Sunday, February 27, 2011

A game of dice?


You get up in the morning and see that sun is rising in the east and by the time it sets, the stars will take center stage. In between these two regular celestial shows, you do your daily chores of getting ready for office, negotiating the traffic, working towards achieving the deadlines in your work and finally coming back home to have dinner and a good night’s sleep. The next day is pretty much the same except probably for a holiday that you take, or a business travel that you want to make. While you are busy chasing life (or being chased by life, depending on which end of the chase you are on!) have you ever wondered or marveled at the predictability of this universe? Oh no, I am not talking about how unpredictable various things like stock market, stability of governments, new scams every day, weather patterns, etc., are. In the grand cosmic stage, things are pretty much predictable. Sun will continue to fuse its abundant stock of hydrogen in a 24x7 schedule, to form helium and in the process releasing energy that comes to us as photons, to keep you and me bright and cozy in this cold dark universe. Sun and its trillions of other counterparts are always in business; never take a sick leave or vacation, until they run out of their hydrogen supply.


It is this predictability that prompted Einstein to make that famous quote “God does not play dice with the Universe”. Even before his time the French scientist Pierre Simon Laplace (1749 – 1827) believed that if at one time we knew the positions and speeds of all the particles in the universe, then we could calculate their behavior at any other time, in the past or future. This was his actual quote:


“We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.”


In fact Napoleon, who was ruling France at that time, asked how God fitted into this system, for which Laplace replied saying that he did not have to consider God in this hypothesis. Laplace did not mean that God did not exist, but he thought God does not intervene to break the laws of science that govern this universe. The idea that the state of the universe at one time determines the state at all other times, has been a central tenet of science, ever since Laplace's time.

But the developments in Quantum Mechanics at the turn of 20th century turned this scientific belief on its head. The German physicist, Max Planck, set out solving a paradox that existed till his time. If you heat an object and leave it, it will start emitting radiation in the form of radio waves, infra red, visible light, ultra violet, x-rays, and gamma rays, all at the same rate. This means the entire universe should be of the same temperature at any given time, but as you know that is not the case. If all hot bodies started emitting x-rays and ultra violet rays, then this world could not have harbored life due to harmful radiations from these rays. Planck suggested that the radiation emitted by a hot body is in the form of packets or quanta of a certain size. He further postulated that the quantum of energy in these packets is larger for x-rays and ultra violet rays compared to infra red rays and visible light. Which further means the quanta varies for different forms of radiations. So unless the hot body is super massive like a star, it cannot have enough quanta for x-rays and ultra violet rays to harm us. So you could still hold that hot cup of coffee on a Sunday morning during monsoon, without getting cooked by the harmful radiation.

Few years later another German physicist Werner Heisenberg unearthed another paradox that came to be known as the Uncertainty Principle. It states that the position and velocity of a subatomic particle cannot both be measured, exactly, at the same time (actually pairs of position, energy and time). To see where a particle is, one has to shine light on it. But by Planck's work, one has to use at least one quantum of light to do this. This will disturb the particle due to the energy released by that quantum of light, and change its speed in a way that we cannot predict. To measure the position of the particle accurately, you will have to use light of short wave length, like ultra violet, x-rays, or gamma rays. But again, by Planck's work, quanta of these forms of light have higher energies than those of visible light. So they will disturb the speed of the particle more. It is a no win situation: the more accurately you try to measure the position of the particle, the less accurately you can know the speed, and vice versa. This is known as Heisenberg’s Uncertainty Principle. This was a complete contradiction to Laplace’s scientific determinism. Einstein was not comfortable with this apparent randomness that this principle will introduce to the cosmos, which prompted him to say that the God does not play dice.


To explain this further, assume you have a box with a partition in between. Assume further that one half of this box is containing oxygen molecules and the other half is vacuum. If we remove the partition the oxygen molecules will start spreading the entire box randomly filling it completely. Applying uncertainty principle we can actually apply a probability that all molecules due to their random movement can actually travel to one half of the box so as to leave the other half as vacuum just the way it did exist when the partition was in place. Possible? Yes, though with an extremely low probability. Therefore this is more like playing dice. So god does play dice with the universe at a micro level!


So all these completely contradict the working of the universe that is largely governed by the Newtonian Physics. Scientists are yet to find a theory that unifies quantum mechanics and astrophysics. In the second and concluding part of this article we will look at the role black holes play to make the uncertainty principle more uncertain. In the meantime, you could continue to invest in that attractive stock, hoping that it will yield a handsome dividend tomorrow!


-To be concluded-

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