Stephen Hawking: A Very Brief History of Time

 Stephen Hawking passed away this Wednesday 14th of March 2018 in Cambridge at the age of 76. Hawking was a renown physicist that specialised in gravitational singularities. He tried to combine the theory of relativity with quantum mechanics, to predict the emission of radiation from black holes. This later became known as Hawking radiation. 

Stephen Hawking is arguably the most influential scientist of his generation. Not only has he changed the way we think about certain ares of physics, but he has done so against all odds, having suffered from ALS for most of his adult life. ALS is a degenerative disease that causes weakening of muscles to the point where one cannot speak, swallow or even breath. When Hawking was diagnosed, he was told he had 3 years to live; instead, he lived and worked until his mid 70s. For his great contribution to science and influence to society I decided to write a blog entry about him.

Hawking specialised in singularities; he mainly worked on black holes and also developed upon the theory that the universe began from a singularity known as the big bang. Nevertheless, Hawking’s most important discovery is Hawking radiation. This theory states that black holes lose mass by emitting radiation and are therefore theoretically not completely black! Hawking realised this when he reflected on the second law of thermodynamics, which led him to the fact that the entropy of a black hole always has to increase. Something that has entropy, must have a temperature, and something that has a temperature must emit black body radiation. 

As most of you know, nothing can escape a black hole, not even light. The point from which nothing can escape is known as the event horizon; this feature is achieved because of the immense gravitational pull of the singularity. If we take a point that is just outside the event horizon, particles could be emitted from the black hole in the form of radiation - Hawking radiation. Let’s take a closer look at what we think is happening.

When people talk about space and vacuums being empty, that is not completely true; there are actually quantum fluctuations that correspond to the lowest energy level of a system. From these fluctuations, particle and antiparticle pairs can be instantaneously created at random. This happens all the time, but we don’t notice it because they annihilate each other immediately after being created. Interestingly, if these pairs are created just outside the event horizon, there will be a huge difference in gravitational strength between the positions occupied by the two particles. This will cause them to separate, making it possible for one particle to fall into the back hole and the other to escape. The antiparticle with negative energy will fall into the back hole, reducing the mass of the black whole. Meanwhile, the particle will escape into space. As this process keeps happening, the black hole will shrink until it eventually evaporates or even explodes.

Questions have been raised in response to this theory. One big problem is the loss of information. If we were to throw diamonds into a back hole and chocolate cakes into another, the radiation released by each black hole would be the same. This doesn’t agree with quantum mechanics, which states that the path of each particle in the universe can be accounted for. Also, we cannot track every piece of the cake as it is getting torn apart by gravity. 

We are still missing a lot of knowledge about this theory and we have never observed it, but we believe it is true because it is predicted through very convincing mathematical results. If true, it is possible that at the singularity of the back hole there is a worm hole that takes particles to a different region in space. This way, the “lost” information would be accounted for and the rules of quantum mechanics held. We still don’t understand quantum mechanics completely, but this theory might be a step towards comprehending it.