Doctor Strange, not only does he sound
remarkably like House MD, he is the
sorcerer supreme, a master of the mystic
arts and as we know from Thor magic is
just science we don't understand yet. Now
his powers allow him to experience
realities beyond those that we
regularly perceive and one of those
hinted at in the film has served as the
home of most of his nefarious foes,
including Dormammu. That's the Dark
Dimension. But does a place like that
actually exist?
First up let's be clear by what we
actually mean by a dimension. The number
of dimensions is simply the minimum
number of coordinates, which are
essentially just numbers, that you need
to define any space.
Let's say we take a line, even a really
wiggly one like that. You just need
one number to define any point on it, say
the distance along the line. A surface on
the other hand, say like the surface of
the Earth, needs two coordinates so it's
two dimensional: latitude and longitude
for example. And our universe seems to
have three spatial dimensions because I
can move left to right, backwards and
forwards, and of course up and down. And
don't forget time as well that is also a
dimension, a slightly different dimension
but we won't get into that here. In
Doctor Strange and other works of science
fiction though the word dimension is
often used to describe other planes of
existence, say alternate or parallel
universes. The idea being that to get to
one of those places you have to travel
through a dimension beyond the standard
three. How Doctor Strange actually does that,
well you can check out a video on the
Hybrid Network to find out.
Let's talk about the word dark too
because it's often used in cosmology,
usually for things that we don't really
understand yet because they don't seem
to interact electromagnetically, they don't
give off any wavelength of light that we
can detect. But we do see their
gravitational effects. Dark matter for
instance is currently thought to be some
sort of exotic weakly interacting
massive particle that shapes the
structure of galaxies and the universe,
 
cosmic scaffolding has often been known;
and dark energy we think is the
cosmological constant the energy of the
vacuum itself which is driving the
expansion of the universe and
accelerating it. So if we're looking for
Doctor Strange's Dark Dimension we really
want to find a dimension thats dark.
Extra dimensions may not be complete
fiction, they've actually been proposed
as a possible solution to the hierarchy
problem.
This is the question of why gravity is
so much weaker than the other
fundamental forces. Now we know at energies
of around a hundred gigaelectronvolts,
or quadrillion degrees C if you
prefer, that the electromagnetic force
and the weak nuclear force have the same
strength and they merge to become the
electroweak force. It looks like the
strong nuclear force does exactly the
same thing at a slightly higher energy,
but gravity still remains 10 to the
power of 32 times weaker. That is a huge
problem for a theory of everything. So
how might extra dimensions solve this
conundrum?
Well if we say that the three other
forces and all matter are confined to
just the regular three dimensions of
space but that gravity is allowed to
spread out not only across those
three but extra dimensions as well, then
what we would observe as gravity and its
strength would in fact be diluted and
only if we could see the full picture
across all dimensions would its strength
equal that of the other forces. Doesn't
that sound like a perfect definition of
a real Dark Dimension in physics? It does
to me. But what are these dimensions
possibly like?
One early answer to this question came
from Kaluza and Klein who proposed that
maybe we don't notice these extra
dimensions because they are really
really small and curled up, known as
compactified dimensions and there's a great
analogy for how these operates which was
actually recently featured in Stranger
Things.
It's the analogy of the tightrope walker
and the ant or flea. Now a tightrope
walker is obviously a lot bigger than
the size of the tightrope so they can
only move in one dimension, backwards or
forwards along the typerope. But because
the ant or flea is so much smaller than
the size of that tightrope,
well they can move around it as well,
they can access an extra dimension.
The idea being to access extra
dimensions you need to probe distances
much smaller than their size. In order to
solve the hierarchy problem you can
either have lots of absolutely tiny
extra dimensions or just a few slightly
larger ones. Now one extra dimension just
won't do the trick,
it'd have to be the size of an
 
astronomical unit in that case, which
means we would have noticed it by now.
But actually two could sort you out they'd
only have to be the size about hundred
micrometers in that case to solve the
hierarchy problem. Or if you believe
string and M theory they suggest there
may be six or seven extra dimensions all
about the size of the Planck length and
curled up into these weird calabi-yau
shapes. But these sorts of dark
dimensions are no good for Doctor Strange
because he is just far too big to travel
through them and of course shrinking is
Ant Man's thing.
But there is an alternative theory. This
is where we need to get brane-y. Just like
the words on a piece of paper are confined
to the two-dimensional brane that is the
surface of the paper itself,
what if we are confined to a
three-dimensional brane that exists
within a higher-dimensional space?
Because we're tied to that brane it
doesn't mean we have to limit the size
of any extra dimensions. One theory, the
Randall Sundrum model or RS model, has only
one extra dimension but two branes at
either side of it. One of those branes is
the universe as we perceive it
containing all of the matter and forces
of the Standard Model of particle
physics, we'll call that the weak brane.
The other is the gravity brane where
gravity naturally lives, though gravity
itself can permeate the extra dimension.
Now if the weak brane contains negative
energy and the gravity brane contains
positive energy, then via general
relativity the extra dimension will be
incredibly warped and that means gravity
itself would exponentially decay across
the extra dimension, meaning we would see
it as being very very weak. Now
technically in this model the Dark
Dimension would be that extra
dimensional space between the two branes,
but what if Doctor Strange is actually
referring to the gravity brane. The
gravity brane would be an incredibly
strange place to visit, distances are
shrunk by 16 orders of magnitude, that
means you'd be a tenth of the size of a
proton, your mass would also be two
million times that of the entire human
race's and time would be accelerated to
such a rate that from the formation of
the planet Earth to now would be 14
seconds to you.
Basically the gravity brane would be
weirder than anything depicted within
the Doctor Strange movie. But it's time
for a reality check, because we have to
this date absolutely no experimental
evidence of there being any extra
dimensions whatsoever, making this entire
video some fancy Maths, but not really
Physics. That's not to say we haven't
looked for them, in fact the LHC has
provided some of the most stringent
conditions on extra dimensional theories
managing to rule them out up to certain
sizes or equivalently their energies
better than pretty much any other
experiment that we've done. On the flip
side though there are still areas that
we haven't yet looked and that leaves
the possibility open of extra dimensions,
dark dimensions from Doctor Strange,
possibly being out there. All we have to
do is find them.
Thank you so much for watching this
video be sure to like and subscribe if
you haven't already but head over to the
hybrid channel to see a sister video to
this. I'll hand over to Michael to tell you
more. How's it going guys it's failwhale
here and great video Martin. If you're
interested in figuring out how exactly
is that Doctor Strange travels across
dimensions be sure to head over to the
hybrid network youtube channel, thanks
guys, take care. So go and check that one
out and thank you again for watching.
