Saturday, July 30, 2011

A game of dice - Part 2: "The dice go missing"

Please read Part 1 before reading this blog: A game of dice - Part 1 

Hope life has been treating you all very well and you were not being subjected to the vagaries of the uncertainty principle and your investments in the stock market have been giving you rich dividends. Things have not been all that predictable for me, as I am still sitting beside the box full of oxygen molecules waiting for all those molecules to move to one half of the box!

In the first part of this article, we looked at the difficulties in predicting the position and speed of a subatomic particle at any given point in time, which has been the basis on which Heisenberg formulated the Uncertainty Principle. We further saw that these contradict the completely predictable macro universe that is governed by Newtonian Physics. So we are yet to find a unified theory that ties the quantum physics (the very small) and the astrophysics (the very large). In this concluding part, let us look at some additional complications in this game of quantum dice.

Have you ever tried leaving your kids alone at home for few hours? What do you expect when you come back home? If your home is exactly the way you left it, you really are one extremely-rare-lucky-parent. I never had any such luck as a parent so far, as invariably I return to a home that has transformed beyond recognition. But then why am I talking about a parental occupational hazard that everyone knows about in an article that is meant for astronomers? Going back to the example of the box full of oxygen molecules, it started off as an ordered state with all molecules neatly tucked away into one half of the box. But when the partition was removed and it spread randomly into the entire box. So we can say that it is less ordered than what it was before. As the time progresses, as the molecules keep moving about randomly, this disorder will only increase. This tendency for any closed system to lose its orderliness and move towards a disorderly system is what is explained by the second law of thermodynamics and the degree of this disorder is known as Entropy. Unlike classical general relativity which is completely predictable, second law of thermodynamics is only almost always true; almost. So those lucky parents with kids who would maintain the homes in perfect order while you are away fall into those categories where the second law of thermodynamics need not be applied. And how fortunate they are!

There is a more simpler way of breaking the second law of thermodynamics than ensuring your kids behave perfectly well while you are away. That is to throw that box full of disorderly oxygen molecules into a black hole. So what happened here? When that box was outside the black hole, the entropy of our “observable” universe was high (to the extent of those misbehaved molecules), because there is no way we can measure anything that happens inside the black holes (as you know nothing can escape from its gravitational clutches). But obviously we cannot do the same with our kids! Even if I have to send them to a boarding school to discipline them, the teachers in the school have to spend lot of energy to make them disciplined and they will be losing that much of ordered energy thus making the universe that much more disordered. So entropy will continue to increase. But then teachers being teachers, how can they break the law of thermodynamics, when they themselves are teaching it!

Stephen Hawking was not comfortable with the idea that the law of thermodynamics breaks down due to black holes. He argued that black hole actually emits radiation so that the law is preserved. This radiation is thus known as Hawking Radiation in honor of his work.

The vacuum that fills the interstellar space is actually not exactly “vacuum”, but it is filled with a pair of opposites: Particle and Antiparticle (also known as virtual particle). An antiparticle has the same mass and spin as the particle, but with opposite charge. For example, electron has positron as its antiparticle. Hawking theorized that when a black hole is nearby, one of the particles in this pair (either particle or anti-particle) may fall into the black hole, leaving the other particle without a partner. In this situation two things can happen: either that other particle also falls into the black hole or it escapes from the hole. To anyone who is observing the black hole, this will look as though the particle is being emitted by the hole.

So if a black hole indeed emits radiation, it must be losing its mass in the process. Which further means there will come a time when it completely runs out of its mass and vanishes from our Universe. So what will happen to all the matter that was sucked into the black hole? Also, in the absence of the particle that fell into the black hole, there is no way we can predict the speed and position of the escaped particle. So according to Hawking “Not only does God definitely play dice, but He sometimes confuses us by throwing them where they can't be seen”. A black hole that emits radiation is a revolutionary idea and it ensured that the second law of thermodynamics is not violated. Which further means, the entropy of our Universe will continue to rise as the Universe expands (what happens if the Universe contracts? Would the entropy starts reducing? Well, let us leave that for a future discussion). In a way entropy is like the fuel price, it can only increase!

I often wonder: Since everything in this universe is made of atoms, including the DNA and the brain cells, even the way we think and behave are governed by the random movements of the subatomic particles? Is it not stupefying to imagine how this random movement of subatomic particles can influence intellectuals to make path breaking discoveries that benefit mankind, leaders to unleash world wars that kill millions, a politician to have a field day of corruption or a terrorist to blow himself up to destroy other fellow living beings? God has strange ways, stranger than the uncertainty principle that we discussed so far. Probably God wanted to make this game of dice more interesting! 

The unification of a theory that governs the very small and the very large seems to be elusive at this stage. The closest attempt to do this has been the formulation of String Theory, though it is still not fully able to address the unification challenges. These are realms of science that are both intriguing and confusing for a far inferior mortal like me. By no stretch of the imagination I am an expert in any of the things that is discussed in this article so far, and my apologies for any errors and omissions. But those experienced parents would agree that it is a lot easier to talk about black holes and the uncertainty principle than making the kids behave in an orderly manner! May better luck be with you in this game of dice, lest you lose it.

-The end-

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