Classical physics states that everything that happened in the past can be exactly know and everything in the future can be exactly predicted, provided you know the position and momentum of every single particle in the universe.
Sure that's an absurd demand, a single droplet of water has number of particles of the order 10^23 which is incomprehensibly huge to just think about let alone measure.
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| A small water droplet has more molecules than the number of grains of sand on earth! |
But philosophical consequences of determinism in classical physics do not concern with practicality. The fact that once things are set in motion, everything from the time universe was born, stars forming and exploding, dinosaurs going extinct, what you'll eat for breakfast tomorrow or do anything for that matter- can be exactly calculated using Newton's laws of motion.
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| From Big bang to Breakfast, everything can be in-principle predicted exactly in classical physics. [Image by GPT 5.2] |
The end of determinism
In 1920s a drastic shift happened in the way we think about nature. A revolution would be an understatement to describe the discovery of the Quantum world.
Multiple experiments - Stern Gerlach, hydrogen spectrum lines, electron interference, and many others hinted towards a deeper anomaly in nature. Classical physics was no longer sufficient to describe the madness that was going on.
Then hell broke loose, physics no longer needed to be fully deterministic in its predictions, probabilities were good enough, or rather the only thing we could predict. Bell's theorem solidified the validity of Quantum Mechanics using clever inequality violation arguments which only occur when a system is truly indeterministic. [See EPR vs Bell]
This means that in the microscopic world outcomes are truly random and we will never be able to predict them no matter how advanced our civilization gets.
Although this is bad for predictive power of physics, for the philosophical argument of free will it's excellent. For a living being to have some free will, at least some of its decisions must be random.
But here's the catch- does the microscopic world really affect the world we are familiar with? You never see a football tunnel through the wall or superposition of a coin or planets going in strange trajectories. Everything feels... predictable. Something strange happens in between, when we go from the quantum to the macroscopic regime.
In statistical physics, when we calculate the fluctuations in macroscopic quantities like pressure or temperature, we find that the quantum mechanical randomness is orders of magnitude lower to make any significant impact to the average behaviour of a system. It's sort of like when adults speak, opinions given by kids are ignored completely.
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| Energy Fluctuations from the average value in the system are negligible. |
This means that for a large system, the quantum correlations are negligible, and the system settles into a predictable state, up to a very good accuracy.
Many scientists due to this reason argue that, in the real world for all practical purposes prediction is possible to a very good degree. And so, the world is effectively still classical. This is bad for free will, if quantum corrections don't apply enough to impact brain activity then all our actions would be effectively deterministic.
[See Quantum decoherence in microtubules for more info]
Does this apply to human decisions also?
Well to exactly answer this question, one must study the physics of neuronal activity in the brain (assuming that psychological activity is not metaphysical and happens purely due to brain functioning).
I'm no neuroscientist but we can safely assume that our brain activities would be governed a system of very complex intertwined non-linear differential equations. Non-linear means that you would have complicated functions of the time dependent parameters in your system. In certain non-linear differential equations, the parameters are very sensitive to even the slightest changes in the initial conditions of the system.
How do these seemingly unrelated differential equations would bring about large-scale impact of quantum fluctuations will be explored in part 2 of this article series on free will.
Note: This article is fully written by me without any AI help and it expresses my own views on the subject at the time of writing. Wherever images generated by AI have been used, due credit has been given.
A very great article on an equally interesting topic. My fascination on this topic stems from a reel I saw quite a while ago that if you were in the place of the other person, you would have done exactly the same thing. If you were in the place of Hitler, with the exact same premise and same factors, you would have done what he did. Decisions are a consequence of all the factors. So free will is really sort of a joke to me. It exists, but is driven by so many factors that if known, we would predict what's next. That's why psychology exists too. And hearing it from a physics enthusiast like you made me want more of this from you. Great read, keep it up :thumbs_up:
ReplyDeleteHey thanks for leaving such a nice comment! Glad you liked it.
DeleteIs true indeterminism equivalent to free will or not, is a very debatable topic.
Part 2 of this article will explore that and will be even more nuanced and interesting, stay tuned.
Nice article man
ReplyDeleteThankyou!
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