The Question of Arrow of Time

Response for the article ‘Complexity and arrow of time’ by Paul Davies


The second law of Thermodynamics states that Entropy i.e. the degree of disorder, in an isolated system always increases. Since 19th century, philosophers and scientist have been seeing if this applies to the universe leading it to its eventual ‘heat death.

While that was being debated, it was clear that there were abundant examples of entropy in the world – even our existence depends crucially on the state of thermodynamic disequilibrium occasioned by this irreversible heat flow.

The intriguing aspect of this was the arrow of time, which brought out themes of atheism and cosmic pointlessness. This in turn led to reactions of evading or refuting the second law to show that the world will get ‘better’. However, many of theories (such as Stephen Hawking’s backward timeline) were disproven or did not have enough empirical evidence (such as mystical belief in ‘cyclic universe’).

The theory finds it difficult to rigid definition of entropy when the cosmological case of an expanding (and later perhaps contracting) universe is compared to the expansion and contraction of piston-cylinder arrangement where the external force applied is replaced by gravitational field.

Dwelling further into this, scientist like Roger Penrose tried understanding the particular directionality of the arrow of time by checking the universe’s initial and final state of entropy. This leads further to an unsolved question in Physics –

Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics?

While the presence of this improbable initial ‘smooth and low entropy’ state of universe can be seen an evidence of design,  a more plausible explanation for it comes from the field of Quantum cosmology, which uses the concept of  ‘wavefunction of universe’ to discuss the possibility of multiple-universe (as branches of the wavefunction). The wave function as a whole can be completely time-symmetric, but individual branches of the wave function will represent universes with temporal directionality.

The introduction of Parallel dimensions or alternative may solve the problem of origin of the arrow of time. Due to the existence of time-symmetry offered by the wavefunction branches, any observers in these universes will by definition call the low-entropy end of their universe the big bang and the high-entropy end the big crunch.


What interested me in  the section on ‘Arrow of Time’ of the article, was not just the problem of directionality of time but the reaction and explanation of scientist and philosophers, as it has a profound impact on the ‘point of life’ question.

Being fascinated by the concept of time and quantum mechanics since childhood, I sought to read books, listen to people and watch movies that learn as much as could understand.  This article just added to my clarity of the subject.

I was experienced a sense of cognitive dissonance while coming across the Hartle and Gell-Mann multi-verse model as though intellectually it sounds rational enough (not to mention exciting by combining two of my favorite topics – time and quantum physics), I particularly find the concept of parallel universes seemingly far-fetched (and like the cyclical universe theory, no way of proving it).

The lectures of ‘Arrow of Time’ by theoretical physicist Sean Carroll made many points clear too.

However, despite its flaws, this seems to be the closest in giving a concrete explanation of the arrow of time.



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One response to “The Question of Arrow of Time”

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