Yesterday, the BBC science news website ran a story about how the a study of the cosmic microwave background, which is basically the very faint echo of the Big Bang that reverberates around through space, has added significant weight to the theory that our universe is one of many others and exists in a kind of "multiverse".
Up until now, the multiverse theory has been just a theory, albeit one that is popular in modern physics, but as you can imagine, is pretty hard to test for - mainly because it was generally thought that in order to find out if there was anything outside our universe, we'd have to somehow be able to actually see outside it. As we already know, we can't even see across to the other side of the Universe, as light from there would not yet have had time to travel all the way to us (which, considering the Universe is 13.7 billion years old, means that that is an unbelievably large distance) and that the other side of our universe is accelerating away in the opposite direction doesn't help much either. So, not knowing where the edge of our universe is is one problem, but even if we knew that, how you get beyond there is anyone's guess and probably impossible, so there's not really much chance we're going to see what's outside and if there's other universes just hanging around out there, putting out their own universey vibe.
The general idea behind the multiverse theory is that other universes exist in their own bubbles of space and time, just like ours, and as these universes have popped in and out of existence, if they're nearby, they occasionally bump into ours. It's these collisions, and the patterns they may leave in the cosmic microwave background, that may enable us to test whether these other universes exist or not.
The current tests suggest that there may indeed be these patterns in the CMB but more data is needed before any more solid conclusions can be drawn. Next in line to run some tests is the cutting-edge Planck space telescope, which can measure the CMB in far greater detail, but results won't be available until 2013 so we're going to have to wait 'til then to find out more (well, I guess we've waited this long, so what's another 18 months...).
So far, so good. I think we're all relatively alright with the idea of other universes as a general concept, it's just extrapolating the scale up another level - our planet near other planets, our solar systems near other solar systems, our galaxy near other galaxies - why not more universes? It does tend to make you think "then what?" or "so what are those universes in?", but it seems that those might be the wrong kind of questions.
Quite reasonably, we tend to think that our universe is a big place, full of things, all bundled in there in a nice 3D kind of way. It turns out that this may be completely wrong; our universe may in fact be a hologram.
Now, unlike with multiverses, this is not quite as easy to explain so I'll skip over most of the detail and try and get the main points.
If you imagine a plain white ball and onto that ball you cleverly projected an image of a man onto it so that it looked like the man was inside the ball. Next, when you rotate the ball, the projection also makes it look like the man is rotating at the same rate so, no matter how you move the ball, it always looks like there's a man inside it, even though you know there isn't. If you did this well enough, it would be impossible to tell whether you were really looking at a man in a ball or a projection of a man in a ball. By using the projection of the man, we have essentially encoded the surface of the ball with all of the information that our eyes need to be convinced they're actually seeing a man in the ball, even though they're not.
This is a bit like how the hologram theory suggests the Universe might work, that we are the man in the ball. From our perspective, inside the ball, you'd think we wouldn't be able to tell whether we were really in the ball or just a projection on the outside - we're just the man in the ball - but it may be emerging that we've found out a way to actually test this without having to step outside the ball (or Universe, which as we said before was probably impossible).
The problem with the man in a ball analogy is that it would actually be impossible to make the projection absolutely perfect, that the surface of the ball couldn't quite contain enough information on its 2D surface to render the 3D man perfectly. For the Universe, the same should be true, that if we are a projection on the outside of the Universe, we should be able to tell if we can find any points at which the 3D universe isn't perfectly rendered.
Now, we know that Spacetime, the thing that makes up our physical universe, is grainy, a bit like pixels on a screen - while the picture looks fine and mulitcoloured mostly, if you got really close you could see the individual pixels which would all be one colour each. By undertanding the Spacetime is made up of these small pixels, we know that these must be the smallest things can get, as they're the most basic building blocks of our physical universe.
The problem is that in an experiment in Germany in 2008, a super-sensitive motion detector, looking at gravitational waves, picked up measurements that were actually smaller than it should be possible to actually detect. These measurements were a bit of a fluke, so now require their own dedicated tests to confirm, but by suggesting that there's something smaller than the building blocks of Spacetime, this adds weight to the theory that we're the projected version of the man in the ball, rather than a real one. If we're the projected version, then we're not really inside the ball at all, we're information about the man, projected onto the 2D surface on the outside.
A bit lost? Fair enough, I don't really get it either. This is head melting stuff; that we're a 2D projection of ourselves (as well as everything else) on the surface of the Universe, somewhere about 42 billion light years over there, is outstandingly high-concept stuff. For the most part, for us, it wouldn't matter either way if were "real" or a hologram, as we've seemed to get on mostly fine so far.
I'm not that convinced that hologram theory will hold up to much in the end; to me it seems that perhaps our understanding of the facts we think we know are more likely to be incorrect than the more esoteric hologram suggestion. This all heads merrily off down Stephen Hawking heavy physics string theory and M-theory routes so we're all pretty out of our depths from here on in.
In conclusion: Space is mental. The end.
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