so over the past week or so brady's got
quite a number of emails from 60 symbols
viewers asking about
a game called portal 2. viewers have
been asking whether
physicists here in in nottingham might
be interested in commenting on the game
because it's quite science-y quite quite
physics-y so this morning i downloaded
portal 2 which took a very long time and
i've been playing it for the last couple
of hours it's been a long time since
i've played video games a long long time
since i've played video games
wormholes are solutions
to einstein's equations
if in 1915 einstein developed his theory
of general relativity in which he was
able to show how
space-time could be curved by the
influence of mata
and that the curvature of the space-time
told the matter where to move
and it's used every day general
relativity
is used to explain things like
the orbits of planets around the sun in
fact what i found is that as a complete
newbie to this that i got overwhelmed i
must admit by the plot because it's
portal 2 so it's a sequel to portal but
in a nutshell what you are you're a
character called shell you've woken up
in a scientific complex
a megalomaniac computer effectively
called glados which is a portal gun and
the portal gun is the most important
aspect of this entire game and hence the
name portal in that it allows you to
blast
effectively portals wormholes in
space-time and the wormhole
is a solution which allows you to
connect one part of space time to
another part of space time simply
through the curvature of the space it's
been put forward in science fiction as a
way of
transporting vast distances across the
universe there are interesting
sciency concepts in here the wormhole
idea first of all that's a that's a
staple of science fiction it's something
that very many scientists physicists
particle physicists cosmologists have
looked at very very seriously in terms
of can we create wormholes in in space
and time perhaps not in this context
that really thought about uh traversing
very large distances light years in this
case it's over much smaller distances
but the overall concept is the same as
that you're sort of moving from true
space and time through a completely
different route than as usual they are
we don't know if they exist
they are
they are solutions
they could in principle exist
the first one it was actually discovered
by einstein i think in einstein and
rosen in 1935 it's called the
einstein-rosen bridge
that linked two regions
of space time together but as an example
of the problems they face they're very
unstable
and so uh in the 1960s another mega star
of general relativity john wheeler
and demonstrated
that that solution of einsteins was
actually unstable so as soon as the
bridge formed connecting these regions
it would pinch off again so that a light
ray couldn't propagate through from one
end to the other before the bridge
collapsed so for physicists i guess
what's most exciting about this game is
that you've got these these wormholes
that you can place in different
locations allow you to to solve
different types of puzzles to to to move
from space to space in
in a very novel way which after a while
gets quite intuitive and
the reason so many 60 symbols viewers
are interested in this is is because i
guess i'm interested well is this type
of thing possible could we actually do
this
and
another mega star of general relativity
kip thorne along with morris came up
with the conditions that you need
and basically what you have to do is
this bridge that forms this tube if you
like that connects the two regions
this has to be stable against collapsing
and the way you have to do it it turns
out you have to have some form of very
exotic matter
and it and it's got negative energy
effectively or negative mass so this is
like having particles with a negative
mass we don't know such particles now
i'm not a particle physicist i'm not a
cosmologist i'll get the disclaimers out
of the way first of all but for my
reading and my understanding of
wormholes you need
huge amounts of energy to actually
create these type of things
we're not talking about you know
sort of uh
you know levels of of of terrestrial
energy we're talking about bill is the
energy of billions and billions and
billions of stars to actually be able to
warp space time in this fashion so you
can move through through space time like
this so this is not going to happen but
again as a thought experiment
as an interesting way of looking at some
unique
physics or strange physics in a
different environment this is really
really interesting for a physicist but
but the general idea is you have to do
something a bit unusual in order for
them to exist
and then and then you in principle can a
particle could traverse from from one
region to another
but that opens a
another problem potential problem
um and that is because it's linking
space time these these
wormholes could either connect one
spatial region to another spatial region
or it could connect one time to another
time
and
it opens up the possibility
of time travel okay which is
how exciting is that
but in particular it opens up the
possibility of going back in time
and then you have all these paradoxes
which emerge as soon as you have these
possible
scenarios where you can go back in time
you could
go through a wormhole re-enter
a minute before you went through and
shoot yourself
and then how have you managed to shoot
yourself because you don't exist
and these are paradoxes and hawking and
thorn and many people think general
relativity can't allow for these and in
fact hawking has a chronology protection
conjecture hawking's um idea of how it
this
affects wormholes is is quite neat it's
a feedback mechanism he said that so
this will prevent the wormholes from
actually allowing this to happen but it
could also be the demise of the wormhole
so that's why i'm telling you
and the analogy is a nice one with sound
so when you go to a rock concert you
often
you hear the speakers go berserk
and there's a feedback loop so what's
happened is the sound has gone through
the microphone maybe from the singer
gone down the wire been amplified come
out of the speaker and as long as it
goes out into the auditorium you're okay
but if some of that sound gets back into
the microphone
and then it goes through the cycle again
it gets amplified it gets louder then it
goes back through and that's a feedback
loop and that's what leads to the
horrendous screeching and of course you
then can't hear what's going on
and hawking has said that um a similar
thing will happen in wormholes
for wormholes to be of any use in the
sense of being able to travel through
time it's got to at least be able to
have light through it or particles going
through it so it has to be a reasonable
size
but as soon as it becomes a reasonable
size then it can allow radiation to to
go through it
and once that radiation goes through it
in fact it can create quantum
fluctuations can create more and more
radiation virtual particles you'll get
this cascade the radiation comes through
and gets
amplified going through and through and
through and eventually will cause the
wormhole to collapse or explode and
disappear
so hawking actually
what uh thinks that wormwood may not
survive because of this
and there's a great debate going on as
to whether they can or they can't
so with many of these games and
particularly portal 2 well the computer
has to has to do the calculations and it
has to take the laws of physics and the
equations of physics and it has to solve
them and what it's doing is basically
solving what we call differential
equations now i don't want the entire
viewership of 60 symbols to switch off
the moment i say the differential
equations differential equation the
simplest possible differential equation
you're probably going to cut this out
pretty but i'll
i need to get a marker
i i don't think people are actively
looking for wormholes that what what
people have done have simulated
what something would look like if you
were looking at them through a wormhole
so if you know if the if we stumbled
across a wormhole and that wormhole was
connecting us to some different parts of
the universe
then
you know the light gets all bent and
distorted as it goes through these large
gravitational fields and and people have
simulated that
because they are just solutions to
einstein's equations so one of the
beauties of einstein's equations is once
you've got this solution there then you
can do things like you can propagate
light through it and you can say well
what happens to light and you can be at
the other end and you can and and
simulate what you would detect what did
you detect what does it look like it
just looks like a mess to me equations
that embed
the reality of the physics
mean that that translates to the
computer game and it feels real to you
but it's mathematics it's mathematical
physics and
we tend to avoid maths and 60 symbols
and brady and i have talked about this
quite a lot this will probably get
caught but
i've never heard of portal 2 you
mentioned it to me never mind portal 2.
i had never been heard of portal i'd
better go and find out what it's about
this is me i'm walking around this is a
character chair in the graham i'm moving
back and forth i'm pressing this key
down now the computer is making those
calculations on the basis when i hold
this key down what's the displacement
what's the speed etc and then
calculating that and updating the
graphics accordingly when we do
something like this something really
neat like this then you can see the gun
recoils the gun comes back recoils
conservation of momentum there's
to make that look real you have to have
the physics and you have to have the
maths underneath the physics and you
have to code that to make that all look
real
neither the makers nor the distributors
of portal 2 have paid us any sponsorship
for this i did this in my own time i did
not waste university resources i'm a
physicist i know nothing about cancer
research so no cancer research has been
hindered by my playing of this game