La revolución de la Cuántica. En lo que se considera la primera revolución cuántica del siglo XX, los científicos observaron propiedades cuánticas que permitieron el desarrollo de tecnologías como los láseres, el transistor, las imágenes por resonancia magnética y los semiconductores
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00:00THE SAGA OF THE NOVELS, EPISODE 4
00:08The saga of the Novels is the story of the great discoveries and ideas of the 20th century.
00:13Einstein, Curie, Paulov, Fleming, as well as Camus, Hemingway, Luther King and Dr. Schweitzer have already entered the legend.
00:21At the beginning of the 20th century, quantum mechanics, born with Max Planck and Albert Einstein, shocked the world of physics.
00:32Several Nobel Prizes will have an important role in the elaboration of this theory, especially the Danish Niels Bohr and the German Werner Heisenberg.
00:41THE QUANTUM REVOLUTION
00:47In Europe, the 1900s are a time of certainty. The world, exhausted by transport and communications, has practically exhausted its mysteries.
00:57The locomotive and the plane allow man to dominate space and a nature whose laws he finally believes and knows.
01:17Lord Kelvin, one of the great physicists of the 19th century, then affirms...
01:27However, there are some dark spots, some disturbing details, which Lord Kelvin will call two little dark clouds.
01:37Trying to dissipate one of these clouds, a German physicist, Max Planck, will trigger a process that will end up collapsing the entire building.
01:48The problem he worries about is the light emitted by an object when it heats up.
01:53The colour of the light emitted by this object varies according to the temperature.
01:57The theories of that time respond to the experimental results of infrared rays and visible light, but they prevent more ultraviolet rays than is observed.
02:06In 1901, to eliminate this contradiction, Max Planck proposes a model according to which energy is emitted in successive stages, by packets.
02:15These packets are given the name of quants, and their value is calculated from a universal constant, which will soon be known as Planck's constant.
02:26This discontinuity introduced into the world of energy is absolutely revolutionary. Max Planck knows this.
02:32It is a desperate act to explain the experimental results.
02:37He will spend the next ten years trying to get rid of the quants of energy, but in vain. He will win the Nobel Prize in 1918.
02:46At the time of his discovery, Max Planck is already a first-line physicist, a professor at the prestigious University of Berlin.
02:54However, most of his colleagues consider his results as a comfortable mathematical shortcut, without any profound meaning.
03:02This is not the case of Albert Einstein. He also believes in the quants of energy.
03:06At the beginning of the 1900s, he was just a dark official at the Bern patent office.
03:13He comes from a German Jewish family, and has come to study in Switzerland to escape the Prussian school system, whose rigidity and strict discipline he has never been able to withstand.
03:22Even in Zurich, where he has completed his studies brilliantly at the Polytechnic School, no one has offered him a university position.
03:28He is too independent, too asocial. He has always preferred to work and reflect alone.
03:34He likes his job at the patent office, which allows him to discover all kinds of inventions, from the most serious to the most extravagant.
03:42A job that also leaves him time to reflect on what really interests him, the fundamental laws of the universe.
03:48Einstein finds Planck too timid. He dreams of a much more radical questioning.
03:53I want to know how God has created the universe. I am not interested in such or such phenomenon, or the spectrum of such or such element.
04:00I want to discover what God thinks. Everything else is nothing more than detail.
04:07His intellectual activity is so effervescent and productive that in October 1905, at the age of 26, he published three articles that shocked the world of physics.
04:16Each of them could have earned him the Nobel Prize.
04:19In one of them he presents his famous theory of relativity. In another, inspired by the theory of the quants of Max Planck, he explains the photoelectric effect.
04:28At that time, light was considered a wave. Einstein started from an experiment carried out by Philipp Lennart, a German physicist, an experiment that no one can explain.
04:38When light is projected on a metallic white, electrons are ejected.
04:43If the light were a wave, when its intensity decreases, the electrons should be slower.
04:48And yet, that is not what happens. The electrons are ejected at the same speed, but what decreases is their quantity.
04:56Einstein is convinced that the idea of the quants of energy could explain this phenomenon.
05:02There, where Planck, a respectable and respected professor, doubted the existence of such a phenomenon,
05:07Einstein has nothing to lose.
05:10What if the light were truly made up of particles? Of quants?
05:14In this case, everything would be explained.
05:17When the luminous intensity decreases, the amount of particles decreases as well, but not their energy.
05:23Less electrons are ejected, but always at the same speed.
05:26Einstein's hypothesis will be confirmed by a new theory of relativity.
05:30In 1914, Einstein's ideas had already spread, and in European laboratories, they began to talk about relativity and quants of energy.
05:37Another novelty is the structure of the atom.
05:39In the first half of the 20th century, Einstein's theory of relativity was first published in the New York Times.
05:45In the second half of the 20th century, Einstein's theory of relativity was published in the New York Times.
05:50In the third half of the 20th century, Einstein's theory of relativity was published in the New York Times.
05:56Another novelty is the structure of the atom.
05:59In 1908, Ernest Rutherford receives the Nobel Prize in Chemistry for his discovery of the atomic nucleus.
06:06He has conceived a planetary model of the atom in which the electrons rotate around the nucleus like planets around the sun.
06:13But his model poses serious problems.
06:16If the electrons are particles with an electric charge, they should emit a radiation when rotating around the nucleus,
06:23and therefore lose energy and quickly crash against the nucleus.
06:27In other words, according to Rutherford's model, matter should suffer a constant implosion.
06:35And in 1912, Niels Bohr, a young Danish, arrives in Manchester to work in the laboratory of the famous Professor Rutherford.
06:42He comes from Copenhagen, where he brilliantly presented his thesis on the electronic theory of metals.
06:48Born in 1885, he is the son of Christian Bohr, a well-known professor at the Danish university.
06:54His fellow students describe him as a young, pale and modest man, with serious difficulties in expressing himself in English.
07:01But even though he doesn't speak much, he listens and learns.
07:04He also reads a lot.
07:06He writes daily to his girlfriend, Margret, who has stayed in Copenhagen, and he constantly thinks about the atom.
07:13To solve the contradictions of Rutherford's atomic model, he tries to apply Planck and Einstein's quantum ideas.
07:19And little by little, he progresses.
07:21He writes to his brother, Harald.
07:31The detonator will be the encounter with the spectroscopy.
07:34Bohr will set up a model of the atom in order to explain why each element has a luminous spectrum made up of characteristic rays.
07:43In Bohr's model, the electron only has access to a limited number of orbits, which correspond to different levels of energy.
07:52It can jump to an external orbit if it receives enough energy, if it captures one or more photons.
07:57Then it can go back down to a lower orbit, releasing a photon.
08:01It is the quantum jump, responsible for the spectral rays.
08:06The idea is great, and it works.
08:08A great number of basic data, which physicists had ordered and labelled over the centuries,
08:13are suddenly taken from their shelves and gain a new meaning.
08:17Physicists believed they had a coherent and almost complete description of the universe.
08:22Quantum mechanics will destroy their certainties.
08:27If the electron can jump from one trajectory to another,
08:30this means that classical physics does not apply to the atomic scale.
08:34More than the structure of the atom, it is the entire scientific building that is questioned.
08:42In 1920, Bohr founded the Institute of Theoretical Physics in Copenhagen,
08:47where the young physicists from all over Europe will soon flow.
08:51It is the beginning of what will be called the Copenhagen School,
08:54seven Nobel Prizes, starting with the one awarded to Niels Bohr in 1922.
08:59So now everything works?
09:01Far from it. Bohr's model only explains the spectrum of an element, hydrogen.
09:07Bohr travels constantly, he is invited to give lectures all over Europe.
09:11At the beginning of 1922, he is in Göttingen,
09:15the most relevant place of German mathematical thought.
09:18There he will meet a 20-year-old physicist who allows himself to be repaired,
09:22Werner Heisenberg.
09:24Impressed, Bohr takes him for a long walk through the field,
09:28talks to him about his research in progress,
09:30entrusts him with his doubts and hopes,
09:32and invites him to work in Copenhagen at the Institute of Theoretical Physics.
09:39Heisenberg will not be able to respond to this invitation until the Holy Week of 1924.
09:44In Copenhagen, he discovers the creative and informal atmosphere that reigns in the institute.
09:48Ping-pong seems to be the only truly experimental activity.
09:56For the next three years, Heisenberg spends much of his time with Bohr and his family.
10:02Little by little, a great friendship is established between the two men
10:06and a new vision of the atomic world.
10:09Unlike Bohr, Heisenberg rejects the analogies extracted from the visible world,
10:14takes away the idea of electronic orbits and focuses the problem under a purely mathematical angle.
10:19His model will lead to a statistical description of the atom.
10:22In a given place and at a given time,
10:24only the probability of the presence of an electron can be known.
10:31Atomic physics records a true explosion in Europe.
10:37In Copenhagen, around Bohr, atomic models and equations proliferate.
10:42Heisenberg, but also Wolfgang Pauli, Paul Gag and others develop the atomic model of the master.
10:50In 1922, the French Louis de Broglie suggested that if light is made up of particles,
10:56matter also behaves like a wave.
10:58From this idea, the Austrian Erwin Schrödinger builds another mathematical theory,
11:03the function of waves.
11:06In this way, he hopes to free physics from quantum mechanics,
11:09which he considers as gross dissonances in the symphony of classical physics.
11:14But after long discussions with Bohr and Heisenberg,
11:17Schrödinger ends up accepting the idea of quantum mechanics.
11:20What's more, he proves that his theory is logically equivalent to Heisenberg's.
11:26De Broglie, Pauli, Dirac and Schrödinger will all receive the Nobel Prize.
11:32But for Bohr, mathematical models are nothing
11:35if they do not lead to a true understanding of the phenomena themselves.
11:39And here, everything gets complicated.
11:41The undulating nature of light is demonstrated by a classical experiment,
11:45Young's grooves.
11:47Light is projected through a first screen perforated by two grooves.
11:51In the second screen, the lines are observed due to the interferences between the waves.
11:57But since the light is composed of particles,
11:59the photons can be projected one by one.
12:01After a moment, we find the same interference curve.
12:04It is as if the photon had passed through the two holes at the same time
12:08and had interfered with itself. Strange.
12:10Bohr and Heisenberg spend the whole autumn and winter of 1926
12:14engulfed in intense discussions, often during long walks through the field.
12:18They try to make a coherent image of the reality described by their equations.
12:22But how is it possible that light is both wave and matter at the same time?
12:25Heisenberg will tell later that at that time he was obsessed with a recurring question.
12:31Is it possible that nature is as absurd as it seems?
12:35The answer to which he finally arrives is the principle of uncertainty.
12:39It cannot be known with precision and at the same time the speed and position of a particle at a given moment.
12:46It is a bit like photographing an object in motion.
12:49If the lens opens for a long time, we will have an idea of speed,
12:52but the image will be blurred, we will not be able to truly see the position.
12:56Instead, if it opens for a very short time, we will see the position better and better, but less and less the speed.
13:03New times are dawning, exclaims Pauli, his old friend, when he learns of this result.
13:13These new ideas will be presented to the great physicists of the time
13:16as a result of a congress held in Brussels in 1927.
13:20Bohr has spent months writing an article about all his discoveries.
13:24He has been using every word to explain with the greatest possible precision
13:28what will later be called the Copenhagen Interpretation.
13:31He waits impatiently for Einstein's reaction.
13:33At that time, Einstein is no longer the young, discontented and isolated man of 1905.
13:39Little by little, the principle of relativity has been imposed.
13:43In a few years, Einstein achieves a celebrity that no other physicist has ever known.
13:48In addition, his personality and his anti-militarist postures
13:51have made him a public figure and a true symbol.
13:55In 1913, Max Planck invited him to return to Germany with the title of professor
14:00and total freedom in his research.
14:03After many hesitations, Einstein has accepted.
14:06In 1927, he holds a leading position at the Kaiser Wilhelm II Institute in Berlin,
14:11at the heart of the Prussian institutions of which he had fled in the past.
14:16Bohr then gives a speech and Einstein's reaction is not to be expected.
14:20He rejects everything in block.
14:22The next day, he proposes a first argument to try to break the principle of uncertainty.
14:28It is the beginning of the famous debate between Bohr and Einstein,
14:31which will continue until Bohr's death in 1949.
14:34Deep down, what opposes them are their different philosophical positions.
14:38Einstein continues to defend a deterministic vision of classical physics.
14:42The universe is a great clock, which has a hidden structure, but entirely decipherable.
14:49In the effort we make to understand the world,
14:52we are a bit like the man who tries to understand the mechanism of a closed clock.
14:56He can see the sphere and the hands that move,
14:59hears the tick-tock, but still does not know how to open the box.
15:07For Bohr, on the contrary, there is no hidden mechanism.
15:11On the contrary, under a certain scale, chance has a fundamental role in the description of the world.
15:16Therefore, the laws of quantum physics are expressed in a statistical way.
15:21This idea collides with Einstein's deepest convictions.
15:25He does not want to believe that chance can have a fundamental role.
15:28God does not play dice.
15:30For him, quantum theory is necessarily incomplete.
15:35For Bohr, on the contrary, uncertainty is a fundamental law of reality.
15:41But Einstein is not the only one who rejects quantum theory.
15:44In Germany, quantum and relativity are happily mixed under the same name.
15:49Jewish physics.
15:52Einstein's antifascist and pacifist positions have made him a preferred target for the Nazis.
16:00Little by little, the atmosphere in Berlin is becoming unbreathable.
16:03When Einstein embarked on his journey to the United States on December 10, 1932,
16:08he already had the feeling that he would not see Germany again.
16:11The Princeton Institute of Higher Studies officially offers a cathedral.
16:15When Hitler came to power, one of the first decrees of the new regime
16:19expelled all Jews from official posts.
16:24Part of the German university students, including Planck and Heisenberg,
16:28reacted by signing a petition.
16:30But it is too little and too late.
16:32Jewish university students and dissidents still abandon Germany,
16:36where Nazi health has become mandatory.
16:39The loss that this exodus means for Europe is tragic.
16:44Quantum theory and relativity
16:46will be condemned with the same title as Marxism and psychoanalysis.
16:50It is only Philip Lennart, Nobel Prize winner
16:53and author of the first experiments on the photoelectric effect,
16:56who directs the fight for an aria science.
16:58Jewish physics can only produce illusory images, hallucinations,
17:03and, at best, a degenerate effect of the aria physics.
17:07Heisenberg, although he does not feel any sympathy for the aria physicists,
17:11who will also direct his attacks,
17:13is too attached to his country to abandon it.
17:16He stays.
17:17What no one guesses, then,
17:19is that quantum physics will have an essential role during the war.
17:24In 1938, in Berlin, Otto Hahn obtains a spectacular result.
17:30Bombarding uranium with neutrons,
17:32he has found barium, a much lighter element.
17:36Lise Meitner and Otto Frisch
17:38will find the correct interpretation of this phenomenon.
17:41The nucleus of the uranium atom has been divided, releasing energy.
17:44This phenomenon will be called nuclear fission.
17:48Bohr is among the first to know the news
17:51that spreads like a powder keg through Europe
17:54and then through the United States.
17:56The nucleus of uranium has been broken.
17:58The word atomic bomb is on everyone's lips.
18:01Lézi Lart, a Hungarian physicist who then works in Colombia,
18:04is convinced that the Germans are already behind the bomb's trail.
18:09In August 1939, Bohr,
18:11who was the first to discover the atomic bomb,
18:15comes to see Einstein with a letter
18:18intended to warn the president of the United States.
18:23Since Hitler came to power,
18:25Einstein's attitude towards pacifism has changed radically.
18:28In the face of Nazi Germany,
18:30it is no longer the time to propose pacifism,
18:33which can only encourage the aggressive will of socialist Germany.
18:37We must close the path to Hitler with all available means.
18:40In September, the war breaks out,
18:42taking Europe by storm.
18:46When Pell Harbour's attack
18:48forces the United States to join the war,
18:50the spectrum of a Nazi atomic bomb reappears.
18:53Roosevelt decides that the United States
18:55must build the bomb before Germany.
18:59In June 1942, the Manhattan Project is launched.
19:02It is a scientific, technical and industrial effort
19:05of unprecedented magnitude
19:07in which quantum theory plays a fundamental role.
19:10Two billion dollars, 125,000 people
19:13and 20 Nobel Prizes from all the countries
19:16begin a dizzying race against German scientists.
19:19On July 16, the first atomic explosion
19:21takes place in the desert of New Mexico.
19:31Three weeks later, it is Hiroshima.
19:36The United States has won the race against the Nazis,
19:39but in reality this race has never existed.
19:41After the war, the Americans estimate
19:43that the Germans had only done
19:45less than 5% of the necessary work to make the bomb.
19:48In reality, the issue was resolved in June 1942.
19:52Heisenberg replied to the German military authorities
19:55that the manufacture of a bomb would require a colossal effort
19:58and could not conclude, in the best of cases,
20:01until 1945.
20:03Hitler wants to win the war quickly.
20:05He can't wait until 1945.
20:08The atomic bomb dossier is then definitively closed.
20:12Heisenberg will say later.
20:14The possibility of making atomic bombs
20:16created a horrible situation for all physicists,
20:19especially for us Germans,
20:21since the idea of putting the atomic bomb
20:23in Hitler's hands was horrible.
20:26His friends from before the war,
20:28especially his great friendship with Bohr,
20:30will never fully recover
20:32due to the ambiguity of his attitude.
20:35Quantum mechanics has projected a new light
20:38on the phenomena that take place inside the atom.
20:41It has allowed an extraordinary number of applications,
20:44from the laser beam to atomic energy,
20:46going through the integrated circuits
20:48that make up computers.
20:50But perhaps the essential resides in something else,
20:53in this radical strangeness
20:55that this theory has introduced
20:57in the heart of scientific thought,
20:59a strangeness to which Einstein
21:01has never wanted to surrender.
21:03The conflict between Bohr and Einstein,
21:05started in 1927,
21:07will continue after the war.
21:09It often revolves around imaginary experiments
21:12with which Einstein thinks he can prove
21:15the erroneousness of quantum theory.
21:17For eight years, he has proposed arguments
21:19that Bohr systematically dismantles.
21:21In 1935, he publishes an article
21:23in which he presents a new thought experiment,
21:26the EPR paradox,
21:28which seems to show that quantum mechanics
21:30is an incomplete theory.
21:33In certain conditions, it is possible
21:35that an atom emits two particles
21:37at the same speed, but in opposite directions.
21:40According to the principle of uncertainty,
21:42the position and speed of each particle
21:44are undetermined.
21:46However, it is possible to accurately measure
21:48the speed of one and the position of the other.
21:51As it is known that their speeds are equal,
21:53but their opposite directions,
21:55it is possible to deduce the position and speed
21:57of both particles.
21:59The principle of uncertainty seems to be in doubt.
22:01Quantum mechanics would then be
22:03an incomplete description of reality.
22:05Einstein seems to have shown
22:07that although they cannot be observed,
22:09the particles have at all times
22:11a given speed and position,
22:13as suggested by common sense.
22:15But Bohr maintains
22:17that quantum mechanics is complete.
22:19He insists.
22:21What Einstein says is logical,
22:23but particles do not obey common sense.
22:25They cannot be applied to the laws
22:27in force on our scale.
22:30The EPR paradox
22:32sums up the Bohr-Einstein debate.
22:34To choose one or the other answer
22:36is to choose a vision of the world.
22:38This debate will continue
22:40to be a philosophical debate until
22:42John Bell, an Irish physicist,
22:44proves in 1964
22:46that an experimental test can be carried out.
22:48The philosophical debate
22:50returns to the field of physics.
22:52Only after 15 years and a certain number
22:54of technical progresses
22:56can the experiment imagined by Einstein
22:58be carried out.
23:00Several scientists go to the task.
23:02The results obtained by Alena Specht
23:04of the Institute of Optics of Auxerre
23:06raise the controversy
23:08in favor of quantum mechanics.
23:10As unlikely as it may seem,
23:12Bohr was right.
23:14It is in fact the measurement
23:16made on one of the particles
23:18that modifies the quantum properties
23:20of the other, at a distance and instantaneously,
23:22that is, without respecting the barrier
23:24imposed by the speed of light.
23:26This time a great black hole
23:28opens in our vision of the world.
23:30The two particles, despite the distance,
23:32continue to form an indivisible whole
23:34that cannot be represented
23:36in space-time.
23:38The objects we know
23:40are not made up of little balls of matter,
23:42as was believed at the beginning of the century,
23:44but of an entity that we do not know
23:46how to represent other than
23:48the equations of quantum physics.
23:50At the moment,
23:52Heisenberg has the last word.
23:56These phenomena cannot be described
23:58as a process that takes place
24:00in space and time.
24:02Of course, this has not advanced much.
24:04In the end, only the fact
24:06that we know nothing has been expressed.