okay well i could tell you one of two
things i could tell you the standard
sort of classical view
of what a vacuum is uh but for me that's
not so interesting i'd rather tell you a
sort of non-standard quantum mechanical
view of the vacuum because we you know
we typically think of the vacuum as
being sort of quite a dull place with
not much going on
quantum mechanically nothing could be
further from the truth essentially
the vacuum is extremely lively place
yeah the vacuum's pretty straight
forward isn't it it's where there's
nothing there there are no particles
um you you can't breathe in a vacuum
many of us have seen the experiments
where you you take air out of a
out of a a jar and you see there's a
flame and the flame gradually goes
because first of all the oxygen is taken
out so you you're extracting something
out from a body and eventually when
there's nothing left that's the vacuum
until you go to the world of the quantum
and it seems to just blow up in your
face this vacuum the the vacuum in
quantum theory isn't quite like that
indeed that in quantum theory the vacuum
doesn't have any
particles that you and i detect
that's so that's common that that's
still the same but what it does have are
these what you call virtual particles
these are particles which because
quantum mechanics works on principle of
uncertainty these particles can pop up
into existence and then disappear again
over a very short period of time i mean
the way i like to picture it is if
you've ever seen i'm a celebrity get me
out of here for example
these guys they they sort of have these
sort of tubs of full of eels and snakes
all wriggling around
like and they always have to get in here
or something for a minute and well that
sort of picture of all these eels and
snakes wriggling around is actually how
you would picture the vacuum quantum
mechanically it's that lively so the
reason it's so lively is is what's
happening is um
you get these particles and
anti-particles they literally pop into
existence and then pop out of existence
again and this happens continuously at
all points in space within that vacuum
so it's kind of like there's this
continuous sort of
hive of activity where particles are
going in and out of the vacuum popping
into existence and then going out of
existence again
and we they've it's been tested the the
idea that these particles are there has
been tested it was originally devised by
a number of eminent
physicists people like paul dorack and
richard feynman
schwinger had the idea that there were
these things that could pop up into the
vacuum so you have you start off if you
like with nothing and then you think of
it as there's no particles there and
then these things are popping up and
disappearing again gives the vacuum an
energy
and we know it gives the vacuum and
energy we've actually tested this
experimentally
there's something known as the casimir
effect where you take two parallel
plates
in a vacuum very close together
if you think classically nothing should
happen but quantum mechanically because
of this vacuum energy and this vacuum
energy is sort of affected by how far
apart these plates are
that gives you a force between the
plates and actually it's being observed
that the plates actually move together
so we actually really you know we've
experimentally tested this vacuum energy
as a real thing but it's a very it's a
way in which we do characterize the
vacuum now that it has this energy this
inherent energy that's there and our
universe
has a vacuum energy if what i think is a
vacuum is in fact this seething mass of
particles popping into and out of
existence
why does a vacuum behave like a vacuum
why does a jar crumple when i suck all
the particles out of it why aren't these
virtual particles still striking the
inside of the vessel and keeping the
vessel inflated and things like that
the virtual particles that are present
don't produce forces that are strong
enough to to to overcome those kind of
pressures that you're talking about they
are there they're all around us i mean
if the world of quantum electrodynamics
is correct and our understanding of the
quantum world is correct everywhere
around us there are virtual particles
being created and annihilated all the
time and in fact some people actually
believe that it's the presence of these
of this force this kind of casimir as an
energy you can associate with it got
like a casimir energy it's called some
people believe that that is accounting
for the expansion of the whole universe
it's called the cosmological constant
and so it's having a huge effect on
large scales but on small scales it
turns out the actual contribution of
these in any small region is actually
relatively small and so it's not big
enough to affect the kind of process
that you've just just been describing so
if you took everything out of the
universe everything you thought you saw
all the planets all the stars all the
dark matter there's still something left
over and that's the vacuum energy
and one of the great mysteries of
physics is that the vacuum energy that
we see
out
that we think is out there is only very
very small the density is very low
theoretically we expect the density to
be very high and we really don't
understand
why it's like that can you create a
super vacuum where even virtual
particles don't exist
that's just that would be a super duper
vacuum not just a super vacuum um i'm
not a i don't think so because
uh any process
um
quantum quantum mechanics can occur at
any on any scale at any time at any
temperature quantum fluctuations can
occur there's
there's nothing to stop them and so
because they can occur they will occur
over some time period or something will
occur and so you will get these
fluctuations popping up i'm not i'm not
aware of any situation where i can
actually suppress the fluctuations
themselves