Well, that depends who you ask: string theory
is still very far from being able to make
conclusive claims about our universe (and, of
course, it could just be wrong!). But a common
model in string theory for our universe is
what's called the brane-world model. In this
model, our universe is actually just a four-
dimensional (three space plus one time) membrane
(or brane) that exists in a higher-dimensional
(ten or eleven dimensions!) space. The reason
this model is popular is because it gives a
possible explanation for why gravity is the
weakest of the four fundamental forces:
evidently, the electromagnetic, weak, and strong
forces are confined to only act between matter
on our brane. However, gravity is free
to "escape" from the brane, and it's
this "leaking" which makes gravity much weaker
than the other three forces.
While that's one of the prevailing ideas,
it's important to remember that it's far from
certain, and it will be a while before string
theory can make definitive claims like this!
There are still many things about string
theory that we don't including how, if it all,
string theory describes the world we live in.
However, one theory is that we are living on a 3-
dimensional object called a 'brane' which is a
part of a 9-dimensional space. (Maybe it looks
something like this
One reason some people like this idea is it
might explain why gravity is so much weaker than
the other fundamental forces (like
electromagnetism) but so far there is no
concrete evidence for or against the idea that
we live on a brane.
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