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¿Y si no existe nada? — Transcript

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0:00What is fundamental? What is the
0:02starting point of reality? What is
0:04everything made of? Western philosophy,
0:06in a simplified way, is an attempt to
0:09answer these questions. And the answers
0:12have been very varied, from matter, God
0:15, spirit, just atoms, numbers, Plato's
0:17forms, energy, information, experiences
0:19, sensations, to language. But it could
0:22be that the answer to everything is
0:24nothing. Friends, prepare yourselves
0:27for a thrilling journey through the
0:29history of ideas, from Thales of
0:30Miletus and the ancient physicists
0:32Democritus and his atoms, to the modern
0:33world ideas of Descartes, Leibniz, and
0:35Newton. And all to try to bring order
0:38to the craziest puzzle in physics. What
0:40is going on with quantum mechanics?
0:42Friends, the story is tremendous.
0:45Heisenberg, a 24-year-old guy lost on
0:47an island trying to make sense of some
0:49absurd numbers. While a few thousand
0:51kilometers away, Schrödinger is in a
0:54spa in the Alps, not with his wife, but
0:56with his mistress, trying to complete
0:58the same puzzle. Both would come up
1:01with two visions of the universe, two
1:03different ways of understanding reality
1:05that remain at odds today. The solution
1:07could have been held 300 years earlier
1:09by a German sage. Friends, the new
1:12season of Date un Vlog begins, with a
1:14new space, but with the same spirit:
1:16mixing science, philosophy, art, and
1:19literature in a unique space to blow
1:21your mind. So we kick off with a video
1:23where you will understand what quantum
1:25mechanics is, its historical
1:27development, the characters involved in
1:29its creation, why quantum is currently
1:31a mystery, and what challenges the
1:33different interpretations of quantum
1:35mechanics pose, in addition to taking a
1:37look at the philosophy behind quantum
1:39and, specifically, at the work of a 17
1:41th-century German visionary. Be ready,
1:44because you are going to flip out this
1:46time very, very much. And many thanks,
1:48by the way, to Enricos a la filosofía
1:50for reviewing this script. A new season
1:52begins on Date un Vlog. Let's get to it
1:55. It was around 3 in the morning when
2:03the final result of my calculations
2:04appeared before me. I felt shaken. I
2:08was so agitated that I couldn't think
2:10of sleeping. This is what one of the
2:12main characters behind quantum
2:14mechanics wrote. 1924 Copenhagen, a 23-
2:16year-old young man suffers his
2:18umpteenth allergy attack, hay fever,
2:20and at the worst moment, he had a
2:22physical enigma in front of him that he
2:24was unable to solve, much to his
2:26frustration. He was totally obsessed.
2:28Desperate, he asks his mentor, Niels
2:30Bohr, for a week off. His idea was to
2:32go to the rocky island of Heligoland to
2:34put an end to that mystery. It was a
2:37small, desolate island without any
2:38annoying pollen, with pure air to help
2:41his health recover. And in the freedom
2:43of that remote place, he sought to find
2:45a space to think. He was on the trail
2:48of an idea that would solve everything
2:50at once, but to reach it he had to take
2:51a terrible leap, close his eyes, and
2:53leave everything behind. He needed a
2:56leap into the absurd. To accept that
2:58nothing is what it seems. Quantum
3:00mechanics was about to be born. The
3:02story of his intellectual rival would
3:04be no less spectacular. Once again, a
3:06health problem, in this case, tougher:
3:08tuberculosis. Zurich, 1925.
3:12Schrödinger felt frustrated; at nearly
3:1440, he hadn't done anything relevant in
3:16physics and felt his time for glory had
3:19passed while he obsessed over the
3:21mystery of quantum theory. What did all
3:24of that mean? In one of his frequent
3:26retreats to a sanatorium in Arosa,
3:27Switzerland, due to his illness,
3:29inspiration struck. This time to the
3:32spa, he took not only his most intimate
3:34lover of the many he had, but also an
3:36article by an unknown scientist with a
3:38new idea: particles are waves. From a
3:41totally different angle, Schrödinger
3:43would arrive at a complementary,
3:45distinct solution to the atomic enigma.
3:49It was another quantum mechanics, and
3:51rivalry was inevitable—not because of
3:53the math, which was soon resolved, but
3:55because of the very meaning of the
3:57theory. They had found the secret to
4:01understanding the atomic world, but
4:02they didn't quite understand the
4:03language in which the answer was
4:05written. What did all that mean? Both
4:08gave rise to two schools, two
4:09diametrically opposed ways of
4:10understanding the scaffolding of the
4:12cosmos. Today, this question remains
4:15open as a possible integrative solution
4:17appears halfway, one that emerged three
4:20centuries before the invention of
4:22quantum mechanics. 1650. We travel to
4:25Germany. The Baroque of the 17th
4:27century, a style marked by rupture. We
4:30move from the vital optimism of the
4:32Renaissance to the pessimism typical of
4:35an era marked by wars, famines, and
4:37disease. Charles V yearns to unify the
4:40Christian world under one banner, the*
4:42universitas christiana*, only to watch
4:44the Reformation shatter his dreams
4:46before his eyes. He and his successors,
4:49Philips II, III, and IV, who are the
4:51Spanish Habsburgs, will see how
4:53Hispanic hegemony vaporizes in a
4:54century dominated by religious wars. In
4:58those 100 years, there were not even 10
5:00years of peace, while illustrious
5:02figures of the period like Quevedo sang
5:04of the decadence of Spain and the
5:06suffering of its people, who saw their
5:08lives ruined more and more.
5:10I looked upon the walls of my homeland.
5:13If once strong, now crumbled by the
5:16passage of time, weary from the one
5:18whose courage now expires. The most
5:21powerful nation in the world at that
5:23moment was bleeding out in Milan and
5:25Naples against the France of Francis I,
5:26against the Protestant princes in the
5:28empire, or the Ottomans in the Caucasus
5:30and the Mediterranean. The Thirty Years
5:32'War, which ended at the close of the
5:34century, is a symbolic turning point.
5:36Europe became even more fragmented as
5:39we reached the peak of the Baroque,
5:41which witnessed a century stained with
5:43blood. Thus, in philosophy, that path
5:45was replicated. From a medieval
5:47scholasticism centered on the divine,
5:49to a colorful, magical Renaissance full
5:52of symbolism, to a more earthly, raw,
5:54and real Baroque. Thus, we moved from
5:57the sums of Saint Thomas to the
5:59Neoplatonism of Ficino, until arriving
6:01at a new philosophy: the rational
6:03school, that of Descartes. His
6:05successors—Bacon, Spinoza, and of
6:07course Newton—with a new tool in
6:09their hands, modern science, would give
6:11philosophy a much more worldly veneer.
6:14Atomism was recovered with Gassendi,
6:16among others. Advancements were made in
6:19astronomy and mechanics with Copernicus
6:21and Kepler, and with the seminal work
6:23of Newton—and by recovering the
6:25elements of Euclid as great examples—
6:27the aim was to renew philosophy: a
6:29logical, structured philosophy
6:30dominated by reason. A new way of doing
6:33philosophy was being founded. It was
6:35modern philosophy. Well, in this
6:38context, one of the successors of
6:40Descartes—another rationalist
6:42following in his wake—would arrive at
6:44an original, groundbreaking, and very
6:46avant-garde idea, so much so that it
6:48perhaps wouldn't make sense until today
6:51. Yes, I am speaking to you about one
6:53of the most brilliant people who has
6:55ever existed. A philosopher, logician,
6:57jurist, theologian, diplomat, writer,
6:59physicist, and also a great
7:01mathematician. He did it all, and he
7:02did it all very well. He only made one
7:05mistake, a big mistake: facing the
7:07great Newton. Perhaps that is why he is
7:10not as well known as he deserves,
7:12because in that fight the English lion
7:14won and made sure that his merits were
7:16downplayed until he died in the deepest
7:18decadence and oblivion. I am talking to
7:20you about the German genius Gottfried
7:21Leibniz. Leibniz was born in 1646. In
7:25the German city of Leipzig. A
7:26contemporary of Newton or Huygens. We
7:28are right in the middle of the
7:30scientific revolution. 100 years had
7:31passed since Copernicus, and a few
7:33decades since the revolutionary work of
7:35Kepler and Galileo as well. His father
7:37died when the German was 6 years old.
7:40So from childhood, and he was very
7:41precocious by the way, he had to learn
7:43everything on his own. His father and
7:46grandfather had been university
7:47professors, so he had a large library
7:49that he devoured in solitude since he
7:51was a child. His formal education would
7:54be in jurisprudence, eventually
7:55completing his doctorate. And here
7:58begins his particular journey rubbing
8:00shoulders with the European elites,
8:02aristocrats and kings, on a route
8:03through the most intellectual corners
8:05of Europe. From 1672 to 1676 he would
8:08reside in Paris as part of a diplomatic
8:11mission where he would personally meet
8:14Huygens or Malebranche. From there he
8:17would go to London, becoming a member
8:18of the Royal Society and establishing
8:20contact, for example, with Isaac Newton
8:21. He returns to his homeland to work
8:24for the Duke of Hanover as a palace
8:26librarian. On this return journey, he
8:28meets van Leeuwenhoek, the famous
8:30discoverer of the microscopic world,
8:32and Spinoza, the philosopher from The
8:34Hague, and was able to read firsthand
8:36the first manuscript of his Ethics, his
8:38great masterpiece. His constant grand
8:41travels would take him to Vienna, Rome,
8:43Naples, and Florence, some of the
8:44intellectual hubs of his world, the
8:46most active of his time. When in 1714
8:49George of Hanover becomes George I of
8:51England, the luck of Leibniz changes
8:54suddenly. The patrons who had protected
8:57him until then, as well as the numerous
8:59academies he himself had founded, now
9:01turn their backs on him. He died 2
9:04years later, in 1716, at 70 years of
9:06age, in complete solitude. It is said
9:09that only his secretary attended his
9:12funeral. Yes, part of his obscurity was
9:15caused by his clash with Newton, which
9:17we have already mentioned, which lasted
9:19more than a decade and which, given
9:20Newton's oppressive zeal, served not
9:22only to eliminate any merit in the
9:24development of calculus, but also,
9:26worse still, to tarnish and dim his
9:27figure. In part also because later
9:30history did not treat him too well.
9:32Ridiculed by Voltaire, misinterpreted
9:34by his disciples like Wolff. And
9:37finally, in part, I suppose due to pure
9:39bad luck, be that as it may, Leibniz
9:41died in total decline and his death was
9:43followed by oblivion. His ideas
9:45remained dimmed several decades later.
9:48His figure was not recovered for
9:49history until much later thanks to Kant
9:51, 50 years after his death, or even
9:53more importantly, Bertrand Russell in
9:551900. Today there is no doubt. Leibniz
9:58was a great genius. He invented
9:59infinitesimal calculus like Newton and,
10:01independently of him, also the binary
10:03system. He made great contributions to
10:06logic, and many physical phenomena,
10:08such as the law of conservation of
10:10energy—or the vis viva, as he called
10:12energy—bear his name. Politics, laws,
10:14jurisprudence. We find them in his
10:15thousands of written pages. They say he
10:18was the last great polymath, but it is
10:20in philosophy where his mark is most
10:22evident. His theory of knowledge with
10:25truths of reason and of fact, his own
10:28paths to the existence of God,
10:29rationally grounded by Leibniz, his
10:31vital optimism seen in his work*
10:33Theodicy*with that famous, "We live in
10:35the best of all possible worlds," which
10:38Voltaire would later ridicule in his
10:40work*Candide*following the 1755 Lisbon
10:42earthquake, or the famous principle of
10:44sufficient reason, according to which
10:46every effect, even if we do not know it
10:48, has its cause, its sufficient reason.
10:51Note that along with the principle of
10:53non-contradiction, as Leibniz indicated
10:56, they are the foundation of
10:57experimental science. In other words,
11:00it is no small feat; thousands upon
11:01thousands of pages collect his thought,
11:03but it is his system of the world, his
11:05ontology, and his metaphysics that
11:07stand out most: the theory of monads. A
11:09theory that, without him imagining it,
11:11yields intuitions about reality that
11:13could perhaps help us better understand
11:15the quantum world today. Thought that
11:18was 400 years ahead of its time. Yes,
11:21it's time to learn about quantum
11:22mechanics. Let's head to the golden age
11:24of physics. The 20th century. Quantum
11:26mechanics was founded in the 20th
11:28century upon finding an answer to three
11:30different enigmas of physics and seeing
11:32that their solutions have something in
11:34common. The word "quantum"—you're
11:36going to freak out. We start with the
11:38first enigma. 1875, Berlin. The
11:41anecdote is told that young, 17-
11:43year-old Max Planck, doubting what to
11:45do with his life, asks a physics
11:46professor what to study. It must have
11:49gone more or less like this.
11:51Master, I have doubts about what to do
11:53with my life.
11:54I see a lot of talent in you for
11:56mathematics.
11:56The truth is that I would like to study
11:58physics.
11:59No, that has no future. Everything that
12:01needs to be known is already known. A
12:03physicist today only works on getting a
12:05new decimal figure. He means there is
12:08no longer room for creative thought or
12:10theoretical work; there are no open
12:11enigmas, and basically everything is
12:13known. The brilliant ideas have already
12:15been had by Newton, Galileo, Faraday,
12:17Kelvin, or Maxwell. They had extracted
12:19all the oil and nothing else was left.
12:22All that remains, if anything, is to
12:24repeat measurements a little more
12:25precisely on things already known.
12:27Something similar is often cited about
12:29Lord Kelvin and other geniuses of the
12:31era like Michelson. Physics, they say,
12:33is finished. So you can imagine how
12:36ironic it would be that it was
12:37precisely that Max Planck, who
12:39stubbornly ignored his teacher to study
12:41his passion, physics, who would open
12:43Pandora's box. Let's move on. The year
12:46is 1894, Berlin. Planck is now a boring
12:49professor at the famous University of
12:51Berlin doing work, well, un-spectacular
12:53, mainly in thermodynamics, an area
12:56that wasn't very lively at the time.
12:58Then, a consortium of electric
12:59companies approaches the boring
13:01professor with a proposal: find a way
13:03to maximize the light emission of a
13:05lightbulb with the minimum amount of
13:07energy. Easy to apply the formulas and
13:09that's it, but that's how physicists
13:10are. Planck found a tiny pebble in his
13:13shoe on the simple mathematical path he
13:15had to take, so small that it didn't
13:17really prevent him from completing his
13:20task, but big enough to keep him awake
13:22at night. He could have perfectly
13:24ignored it, yes, but it bothered him,
13:26it distressed him. That little hole he
13:28found in the theory of thermodynamics
13:30would occupy all his thoughts from then
13:33on and lead him to a new world. That
13:36small problem he found is what is known
13:38today as the ultraviolet catastrophe.
13:40To summarize, so as not to get too
13:42long-winded, everything revolves around
13:44black bodies. A physical abstraction to
13:46study lightbulbs or stars. A black body
13:49is like an ideal black box that absorbs
13:50all the light that reaches it; it emits
13:52nothing. Easy, because if it is allowed
13:55to reach thermal equilibrium with the
13:56environment, that is, you wait a few
13:58seconds there quietly and make a little
13:59hole in the box, the energy trapped in
14:01the box due to its temperature comes
14:03out. Well, the curious thing is that
14:05stars and lightbulbs emit light as if
14:07they were a black body. So studying
14:09this black body theoretically and
14:11experimentally is a great way to do
14:13astronomy or get an electric company to
14:16fund your laboratory. Great. So anyway,
14:18what does Planck do? He starts studying
14:19this black body. And the truth is, he
14:21was not the first to do so. The German
14:22physicist, Robert Kirchhoff, had
14:24already done it in the 1850s, and
14:25nothing strange, everything was great.
14:27The shape of the black body radiation
14:28is something like this. For high and
14:30low frequencies, the radiation energy
14:32is small, with an intermediate peak
14:34that depends only on the body's
14:35temperature. Fascinating. This explains
14:38why a star is red, yellow, or blue
14:39depending on its temperature. It
14:41changes the position of the peak, that
14:43is, the frequency at which it emits the
14:44most and therefore its color. Or the
14:46expression "red hot." It is also a
14:47consequence of this that metal turns
14:49red when you heat it, or the very color
14:51of flames. Everything is an effect of
14:53temperature on the color of radiation.
14:56But let's not digress any further.
14:57Kirchhoff experimentally obtains the
15:00black body curve, and look out, because
15:02a few years later the theory to study
15:04it appears—the theory of radiation,
15:06thanks to the mathematical genius James
15:09Clerk Maxwell. He comes up with these
15:11four equations, which were originally
15:13eight, describing the radiation of
15:15bodies, electromagnetic radiation. And
15:17here comes the fun problem. When
15:20Maxwell's theory, which was otherwise
15:21fantastic and wonderful, is applied to
15:23the black body problem, everything goes
15:24to pieces. The equations tell us that
15:27it should be easier for a black body to
15:30radiate energy at high frequencies.
15:32Basically, everything is fine here with
15:34the theory, great here, but when it
15:36gets to here, things go completely off
15:38the rails. And since this region of the
15:41spectrum is known as the ultraviolet
15:43region, and this here is madness, this
15:44is known as the ultraviolet catastrophe
15:46. Well, this is the pebble in the shoe
15:49that Planck saw, which others saw and
15:51basically knew about, but no one gave
15:53it any importance. In fact, an
15:54intermediate solution had already been
15:56found to get by. Wien found a formula
15:59that fits well. The physicist Wien
16:04found a formula that fits well on this
16:06part of the curve, and Rayleigh and
16:08later Jeans found another for this part
16:10of the curve. So, mathematically, there
16:12was no problem. Planck could have done
16:14the calculation they asked for, cashed
16:16his check, smoked a cigar, and that
16:18would be it, but no, those formulas had
16:20no physical explanation. Besides, there
16:22were two of them, and that is very
16:23strange. This bothered Planck; it
16:25wouldn't let him be at peace, it
16:27obsessed him. He wanted to get to the
16:29bottom of the matter, and the truth is
16:31he was the right person to do it,
16:32because Planck, besides being an expert
16:34in electrodynamics, was also an expert
16:36in statistical mechanics. Carnot,
16:39Clausius, Kelvin, and other geniuses of
16:41the first half of the 19th century had
16:43arrived at the rules of thermodynamics
16:45heuristically—that is, by trial and
16:47error. Those famous four laws. They
16:49achieved it through trial and error,
16:51more from engineering than from physics
16:54, driven by the industrial revolution
16:56they were fueling. And its center was
16:58the steam engine. Their physics was
17:00simple at that time. A gas is heated,
17:03it expands, there is temperature,
17:04volume, pressure, and all that. The gas
17:06is treated as a whole, as a single
17:08element. And the good thing is that the
17:09theory worked, but no one really
17:11understood what was happening. Well,
17:13all this would change a few years later
17:15, when some physicists thought of
17:17applying the concept of the atom to
17:19thermodynamic processes. A gas is no
17:23longer a single mass; now it is a huge
17:25collection of independent and
17:26indestructible atoms, bouncing and
17:28colliding with each other and the walls
17:31. Pressure is the product of the
17:33impacts, and temperature is the speed
17:34of the atoms. Now everything finally
17:36makes sense. The laws of thermodynamics
17:39emerge naturally from those collisions
17:41between atoms. A new branch of physics
17:44was born, the mother of thermodynamics.
17:46It is statistical mechanics. Well, the
17:48fathers of this new branch were the
17:51same James Clerk Maxwell from before,
17:53and especially Ludwig Boltzmann. And
17:56that was great, because by coincidence
17:58in the 70s, Boltzmann had worked at the
18:00University of Berlin, so his
18:01statistical theory was familiar to
18:03Planck throughout his studies. There,
18:06Planck would find the inspiration to
18:07solve the black body problem. Planck
18:11began his attempts in the summer of
18:121900 with a model of electromagnetic
18:14oscillators on the walls that emitted
18:16radiation like a Maxwell wave, but he
18:18achieved nothing. In October, not being
18:22much of a fan of Boltzmann's methods,
18:24in desperation, he repeated his
18:25oscillator method, but in a
18:27Boltzmann-like way, cutting energy into
18:29pieces, and surprisingly, it worked.
18:32December 14, 1900, without truly
18:34understanding what he was doing, he
18:36presented it at a meeting of the Berlin
18:38Academy of Sciences. It was a great
18:41success, but he knew it came at a high
18:43price. Boltzmann's hypothesis, which
18:46also worked, implied an ad hoc
18:48hypothesis to make things fit. This is
18:51the new distribution, intermediate
18:53between Wien's and Rayleigh-Jeans',
18:55which finally fits everything seen in
18:57the laboratory. Here you can see
18:59Boltzmann's mark, his constant. Now
19:01look at this here, H times frequency.
19:04Those are the chunks of energy from
19:06Boltzmann's method. He called them
19:08energy elements. We know this H as
19:11Planck's constant in his honor. This
19:14time we can finally say it. The H was
19:15missing. Anyway. Energy goes in jumps.
19:19These are the quanta of energy. This is
19:21the first quantum equation in history.
19:23What followed was silence. No one
19:26seemed to fully understand the
19:27implication of such a radical proposal.
19:30In fact, another 5 years would have to
19:32pass for someone to take up the
19:33gauntlet. 1905. Einstein, a failed
19:36student who leaves university and
19:38cannot find a job. Finally, in
19:41desperation, with a friend's help, he
19:43gets a random job as a third-class
19:44expert technician at a patent office in
19:47Bern. A boring job that didn't have
19:50much to do with physics, but enough to
19:52marry his girlfriend and live together.
19:55You already know who I'm talking about,
19:57obviously it's Albert Einstein, for on
19:59one of those boring office days, after
20:02he had finished his routine work, he
20:04has a small but brilliant idea. We move
20:06on to the second enigma. 1899, just 6
20:09years earlier, German physicist Philip
20:12Lenard, who by the way would later
20:14become the leader of Nazi physics and
20:16start a campaign to sink Einstein and
20:18his "Jewish physics," well, that year
20:20he conducts an interesting experiment,
20:23a circuit that doesn't close with some
20:25plates. Lenard saw that if you shine an
20:28ultraviolet light lamp, suddenly the
20:30circuit closes and a current appears.
20:33He had discovered the photoelectric
20:35effect. And everything is fine because
20:37there is nothing surprising here for
20:38physics. The physics that was known at
20:40that time. An electron requires energy
20:42to make this jump. Light has energy, so
20:44like Super Mario who eats a mushroom
20:46and grows, the electron eats that light
20:49to make the jump and the circuit closes
20:51. How nice. The shock comes from a
20:54subtle, but important detail. If you
20:56now increase the distance between the
20:58plates, the jump is greater. One would
20:59think that to cover the jump you have
21:01to increase the light intensity, but in
21:02reality, you don't achieve anything
21:04with that. No, you don't have to
21:05increase the intensity of the light to
21:07manage to make that jump. What it needs
21:09is not more intensity, but a higher
21:11frequency of light. With Maxwell's
21:14theory under his arm, this made no
21:16sense. 1899, this was a great enigma,
21:19for just 5 years later, this 24-
21:22year-old, rejected by every European
21:24university, came up with a solution. If
21:29Planck is right, he thought, the energy
21:30of light depends on its frequency and
21:32travels in packets. With this quantum
21:35formula, higher frequency, more energy.
21:37The mystery with this solves itself.
21:39It's obvious. Simple solution, yes, but
21:42very crazy. The problem is solved
21:45naturally and mathematically
21:46comfortably. Yes, it's true. But in
21:49doing so, another much, much bigger
21:51problem arises. Hadn't we said after
21:53more than two centuries of fighting
21:55that light was a wave? Contrary to what
21:58Newton said, Young had proven it with
22:00his double-slit experiment. This
22:02happens because light is a wave. Case
22:04closed. Well, Einstein reopened the
22:07case in 1905. Now, according to him,
22:10light is a particle. A quantum. What
22:12the hell is that? Well, here is the key
22:14. It's solved by adding the word "also.
22:16" Light also...is a particle; that is,
22:19light is a wave and it is a particle.
22:22Tremendous. If you notice, the black
22:25body and the photoelectric effect are
22:27two enigmas with the same solution:
22:28quanta. Energy is quanta, light seems
22:31to be quanta. But what is quantum
22:33mechanics? Where does all this come
22:35from? That is something that, by then,
22:37in 1905, no one could answer. For the
22:40moment, it was stuff about energy and
22:41light, but they couldn't say much more.
22:44To decipher it, we must meet another of
22:45the great protagonists of this story,
22:47who also solves the third enigma. I’m
22:49talking about the unique Danish genius
22:51Niels Bohr. But before we get to know
22:53him well, let's take another leap in
22:54history. 1896, Paris: Henri Becquerel
22:57is studying phosphorescence, that is,
22:59how an object you put in the sun then
23:01emits light, which wasn't anything
23:03spectacularly rare back then. What was
23:06spectacular was the serendipity of the
23:08story. Friday afternoon, a typical
23:09overcast, gloomy day in Paris. Facing
23:11the uncontrollable, Henri Becquerel
23:13gives up. Well, clearly, it’s not a
23:15day to conduct light experiments.
23:17Better to go have some vermouth at the
23:18bar on the corner. He takes his
23:20phosphorescent salts and leaves them in
23:22an office drawer. Curiously, he placed
23:24a photographic plate protected by
23:26double black paper on top. On Monday,
23:28when he arrived at the office, surprise
23:30: the salts had left a mark on the
23:32photograph. But, how? But if they
23:34haven't seen the light, how can that be
23:35? Besides, they had two layers of black
23:37protective paper. Well, today we have
23:39an obvious answer. Becquerel's salts
23:41weren't like your table salt—that is,
23:43chlorine and sodium. They were uranium
23:45salts. Becquerel had just discovered
23:48radioactivity. Something that was
23:50absolutely insane compared to what was
23:51known at the time. Energy was coming
23:52out of nowhere. It went against
23:54Leibniz's vis viva, Newton's mechanics,
23:56everything. Well, the key to
23:59understanding it would appear on the
24:01other side of the English Channel just
24:02one year later. 1897, London. Joseph
24:06John Thomson gives a historic lecture
24:08at the Royal Institution in London.
24:10Atom is a Greek word; it comes from "
24:13tomos," which means to cut, and "a,"
24:15which is a prefix of negation. An atom
24:18is something that cannot be cut. The
24:20atoms of philosophy, from Leucippus and
24:22Democritus to Epicurus and Titus
24:24Lucretius, were just that: minimal
24:26components of matter that, by
24:27connecting and remixing in the void,
24:29gave rise to everything that exists.
24:32This was a theory that, in the face of
24:34Aristotle's continuism, hardly had any
24:36impact until modernity. Gassendi
24:38recovered it at the dawn of the
24:40scientific revolution. Dalton gave it a
24:42serious chemical form, although it did
24:44not impose itself as a material reality
24:46until Boltzmann and his statistical
24:48mechanics and Einstein's Brownian
24:50motion in 1905. The fact is that by the
24:53time of Becquerel's 1896, atoms were
24:55consolidated in science. They are the
24:59basic elements of nature according to
25:00Mendeleev's periodic table, such that
25:02by joining atoms like Lego pieces we
25:04form everything we see around us. But
25:06if we asked what an atom is, well, they
25:08looked to the past at Democritus and he
25:10would answer that it is something
25:12unbreakable. An atom cannot be divided.
25:15They lied to you. So let's return to
25:16that lecture at the Royal Institution
25:18in London. That day, history was being
25:20made before a surprised audience.
25:22Joseph John Thomson showed that
25:24everyone was wrong. With a vacuum tube,
25:27he managed to measure a particle
25:29smaller than the atom. The atom can
25:31indeed be broken. Friends, he has
25:33demonstrated the existence of the
25:34electron. Okay, we now have another
25:36ingredient to understand what on earth
25:38was happening with this quantum
25:40mechanics thing. Energy is quanta and
25:42the atom can be broken. Then Thomson
25:45thinks, if the atom can be broken,
25:47could it be because it has a structure?
25:50Thus he is the first to propose what an
25:53atom is like. He gives us the first
25:55atomic model. Thomson imagines that an
25:58atom is like a solid mass of positive
26:00charge with negative point-like
26:01inclusions, like raisins in a muffin.
26:04Those would be his electrons. "This is
26:06not true," someone would have to tell
26:08him in a strange New Zealander accent.
26:10One of the greatest experimental
26:11geniuses in history. By the way, one of
26:13Thomson's students in London, the
26:15good-natured giant Ernest Rutherford.
26:18Let's take a little jump into the
26:19future. The year is 1909, Manchester;
26:22Rutherford has left Thomson's
26:23laboratory in London and is working in
26:25Manchester with his students Geiger and
26:28Marsden. He then proposes an experiment
26:30that the three of them carry out, one
26:32that is as famous as it is beautiful.
26:34They launch radioactivity particles,
26:35like those of Becquerel, against a thin
26:37gold foil and see what is received by a
26:39detector behind it. What they observe
26:41is very strange. Most of the particles
26:43pass through the gold foil and very few
26:45bounce straight back. Rutherford turns
26:48his results over in his mind and
26:50realizes that his mentor Thomson must
26:52be in grave error. This is how
26:54Rutherford proposes another way of
26:56understanding the atom. I'm sure this
26:58one seems more natural to you now. The
26:59atom cannot be a solid sphere. Of
27:02course, most of the particles pass
27:03through the atom; it must be
27:05essentially empty. So he proposes a
27:08small, positive nucleus with electrons
27:10orbiting around it. This is a new
27:14atomic model, Rutherford's atomic model
27:16. Don't be impatient; we're almost
27:18there. Okay, good. This model of the
27:20atom has two things, one very good and
27:22one very bad. The good part is this.
27:24This would be an atom and this is the
27:26solar system. Don't you think they look
27:28a lot alike? What's more, this is one
27:30of my favorite memes, I love it. And it
27:33makes us notice the similarity between
27:35the law of gravity and the electric
27:37force of the atom. Mathematically, they
27:39are very similar. I mean, it was all
27:41set. An atom is a miniature solar
27:43system. Same system and same laws. And
27:46this is good news. Copy-paste and
27:47that's it. The bad part, because
27:49there's always a bad part, is that it
27:51ruined everything. It was the end of
27:53matter. According to what was known
27:56about the theory of electricity at that
27:58time, 1910, in this solar system-atom
28:00analogy, there is a small but important
28:02difference between an electron and a
28:05planet. A charged particle that rotates
28:07emits radiation, light, just by the
28:09fact of rotating. This was something
28:11that was already known. A planet, on
28:13the other hand, does not. But what does
28:14a particle do when it emits light? It
28:16loses energy. And what happens when an
28:18orbiting system loses energy? Well, it
28:20lowers its orbit. But as it rotates, it
28:22keeps losing energy, lowering its path
28:24more and more and more and more until
28:25the collision. The electron would
28:27spiral down until it crashed into the
28:28nucleus. The atom would disappear, and
28:30this is something that, well, doesn't
28:32happen; we are alive. So this theory
28:34necessarily had to be wrong. But why?
28:37What is an atom like then? This is,
28:40friends, the third great enigma. The
28:43solution, as with the previous enigmas,
28:45would come from an audacious, brave,
28:47and highly educated person, up to date
28:49with the scientific innovations of his
28:51years, who would later stand as the
28:53beacon of his entire generation, father
28:54to physicists for several decades, and
28:56the leading light of the quantum
28:58movement. I am speaking of the Dane
29:01Niels Bohr, slow to develop his ideas
29:03and even clumsier at explaining them.
29:05His wife wrote the scientific articles
29:07that he dictated to her. He was
29:09hopeless with experiments, but had a
29:10special talent for connecting ideas,
29:12for seeing beyond what anyone else
29:14could see. Today it is said that this
29:15genius of physics was actually more of
29:17a philosopher than a scientist. He came
29:19from a scholarly family that was also
29:21very athletic. Bohr was a prominent
29:23soccer goalkeeper, and his brother even
29:25went with Denmark to the 1906 Olympic
29:26Games without, of course, ever ceasing
29:28to be a nerd. His brother was also a
29:30great mathematician, and Bohr would
29:32write equations on the goalpost when
29:34his team was on the attack. He would
29:35become so absorbed that his fans had to
29:37warn him when there was a counterattack
29:39so he would return to the goal. And as
29:41a physicist, Bohr had another important
29:44virtue for being in this story. He was
29:46in the right place, at the right time,
29:48and surrounded himself with the best
29:50minds. After graduating as a physicist
29:52in Copenhagen, he first goes to
29:54Cambridge to research in the most
29:56important laboratory of the time, the
29:57Cavendish Laboratory, under the
29:59tutelage of the father of electrons,
30:01J.J. Thomson. There he meets Ernest
30:03Rutherford himself, so he decides to
30:05follow him to Manchester. In short,
30:07Bohr is following the trail of this
30:09great enigma alongside its leading
30:11figures. It's like playing soccer first
30:13with Messi and then with Cristiano.
30:141911, Manchester; it is there, working
30:17with Rutherford, Geiger, and George
30:19Darwin, Charles's grandson, that Bohr
30:21comes up with a tremendous idea. He
30:23takes up the enigma that his mentors
30:25had left on the table. Why doesn't an
30:27atom destroy itself? Well then, let's
30:29take the new quantum ideas. He thought,
30:33if Planck proved that energy moves in
30:35quantum leaps and Einstein that light
30:37follows leaps, couldn't it be that the
30:39orbits of atoms also take leaps? Well,
30:42here comes his master solution. He said
30:44to himself,
30:46an electron cannot be at any distance
30:48from the nucleus, the way a planet can
30:50be at any distance from the Sun. There
30:52will only be quantum orbits permitted
30:54by this rule. This is Bohr's rule
30:57solved. In those orbits, the electron
30:59does not radiate energy and the atom
31:01does not die; it remains stable, it is
31:03saved. The rest of the orbits are
31:05simply forbidden. And so, why aren't
31:07all the electrons in the orbit closest
31:09to the nucleus? He asks himself. Well,
31:12Bohr has an answer.
31:14The orbits fill up, so as you put
31:16electrons into the atom like an
31:18audience in a theater, they have to
31:20move up to other tiers as the lower
31:22ones fill up. This, friends, is the
31:26model of orbitals. It is the Bohr
31:28atomic model, which comes with an extra
31:31gift. By 1910, experimental physicists,
31:35knowing that everything is made of
31:37atoms, were already performing intense
31:39experiments to understand them and
31:41found that the best method for studying
31:44the atom is spectroscopy: shooting
31:46radiation, or light, at an atom and
31:48observing what happens. When doing this
31:52, they noticed that the atom only
31:53responded to certain frequencies of the
31:55light they used, only a few of them.
31:58With this, experimentalists filled out
32:00tables and graphs like this one, where
32:02they recorded the energy levels that
32:05the atom preferred. Well, with Bohr’s
32:07model, there is now an explanation for
32:09these preferred energy levels of the
32:11atom. Bohr says an electron is in an
32:13energy level. If it receives radiation,
32:15it consumes it like a Super Mario
32:17mushroom and jumps to the next level.
32:19Or the opposite can happen. An electron
32:21is in a higher level than it belongs,
32:23it returns to its original level and
32:25emits the excess energy. With this, it
32:27is now possible to explain those
32:28preferred energies of the atom. They
32:30are the jumps between its orbits.
32:32Mystery solved, the third one. And with
32:35this, friends, the first quantum
32:37revolution comes to a close, taking
32:39place between 1900, when Planck
32:41released the first publication on the
32:43quantum nature of radiation, and 1912,
32:45when Bohr came up with his atomic
32:47theory based on this quantum physics.
32:49And now, take note. We now have a
32:51better definition of what quantum
32:53mechanics is. It is the theory that
32:55explains the discontinuous nature of
32:57energy, Planck’s little jumps, of
32:58light, Einstein’s work, and, notably
33:00thanks to Bohr, of matter as well. The
33:03world is also quantum, discontinuous;
33:05meaning not only radiation and energy,
33:07but also atoms and molecules follow
33:10little jumps. Those quantum rules. This
33:13, friends, is quantum mechanics. To
33:15summarize in very few lines, as when I
33:17asked Wescol, "What is quantum
33:19mechanics?" He told me, "Well, it's the
33:21physics behind everything, because it's
33:22the physics of what makes up our world,
33:24of the smallest things that exist."
33:26They are the rules followed by the two
33:28elements that form the world: radiation
33:30and matter. Okay, yes, those are many
33:32ideas I've thrown at you, very
33:33concentrated. If your head hurts,
33:35it’s normal. If you got lost, it’s
33:37also normal. The first time you hear
33:39all this, it sounds alien. In summary,
33:42three revolutions in one. Planck’s
33:44regarding energy, Einstein’s
33:45regarding light, and Bohr’s regarding
33:47matter. All three, as you saw, with
33:48something in common. that require that
33:51H, Planck's constant, which tells us
33:52that everything happens in little jumps
33:53, those are quantum leaps. Today this
33:56triple revolution is known as the first
33:58quantum revolution because, yes, you
34:00guessed it, there is a second one. The
34:03fact is that, more or less at this
34:05point, people knew what quantum
34:06mechanics was, but not the why, or
34:08where all this came from. That is to
34:09say, they were looking for something
34:11similar to Newton's laws, a complete
34:13system of laws to explain why these
34:15things happen, but obviously applied to
34:17quantum phenomena. So the search begins
34:19. But before reaching the solution,
34:21there is basically a gap, a void of
34:23about 10 years in which two things
34:25happen. On one hand, experimental
34:27physicists rack their brains measuring
34:29those atomic spectra. They realize that
34:32the key to understanding everything
34:34lies there, in those energy jumps of
34:36the electrons. So they start measuring
34:38like crazy. And with those data, the
34:41theorists start making tables and
34:42looking for some relationship, some
34:44order behind the tangle of numbers,
34:45something to explain it all. Imagine,
34:48without success. On the other hand, a
34:50new generation of physicists emerges.
34:52Left behind are Einstein, Rutherford,
34:53Bohr, or Planck, the protagonists of
34:55the First Revolution. Some simply
34:57disappear from the scene like Planck;
34:59others become guides or mentors for the
35:01second, like Einstein or Bohr. Instead,
35:03other protagonists now arrive, a new
35:05generation. They are young. At this
35:08point, what happens is very interesting
35:09. They are born already with this new
35:11vocabulary. Jumps, energy lines,
35:13quantum. What was alien to Einstein or
35:16Planck is no longer such a strange
35:18world to them. It is the world they
35:20already study in their physics
35:21textbooks; it becomes natural to them.
35:24These youngsters are Heisenberg, Pauli,
35:25Fermi, Dirac, Jordan; they will be the
35:27new protagonists of the story. But
35:30before we get there, since your brain
35:32is surely more than fried, it's worth
35:34taking a little break from physics to
35:36return to the thread we left loose at
35:38the beginning. Remember that German
35:41sage who knew everything. Law, physics,
35:44logic, mathematics, but above all,
35:45philosophy. What had happened to him?
35:47We had left him in his philosophical
35:49thought, in his philosophical system.
35:50We are in the second half of the 17th
35:52century. Leibniz, as a good rationalist
35:55, takes up the line of thought of
35:57Descartes, what he calls the new
35:59philosophy, but he actually creates his
36:01new system at a point by breaking with
36:03him, moving away from his system, from
36:05his mentor. And it was thanks to his
36:08work in physics. Yes, our beloved
36:10physics. Leibniz is a child of that
36:12historical moment, the scientific
36:13revolution; he is a contemporary of
36:15Newton and lived a few years after
36:16Kepler or Galileo. And like them, he
36:19himself works on the laws of motion. He
36:21is the father of ideas such as momentum
36:23or vis viva, energy. For it is while
36:25working with these ideas that he
36:27believes he sees a serious error in
36:28Descartes. From physics, he finds a
36:31crack in his system of the world.
36:33Descartes founds his system first by
36:35denying past tradition. The Greeks,
36:37Aristotle, Plato, and all of them, whom
36:40he considers surpassed in light of
36:42modernity. Thus he tries to create a
36:45system from scratch, ex nihilo, and
36:47does so with a method based on doubt,
36:49doubt as a method, methodical doubt.
36:52From his first certainty, his famous
36:54cogito ergo sum, he reaches his three
36:56essences, the three things that exist
36:58for him. The thinking self, which is
37:00the res cogitans, reaches it through
37:02clarity and distinctness. God, who is
37:04the res infinita as the guarantor of
37:06good and truth. And three, the physical
37:09world, the res extensa, bodies, motion,
37:11which are real by the very goodness of
37:12God. Well then, Leibniz disagrees with
37:15him on this point. That cannot be, he
37:17tells himself, and he does so rooted in
37:19physics. And inertia, what is it if not
37:21that? He asks himself. Because of
37:23inertia, for motion to occur, you need
37:25to overcome resistance. You need
37:27something external to extension. To
37:29physics, something beyond it, which has
37:32no geometric-mathematical nature,
37:34something therefore metaphysical. You
37:36need a force, from force, he concludes,
37:39proceeds motion and extension.
37:41Therefore, it must be above it. Thus,
37:44the elements of reality, Leibniz thinks
37:46, transcend time, space, and motion.
37:49They are substances, the substances
37:51behind the material, those elements of
37:53Greek metaphysics that Descartes had
37:55rejected. Yes, if Descartes
37:58intentionally moved away from the
38:00ancients whom he considered surpassed,
38:02Leibniz, also a rationalist, denies his
38:04master. Descartes proposes updating it
38:08with an ingredient he takes from the
38:10philosophical past of Aristotle and his
38:12friends. It is substance. And what
38:15would be the nature of this
38:17non-material substance? It would be a
38:19kind of force principle. They would be
38:21metaphysical points, original forces.
38:24He called them monads, the substances,
38:27Leibniz's primal forces. And from his
38:29own physics, the properties of these
38:31monads would be understood. They would
38:34be metaphysical points. Immaterial
38:36centers of activity from which
38:38everything would arise. They would be
38:41like our psychic activity, unitary yet
38:43varied and multiple with two activities
38:45. There would be perception or
38:48representation, which are internal
38:49actions of the monad, and its appetites
38:51. Each monad would represent all the
38:54others, the entire universe, through
38:56its relations with other monads. As he
38:59says,
38:59in every monad there is a cooperation
39:02of all things. This is something
39:05similar to Thales '"all in all" or the
39:07Renaissance concept of man as a
39:08microcosm. He would put it this way.
39:11The present is pregnant with the future
39:14.
39:14In every instant lies the totality of
39:16time. Something very interesting to
39:18analyze in light of what we know today
39:20about time and relativity, but that
39:21would take us off topic. We return to
39:24the monads and how they give rise to
39:26reality. For Leibniz, God is the
39:28primitive, original, and simple monad.
39:30The others are created by Him. Of these
39:33latter ones created by God, their
39:35activity would be limited and therefore
39:37imperfect. And that is what constitutes
39:39materiality, the corruptible world,
39:41which explains, for example, the origin
39:42of evil. Here Leibniz is somewhat
39:44attacked by the aporias of his own idea
39:46. He has eliminated Descartes' dualism
39:49of mind and matter. Now there are only
39:52monads, but in doing so, he pays a high
39:54price. His system has infinite and
39:57isolated monads, but how are they
39:59differentiated and how do they relate?
40:01How do they give rise to thinking
40:03matter like us? It is at this point
40:05that he has a brilliant idea that today
40:06we can review in light of quantum
40:08physics. But before telling you about
40:09it, let's return to Europe to complete
40:11our story about quantum mechanics. We
40:13return to the 20th century, but mind
40:14you, we have jumped 10 years. We are
40:16specifically in 1924. Remember that we
40:20had left the scientists lost in 1912,
40:22and we let those 10 years pass where
40:24they tried to fit these quantum rules
40:27and make sense of them. They had
40:29accepted them. The world is like that,
40:30but where did they come from? What was
40:32happening in the atom? And to provide
40:34an answer, they tried to perform
40:35experiments with atoms, measuring those
40:37energy lines one by one, because that's
40:39how they were. They were searching for
40:40a complete theory that would explain
40:42everything. A Newton's law for atoms.
40:44It would be quantum mechanics. What
40:46they couldn't even imagine when they
40:48were looking for it is that finding it
40:49would only be the beginning of the
40:50great problems. At this point, the
40:52story divides in two. Two stories that,
40:55although they travel in parallel and
40:57often touch, converge, they become
41:00forever irreconcilable. 1901, Munich
41:02saw the birth of a child into a family
41:04with an academic tradition, Werner
41:06Heisenberg, brilliant in everything
41:08from birth, the typical pedantic child
41:10who does everything right. He played
41:12the piano, beat everyone at chess, read
41:13poetry and philosophy, and was even the
41:15fastest in his class at sports, but he
41:17especially had a supernatural talent
41:19for mathematics. He handled
41:20calculations and numerical games in a
41:22truly astonishing way, and he did it as
41:24if it were just a game. And he also had
41:27another fine virtue that we've seen
41:29before, that of always being in the
41:30right place at the right time. And so,
41:33when it came time to choose his studies
41:35, he set his sights on physics. First
41:36in Munich under the guidance of the
41:38great physicist and even better teacher
41:40Arnold Sommerfeld, later in Göttingen
41:42with another of the great quantum
41:43geniuses, Max Born. And finally, he
41:45would complete the triangle in
41:46Copenhagen with the sensei of quantum
41:48physics, Niels Bohr, thus passing
41:50through the three great cathedrals of
41:51quantum mechanics: Munich, Göttingen,
41:53and Copenhagen. And from the beginning,
41:56he showed his great virtue: applying
41:58his main talent, unique in the world,
41:59his numerical vision to physical
42:01problems. Physicists were struggling
42:04with tables of quantum leaps, trying to
42:06find an order, racking their brains
42:08without finding anything. For him, a
42:10lover of these mathematical challenges,
42:13this was mere child's play. That is how
42:15he found numerical relationships in
42:17these tables that no one else could see
42:18. His talent was exactly suited for
42:20this task. In particular, he saw a
42:22numerical relationship that became his
42:24personal trademark. He noticed behind
42:26these tables an order based on
42:28half-integer numbers: one-half,
42:29three-halves, five-halves. They were
42:32like quantum numbers guiding the leaps.
42:35With them, magically, things fell into
42:37place. But he had no idea why it was
42:39that way. Munich, Göttingen. To his
42:41colleagues, obviously, his methods
42:43seemed aberrant. He needed something
42:46deeper to gain the approval of his
42:48peers and be taken seriously. He needed
42:52a quantum mechanics. This is how we
42:54arrive at Copenhagen in 1925. He is
42:57spending time there with Bohr, who had
42:59invited him personally, very surprised
43:01by the mathematical ability and deep
43:03philosophical thought of this 24-
43:05year-old. Toward the end of his stay,
43:08Heisenberg suffered a terrible attack
43:10of hay fever, a severe allergic
43:12reaction, so to calm it, he asked for
43:14two weeks of vacation. He needed a
43:16place far from the pollen that was so
43:17bothersome to him. A quiet place where
43:20he could recover and think clearly
43:22about all those numbers coming to his
43:24mind. That is how he retreats. 15 days
43:26alone on an island in northern Germany.
43:28Helgoland, June 7, 1925. In solitude,
43:33watching the waves break, surrounded by
43:35nature and clean air, he finds the
43:37health and tranquility to bring order
43:39to everything swirling in his mind. In
43:43those days, working with his
43:45mathematical games, he formed new
43:47tables that, when ordered correctly,
43:49surprisingly made everything make sense
43:51. Upon his return, it was later seen
43:54that those tables were actually already
43:56known mathematical tools: matrices.
44:00Simply by taking Newton's law and
44:02replacing quantities like position and
44:04velocity with those tables, things
44:06worked very well, and those strange
44:09half-integer values he used—1/2, 3/2,
44:115/2—were actually due to quantum spin
44:13. He had created matrix quantum
44:17mechanics. That fascinating work would
44:20be published shortly after, in
44:22September 1925, "Quantum-Theoretical
44:24Re-interpretation of Kinematic and
44:26Mechanical Relations," a historic
44:27article that would mark the true
44:29beginning of the quantum revolution.
44:32Heisenberg was already a legend; he was
44:34only 24 years old. Allow me just one
44:37note; it is small, but very relevant to
44:39this story. The key to arriving at his
44:42idea of mathematical tables came from a
44:44comment by a colleague, possibly his
44:46friend Pauli.
44:47If we only see the quantum jumps, which
44:49is what we measure—the spectra—why
44:51ask ourselves what the electron does
44:53between the jumps?
44:55What is an electron or an atom, deep
44:56down? And what do they do when we
44:58aren't looking at them? That was what
45:00he was determined to answer. But
45:02perhaps that was the problem. Perhaps
45:04it is a question that makes no sense.
45:06Perhaps it only makes sense to ask
45:07about what we can see, what we can
45:09measure. The quantum jumps. Those
45:11things that we can actually measure, he
45:13called observables. He thought of
45:15creating a theory of observables and
45:17nothing more. In fact, the tables he
45:20made were of quantum jumps of those
45:22observables, connecting the electron's
45:24starting level with its arrival level.
45:27Hold on to the seed of this idea,
45:28because it will be fundamental to the
45:30conclusion of the video at the end.
45:31Heisenberg presents his idea. The
45:33reaction on all fronts was triumphant,
45:35and it would also trigger a creative
45:37wave in Copenhagen, Munich, and
45:39especially in Göttingen, where Pauli,
45:41Born, and Jordan would get to work to
45:43extract the full potential of Werner's
45:45great idea. In a few weeks, Born and
45:48Jordan systematized Heisenberg's
45:50procedure, laying the foundations for
45:53matrix mechanics. That same year,
45:55Uhlenbeck and Goudsmit proposed the
45:58existence of spin, which gives meaning
46:00to the half-integer quantum values of
46:02his mathematical games. And furthermore
46:05, Dirac gives greater mathematical
46:07breadth to the theory. The work was
46:09finished. The wind seemed to be blowing
46:12in Heisenberg's favor until, in early
46:141926, his luck would suddenly change.
46:171925, Zurich, Professor Erwin
46:19Schrödinger is frustrated. He was one
46:21of the great promises of physics and
46:23philosophy. And at 37, he hadn't
46:25achieved anything. While his
46:27contemporaries, Einstein and Rutherford
46:29, had triumphed very young—the most
46:31productive age in physics, their
46:33twenties—he had reached his 40s
46:35almost buried in irrelevant physics
46:37problems. He couldn't hit the mark; he
46:39was pulling at threads that led nowhere
46:41. In that year, 1925, he sees a thread
46:44and decides to pull it to see what
46:45happens. In the famous Annalen der
46:47Physik, a curious article by an unknown
46:49young physicist had just been published
46:51. It was basically a copy of his
46:53doctoral thesis, a document of about 70
46:56pages titled simply, "On the Quantum
46:58Theory." It was the doctoral thesis of
47:00Louis de Broglie. Louis did not look
47:02like a physicist of the time; he was
47:04the son of a noble French family. He
47:06would soon even acquire the title of
47:08prince. He studied history to work as a
47:11diplomat, but his brother Maurice, 17
47:13years his senior and a physicist by
47:15profession, managed to get him so
47:16hooked on physics that he ended up
47:18leaving the diplomatic profession aside
47:20. Louis, once trained as a scientist,
47:23would work during World War I on radio
47:25communications from the Eiffel Tower.
47:27After the wartime break, he decides to
47:29undertake his doctoral thesis. He would
47:31do it on quantum mechanics, following a
47:34very simple idea he had—so simple
47:36that its simplicity makes it brilliant.
47:3920 years earlier, as we saw, in 1905,
47:41Einstein surprised the world by saying
47:43that light, which was supposed to be
47:45waves, is also particles. It is dual,
47:47one thing and the other. Well, Louis de
47:50Broglie said in his thesis, if
47:51something that is a wave is also a
47:53particle, could it be that something
47:55that is a particle should also be a
47:57wave? This is absolutely fabulous
48:01because we physicists love symmetry, we
48:04love unification—that things that
48:06don't look alike at all are suddenly
48:08related. With this idea, he is unifying
48:12, pairing up light and particles. Deep
48:14down, he says they are the same thing,
48:16but the idea was so extravagant and
48:18strange that even his professors didn't
48:19know what to do with it. They didn't
48:22know how to evaluate it, whether it was
48:24the idea of a madman or, instead, an
48:25absolute genius. The thesis judges were
48:28stunned. So his tutor, the famous
48:30physicist Paul Langevin, makes a
48:31decision: to pass the idea on to his
48:33friend Einstein. To see what he thinks.
48:36Einstein read it and was amazed. He
48:38found it interesting, or rather, very
48:40profound. With Einstein's support, the
48:43thesis was approved without difficulty,
48:45and the subsequent article on quantum
48:47theory using De Broglie's hypothesis
48:49was published in the Annalen der Physik
48:52, an article that Erwin Schrödinger
48:54read a year later in 1925. That article
48:57fascinated Schrödinger, much like it
48:59did Einstein, to the point that he
49:02wrote to Einstein himself. A few days
49:04ago, I read the ingenious thesis of De
49:06Broglie with the greatest interest.
49:09Thanks to it, your work becomes
49:11completely clear to me for the first
49:14time. He was so enthusiastic about this
49:18idea that his boss—and his wife's
49:20lover—the great physicist Peter Debye
49:22, suggested he prepare a talk about it
49:24at their university, ETH Zurich. The
49:27physicist Felix Bloch, who was present,
49:29would later recall it this way. He gave
49:32a clear explanation of De Broglie's
49:35theory of particle waves. When he
49:38finished, Debye commented that he found
49:40it somewhat childish. As a student of
49:43Sommerfeld, he had learned that to deal
49:46with waves, one must find the wave
49:49equation.
49:50His boss and his wife's lover had
49:51thrown down the gauntlet. Schrödinger
49:53was ready to pick it up. By the way, if
49:55the fact that his boss was also his
49:56wife's lover throws you off, don't
49:58worry, because it didn't bother
49:59Schrödinger. His professional life was
50:02boring, but his sex life certainly was
50:04not. In fact, it was truly very
50:05controversial. Some of his escapades
50:07include falling in love with a 14-
50:09year-old student he tutored, whom he
50:11then impregnated, and pursuing his
50:13friends 'wives until he slept with them
50:15, as he did with Arthur March, whose
50:17wife he also impregnated. He even did
50:19the same after meeting Hassi, a woman
50:21he encountered on his own honeymoon. He
50:23got several women pregnant and then
50:25raised his lovers' children with his
50:27wife, with whom he also lived,
50:28sometimes even including their husbands
50:30in the arrangement. Total madness. In
50:32fact, he would often travel to physics
50:35conferences with his wife and his
50:37mistress, and others as well. So, as I
50:40said, it wasn't much of a problem that
50:42Schrödinger's boss was having an
50:44affair with his wife. Well then,
50:46Schrödinger picks up Debye's gauntlet.
50:48To find a wave function. Let's get to
50:51it. And so, the Christmas holidays of
50:521925 arrived. For a long time, Erwin
50:55had been struggling with health issues,
50:57specifically tuberculosis. Usually, as
50:59part of his treatment, he would spend a
51:01few days at an idyllic spa in
51:02Switzerland, in the mountains of Arosa.
51:06So, for Christmas of 1925, he hatched a
51:08plan: to retreat to the mountains of
51:10Arosa with one of his lovers, some
51:12earplugs, and de Broglie's paper, to
51:17find that damned wave function. The
51:19fact is that during those days he had a
51:21burst of creativity that allowed him to
51:22come up with that wave function he was
51:24looking for. It was the foundation of
51:26quantum mechanics. Schrödinger’s
51:28wave quantum mechanics. It is, in truth
51:30, a simple equation. This one right
51:32here, there’s nothing more to it, but
51:33it is truly very profound. Upon his
51:35return, he systematically applied this
51:37equation to those endless tables that
51:39theorists had managed to compile from
51:41experiments on atoms, and to his
51:43delight, it gave the correct answer.
51:46Thus, he published his first article in
51:48the Annalen der Physik on January 27,
51:501926, just a few days later. The last
51:52one would be in September of that year.
51:54There were six in total. In them, he
51:57demonstrated that wave quantum
51:59mechanics was correct. He had found the
52:01Newton’s law of atoms. But where you
52:03might imagine overflowing joy in the
52:05physics community, there was actually
52:07terror, because if you’ve noticed, we
52:09went from having no quantum mechanics
52:10to having two. And this, how can you
52:13imagine? It cannot make sense. The
52:15world, the universe can only have one
52:16set of rules. It will either be
52:18Heisenberg’s or Schrödinger’s.
52:20That is why the young Heisenberg was
52:22dismayed by the news coming from Zurich
52:24; because he knew it: young 24-year-old
52:26Heisenberg was destined to lose, and
52:28not because of his young age. No, it
52:31was because compared to
52:32Schrödinger’s gentle, continuous,
52:34and deterministic waves, his abrupt,
52:36probabilistic jumps, his mathematical
52:38games, and his strange tables seemed
52:41like monsters straight out of a horror
52:43movie. No one would want to use them.
52:46Worse still, his mechanics brought an
52:47image of the world that no one would be
52:49willing to accept. You have a three and
52:51you have a five; you multiply them, and
52:53you get 15. Very well, do you know how
52:54to multiply? Well, now we can flip it,
52:55the five first and then the three.
52:57Multiply them and the result is the
52:58same. 15. Little surprise there. It’s
53:00because multiplication is commutative;
53:02we all know that from school. The order
53:04of factors, they say, does not alter
53:06the product. But what seems obvious is
53:07not always the case. For example, it
53:10doesn’t happen with tables of numbers
53:12, matrices. You have a matrix A and you
53:14multiply it by another B; well,
53:15mathematically, you don't get the same
53:17result if you multiply B by A. It is
53:18said that matrices do not commute. The
53:21problem is that in Heisenberg's matrix
53:23theory, these matrices, as we saw, are
53:24magnitudes like position and velocity.
53:27They are the observables used to
53:29measure particle states. In other words
53:32, the theory subtly tells us that since
53:34position and velocity are matrices,
53:36they do not commute. That is, measuring
53:38position and then velocity is not the
53:39same as doing it the other way around.
53:41This madness would lead Heisenberg a
53:43few years later to shape the most
53:45important and craziest principle of
53:47quantum mechanics. The one that bears
53:49his name is Werner Heisenberg's
53:50uncertainty principle, which is
53:52mathematically formulated this way.
53:54This is the uncertainty in the position
53:56measurement, this in velocity, that is,
53:58how much do we know about these
53:59magnitudes? The equation tells us that
54:02there is a natural limit on what we can
54:04simultaneously know about a particle's
54:06position and velocity. Since Newton's
54:09time, there has been a fantasy of
54:11determinism that by knowing the
54:12position and velocity of, for example,
54:14three balls in a moving box, we can
54:15know where they will be at any future
54:17moment. Heisenberg tells us that
54:19something like that makes no sense.
54:21Impossible. Of a system, in this case
54:23the three balls, which is given by
54:24their three positions and their three
54:26velocities. At any given moment, we can
54:28at most know half of them. The other
54:31half is not that it's technically
54:33impossible to know, it's that it makes
54:34no sense to talk about it. The
54:37uncertainty principle makes us blind to
54:39half of what we can know about the
54:41world. But it's even worse when the
54:43random nature of quantum mechanics is
54:45observed in experiments. Anyway, it was
54:47all truly a mess. But what seemed to be
54:50an unequal war, Schrödinger and his
54:52continuous, deterministic waves versus
54:54Heisenberg and his quantum leaps and
54:56uncertainties, was all an illusion.
54:59Working with Schrödinger's formulation
55:01, one arrived deep down at the same
55:03conclusions. Its continuity and its
55:06determinism were just that, illusory.
55:09It was inevitable to reach the same
55:10crossroads. Heisenberg's uncertainty
55:12and the discontinuity of matrix theory
55:14were real. And this is only confirmed a
55:17short time later. First Dirac, then
55:19Pauli, but definitively the genius of
55:21Paul Dirac gave a resounding answer.
55:24The two mechanics are really two
55:26mathematical forms of the same theory.
55:28Schrödinger and Heisenberg had
55:29basically discovered the same thing.
55:31Things are becoming clearer, but we
55:33still have many scraps of fabric: waves
55:35, leaps, matrices, uncertainties,
55:37non-commutation. It was necessary for
55:39someone to be able to sew it all
55:41together properly, to give it a final
55:42shape. 1927, in Como, Italy, on the
55:45occasion of the centenary of Alessandro
55:47Volta's death, some of the leaders of
55:48the Quantum Revolution gathered on
55:50September 11. A historic conference
55:53took place there. It would be given by
55:55the master of the entire generation,
55:56Niels Bohr. Bohr decides to take the
55:58best of the pieces and sew a good shirt
56:00out of them. Let's take a classic
56:02experiment. An electron that is
56:04launched through a tube and arrives at
56:06a screen. What do we know about all
56:07this thanks to quantum mechanics? It is
56:09said, well, that the electron, whatever
56:10it may be, does not matter to us. It
56:12evolves like a wave on its journey. It
56:15is in all these places at once, but
56:16when it hits the screen, it appears in
56:18only one place. Then, it manifests as a
56:20particle. There we have all the
56:22elements, Schrödinger's waves, which,
56:24being waves, we can only know 50%of
56:26their dynamics. There we have
56:28Heisenberg's uncertainty principle, but
56:30then, when measured, the wave
56:31disappears and the particle appears. At
56:33this point, one asks: what is happening
56:35? Well, Bohr answers: by observing, the
56:38wave is collapsing. The wave fades away
56:40and in its place the particle appears.
56:42And where does the particle appear?
56:44Here, Bohr borrows a brilliant idea
56:46from his friend Max Born, which also
56:48allows for the random nature of quantum
56:50phenomena. Schrödinger's wave is a
56:54probability wave, so we don't know
56:56where the electron will appear on the
56:58screen, but we can know one thing: it
57:00will be more likely to see it where the
57:02wave is greatest. The wave is nothing
57:05more than a probabilistic wave. Now
57:07this whole concoction is missing only
57:09one element. And Bohr puts the special
57:11cherry on top of this theoretical
57:13framework with an idea he had himself.
57:15Wave and particle? He asks himself.
57:17Well, the two visions of wave and
57:19particle are both correct at the same
57:21time, because they are complementary
57:23visions; there is the keyword. What the
57:25electron really is does not matter to
57:27us; it is totally irrelevant. Depending
57:31on how I go about studying it, it will
57:32have a particle nature or a wave nature
57:34. But surely, deep down, it is neither
57:37of the two. It is surely, in fact,
57:39something that even we humans cannot
57:41understand. Hold on to this second
57:42philosophical contribution that we are
57:44providing in this historical review. It
57:46is Bohr's: the limits of human
57:48knowledge and the purpose of science,
57:49which is none other than to explain
57:51what can be observed. This, friends, is
57:53what is known as the Copenhagen
57:55interpretation of quantum mechanics.
57:56With this, the second quantum
57:59revolution concludes. Applause. But
58:02don't worry, because what seems like
58:04the end of the story—where the
58:06credits would roll and the final
58:07screens appear—is actually just the
58:09beginning; because what appears to be a
58:11way to reconcile all the brilliant
58:13ideas of those 10 years, in reality,
58:15like the apple of Eris in the Iliad,
58:17carries within it the seed of discord.
58:20Mathematically it all works, physically
58:22it might make sense, but for many,
58:24philosophically, this solution was
58:26totally absurd. This is the story.
58:30While the Copenhagen school grew and
58:31expanded, with its numerous members
58:33taking over the most important
58:34universities in Europe—Pauli,
58:36Heisenberg, Jordan, Kramers. And with
58:39that, imposing this vision of quantum
58:41mechanics, that of the collapse, on
58:42future generations, others acted as
58:44opposition, as resistance. And it's
58:47because they saw that this formulation,
58:49by forcing reality, reached a state of
58:51nonsense. At the center of this
58:53resistance, opposing this vision—
58:54Bohr's vision, that of the Copenhagen
58:56school—were two of its creators, two
58:58of the creators of quantum mechanics.
59:00We are talking about Albert Einstein
59:01and Erwin Schrödinger. "If all this
59:03quantum jumping is here to stay, I
59:06regret having had anything to do with
59:08this theory."
59:09Schrödinger would say. Oh,
59:11I like to think that the moon is there,
59:13even if I don't look at it.
59:14Even his famous. "God does not play
59:17dice."
59:17What would Einstein say? Neither of
59:19them was against the mathematics of
59:21quantum theory. Everything was fine
59:22with that. They were against, however,
59:24its final form, the Copenhagen
59:26interpretation, the philosophical
59:27premises it started from, and also its
59:29metaphysical consequences. In fact,
59:32together, Schrödinger and Einstein—
59:35both convinced of their opposition—in
59:37an exchange of letters, created the
59:39famous Schrödinger's cat, a thought
59:42experiment they devised to ridicule the
59:44Copenhagen interpretation. You put a
59:47cat in a box with a poison that is
59:48triggered by the passage of a quantum
59:50particle. Since the particle actually
59:52acts like a wave, it can be in two
59:54places at once, triggering and not
59:56triggering the poison. So, until
59:58someone observes the system, someone
1:00:00opens the box and the wave collapses,
1:00:02the cat is, according to the Copenhagen
1:00:04interpretation, both alive and dead at
1:00:06the same time. This, we all agree,
1:00:08makes no sense at all. The cat cannot
1:00:10be alive and dead. Well, with this
1:00:12question, this interpretation, a war
1:00:14broke out at the center of the debate
1:00:16between the two sides: the supporters
1:00:18of the Copenhagen interpretation, led
1:00:20by Bohr, and the revolutionaries
1:00:22against it, led by Einstein. A war that
1:00:25had as its symbolic high point that
1:00:27famous 1927 Solvay Conference, the
1:00:29greatest gathering of geniuses in
1:00:31history with one topic to address: the
1:00:33meaning of quantum mechanics. At that
1:00:36time, the fights between Einstein and
1:00:37Bohr at the congresses became famous.
1:00:39Einstein would devise a thought
1:00:40experiment to show that quantum
1:00:42mechanics made no sense. A while later,
1:00:44Bohr could be seen angry, muttering to
1:00:46himself as he walked through the
1:00:48hallways. At night, the solution would
1:00:50come to him and he would tell Einstein,
1:00:52who would lock himself away to
1:00:53complicate the experiment more and more
1:00:55to start over and drive Niels Bohr
1:00:57crazy. This was one of the most intense
1:00:59and beautiful intellectual battles in
1:01:01history, which in reality had no winner
1:01:03. As of today, October 14, 2025, the
1:01:07fight is still not over; it remains
1:01:09open. And at the heart of the matter in
1:01:11this battle is the philosophy of
1:01:13quantum mechanics. What is the world?
1:01:15Does the observer affect it by
1:01:16measuring? Does reality exist outside
1:01:18of us or only in our minds? What are
1:01:20those waves that we cannot observe?
1:01:22Does it make sense to theorize about
1:01:23something that cannot be seen? Instead,
1:01:25should we just be content with
1:01:27understanding what we measure, or can
1:01:29we try to reach the king of all? No one
1:01:31currently has a clear answer to these
1:01:33questions, which actually point to the
1:01:35true meaning of quantum mechanics. But
1:01:37before entering this intense and
1:01:39precious debate, let's return to the
1:01:41German genius. Do you remember Leibniz?
1:01:44And I believe he has something
1:01:45interesting to tell us across time,
1:01:47those 400 years that separate us from
1:01:48him. The germ of the theory of monads,
1:01:51as we said before, was in physics.
1:01:54Leibniz thought that inertia, the
1:01:56resistance to movement through space,
1:01:57implied something of a metaphysical
1:01:59nature, something external to space
1:02:01itself, a kind of originating substance
1:02:03not founded on the geometrically
1:02:04mathematical. Those points of
1:02:07immaterial metaphysical force, those
1:02:09would be the monads. They would be
1:02:11infinite, incorruptible, containing the
1:02:13whole, a cooperation of all things, but
1:02:15at the same time, they were imperfect.
1:02:17And how do these monads give rise to
1:02:18the world we see? Here is Leibniz's key
1:02:21idea. For him, space is not something
1:02:23fundamental; it is instead a product,
1:02:25it is a phenomenon, or as he called it,
1:02:28a phenomenon bene fundatum. It is the
1:02:30way in which reality appears before us.
1:02:32Thus, space is born as an effect of
1:02:34something more fundamental, the order
1:02:36of things that coexist. Space is the
1:02:38fruit of the relationship of things
1:02:39with one another. It is a result of the
1:02:41relationship that we perceive as
1:02:43existing between things. Something
1:02:44similar happens according to Leibniz
1:02:46with time. It becomes a*rationis*. It
1:02:49is not a subsistent reality like the
1:02:52unstoppable flow we all feel, but
1:02:54rather a*phenomenon bene fundatum*, a
1:02:57phenomenon. Thus, time arises from the
1:02:59relation of coexistence between things.
1:03:02Time appears because things pre-exist,
1:03:05coexist, and post-exist through their
1:03:07succession, but not as something
1:03:09fundamental, a basic being, or an
1:03:12absolute entity. Thus, for space, it is
1:03:15the order that makes bodies locatable
1:03:17and through which, by existing together
1:03:19, they have a position in relation to
1:03:21one another. Time is an analogous order
1:03:24in relation to their successive
1:03:26position in space. Look and be amazed
1:03:28at how far Leibniz takes us in the
1:03:30middle of the 17th century. What an
1:03:33original and modern line of thought. We
1:03:35are moving from space as the essential
1:03:38foundation of existence. From Descartes
1:03:41'nature of bodies, passing to Newton's*
1:03:43sensorium Dei*, to becoming something
1:03:45constructed by experience through a
1:03:47relation between things. As Leibniz
1:03:49says, time and space would be an
1:03:51illusion. Or better yet, one of
1:03:53Bacon’s idols. Space would be a
1:03:56subjective way for things to appear,
1:03:58with the real, the fundamental, being
1:04:00only the relation between them. I am
1:04:02honestly blown away by the modernity of
1:04:05this idea. It leaves me absolutely
1:04:07paralyzed how, while other geniuses
1:04:09like Descartes, Newton, Bacon, or
1:04:11Hobbes built a materialism and a
1:04:13mechanism that today, with the benefit
1:04:15of hindsight, we could label as naive.
1:04:18Well now, of course, we know things
1:04:19like fields, quantum phenomena, or the
1:04:21principles of relativity. He was taking
1:04:24a step into the unknown in another
1:04:26direction, getting ahead of them all to
1:04:28anticipate questions that are still
1:04:30relevant 300 years later. To me, this
1:04:33seems truly astonishing, incredible,
1:04:35and very praiseworthy. Of course, these
1:04:38ideas are so interesting and fruitful
1:04:40that we can find echoes of Leibniz's
1:04:42ideas in Kant, for example, and the
1:04:44revolution he brought to the
1:04:45interpretation of space-time, which
1:04:47would later influence Einstein and
1:04:49relativity; but it is even more
1:04:51surprising that we can adopt many of
1:04:53his interesting ideas, even 400 years
1:04:55later, to approach the quantum mystery.
1:04:59We return to quantum interpretation, we
1:05:01return to our story, but now we leave
1:05:03the chronological path to see it from
1:05:05today, from the present. 100 years have
1:05:07passed since that famous Solvay
1:05:09Conference that put an end to the
1:05:11quantum revolution. And the truth is,
1:05:13with some nuances, things remain much
1:05:15the same. Universities continue to
1:05:17teach the Copenhagen interpretation in
1:05:18their classrooms. This has historical
1:05:20motives, like the influence of Bohr and
1:05:22his disciples, but also practical or
1:05:24instrumental ones. The fact is that
1:05:26this interpretation is taught well,
1:05:27applied well, and presents mathematical
1:05:29clarity. Generally, moreover, it is
1:05:30taught without getting into trouble. It
1:05:32is this way, it is done this way, and
1:05:33that's that. And if the only thing at
1:05:36stake here were building bridges,
1:05:37putting rockets on the moon, making
1:05:39electrical circuits, or sending a
1:05:41WhatsApp message from Madrid to Cali,
1:05:42everything would be fine. We could stop
1:05:45here and everything would be fantastic.
1:05:48But when the issue at stake is deeper,
1:05:50such as answering the question of what
1:05:52reality is, the matter is not only not
1:05:54so easy, but it is not trivial either.
1:05:58That it is not trivial can be easily
1:06:00seen in how what I am about to tell you
1:06:02currently stings. I will surely even
1:06:04receive criticism for this video.
1:06:06Talking about the Big Bang, all good.
1:06:07Talking about string theory, no problem
1:06:09. Here things get more serious because
1:06:11what I am going to tell you, friends,
1:06:13is no longer just science, nor is it
1:06:15even just philosophy. This encroaches
1:06:18on the meaning of the world and
1:06:20therefore on the political, the
1:06:21religious, and the economic spheres—
1:06:23that is, on the narratives of control
1:06:25and power. Neither the fundamentalists
1:06:29of Marxism and communism nor
1:06:30ultra-conservative Catholic movements
1:06:32are oblivious to this issue. Because we
1:06:35know that questions about ultimate
1:06:36reality also imply asking ourselves
1:06:38about things like the existence of the
1:06:40soul, the preponderance of humans in
1:06:41the world, or the afterlife, and
1:06:43obviously their opposites, like atheism
1:06:45. Thus, the dominant ideologies in the
1:06:47world, which in principle have nothing
1:06:49to do with quantum mechanics, fight to
1:06:51be right on this matter as well, from
1:06:53their own narrative marked by their
1:06:54ideology. Therefore, friends, this is
1:06:58no longer just science, but let's
1:06:59pretend it is only science and
1:07:00philosophy, because I find it more fun
1:07:02and I like it much more. Let's get to
1:07:05the point. I'll summarize it for you
1:07:06quickly. On one hand, we have some
1:07:08absolutely unquestionable facts. I
1:07:10don't think anyone could disagree with
1:07:12me. Experiments with atoms show strange
1:07:14things, such as the electron and the
1:07:16rest of the particles evolving over
1:07:18time like waves, and in doing so, they
1:07:20hide 50%of reality from us. We are
1:07:23blinded by the wave-like nature of
1:07:25matter to 50%of what is happening. Up
1:07:28to that point, there is little to argue
1:07:30, and this is applied in the laboratory
1:07:31with success, and the physicist goes
1:07:33home happy. The problem is when we ask
1:07:35ourselves why things are this way for
1:07:38an electron—wavelike, diffuse—but
1:07:40when we go to the park and touch a ball
1:07:42or a plant, things are no longer like
1:07:45that. Things appear with a marked
1:07:48material nuance; they have a very
1:07:49different nature. The wave is tangible,
1:07:53it is point-like; how? Why? That is the
1:07:56origin of this discussion. It is what
1:07:59is known as the observer problem in
1:08:00quantum mechanics, or how we can move
1:08:03from an intangible wave nature to
1:08:04something we can touch, like a wallet.
1:08:07The fact is that depending on how this
1:08:09problem is approached, the nature of
1:08:11reality changes drastically. These are
1:08:13the interpretations of quantum
1:08:14mechanics. To bring a little order, the
1:08:17questions we want to resolve in light
1:08:18of the observer problem in quantum
1:08:20mechanics are two. The first: does the
1:08:23world exist independently of our mind?
1:08:25And if it does exist, the second
1:08:27question: can we understand its
1:08:28fundamental laws? Quantum mechanics,
1:08:30from its mathematical success,
1:08:32uncontroversial and indisputable as far
1:08:34as is known today, is open to many ways
1:08:36of answering these two questions, with
1:08:38a tremendous impact on our way of
1:08:40understanding the world. Let's start
1:08:42with the most radical way. It would be
1:08:44to answer "no" to the first question.
1:08:46That is what someone would do who takes
1:08:48the subject of observation in quantum
1:08:50mechanics......in the most literal way
1:08:52possible. These physicists would grant
1:08:55the conscious act of looking a
1:08:57fundamental role in existence, which
1:08:59can be taken to its ultimate
1:09:01consequences. Imagine we have Wigner, a
1:09:04scientist, doing the Schrödinger's cat
1:09:06experiment with a box in a room. For
1:09:08Wigner, the cat is alive and dead at
1:09:10the same time until the box is opened.
1:09:11He does it and, for example, it turns
1:09:13out to be alive. Great, end of the
1:09:14matter. But for a person outside that
1:09:17room who hasn't entered yet, hasn't
1:09:19opened the door, doesn't know what
1:09:20happened inside, hasn't observed it;
1:09:22therefore, the cat remains alive and
1:09:23dead for him. The point is that we can
1:09:26imagine another person who is outside
1:09:28and so on, and by following this
1:09:29logical path, we can arrive at the need
1:09:31for the entire universe to be observed
1:09:33in order to exist. This is the famous
1:09:35thought experiment known as "Wigner's
1:09:37Friend," and it is not the only exotic
1:09:38interpretation. John Wheeler, also
1:09:41using quantum mechanics, would arrive
1:09:43at very curious things that give a very
1:09:45important role to the observer. It is
1:09:48the theory of the participatory
1:09:49universe that I explain in this video.
1:09:51Basically, that the human being has an
1:09:52important role in the universe for its
1:09:54own creation. The existence of the
1:09:56human being makes the universe collapse
1:09:57and begin to exist at the Big Bang,
1:09:59with a sort of journey into the past.
1:10:00Okay, this is the most philosophically
1:10:02wild way to interpret quantum mechanics
1:10:04. It goes along the lines of a tree
1:10:06making no sound in the forest if there
1:10:07is no one there to hear it. In reality,
1:10:09it is nothing that extravagant, nor
1:10:11that new in history. It is the esse est
1:10:13percipi of the philosopher Berkeley.
1:10:15But let's move in another direction.
1:10:16Let's see what happens if we answer the
1:10:18first question in the negative. No, we
1:10:20do not need a consciousness observing
1:10:22the universe for the outside world to
1:10:25exist. When we talk about observing or
1:10:27measuring in quantum mechanics it
1:10:30sounds very anthropocentric, but in a
1:10:32general way it can have another meaning
1:10:34, another significance: simply
1:10:36interacting. Can a stone, for example,
1:10:39observe the sea if it falls off a cliff
1:10:41, for example, where there is no human
1:10:43being? Observing, we could change it to
1:10:45interacting. Here, two very interesting
1:10:47positions appear depending on how we
1:10:49answer the following question. Whether
1:10:51it is possible to understand the
1:10:52universe in its most fundamental
1:10:54features. If we answer this question
1:10:55with a no, that it is not possible to
1:10:57understand the universe in its
1:10:58fundamental features, there are two
1:10:59possibilities. We could be quantum
1:11:01epistemologists, for whom the very
1:11:03question, what is an electron? We don't
1:11:05know, nor can we even know. Science
1:11:08deals with our knowledge about the
1:11:10world, not what it really is.
1:11:12It is incorrect to think that the task
1:11:15of physics is to describe how nature is
1:11:17. Physics only deals with what we can
1:11:20say about nature,
1:11:21which is the philosophical stance of
1:11:23Bohr or Bertrand Russell, and much in
1:11:25the line of Kant as well. We perceive
1:11:26phenomena through the senses and not
1:11:28the noumena, the essence of objects,
1:11:30the thing in itself. But also in this
1:11:32line we have the operationalists. For
1:11:35them, that same question, what is an
1:11:37electron, is not just that we cannot
1:11:39know it because human beings lack that
1:11:40possibility, that access. It is simply
1:11:43a meaningless question. We can only ask
1:11:46ourselves about what we can experience:
1:11:48the observables, such as the position
1:11:50of the electron. But what does the
1:11:52electron do when we aren't looking? It
1:11:54simply makes no sense. Science only
1:11:56keeps a record of the observable. In
1:11:59fact, those observable quantities only
1:12:01come into existence by the act of
1:12:02measuring them. In this strict sense,
1:12:05Heisenberg was an operationalist. And
1:12:07finally, there is the last option:
1:12:09answering that consciousness does not
1:12:10play an important role and that we can
1:12:12indeed know the foundations of the
1:12:14world. There are the realists, those
1:12:16who believe that the world exists
1:12:17outside of us and can also be
1:12:18understood. This would be the stance of
1:12:20Einstein or Schrödinger, the
1:12:22intellectual rivals of the Copenhagen
1:12:23interpretation. Here within this team,
1:12:25the problem is that this isn't a view
1:12:27compatible with quantum mechanics as it
1:12:30stands today, but it can be saved.
1:12:32Einstein, for example, thought that
1:12:34quantum randomness is like the
1:12:36randomness of rolling a die. When you
1:12:39roll a die, we don't know what will
1:12:40happen, what will come up, because we
1:12:42lack all the information to calculate
1:12:43it, but if we could have it, we would
1:12:45know. In this case, randomness is a
1:12:48reflection of our ignorance. Einstein
1:12:51thinks the same thing happens with
1:12:52quantum mechanics. Yes, it is random,
1:12:54but only in appearance. Underneath,
1:12:56there is a more fundamental theory
1:12:58where everything makes sense and is
1:12:59realistic. These are the hidden
1:13:01variables he spoke of. There are
1:13:03several options here, such as the pilot
1:13:05wave theory by De Broglie and later
1:13:06David Bohm. This is a realistic theory
1:13:08in this sense. There are other forms of
1:13:10realism as well, though they may seem
1:13:12more exotic. L.S.M., in a book I will
1:13:13add to the bibliography, calls them
1:13:15magical realism. One proposal for this
1:13:17magical realism would be an explanation
1:13:19of what happens when a quantum
1:13:20phenomenon occurs in the world. What it
1:13:22proposes is that the world is dividing
1:13:24into several realities, giving rise to
1:13:26a quantum multiverse. This is a
1:13:28realistic theory that resolves quantum
1:13:30paradoxes, but at the cost of
1:13:31multiplying entities to infinity. This
1:13:33is Hugh Everett's many-worlds
1:13:35interpretation. Actually, there are
1:13:37other modern realistic interpretations
1:13:39that try to accommodate all the madness
1:13:41of quantum mechanics, like the physical
1:13:43collapse of quantum states, or the
1:13:45Montevideo interpretation, or QBism, a
1:13:47Bayesian interpretation of quantum
1:13:48mechanics. And why is the question
1:13:50still open today? Well, because no
1:13:52interpretation is fully satisfactory.
1:13:54The Copenhagen interpretation implies a
1:13:56rather strange collapse of the wave
1:13:58function, plus such strange and
1:14:00realistic views of the world will
1:14:01always be under suspicion. The
1:14:03many-worlds interpretation is very
1:14:05strange in itself. Acknowledging the
1:14:07existence of infinite material
1:14:08realities doesn't leave anyone at ease.
1:14:09The pilot wave, furthermore, seems to
1:14:11violate relativity, physical collapse,
1:14:13and the conservation of energy. The
1:14:14fact is that there isn't one that
1:14:15satisfies everyone at once. It is in
1:14:17this situation that an interpretation
1:14:19arrives, I would say intermediate
1:14:20between them all, and one that would
1:14:22make Leibniz himself very happy: Carlo
1:14:23Rovelli's relational interpretation of
1:14:25quantum mechanics. He tells it in his
1:14:28book Helgoland, which I include in the
1:14:29bibliography, particularly in a chapter
1:14:31with the illustrative title: is it
1:14:32possible that something is real for you
1:14:34but not for me? If Heisenberg started
1:14:37by ignoring everything that cannot be
1:14:39observed, leading to his famous
1:14:40matrices, Rovelli takes this as the
1:14:42core of his interpretation. Only what
1:14:44is observed exists. Observed not in a
1:14:47human sense, but in a much more general
1:14:49one. Only that which has interaction or
1:14:51a relationship with other things exists
1:14:53. Properties, which are what we measure
1:14:56like an object's position, speed, or
1:14:58color, do not reside in objects; they
1:15:00are bridges between them. This is the
1:15:02relational interpretation of quantum
1:15:04mechanics. The world is a dense web of
1:15:06interactions, says Rovelli, in which
1:15:07everything is in continuous
1:15:08relationship with its environment
1:15:10through these interactions. The knots
1:15:12in this web of interactions are objects
1:15:14. Thus, a thing like a stone makes no
1:15:17sense in itself, but only based on the
1:15:19relationships it has with its
1:15:20surroundings; something that relates to
1:15:22nothing truly does not exist. At this
1:15:24point, many of the paradoxes of quantum
1:15:26mechanics disappear. We saw that as
1:15:29long as something is not observed, it
1:15:30shows strange behavior. It is actually
1:15:33that it does not exist for me as an
1:15:34observer of the world because I do not
1:15:36yet have a relationship with it. So all
1:15:38we can conjecture are possibilities of
1:15:41existence. That is where the famous
1:15:43randomness comes from. Once I observe
1:15:45it, I relate to it. It exists insofar
1:15:47as its properties are shared with me.
1:15:49This interpretation, as the chapter
1:15:50title suggests, gives rise to what seem
1:15:52like glaring inconsistencies. That
1:15:54electron I do not observe behaves very
1:15:56differently if you do observe it, but
1:15:58the contradiction is only apparent. For
1:16:00you, it exists because you have created
1:16:03a relationship, and what exists are
1:16:04relationships. For me, as long as I do
1:16:06not observe it, it does not exist. But
1:16:09there is no problem with something
1:16:10existing for you and not for me,
1:16:11because we have contradictory views.
1:16:14But we are not unrelated to each other.
1:16:16Relationship is everything. You might
1:16:18be a bit in shock at this point, but
1:16:20for a physicist, having relational
1:16:22magnitudes or potentially contradictory
1:16:24positions is something natural. That
1:16:26things are relational can be seen, for
1:16:28example, in motion. It is a key element
1:16:30in Galileo's relativity or Einstein's
1:16:32relativity. It is also relational. And
1:16:34the same happens with electromagnetism,
1:16:36another relational theory. There are
1:16:37also famous physics paradoxes that
1:16:39arise from this appearance of a priori
1:16:41contradictory points of view. An
1:16:43astronaut falling into a black hole,
1:16:45from the outside, we would see them
1:16:46slowing down until they appear frozen
1:16:48on the surface without entering. The
1:16:50astronaut, however, does not feel that,
1:16:52only how they are falling in, with
1:16:54increasing speed, heading toward the
1:16:55center. He does not stop. To one he is
1:16:57stopped, to the other he is entering a
1:16:59black hole, and both are correct. Well,
1:17:01they are two different visions, no
1:17:03problem there. The answer is both,
1:17:04because since there is no way to share
1:17:06information, there is no paradox. The
1:17:08same thing happens with the other
1:17:10famous relativity paradox, the twin
1:17:11paradox. Two twin astronauts can both
1:17:14think the other is younger than them
1:17:17due to space travel, and both are right
1:17:19. Two people who say the other is
1:17:21younger than them, and at the same time
1:17:24, both are correct. Yes, it sounds like
1:17:26it makes no sense, but in relativity,
1:17:28it is resolved relationally. Neither
1:17:30knows about the other, nor can they
1:17:31communicate with one another. So the
1:17:33paradox doesn't actually exist outside
1:17:35of our minds. And we can go beyond
1:17:37physics. In biology, living systems are
1:17:39relational to the environment. In
1:17:41chemistry, in economics, in psychology.
1:17:44Relational theories are everywhere. It
1:17:46is not so strange that a German
1:17:48philosopher 400 years ago thought that
1:17:51relationships between things shape
1:17:53reality, a reality that exists based on
1:17:56those relationships. There was an
1:17:58Indian philosopher, Nagarjuna, who in
1:18:00the second century AD asked what was
1:18:02fundamental in the universe. It was in
1:18:05his work, "Verses on the Fundamentals
1:18:06of the Middle Way." Nagarjuna arrived
1:18:08at a relational view of the world very
1:18:10similar to the one we just described.
1:18:13Only the relationships between things
1:18:15exist, not the objects themselves.
1:18:17Everything exists in that dependency,
1:18:19that relationship. To that lack of
1:18:21inherent existence, Nagarjuna called it
1:18:23sunyata, emptiness. My "self" would
1:18:25also play a role in that network of
1:18:26connections. What I perceive, what I
1:18:28feel, what I think. It would only exist
1:18:32in relation to other things as an
1:18:34element of that network of interaction
1:18:35in which, deep down, fundamentally,
1:18:37there is nothing, nothing, nothing.
1:18:41Isn't that incredible? Well, I hope, my
1:18:43friends, that you enjoyed this marathon
1:18:45video, which, by the way, sets a record
1:18:46again, over an hour of spectacular
1:18:48video. It has been an immense effort
1:18:51over several weeks. For the first time,
1:18:53it took me a week to write a script,
1:18:55dedicating day after day and several
1:18:57weeks to prepare it. And as always,
1:18:59when we reach this point, I want to
1:19:01share a little bibliography with you in
1:19:03case you are curious. This is only part
1:19:05of the bibliography consulted because,
1:19:07well, I have read a lot about quantum
1:19:08mechanics and not all the books are
1:19:09included here. Here are just the ones I
1:19:12directly based myself on to draft this
1:19:14history script, because I included
1:19:16historical facts about Heisenberg's
1:19:18life, "Beyond Uncertainty," the whole
1:19:20topic of quantum mechanics
1:19:21interpretation, Lee Smolin...what I
1:19:23mentioned about Schrödinger's life.
1:19:26All the history of quantum physics I
1:19:28basically pulled from here along with
1:19:29other books, but mainly from here. And
1:19:32finally the book I mention by Carlo
1:19:33Rovelli, which was fundamental for
1:19:35drafting this script, well, Helgoland,
1:19:36where he explains his relational theory
1:19:38. Well, that's all, my friends, I'll
1:19:40sign off now. A new season of the blog
1:19:42begins on a high note. I hope it
1:19:44excites you, that you tune in, and that
1:19:46we are here enjoying physics, knowledge
1:19:48, and the world. A kiss to you all, and
1:19:50as always, put your brains to work and
1:19:51study, because one of you could be the
1:19:53next one, see you in the next one. See
1:19:54you as always, see you as always in the
1:19:56next video, you little scallywags. See
1:19:58you soon.

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