- 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.
Thanks for watching my video,
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Okay, remember to stay safe
and be nice to each other.
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.
