It is with immense pleasure that I came across this passage in Brief History of Time. I remember reading this sentence when I was 16 but in the last 20 years I had forgotten where I read it. The only thing I could remember was that there were some physics calculations which took 3 years to complete and no one had the courage to take them on. Now I've found that passage again. I guess I did read BHOT when I was 16 and moreover I got to the end since this passage is in the final pages. I didn't understand the book though and probably just plowed through it just to say I had done it.(adsbygoogle = window.adsbygoogle || []).push({});

My question is did anyone ever do these calculations? Was it eventually discovered to be a dead-end anyway? Did they ever build better computers to help out with the calculations? This problem in combining general relativity and the uncertainty principle had been suspected for some time, but was finally confirmed by detailed calculations in 1972. Four years later, a possible solution, called “supergravity,” was suggested.

The idea was to combine the spin-2 particle called the graviton, which carries the gravitational force, with certain other particles of spin 3/2, 1, 1/2, and 0. In a sense, all these particles could then be regarded as different aspects of the same “superparticle,” thus unifying the matter particles with spin 1/2 and 3/2 with the force-carrying particles of spin 0, 1, and 2. The virtual particle/antiparticle pairs of spin 1/2 and 3/2 would have negative energy, and so would tend to cancel out the positive energy of the spin 2, 1, and 0 virtual pairs. This would cause many of the possible infinities to cancel out, but it was suspected that some infinities might still remain. However, the calculations required to find out whether or not there were any infinities left uncancelled were so long and difficult that no one was prepared to undertake them. Even with a computer it was reckoned it would take at least four years, and the chances were very high that one would make at least one mistake, probably more.

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# Supergravity, does anyone work on it now?

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