Monday 8 June 2015

The Unparalleled Excitement of Uncertainty

What if I tell you just a single detail from the end of the movie— The Sixth Sense?

I’m sure I’ll render it worthless for you. There is a reason why movie (or book) spoilers are frowned upon. Once you’re aware of what you’re heading to, you squeeze out the excitement from the event.


Is the future predictable?

Some events will occur definitely tomorrow and other won’t. There’s a certain level of determinism inherent in classical systems.

Laplace said:
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.
    —A Philosophical Essay on Probabilities

‘An intellect’ referred to in the above quotation is popularly known as Laplace’s Demon. Since the entire universe is comprised essentially of the 12 fundamental particles which interact in 4 possible ways, if one could predict where every particle will be, one would be able to predict everything about the future, even the way you will behave tomorrow.

With the advancement of Quantum Mechanics however it became clear that you cannot predict the exact location of a quantum particle. What you can do is find the wave function of a particle which is a probability density. It’s just like tossing a coin or throwing a dice. In the case of coin however, if you could know about every property of the coin, the force applied, the air density etc. you could in practice tell if it would be a head (or a tail). This is not the case with quantum particles; with any level of technological advancement you can only know the probability of a particle of being at a certain place. This led Einstein to make his famous comment—

God does not play dice with the universe.

To which Neils Bohr responded—

Einstein, don’t tell God what to do.


What are we governed by?

It seems that at the smallest of scales we’re governed by pure randomness— chaos. This is however not just true for quantum systems. In systems as simple as a double pendulum, a slight change in the initial conditions leads to an entirely different trajectory of the pendulum (test it). This is a classic example of a concept in Chaos Theory known as The Butterfly Effect which is to say that a butterfly flapping its wings in South America can initiate a chain of events which may lead to a tornado in Central Park, New York.

This governance by chaos is what makes the universe non-deterministic. For us to truly have free will we need to live in a universe where Second Law of Thermodynamics holds and new information (randomness) is created every instant, which is to say that God needs to keep playing dice with the universe for our universe to continue.


What makes uncertainty exciting? 

The fact of not knowing tomorrow is what adds the spice to life. A life where you knew the future (however good) isn’t worth living just like reading a detective novel with a predictable plot. In only a non-deterministic universe can the truly unexpected happen and you can carve out of yourself whatever you wish to.

Further Reading:

Does God play dice?
Uncertainty Principle
Laplace’s Demon
Butterfly Effect 
This article is based on the video: What is not Random?


  1. Nicely written ! I think the philosophical interpretation of uncertainty is still open. (perhaps it will never cease to be, and that's its beauty!). We cant just explain it in classical terms, i e , in terms of any other thing we know. Werner Heisenberg has written very extensively on this. His writings are mostly about philosophical footings of Quantum theory. You might like them. Here are a few :-
    The Physical Principles of Quantum Theory
    Physics and Philosophy
    Physics and beyond
    A physicists conception of universe
    Philosophic problems of Nuclear theory

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