Historical story

Albert Einstein, the genius

Many consider him to be the greatest physicist ever. With just a pen, paper and his thought experiments, Albert Einstein designed a radically new picture of our world. Einstein became the first scientific "superstar". A brilliant and idiosyncratic genius, but also a man with humor and an outspoken political leaning. Kennislink did a 'fictional interview' with the famous scholar.

It's a great script for a movie. At the end of the nineteenth century, scientists believed that nature no longer held any great secrets for them. The most important phenomena, such as electricity and magnetism, were neatly laid down in laws. Physics was pretty much finished. They thought.

But what were they wrong with. Albert Einstein (1879 – 1955) made that painfully clear. His theories of relativity painted a completely different picture of nature than people were used to. No fixed place and time, but a deformable 'space-time', curved by gravity. His theories led to modern physics, such as quantum mechanics, but also play a crucial role in technologies we use today. Kennislink imagined what it would be like to be able to interview the famous scholar. Here you can read the result.

Professor Einstein, you know better than anyone that this interview with you has to be fictitious are, isn't it? “Haha, a joke to start with, I like that. But you're right, time travel is impossible as far as I know. You must then be able to go faster than light; the premise of my theory of relativity is that this is not possible.”

We'll get to that in a moment, but we'll start at the beginning. What does the youth of a genius look like? “I think I know why you are asking, because it is sometimes said of me that my childhood was not a prelude to my later success. For example, according to my mother Pauline, it took me an unusually long time to learn to talk and was very introverted. The latter is true, that also applied to my later life, but that I would be a lazy and uninterested student – ​​which I also sometimes heard – is a myth.

Well, I found the gymnasium in Munich a horror, with all its strict rules. But in the end I only had bad marks for French and Italian. In 1896 I started at the Technical High School in Zurich, the ETH. Teachers thought I was lazy and slow, but in reality I wasn't. With assignments I always searched to find even better solutions, and that simply took more time.

Moreover, the lectures were old-fashioned. For example, I was very interested in the theories of Maxwell, Lorentz (electromagnetism) or Boltzmann (thermodynamics), but they were not covered. I therefore preferred to go my own way and immersed myself in their work with my own hands. In the end I got good grades; for most parts I was the best in my year."

Five years after your graduation, in 1905, you will experience a 'miracle year'. You write four influential scientific articles in a short period of time. Describe your situation at that moment. “I was 26 years old and just married my Hungarian wife Mileva Marić. My first son Hans Albert was one year old. After graduating, I couldn't find a decent job for a while. Finally, in 1903, I started working at the patent office in Bern, as an 'expert third class' (the lowest rank as an academic, ed.). There I translated inventors' ideas into patents. Nice work, but I missed a real challenge. During my work I often daydreamed about current issues in physics, which I delved into in my spare time. In the spring of 1905 all ideas came together for me.”

In 1905, Albert Einstein published four articles in the leading German journal Annalen der Physik in three quarters of a year. . They all contain groundbreaking insights. In the first article he shows that light consists of particles and explains the photoelectric effect (see below). In the second, he proves that microscopic particles in solution perform a disordered motion known as the 'Brownian motion'. In the third article he describes his famous special theory of relativity. The fourth article is a supplement to this, which also includes the world's most famous formula E =mc 2 sees the light of day.

The most famous article of the four deals with your special theory of relativity. Can you explain what the theory is and how you came up with it? “As a little boy I often fantasized about what it must be like to move on the back of a beam of light. What would the world look like then? During my work at the patent office, my mind often wandered to this question. One day when I was driving the bus through Bern and saw the church bell, a storm broke loose in my mind. If the bus went faster and faster, I fantasized, the clock's light would take longer and longer to reach me. In other words, I would see the clock ticking slower!

The physicist James Clerk Maxwell had shown in his equations on electromagnetism that the speed of light has a finite value. And observers played no part in this. Suppose, I thought, that you assume that the speed of light is the same for everyone, what does that mean for our observations?

In the equations I then derived, I was able to show that measures of length appear shorter to inter-moving observers and clocks tick more slowly. Lorentz had already arrived at this, although he assumed a moving ether that changes the properties of objects."

That's hard to imagine. Can you give an example? “Yes, in lectures to a large audience I often used the example of a clock consisting of two vertical mirrors. A beam of light bounces back and forth between them. Every time the light hits a mirror, the clock is ticking. So if the distance between the mirrors is one meter, the clock will tick 300 million times per second (the speed of light is 300,000 kilometers per second, ed.). At least, for someone standing next to the clock. That may be hard to imagine, but it's a thought experiment, remember!

Now suppose the clock is in a fast moving train. What does someone standing on the platform see and see the train with the clock passing by? For those, the light does not only move in a vertical direction, because in the time that the light beam moves from one mirror to the other, the train travels a distance. This observer sees the light going back and forth in a zigzag shape. For him, the light travels a longer distance between the mirrors than for the person in the train. But because the speed of light is the same for everyone, the clock for the person on the platform is ticking slower.

What this example, and my special theory of relativity in general, shows is that space and time are not a fixed framework in which we live, as Isaac Newton thought. Space and time form one whole – the space-time – that molds itself to your perspective. What you see, where you see it and how quickly you see it are all determined by the movement you have yourself. In other words, time and space are relative."

An earth-shattering conclusion. How did the physics community react? “Of course I was very curious about the reaction of physicists, but I heard nothing. For four months! So I did get a little insecure, as you can imagine. Max Planck, the editor-in-chief of the journal in which the article was published, was the first to appreciate its value. He gave a lecture on it in 1906. But my idea was not accepted by the community until Hermann Minkowski, a former lecturer of mine at the ETH in Zurich, gave a speech to some eighty German natural scientists in 1908.”

In the meantime, your fourth article was already published, an addition to the special relativity with the well-known formula E =mc 2 . How did you come up with that? “I didn't allow myself a lot of rest, even though working on the articles – in addition to my work in the patent office – cost a lot of energy. But I kept thinking about that universal speed of light. Think along with this thought experiment:if you nudge an object, it gains a higher speed. Another push gives it a higher speed. Logical, I think. Can you keep doing that indefinitely? No, because I had taken the premise that the speed of light is the same for everyone; you can't go faster than light.

That must mean that there has to be some kind of natural brake on the object the more you accelerate it. The object will somehow resist a higher speed. But here comes the crux:that is the same as when an object gains a greater mass, because a heavier object is also more difficult to move. In short, the more energy you put into the object, the more mass it gains. So you see – put very simply – that the mass of an object depends on its energy. An interesting conclusion, isn't it?

I worked out the equations of motion for this situation and that led me to the formula that gives a measure of the relationship between mass and energy. The energy (E) of an object is equal to its mass (m) times the speed of light squared (c 2 )."

In the meantime, your formula has become the world's most famous formula. Perhaps also because it found application in the atomic bomb. Did you foresee something like this? "No not at all. Splitting atomic nuclei to gain a lot of energy was still a long way off when I came up with the formula. We knew very little about atomic nuclei at all. I have always been quite skeptical about the idea that by splitting nuclei you can release a lot of energy. I compared it to shooting crows in the dark, where there are no crows.”

But haven't you been involved in the Manhattan project, the American research into an atomic bomb? “It is not, I was not involved in the project in any way and was hardly aware of it. I heard on the radio that there had been bombings and it was a surprise to me. What I did do, and for which I was later criticized, was to send a letter to President Roosevelt in 1939. In it I made known that Germany was working on a superweapon. I urged intensive research into the possibility of an atomic bomb.”

You were an outspoken pacifist. And yet you urged the Americans to develop a terrible weapon? “I know, I was very sad about it. All my life I have advocated for peace and against violence. Violence can never be a solution to conflict. But what I've explained many times is that sometimes you have to make an exception when the enemy threatens to destroy your group. Such was the case with Germany under Hitler. I was not welcome in this country since 1933 because of my Jewish background. I'd rather have the Americans make a bomb than the Nazi regime. But when I saw the effect of such a bomb, I made an intensive effort to ban nuclear weapons.”

Back to relativity for a moment. Because with that you would achieve your worldwide breakthrough in 1915, when you extended the theory with gravity. "That's right. My 1905 article described the special theory of relativity. It only concerned constant speeds. But in 1907 I started to wonder what happens when something accelerates moves. And besides, I wanted to describe gravity.

My first impression of this general I got the theory of relativity while working in the patent office. I suddenly thought of the situation where a man falls from the roof. Gravity pulls the man down, but the man himself does not feel his own weight during the fall. Apparently acceleration is the same as gravity! I called this the 'equivalence principle'.

It also meant that gravity can change the shape of spacetime. In other words, the mass of an object makes space-time curve around it! But even though I had this idea in mind pretty quickly, to write it down in proper equations was a nightmare and took me many years. I had the greatest difficulty understanding the math of multidimensional transformations.

Fortunately, I got help from my old college friend Marcel Grossman. At the end of 1915 I knew I was ready when I studied the course of the perihelion (the shortest distance between the planet and the sun, ed.) of Mercury's orbit correctly. I was delirious with joy for a few days."

You only had to convince your colleagues. “Yes, because at first they were skeptical. Logically, they realized I was pushing Isaac Newton's ideas aside. He was a kind of God. They needed proof. That evidence could be found in the starry sky. According to my theory, a heavy object curves the space around itself, so that light also experiences a bend. The light from the stars behind the sun is therefore slightly bent by the sun when it reaches the earth.

In 1919 an expedition that included British astronomer Arthur Eddington observed a solar eclipse. The light from the stars around the sun had shifted exactly according to my predicted calculations. That was for the better, because my theory was correct. That may sound arrogant, but I just knew I was right."

The evidence for your theory made headlines worldwide. “I still remember the headline of the American newspaper The New York Times :'Einstein theory triumphs'. It was really crazy, all those photographers and reporters! They stood at my door for days. And everyone wanted me to give lectures or interviews! I found it very amusing that people get so worked up about theories that they themselves did not understand.”

You weren't always charmed by the photographers. We remember the striking photo with your protruding tongue. “That was on my 72nd birthday, in Princeton. We had been out one night and I was sitting in the back of the car. Photographers had been waiting for us and didn't want to leave. In all my irritation I stuck out my tongue. In the end I was able to laugh a lot at the photo. I have often used the photo on postcards for friends.”

In addition to your rise to superstardom, your general theory of relativity also led to "your biggest blunder." Please explain that. “It followed from my theory that the universe is either expanding or shrinking. But measurements seemed to show that the universe must be static. I therefore added a constant to my equations so that my model predicted a static universe and the other outcomes remained the same, the cosmological constant. But it would later turn out, thanks to Edwin Hubble in 1929, that the universe was expanding. So that cosmological constant was not necessary at all! I have indeed called that my biggest blunder.”

It will do you good to know that the universe is speeding up expands and a comparable cosmological constant seems to describe it well. So maybe it wasn't such a blunder. Another thing, we need to talk a little bit about your theory of light. You even called it your most revolutionary idea. Why? “The special theory of relativity was actually in the air. That the speed of light is the same for everyone follows from Maxwell's descriptions of electromagnetic waves. The derivation is so simple, that if it wasn't me, someone else would have done it sooner or later. I found the energy properties of light to be truly revolutionary.

I found it curious that states of gases and liquids are determined by individual atoms, while electromagnetic waves propagate over all points in space. However, many phenomena involving light are easier to understand if you also see light made up of a series of separate particles. Planck had done that too, but only as a math trick. I saw it as reality, even though the evidence for it was lacking."

The proof came with the photoelectric effect. “Indeed, that's the effect where light generates electricity when you aim it at a metal surface. The color of the light was decisive for whether or not electricity was generated and the current did not increase as the intensity of the light increased. Those were strong indications for my theory that light consists of energetic particles that knock electrons out of the metal. The Nobel Committee also apparently saw its revolutionary value, because I was awarded the Nobel Prize for it in 1922.”

It is perhaps more interesting that your theory of light was the basis for the new theory of quantum mechanics, which was later developed by Niels Bohr and Werner Heisenberg. You argued with Bohr about this theory for years. Tell your side of the story. “Uncertainty was central to quantum theory. Properties of matter and energy could only be expressed in probabilities. I couldn't accept that. As if nothing is certain and chance dominates! It cannot be that God plays dice with nature. There must be a cause for everything. So there had to be some kind of underlying reality that we couldn't see. That made the theory incomplete in my opinion.”

Unfortunately, you were proved wrong. Later experiments showed that Bohr was right. “I don't believe any of that. It is a theory where intuition has no place. There must be deeper processes that we haven't found yet.”

In 1920 you were awarded an honorary doctorate in Leiden. What kind of relationship did you have with the Netherlands? “The Netherlands played an important role in my life. Firstly, I saw Hendrik Antoon Lorentz as a kind of spiritual father. Lorentz was a genius. We first met at the first Solvay conference in Brussels, in 1911. But we corresponded very intensively about relativity and radiation.

Furthermore, Utrecht and Leiden have both tried to appoint me as professor. I didn't want that, but at the insistence of my good friend Paul Ehrenfest I accepted an honorary doctorate in Leiden. The appointment was still a bit tricky. The Dutch government did not agree until late, because there were rumors about conflicts with students and intimate relationships. All misunderstandings. I eventually came to Leiden regularly and stayed with Paul. I found peace here between the hectic pace in Berlin."

Thank you for the interview. You have now been through the magazine Time proclaimed personality of the 20 e century. A nice recognition, isn't it? “Certainly, and appropriately given the name of the magazine. You could say that I have changed the concept of time.”