TCS Presents: A Very Special...
What lies outside the universe?
Alright guys, reality is about to get multi-dimensional up in here.
Firstly, when I say "universe", I am referring to the observable universe, and that is defined by the speed of light. We can only see things due to light emitted or reflected from an object, and as such, we will never be able to see farther than the distance that light could have traveled since the beginning of the universe, about 13.87 billion years ago.
However, the observable universe is probably not all there is, and there are a few pretty interesting theories as to what might be going on outside our universe-monkey-sphere, as it were.
The image below is the Cosmic Microwave Background. It is the very limit of our observable universe, and it takes us pretty close to the beginning of space and time. This picture is what the universe was like only 380,000 years after the Big Bang. That is like the blink of an eye, in astronomical time scales. Basically, this image is when the lights first turned on in the universe. Beyond this point, we will never be able to see.
To think of anything as "outside" the universe is a fairly difficult concept. To truly understand the concept, we would have to truly understand the state of our own universe, and though we know a lot, there are many problems in our basic theories that must be understood before we can reconcile quantum theories with relativistic theories.
I need to get all kinds of dimensional on your asses now, so brace yourselves.
We occupy and experience four dimensions, with the fourth being time. To imagine the shape of the universe, we need to think only in three dimensions for now. Except technically, we will be imagining in two dimensions. Bear with me here...
It is ok if it is a little hard to follow. Michael still thinks this is fact.
Imagine a two dimensional sheet, curved to form a sphere. So the material is two dimensional, curved into a three dimensional shape. Now, that is not what space is like. We need to bump everything up one dimension, a three dimensional "sheet" curved into a four dimensional shape. Since that is impossible for our puny minds to imagine, just pretend it's like a hollow spherical shell, and that everything we observe resides on this shell (it's actually thought that the universe is more of a saddle shape, and not in fact closed but open, but we don't need to get into that here).
"Like this! Except not like this at all." -Science
Now, we know that the universe is expanding, and it has been since the Big Bang. We also know now that the expansion of the universe is, in fact, accelerating. From the point of view of our local cluster of galaxies, it appears that everything else in the universe is rushing away from us, which I'm sure hurt a few galactic feelings. This is thought to be due to the presence of Dark Energy, and well, we don't quite know what that is, but we are almost certain that it's there. But Dark Energy may not be the only force at work here.
So, you might ask, what is the universe expanding into? The answer, confusingly, is nothing at all. Not even a void or blank space, just nothing. The "bubble" of our universe was created at the Big Bang, and outside of this we have no means to define space or time.
Some theories suggest, though, that multiple universes came into existence at the time of the Big Bang.
This paints a picture of a whole bunch of universe bubbles, all snuggled up against each other, expanding away, with no means for us to ever see across the "border" into a neighbouring universe due to the whole speed of light thing I mentioned above (you might have heard of it). It is thought that these other universes could have different fundamental laws of physics, and that they could be "tuned" differently to our own.
However, these universes may be making themselves known by the effect that they have on our universe. Over the past five years or so, we have observed a phenomenon referred to as Dark Flow. This is the movement of a bunch of galaxy clusters all in the same direction. This could not be explained with our current understanding of the distribution of matter in the universe, and, as such, points to some external source of gravity tugging on our universe from the outside. This is pretty healthy evidence towards the existence of a multiverse.
That is perhaps the most popular, but by no means only, theory as to what exactly is going on here.
Some cosmologists and quantum theorists suggest that in the quantum foam of our reality, there are infinitely many universes existing alongside our own. Now, though this is rather more philosophical in nature than physical, it is interesting nonetheless. They suggest that there are infinitely many universes, some almost exactly like ours, some so completely different that we couldn't even imagine them, and literally every other possibility in between.
With infinitely many universes, it's reasoned that anything that could have happened will have happened in one or more of these universes. The implications of this go from the extremely insane to the extremely mundane. Perhaps in one universe, matter was perfectly evenly distributed at the beginning, and as such no galaxies or stars or black holes, would have formed. That universe is just a perfectly boring fog.
Perhaps, every universe is dinosaurs, or zombies, or some other crazy-awesome Sliders episode.
Perhaps there is another universe just like ours. So much like ours that it even has a you. Theoretically, out there in in the multiverse, there are infinitely many universes almost identical to our own apart from absurdly small differences.
We are all Jet Li, somewhere.
Maybe the other you wore a different pair of shoes today. Or maybe the other you is Batman. In fact, given the theory, not only are all these variations possible, they are actually probable. So basically, somewhere, we are all Batman. Probably. Sweet.
Pictured: You, somewhere. Probably.
There is a really interesting theory in Black-hole Cosmology, that suggests that our universe exists inside the event horizon of a black hole, which exists within another universe. Not just any black hole though, of course. It would have to be a super-duper fucking ginormous one, but that idea is not of the question. (The Schwartzchild radius of said black hole would have to equal or exceed the radius of our universe, and a black hole this size is, indeed, theoretically possible). This is by far my personal favourite of all the theories, because, damn...that's pretty cool. And if you think about it, it totally makes sense.
The Big Bang as we know it could theoretically have occurred at the singularity of a black hole, and the limits of our observable universe match up nicely with the limitations of observing farther than the event horizon of a black hole. Now, obviously, we know how a black hole is formed, but our laws of physics break down at the singularity. We pretty much have no way of knowing for certain what the hell is going on in there, because we will never ever be able to see inside. So - universes? Maybe!
We have come to terms with the nature of our three dimensional universe (plus time), right? Well, here's the thing. It might be a teeeny weeeny bit more complicated than that. Now, please bear in mind that the following theories are mathematical and theoretical constructs, and are not satisfactorily predictive, and therefore un-testable. Possible? Sure, why not. But testable? I'm afraid not, and as such, they are more of a tortuously-awesome and mind-fucking thought exercise.
There are quite a few theories floating around. Some are more plausible than others, and some suggest that reality consists of eleven dimensions, not just four. Eleven. Dimensions.
Yup.... But it's cool, and not that complicated, because five or six of those are probably kind of folded up, and thus we don't have to worry about them. Think of it like this: we have up, down, and sideways. That's our 3D space. The universe, or rather more specifically reality, apparently has seven more directions perpendicular to those three that we are familiar with, in addition to time.
Still with me? Awesome! Onward down the rabbit-hole!
All these extra dimensions are required in order for the M-theory to hold any water. Basically M-theory is as follows:
Well, duuuuh. That clears that up.
M-theory is basically an extension of String Theory (or a unification of the five String Theories), in which every particle is said to exist on a three dimensional structure called a brane. (Also, every particle is also a little vibrating string, but we don't need to get into that.) So everything in our universe exists on a brane, and there are infinitely many more branes just kind of hanging out, existing in parallel to us.
Ohhhhh, well when you put it like that it's so obvious!
Now, the branes themselves can exist in any dimension from one to nine, and the tenth is the spatial dimension which encompasses them all, the eleventh is time. However, not all particles (or strings) are bound to their brane, with particles such as gravitons thought to be capable of free roaming. If this is in fact the case, it would go a long way to reconciling the problems between Einstein's General Relativity (interactions of very big things) and Quantum Theory (interactions of very small things). Remember the singularity of the black hole from earlier? Perfect example of how our laws don't quite work together. That is pretty much the number one problem in physics right now, it's a pretty big deal, and that is one of the things physicists are trying to test with the LHC.
Within this theory, it is supposed that when two of these branes collide - boom - we have ourselves a Big Bang caused by the unleashing of massive amounts of energy from the collision, and a brand new universe. This new baby universe might have different laws of physics to ours, or identical, or somewhere in between.
There are many complicated problems with this theory, but the main one in my opinion is the presence of the Hubble Volume. The Hubble Volume is basically all the stuff in our universe. Get all the stuff, squish it all together, measure it, that is the Hubble Volume. Now, in every theory regarding multiverses, be they plausible or implausible, one thing remains a necessity, the amount of stuff required to kick off a universe. There needs to be a certain matter-energy ratio in order for a universe to happen. We know we cannot just create energy (thanks Newton!), and because of the energy-mass equivalence (thanks Einstein!) there needs to be an appropriate amount of matter/energy in order for anything to happen.
So when two branes collide and create this new universe, where does the matter and energy come from? The energy can be provided by a massive collision, but that means energy must be lost from the two colliding branes. Same goes for matter. So if this theory were true, it is conceivable that we would observe energy and matter loss from our universe, were it involved in a collision. If every brane is taking part in this weird multi-dimensional orgy, then we should see matter and energy loss all over the place, in order to make up the Hubble Volume for the new universe. But we don't see that, not at a scale that would confirm this kind of activity, anyway. That is not to say that it is not happening elsewhere, just not in our own universe, and as such we will never be able to study it.
Now in fairness, these theories get absurdly complicated the deeper you go, and I have barely skimmed the surface here, but that is a general idea of some of the various multiverse theories that we have, so far.
"Which wild theories are true?", you ask," How can we ever know the truth?".
Well, the truth is, we really don't know, but everybody is having a lot of fun working on it. Let me get back to you on that in about twenty years.
http://www.bbc.co.uk/science/horizon/20 ... rans.shtml
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