Great Physicists: Niels Bohr, the Father of Atomic Physics

[Music] welcome to real physics the channel about the fundamental laws of nature i'd like to start this series on great physicists with niels bohr the dominant figure of atomic physics at the beginning of the last century and of course this is not a biography with any aspiration to give a complete picture of his life just a personal assessment of his accomplishments the things that impressed me most bohr was a genius of intuition he had often the visionary idea everything was built upon and in retrospect such ideas may also seem quite easy because the concept behind is very simple i give an example everyone knows that the number of electric charges in the nucleus the number of protons determines the chemical element right so the entire system of chemical elements the periodic table discovered by mendeleev and meyer in the 1860s it just boils down to counting protons okay instead of talking about hydrogen helium lithium and so on you just say one two three four five proteins and that's it and this is a tremendous accomplishment it's one of the most important pieces of mankind's knowledge right if you want it completes the old idea of the philosopher democritus about matter consisting of elementary building blocks and someone had to understand it first it was niels bohr you might say someone else could have discovered it as well and incidentally saw the belgian chemist got the nobel prize for it but someone had to be the first and that was niels sport it's interesting that for such breakthroughs you don't need necessarily much mathematical sophistication and that particularly holds true for the atomic model named after board max planck in 1900 had discovered a very important constant of nature called the quantum of action and but it was einstein who discovered its uh real significance by uh finding the famous formula e equals hf for the energy of light quanta that was revolutionary because it fundamentally changed our understanding of light but on top of that it was nilspor who revolutionized our understanding of atoms by pondering over that strange constant of nature and again it's quite simple you write up the physical units rearrange them by using the definition of force and then you eventually realize that this unit which was originally energy per frequency turns out to be mass times distance times velocity which is a well-known quantity the angular momentum okay and this was the key for developing his model also the mathematician john william nicholson had expressed the idea but it was niels bohr who first understood that electrons orbiting the nucleus always carry multiples of h-bar as angular momentum and this was huge because for the first time you could see a reason why these electrons were allowed to stay only at a certain distance from the nucleus okay and when they jump from a higher orbit to a lower orbit they would release energy in the form of a light quantum this had been a mystery for decades and board discovery eventually explained the structure of atomic spectra found in 1885 by johann jacob palmer who analyzed the hydrogen atom and found his famous series formula which is valid for all shells and almost all atoms and you can hardly overemphasize this i mean this is the essence of quantum mechanics okay explaining this light spectra by first principles by using contents of nature and well you might say that the idea at the very end is simple but few people realize what leap of imagination was necessary at the time then to complete bohr's model a lot of brilliant and mathematically challenging work had to be done by heisenberg sheridan and iraq and boer probably was unable to do that sometimes paulie and heisenberg mocked bohr's lack of mathematical capabilities but without him the their own work would not have been possible or in turn defended heisenberg's most important finding the uncertainty principle against the continuing criticisms of albert einstein at the soloway conference in 1930 einstein came up with one of his famous ge duncan experiments seemingly disproving the uncertainty relation by a setup that precisely measured both the energy of an outgoing photon and the remaining mass and there it is said that poor had a sleepless night until he came up with his counter argument and ironically einstein had forgotten to take into account his own theory of general relativity and so well you might say poor defeated einstein at a very important point in the history of physics it's also interesting to look how physics was practiced back then in this scientific tradition people are discussing a lot at the personal level and the legion says that einstein and boar once absorbed by an argument forgot to get out of the streetcar and shuttle back and forth through copenhagen before eventually arriving at their destination board was notorious for his talking paul ehrenfest the dutch physicist complained that at the conference poor would knock at one o'clock in the morning at his door for just one word and that one word never finished before three o'clock in the morning there is another funny story when schroedinger visited boar in copenhagen in 1926 he was so overwhelmed by the discussions of poor that he fell ill but that didn't stop boar from sitting at the edge of his bed and continuing to talk to him surely you have to understand the principle of complementary complementarity and so on and paul durack who is on the other hand famous for not talking at all he he said a very very funny thing i had my abort very much we had long conversations long conversations in which poor practically did all the talking there was also i hate to say it but poor wasn't always clear in his uh in his phrasing in his writing and um he struggled to to express uh something properly but that struggle wasn't always successful allegedly in one of his papers about complementarity the pages got mixed up but neither the editor nor many readers didn't realize because it was so unclear and they didn't notice the change in pagination yeah unfortunately this weakness of por helped to dismiss the european tradition of physics as philosophy and particularly in post-war physics the predominant paradigm changed to calculation testing observation that's perfectly fine to test theories but i think that current physics is missing deep thinkers such as needle spore and i give you your last example one big riddle of physics is beta decay neutron decays into a proton and an electron and there is some energy missing we'll have a separate video on that but in short it was a mystery where i had this energy gun and wolfgang paoli 1930 postulated a new particle called neutrino that would carry along this missing energy and but to make the long story short um physicists today believe that there are electron neutrinos moving neutrinos tau neutrinos oscillations between them and now they're about to postulate the fourth fifth and sixth generation of neutrinos from the point of view of natural philosophy this is a mess that reminds you from the epicycles in geocentric astronomy and at boar's time everyone would have considered this ridiculous so i think that physics has gone straight back then and i have some sympathy for an idea of niels bohr expressed at a conference in san diego in 1930. and he said something very controversial energy might be violated okay we were talking about the energy loss during the beta decay and he said well who says that energy is conserved there was an outcry and the idea wasn't developed any further but i think it's very interesting because if you think about the about the cosmos why do we have all these quantities we have momentum because we want the loss of nature to be independent of position and physicists invented the concept of energy because we like the uh constancy of the laws of nature they shouldn't depend on time right but if you look at the cosmos that's not for sure at all there could be a slight change in the laws of nature and the concepts of nature and there are many riddles of physics uh dating back then in the 1930s which are not solved to this day and boar in a more general sense said that for resolving the riddles of the nucleus probably another revolution like quantum mechanics was necessary and i think that's a very interesting idea even if paul was not vindicated i think that current physics misses deep thinkers such as niels bohr he didn't give always clear answers but he was asking the right questions thank you very much for watching don't forget to give a like and if you're interested in fundamental physics subscribe to this channel

Channel: Unzicker's Real Physics

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Length: 12min 9sec (729 seconds)

Published: Fri Jul 31 2020