I posted some of this on another thread, but it fits here too.
The word “universe” actually means “all there is.” There could be no “multiple universes,” they would all just be different views (huh?) of the “universe.”
Our current space-time continuum came into existence at (or picoseconds after) the Big Bang. That includes all matter, free space, and time. Before that was a singularity. (This all hinges, of course, on the Big Bang theory being correct.)
There is no “outside” the universe because we take it with where ever we may go. There is no “before” our universe because our time did not exist until after the Big Bang.
And try not to think about the Big Bang as an actual explosion. Consider it more like a super rapid expansion of very strange particles and energies.
For more insight about the Big Bang and what could have caused it, do a search of “First Cause” theories. Or, delve into theology. Either way, a verifiable answer seems to be non-existant.
One, the Big Bang is a fairly well proven theory. There are three stool legs on which it stands: primordial abundances of nuclei, the Hubble Recession, and the “Big Bang echo” known as the Cosmic Microwave Background (or the CMB). Any competing theories have to take the success of analyses of these evidences into account. This either requires that your theory look almost exactly like a Big Bang with little variations at times less than a second after the “initiation” or that you come up with a completely different explanation that adequately accounts for all phenomena. For a while, the “Steady State” theory was held by a few die-hards, but they’ve all either kicked the bucket now or have had to admit that they cannot explain the observations as well as the Big Bang. Still, there are a few “alternative cosmologies” out there that attempt to rustle the feathers of the establishment. So far, none has been very successful.
We really don’t know what is going on in our universe much before the 1 second mark. Sure, we understand the decoupling of various particle species using quantum chromodynamics and quantum electrodynamics, but a “grand unified theory” we have not, therefore we really can’t say how it all fits together. Some string theorists think they have a pretty good idea and supersymmetry has also lead us to be encouraged, but, for example, the dark energy component of our universe has most scientists completely puzzled.
The balloon analogy is a good one for a positively curved universe and ONLY makes any sense if you confine yourself to the surface of a balloon. Of course, to extend it to reality you have to realize that we live in a four dimensional universe not a two dimensional one and that there are other possibilities for curvature. Right now, theorists expect that the universe is flat which is a fairly difficult concept to wrap your head around if you’re thinking about balloons.
The “singularity” at the Big Bang is just one possibility. There are plenty of other models out there which don’t require a singularity. They are all consistent with current observations too. A cyclic universe is one idea that cannot be ruled out. Likewise there are models for universes that spawn separate “universes” that will never be observed by us (and therefore can never have their “existence” confirmed by us). There is no way we know of right now to check the veracity of any of these models. We are in the dark.
But we do know the history of the universe pretty well back to the first fractions of a second. I’d say that’s pretty good progress. We still have a long way to go.
Since you’re here JS Princeton, have any scoop on recent findings pro/con concerning gravity not following the inverse square law at very long distance?
There are two things you may be referring to. One is the so-called MOND theory. It’s a rather pernicious thing that has been purposed as an alternative to dark matter and therefore GR-based cosmology in general. The idea is to modify newtonian dynamics and reclaim a sort of gravitational relationship that holds for local universe but allows for the rotation curves to remain flat for galaxies and clusters. However, resent gravitational lensing studies and forrays into X-ray emmission in the intergalactic medium of clusters have basically provided a huge thorn in the side of this idea that I don’t believe has been adequately answered. As far as I’m concerned, GR and its consistency over a period of time is still right.
There is another proposal on the table that the gravitational constant might be slowly changing over time. This one might very well be true and has measurable effects that are currently being explored. We don’t have evidence one way or the other for it at this point.
Now that I think of it, you may also be thinking of the recent hooha over the possibilities of changing QM over cosmological scales by looking at the spacing of emmission line pairs from distant quasar sources. While an effect may or may not have been observed, I think it’s fairly well established that any change would have a relatively minor effect on the overall future cosmology of the universe.
MOND is exactly what I was talking about. Thanks for the update on that. Even the guy putting MOND forward didn’t give it much of a chance to be correct, but thought it worth investigating.
On the other thread, you linked back to this one… I don’t see that any of this could be relevant.
For completeness sake, according to Hoyle (Fred, that is). He was an ardent steady state advocate, and never did renounce that theory in spite of overwhelming evidence for the Big Bang. He always managed to explain away the evidence.
Without getting too complex, the effects would be seen in the relative abundances of various nucleons. Right now the observed cosmic abundances fall within an appropriate margin of error of a non-changing gravitational constant when you parameterize this with CMB and Hubble Recession information.
Ok, I can see that. (I thought I was gaining weight).
But if the gravatational constant did change, wouldn’t that alter the curvature of space-time, changing the clock that we use to calculate velocities, reactions, interactions, etc…?
If the clock and the constant changed in the same direction, it would be virtually unnoticeable, wouldn’t it?
And an abundance of exotic particles and and “dark energy” could probably be explained away by other theories.
So, anyways… This obviously isn’t my field of expertise, just a very curious ameture. Any non-math explanations would be appreciated.
There have been some suggestions that black holes formed in this universe become the Big Bang of another universe. Of course this means our universe might have started as an offshoot of some other universe.
In one version, the values of the physical constants get reshuffled in each “bang”. Then the theory makes an actual prediction: the most likely universe is one that has values of the physical constants that maximize the production of black holes. (Because the universes with the most black holes will produce the most new universes, which will in turn produce more universes, etc.) I think there’s a book called “The Evolutionary Universe”. Problem: we don’t know if in fact the values of the constants are the right ones for maximum BH production.
I’m using “universe” in the sense of “stuff accessible to investigation” rather than in the sense of “all there is”. Since these other “universes” are, by definition, inaccessible to us, I for one think it’s a waste of time to speculate about them.
If the universe started out the size of an atom, would this mean that all of the elements known to man were a part of this atom? And it also had all the mass added into it?
And scotth had said
So if there was no space, how would the super atom have expanded into it’s vast distance?
I suppose everything that became the elements known to man would have been there, but (as far as my limited understanding goes) matter itself wasn’t around in the early stages - it kind of ‘condensed’ as expansion occured.
EVERYTHING you see or touch was originally in the Big Bang singularity (or whatever you want to call it…the atom sized thing although it was probably smaller than that). No mass was added to it at all. It had everything to start with.
Realize that what comprised the Big Bang singularity were not elements but rather energy. Our understadning of physics isn’t good enough to say what exactly was going on in there. Once the Big Bang occured the energy was no longer ‘compacted’ and it started cooling off. The cooling process allowed matter to form (mostly hydrogen) which ultimately made the first stars. The stars themselves then manufactured the rest fo the elements we see today.
ALL space was within the ‘super atom’. Space itself expanded. I know it’s hard to imagine but the ‘super atom’ didn’t expand into anything…there is no ‘space’ outside of our Universe.
That sounds to me like your saying the universe has a “hard” defined outline. Are you saying that space is created by the expansion itself? Maybe we need to define “space” as used in this discussion…
If you could hypothetically travel faster than light and reach the edge of the expanding matter we call the universe, what would you encounter? or would you be creating your own space behind you?
Yes, space is created by the expansion. A popular analogy is consider space to be the surface of an inflating balloon. As the balloon gets larger, there is more surface area. It is being created everywhere, and there is no edge.
Very good question… now you are getting to why this is confusing.
Depending on the geometry of space, a couple of things could happen.
One such possibility is that you would never hit the edge of space (as it doesn’t exist) and would eventually return to your starting point while traveling in what appeared to you as a straight path the entire time.
This would be analogous to going heading east at the equator of the Earth until you returned to your starting point. If you did not know the earth was round, that would be very confusing.
Doing this trick with space is very confusing mentally, but pretty clear mathmatically. If you consider an extra dimension for space to bend or distort in (and General Relativity requires this), it is possible.
This is why astronomers/astro physicists are so interested in the total mass of the contents of the universe. If that was know exactly (as well as its distribution), the curvature of space could be worked out mathmatically and specific answers could be provided to questions like yours.
Whuckfistle: you are now entering into the domain of “horizons”, which is a fancy way of talking about what having a maximum speed limit will do to an observable universe. Outside a “horizon” we really can’t say what the universe appears to be, but we sort of have an intuitive feel that it should be the same as inside. Of course, the “horizon” is different for each different location, so this is what leads us to believe this. There is a bit of a struggle between the Copernican principle (we are in no special place) and the anthropic principle (we are in a universe that allows us to exist) that isn’t resolved well. A decent answer to your last question might be summed up in “I don’t know”.
As far as the “cosmic egg” or the initial “atom”, realize that it wasn’t an “egg” or an “atom” at all, but actually the entire universe: space, time, energy density, and the stuff that makes your parents as well as the galaxy Andromeda and the most distant quasars were all “on top of” each other. It’s rather mind blowing to be sure, but that’s the consequence of the universe expanding.
Finally, with regards to changing gravitational constant: since the change is so small (we know it has to be because we can measure dynamical and kinematic effects in the universe and see them to obey our laws of gravity), it has a negligible effect on the actual curvature of the universe. It also will have no effect on the clocks in our universe since the speed of light should remain constant. Of course, there are those who believe the speed of light may be changing, but that’s another topic.