I promised that I would write another blogpost (click here for the first) about how I cope with the whole quarantine situation, so here it is. The second part of my strategy is to do a lot of writing. That works very well for me, because it makes me feel less alone, as if I am interacting with those who read my texts.

But this strategy is not as easy as it seems. The moments I need company the most, the moments I am most lonely, are also the moments at which it is most difficult to put myself to work, to actually start writing. So this strategy only works in combination with something else: I need to plan my writing activity. On the evening before a writing day, before I go to bed, I try to come up with an idea about what I want to start writing about the next morning. Only that makes it possible for me to start writing even when I am feeling lonely or sad.  

In the past few days I coped with the quarantine by translating the first chapter of my book about relativity theory into English:

Down the rabbit hole

It is often said that the beginning of the 20^th century is an era in which physics has become too complicated for ordinary mortals. We have a clear intuition for the ideas of Newton and his contemporaries (often called classical physics), in which gravity explains why stones fall and the earth moves around the sun. This intuition comes to a sudden end when relativity theory and the theory of quantum mechanics appear.

In Newton’s physics, space and time are abstract but simple concepts, that can be measured with clocks and measuring sticks. Space and time enable us to understand the world around us, because they make it possible to describe any kind of physical change. But in the 20^th century we no longer know which measuring sticks are straight and which clocks are synchronous, so it has become a challenge to understand what space and time are, which makes the transition from Newton’s to Einstein’s worldview seem like a radical transformation.  In this book I will show that the transition from classical to modern physics is not as abrupt as it is often presented – Newton and Einstein are more alike than we think.

The classical Newtonian worldview is not as obvious or easy-to-understand as is usually assumed, because much interpretation is needed to get from Newton’s physics (his mathematical equations) to a coherent view of what ‘reality’ is like. When we try to find out what Newton’s formulas tell us about the world outside ourselves, we will see that the concepts that lie at the foundations of classical physics are the same as those on which early 20^th century physics is built.

Gerard ‘t Hooft and Alice in Wonderland

A couple of years ago I was at a physics conference with a philosophical bend, a conference about the foundations of spacetime theories. During one of the coffee breaks I had a chat with the keynote speaker of the conference, the Nobel laureate Professor Gerard ‘t Hooft. We agreed on many things – the location of the conference, Varna, Bulgaria, was great, and the weather was perfect. Then he said something that really surprised me: he was not there for the philosophy of space and time. “Then what are you doing here?!” I asked him full of surprise. “I have a new theoretical toy-model for black holes, and I want to discuss that”, he said, shrugging his shoulders.

            Gerard (we have become very good friends since then) is not the only physicist for whom the philosophy of space and time, and philosophy in general, is not the primary reason to visit a conference on physics. I find that difficult to grasp. Why are we interested in physics? Of course, we want technological advance, so we want to know how we can make new discoveries and which experiments are necessary for that, but we also want to find out something about the world – We want to understand the reality that exists independently of us and our experiments.  

            Physics gives us a model of reality outside of us, but that model does not say of itself whether it is a good model. It’s as if you’re trying to check a calculation that you made with a calculator by using the calculator itself. If the calculator made a mistake the first time, for example because of a loose key or because something went wrong in the factory when the calculator was manufactured, then probably the calculator will make the same mistake when checking the calculation. The physicist who wants to check whether their model of reality is a good model, is also checking their own calculations, just as the calculator.

The plight of the physicist is comparable to that of Alice in Wonderland. Alice wants to know whether she has grown after she drank from a small bottle and she tries to find out by holding her hand above her own head. That doesn’t work because she has no external point of reference, like a measuring stick. When physicists try to find out whether their model of reality is a good model, they are doing the same thing as Alice. They do not have an external point of reference, so the best they can do is hold their own hand above their heads.