The background or the inward journey (unedited)

Before start to talk about string theory let me tell you the brief history of inward journey of the physicists. Where to begin? Rutherford? Or Bohr? Or the Modern quantum mechanics of Schrödinger, Heisenberg, De Broglie? Or the Mr Dirac? Well everyone of them studied hard and involved themselves to learn the physics of tinier to tinier particles. The quantum level learnt by 1920 seem so bizarre. That it really doesn’t seem to anybody a pure physics, rather a physical description of subatomic level. When Dirac gave his equation he didn’t even know he produced or predicted a particle –positron. However at that time it was so strange o have a particle which is similar to electron but positively charged. So it seem to him as a mathematical solution. But later in just 2 years experimentalists could find the positron, not only that but Pauli another physicist guessed the existence of neutrino. Though he earlier didn’t boldly said that. He explained the beta decay and predicted it. However later a marvelous theory by H. Yukawa introduced another subatomic force, which wasn’t previously, recognized….is the strong force. Though the theory developed by the journey, but still the credit goes to Yukawa.

Due to the world war II the research stopped and later after the war, the golden age of particle physics started…(sometimes I feel, unless the US never used nuclear weapon to Japan- the particle physics would not come to this far so fast!) Mr R.P Feynman himself was engaged himself in such a project, and Hans Bethe himself too. This Feynman was the man who developed quantum electrodynamics a renormalized theory yet so powerful. However after the WW-II the US government funded largely to the physicists to their high energy research. They started to set up accelerators to study particles.. by that time in 1960s experimentalists found so many particles but could not arrange them in order, there have been few propositions. But none seem enough until Mr Murray Gell-Mann . Murray Gell-Mann (independtly Kazuhiko Nishijima, Yuval Ne'eman) ordered the particles found by 1960s. Named very strangely ‘the eightfold way’. They by introducing quark model seems like finished the job. But there have been problems with that too. In those years accelerators were busy producing particles. There have been explosion of particles. [And the Greek alphabet was inadequate naming them. ;)] in the mean time, Sheldon Glashow, Abdus Salam and Steven Weinberg Unified the electromagnetism with the weak interaction. And which is known as electro-weak interaction. It was developed to describe the beta decay. So far, I have talked about 3 fundamental interactions.

1. Electromagnetism (the interaction for charged particles)
2. The weak interaction (for beta decay)
3. The strong interaction. (for strongly bound hadrons-quarks)

Remember, I haven’t talked much about the history as it proceeded. Electromagnetism was unified long ago. And the weak interaction was unified with the electromagnetism. And the role player of successful quantum theory of electromagnetism was Dirac and later Feynman. This Quantum Electrodynamics is very logical but a price had to pay for this. Even Mr. Dirac wasn’t happy with the renormalized theory. Well, let me introduce this way. The electron has its own field and due to the inverse square law the self energy diverges as we go farther inside. So, the technique was-cut it to a finite level, give this a finite size. So that we’ll stop calculating down to that scale. So we are making the electron a point like, and also defining the interaction. Again, if you are familiar with Feynman diagram, you can check that the electrons interaction was made a simple just a within a simple vertex. So, even though there are wide possibilities and also ignoring the vacuum polarization. So, there it is. Renormalization is what made QED powerful and also not very accurate or general physical view. And there it started. Though, after the success of QED, QCD develops with even more complicacy. QCD is quantum chromo dynamics. And it’s also a renormalized theory. So quantum field theory is facing a problem this. Again, the standard model introduced by the particle physicists (almost similar to the one we use to categorize atoms in periodic table) is very strange number one, it is based on renormalized theory and number two, where is the gravity?? Or graviton- the quantum of gravitational interaction? In GUT (Grand Unified Theories) the gravity is simply ignored or not introduced and seems like it’s irrelevant. But how come our everyday known interaction is absent?

This is where the String Theory comes to help with their views. The standard model & GUT have many other problems like there have been 3 generations of quarks and leptons but why? There where The String Theory comes.

So the history can be seen like this:

Pre WW-II
1. Age of photons, new quantum era
2. The mason theory of Yukawa
3. The antiparticles
4. Neutrinos
5. Quantum Electrodynamics

Post WW-II
1. Strange particles
2. The success of QED
3. The Murray Gell-Mann’s Eight Fold Way
4. Murray Gell-mann’s Quark Model
5. Quantum Chromo Dynamics
6. The Electro- Weak theory
7. The November Revolution as it’s called
8. The Standard Model.

Ref:
1. D. Griffiths -Introduction to elementary particles
2. Michio Kaku-Quantum Field Theory, a Modern Introduction
3. B. Zwiebach- A first Course in String Theory
4. K Becker, M Becker & J H Schwarz- String Theory and M- theory A Modern Introduction
5. Brian greene- The Elegant Universe
6. wikipedia

### The book that has a total history and a vast detail background is named "Inward Bound of Matter and Forces in the Physical World" by Abraham Pais. He started telling the story from 1900 when the X- ray was just discovered. Finishes his book with the modern time physics of 80s.... i cant avoid quoting a paragraph from his book...


" The most recent phase in the development of supersymmetry is super string theory, a development that once again started its roots in the seventies. Here the fundamental operator fields are no longer functions of a point that tracks a world line in space-time, but of a one-dimensional structure, a string, that sweeps a world sheet. Theories of this kind can be formulated consistently only on the manifolds with more than three spatial dimensions (there is always only one a time dimension). By means of a spontaneous symmetry-breaking mechanism ('compactification') the extra dimensions are supposed to shrivel to extremely tiny dimensions. Theories of this kind are generalizations of the Kaluza-Klein theory, also conceived in its day as a unified field theory. It appears that this approach may lead to a consistent renormalizable theory of gravitation, that, in fact, it is a candidate for TUT, the totally unified theory of all forces, the marriage between GUT and gravity. these theories contain super-high mass excitations, of the order of the Plank mass, necessary for consistency but negligible on the mass levels of the physics of known particles. In the limit where these supermass are dropped, string theory reduces to point theory. Intis picture even the GUT scale appears as a medium energy scale"

[page 624.]

so the total journey of inward physics can be found in this book up till 1985. The book provides huge resources. That is very helpful. Anyway.. cheers!

(this entry is still unedited, so keep browsing till i edit and get it ready for you-sagar)