Build a basic model



Now you see which states are bound and are stable and interact and ………


In principle all of the real world physics should be derivable from this platform.


There are many more stories about extrapolating the underlying theory to the solution of an interesting problem,

Can we predict the where the charge of a proton is located based on the movement of the quarks ?

Can we predict the masses of the particles that we observe: proton, neutron, pion, kaon… ?

Can we predict yet unseen particles and how to look for them ?


The questions may be similar to extrapolation from atomic physic to chemistry and then to biology.

We can describe the hydrogen atom in a detailed and fairly complete way.

We can understand the overriding chemistry of the periodic table based on



What are the differences and similarities between quark-lepton particles and the interaction particles photon-gluon-W


Fermions è spin ½ and therefore don’t occupy same space.  { We identify this characteristic a matter}

·        Two tennis balls cannot be at the same place.

Bosonsè spin 1 particles and overlap

·        Two words or sounds can be at the same place.


So we can write down a set of equations for all particles è  Free particle solutions

·        Then we add interactions


Feynman introduced a lovely pictorial representation of the particle world.






QED vertex


Electric and magnetic fields interact with moving charges.





Two electric charges can interact by creating a field and then the field interacts with the particle.


Given the verticies (INTERACTIONS) all types of diagrams can be written down. No requirements on the exchanged particle. Any particleconsistent with the conserved quantities can be exchanged.


Physics recognizes that some things are not changed == conserved,  invariant..






All particle satisfy a free particle equation

Introduce Ad Hoc the particles

Particles can interact

Introduce Ad Hoc the interactions


Invariance, transformations and symmetry.

 Define each one.




  And accelerating region cannot be distinguished from a gravitational field.

Elevator on earth

Elevator dragged through space in a rocket ship.



Noether’s Theorem:

An example of the early use of symmetry to constrain the laws of physics is Noether’s theorem:

Every symmetry  => conserved quantity.

         Translation – conservation of momentum

         Rotation – conservation of angular momentum

         Time translation – Energy conservation


Space time curvature explains gravity, one of the fundamental forces.

Curvature is the process of twisting each point in space time by an amount.

 This local variation in the curvature results in a change in motion that is equivalent to a force.



Curvature can be thought of as rotating your coordinate system by different amounts as you move around your space.

Applying your Poincare Transformations as a function of your position


























Weyl tried to find a geometric interpretation for the electric force. Added space stretching.

setting the GAUGE (or spacing).


Failed until the transformations were applied to quantum states.


GLOBAL PHASE CHANGE implies conservation of electric charge.

LOCAL  PHASE CHANGE requires the introduction of electromagnetic interactions.



Transformations determine the interactions.

Gravity == Poincare

QCD == SU3 (color)

QED == U1 (phase)

Electroweak == SU2xU1 (Weinberg Salam)

            {u,d}  {e, ν }



There has emerged a very elegant and compelling view of the fundamental laws of nature.

The symmetries and associated transformations of our world may serve as the starting point for our understanding.

The application of these ideas is riddled with mathematical pitfalls and details that are quite complex. 


Based on the success of SU2xU1 perhaps one should start with a larger group of transformations


Poincare group (Normal space time transformations)





SuperSymetry  SU(5)

This divides into subgroups mentioned above SU(3), SU(2) ….


Excerpts from Brian Green’s web site



Einstein took a very bold step, and reached out to some radical new mathematics called non-Euclidean geometry, where the Pythagorean rule is generalized to include metrics with coefficients that depend on the spacetime coordinates in the form

Metric tensor

where repeated indices imply a sum over all space and time directions in the chosen coordinate system. Einstein extended the idea of Lorentz invariance to general coordinate invariance, proposing that the values of physical observables should be independent of a choice of coordinate system used to chart points in spacetime. He called this new theory the General Theory of Relativity.
   In Einstein's new theory, spacetime can have curvature, like the surface of a beach ball has curvature, compared to the flat top of a table, which doesn't. The curvature is a function of the metric gab and its first and second derivatives. In the Einstein equation

Einstein equation

the spacetime curvature (represented by Rmn and R) is determined by the total energy and momentum Tmn of the "stuff" in the spacetime like the planets, stars, radiation, interstellar dust and gas, black holes, etc.
    The Einstein equation is not strictly a departure from classical field theory, and the Einstein equation can be derived as the solution to Euler-Lagrange equations that represent the stationary point, or extremum, of the action



But particles in string theory arise as excitations of the string, and included in the excitations of a string in string theory is a particle with zero mass and two units of spin.


the particle that would carry the gravitational force would have zero mass and two units of spin. This has been known by theoretical physicists for a long time. This theorized particle is called the graviton.

This led early string theorists to propose that string theory be applied not as a theory of hadronic particles, but as a theory of quantum gravity.


One can add a graviton to quantum field theory by hand, but the calculations that are supposed to describe Nature become useless. This is because, as illustrated in the diagram above, particle interactions occur at a single point of spacetime, at zero distance between the interacting particles. For gravitons, the mathematics behaves so badly at zero distance that the answers just don't make sense. In string theory, the strings collide over a small but finite distance, and the answers do make sense.

.This doesn't mean that string theory is not without its deficiencies. But the zero distance behavior is such that we can combine quantum mechanics and gravity, and we can talk sensibly about a string excitation that carries the gravitational force.

.This was a very great hurdle that was overcome for late 20th century physics, which is why so many young people are willing to learn the grueling complex and abstract mathematics that is necessary to study a quantum theory of interacting strings.


In 26 spacetime dimensions, these extra unphysical states wind up disappearing from the spectrum. Therefore. bosonic string quantum mechanics is only consistent if the dimension of spacetime is 26.