Neither am I sitting on my toes nor writing about them. This write-up
is about the theory of everything (TOE) in physics. The time when I was
called upon to write(my college magazine) coincided with something I was reading about this.
Most of the books I have read on physics are on similar lines. They all
talk about Galileo's discovery of planetary orbits being elliptical.
They speak about newton’s ideas on inertia and motion. Then fast forward
a century and a half, they talk about faraday’s laws of
electromagnetism. Some thirty years later Maxwell explains the
propagation of light waves and their speed. My narrative follows on
similar lines.

This post might even qualify as a book review since the
book i am reading "Trouble with physics" by Lee Smolin has influenced
it a lot.

Max Planck gave a formula about the energy of radiation E=hν in 1900. This started the quantum revolution and soon Einstein came up with an explanation of the photoelectric effect. In the next thirty years great progress was done in explaining the atomic spectra(Niels Bhor), Wave nature of matter(De-Broglie) and the bending of light around gravitating matter(special and general relativity). Ervin Schrödinger wrote down an equation explaining the group velocity of matter waves. He extended it to a general equation of motion of wave functions (Ψ). Max Born interpreted the wave function as the probability of finding a particle in a particular region. Hiesenberg placed a limit on the accuracy of finding the position and momentum of any particle. These developments drove a nail in the coffin of determinism that Lorentz had propounded.

Attempts to reconcile the geometric nature of space-time due to gravity and the quantum nature of matter proved difficult. Physicists were of divided opinion when it came to interpreting quantum mechanics. Some were downright skeptical (eg. Schrödinger, Einstein etc) criticizing the born interpretation with the now famous “cat in a box” paradox. In future the field would get murkier with the introduction of multidimensional space-time.

Efforts to unify electromagnetism with quantum mechanics led to quantum electrodynamics (QED). This quantum field theory was integrated first with the weak nuclear force called the electro-weak theory and then with the strong nuclear force. It was discovered in particle collisions that protons and neutrons had finer structure. You might still find books that speak of basic particles like mesons and baryons without any mention of the quark model or the standard model which has come to describe particle physics now.

Max Planck gave a formula about the energy of radiation E=hν in 1900. This started the quantum revolution and soon Einstein came up with an explanation of the photoelectric effect. In the next thirty years great progress was done in explaining the atomic spectra(Niels Bhor), Wave nature of matter(De-Broglie) and the bending of light around gravitating matter(special and general relativity). Ervin Schrödinger wrote down an equation explaining the group velocity of matter waves. He extended it to a general equation of motion of wave functions (Ψ). Max Born interpreted the wave function as the probability of finding a particle in a particular region. Hiesenberg placed a limit on the accuracy of finding the position and momentum of any particle. These developments drove a nail in the coffin of determinism that Lorentz had propounded.

Attempts to reconcile the geometric nature of space-time due to gravity and the quantum nature of matter proved difficult. Physicists were of divided opinion when it came to interpreting quantum mechanics. Some were downright skeptical (eg. Schrödinger, Einstein etc) criticizing the born interpretation with the now famous “cat in a box” paradox. In future the field would get murkier with the introduction of multidimensional space-time.

Efforts to unify electromagnetism with quantum mechanics led to quantum electrodynamics (QED). This quantum field theory was integrated first with the weak nuclear force called the electro-weak theory and then with the strong nuclear force. It was discovered in particle collisions that protons and neutrons had finer structure. You might still find books that speak of basic particles like mesons and baryons without any mention of the quark model or the standard model which has come to describe particle physics now.

**The Standard model**(Image:Wikipedia)

In the standard model all particles are composed of seventen basic building blocks. twelve of them are fermions obeying fermi-dirac statistics and the other four are bosons, particles that obey Bose-Einstein statistics. Two types of fermions are quarks(6) and leptons(6). A few years after the standard model was put forward Steven Weinberg and Pakistani scientist Abdus Salam independently discovered that a combination of the gauge principle and spontaneous symmetry breaking could be used to construct a concrete theory that unified the electro-magnetic and weak nuclear forces. This electro-weak theory predicted the existence of three particles W+ , W- and Z that carry the weak nuclear forces. In the early 1970s the gauge principle was applied to the strong nuclear force, the force that binds the quarks, and it was found that a gauge field is responsible for that force too. The resulting theory is called Quantum Chromo Dynamics (QCD).

A new theory SU (5), a code for the five particles (3 quarks and two leptons), predicted that protons would decay but this was not observed even after a lot of experimentation. One of the big ideas in unification is super symmetry which tries to unify the fermions and bosons. It predicts that every known particle has a heretofore unseen super partner. It also predicted that you can replace one of the fermions by a boson in some experiment and the probabilities of the various possible outcomes will not change.

Neither have the super partners been observed nor have the energies needed to observe super-symmetry been realized. If the Large Hadron Collider (LHC) at CERN had not suffered the problem of magnetic slack and the consequent leakage of liquid helium in September last year we would have by now conclusively observed (or disproved) the existence of Higgs boson (the massive particle predicted by the standard model to exist).(Plz note this article was written in 2010)

**String Theory**

In the fall of 1984, a branch of particle physics called string theory received a shot in the arm. It explained the existence of particles as vibrations of one dimensional string. Shcwarz and Green proved that string theory was a finite and consistent theory. They proved That infinities were absent in supersymmetric string theory in ten spacetime dimensions. It was known that a theory called super gravity would hold only upto eleven dimensions. So scientists were trying to incorporate one more dimension into string theory to make it consistent with quantum gravity. The number of dimensions was increased by one by proposing an emergent dimension due to the movement of branes in nine spaces and one time dimension.

String theory is based on two important dualities called T-duality (Topological) and S-duality (Strong-Weak). It was proposed that forces are due to the vibration of closed strings and particles are vibrations of open strings. Strings can join and break. They move in such a way that the area covered by them is minimal. The string theory got extended to the M-theory, Then D-brane theory came along. The field got support when it explained the geometry of extremal black holes using the brane system.

An alternative in the form of loop quantum gravity developed that treated quantum theory and relativity in a background independent manner. The starting point was Indian scientist Abhay Ashtekar’s revolutionary reformulation in 1986 of general relativity. It formulated Einstein’s theory in a form very close to gauge theories- the theories that underlie the standard model of particle physics.

Scientists now believe that space-time is an emergent property something like temperature which is fundamentally due to vibration of atoms held together. Another example would be sound. They also believe that space time is discrete i.e. there is a smallest unit of space called Planck’s length and a smallest unit of time called Planck’s time.

There have been corrections to special relativity called Doubly Special Relativity (DSR) in which observers in two systems agree on the Planck’s length being smallest even if they are moving with respect to it, along with the constancy of speed of light. By treating the relations of causality as fundamental Roger Penrose has formulated the Twistor theory. This holds in a special space-time called Twistor space. Loop Quantum Gravity has been applied to black holes and it has been found that they contain internal structure and not a singularity where time stops. This has solved the black-hole information paradox.

A young Australian physicist recently published a preon model of elementary particles. A preon is a ribbon like structure and the various kinds of preons correspond to the ribbon being twisted in different ways. Three ribbons can be braided together, and the various ways to do this correspond precisely to the various particles of the standard model.

**Exciting observations**

Recent observations have suggested that cosmic microwave background radiation is not uniform. It had been found to be coming from all directions of the sky. At the level of a few parts in 1, 00,000 there are fluctuations in it. The inflation model of the big bang predicts that there was no one point from which matter was created and spread out. It says the universe started from small volume and due to rapid expansion grew to the enormous size it is now. We still see evidence of this inflation in the form of red shift between galaxies. If there is a preferred direction it might point to the center of the big bang (some call it the “axis of evil”).

Another observation has been with some stars orbiting galaxies which don’t seem to obey the newton’s laws of gravitation. The dividing line seems to be their rate of acceleration. After about 1.2x10-8 cm/s2, the acceleration of stars seems to be decreasing rather than with the square of the distance, it decreases only by the distance. This is called the milogram’s law and such motion is called Modified Newtonian Dynamics (MOND). Ordinarily Newtonian force is proportional to the mass of the body causing the acceleration times a constant (g-on the surface of earth). MOND says that when acceleration is small the force is proportional to the square root of the mass times Newtons constant.

NASA had sent several spacecraft out of the solar system. Two of these- pioneers 10 and 11 have been tracked for decades. The velocities of both the pioneers seem to be less than anticipated. They seem to be attracted to the sun by an additional acceleration of around 8x10-8 cm/s2 (bigger than the anamolous acceleration measured in galaxies). Some experiments have tried to measure the velocity of light since big bang to see if it had changed. There is evidence that the fine structure constant (ratio of the charge of the electron squared, divided by the speed of light, times Planck’s constant) alpha was smaller by about 1 part in 10,000 about 10 billion years ago.

Another experiment named AGASA designed to measure the energy of protons in the cosmic rays found them to be having more energy than allowed. This points to a breakdown of special relativity wherein the protons are travelling with higher energies.

**The Final Word**

The possibility of nature’s constants themselves changing with the age of the universe seems tantalizing. My intension of writing on such a topic was to make students aware of the recent developments and my purpose will be served if you search for these topics I mentioned and learn more. Many people consider the development of a successful TOE to prove the non-existence of god. We all should be hoping to hear the final word within our lifetime.