It's been another year in the life of our fellow human, Stephen Hawking and I was just revisiting his idea about the infamous Firewall paradox. Hawking is one of the few to actually popularize Black Holes among masses, so his paper declaring theoretical impossibility of black holes was an obvious rager.
Going back gives us the root problem about black holes. And it is a very basic one. The Black hole Information Paradox, defying the second law of thermodynamics.
The second law is about entropy, or rather information. The law hinders decrease in information content of the universe. This is what gives time, an arrow. This is what creates now, and tomorrow. One of the most beautiful, but also one of the most controversial thing. It comes in question every time quantum mechanics and general relativity have a playoff.
1. The Firewall
Black hole firewall is a recent thing (2012-13). Read here. According to Hawking process, black holes radiate and evaporate as a result of quantum fluctuation, which is a well established fact now in modern Physics.
But, here is the thing, if, accidentally, your water bottle gets sucked in a black hole, and if the black hole evaporates after few years, you loose information! This is the information paradox. The violation of the second law. Many believe its okay to have this loss. But, an interesting solution came when information was supposed to escape from black holes. Firewall.
Firewalls are literal firewalls of energy on the surface of black holes. This happens due to the breaking of entanglement of particles in black hole evaporation process. This is similar to breaking of chemical bonds. So, this gives an alternate ending to Interstellar, where Cooper dies abruptly and foolishly. But this isn't fun.
Firewall plays with general relativity on the other side and again, this raises questions on the second law.
Hawking, in 2014, proposed an Apparent horizon rather than the hyped, Event horizon. The event horizon is what makes black holes what they are in popular literature. An apparent horizon doesn't take the incoming stuff to singularity, it returns things back, busting the whole black business.
Whatever happens, it's really amusing to see what are the implications if the second law is flawed, or it is not what we think it is.
2. The Second Law
I personally feel, the second law of thermodynamics is highly underrated in engineering institutions (in India at least). People take away the beauty of it by associating it only with engines and refrigerators. It is much (much!) more than that, it is the theory of information, about what has happened and what can happen. Prick it, and the whole Universe's history will change.
The second law governs what will happen and thus gives a direction for movement in the time dimension. Assuming now is only a construct of human brain which itself is due to the second law, it is fascinating to look at the true nature of time. Is there an inverse which leads to undoing things, unrolling the usual? Is it possible that time is and always was a two way street?
Time is exciting! Especially right now, when there are questions raised on the second law, and time itself is feeling elusive (no pun intended).
Does the entropy always increase ? Or is it just a convex function of time?
I hope, we will learn the answers someday, or maybe we already have.