Wednesday, March 20, 2019

How Carlo Rovelli dismantles the order of time

Time is so fundamental to our perception of reality that it is hard to imagine that it could be similar to Santa Claus – just an abstraction. And this is exactly what physicist Carlo Rovelli attempts to show in his lecture titled “The physics and philosophy of time” delivered at the Royal Institute in April 2018. In this process of dismantling the notion of time, Rovelli takes five properties of time and tries to show how each of them could be an approximation relevant in a context and meaningless beyond it. Here are the five properties:

Synchronized clock-time:  (9:35) We know that clocks measure time. And in our business meetings with participants from different continents, our clocks are usually synchronized. However, that is an approximation. Rovelli says we live in the “Netherlands” of space-time region – which is very flat. And even in this region, atomic clocks with an accuracy of 10-17 second show that one atomic clock placed 40-50 cm above the other runs faster than the one below.  The conclusion is staring at us: Our head is older than our feet. And there is no such thing as synchronized clock-time.

We both have the same NOW: (14:00) When we watch a live telecast of a match, we know that everybody is watching the same thing. But are we watching it NOW? No. We are watching it with a delay of a few seconds. If you are visiting Mars and I am on Earth, our NOWs are separated by 3 minutes. And we have not even taken our relative speeds into consideration. In short, Rovelli points out that there is no universal NOW. We all live in a local NOW bubble which has a length given by the speed of light.

Disorder grows in the future: (20:45) Second law of thermodynamics says that entropy which in layman terms means disorder grows in the future. For example, if we have a box with green balls on one side and red balls on the other side, we would call it order. And then if we mix them, we could say that the disorder has increased. Rovelli asks, “But, what if a colour blind person watches this transition? Would he say that the disorder has increased?” Perhaps not. Rovelli points out that if the universe looks more ordered in the past, it doesn’t mean the perceived order is a property of the universe. It just means we, the observing sub-system, has chosen a set of variables that makes us see it more ordered in the past. What could be that perspective from which disorder may not grow in the future? That leads us to the next property.

Time is continuous: (33:05) What Rovelli’s research in Loop Quantum Gravity (LQG) suggests is that if we look at the time at sufficient granularity i.e. divide time in small intervals, say of 10-44 second each, then time is no longer continuous. Every unit of this granular entity is independent. If a stone seems to carry the same structure over a long period, then it means the quantum process at each event of this granularity is expressing itself in a similar way at least as far as our perception is concerned.

Experience of time flowing: (44:15) Towards the end of the talk, Rovelli turns to the question, “All this is fine, but what about the flow of time I experience?” He considers the possibility that perhaps all these properties physicists study don’t capture something about time which creates a flow of experience. This is where he steps outside his field of expertise to neuroscience. He suggests a possibility that the flow of time is an outcome of neurological processes. Perhaps the human brain is a time machine which creates an emotional fog around the memory traces it weaves and calls it life and that fog doesn’t allow us to see the real nature of time. In fact, he interprets Buddhism’s second noble truth which emphasizes impermanence as “time is the source of human suffering”. After all, we lose things because of time. And what we are most afraid to lose is oneself – i.e. death.

As a student of mindfulness, the illusion of time has been an important area of exploration for me. The talk shed light on some aspects of time which were new to me especially I found the perspective on the second law of thermodynamics insightful.

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Watch the talk on YouTube: 


  1. Hey - Thanks for pointing this talk to us. The summary you have posted in itself is rivetting .. Hopefully so will be actual talk. :-)