton field, Casimir energy) will cause space-time to open up, which we see as slowing contraction, and accelerating expansion. I would re-phrase this as - how can the small amount of (positive energy density) mass in the Universe make the Big Crunch happen, when it is so small compared to the (negative energy density) dark energy?Answer - it can't, given the present relative quantities of matter/dark matter on one side and dark energy on the other.If dark energy diminished or vanishes, then the positive energy density will again dominate and we will see slowing expansion, and possible eventual re-collapse and Big Crunch. Forces are what we 3d humans perceive as the action of the fields that make up reality. Because that is not how space-time responds to the energy distribution in our Universe. Of all possible rates of expansion and contraction, a uniform rate would be very surprising and would require very specific (and probably artificial) energy distributions. Yes - if our Universe is a 4d "membrane" within a higher-dimensional space (as many of us speculate) then neighbouring membranes could affect the response of our 4d space-time to the energy distribution. We could potentially measure this affect and use it to study the higher-dimensional physics of the "multiverse".

That's very interesting. Upon hearing about this multiverse theory in relative detail for the first time (through Richard Dawkins, but he was just relaying what someone else told him) I had thought of this "multiverse" as a sort of foam, where all the universes are in contact with some other universe.If what you say could be true, what would occupy the space in between the universes? (So hard to visualize...)

That's just it. It wouldn't be "space" as we 3d humans percieve it, it would be at least 5d space and possibly even 11d space if string theory is right.

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I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.
- Stephen Roberts

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I'm a polyatheist - there are many gods I don't believe in
- Dan Foutes

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"In the beginning, the Universe was created. This has made a lot of people very angry and has widely been considered as a bad move."
- Douglas Adams

I can find no reference to this quote or anything close to it. Please provide some sort of source.Since Hawking never said this your premise is faulty from the beginning.

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Facts don't lie or have an agenda. Facts are just facts

I'll leave aside what you say Hawking said - I can't find his words.Others have answered, they may be better answers than mine. I may be wrong.don't shoot me if I am!1. What is the force to drive the universe to expand?
1) the force that drives the universe' expansion is the big bang. It was THAT big2. Is gravity the only force to make universe to contract?
2. Yup.3. How could the gravity, as a very weak force, to make the Big Crunch to start, where it has only 1-2% of the mass in the universe?
3) we don't know it will, but the idea is that even though it's weak, it's very pervasive and even a small pull would eventually stop the expansion because it carries on pulling all the time4. Where do the force(s) come from and what kind of characters this or these force(s) would have if they do exist?
4) the forces of the universe? I am NOT the right person to answer, but I think it's to do with how our universe is. "it just is" might be a bad answer, but...apparently there had to be forces as there are, and they are like they are because...they are?If you get into multiverse theory, we're the random collection of forces that not only resulted in a semi-stable reality but life evolved to figure them out.Some say "gee, it's so amazing it's got to be MADE", in which case it's real easy. Godidit.5. Why does not the universe expand with a uniform speed?
5)How do you know it doesn't?6. Is there anything to do with its neighbouring universes while an universe is expanding or contracting? If there is, why and how?
6)Don't think so, unless our space/time matrix impinges on another, in which case...there would be some sort of underlying reality superceding our own, and I'm really not able to tell you if that's at all possible or probable.Edited by greyseal, : No reason given.

I have a question about the universe that seems to fit into this thread:I understand (at least at a layman's level) that time is a characteristic of the universe, so it doesn't make sense to talk about "before" and "after" the universe. But can we say that for sure? More generally, can we say ANYTHING about what is outside the universe? Maybe whatever is outside the universe is very similar to what is inside, to the point where there is spacetime, or something very much like it. Can we rule anything out? I am looking for an answer from what science can tell us more than a philosophical answer.Anyone?

Hi Aware Wolf!I suspect you aren't getting any responses because everyone is sick to death of making the begging-the-question noises that the topic requires. So let me just step up and get it out of the way, and maybe help answer your real question a little too. Sadly, the semantics have shifted. I'm a big fan of Wheeler, and love to ramble on about the many alternate universes that comprise the multiverse myself. But lately good people with attention to the real impact of words have begun insisting that uni- means "one" and that the "universe" therefore ought to mean, absolutely everything.What's outside the observable universe, is the implied universe. What's outside the known universe, is the unknown universe. What's outside the current universe, is the larger more permanent universe. And so on, capiche?That doesn't mean those lovely concepts are gone though! With the advent of superstring theory, they like to refer to those other spacetimes as "branes". And it's still perfectly legitimate to discuss Wheeler's alternate histories as well, only we need to stick with the word "worlds". It's all the same stuff as before really, we just have to be more exact in our speech or someone will waste dozens of posts arguing semantics instead of talking about what's important. Oh certainly, at least to some extent. For example, the observed universe is only 26-27 billion light years across; the implied universe, which is what the observed universe has likely become over the past 13ish billion years, is believed to be about 150 billion light-years across. And it constitutes spacetime as much as anything can, very definition of the word.As for the alternate worlds, if they exist they are by nature spacetime too, just different versions of what happened in our world, because one or another quantum event twitched a different way. We are still pretty close to home here.These "branes" are bit more imposing. Some of them may be very much like our reality, and some may be very different. We are going to need a lot more math and some successful experiments to start getting more specific about how this ought to work.As for what's in our own spacetime, but outside the known and implied universe, well, it's probably much the same as what we do know and imply. At least however far spacetime reaches, the rules will be much the same. As for how far it doesn't reach, we won't ever know or guess. Well, we can talk about the first few gillionths of a second of this spacetime, which involved every possible quantum reaction going off at once in an extremely limited and probably unmediated bit of nothing and immediately expanded to several billion light-years worth of evenly distributed matter/energy. To discuss what was "before" this, it's a good idea to look at how it will end.Depending whether the universe is finite (curved inward) or infinite (curved outward), this spacetime is either going to run out of steam and collapse in on itself (Big Crunch / Big Gnab), resulting in a cyclical series of expansions and contractions; or else, it is going to just keep expanding (Big Freeze / Big Rip) and eventually arrive at a point where no existing particle has any effect on any other existing particles, causing the space between them to become unmediated and collapse into a true vacuum, potentially allowing a near-infinite amount of virtual particles to explode out of the haze into reality and start competing again as matter/energy in a new spacetime.So what was "before" this spacetime really depends on what kind of spacetime "that one" was. It's all speculation anyway, no one is going to hang around and take pictures, you know? But these are the options the math has implied so far.

Thanks for the reply, Iblis. I have to admit, I'm not sure if I understand everything you said, or even if you answered my overall question. Probably I just don't have a good enough grasp on the whole multiverse/brane/whatever theories.I've been talking with a friend about the beginning of the universe, and I've been saying things like "We don't know how this universe came to exist." and "We don't know anything about what may or may not exist outside the universe, science has no way of measuring that." and it occurred to me that I really didn't know if those statements were true. Hence the question.

You aren't wrong.Especially if we use the word "universe" correctly, as meaning, everywhere we know of and then also everywhere we don't know of, all "wheres" whatsoever.Most of the other things I mentioned relate to theories that the math could imply, that we have no idea how we could ever test. You follow? Some of it, like the branes, we may soon figure out a way to, at least have better theories about.All the other stuff I've mentioned relates to subdivisions of the larger question. For example, when you look out into the sky, all those stars you see, are in our galaxy. Most of them are within a few thousand light-years, the whole Milky Way is only about 100,000 light years across. And a lot of those stars aren't visible to the naked eye, you need telescopes of various kinds to see them. Some of the brighter areas you see (not stars, just bits of less dark) are other galaxies, the nearest one you can easily make out is Andromeda, about two and a half million light years away, but there are many that are closer but smaller and therefore harder to see. There are other bright spots within our own galaxy, which are nebulae, ie hot clouds of gas, and distinguishing these from real galaxies was a fight that didn't really start to get settled until around 1920.So that's it for eyes and telescopes, only a few million light years. Once we add in radioastronomy though, we can see a lot farther. The farthest we can see is around 13 billion light years, which is also what the Hubble math tends toward seeing as the age of the universe. Keep in mind though, that we are seeing it as it was, back then, not as it is now. We can measure the expansion we see happening then, and since then in places closer, and make some guesses about how it is doing now. That's the implied universe I mentioned. But, they really are guesses, just educated ones. Everything more than a million light years away could have turned into giant fruit loops a few thousand years ago, and you and I would never know unless someone figured out a way to wormhole out there without breaking causality.Then also, the math allows us to guess how it all might end. And taking that and correlating that with how it all began, provides some room for guessing about what was "before" it. But that's a long ways away and a long time getting there, and no imaginable tech as of yet to do the job.So the best bet for something "outside" the universe we know is other dimensions. A few feet away, in some odd direction we can't measure yet, there might be another you eating fruit loops instead of typing on the internet. And a few feet away, in a different unknown direction from some totally other theory, there might be a place where light only travels a few feet per second. These places, we are likely to get to, before we ever get to even another galaxy.Edited by Iblis, : detail