Seven Brief Lessons on Physics by Carlo Rovelli
It is hardly surprising that there are more things in heaven and earth, dear reader, than have been dreamed of in our philosophy - or in our physics.
Nature is behaving with us like that elderly rabbi to whom two men went in order to settle a dispute. Having listened to the first, the rabbi says: ‘You are in the right.’ The second insists on being heard, the rabbi listens to him and says: ‘You’re also right.’ Having overheard from the next room the rabbi’s wife then calls out, ‘But they can’t both be in the right!’ The rabbi reflects and nods before concluding: ‘And you’re right too.’
Physics opens windows through which we see far into the distance. What we see does not cease to astonish us. We realize that we are full of prejudices and that our intuitive image of the world is partial, parochial, inadequate.
With brevity and acute analogies, Carlo Rovelli describes the histories and the theories of general relativity; quantum mechanics; the construction of the cosmos; particle theory and the standard model; thermodynamics, statistical physics, and the nature of time.
I’m left with an appreciation for what science is and by contrast for what it is not… an appreciation that it is not ‘myth’, but a series of conclusions about the world around us created by experimenting and iterating on hypotheses. It is the realm for the creative and the quantifiable; as always, truth is not for the faint of heart.
Outline
First lesson
The theory of general relativity
Newton’s ‘space’, through which things move, and the ‘gravitational field’ are one and the same thing
The sun bends space around itself and Earth rolls down like a marble down a funnel
Carl Friedrich Gauss created a formula to describe 2D undulating surfaces (surface of hills)
Bernhard Riemann’s thesis showed the properties of a curved space are captured by mathematical letter ‘R’
Einstein said:
R is equivalent to the energy of matter, that is that space curves where there is matter
Time passes more quickly high up than below, nearer to the Earth
If a man who has lived at sea level meets up with his twin who has lived in the mountains, he will find that his sibling is slightly older than him
When a large star has burnt up all of its combustible substance (hydrogen) it goes out. What remains is no longer supported by the heat of the combustion and collapses under its own weight, to a point where it bends space to such a degree that it plummets into an actual hole. These are the famous ‘black holes’
Space cannot stand still; it must be expanding
The expansion ought to have been triggered by the explosion of a young, extremely small and extremely hot universe: by what we now know as the ‘Big Bang’
It was proved by cosmic background radiation (the diffuse glare that remains from the heat generated by the original explosion) actually being observed in the sky
TL;DR of the theory: universes explode, space collapses into bottomless holes, time sags and slows near a planet, and the unbounded extensions of interstellar space ripple and sway like the
Second lesson
Einstein’s quantum mechanics
Light is made of packets (particles of light) called photons
“The energy of a light ray spreading out from a point source is not continuously distributed over an increasing space but consists of a finite number of ‘energy quanta’ which are localized at points in space, which move without dividing, and which can only be produced and absorbed as complete units.”
Dane Niels Bohr: quantum leaps
The energy of electrons in atoms can only take on certain values, like the energy of light, and crucially that electrons can only ‘jump’ between one atomic orbit and another with fixed energies, emitting or absorbing a photon when they jump.
These are the famous ‘quantum leaps’.
Why is the periodic table the way it is?
Each element corresponds to one solution of the main equation of quantum mechanics. The whole of chemistry emerges from a single equation.
Werner Heisenberg: electrons do not always exist.
They materialize in a place, with a calculable probability, when colliding with something else. The ‘quantum leaps’ from one orbit to another are the only means they have of being ‘real’: an electron is a set of jumps from one interaction to another.
It’s as if God had not designed reality with a line that was heavily scored, but just dotted it with a faint outline.
In quantum mechanics no object has a definite position, except when colliding headlong with something else.
Probability of an electron being in a position
It is not possible to predict where an electron will reappear, but only to calculate the probability that it will pop up here or there.
The question of probability goes to the heart of physics, where everything had seemed to be regulated by firm laws which were universal and irrevocable.
Quantum theory doesn’t give us a clear picture of what a single particle is doing at any moment. Instead, it tells us how particles or systems influence each other when they interact. It’s more about understanding the effects and relationships between systems than pinpointing the exact details of one system
We’ve used the theories to make advances in applications like transistors, but while our knowledge grows in real terms, but it leaves open-ended questions
Third lesson
The solar system itself is only one amongst a vast number of others, and that the sun is no more than a star like others. An infinitesimal speck in a vast cloud of one hundred billion stars – the Galaxy
Imagine the texture of the universe, with its splashes of galaxies, being moved by waves similar to those of the sea, sometimes so agitated as to create the gaps which are black holes.
Fourth lesson
Light is made of photons
The things we see are made of atoms. Elementary particles:
Every atom consists of a nucleus surrounded by electrons
Every nucleus consists of tightly packed protons and neutrons
Both protons and neutrons are made up of even smaller particles named ‘quarks’
Everything we touch is therefore made of electrons, and of these quarks
The force that ‘glues’ quarks inside protons and neutrons is generated by particles that physicists, with little sense of the ridiculous, call ‘gluons’.
Even if we observe a small empty region of space, in which there are no atoms, we still detect a minute swarming of these particles.
There is no such thing as a real void, one that is completely empty.
Particle theory built in 1950-70s by Richard Feynman and Gell-Mann
The Standard Model was confirmed in 1970s but has never been taken entirely seriously by physicists
‘Renormalization’
To obtain meaningful results it is necessary to imagine that the parameters entering into them are themselves infinitely large, in order to counterbalance the absurd results and make them reasonable.
A limitation to the standard model is Dark matter
Around every galaxy astronomers observe a large cloud of material which reveals its existence via the gravitational pull that it exerts upon stars, and by the way it deflects light.
Perhaps on closer inspection it is not the model that lacks elegance. Perhaps it is we who have not yet learnt to look at it from just the right point of view; one which would reveal its hidden simplicity.
Fifth Lessons
Nature is behaving with us like that elderly rabbi to whom two men went in order to settle a dispute. Having listened to the first, the rabbi says: ‘You are in the right.’ The second insists on being heard, the rabbi listens to him and says: ‘You’re also right.’ Having overheard from the next room the rabbi’s wife then calls out, ‘But they can’t both be in the right!’ The rabbi reflects and nods before concluding: ‘And you’re right too.’
The effort to synthesize has in the past been rewarded with great strides forward in our understanding of the world
Newton discovered universal gravity by combining Galileo’s parabolas with the ellipses of Kepler. Maxwell found the equations of electromagnetism by combining the theories of electricity and of magnetism. Einstein discovered relativity by way of resolving an apparent conflict between electromagnetism and mechanics.
Loop quantum gravity – trying to combine general relativity and quantum mechanics
There is no experimental verification yet
“Space is not continuous, that it is not infinitely divisible but made up of grains or ‘atoms of space’. These are extremely minute: a billion billion times smaller than the smallest atomic nuclei. The theory describes these ‘atoms of space’ in mathematical form, and provides equations which determine their evolution. They are called ‘loops’, or rings, because they are linked to each other, forming a network of relations which weaves the texture of space, like the rings of a finely woven immense chain mail. Where are these quanta of space? Nowhere. They are not in a space because they are themselves the space. Space is created by the linking of these individual quanta of gravity.”
Consequential implication on the nature ‘time’: At the minute scale of the grains of space, the dance of nature does not take place to the rhythm of the baton of a single orchestral conductor, at a single tempo: each process dances independently of its neighbors, to its own rhythm.
The great explosion or ‘Big Bang’ may have actually been a ‘Big Bounce’.
Our universe may have been born from a bounce in a prior phase, passing through an intermediate phase in which there was neither space nor time.
Physics opens windows through which we see far into the distance. What we see does not cease to astonish us. We realize that we are full of prejudices and that our intuitive image of the world is partial, parochial, inadequate.
Sixth lesson
A hot substance is a substance in which atoms move more quickly. Why does heat go from hot things to cold things, and not vice versa?
Friction produces heat. And immediately we are able to distinguish the future (towards which the pendulum slows) from the past.
The fundamental phenomenon that distinguishes the future from the past (aka time) is the fact that heat passes from things that are hotter to things that are colder.
Again, why does this happen from hot to cold and not the other way around?
(Boltzmann idea) It is sheer chance… heat does not move from hot things to cold things due to an absolute law: it only does so with a large degree of probability.
It is statistically more probable that a quickly moving atom of the hot substance collides with a cold one and leaves it a little of its energy, rather than vice versa.
It is not impossible for a hot body to become hotter through contact with a colder one: it is just extremely improbable.
Mind blowing. Queue the randomest events from the improbability drive
As frequently happens, no one took Boltzmann seriously. On September 5, 1906 in Duino near Trieste, he committed suicide by hanging himself, never having witnessed the subsequent universal recognition of the validity of his ideas.
Quora: The sadness of his demise came from the fact that his statistical hypothesis cannot be derived from mechanics (Newtonian, relativity, quantum). The microscopic reversibility turns out to be compatible with macroscopic irreversibility. Think that many water molecules from rivers flow into the ocean, but fewer water molecules from the ocean flows back into the rivers. When two heat reservoirs connect, the spontaneous mixing would increase entropy, by increasing possible number of possible configurations.In his life time, he tried his best to explain that his idea was correct, it was indeed correct, but it was a fundamental principle on par with Newton, Einstein relativity and quantum mechanics, and cannot be proven or derived from there. His attempt of proving them was futile, and he fell victim to depression caused by this difficulty.
The probability in play in the science of heat is in a certain sense tied to our ignorance. I may not know something with certainty, but I can still assign a lesser or greater degree of probability to something.
The branch of science which clarifies these things is called statistical physics → we understand the probabilistic nature of heat and temperature, that is to say, thermodynamics.
What is a heated EMF?
We know what happens to a heated electromagnetic field: in an oven, for instance, there is hot electromagnetic radiation which cooks a pie, and we know how to describe this. The electromagnetic waves vibrate, randomly sharing energy, and we can imagine the whole as being like a gas of photons which move like the molecules in a hot balloon. When the oven produces electromagnetic waves, these waves move around inside it and hit the pie. The surface of the pie absorbs the energy from these waves, causing the molecules in the pie to vibrate more intensely. As the molecular vibration increases, the temperature of the pie rises, leading to the pie heating up. The continuous absorption of energy and the resulting increase in molecular vibrations cook the pie.
But what is a hot gravitational field?
The gravitational field is space itself, in effect space-time. Therefore when heat is diffused to the gravitational field, time and space themselves must vibrate… But we still don’t know how to describe this well
Bc what is a vibrating time? Time seems to flow, unlike the matter, but what exactly is the flow of time?
Another way of posing the problem is to ask oneself: what is the ‘present’?
In physics there is nothing that corresponds to the notion of the ‘now’ because it is ‘indexical’
No one would dream of saying that things ‘here’ exist, whereas things which are not ‘here’ do not exist. So then why do we say that things that are ‘now’ exist and that everything else doesn’t? Is the present something which is objective in the world, that ‘flows’ and that makes things ‘exist’ one after the other, or is it only subjective, like ‘here’?
To trust immediate intuitions rather than collective examination that is rational, careful and intelligent is not wisdom: it is the presumption of an old man who refuses to believe that the great world outside his village is any different from the one which he has always known.
For a hypothetically supersensible being there would be no ‘flowing’ of time: the universe would be a single block of past, present and future. But due to the limitations of our consciousness we only perceive a blurred vision of the world, and live in time
Like in Kurt Vonnegut's novels, the aliens would see things in all their states happening at once.
Like in Siddhartha, when the river is used to describe time. Time is an illusion
Stephen Hawking
Demonstrated that black holes are always ‘hot’. They emit heat like a stove. It’s the first concrete indication on the nature of ‘hot space’.
The heat of black holes is like the Rosetta Stone of physics, written in a combination of three languages – Quantum, Gravitational and Thermodynamic – still awaiting decipherment in order to reveal the true nature of time.
Closing philosophical takeaways from Carlo Rovelli
The confusion between these two diverse human activities – inventing stories and following traces in order to find something – is the origin of the incomprehension and distrust of science shown by a significant part of our contemporary culture. The separation is a subtle one: the antelope hunted at dawn is not far removed from the antelope deity in that night’s storytelling.
Integration information theory’ shows advances in understanding consciousness
An attempt to characterize quantitatively the structure that a system must have in order to be conscious: a way, for example, of describing what actually changes on the physical plane between when we are awake (conscious) and when we are asleep but not dreaming (unconscious)
Me: We focus on consciousness in the brain via neuroscience but according to SN Goenka (Vipassanna buddhism), we haven’t found much grounding here because it exists throughout the body too. Need more color on this. TBD
Also look into Majmudar’s reads on non-dualism and consciousness
We do not know our own unconscious:
Our intense sensation of internal liberty, as Spinoza acutely saw, comes from the fact that the ideas and images which we have of ourselves are much cruder and sketchier than the detailed complexity of what is happening within us. We are the source of amazement in our own eyes
We are an integral part of nature; we are nature, in one of its innumerable and infinitely variable expressions. That which makes us specifically human does not signify our separation from nature; it is part of that self-same nature… We are made of the same stardust of which all things are made, and when we are immersed in suffering or when we are experiencing intense joy we are being nothing other than what we can’t help but be: a part of our world.
Me: This is exactly my takeaway from spending the week in Gamboa, Panama with the ecology/biology PhD’s. They intuited this systems-level world view as well