Physicists
have come up with a bold new idea to explain the enduring mystery of our
expanding Universe – we might actually be living in a 'bubble' between other
five-dimensional spaces.
If that
makes your brain hurt, don't worry, it's supposed to. But we can break this
down.
Our Universe
as we know it has four dimensions: the three dimensions of space (up and down,
left and right, back and forth), and one dimension of time that keeps us all
ticking along.
But this new
solution from physicists at Uppsala University in Sweden suggests that are
other types of space that are five dimensional, and where two of those spaces
come together, the junction forms an expanding bubble.
"The
whole Universe is accommodated on the edge of this expanding bubble," anUppsala press release explains.
"It is
conceivable that there are more bubbles than ours, corresponding to other
universes."
It's pretty
crazy stuff, but there's an incredibly important goal here – to try and finally
explain what's going on with 'dark energy', the theoretical force responsible
for our Universe's constant expansion.
For decades,
researchers have tried to solve the dark energy problem using string theory,
without a whole lot of luck.
String
theory is one of science's "great idea, shame about the facts"
concepts. It's elegant, and carries the hope of reconciling incompatible ideas
of physics.
It emerged
from early efforts to add dimensions to general relativity, suggesting that
properties of matter like charge and spin are a consequence of
single-dimensional 'strings' wiggling multiple dimensions.
Those
strings can behave in a huge variety of ways, depending on how many dimensions
you add or other constraining properties, resulting in some 10^500 solutions,
of which our Universe's mix of features is just one.
The problem
is it's becoming increasingly clear that string theory is also wrong, and
incompatible with what we observe in the Universe.
And where
it's not even wrong, it's impractical, if not impossible to test. So why
bother?
Well, there
is more than one way to be wrong in science. Some wrongs are worse than others,
and while it has major problems, string theory is like an old car that no
longer runs but has plenty of scrap left in it.
Take this
whole expanding space thing.
For a while
now, we've blamed this on a force called dark energy – a phenomenon that sees
more space being added without ripping up stuff floating inside it.
We've named
this the de Sitter Universe solution, after the Dutch astrophysicist Willem de
Sitter, and it's pretty broadly accepted as being a good match for what we see.
Unfortunately
none of the past variations of string theory are up to the task of describing
what's going on. They only work if the vacuum energy is dropping, or at least
steadily negative.
So we can
ditch the whole string idea or throw out the de Sitter model we've all come to
know and love.
But now the
Swedish researchers have come up with a new solution that keeps both string
theory and the de Sitter Universe solution.
It's based
on another idea that emerged around 20 years ago. Back then, American
theoretical physicists Lisa Randall and Raman Sundrum proposed alternative
models of the Universe based on different kinds of 5D spaces meeting at a point
called branes, aiming to solve the problem of why gravity is so much weaker
than other forces.
Think of a
kind of space that ticks with time, and has an up and down, left and right,
back and forth … and something else. No, I don't know what it looks like
either.
Importantly,
it is also what we call an anti-de Sitter space. Unlike our own, this one isn't
dominated by dark energy and has the right kind of negative energy.
Glue two of
these 5D anti-de Sitter spaces together. Randall and Sundrum proposed different
branes that could help explain different forces.
In this
case, the researchers used the same kind of spaces to describe our own
expanding 4D Universe, complete with particles that transfer the right amount
of gravity.
Where does
string theory come into play? Well its the 'strings' (the light beams in the
image at the top of this page) that are expanding out of the extra dimension
into our Universe, giving it its particular 'flavour'.
"All
existing matter in the Universe corresponds to the ends of strings that extend
out into the extra dimension," the press release explains.
More
importantly, unlike existing string theory models, it still works thanks to
those anti-de Sitter spaces. In fact, it describes something like a growing
bubble, with a 5D space inside and outside.
Just like
all other string models, they're unlikely to have nailed the solution in one
shot. Living on the surface of an inter-dimensional bubble is a poetic thought,
but still hugely speculative.
Physics is
getting to the point we're going to need to throw down interesting ideas that work
on paper and then see what matches reality.
Somewhere in
those strange notions of vibrating strings and bubble Universes there are going
to be conclusions that look eerily like strange statistics that pop up in
particle accelerators or numbers that refuse to add in astronomical
observations.
And maybe –
just maybe – those scraps of string theory will find themselves inside the next
generation of physics' greatest ideas.
This
research was published in Physical Review Letters.
Comments
Post a Comment