Translator: Nabil Tbolbi Reviewer: Rhonda Jacobs
On July 4th of this year,
scientists at the CERN laboratory in Geneva, Switzerland,
announced that they had discovered a new elementary particle
that we call the Higgs boson.
The Higgs boson's a big deal.
The press likes to call it the "god particle"
or sometimes the "holy grail of physics."
And if you've been paying attention for the last six months,
you can't have helped but to have noticed the Higgs boson in the press.
It's been covered by every major media news outlet around the world
in this country and elsewhere.
It has even inspired the composition of its own symphony orchestra
and its own variety of beer.
But despite all this attention,
there's a good chance very few of you know what the Higgs boson is
or what it means about the understanding we have of our universe.
Prior to the Higgs,
physicists had uncovered 16 different forms of matter and energy
that takes shape in our universe.
Six of these are called quarks -
the up and down quarks are the particles that make up protons and neutrons;
six of these particles are called leptons, including the electron;
and then there are four other particles
that communicate forces through space like the photon does.
These 16 particles make for a beautiful theory
that explains a huge ray of phenomena and is successful by all accounts,
except for one.
We know that this cannot be a complete picture;
it just doesn't hold together mathematically without some new element.
And for years we've thought, but haven't known,
that this new element would be the Higgs boson.
To understand why this theory needs something like the Higgs boson,
consider the phenomena of electromagnetism.
For a long time, physicists have understood that electromagnetism,
or the electromagnetic force, if you prefer,
is nothing more than photons,
or particles of light being transported through space between charged particles.
In this diagram, for example, we have two electrons coming together,
exchanging photons between them, and being repelled as a consequence.
This is the electromagnetic force.
In other words, if it weren't for the photon,
we wouldn't have this force in nature.
This theory works great.
It's probably the most accurate and precise theory
that physicists, or any scientists for that matter,
have ever created in the history of intellectual endeavor.
But, in order for this theory to work,
it also has to follow some very specific rules.
In particular, in order for this theory to hold together
in a mathematically self-consistent way,
the photon has to be exactly massless - it can't have any mass whatsoever.
If it did have a mass - if you tried to calculate things
with a theory with a mass of photon included -
you would find that calculating the same quantity in different ways
would give you different answers,
and sometimes you'd predict probabilities of things happening
that would be greater than 100 percent or less than zero.
Nonsense, right?
So, if you want this theory to hold together,
the photon had better be massless.
Fortunately, all of our measurements of the photon
indicate that it is consistent with being massless,
so all is well with electromagnetism.
With other forces, however, things are not necessarily so clear.
Here's the weak force.
This is a force that is only really evident inside of the nuclei of atoms.
It causes neutrons to decay into protons, electrons and antineutrinos.
And in these sorts of processes,
you see all sorts of heavy nuclei decaying into slightly lighter nuclei,
like this carbon to nitrogen process shown here.
And like electromagnetism, this force is communicated by a particle, or particles,
the W and Z bosons shown in this diagram.
And just like the theory of electromagnetism
requires that the photon should be massless,
the theory of this weak force seems to require
that the W and Z should be massless,
but they're not;
they're about 100 times heavier than a proton.
So to explain this, we need some sort of new element to come in
and solve this apparent mathematical inconsistency.
But before we talk about how the Higgs does that,
let's consider for a second what physicists mean by the word "mass."
We all have an intuitive idea for what mass is.
We know, for example,
it takes more energy or force to make something move
if it is more massive than if something is less massive.
It takes a bigger engine to power an aircraft carrier than a moped.
Good. We have that as sort of intuition.
We also know the force of gravity acts more strongly on more massive things.
While both of these statements are true,
they miss a very important element about what physicists know mass to be.
If we think about Einstein's most famous equation, E = mc squared,
we realize that mass can be transformed into energy,
and energy can be manifest as mass.
So I can take a small amount of mass, in a nuclear power plant, for example,
or in the core of the Sun, and convert that into heat,
in the form of sunlight or energy.
On the other hand,
if there's a collection of particles that are interacting among themselves,
or moving among themselves,
that motion, or that energy, can appear as mass.
It's this connection between matter and energy
that was at the heart of the solution to this problem,
as proposed in 1964 by the scientists shown here including Peter Higgs.
Their radical idea was this:
they said all of space, everywhere in the universe,
is filled with this quantum field of energy.
We call it the Higgs field now - it wasn't called that at the time, of course.
Some particles travel through this field without knowing it's there.
The photon, for example, simply doesn't interact in any way with the Higgs field.
On the other hand, other particles, like the W and Z,
travel through this field and interact a great deal.
All of that interaction, in motion,
ends up appearing to us as masses for the W and Z boson.
So you have a theory now where the W and Z act as if they're massive
but without ruining the self-consistency of the theory.
Until this year,
the idea that the universe was filled with this Higgs field
was really just a hypothesis; we had no direct evidence that it existed.
To convince the physics community and the rest of the world
that these particles existed, or this field existed,
we had to create individual pieces of the field,
which we called the Higgs boson, and observe them in a laboratory.
Just like the electromagnetic field's made of photons,
the Higgs field are made up of these smaller particles,
or smaller bits of the field called the Higgs boson.
With this goal in mind,
thousands of scientists and engineers from around the world
built this machine called the Large Hadron Collider shown here, or LHC for short.
This, in short, is the most complex and sophisticated machine
humans have ever built, by a big margin.
It's absolutely staggering, the kind of engineering that went into this.
The lines shown along this map is about 17 miles in circumference,
and it represents a large tunnel; here's the inside of the tunnel.
Around that tunnel,
a beam of protons is shot at speeds just shy of the speed of light.
And then two beams are smashed head-on into one another
inside of these enormous particle detectors.
In those collisions, so much energy is fit into one place at one time,
that through E = mc squared,
new forms of matter can be created
that [are of] much more mass than can be sustained in normal circumstances.
So let's follow along for a second as the LHC accelerates a proton.
In each of these successive rings,
the proton gets accelerated to higher and higher velocities
and contains more and more energy.
In the first ring, it's traveling at about half the speed of light,
but by the time, it reaches the main ring - the 17 mile ring -
the protons get moving at 99.999997 percent of the speed of light.
Here we're going to follow one of the beams,
a proton beam, through this tunnel.
If we can look inside of a proton,
we’ll find that this proton isn't a single particle at all,
but is actually a collection of particles, quarks, being held together by gluons.
Those quarks and gluons will be the things that actually do the colliding
in a moment.
Here we have one of the detectors at the LHC,
and two beams of protons smashed head-on in the heart of this detector,
and you can see a spray of particles comes out.
Hopefully, in a small number of these collisions,
you could actually produce Higgs bosons in such a collision.
We collide about a hundred million pairs of protons together
each second in this machine,
and most of them do not produce Higgs bosons.
In fact, Higgs bosons are extraordinarily rare in these collisions;
about 1 in 10 billion collisions result in a Higgs.
But in those few collisions that do produce Higgses,
you can assign supercomputers to sift through this data
and actually find evidence that this is going on.
Making this even more difficult,
is the fact that the Higgs doesn't stick around for very long.
It takes about 10 to the minus 22 seconds
for an individual Higgs to decay into other forms of energy.
So you end up with these complicated pictures like the one shown here,
and with these supercomputers, though, you can sift through this data
and find that you're actually looking at evidence of a Higgs.
I said at the beginning of this talk that in July of this year,
the scientists at CERN announced
that they had discovered this particle, finally.
What I mean by that is they can say with very high statistical significance
that there's a new particle that exists.
It has a mass that's about 125 giga-electron volts,
which is about 133 times as heavy as the proton.
And the best we can tell,
it behaves essentially like a Higgs boson is supposed to behave.
On the one hand, this represents
the completion of what we call the standard model of particle physics.
This is a mathematically self-consistent theory
that explains all the known forms of matter and energy in the universe
and all of their interactions.
It's a remarkable scientific achievement of the highest order.
On the other hand, there's a fairly good chance
that as we scrutinize this data
and collect more data at the LHC over the coming years,
that we'll find even more surprises.
If you look at the Higgs data as it currently exists,
there are already some tantalizing hints
that this particle that we're calling the Higgs
might not behave exactly like the Higgs is supposed to
according to the laws of the standard model.
If future data confirms this picture,
it may indicate that there are new particles involved
or new forces involved
in the processes involved in creating and decaying the Higgs boson.
So in either case, we may be looking at something
that isn't just the beginning of studying Higgs physics,
but the beginning of a whole new era of discovery in particle physics,
where we discover a whole new array of forces or particles
that dictate our universe's behavior.
I, for one, feel very privileged
to be witnessing this special time in the history of science
in this important era of discovery.
Thank you.
(Applause)