- Niels Bohr said later in
his life that back in 1913, almost nobody thought
that the colors of light that you get from burning hydrogen would tell you anything about physics even though they follow a pattern. He said it was just like
butterflies have patterns with color on their wings, but, "nobody thought one
could get the basis of biology from the coloring on the
wings of a butterfly." However, in February 1913, 27-year-old Niels Bohr read a
book about the spectral lines of hydrogen and everything clicked. Within weeks, he wrote a paper
that revolutionized physics. Ready for the story? Let's go. ♪ Electricity, electricity ♪ ♪ Electricity, electricity ♪ I like to start two years before then, in September 1911, when 25-year-old Niels
Bohr went to Cambridge. He was so excited, he
wrote his fiancee Margrethe that he "rejoiced" when he, "happened to read the address
Cambridge over the door." Bohr was thrilled with the opportunity to work in a top-notch department with the incomparable JJ Thomson, who had discovered the
electron 14 years earlier, and his dizzying array
of influential students. Instead, it was a total disaster. The students didn't want
to talk to a mumbling Dane with weird ideas and his relationship
with JJ Thomson started on the wrong foot. Because on the very first day, Niels Bohr went to Thomson with a copy of one of
Thomson's books, opened it up, and told the Nobel Prize
winner in halting English, "This is wrong." Bohr actually thought this
first conversation went well, but after a few weeks, it became clear that it didn't go so well. And he wrote his brother Harold, "Thomson has so far not
been as easy to deal with as I had thought on the first day. He has not yet had time to read my paper, and I do not know if he
will accept my criticism." For the next three months, Bohr was miserable and mostly alone. Then on December 6, 1911, his life changed when JJ Thomson had this annual dinner for his current and former students. This was a strangely raucous affair. I mean, it was a formal dinner with formal attire and 10 courses, but also people would
stand on tables and chairs and sing limericks and songs about physics and about Cambridge. ♪ Oh my darlings, oh my darlings ♪ ♪ Oh my darlings, ions mine ♪ ♪ You are lost and gone forever ♪ ♪ When just once you recombine ♪ So yeah, physicists were dorks then, too. We didn't just invent it. And for dessert, they serve plum pudding. This was also a dorky physics joke because the accepted view of
atoms came from JJ Thomson and was called the plum pudding model where Thomson imagined
that the negative electrons were like the raisins, or if
you're British, the plums, in a sea of positive pudding. However, this was a slightly
controversial dorky joke as Thomson's former student,
Ernest Rutherford was there. And nine months earlier, Rutherford had proposed
a new model for atoms, which was not food related, and which Rutherford thought
was, "superior to JJ's". At this time, Rutherford
was only 40 years old, but he had already discovered
alpha and beta radiation, discovered the half-life of radiation, and use that to suggest a method to determine the age of the
earth that we still use, and determine that radiation
can change the atomic number of a material, for which
he won a Nobel Prize, and had accidentally
determined that alpha particles can bounce off thin pieces of metal. Whew! Rutherford is amazing. Anyway, that accidental discovery that alpha particles can bounce off thin pieces of metal sometimes was what made Rutherford think that the plum model wouldn't work. Rutherford realized that the
scattering of alpha particles "must be the result of a single collision. And when I made calculations, I saw it was impossible
unless you took a system in which the greater part
of the mass of the atom was concentrated in a minute nucleus." This is why on March 7th, 1911, Rutherford wrote a paper where he assumed that atoms were composed with, "a positive charge Ne
at the center and surrounded by a distribution of
negative electricity Ne uniformly distributed within
a sphere of radius R." By the way, Rutherford wasn't
wedded to this whole idea of the electrons being
uniformly distributed as he also mentioned the work of a Japanese scientist
named Hantaro Nagaoka, who had made a Saturn model of the atom, where the electrons were in a
ring around a positive center. Honestly, Rutherford really
wasn't that concerned about the electrons. Anyway, Rutherford's model was almost universally
disliked and ignored. For one thing, it made
solids not very solid For example, if an atom was expanded to be the size of a cathedral, the nucleus with 99.9997% of the weight would be the size of a fly. Moreover, Rutherford's atom had a significant physics problem. Opposites attract, so what
keeps the negative electrons from being sucked into
the positive nucleus? Even if the electrons are spinning around the nucleus like planets, they would be accelerating charges. Spinning is a form of acceleration, which should, according to Maxwell's laws, be creating electromagnetic waves, which would cause the
electrons to lose energy and spiral into the nucleus. In other words, according to
the laws of classical physics, Rutherford's atom should just implode. Not surprisingly, JJ Thomson
was particularly displeased with this model and the students that
Cambridge followed suit. In 1962, Bohr was asked
if he was the only person at Cambridge who responded
well to Rutherford's atom. And he replied, "Yes, but you see, I did not even respond to
it, I just believed it." At that dinner in December 1911, Bohr realized starkly that he
was working for the wrong man. Here was the physics and the
physicist that he needed. It didn't hurt that Papa
Rutherford was a big, loud, exuberant New Zealander,
described by contemporary as "always a charming blend
of boy, man, and genius." Bohr sheepishly asked JJ Thomson if he could spend some time
in Manchester with Rutherford to learn a little bit about radioactivity, and Thomson let him but
made him stay in Cambridge for the winter term. By March 1912, Bohr
had moved to Manchester and wrote his brother that he was working "in a lab full of characters
from all parts of the world, working with joy under the energetic and inspiring influence of the great man." After a few weeks of
working in this laboratory, that was very well run, Bohr decided that experimental
work just wasn't for him, and told Rutherford that he would like "to concentrate on theoretical things" and basically never experimented
in any laboratory again. Rutherford usually hated theoreticians, but he made an exception for Bohr because he thought Bohr was brilliant, and also because Bohr was
really good soccer player and Rutherford respected that. Anyway, at the time, Bohr was fascinated to learn about the Solvay Conference that Rutherford had gone
to in October of 1911. At this conference, it
became clear to everyone that quantum ideas were here to stay. As a scientist, Marcel Brillouin
said at the conference, "From now on, we will have to introduce into our physical and chemical
ideas a discontinuity, something that changes in jumps, of which we had no notion
at all a few years ago." Brillouin was a little late to the game as Max Planck and Albert
Einstein had these ideas more than a few years by this time. How to introduce quantum ideas and how to make it work with atoms, no one, even Einstein, knew. In fact, Einstein started to joke that quantum ideas would drive you crazy and told a friend that, "The h-disease looks ever more hopeless." According to Bohr, Rutherford
wasn't that interested in what he heard at the Solvay Conference and just said it is odd. But Bohr, once again, just
believed. In mid-July. Bohr wrote Rutherford (in
the reverse of Einstein) that you needed quantum
theories to describe atoms as, "It seems hopeless," with
only classical mechanics. By the end of July,
Bohr returned to Denmark and to his fiancee Margrethe Noland. A small comment about their relationship, because I think it's important for understanding how Niels Bohr worked. So when Bohr was depressed at Cambridge, he wrote his fiancee a letter, worried that she wouldn't
be interested in his work, and she replied, "Oh, dear Niels, I cannot at all describe
to you how much I love you and how much I love your work, and I cannot distinguish you from it. And I cannot at all describe to you how much I long for the future, for being allowed to help
you a little sometime if only I can." Niels Bohr was elated by this response and wrote her a letter
asking her for her help. "To try to lead a great and active life. My head is so full of
plans, and they are all, all of them, based on you." They married in August of 1912, and Niels Bohr would
dictate all of his paper and Margrethe Bohr would
edit them, transcribe them, and be a source of logic and sanity. Even after they had six sons together and he got an assistant, nothing could be published
without Margrethe's approval. Anyway, soon after the
marriage in September 1912, Bohr recalled that he, "Went
into the country with my wife and we wrote a very long paper
on these various things." However, it didn't go very well. And Bohr wrote Rutherford
that he was facing "some serious trouble" with the work and nothing productive
happened for months. Then in February 1913, Bohr was discussing some of his theories with a colleague and the colleague asked him how it worked with the spectral lines
from burning hydrogen. Bohr was astonished. He had forgotten that there were equations for how light was emitted
from various glowing gas. It turns out the back in 1885, a 60-year-old school teacher
named Johann Balmer had noticed that the frequency of
light from glowing hydrogen follow the geometric pattern where the frequency
depends on the difference of the reciprocal of two integers squared. Amazingly, Bohr didn't know, or had forgotten, about
this empirical formula, meaning a formula based on experiment with no theoretical backing, until he read about it in February 1913. Years later, he recalled, "As soon as I saw Balmer's formula, the whole thing was
immediately clear to me." In less than four weeks,
Niels and Margrethe Bohr banged out one of the most
influential papers of all times. In this paper, Bohr
started with one electron and assumed it was going in a circle or a shell around the nucleus, where the electron is limited, and that it can only be
at certain set distances from the nucleus where the lowest energy corresponding to the
closest to the nucleus is now called the ground state. What about the problem
of the spinning electron radiating out energy and then
spiraling into the nucleus? Well, Bohr just declared it didn't happen. Really, this was described
by Bohr's biographer as, "One of the most audacious
postulates ever seen in physics. [Bohr] simply declared that
the ground state is stable, thereby contravening all
knowledge about radiation available up 'til then." Bohr then made two more
radical assumptions. First, he assumed that
the electron was spinning around the nucleus with an
energy equal to an integer times Planck's constant times the frequency of
spinning divided by two. Why divided by two? Well, he gave an awkward explanation. Years later he said that was
confusing because of the, "stupidity of the way of writing it." His words, not mine. Don't get mad at me. But he said it had to do
with averaging the energy that was zero once the electron was free. He also might've divided by two because then the results
worked amazingly well for the hydrogen spectrum,
and he backtracked to find a reasoning that would make sense. With this assumption and
equations for electrical force and electric energy, Bohr could determine the
position of the electron as a function of fundamental constants, and Bohr got that the radius of electrons is a constant times an integer squared. So the possible radiuses
would be r, 4r, 9r, 16r, I think you get the pattern. As the distances depend
on an integer squared, And the energy depends
on one over the distance, the energy depends on one
over an integer squared. Bohr made one more assumption, this one even more
radical than the others. He decided energy of the
light, the radiation, came not from the energy of the electron, but from the change in
energy when it jumped in a quantum leap from
one shell to the other. This was an absolutely
new and radical idea, so crazy that when
Einstein heard about it, Einstein admitted that,
"He had one similar ideas, but he did not dare publish them." With these assumptions, it
was a basic physics problem to make the change in energy
equal Planck's constant times the frequency of light emitted and get an equation for
the frequency of light that is possible to be
emitted from a hydrogen atom. Bohr not only gotten the
equation from fundamental ideas that fit the hydrogen spectrum equation, he also derived the constant in front, called the Rydberg constant
from fundamental constants. But Bohr wasn't done yet. It turned out that he
could use his equation to explain a mystery of spectroscopy called the Pickering series, which was a series of shadows from a star that looked like half
of the hydrogen lights. Now, in order to tell
the Pickering series, I'm gonna tell you the
little bit of the backstory because it's fabulous. The Pickering series
was actually discovered by a woman named Williamina Fleming. Now Williamina was a
school teacher in Scotland, and then when she was 21 years
old, she moved to Boston. But then after two years in Boston, her husband left her pregnant
and alone and destitute. Luckily, she got a job as
a maid to Edward Pickering, a professor of astronomy at Harvard. The story goes that one day
Pickering was complaining to his wife that his
assistants were so bad his maid could do a better job. And his wife said, "Actually, you have a maid who
could do a really good job. Give Williamina Fleming a chance." And he did. Pickering was amazed to find that Fleming was a naturally
fantastic astronomer. And by 1881, after the
birth of Fleming's son, Edward Pickering Fleming, he
hired her as his assistant. In 1886, Pickering was given
a moderately large sum of cash by the widow of another
astronomer named Henry Draper to use photographic spectroscopy to catalog as many stars as possible. The next year, Pickering
put Williamina Fleming in charge of the project, and she hired an army of
women to study the stars. Pickering specifically wanted women as they were cheaper than men, and he wanted to prove to the world that women could make
scientific discoveries. Pickering called the women his computers as they computed thing, but his rivals called them his harem. Anyway, while cataloging the spectrums from over 10,000 stars, as well as discovering four new stars and discovering white dwarves, she noticed something
strange with one star. It had an odd spectrum. It seemed to have only
half the hydrogen lines and Pickering and Fleming
published an article called "Stars Having
Peculiar Spectra" in 1896. The following year, Pickering published that these lines were from hydrogen that followed a half
integer transition level. Fast forward to 1913, Niels Bohr realized that these spectral
lines could be explained if they came from ionized helium, meaning helium with only one electron instead of the usual two, where, because the helium has
two protons instead of one, that would multiply the possible
frequencies by two squared and one would no longer need
the halves in the equation. By March 6, 1913, Niels Bohr
sent his paper to Rutherford to have it published in England, and Rutherford had mixed
feelings, writing Bohr, "Your ideas are very ingenious
and seem to work well, but the mixture of Planck's ideas with old mechanics make it very difficult to form a physical idea of what
is at the basis of it all." Yeah, that is a problem with
quantum mechanics, isn't it? After Bohr visited Rutherford in April to hash out the details, Bohr published the first
of his three papers on this model in July of 1913, and it was the talk of the
town for every physicist. Niels Bohr's brother Harold
was in Germany at the time and told Niels that everyone
wanted a copy of the paper, but most found it a little
too radical for their tastes. A scientist named Carl Runge's sighed, "Well, Bohr is such a nice
man and so intelligent, but this man has become completely crazy. This is the sheerest nonsense." Eventually, he would change his mind and they would become close friends. But not everyone hated
Bohr's paper on site. Many young scientists were
very excited about it. One of Bohr's only friends from Cambridge, a man named Georg de Hevesy, happened to be in Berlin at the time and talked to Einstein. And Albert Einstein told Hevesy that if Bohr's theory was right, it "is of the greatest importance." According to Hevesy, when Hevesy told Einstein
about the results with helium and the Pickering lines, the "big guys of Einstein's
looked still bigger," and Einstein remarked, "Then the frequency of
light does not depend at all on the frequency of the electron. This is an enormous achievement! The theory of Bohr must be right." Later in Einstein's life,
Einstein recalled that in 1913, "All my attempts to adapt
the theoretical foundation of physics to this quantum
knowledge had failed completely, [which is why] Bohr's theory
appeared to me like a miracle and appears to me as a miracle even today. This is the highest form of musicality in the sphere of thought." It's important to note that
no one, including Bohr, thought this was a complete theory. It was obviously a makeshift theory that barely worked with one electron, but it gave a path forward. And the idea that radiation
is due to quantum change in energy is a fundamental
concept of physics that is still used to this day. Still, Bohr knew that spinning
electrons do radiate energy. So what's going on with the electron? By 1927, with the help of Heisenberg's uncertainty principle, Bohr came up with his answer:
you can't ask that question. You can't ask what the electron is or what the electron is doing. You can only ask what can you
measure about an electron. This viewpoint, currently called the Copenhagen interpretation, is the most commonly taught interpretation of quantum mechanics,
and Einstein hated it. It quickly became a huge debate
between these two friends, involving God playing dice,
spooky action at a distance, a disappearing moon, and a cat that maybe is
alive and maybe is dead. The great Bohr-Einstein
debate is next time on the Lightning Tamers. Thanks for watching my video. If you're interested in more
details about Rutherford, or JJ Thomson, or the
history of radiation, or Einstein, or Max Planck,
I made a lot of videos, you can go check them out. I'll see you next week. As usual, a big thank you to my patrons. Thank you, patrons. If you wanna be thanked too,
there's a link down below. And don't forget, put a thumbs
up, share it on social media, put a comment, even if you're
just saying "Hi, Kathy." Hi! And also, obviously, I'm gonna make a video
about Williamina Fleming. I just learned about her two days ago, and Pickering and his harem
of female human computers because... Yeah, that's pretty cool,
and I love that stuff. Okay, you stay safe out there, okay? Bye!
I have a professor from Denmark at my university and his professor was a student of Nils Bohr. These stories are not as long ago as they feel like. We gathered so much knowledge in such a short time, it's crazy when you think about it.
This is great. Looking forward to watching more of your videos!
This was absolutely lovely!
Very nice, well researched and well told video! Must have taken a long time to compose - I appreciate the effort. I learned a lot of fascinating history.
Subscribed
"The Boring World of Niels Bohr" r/simpsonsdidit
Very enlightening and entertaining! I just an hour earlier finished watching a 3 episode series called Atom on Amazon Prime and it was great to learn more details through your video!
It’s utterly amazing to me how many brilliant physicists there were in the early 1900s who literally created the foundation and paradigmatic shift in our understanding of the world and cosmos.
Crazier to me is the fact that in the history of our time on Earth, this quantum leap in understanding began barely 100 years ago and look at the rapid advancements (both impressive and scary) we have made as a result of these brilliant minds in this short amount of time.
It makes me wonder what might we learn or accomplish in the next 100, or 1000 years as a result of this foundation.
wow, thanks!
Thanks you for make me aware of this YouTube Channel.👍