Seven brief lessons on physics

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Author: Carlo Rovelli 

Seven brief lessons on physics Carlo Rovelli 2014

Seven brief lessons on physics
Seven brief lessons on physics

Seven brief lessons on physics :Seven small chapters about the structure of the world

Seven brief lessons on physics: Carlo Rovelli is the founder of the theory of loop quantum gravity, he tries to connect physical theories based on different principles: general relativity and quantum physics. If successful, this will allow him and his colleagues to close the gaps in the science of the laws of nature and build a universal theory of everything. In his book Seven Studies in Physics, Rovelli argues that the above theories for the most part do not contradict each other, but look at the world from different angles. He talks about complex things simply and clearly, because his studies are an extended version of a series of articles from the supplement of the Italian newspaper Il Sole 24 Ore, which he wrote specifically for those who know little or nothing about modern science.

Etude 1. Albert Einstein’s general theory of relativity

In 1905, the prestigious German scientific journal Annals of Physics published several articles at once by Albert Einstein, a recent graduate of the Swiss Polytechnic University. One of them described his first theory of relativity, later called special. The article explained that time does not pass in the same way for everyone: the present is subjective. Despite its recognition by scientists and the job offers that rained down on Einstein after that, his theory was not consistent with the already existing law of universal gravitation of Isaac Newton. 

Einstein worked on this problem for 10 years and as a result, published the general theory of relativity – the Russian physicist Lev Landau called it the most beautiful of the existing physical theories.

Newton explained the fall of objects and the rotation of planets by the force of gravity, which, like a magnet, attracts material bodies to each other. He imagined the space of the universe as a capacious container or a huge box, where all objects move in a straight line until the force makes their paths bend. What this world container consists of and how the force of gravity acts on objects distant from each other remained a mystery. 

Even before the birth of Einstein, the Englishmen James Maxwell and Michael Faraday added an important element to the Newtonian world: an oscillating and space-filling electromagnetic field. From his youth, fascinated by the electromagnetic field that turned the rotors of the power plants his father built, Albert Einstein realized that gravity (the interaction of material bodies or objects) was similar to him. It dawned on him that space and the gravitational fields are one and the same. We are not inside a rigid structure: the Earth revolves around the Sun, because it is in a curving space and spins in it, like a ball in a funnel. 

According to the general theory of relativity, space and time are curved. Further from the surface of the earth, time flies faster: the twin living by the sea is slightly younger than the highlander relative. Sometimes space is curved to such an extent that it disappears – turns into a black hole. This happens when a large star burns out: its remnants are compressed into one point.

In addition, Einstein presciently suggested that space is constantly expanding and oscillating. Its expansion, triggered by the Big Bang of the then small and very hot Universe, was first recorded in 1930.

“The theory [of relativity] describes a multi-colored and stunning world where universes explode, space collapses into bottomless holes, time slows down near planets, and ripples run through the boundless interstellar space, as if on the surface of the sea …” – Carlo Rovelli sums up the first chapter.

Seven brief lessons on physics

Etude 2. Quantum mechanics

The theory of quantum mechanics originated in 1900, when the German Max Planck, using an experiment with a hot box, presented the energy of an electric field divided into portions – quanta. Prior to this, the prevailing view was that energy is continuous.

Later, Einstein, in an article for which he was awarded the Nobel Prize, showed that light also consists of “bricks”. Today we call portions of light photons.

Planck turned out to be the “biological father” of the theory; Albert Einstein “educated” it. Further, it developed thanks to the “mentors” – the Dane Niels Bohr and the German Werner Heisenberg. 

In the 20-and 30s of the 20th century, Niels Bohr realized that the energy of electrons inside atoms takes only specific values: electrons jump along atomic orbits, releasing or absorbing a certain amount of energy. 

An electron is an elementary particle with a negative electric charge. It is part of atoms along with protons (with a positive charge), neutrons (with a neutral charge) and other particles. The number of electrons and protons in an atom is always the same: it corresponds to the serial number of the element in the periodic table.

Seven brief lessons on physics

The best minds of the time began to study these quantum leaps at the Bohr Institute in Copenhagen.

Werner Heisenberg, who wrote the first equations, suggested that electrons materialize only when they collide with something. They don’t have a specific location. Reality seems to be drawn with a dotted line. Quantum jumps are the only way for electrons to become real. In this case, jumps are random. It is impossible to predict exactly where an electron will appear, it is only possible to calculate the probability with which it will end up somewhere. This was very unusual for physics, which has traditionally been dominated by strict laws. 

Einstein nominated Heisenberg for the Nobel Prize in Physics, acknowledging the importance of his work, but grumbling that his colleague’s claims made little sense. Having questioned the foundations of Newtonian physics, Einstein now doubted that “the world could not be so strange.” Arguments with Bohr took many years. The two great physicists never came to a common opinion, their discussions are captured in letters, articles, and lectures. At the same time, Bohr openly admired the genius of Einstein, and after his death, on a slate board in Niels Bohr’s office, they found an image of a box filled with light, which was invented by the author of the theory of relativity. 

“Until the very end, the desire to argue with oneself in order to understand more. And to the last – doubt, ”writes Rovelli.

Seven brief lessons on physics

Today, quantum mechanics plays an important role not only in physics, but also in chemistry, biology, engineering, and technology. Without it, there would be no transistors – electronic components that underlie all modern electronics. 

Quantum theory has revealed questions, the search for answers to which is still ongoing. What is she herself – a randomly working miscalculation, a piece of the puzzle, or the key to the fundamental principle of the world? This is the question asked by the author of the book.

Etude 3. Macrocosm: a map of ideas about the Universe

Carlo Rovelli describes six basic ideas about our universe.

1. For thousands of years, people have represented the cosmos primitively: the Earth is below, the sky is above.

2. Anaximander replaced the previous scheme 26 centuries ago. He presented the Earth as a huge block floating in space: the sky began to surround it from all sides (and not just from above). 

3. Then Parmenides or Pythagoras (not exactly known) suggested that the Earth has a spherical shape. Aristotle proved this in his treatise On Heaven. He was also sure that both the Earth and other celestial bodies that revolve around it were round. The Aristotelian picture of the world “lived” until the end of the Middle Ages: Dante and Shakespeare received such an idea of ​​the world.

4. The next breakthrough was made at the beginning of the 16th century by Nicolaus Copernicus, who realized that the Sun is located in the center of the round dance of the planets. Our planet has become one among others, rotating around its axis and around a common star. 

5. Later, thanks to improved instruments, it became clear that the Sun is just one star out of a hundred billion other stars in our Galaxy, and the solar system is one of many systems.

6. In the 1930s, precise astronomical measurements showed that our galaxy itself is a speck of dust in a vast cloud of galaxies. A picture taken by the Hubble telescope showed a deeper image of the sky than previously seen:

Each black dot in the image (to the naked eye, the entire sky would look black) is a galaxy. In the past few years, it has been possible to see that in these galaxies around most of the stars similar to our Sun, planets revolve, of which there are billions in the Universe.

Considering that space is curved, sometimes so strongly that dips appear – black holes, the Universe sways in huge waves similar to sea waves. 

This endless flexible space, dotted with galaxies and developing for 15 billion years, arose from a hot and dense cloud, so the history of the Universe can be schematically represented as follows:

The universe began as a small ball and then expanded to its current size. This is the most modern and largest vision of the universe that we know of. Whether there are other similar or dissimilar universes, science is not yet known.

Etude 4. Microcosm: elementary particles of matter

Light is made of photons, and objects that you can touch with your hands are made of atoms. Inside every atom, there is a nucleus. It is surrounded by electrons. And in the core itself live protons and neutrons, consisting of even smaller particles – quarks. 

The name “quark” has literary roots. American physicist Murray Gell-Mann named these particles, inspired by a phrase from James Joyce’s Finnegans Wake: “Three quarks for Master Mark!”

Seven brief lessons on physics

Quarks inside protons and neutrons “stick together” gluons (from the English glue – glue). 

Photons, electrons, quarks, gluons and other elementary particles (there are less than 10 types in total) are the components of everything around us. They, like small details of a giant constructor, build the material reality around us.

The void, where there is absolutely nothing, does not exist. The fields that form the material world fluctuate, and elementary particles constantly arise and disappear under the influence of these movements. Their life is short. The microcosm is described by quantum mechanics and the theory of elementary particles in the world of events, not objects.

The theory, called the “standard model of elementary particles”, was built by Richard Feynman, Murray Gell-Mann, Peter Higgs, and other physicists in the 1950s. Despite successful experiments, scientists don’t take it too seriously. It consists of various equations put together in no apparent order. Moreover, these equations are far from the elegant simplicity of the equations of general relativity and quantum mechanics. One of the authors of the first and main equations of the “standard model” Paul Dirac in the last years of his life was dissatisfied with this state of affairs: he said that the problem had not yet been solved. 

In addition, astronomers have recently been observing a large cloud of matter around each galaxy, acting on stars with gravitational attraction and refracting light. This huge cloud cannot be seen directly, and it is not known what it consists of. Obviously, there is something there, but scientists do not yet know what exactly. Today, this something other than photons and atoms is called dark matter.

There are many things in the world that physicists never dreamed of. But the “standard model” is still the best we have for the world of objects. Apart from dark matter and gravity, the “standard particle model” describes well every aspect of the perceived world. Servants of science put forward alternative theories, but they were all experimentally refuted. Perhaps scientists will yet learn to look at the “standard model” from an angle that will reveal its hidden elegance and simplicity.

Today it is known that matter is a handful of elementary particles that constantly oscillate between existence and non-existence, flit through space even when it seems that it is empty, and combine to create infinity.

Etude 5. Loop quantum gravity

Since general relativity contradicts the theory of quantum mechanics, a group of theoretical physicists from different parts of the world are trying to combine them. The line of research they are working in is called loop quantum gravity. Since the 1980s, its proponents have sought to understand space, time, and matter a little better than previous physical theories allow.

A student listening to lectures on the theory of relativity and quantum mechanics is forced to imagine the world either as a curved continuous space, or as a flat one with jumping energy quanta.

Seven brief lessons on physics

The theory of loop quantum gravity claims that flexible, dynamic, curving space consists of small “grains of sand ” – gravity quanta, billions of times smaller than the smallest atomic nucleus. Quanta are woven together like chain mail rings, which is why they are called loops.

The theory describes the Universe, in which the quanta of space and matter endlessly interact with each other. Consequently, time – the sequence of moments familiar to us – does not exist. This is just an illusion, our perception of the processes occurring at the level of elementary particles.

If mankind had a powerful magnifying glass, it would show the coarseness or cellularity of space:

So far, scientists cannot test the theory of loop quantum gravity empirically, but they have come up with several hypotheses.

One of them is related to black holes. According to the theory, the matter of the disappeared stars could not simply shrink to a point but should have condensed as much as possible to the state of a Planck star.

If the Sun were to transform into a black hole, its diameter would be about 1.5 km. Inside it, the matter of the luminary would shrink to the Planck size – the size of an atom, and then begin to expand again, which would provoke an explosion of a black hole. An imaginary observer riding a Planck star would see this process as a ricochet at colossal speed. But for the same reason that time flies faster in the mountains than near the sea, what the “rider” inside a black hole sees as very fast, outside, looks incredibly long. Therefore, for us, black holes do not change for ages. According to physicists, black holes are expanding stars that humanity observes in what seems to be very slow motion.

Seven brief lessons on physics

Perhaps some of the black holes formed in the first moments of the universe are now exploding. If so, then physicists will record their expansion. If not, it would mean that there were few black holes in the original universe. One way or another, the search for signals has already begun. 

Another assumption of the loop theory concerns the origin of our world: The Big Bang could actually be the Big Rebound. Perhaps today’s universe formed from the previous one – the one that shrunk to the size of a walnut, and then rebounded and began to expand again. In a moment of bounce, space and time disappeared, and the world blurred into a swarming cloud of probabilities. Then the scheme of the development of the Universe looks like this:

Etude 6. Heat, probability, and time

Along with the theories described above about the basic components of the world, there is another impressive layer of physics – thermodynamics. Its emergence led to the question: what is heat? Until the 1950s, physicists thought that heat was a liquid (they called it “caloric”). But the Austrian Ludwig Boltzmann and the Briton James Maxwell guessed that there is no caloric in the hot matter – atoms simply move faster in it. Of course, they move all the time, but in the cold, they move more slowly.

As you know, heat is transferred from hot substances to cold ones. Why not otherwise? It happens by accident. Boltzmann found that a fast atom of a hot body, hitting a slow cold one, is more likely to share its energy with it than a cold particle is with a hot particle. Usually, the energy is distributed evenly. A hot body can become hot from contact with an icy one, but this is unlikely.

The probability associated with limited knowledge concerns most physical objects: we do not know everything about them, so we can only try to predict.

Our ability to predict the behavior of the spoon and the balloon is limited by the incomplete set of properties we interact with and the way we interact with them. The available data is not enough to predict the flight path of a deflating balloon after the rope is untied on it. But they are enough to predict the heating of a spoon in hot water.

Seven brief lessons on physics

How the gravitational field behaves when heated is not yet known. In theory, space and time should fluctuate, but physicists have not yet been able to correctly describe the fluctuating time. These questions give rise to even more fundamental ones: what is “now” and can we talk about the passage of time? 

According to the author of the book, on the scale of the Universe, there is nothing corresponding to the concept of “now”.

Einstein wrote to a relative of his deceased friend: “Michele left this strange world a little before me. This means nothing. People like us who believe in physics know that the distinction between past, present and future is nothing more than an illusion.”

Seven brief lessons on physics

“Due to the limitations of our consciousness, we perceive only a blurry image of the world and live in time,” explains Rovelli. 

Seven brief lessons on physics

But then why do people feel the passage of time and divide events into “was”, “is”, and “will be”? The physical riddle underlying the tangle of general relativity, quantum mechanics, and thermodynamics are waiting to be deciphered: there is no theory that unites all three fundamental knowledge yet. Only a small hint is given by Stephen Hawking’s calculations, which showed that black holes constantly radiate heat. In those that physicists have already observed, the heat is weak, but Hawking’s calculations are verified and generally accepted. The author is sure that the answer to the nature of time will be based on heat. 

Etude 7. Mankind as part of the world

What role is assigned to people in the world that modern physics describes? We, too, are made of atoms. We are part of nature, it is our home. And it’s in our nature to want to know more. At the same time, we are also learning to gradually change our system of concepts.

Our exploration of the world is like looking for an antelope. The hunters study the tracks of the animal – hints of something that cannot be seen directly. They understand that they can make a mistake and are ready to change direction if a new trail appears. But they also know that if they try, they will find what they are looking for. Knowledge is valuable: by catching an antelope, people can eat.

Seven brief lessons on physics

The author of the book predicts in the indefinite future the death of our civilization – like the one experienced by the Mayans or the Minoans – or the complete extinction of the species homo sapiens. In his opinion, we have no chance of survival, because we are destroying the planet – our home. 

Nevertheless, Rovelli, a connoisseur of nature and life, continues to seek answers to scientific questions. He is fascinated by the secrets and beauty of the world, shining on the border between the known and the unknown: 

“We are born and we die as stars are born and die. Life is precious because it is fleeting.

Seven brief lessons on physics

Top 10 Thoughts

1. The theories of recent years that are most important for understanding the structure of the world are the general theory of relativity, quantum mechanics, the standard model of elementary particles, and thermodynamics.

2. Theoretical physicists are trying to combine conflicting general relativity and quantum mechanics with the help of loop quantum gravity. There is still no theory capable of logically adding thermodynamics to this knowledge.

3. The idea of ​​the Universe has changed over the millennia from the primitive “Earth below – the sky above” to an endless flexible cosmos with thousands of galaxies, which include many systems like our solar system. 

4. According to Albert Einstein’s general theory of relativity, time and space are curved. Space is constantly expanding and swaying, and sometimes collapses into a black hole. Nearly 15 billion years after the Big Bang, the universe expanded from a small cloud to its current size.

5. The theory of quantum mechanics states that energy consists of portions or “bricks” – quanta. It can only take on certain values. Electrons inside an atom randomly jump from one orbit to another and do not have a specific position – they materialize only when they interact with something.

6. The Standard Model of Elementary Particles describes the material reality as consisting of photons, electrons, quarks, gluons, and other smallest elements. They arise and disappear, flicker in space, but the void does not exist. The Standard Model does a good job of explaining everything except dark matter and gravity.

7. Loop quantum gravity states that flexible, dynamic, curving space is made up of quanta, many times smaller than an atomic nucleus, intertwined with each other like chain mail rings, and constantly interacting.

8. The theory of loop quantum gravity made it possible to build two important hypotheses: about Planck stars that collapsed into black holes and are now expanding, and about the Big Bounce, which resulted in our Universe.

9. Time is just an illusion: there is no presence common to the entire Universe. At the level of physics, the future differs from the past in the distribution of heat. 

10. Answers to questions such as “Are there other universes than ours?”, “How does a hot gravitational field behave?” and “What is the real nature of time?”, still not.

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