One of the major questions in cosmology today is how large
the universe really is. While there are indicators that it is at least very,
very large, the fact is, we don't know for sure, and it may be the case that
the universe isn't just big, it's infinite. And if that is indeed the case,
then the nature of our universe starts looking really weird. For example, in an
infinite universe, there is in fact other intelligent life in the universe. Statistically
speaking, it must be so. But not aliens, per se, rather almost exact copies of
earth and the human race.
In fairness, some astronomers suspect that the universe is
finite in that it has some special geometry such as a donut shape that allows
for no boundaries, but limited volume. But on the other hand, those models of
finite universes don't fit the data we have as well as an infinite universe
does.
Why can't we tell for sure? The problem is the expansion of
the universe. Driven by dark energy, space is expanding. This means that the
further you are from an object, say a distant galaxy, the more expanding space
there is between you and it.
Ultimately, that cumulative amount of expanding space
becomes so great that it cancels out the speed of light and light waves can't reach
us from an object because the expanding space in between would require them to
travel faster than light, which light can't do. This leads to a sphere of what
we can see known as the Hubble Volume, or the observable universe. Beyond the
boundaries of this volume, we can't see a thing which means part of our
universe is invisible to us.
The trouble is, we don't know how much of the universe lies
outside the Hubble Volume. It could be only a small part, or it could be most
of the universe. Or, the universe could be infinite and never ends. And that's
the kicker, any universe that is infinite would mean that anything that's
possible in the universe happens ... somewhere, no matter how unlikely.
Infinite is infinite, after all, so if it's possible it's happened.
So long as matter is evenly distributed across the universe,
something which astronomical observations support, then that means that past
the Hubble Volume there should be exact copies of earth, our solar system and
ourselves that vary a bit in the details, but overall are nearly identical.
Your doppelganger would have many of the same memories that
you do, share the same likes and dislikes, the only difference being that your
counterpart may have eaten pizza for dinner while you had soup. And since it's
infinity we're talking about here, then the numbers of these copy planets would
be staggering. Think an infinite number of doppelganger you's.
So how far do you have to travel to find such a copy planet?
Physicist Max Tegmark has calculated that our nearest, almost perfect twin would
be about 10 to the 1028 meters from here. That's an
incomprehensibly huge distance, so you probably won't be meeting your
doppleganger any time soon. But you will see other, closer, less perfect, earth
copies, perhaps ones where the dinosaurs didn't go extinct or life took a
completely different evolutionary path.
The infinite universe possibility is actually based on
pretty solid physics and statistics making it the least questionable of any of
the multi-verse theories. Often termed a level 1 multiverse, this one would
simply be the universe at large where an infinite amount of Hubble Volumes
exist, some of them being virtually identical to our own, some of them being
very different, all of them too distant to see or reach.
The next level of a multi-verse is level 2. This is where
there are more than one level 1 multiverses. In other words a potentially
infinite amount of individually infinite universes. While not exactly
intuitive, there is a very good principle backing this: the anthropic principle.
Our universe just so happens to be perfect for supporting human life. Uncannily
so, but it didn't have to work out that way. In fact, we have no idea why it
did.
But if you've got an infinite amount of universes, then it's
no big deal statistically if you just so happen to be in the lucky one. But if
there is only one universe, then the odds of it existing just so to allow life
are astronomically against it existing. Since it clearly does, or something
does, then one must look at alternative theories such as if this is a computer
simulation.
But there is a third level, where there theoretically are
also many copies of you. The level 3 multiverse is the most controversial of
the three, but also the most mind-blowing. This theory suggests that all
possible outcomes split off from our universe and become parallel universes. In one universe, you went
to the theater. In another, you went swimming instead. You can't see these
other universes, but they would be there hovering just above you.
For me, the most interesting aspect of this thinking is that
if we can answer the question of whether the universe is finite or infinite, it
would instantly answer the question of whether there is other intelligent life
in the universe. If infinite, then statistically speaking it's a certainty.
It's just not the kind of alien life we thought it would be, its just other
versions of us. But there may be other versions of them too.
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