- In 1930, 28-year-old Werner Heisenberg wrote
an introduction to a book where he boldly stated
that the Copenhagen spirit of quantum theory
has directed the entire development
of modern atomic physics.
Soon Heisenberg's term, Copenhagen Spirit
was reframed as the Copenhagen interpretation.
And according to Wikipedia, the Copenhagen interpretation
is "one of the oldest interpretation in quantum mechanics
"and remains one of the most commonly taught."
But what was the Copenhagen Spirit
and where did it come from?
Aside from Copenhagen, Denmark of course.
This is mostly the story of the friendship
between Warner Heisenberg and Niels Bohr.
Ready, let's go.
♪ Electricity electricity electricity ♪
When 20-year-old Warner Heisenberg met 36-year-old
Niels Bohr for the first time on June 14th, 1922.
He was so excited he wrote his parents,
Bohr is the first scientists who also makes
an impression as a human being.
He's not just a physicist but much more.
With me he's always especially nice
and he has invited me to see him once again next week.
Heisenberg then quickly finished his PhD in Munich
and then got a job as an assistant to the physicist
Max Born in Goettingen.
Sorry Born and Bohr sound so similar.
At the time Born was working to try to "find the weak
"points and contradictions" in Bohr's semi-classical
theory of atoms.
By the end of 1923, Heisenberg has formed a new theory
and sent it his his friend Wolfgang Pauli
to send it to Niels Bohr.
Bohr immediately responded with an invitation to Heisenberg
to spend Spring Break with him in Copenhagen.
Wolfgang Pauli was particularly pleased to hear this
because he found Heisenberg's theory ugly
and without deep connections.
And Pauli wrote Bohr, I was therefore very pleased
that you had invited him to Copenhagen.
Hopefully then Heisenberg will return home
with a philosophical orientation to his thinking.
In Copenhagen, Heisenberg and Bohr got along like
gangbusters, discussing philosophy and physics
til midnight every night.
Soon Bohr worked out a deal so that Heisenberg
could complete his grant with Max Born in pieces
and then Heisenberg spent many months
of 1924-1925 in Copenhagen.
When Heisenberg returned to Germany
he used some of the ideas Born in his conversations
in Copenhagen to come up with a new mathematical
model for quantum mechanics,
which he gave to his advisor Max Born.
Born then realized this was a math concept called a matrix
and for six months, Heisenberg, Born
and Born's new student, Pascual Jordan created
a series of papers that are widely considered
the beginning of modern quantum mechanics.
Although the mathematics were terribly difficult,
Bohr was as excited as anyone.
Although, according to Heisenberg,
he wasn't very good at math.
Bohr was not a mathematically minded man.
He was, I would say, a Faraday but not a Maxwell.
As a historian I like that analogy.
Then in January 1926, Erwin Schrodinger
published a wave theory of quantum mechanics.
And soon there was a fierce debate between the two methods.
Which everyone assumed were incompatible.
However, by May both Schrodinger and Wolfgang Pauli
proved that they were mathematically equivalent.
This gave the advantage to Schrodinger
as his math was much easier and more importantly,
people, including Schrodinger himself
held the philosophy that using Schrodinger's theories
quantum mechanics could be made into a branch
of classical mechanics.
In July, Heisenberg went to a talk by Schrodinger
and was told to be quiet as "We are now finished
"with all that nonsense about quantum jumps."
Depressed, Heisenberg wrote Bohr that very night
and Bohr then invited Schrodinger to Denmark
to debate the issue.
Once in Copenhagen even Heisenberg was surprised
by the ferocity of Bohr's feelings on the issue.
Bohr now appeared to me almost as an unrelenting
fanatic, who has not prepared to make a single concession.
It will hardly be possibly to convey the intensity
of passion with which the discussions were conducted
on both sides.
It got so intense that when Schrodinger fell ill,
Niels Bohr's wife Margarethe while Niels Bohr continued
the discussions bedside.
Interestingly, Schrodinger had a far different view
of the encounter.
And a few weeks later we wrote a friend,
"In spite of all out theoretical points of dispute,
"the relationship with Bohr and especially Heisenberg
"was totally cloudlessly amiable and cordial."
Schrodinger was also quite surprised and a little
bit disappointed to find that someone of Bohr's fame.
He described Bohr as being honored almost like a demigod,
would be so shy and timid.
"Bohr talks often for minutes, almost in a dreamlike,
"visionary and really quite unclear manner.
"Partially because he is so full of consideration
"and constantly hesitates fearing that the other
"might take a statement of his point of view
"as an insufficient appreciation of the other."
Despite all the talk, Schrodinger remained unconvinced.
Then in October 1926, Wolfgang Pauli wrote Heisenberg
about a strange phenomena.
If he used Heisenberg matrices then the more he studied
the position of an electron, then noted with the letter Q,
but now use the letter X.
Then the harder it was to describe the object's momentum
or mass x speed.
Then and now denoted with the letter P.
Wolfgang Pauli wrote Heisenberg,
"One can look at the world with the P eye and one can look
"at it with a Q eye.
"But when one would like to open both eyes,
"then one gets dizzy."
In the beginning of 1927, while Bohr was on a ski trip
to Norway, Heisenberg realized that he could derive
this relationship, which he called the Imprecision Relation.
By mid-March Bohr returned to Copenhagen
and immediately noted problems with some of the concepts,
which left Heisenberg in tears.
After 10 days, that were described as very disagreeable,
Heisenberg edited the paper to Bohr's satisfaction
and published it on March 22nd, 1927.
Bohr happily then sent copies of the paper to Einstein
with a comment that he felt that it,
"represents most significant exceptionally brilliant
"contribution to the discussion of general problems
"of quantum theory."
Einstein was not impressed.
In fact, he hated it with a passion and Einstein debated
it with Bohr for the rest of his life.
Meanwhile, in about April 1927, Heisenberg and Bohr
were having conflicting arguments about quantum mechanics.
Heisenberg recalled, "we are unable to find the same
"language for the interpretation of the theory."
Part of it was a question of mathematics,
Heisenberg felt that we must realize
that our words don't fit.
They don't really get a hold in the physical reality
and therefore a new mathematical scheme
is just as good as anything.
Whereas, Bohr was determined to make it work
outside of mathematical.
His biographer wrote that Bohr believe that,
"Our words have to fit, we have nothing else."
Bohr's assistant recalled that these disagreements
about Heisenberg's work became a source of inspiration
and Bohr decided that quantum mechanics
needed new works to describe physics
that didn't originate in classical theories.
According to Bohr's assistant, Bohr dictated
and the next day all that he had dictated was discarded
and we began anew.
So it went all summer.
Buy July 1927, Bohr published an article
originally titled The Philosophical Foundations
of Quantum Theory.
Ironically, Bohr's devotion of the science
of how to communicate quantum mechanics without math
was incredibly difficult to follow especially
in the beginning.
So I'm gonna give you his biographer's paraphrasing of it.
The question of whether an electron is a particle
or wave is a sensible question in the classical context.
Where the relations between object of study
and detector needs no specification.
In Quantum mechanics that question is meaningless however.
There one should rather ask,
does the electron or any other object behave like a particle
or like a wave?
That question is answerable but only if one specificies
the experimental arrangement by means
of which one looks at the electron.
Bohr called this complementarity.
Pairs of complementary properties which cannot
all be observed or measured simultaneously.
Like position and momentum
or wave versus particle properties.
The debates about the uncertainty principle
and Bohr's philosophies got so intense that the Solvay
Congress decided they could no longer continue
their embargo of German scientist and dedicated
their entire meeting to the debate.
At the conference Einstein would wake up every
morning to give Bohr a new thought experiment
that was supposed to disprove uncertainty
and Bohr would find a solution by dinner time.
Meanwhile, by June 1927, 25-year-old Heisenberg
was offered a position as a full professor in Leipzig,
making him the youngest full professor in Germany.
Heisenberg became dedicated to starting a world-class
physics program in Leipzig
with deep connections to Bohr in Copenhagen
and Born in Gottingen.
And for a few years every physicist worth his or her salt
learned German and went to Leipzig, Copenhagen or Gottingen.
And usually all three.
By 1928 any disagreements between Bohr and Heisenberg
were completely passed.
Heisenberg wrote Bohr apologizing for his ungrateful
behavior and Bohr replied, "Rarely have I felt myself
"in more sincere harmony with any other human being."
In February 1932, the English scientist James Chadwick
discovered the neutron, which is a heavy chargeless
material found in the nucleus.
When Bohr found out about it,
he immediately wrote Heisenberg.
Here we have become very interested in the neutron problem.
Where upon Heisenberg also wrote his own paper
on the neutron to "apply quantum mechanics to the nucleus."
Bohr's liquid drop model ended up having major
implications for the development of quantum mechanics
and the development of the nuclear bomb.
Heisenberg's theory from this time, as far as I can tell,
was discounted pretty quickly as he assumed the neutron
was just an electron and proton sort of smushed together,
which violated Heisenberg's own uncertainty principle.
In January 1933, Heisenberg and Bohr's relationship
got much more challenging because Hitler came to power.
Heisenberg was convinced he was a flash in the pan
and tried to convince all the scientist he could find
to stay in Germany or if they were forced to flee
that it was only a temporary thing and maybe they should
just take a leave of absence.
Bohr had no such ideas, was very concerned about Hitler.
And formed committees, which eventually helped
over 300 scientists.
Years later Bohr's wife Margarethe recalled.
Oh the 30s were such terrible years.
There we nearly collapsed.
I remember when we went to America in '33 we had such
a long list of people for whom we should try to find places.
In addition, despite the fact that Bohr wasn't at all
religious, he had something personal to fear from the Nazis
because his mother was Jewish.
Despite their differences on politics, Bohr
and Heisenberg continued to be very close and visit often.
Meanwhile, Heisenberg formed a very very close relationship
with his student, Carl Friedrich von Weizsäcker
and according to Heisenberg,
"I saw Weizsäcker almost daily during the years 1931 to 35."
For example, in October 1934, Heisenberg wrote his
mother that the only way he could understand the rise
of Hitler was with the friendship of Carl Friedrich
who struggles in his own serious way
with the world around us.
Heisenberg's relationship with Weizsäcker got a little
bit more complicated in 1936 when 34-year-old
Heisenberg fell in love with Weizsäcker's 19-year-old
sister, Adelaide and her parents rejected the suit.
A few months later Weizsäcker ended his assistantship
with Heisenberg and started an internship
with Lise Meitner in Berlin.
Their friendship remained a little distant until 1939
at the start of the war, when Weizsäcker invited
Heisenberg to join the Uranium Club to study
the military aspects of nuclear fission.
Back in 1936, Heisenberg felt very lonely without
the young Weizsäcker.
But then in January 1937, he met a young woman named
Elizabeth Li Schumaker and two weeks later they
were engaged.
Heisenberg wrote Bohr that we would be worried
about being a successful scientist and family man
if it weren't for the great example of his idol, Bohr.
After their quick marriage, Heisenberg brought his new
bride to Copenhagen to meet Bohr.
In Copenhagen Margarethe Bohr was a bit disturbed
by the politics of her husband's protege and his wife.
Margarethe took Li on a private walk away from prying eyes
where there was no fear of being overheard
and said, "Wouldn't it be nice for you to get rid
"of this terrible government and get some decent people?"
To which Li replied,
"Oh, but what would we do without a Fuhrer?"
Margarethe recalled, that was the attitude of nice
young Germans so I gave up.
As far as I can tell, Niels Bohr and Werner Heisenberg
did not see each other for over four years.
But the drought ended in September 1941,
when Werner Heisenberg went back to Copenhagen
and Heisenberg wrote his wife, "I am once again in the city
"where part of my heart has stayed stuck."
But much had changed, Germany had been at war for two years
by this time and although Denmark had tried
to stay neutral they had been occupied by the Germans
16 months earlier.
So Heisenberg wasn't just a visitor,
he was a representative of a repressive regime
that was oppressing their country.
This time Heisenberg's pro-Nazi comments were too prevalent
to be ignored by Niels Bohr.
And even stranger Heisenberg told Bohr outright,
that he was working on nuclear bombs for Hitler.
Which brings up the question, why?
And that mystery is solved next time
on the Lightning Tamers.
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Have a good day.
(upbeat music)
Which would turned. (rolls tongue)
Oppressed them about 16 months before as well.
(mouth jarbles)
Let me do it again.
That's good.