Transcriber: Queenie Lee Reviewer: Denise RQ
Good evening.
I'm going to talk about transitions.
Let's start with birth.
We all undergo a transition like that at the beginning of our life.
In fact, we can imagine how it takes place
if we invoke the presence of oxytocin, the love hormone.
It is exactly that hormone which induces labor,
and eventually, leads to oscillatory contractions of etc.,
leading to the happy event.
Of course, I'm a physicist,
and I'm not going to go into details about that particular event.
It's also too complicated to describe mathematically,
and it's also sometimes controversial, like in the case of virgin birth.
What I'm going to do is move on to something simpler,
like the creation of the Universe.
(Laughter)
Of course, for a physicist, this is quite a challenge,
and it has been for a while, indeed.
It's much easier to model mathematically, or at least we think so.
But unfortunately, I'm an experimentalist,
which means, for me, it's very difficult to be present while it takes place.
It's very unlikely that any of us will live for long enough
for this to happen again, and even if we did,
it's unlikely that we would survive through it to record it in a logbook.
So, I think, it's very unlikely
that we will be able to do experiments on the event itself.
Let me move on to another example of a transition,
which has been very much in the news recently.
That is the stock market transition; we call it a crash usually.
This is a typical event which takes place collectively.
A bunch of people called stockbrokers or bankers
essentially, collectively collude towards raising the price of stock
to the point where it becomes untenable,
and essentially, the whole thing, the system breaks down.
The effect of greed, virtually, we are all familiar with that.
But I'm going to illustrate the simple principles
of phase transitions on that example.
Let me go on to the case of the usual supply-demand economics.
That's the stuff that is supposed to work nicely.
In fact, it's very simple.
When we increase the demand, the stock price goes up,
when we decrease demand or it falls, the stock price goes down.
Fine. Everything is nice and linear, everything is well understood.
Everybody is happy.
In fact, it is a situation which is normally present,
and most macroeconomic calculations are done in this way.
You just increase a little bit the money supply here,
and you watch the inflation rate.
But in fact, that's only a very small view of what is going on.
The minimum complexity we could introduce
is shown by this curve.
Let's do the same thing again, let's increase demand, trading goes up.
Sooner or later, we reach a point
where things become complicated and untenable.
What happens at this point?
It's clear that at this point,
and we know this from non-linear system behavior,
it's only a proverbial butterfly wing flap away
from chaotic solutions
and essentially, a stock market crash.
What happened was, in that case, we go from a situation where we started,
where everybody is more or less happy,
to a situation of total craziness,
into another situation where most people are unhappy,
except for a few people who may have profited
from a stock market crash of course.
As a scientist, or as a physicist, I generally discuss things
which are more like the melting ice, or forming ice from water.
In this case, a phase transition,
which you can easily envisage one form,
you can envisage ice molecules forming a nicely ordered array
and you can envisage water molecules whizzing around and kicking each other,
and so on and so forth, and that's fine.
But how can you actually go from water to ice?
If you think about it, it's not so obvious,
because if you take one molecule at a time and assemble a cube of ice,
that'll take an enormous amount of time.
So, another problem with the ice is actually, there is not just one form,
there's 15 forms of ice.
All of them have slightly different structures.
The complexity here is enormous.
Even further, only the first form of ice, the hexagonal ice,
can form an almost infinite number of different kinds of crystals,
we call them snowflakes.
Nicely photographed at the beginning of the previous century
by a guy called Bentley.
In fact, just a brief note, there was one occasion
when it was reported that two identical snowflakes were found.
In fact, this is a very rare occurrence.
What we are interested in
is how a huge number of molecules or particles conspire to form a crystal.
This is what we are interested in.
Normally, what we do in our experiments
is change the external temperature, pressure, or something like that,
and watch how things crystallize.
But actually, if you consider the transition I started with,
those are more interesting in a sense.
They are happening in time.
So they are freely evolving;
we are going from one state to another through free evolution.
The idea actually came up
while I was driving from a very nice conference in Tuscany -
I was driving through the hills, it was a nice day -
and I was wondering how one could actually set up an experiment to do exactly that,
to look at the very minute details
of the phase transition happening in time.
In that case, instead of a thermometer,
we would use a clock, or even better a stopwatch,
or even better, a very, very fast movie camera.
We won't use ice or anything else, we'll use a particular type of crystal
which is shown here, which I photographed just for this event.
It's actually a very nice shiny metal in which normally, electrons –
you've heard about electrons –
whiz around a bit like water molecules in a gas.
The special property of this crystal
is that the electrons in this crystal
like to crystallize themselves.
They form a regular array.
This has nothing to do with the atoms themselves.
They actually like forming an array that looks a bit like that.
What I'm going to do is study the transition from one state to another.
This was the idea that we tried to realize in the last few years.
Unfortunately, this happens very fast, in one hundred trillionth of a second,
but actually, that's not an impediment
because we have lasers which have very short laser pulses.
This is the experiment we do; it's a very conceptually simple thing:
you take your crystal, you use a very short laser pulse
to vaporize this electronic order, and then it comes back.
I'm going to illustrate that on my schematic.
This is the first step as I vaporize the crystal,
I create again a random distribution of electrons,
and then I'm going to watch it go back with my movie camera.
This is the actual experiment. This is what I expect to see.
Now, let me explain what we do see.
First of all, we don't see a direct transition
back to the original state.
In fact, the crystal likes to oscillate for a while between two different states.
It is not doing what we expected.
And at the end of that oscillation, if we wait for a while,
we get two crystals; we don't get one, we get two.
Strange.
The two crystals are separated by a wall, in fact.
If we do something slightly different, change the conditions very slightly,
we end up with a totally different crystal,
so our electron order is completely different yet again.
In fact, in this case, the electron order has nothing to do with any kind of order
that we can reach just by adjusting temperature or pressure.
It's really a new, hidden state which doesn't exist
in this world, or in this universe
unless we reach it with a specific laser sequence.
Another situation that occurs:
if we change the parameters slightly, we get a multiple crystal,
we get three different kinds of crystal forming after it relaxes.
The next event, if we wait for three trillionths of a second -
which is quite long, in fact -
the walls in the crystal annihilate.
They emit energy,
and the energy that's released is the form of a particle
which is mathematically very closely analogous
to the famous Higgs boson.
Now, how does that work?
In our case, we had a laser which induced electron plasma,
which then cooled with the emission of energy.
In the LHC collider at CERN,
it's slightly different: they don't use a laser,
they use two elementary particles which interact and form hot plasma.
Once they do that, they also release energy,
and if they do this in the right experiment,
they can actually record the particles that come out.
One of those particles that has been discovered -
and for which the Nobel Prize was rewarded just this week -
is the Higgs boson.
At this point, I think it's worth noting
that the original idea, and the original inspiration
for the model and the theory for the Higgs boson -
which was awarded the Nobel Prize back in the early 1960s -
actually came from a model describing yet another transition.
That is - I'm not going into the details of that one today -
but it's a transition from a normal metal to a superconductor.
The analogies in these cases are all relying on non-linearity.
Let's go back to our nice little example
we started with:
the Big Bang.
If we carry on this analogy,
it's very difficult at this point for a physicist to predict
how far these analogies can go, but we can certainly speculate.
The analogy would be that when we go through the Big Bang,
in fact, what is happening is not that we are going through
the Big Bang once,
but in fact, the Universe is oscillating on a very short time scale.
And eventually, when it decides what it wants,
it may form a universe and an anti-universe
or it may form
multiple universes.
And when these annihilate, again, we get the same kind of particles,
or the same kind of energy release as we did in our experiment.
We also saw another crystal forming.
That was a very peculiar case in which a state was reached
which is not normally accessible, it doesn't normally exist.
We can't predict its existence in advance,
because it's only reached through a very particular route.
This is the case if we imagine that we went through the Big Bang,
and there was another universe created which is totally different,
in which we are actually not people but butterflies.
Let me now finish off
by going back to the original example I used,
of course, in the over-simplified fashion to illustrate the principles.
I was very happy to find this picture here,
which shows oscillations prior to the stock market crash.
In actual data, there are oscillations of the stock market prices,
there are actually many reasons for them, and it's not clear at this point
whether we could associate them with the same mechanism.
But nevertheless, if we could,
we could anticipate the proximity of a transition
by understanding how it takes place.
On the other hand, if we want to keep things steady,
if we are interested in keeping things ... not having too many stock market crashes,
the message is very simple.
We have to keep things linear,
and we do that by simply putting a very large tax on greed.
(Laughter)
These experiments have been going on only for a few years,
and it's really very exciting for us - that means me and my colleagues -
that we've been able to find so many different, interesting cases
just in one particular example.
Certainly, what we are very happy with
was that the first publication of these results,
which appeared on a cover of a Nature journal,
actually helped attract funding, and that was wonderful
because it means that the team can now work on science
and not on filling in forms for new applications for money,
and filling in reports, and so on and so forth;
so we actually work on the science.
It's very early to predict what else we can observe.
And certainly there is one interesting aspect
we'd like to investigate,
and that's the presence of dark matter.
The idea is to draw analogies between different systems,
and then look at how this behavior is repeated.
Now, remember the oscillations in the contractions at birth?
It turns out that the analogy actually goes quite deep.
The origin in both cases is the non-linearity of the system.
Let me finish off by quoting Douglas Adams
in his "Hitchhiker's Guide to the Galaxy"
where he says at some point the universe was created in the beginning
which generally made a lot of people very angry
and was generally thought to be a very bad thing.
In our case, we do these experiments in many different systems.
In fact, the experiment is repeated about 100,000 times a second,
so maybe not every one of these is a bad thing.
Thank you very much for your attention.
(Applause)