One of the big ideas that scientists are studying is called supersymmetry.
If true, it will become a fundamental part of our understanding of nature,
like relativity theory and the gauge principle.
Space and time were originally two different concepts.
The special theory of relativity unified them.
Geometry and gravity were once quite unrelated.
General relativity unified them.
There are still two big classes of things that makeup the world.
The particles, -like quarks and electrons-, that comprise matter,
and forces, -or fields-, by which they interact.
The gauge principle unifies three of these forces.
We are still left with two distinct entities.
Particles and forces.
Supersymmetry is an attempt to unify them.
Quantum theory says that particles are waves, and waves are particles.
This does not really unify the particles with the forces.
The reason is that in quantum theory there are two broad classes of elementary objects.
They are called fermions and bosons.
All the particles that make up matter, like electrons, protons and neutrinos and fermions.
All the forces consists of bosons.
The photon, the W and Z particles are bosons.
The Higgs particles is also a boson.
Supersymmetry offers a way to unify these two big classes, the fermions and the bosons.
It proposes that every known particle, has a super partner.
Fermions and bosons have two different properties.
Fermions must obey the Pauli's exclusion principle.
It says that two fermions cannot occupy the same quantum state.
That is why all the electrons in an autumn do not sit at the lowest orbital level.
Once an electron is in a particular orbit, or quantum state,
you cannot put another electron in the same state.
This principle explains many properties of matter and materials.
Bosons behave in the opposite way.
They like to share states.
When you put a photon, into a certain quantum state, you will make it more likely that another photon,
will find its way to the same state.
This affinity explains many properties of fields, like the electromagnetic field.
Scientists proposed to theory in which you could replace a boson with a fermion,
and still get a stable world.
This is called supersymmetry.
One of the new theories was an extension of electromagnetism.
It unified the photon with a particle like the neutrino.
The other discovery of supersymmetry is connected with string theory.
Unfortunately supersymmetry still has no unambiguous testable predictions.
Particle accelerators have yet to find particles that supersymmetry predicts.
The Large Hadron Collider or LHC, however discovered the Higgs boson.
The LHC hopefully will tell us about one of the key challenges of physics.
This is discussed in Challenges of Physics.
We need to explain the values of the free constant in the standard model.
It is either very large or very small.
For example, the electrical repulsion between two protons is 10 to the power of 38.
There is also a huge difference in masses.
The proton is 1800 times heavier than the electron.
Particle physics seems to be hierarchical.
The four forces span a large range of strengths, from strong to weak,
which is nuclear physics to gravity.
The masses also formed a hierarchy.
At the top is the Planck mass.
This is the energy at which quantum gravity effects will become important.
Ten thousand times lighter , than the Planck mass is the scale at which,
the difference between electromagnetism, and the nuclear force should be seen.
Experiments conducted at that energy, which is called the unification scale,
will not see three forces, but one single force.
10 power minus 16 times the Plank's scale is a tera-electron volt, or T e V.
One tera-electron volt, is 10 power 12 electron volts.
This the energy at which unification of the weak and electromagnetic force takes place.
This is the region we see the Higgs boson.
Scientists expect supersymmetry in this region.
A proton is one thousandth of that.
An electron is one thousandth of the proton.
A neutrino is one millionth of that of an electron.
At the bottom, we have the vacuum energy, which exists throughout space,
in the absence of matter.
The hierarchy problem has two challenges.
The first is to determine, what sets the constants, that makes ratios large.
The second is how they stay there.
The stability is puzzling.
Quantum mechanics has a tendency to pull all the masses towards the Planck mass.
Intrinsic mass, is the mass without quantum effects.
Scientists have to tune the intrinsic mass, to keep them apart.
The masses of gauge bosons is not a problem, because of their symmetry.
The photon, which is the carrier of the electromagnetic field has no mass at all.
Part of the mass of quarks and leptons come from quantum effects.
The masses of quarks and leptons are proportional to their intrinsic mass.
If the intrinsic mass is small, so are the total masses.
We can say that the masses of gauge bosons and fermions are protected.
Quarks have two properties.
Colour and charge.
Each kind of quark comes in three versions called colours.
This triplication provides the symmetry required for gauge theory.
Each quark has an electrical charge.
They come in units of one by three, and two by three, of the electrons charge.
The coincidence of the by three fraction, is not yet explained.
Many scientists believe in supersymmetry.
Supersymmetry is a compelling theoretical idea.
The idea of unification of forces and matter,
offers a resolution of the deepest duality in fundamental physics.
Some of the discoveries made by the Large Hadron Collider or LHC,
may help to validate supersymmetry.
Supersymmetry theories have much more symmetry, but they are not simpler.
They are in fact more complicated.
Supersymmetry would be absolutely compelling, if it uncovered a deep commonality,
between two known things, like the photon and electron.
We need to wait for more advanced theories, and results of the experiments of the LHC,
to shed more light on this theory.