Monday, 26 January 2015

Newton, Einstein . . . and Hawking

by Reetobrata Chatterjee

Stephen Hawking has become a household name, so much so that there has even been a movie about him (see Kelvin Shiu's review of 'The Theory of Everything' here. He is held in high esteem in the ranks of the greatest scientists of all time, among big names such as Newton, Einstein and so on. However his contributions are not that well known. He is perhaps best known for his book, A Brief History of Time, which became an international bestseller, after being first published in 1988. In 20 years, this book sold 10 million copies and has been translated into a plethora of languages. He was also a professor of Mathematics at Cambridge for 10 years and has his name associated with some of the greatest discoveries of the late twentieth century. 

All this while fighting Early-Onset Motor Neurone disease. 

His first contribution was during his doctoral thesis, on the very creation of the universe and how and why the Big Bang had taken place. His work theorised that the Big Bang had been an infinitesimally small point, which contained all the matter in the Universe today, not dissimilar to Black Holes. This was first predicted by Einstein, but Hawking provided additional evidence and proved it was the Big Bang which was the singularity. A singularity is a point in spacetime which is infinitely curved, thereby allowing it to have theoretically infinite gravity, so strong that even light cannot escape, hence the name “Black” Holes. Not bad for someone in his twenties who couldn’t walk without external help.

Later he went on to improve the current understanding of Black Holes. Previously, it was very limited. All that was known was that a stationary Black Holes had a constant surface gravity, which would not change over time and if the Black Hole was moving (or rotating) it would change some of its properties such as angular momentum and Electric Charge. At first, he proposed that the surface area of Black Holes will never get smaller, if viewed in normal space. However this created a paradox, it suggested that Black holes were “hot” objects, which emitted electromagnetic radiation such as light. This was puzzling because the current theory was that nothing could escape a Black Hole, not even light.

So, Hawking delved into the weird world of quantum theory (in which cats can be dead or alive or both).

As a result, he discovered that certain Black Holes (really small ones) CAN actually get smaller over time. This is a result of the fact that quantum theory allows small particles, such as electrons, to spontaneously exist, as long as they only exist for very small amounts of time and vanish again immediately afterward. However, this could also mean that some particles may form at the edge of the Black Hole, some of which may be just outside its reach and some may be just inside. The ones which are inside will get absorbed by the Black Hole, since (as previously stated) nothing can escape from them. However, this violates the laws of physics, which state very simply that something cannot spontaneously form out of nothing (Energy (and mass) must be conserved).

Therefore, the only logical explanation is that the Black Hole must lose energy when this happens (i.e. it shrinks over time). For Black Holes the size of the sun, however, this would take longer than the current age of the universe; on the other hand, significantly smaller ones can vanish very quickly and produce a lot of energy as they disappear. How much energy? About a million one megaton hydrogen bombs.

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