What is time? Why is it strange?

#6 The Order of Time by Carlo Rovelli. About time, entropy and why everything will turn to dust.

This is my 6th book summary. Another interesting book; check if it can inspire you as well. Previously: Do you burn like a good bonfire? Subscribe for more.

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Carlo Rovelli (1956) is a theoretical physicist who decided that it would be fun to teach the plebs about physics.

First published in Italian in 2017, “The Order of Time” (Goodreads: 4.11, 21.5k ratings) is one of his six “popular” books. This one is about space and time, or spacetime.

Who should read it?

Everyone interested in the concept of time. What is time and how does it relate to heat? Why is time strange?

Top ideas that I can also explain

I hated physics, closely followed by mathematics and chemistry, and I am sorry, but I will blame my teachers too. The way you are taught makes a difference; I went on to study political science because my philosophy professor, prof. Ručigaj, was excellent.

If you really understand something, you should be able to explain it to a child. Rovelli, our excellent teacher, undoubtedly understands spacetime, but still sometimes forgets he is writing for the plebs and not his students.

I cannot improve his explanations, so I leave you with a couple of points. Let’s begin with the fact that people living higher are ageing faster. But if you are reading this in Nepal, don’t worry, the difference is negligible.

There is no single time, no such thing as “now”

I am writing these lines NOW, you are reading them NOW and we both have our own past, future and present. Say you were on a planet 10 light years away and I asked you what are you doing? I would wait for your answer for 20 of my years.

How many of your years would you wait for my question? Well, I would probably say that it depends on the gravity of your planet, but even if I knew it, we would still face the problem that I have no clue about physics and could not calculate anything. But you get the picture: there are many different times and the further away we are, the bigger the time lag.

If we were much closer, in the same room, your answer will travel light-nanoseconds, if in different cities maybe light-milliseconds. So,

“our present extends to a bubble around us. /…/ As humans, we distinguish tenths of a second only with great difficulty; we can easily consider our entire planet to be like a single bubble where we can speak of the present as if it were an instant shared by us all. This is as far as we can go.

The idea that a well-defined now exists throughout the universe is an illusion, an illegitimate extrapolation of our own experience.”

We measure time with clocks, but the era of clock-regulated time is a fairly new concept. It started to expand with mechanical clocks on churches regulating the rhythm of collective activities. All of this worked because people were walking or using horses.

But with the arrival of telegraph and trains in the 19th century, the problem of synchronised time became obvious. Take midday when sun is the highest. At what time is it the highest in Madrid and when in Berlin?

You are not gonna believe this, but guess who was dealing with patents relating to synchronisation of railway clocks? Albert Einstein! He recognised that the exact synchronisation is impossible, because time is relative: the rate at which time passes depends on your frame of reference.

This time dilation explains why two working clocks will report different times after different gravity or velocity. According to Wikipedia, “time goes slower at the ISS, lagging approximately 0.01 seconds for every 12 Earth months passed. For GPS satellites to work, they must adjust for similar bending of spacetime to coordinate properly with systems on Earth.” Yea!

Time only appears where there is heat?

I understand the concept of entropy only because I am writing these lines. Entropy measures uncertainty and randomness in a system; with time everything is getting more and more random. In other words, entropy is a loss of energy, because

“energy (mechanical, chemical, electrical or potential) transforms itself into thermal energy, that is to say, into heat: it goes into cold things, and there is no free way of getting it back from there to reuse it to make a plant grow or to power a motor. In this process, the energy remains the same but the entropy increases, and it is this which cannot be turned back.”

This is the second law of thermodynamics. But how does this relate to time?

“What makes the world go round are not sources of energy but sources of low entropy. Without low entropy, energy would dilute into uniform heat and the world would go to sleep in a state of thermal equilibrium - there would no longer be any distinction between past and future, and nothing would happen.”

The only reason you and me have a feeling of passing of time is that our source of low entropy, the Sun, sends us one hot photon and then Earth radiates ten colder photons back towards the black sky. One hot photon has less entropy than ten cold photons, because ten cold photons are more random than one hot one.

Further,

“inside every living cell, the complex web of chemical processes is a structure that opens and closes gates through which low entropy can increase. Molecules function as the catalysts that allow the processes to intertwine; or, conversely, they put a brake on them. The increase of entropy in each individual process is what makes the whole thing work.

When all the sources of low entropy will be exhausted everything will stop and there will be no more time. Hja. Everything what we call a ‘thing’, take your phone or computer, is in fact not a thing, but a temporary event which will eventually turn to dust. Yea, I know. To understand this properly you will need to read the book (p. 86 onwards).

How did it change me?

This was one of the impulsive purchases because of a tweet and I am happy it happened. It is hard to teach people like me about physics. It is not that I am a retard, it is just that I am in the “Explain Like I’m 5” camp.

Takeaways:

• I finally understand what entropy means,

• talking about everything turning to dust won’t make you fun at the parties,

• I am mailing Rovelli and volunteering to be a beta reader of the next book, so that he can make it even more ELI5.

Also, in the grand scheme of things we should not take ourselves too serious, but we already knew that, didn’t we?

Closing remarks

This is one of the “wow” & “wtf did I just read” or interesting-but-probably-won’t-have-serious-impact-on-your-life type of a book. Sometimes I got completely lost, gave it another chance, but it did not improve. Some parts were likely lost in translation from Italian and I felt the editing could be better.

At some point even Rovelli suggests, “You can skip this.” And I should have.

More 4 than a 3 out of 5. Warmly recommended to see that we know something, but not much:

“We are more complex than our mental faculties are capable of grasping. /../

We barely see just a tiny window of the vast electromagnetic spectrum emitted by things. We do not see the atomic structure of matter, nor the curvature of space.”

Before I give you a chance to like this post, here is another great guy explaining why he cannot really explain why magnets repel each other:

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