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The science of string theory


STRING THEORY IS SURPRISINGLY EASY to explain. It goes like this. The fundamental particle is not a quark, but a string whose dimensions are calculated to be 10-33 centimetres. The important feature of this string is that, in the same manner as the strings of a violin, it vibrates to produce different notes and harmonics. This is how strings create the universe as recounted in Kaku’s catechism:

Q. What are the particles of the world we see?
A. The notes on the string.

Q. What is chemistry?
A. The melodies on the string.

Q. What are the laws of physics?
A. The laws of harmonies on strings.

Q. What is the universe?
A. The symphony of strings.

Q. What is the mind of God?
A. Music resonating through hyperspace.

Unquestionably very poetic but where did this theory come from, and why should anyone believe it?

In biology, theories generally arise to explain data encountered in the real world. For instance, the theory that the structure of DNA was a double helix was developed after Rosalind Franklin took hundreds of X-ray crystallography images of DNA. The idea of a double helix explained her images as well as data obtained in other experiments.

But unlike biological theories, string theory did not arise from data. Instead, it was born of the belief that the universe is elegant and simple, and that the four known fundamental forces of the universe would be unified, as Einstein believed.

In the 19th century, James Clerk Maxwell rocked the world by showing that electricity and magnetism were part of one force – electromagnetism. Ever since then, a mathematical ideal that allowed for the ‘unification’ of all the major forces in nature has been a primary goal for theoretical physicists. Besides electromagnetism, these include gravity and the two forces that operate at the subatomic level: the weak and the strong force. The strong force holds quarks together inside protons and neutrons and stops atoms from disintegrating. The weak force explains why atoms sometimes do disintegrate – it underlies radioactive decay.

The blithely named ‘standard theory’, has done a masterful job at explaining the operations of the strong and weak forces. And it has also managed to unify the strong and weak forces with the electromagnetic force. But it hasn’t been able to accommodate the existence of gravity.

What Einstein struggled to do – and what has defeated everyone until the 1980s – was to unify all the forces with a single type of law. This law should be as simple and elegant at describing the interactions and manifestations of the four forces as Einstein’s equation of E=mc2.

String theory achieves this goal. Just as the mathematics of a vibrating violin string can explain all of music, so the mathematics of tiny vibrating strings that vibrate in 11 dimensions, are capable of explaining the four forces, plus matter and energy; and hence the universe itself.

The gestation of string theory has so far taken the past four decades and is still far from being fully developed. Its beginnings trace to Gabriel Veneziano who, in 1968, while studying at the European Centre for Theoretical Physics (CERN) in Switzerland, stumbled across a mathematical formula that explained the interactions of the strong force.

The formula turned out to describe not ‘point particles’ but vibrating strings. However string theory as an explanation for the strong force was abandoned because it predicted something absurd: a ‘massless spin 2 particle’. Later physicists realised this was just the characteristic of a graviton – the hypothetical particle proposed to carry the force of gravity. With that, a number of enthusiastic physicists proposed that string theory could be used to explain gravity, and in 1984 – after some more mathematical alchemy – John Schwarz at California Institute of Technology and Michael Green at Queen Mary’s College in London, found that string theory could also encompass all the other forces.

String field theory is to string theory what the electromagnetic field is to photons: a way of describing how strings act coherently in the real world. In 1974, Michio Kaku and Keiji Kikkawa demonstrated that it could work in 10 dimensions. Nearly 20 years later, in 1993, Ed Witten at Princeton University in the U.S. sparked a mini-revolution when he showed that string theory worked best in 11 dimensions. His seminal demonstration has taken string field theory physicists, Kaku among them, back to the drawing board.

String theory predicts alternate universes because it fits with the physics of the subatomic scale (quantum dynamics) as well as with cosmology (it is the only theory to achieve this unification, and that’s why it remains compelling).

At the quantum level, particles of matter such as electrons can be in two places at once. In fact, this seemingly absurd statement is validated by modern electronics. Extrapolated, this means that the building blocks of our world might actually be leading an alternative existence somewhere else ... as you sit reading this, there may be another you reading in another parallel world.

String theory as applied to cosmology suggests that strings were the first thing to be created, and they were originally created in 11 dimensions. Since the world as humans experience it has only four dimensions (three of space plus one of time), these other dimensions are probably out there and our universe is perhaps just one bubble in an infinite sea of bubble universe

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Elizabeth Finkel is editor-in-chief of Cosmos.
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