Einstein and the Quantum: The Quest of the Valiant Swabian
>> Amy Draves: Thank you for coming. My name is Amy Draves and I'm here to welcome
Douglas Stone to the Microsoft Research visiting speaker series. Doug is here to discuss his
book, Einstein and the Quantum in which he examines Einstein's early career and foundation in
quantum mechanics. He is the Carl A. Morris professor and chair of the applied physics
department at Yale and has been the recipient of several awards and honors including the
Alfred P. Sloan fellowship, a Rhodes scholarship and the Presidential Young Investigator award.
Please join me in giving him a very warm welcome.
>> [applause]
>> Douglas Stone: Well, thank you Amy for inviting me and you know this is a small room. Do I
need the microphone for the people on line?
>> Yeah.
>> Douglas Stone: Oh I do, okay. Too bad, because I hope I'm not blasting them out. I'll try to
talk, I get excited and my voice elevates. So, it's a pleasure to be here to talk about this book.
I'm a first-time author, I'm actually mainly an active physicist doing work, theoretical work
relating to lasers and microelectronics. But I had this previous existence as an undergrad and as
a Masters student studying philosophy and things like that so I got an opportunity which I'll tell
you about to sort of exercise that part of my brain in writing a book for popular audiences
which is something I wanted to do for a long time but I didn't know whether people would be
that interested in PT symmetric wave equations, so I couldn't figure out how to do a popular
book on that. This seemed little more accessible, at least of more general interest.
Okay, so I'm going to say today in my lecture, how did I come to write this book, why write
another book on Einstein. There are thousands of books on Einstein and some of them are
actually pretty good. And after explaining those things I'll just give you a flavor some of the
dramatic episodes in the history of science that actually got me excited to write this book which
are not as well-known as the episodes recounted in those thousand other books. And I'll say a
little bit about what Einstein was like. One of the fun things in this project is was that I was able
to read all his letters from essentially 1896 up to the 1920s. Those are the ones are all published
and translated in his papers, so you really get a sense of what kind of person he was and then
finally many of you may know that the thing that's most famous about Einstein in quantum
theory is that he didn't like it. He actually refused to work on it and remained a doubter that it
was the complete truth until the end of his career, until he died in the 50s. So, the actual
subject of this book is somewhat surprising because it's all about how fundamental his
contributions actually were to quantum theory. So this came about because I was working in a
branch of modern quantum theory called quantum chaos where you try to understand how
chaotic systems that would classically behave in this strange unstable way actually interact with
the laws of quantum mechanics and what's the manifestations are of that chaos and my PhD
student shown here, Hakan Tureci, now professor at Princeton was trying to write the
introduction to his thesis and he was having trouble explaining the fundamental essence of this
problem. And I said you know I heard Einstein wrote something about this in 1917 so you know
maybe Einstein can solve our problem. So, and it is true that he wrote a paper in 1917 that's
relatively obscure. I talk a little bit about it in the book, but it's a little bit too technical. It's not a
historic paper, but it's a fabulous paper which has been misunderstood and I read that paper
and ended up actually using Einstein's approach to explain what was going on with this problem
and I found myself thinking for the first time in a long time, wow this guy was really a genius.
Right, this is a very minor paper for Einstein but for me it would've been a career shaping paper
and is a little bit like Beethoven who I'm going to come back to at the end where you know,
you just taken for granted. You don't really think about him if your composer in the 21st
century. You're not necessarily, you learn about Beethoven a long time ago and haven't thought
about him too much. So, because I studied this one paper and then wrote this article explaining
it in physics today, I knew this tiny little corner of Einstein's work but it was 2005. Do people
here know what was special about 2005? Someone must know.
>> [Beethoven]
>> Douglas Stone: Right, so what was the hundredth anniversary of his so-called annus
mirabilis, miracle year when he wrote four papers that revolutionized physics and so they had a
big celebration. It was the world year of physics and it was sort of a run on people that could
talk about Einstein and so they even got down to people like me who, you know I said I only
know this one little paper guys. But they didn't want to hear about that one little paper, so I
had to cram on Einstein and quantum mechanics and as I did this cramming so I could talk
about something more general, I came to this stunning realization. Okay, so I will concede that
Einstein has received a reasonable amount of attention in the scholarly literature in the media
literature, nonetheless I came the realization that he doesn't get enough credit, which is pretty
shocking. At least this Einstein, the 1905 guy who I really like doesn't get as much credit. That
actually eventually, I didn't still plan to write a book, but then after I give a few talks, people
kept saying well where can I buy your book and so, anyway the rest is semi-history.
Okay, so the reason this is so important is that quantum mechanics is a turning point, the
discovery or the invention however you want to put it up quantum theory and quantum
mechanics is a turning point in human civilization. Basically around 1900 physics had run in,
chemistry had run into this fundamental roadblock. We didn't really understand the laws that
governed the atom. Okay, so all of science had been culminating to this point where either we
were going to be able to understand the unseen realm of the atom or we weren't. And for a
while it was in doubt. It took 26 years, it basically started in 1900 and it wasn't until 1926 that it
was more or less the big breakthrough occurred and as late as 1924 people were despairing and
I actually read in my studies, people saying maybe humans who evolved to you know, hunt
mastodons on the savannas just are not capable of understanding the atom. There's no reason
that we are necessarily going to be able to understand this unseen realm, but it turned out we
were able to. So the fact that the most famous physicist in history actually played this key role
which is not appreciated makes this I think an interesting book in the history of ideas. And of
course as people here will know, the success in understanding the atom unleashed the
technologies of the 20th and 21st centuries. So, and just one example relevant to what
everybody here probably is involved with his old versus new electronics.
Basically we understood a lot about electricity and magnetism in the 19th century and we could
make components like this, this is a transistor, you know about an inch or two long. Was based
on a vacuum tube and then we could gang them together and we can make an amplifier or
something like that with this. But the big change came in the 40s and 50s when we started to
understand how to build electronics at the micro and even nano scale were this is now the
same kind of device, a transistor but on this hundred nanometer scale of modern printed
integrated circuits. So to understand how to build electronic devices into a material at the
microscale, we absolutely had to know the laws of quantum mechanics and the quantum
structure of matter. Okay.
So let me start with a little biographical information about Einstein. Some of you may be big
buffs, others of you may not be. So he was born in 1879 to an aspiring somewhat struggling
middle-class secular nonreligious Jewish family. There was engineers in the family and they had
an engineering firm. This was in Ulm Germany where he was born. He was educated in Munich
till age 14 and he was an excellent student unlike the urban legends. I'll go into that more if
you're interested. But he always had this kind of slightly superior look to him that annoyed his
authoritarian German teachers. One of them, the Latin teacher Dagenhart told him that you
know he'd better shape up and Einstein said, you know I haven't said anything and Dagenhart
said, your mere presence here in the class undermines the classes respect for me. So something
about the way he was behaving with respect to authority would persist through life was
showing up there. And I think he really was a bit of a pain as a student having read all these
letters and incidents. Okay, so at age 14 he actually just drops out you know unbeknownst to
his parents who have moved to Italy because their engineering venture has failed in Munich. He
shows up at their doorstep, nice Jewish family, brilliant sun. He's dropped out of school, what's
going on here, you know. So he says, don't worry, don't worry I have a plan. You don't need a
high school degree to go to the Zürich Polytechnic which is now the ETH in Zürich and he would
just study himself, which he did and take the entrance exams. So he tries the first time any
actually excels in math and physics and would've passed. He's only 16, so he's two years
younger than they normally accept. He does very well, he doesn't do so well in history and
French and so on, so he technically fails and then he goes for another year of schooling and
then he gets in. Okay, and then for the first two years he's the top student in the physics
section, he's very popular with professors and then something changes. He realizes that they
are not going to teach him about the modern developments in physics, particularly really about
electro-magnetic theory which she's very interested in. So he stops going to class, his
performance plummets. I love the antic dote in the experimental class. They hand him a chit or
an instruction sheet. And he would not look at it, and he would walk over and they just drop it
in the waste basket and try to do the experiment without looking. And he eventually did cause
an explosion in the lab and so on, so he failed that class. And so he barely gets his degree and
he is refused an assistant's position. Heinrich Vaber who is the head of the physics division who
initially really supported him was so mad at him that he engaged to engineering students as his
assistants instead of hiring Einstein. So he's essentially almost kicked out of academia there.
While he was at the Polytechnic he falls in love with his classmate Mileva Maric, a Serbian
woman. Very unusual to have a woman student in the class, and there they are at their
marriage photo in 1903. And they have three children, but eventually their marriage falls apart
in 1913 when Einstein is wooed a way to Berlin after many, much has happened that I will get
to. And eventually they are divorced in 1918. For the next two years he is literally penniless. He
ekes out a living giving private lessons and then he finally gets a job at the famous patent office
in Bern because his friend Grossman's father has pull there. But he never gets discouraged.
There's this quote in the letters of the time, "I am a cheerful fellow and have no talent
whatsoever for melancholic moods". Now another thing, he's just such an ebullient character
that it really attracted me. One thing that I got a kick out of is that he used to sign his letters to
his wife with his sobriquet, The Valiant Swabian. The valiant Swabian is not afraid. His family is
from Swabia which is a region in Germany and there's this poem about a Crusader knight
Devacarer Scwabe, something like that who is somehow the heroic essence of what it means to
be a Swabian. And he would sign his letters that way, little bit like someone signing their letters
Indiana Jones, something like that. So, he had this kind of very outgoing and very you know just
a lot of joie de vivre. His life, here's a picture of him as a student at age 19 at ETH. He sort of
looks like that there. And then this is a little bit later, in 1904 with his first son Hans Albert and
Mileva.
Okay, so now let me talk a little bit about the science. That's a little overview of the biography,
and I can certainly tell you more later if you're interested, but let's talk about the science. So in
1900, Max Planck begins the quantum era and I'm going to, you go to that episode shortly.
That's the episode that started me working on the book. In 1905 we have the miracle year, I'm
putting down quanta of light, special relativity, E=mc2. He also did this famous work on
Brownian motion which I don't talk about at all. In 1906, 1907 he did a very important but very
underappreciated work on quantization of energy. I'll explain a little bit about what that means
and quantum theory of specific heat of solids. That was actually incredibly important, not very
well appreciated. 1908, he did work on wave particle duality, we'll come back to that briefly.
And he did a failed theory, quantum theory of light. Then, from 11 to 15, he works on the
famous general theory of relativity, space is curved, gravity is a result of the curvature of space.
I talked very little bit about that in the book, but it's a turning point in his life because two years
later he becomes a worldwide celebrity when it's confirmed, or actually four years from 1915.
And then in 16, 17 he comes back quantum theory. Talks about how it's a random theory which
is going to be a theme in quantum theory and then his last great work and quantum theory is
about quantum statistics. Working with this unknown, stimulated by this unknown Indian
physicist Bose. And then finally in 25, 26 quantum mechanics is proposed as a final theory by
Heisenberg, Schrödinger and Born and Einstein has a response that I'll tell you about. I've
already hinted he obviously doesn't like it. So this is about 20 years, from 1905 to 1925. I would
say his contributions briefly summarized here are about eight Nobel's worth, six of which are in
quantum theory. We're not going to count these minor contributions in relativity E=m squared
and general theory of relativity. So it's interesting because those are such spectacular insights
that if you just take that away, you still find six phenomenal contributions to the foundations of
physics.
Okay, so I'm going to just tell you where not going to have a big long lecture here. I'm going to
tell you little bit about this idea of quanta of light and quantization of energy and then just a
word or two about randomness and quantum statistics and then a few words about Einstein as
a person at the end. Okay, so one more thing about Einstein as a person to get us into the
science. When he was in Bern he formed this little kind of study group which they humorously
called the Olympia Academy. They were basically unknown struggling, you know starving
people. This Conrad Habicht was a mathematician, mathematics student. This Maurice Solovine
was a philosopher. And Einstein, this Ritter von Steissbein was a funny nickname that Conrad
Habicht gave him and all their letters have this kind of frat boy character to it which I found
very amusing, to give you little sense of it. So first, these guys were really struggling and sort of
reminded me of the opera La Boheme instead of having you know, the philosopher and the
musician and the artist, instead you've got the mathematician, physicist and the philosopher.
Starving but pretending that they are going to do great things, and one of them actually does
do historic things. So this is a little, sort of souvenir from that time. Maurice Solovine drew this
cartoon of Einstein as the president of the Academy surrounded by links of sausage which is all
they could afford. And here's a very grandiloquent dedication to him in Latin which translates
partially as a man of Hechingen, which is Hechingensis that's his ancestral part of Swabia he
was from. Expert in the noble arts, steeped in the revolutionary science of the cosmos, bursting
with them knowledge of natural things. Powerful guy to those fabulous molecules. So they
were having a lot of fun and unfortunately Habicht got a job, moved away and Solvine got a job,
moved away. So in the miracle year, the Academy wasn't meeting and we only have this one
letter that Einstein sent to Habicht to know what he was thinking then. Because he wasn't
writing to anybody, nobody knew him right. So he announces this and this is one of the most
famous letters in the history of science. It's in early 1905 and it starts with dear Habicht. Such a
solemn air of silence has descended between us that I almost feel that I am committing a
sacrilege when I break it now with some inconsequential babble, So what are you up to, you
frozen whale, you smoke dried canned piece of sole. Why have you not sent me your
dissertation. Don't you know that I am one of the 1 1/2 fellows in the entire world that would
actually read it with pleasure, you wretched man. Okay, so that's how they talked to each
other. So, and then he says I promise you four papers and return. The first deals with radiation
and the energy properties of light and is very revolutionary. The fourth study is still a mere
concept. The electrodynamics of moving bodies by the use of a modification of the theory of
space and time. So of course, this is relativity theory and this is the beginning of the quantum
theory of light and there are two other really good things in there too. So he kind of just tosses
this off in this sort of sarcastic letter to Habicht. This is the famous volume of Annalen der
Physik where it was three of the papers were published. Max Planck, who will feature in our
story shortly, the great German physicist was the theory editor and looked at all these papers.
Unfortunately we don't have any referees reports. I mean no one knows what they actually said
about it. They got published, that's all we know. Okay. So very revolutionary, this was the only
time we know that Einstein actually said a work of his was revolutionary. So I will be focusing on
that. So why was it revolutionary? So what we did know about light in 1905?
Oh.
>> [laughter]
>> Douglas Stone: Wow. So, did I hit, that could not be .
>> Audience: No, it wasn't you. You may continue.
>> Douglas Stone: Okay, wow. So what did we know about light? Well, we knew it that it was a
traveling wave of electric and magnetic energy and it traveled at the speed of light so all these
waved traveled at this 300,000 km/s, the theory of this was put forward by the great Scottish
theoretical physicist James Clerk Maxwell and I talked a little bit about him. He's a very
interesting character in the book. And we can characterize the wave by its frequency which we
call nu and its wavelength which is inversely related to its frequency by the speed of light. And
this leads to the idea of the electromagnetic spectrum which goes from radio waves in
megahertz up to x-rays at 10 to the 18th cycles per second and this is our electronics now in the
gigahertz range, I'm sure many people here know about. And actually there is no lowest and
highest frequencies in infinite spectrum. Light being there in the middle at hundreds of
terahertz. And the other thing that was going on at the time was the people realize that matter
is continually emitting and absorbing radiation. Okay, so we're emitting and absorbing some
kind of radiation all the time and in fact due to our temperature it's roughly this infrared
frequency that we emit and absorb and that's what you see with the night vision goggles, okay.
So the person that was working on this in 1900 was Max Planck. Here he is on a particularly bad
hair day, but it's the only 1900 picture that I could find of him. And the technical term for this
was black body radiation. I think most of you know that black is the color that sort of absorbs all
colors, all incoming colors. So something black is going to absorb the blue light and then it's
going to thermalize the light and readmit typically at infrared which you can't see. So it was red
here but actually you wouldn't be able to see this, okay. And the question was, for the
temperature of the black body, how much energy do the emit as radiation for a given
temperature? What was energy density? Planck thought he knew the answer in 1899 that it
was basically something conjectured by Wilhelm Wien a few years earlier, now Planck thought
he had proved it. He wrote a paper saying it must therefore be concluded that the Wien
distribution for this energy is a consequence of the second law of thermodynamics. So that is
the strongest assertion you can make, the second law of thermodynamics that entropy always
increases is one of the fundamental laws of physics that has never been shown to be violated
and Planck thought that he had proved Wien's conjecture. So now this talk I'm giving without a
lot of equations and so on, well here I'll show you one more slide and I get back to that. Okay,
so he said this in 1889 and about nine months later his colleague Kurbaum was presenting their
latest data for how this energy that they were measuring coming of the blackbody depended on
temperature and frequency. This is a plot of the energy density versus temperature and the
data fall on this nice line but the Wien theory that Planck had committed to goes like that. So it
doesn't agree at all. So this was a theorist's worst nightmare because he had predicted
something that was clearly in contradiction with experiment and also he had not said it was an
approximation. He said that it followed for the most fundamental laws of physics. So I found
this a classic, you know gee I wouldn't want to be him situation being a theoretical physicist
myself, this is really your worst nightmare. You obviously just done something wrong, right. I
mean that's, you know what's he going to do. He standing in front of the same people to which
he made this claim nine months earlier. So what he does is he kind of graphs around and tries
to find a way to get this linear dependence. And I'm not going to go through this whole slide
because I don't want to go for too long. This is the one technical slide, so let me just skip
through, I'll come back to it if you're interested. But this is the law, the mathematical law for
the energy density, the black body radiation thermal energy law. And it turns out that in two
limits, one limit you get Wien law when you look at high frequencies and the other limit you get
this thing which is linear in temperature which is called the Rayleigh law and that's essentially at
low frequencies or high temperatures. So, the data I'm showing you here is the Rayleigh limit
where it's linear in temperature and in the Wien limit it isn't. So he guessed this answer, he
guessed this formula for technical reasons that I can go into and it was able to explain the data,
but he didn't have any justification. Okay, so he guesses the right answer and he says look I'm
kind of at a loss but this is what I think the right answer risk and then two months later he says
after some weeks of the most strenuous work of my life, some of light came into the darkness,
okay. So this is what he proposes. Okay, that for some reason the matter that's absorbing
radiation can only exchange energy in little increments of h times nu. Now nu is the frequency
and h is this thing that he introduced called Planck's constant which is the signature of all things
quantum. So what's so strange about this idea? Well, energy in macroscopic physics. Why am I
doing this? I'm trying to hypnotize you. Okay, so what Planck was doing, was he was imagining
that the atoms that were absorbing the light were little springs with charges on them. That was
just sort of a model that he had, he called them resonators. And this was his statement, that
the resonators could only change their energy by a discrete amount. But if you think of a
macroscopic resonator like a pendulum, this is the closest thing I have to a pendulum. Thank
you dear. Then, you know the energy in the pendulum depends on how much you displace it,
right. It has more energy now if I displace it higher. And it looks like the energy that I can give to
this pendulum, obviously there's some biggest energy I'll start doing that. But it looks like it's
continuous because I can just kind of displace it from its lowest energy state by any continuous
amount. So it looks like energy should be relayed continuous just the way space and time are
continuous. So to say that this is true is really an insane, crazy conjecture, that's the point.
Okay. And he says that. What I did can simply be described simply as an act of desperation. By
nature I am peacefully inclined that I reject all doubtful adventures, that's what he said. But
however he didn't reject this one. However he hints that maybe this is a provisional hypothesis,
maybe we can get rid of this. Then he says nothing more about it for the next five years. He
doesn't publish anything. In the book I say it's like a family that agrees never to discuss again a
traumatic episode. So the only person that is actually mulling this over in those five years
essentially is this young patent clerk in Bern, Albert Einstein. And stimulated by Planck, he
actually challenges the wave paradigm. He writes this paper on a heuristic point of view
concerning the production and transformation of light. It's heuristic because it's not a full
theory he, it's not a full mathematical theory and he begins it by saying it seems to me that the
observations regarding black body radiation and the photoelectric effect can be better
understood on the assumption that the energy of light is distributed discontinuously in space
and that light consists of a finite number of energy quanta. Local lights in space which move
without being divided and cannot be, can only be absorbed or emitted as a whole. So this is
essentially light acting like a particle, not like a wave. Okay, and this has a clear connection to
Planck's quantization because of light can only be absorbed in units of h nu, then the energy of
the atoms can only change that way. Okay. But he also points out that if you don't make this
hypothesis, you just use classical physics, you find a total disaster that radiation sucks all the
energy out of matter and we all freeze to death. And I have a long discussion of this thing called
the ultraviolet catastrophe in the book which doesn't happen, because of quantum mechanics.
Okay. But there was obvious problems with saying that light was made up of particles. Okay, we
knew that light was a wave and how did we know that? Well waves interfere. This is you know a
water wave which are being produced here by an oscillating rod or something like that and you
see there is these calm reasons where the peaks in the troughs are canceling and then there's
these very uneven regions where the peaks and the troughs are adding up. That's from wave
interference. Okay. So what was the medium for light if it interfered because water waves are a
disturbance in a medium. That was a problem. The controversy raged in the first half of the
19th century and I want to tell you a little antic dote about the Spot of Arago. So in 1818, the
French Academy of scientists announced a competition for the theory of the properties of light,
and this guy, a Gustav Fresnel proposed the mathematical theory and the famous
mathematician Poisson, who you may have heard of the Proisson process. He thought that this
was nonsense and he derived what he thought was a contradiction. So he proved that if I had
this round object and I looked in it's shadow, that if the wave theory was right there would be a
bright spot in the middle of, behind in the middle of the shadow. And that then was a proof
that obviously they weren't waves because obviously that was wrong. But Fresnel had a friend,
okay. This friend was named François Arago and he seems to remind someone of the most
interesting man in the world because in addition to being a great physicist, he also was the
Prime Minister of France, he was the person that abolished slavery in the French colonies and
he was a military hero and so on. So he was the most interesting physicist and he actually did
the experiment, and yes there is actually a bright spot in the middle of the shadow. The round
thing has to be very smooth or you don't see it, so it took some extra effort to see it, but it's
definitely there. So that was you know this sort of fantastic experiment that showed that the
wave theory was right even when it looked contradictory and then it became routine. You could
send light through a slit and see these interference bands and so people made up a medium for
light to travel in called the ether. You couldn't see it, but that's what light supposedly travelled
in and they invented a disruptive technology radio which already was working in the 1890s
based on this theory. So if we knew anything certainly in physics in 1905 we knew that light was
an electromagnetic wave. Okay. So Einstein said that the photoelectric effect gave pause, made
you reconsider this point of view. What's the photoelectric effect? Well, imagine that you have
ultraviolet light or purple light incident on something, it could be a black body, some piece of
stuff. If it's a metal, what you find is instead of it being just absorbed and reemitted as radiation
actually comes out as an electron. That's called the photoelectron. Okay, and you can measure
that with the voltage or current that is then detected photocurrent, okay. And the observation
was no matter how intense the radiation, no electrons would come out if the frequency of light
was too low. You needed a certain frequency threshold to see any photocurrent. Now why was
this? So, it doesn't make sense in the way theory that the more intense the wave, the more
energy, it shouldn't matter what the frequency is. But in particle theory you say that the
lightwave is actually a train of particles each having energy h nu. And one of them interacts
with an atom at a time. It can give all of its energy to that atom. If the frequency is too low it's
not enough energy and the electron jiggles around but it doesn't come out because it's bound
to the atom, right. But if it has high enough frequency and high enough energy then it will get
knocked out. So that was his explanation for how you could explain the photoelectric effect
with some new type of physics of quanta of light. But there were no good experiments for 10
years, and no significant theorist believed Einstein was right for probably more like 20 years.
Okay. So in 1913 Einstein gets recruited to Berlin. He's now become in physics a celebrity. This
is a much later period like 1929. That is one of the people, this was the godfather of German
physics and chemistry at the time, Walter Nernst. That's Max Planck, there's Einstein a little
older, this is Millikan and Van Loway. They all won the Nobel Prize in physics but it's a little bit
later. Anyway, these two guys went and twisted his arm to come to Berlin and get him into the
Prussian Academy of Sciences and they talked about how he was the greatest physicist since
Newton and Galileo except they had to apologize for one thing. He may sometimes have missed
the target of his speculations, for example in his hypothesis of light quanta, but that can't really
be held against him. So this thing which we now see as the foundation of modern quantum
theory was a thing they had to apologize for, okay. So what about the photoelectric effect. So
this guy Millikan was a great experimentalist. You probably know about the Millikan oil drop
experiment. He really wanted to do this experiment. So this is how you do the experiment. You
have an arc lamp, you put it through a prism to get the violet end of the spectrum, through a
slit, it hits this thin metal foil and then you measure the electrons coming off and there's a
current there. But they also had this little grid of metal and if you charge that up negatively, you
can actually stop the electrons from getting to the collector. That's called the stopping voltage
and according to Einstein's theory, that stopping voltage should just be a straight line versus
frequency. So he did this experiment. It took him 10 years. He did this experiment, and this is
what he found. Perfect straight line. And when he measured the slope, I'm sorry I should've said
that the slope is h Planck's constant, universal. Okay, he gets a straight line, calculates the
slope. Those of you that recognize Planck's constant will see its Planck's constant. Okay. And he
says, I spent 10 years of my life testing that 1905 equation of Einstein, contrary to all my
expectations I was compelled to assert its unambiguous experimental verification in spite of its
unreasonableness since it seemed to violate everything we knew about the interference of
light. Okay, so this is how Einstein got eventually one Nobel Prize in 1922, I can tell you more
about that if you're interested because this was unambiguously correct. So which is it then?
What did Einstein say? Is he saying that lights a particle or is it a wave? Well Einstein in 1909
said very clearly that it was both. It is therefore my opinion that the next stage of development
of theoretical physics bring us a theory of light which can be regarded as a fusion of the wave
theory and the emission or particle theory. So that was the beginning of this wave particle
duality of quantum mechanics. I think I'll skip over this a little bit. This is the quantum theory of
the atom in 1916 where Einstein talks about the fact that when an atom emits a beam of light,
that this is a random event. There's no cause for it. And he struggled with this a lot. He says the
weakness of the theory lies in the fact that it leaves the time and direction of the emission of
light to chance, nevertheless I have full confidence in the reliability of the course I have taken
this. This was 1917. But then in 1920 he's still kind of mulling it over, he's unhappy. He writes to
his friend Max Born, "This business about causality gives me a lot of trouble, I would be very
unhappy to renounce complete causality". And that's a feature of quantum mechanics is
uncaused events. The last thing I'm going to say of just a brief word about, in terms of science is
in 1924 Einstein got just in the mail a paper from an unknown physicist Satyendra Nath Bose
from India. He reads this and he understands there's a deep insight in there which we call
indistinguishability. And I have another prop here to explain indistinguishability. So I have two
coins here and if I toss it, let's see what I get. Okay, I got two heads. Let me do it again. Okay I'm
going to fudge this, okay there. I got a heads and a tail. So if I keep doing it, what's the
probability I'm going to get a heads in a tail.
>> Audience: Half.
>> Douglas Stone: Half, exactly. Because there are two ways, there are four outcomes. Two
ways I can get heads and tails and only one way I can get heads, heads or tails, tails. Well what
was buried in Bose's paper was the idea that atoms aren't like that. Okay, that if I interchange
to electrons, I can't count that as a separate state. So if these were quantum wanes, the
probability of getting heads and tails, there would only be three states. Heads tails would be
one state, there would be one state of heads tails tails head, and then heads heads tails tails
and the probability would be one third. So that changes all your counting and your counting
determines entropy and all of physics is then changed. Obviously I cannot go into the details of
that, but trust me. This discovery of this new type of statistics that atoms behave leads to an
idea of quantum condensation, Bose Einstein condensation. Six Nobel prizes are related to it
because it underlies superconductivity and other things, so it was a huge breakthrough. And
mostly due to Einstein, not Bose. In 1925, Einstein gets a letter from Schrödinger, Schrödinger
the famous Erwin Schrödinger and Schrödinger says you've just done this wrong because you've
done your statistics wrong. Einstein says, no no thank you Herr colleague, I have made no
mistake. Let me explain it to you. And now here, this is what I love. This is the same example
that I just gave you. Do you see it, right. He's got the four cases classically where you have the
two interchanges, here there's only one case, so you see in Bose statisticia, so you know this is
Einstein explaining Bose statistics just the way I did to you. Okay. So Schrödinger is inspired by
this and in the next year he and Heisenberg independently invent the modern form of quantum
theory. He gives, Schrödinger says my theory was stimulated by de Broglie and by brief but
infinitely farseeing remarks by Einstein. Okay, there they are. That Schrödinger on the right,
Heisenberg on the left, they were both well, Heisenberg was very young. Okay, but Einstein
after studying this for half a year comes to the following conclusion. Quantum mechanics is very
impressive but an inner voice tells me is not yet the true Jakob. The theory produces a good
deal but hardly brings us closer to the secrets of the old one. That's his funny way about talking
about nature. Some people think it's God, but we're really talking about nature here. I am at all
events convinced that he does not play dice. That's the famous quote and he just stuck by that
for the rest of his career. Now we have the old guy there. He says all these 50 years of
conscious brooding have brought me no closer to the answer to the question what are light
quanta. Of course every rascal thinks he knows the answer, but he is deluding himself. Okay. So
now before I close, just a few comments about Einstein as a person, what was he like. Yes you
can tell he had lots of joie de vivre, sense of humor, enjoyment of life. Here's a quote from a
friend, his sense of humor was readily apparent. When someone said something funny the
laughter that welled up from the very depths of his being was one of his characteristics which
immediately attracted one's attention. Obviously this independence, he was a secular human.
Humanist, early proponent of universal human rights. Sympathetic to the underdog, hated
militarism, loved music as you probably know. Very well-rounded intellectual, knew about
literature and so on. He was very charismatic, he was adored by his friends. He was very
attractive to the opposite sex. A lot has been written about that, though I only hint at it in my
book. And here's a great quote that I like. "The strongest impression one gets is a stunning
youthfulness, very romantic, reminiscent of the young Beethoven and then laughter erupts in
one is based in one is faced with a student". So that's a description of Einstein at age 43. Here's
a picture of Einstein, you can see all this. He's loving music, he's kind of looking at the opposite
sex.
>> [laughter]
>> Douglas Stone: He's having a good time. That's in 1913. Okay, what was the nature of his
genius? Well he was a deep thinker but I would not say he was a mathematical genius. He was
more of a conceptual genius. He was intensely curious about nature. He made this modest
claim, I have no special talents I'm only passionately curious. I don't think that's true, I've
already said that. He had this talent for unification and simplification. Very flexible thinker. I
have a chapter called entertaining the contradiction where he's really beginning to think you
could have particles and waves coexisting which nobody else did at the time. And he was a very
insightful critic including of quantum mechanics. I could go on to that more. Science was his
existential philosophy. That's the last thing I want to say so here's a couple of quotes from him.
"Physics is an attempt to conceptually grasp reality as it is, independently of it being observed".
And then to his friends he would say do you really believe the moon exists only if I look at it.
And this was his critique of quantum theory that it was always talking about the observer. So he
didn't like that, okay. And finally he said, I believe with Schopenhauer that one of the strongest
motives that leads men to art and science is escape from everyday life with its painful crudity
and hopeless dreariness from the fetters of one's own everyday desires. A finely tempered
nature longs to escape from the personal life into the world of objective perception and
thought. That's what he was trying to do with his science. His rejection of quantum mechanics
reminds me of Beethoven in the end of the ninth Symphony in the final act after the first three
he says, nicht die diese tena, you know, not these talents we need something different and he
tried for the rest of his life unsuccessfully to complete a harmonious resolution. So thank you
for your attention.
>> [music]
>> [applause]
>> Douglas Stone: Okay, so the floor is open for questions.
>> Audience: I have a question that I had before I listen to this lecture.
>> Douglas Stone: Okay.
>> Audience: If man never saw light or knew the existence of light, what would be the Planck's
constant? The reason why I'm asking this question is Planck's constant comes because we see
light and when we see light we disturb particles that we see with light. And with lights property
is it better than the Planck's constant and then you get the uncertainty and everything that
comes with Planck's constant. So the reason why I'm asking this question is the quantization in
the theory of quantization change if you find another medium or reflecting objects that is
nearing the light of some. That is faster.
>> Douglas Stone: No. That's actually, that's probably not the right way to analyze it so,
Heisenberg tried to explain the uncertainty of quantum mechanics by saying every time you
observe, you disturb. And there's a famous microscope experiment where you know, you're
trying to observe the atom and the light bumps it and it moves off so you don't know where it is
after you've observed it. But now we've come to understand that, that is not the right picture.
And actually Einstein played a big role in proving that that couldn't be the right picture because
now we know things that are far away and don't actually disturb each other to the effect
through you know observation here can affect something over there. So we now say that things
really are just uncertain. It has nothing to do with whether we disturb them. And in particular,
Planck's constant is just the scale at which you can stop resolving things. You have to worry
about the fact that the electron is spread out and so on. So if you measure things in the right
units, you'll say I really have to worry about the fact that the electron can go this way and that
way through the wire and interfere whereas if the scale of billiard ball, I'd no longer have to
worry about that. So it's sort of, it really doesn't have to do it light anymore than it does with
matter.
>> [inaudible]
>> Douglas Stone: Yes.
>> [inaudible]
>> Douglas Stone: Okay, so this is rather technical, right. So the paper was about the following.
In the intermediate stage of quantum theory, Bohr and then Arnold Sommerfeld came up with
the prescription called the Bohr Sommerfeld rule where you basically look at a class as if an
electron were moving with Newtonian mechanics and but you said the only orbits that were
allowed were orbits where when you went back and forth, the action accumulated which is
something you measure in classical mechanics. The action is the thing that's minimized to
determine the nonlocal property of the trajectory which determines, yeah which in quantum
mechanics has to be quantized to be equal to an integer times h. So you have these classical
trajectories and then the only ones that are allowed by quantum mechanics are those where
you have an integer number of values of h bar when you go along the complete one traversal,
the trajectory. Yet this problem that with chaos, you can have trajectories that never kind of
close on themselves in a nice simple way. They are pseudorandom and therefore you can't
construct a Bohr Sommerfeld theory of chaotic motion even though it's a classical motion, it's
Newtonian motion. And so Einstein brilliantly found a way to generalize Bohr Sommerfeld to
more complicated motion but he also identified the problem with chaos and said there's this
other type of motion which Planck Courier has found where clearly there aren't enough
constants of motion and you won't bail to do this. We don't how to solve that problem. And
that's the problem were still trying to solve in 2000, right that I was working on. So there's
some partial solution. And the interesting thing is that the same formula that Einstein derived in
1917 was re-derived by mathematical physicist Joseph Keller in the 50s. People have forgotten
about it and there was a guy from Berlin Fritz Rieke who had known Einstein and when Keller
showed him the formula he said, "Zat reminds me of something Einstein did". And it turned out
it was really the same thing, but Keller didn't understand this thing about chaos versus regular,
so actually, his paper is not as good as Einstein's paper. So that's what I was explaining.
>> Audience: You said there was no upper or lower limits in the electromagnetic spectrum. I
just thought there would be some minimum wavelength just like related to maybe Planck's
constant or the onset to principal way each kind of get smaller than that.
>> Douglas Stone: Within modern you know quantum mechanics, quantum field theory etc.,
there is no limitation. It's you know somewhat related to photons having zero mass and so on,
however you know people in string theory, we don't have a quantum fear of gravity. They do
conjecture that there might be some scale coming in, you know at this so-called Planck scale.
It's tiny, tiny but you know within the current theory there is no limitation. It's not always easy
to generate waves at arbitrarily long wavelengths and so on. Yeah.
>> Audience: So, I'll see how to phrase this because it also adds to your teacher [indiscernible].
You hear in many conversations the nature of the intersection of creativity and technology in
specific the sciences and different approaches, Microsoft tends to be classical and it's kind of
Legos and putting together, snapping together solid states in the creative and arts spaces. It's
much more common to have people that process information, I want to save intuitively but
nonverbally spatially. When we talk of the sciences it wants to put this in like a genius level but
it's not, it's much more common in other states. Are you seeing a change in, so I was always
thinking of Einstein as a person who processes information, full signal from most intuitively and
then works backward to the initial causes because that's how we tend to problem solve, but
that's okay, it's a very comfortable for traditional sciences. Are you finding a shift in students
and despite [indiscernible], how can we stimulate this in stem without saying it's magic or it's
genius? Can you confirm like stem to steam, introduce arts and creativity so that all these leaps
in lateral thinking that seems to be the things that create these [indiscernible].
>> Douglas Stone: Well I think the, I think the thing that I find very impressive in reading
carefully Einstein's reasoning is his flexibility. You know the fact that he was actually able at the
same time he was working on relativity which assumes the classical theory of light, he was able
to proposes this modification and you know, even the greatest physicists of the time were
saying look, look interference. It's obviously wrong, it's obviously wrong, it's obvious the wrong.
And he just persevered with it, so you know this ability to suspend your, you know your critical
faculties a bit and entertain the contradiction was something that impressed me in his thinking.
But you know he was a conceptual thinker. He really, you know general relativity arose because
he was troubled by the fact, or he was aware of the fact that you couldn't tell the difference
between acceleration and, you know the acceleration of gravity. The same thing that Galileo
was studying that didn't matter how big the rock was, it fell at the same rate, neglecting
friction. So, you know most of his things he had a very clear concept, which is I would say
almost a verbal concept not a mathematical concept which he then filled in bit by bit over the
years. And when he tried to go totally mathematically, mathematical and look for unified field
theory in the last part of his life, the last 20 years. He made no progress at all. Nothing he did
there has actually survived. Yeah.
>> Audience: So I'm curious if Einstein or if the current theory holds that have, there's a line at
which a particle is too large and can no longer show wave particle duality.
>> Douglas Stone: So right now we see no boundary and this actually gets to something really
interesting which I didn't say a word about. And actually my department we are very involved
with quantum computing and trying to demonstrate macroscopic quantum behavior in circuits
so that you can do calculations with quantum algorithms. And some people here may know
about that. Definitely in Microsoft as a whole, I'm sure you have real experts. So, you know one
of the things that it's relatively easy to see wave particle duality in a light particle like the
electron. That's why we found that in the 20s and with even an atom which is not that big by
our standards, is big compared on the scale of seeing that kind of interference effect. And in the
90s we figured out how to cool atoms to ten to the -9° above absolute zero and then sure
enough, we're doing atom interferometry and one of my former colleagues is flying these
things in you know helicopters and putting them in submarines because the interferometer can
then detect changes in the gravitational fields and we can find where there's an oil deposit or
maybe an underwater mountain or something like that using these interferometric methods.
Anyway, that's what they're used for but that was a case where suddenly we could take out
much bigger object and see quantum effects. The same thing is happening with these circuits.
We now have circuits where a current of electrons of say hundred nano amps can be
simultaneously going that way in this way at the same time is a quantum effect. So we're
pushing that boundary and nobody has found a point at which quantum mechanics fails,
although they were very reputable theorists who think there might be such a boundary.
>> Audience: And if there is a boundary, what is the reason they think. I mean I haven't heard
this, it's the first time I'm hearing that there is [indiscernible] particles based on size, stop
strength, duality.
>> Douglas Stone: So, I'm not sure what people's reasoning is. One person that certainly was
very interested in this is a noble laureate Antony Leggett who is one of my heroes and you
know, initially when he proposed these macroscopic quantum experiments he was one of the
leaders. He thought they would show quantum mechanics was wrong, but so far they've all
shown that quantum mechanics is right. And I saw him fairly recently, so I said, well what is the
scale? There has to be some new constant of nature that says you can't do this. So I actually,
since I'm kind of a believer in quantum theory and I just think the worlds that way then I don't
have an argument for what scale would be. But his argument certainly the simplest argument is
just we've never tested. So it could be wrong, whereas you know we've tested all the chemistry,
all the solid-state physics has been tested in 1000 interconnected ways so that you couldn't
really find something wrong with it for everything else to be a mess too. Yeah.
>> Audience: With the latest findings to date, how would we explain the double slit experiment
differently to say years ago? I mean do we have a different definition of observation? How do
you explain that experiment right now?
>> Douglas Stone: I mean, I don't. People struggle very hard for some words that make it seem
more intuitive that these, you know that things can sort of be going into different places at
once and until you do interaction with it. And I don't find any of them helpful at all. I certainly
don't find many worlds at all helpful. That annoys the heck out of me. You know like every time
an electron is measured this way, there's one world where it went that way and another world,
okay. But the thing that has come out very clearly from all this work and quantum information
physics and computing and so on is that observation doesn't have anything to do with people
you know. Observation is an interaction with another degree of freedom and so if you, it
doesn't matter whether a person measures it. It can be measured by the cosmic microwave
background and that's why Schrödinger's cat could never really be, because a complex living
organism is interacting with so many things that it doesn't show quantum effects. It's always
being measured if you like and if you isolated it from the environment, then it would die. So
then you would only have a dead cat. So you know in a practical sense Schrödinger's cat is
never going to happen. You probably know about Schrödinger's cat. Most people here know
about Schrödinger's cat? Yeah. So I find that somewhat comforting. But it's still a bit of a puzzle.
We still argue about it and you know there's this other school that dominated for a long time
called shut up and calculate, but now you know it's under siege because of all the quantum
computing work which makes you actually think about these things again.
>> Audience: What is your most irritating pop culture misrepresentation of quantum theory
today?
>> Douglas Stone: Thank you for that question. Actually I'll just slightly divert it to, but it's very
close to your question. The thing that bothers me is that quantum is famous for the weirdness,
right. So it's famous for the cat that's half alive and half dead and stuff like that. Whereas end
quarks and Higgs bosons and so on. But actually quantum is the basis of all our technology.
That's what I said at the beginning. So, you know the laser and the transistor and all that is
fundamentally requires quantum to understand and so when I tried to, you know people were
saying, no one's going to read this book because quantum's in a scare everybody away. But if
you're going to talk about quantum you have to talk about the gee whiz, going backwards in
time, beginning of the universe, etc. You know, because that's all they want to do is be amazed
and I don't want to amaze people. I want people to say, isn't this amazing that people figured
this out but now we understand it. All right now we understand it, you could understand it.
Read the book. You could partially understand it.
>> [laughter]
>> Douglas Stone: Somewhat understand it. So you know I hate the gee whiz, this is just
confusing and you can't understand it part of it. We all work with quantum theory, you get used
to it, it's beautiful, it's truth. I mean I personally have predicted things in quantum theory that
were never measured. People went and they measured them and they worked. So that is the
most exciting thing you could have as a theoretical physicist. And so you feel this is true, this is
beautiful, you get very excited about it and it's kind of amazing the first time. Yeah.
>> Audience: So this goes back I think one of the questions over here. Over here was asking
about finding ways to describing ways of making [indiscernible] intuitive. You think that more
will be discovered about the fabric of the universe that helps people to understand the universe
in a way that is intuitive or do you think maybe that's just not things that we should be
concerned about.
>> Douglas Stone: I mean this is of course wildly speculative.
>> Amy Draves: Could you repeat that question?
>> Douglas Stone: So will new things about the fabric of the universe lead us to have a more
intuitive understanding of these things that seem very odd? And I mean, okay wildly speculative
answer, just gut feeling is that when we figure out what dark energy is and so on it's just going
to be worse, not better. That's my guess, you know because at some particles that doesn't even
interact with matter but has gravity, you know so it's not going to have any connection to
anything we understand on earth. You know, so I feel like none of these things, we will get a
deeper predictive understanding but not an intuitive understanding. And it gets to my point
that the fact that human beings can understand something that's you know 1000 times smaller
than a human hair. No it's actually like 10 to the fifth times smaller like an atom. I'm not even
counting quarks. Okay, if you throw them in then it's you know, a billion times smaller and so
on. That's amazing. We worked even evolved to do this. That's incredible that we got this
understanding and the fact that Einstein kind of got the key ideas, you know of about 80% of it
is also astonishing. This one man who was so brilliant and this other related spear of relativity.
Yeah.
>> Amy Draves: An on-line question. If Einstein was to win the Nobel prize for something
besides the photoelectric effect, what "quantum" thesis discovery should it be for?
>> Douglas Stone: Well, I mean, okay. So I have two candidates. So one thing that everybody
agrees is spectacular but it's a little more technical, it's this Bose Einstein thing that I talked
about at the end because it's kind of one of the fundamental many body effects. The
fundamental features of matter at low temperature that shows up everywhere and underlies so
many phenomena in quantum physics. And the fact that, I mean that's just like a slamdunk.
We've given like six Nobel prize since for manifestations of that, so why didn't he, you know
okay. So that one is kind of ridiculous. I have no idea why they didn't give him a Nobel. I think
he just said he doesn't care anymore. That's like, you know he's got it. He doesn't care, he
honestly doesn't care. One of the stories I tell you in the book is that he got a note like in
September of 22 saying you know, you really should stay around because something might be
happening in Stockholm in December and he had planned to go to Japan. And he wrote back
and said sorry I'm going and then he got a telegram during the voyage at some point saying he
had won the Nobel Prize. He didn't mark it in his travel diary. You know so he says, played
quartets on May 12 or something but it doesn't mention won Nobel Prize today.
>> [laughter]
>> Douglas Stone: So, you know he didn't, I mean you know obviously he wasn't insensitive to it
but at that point, you know. So that certainly the Bose Einstein, but that's a more technical
thing. The thing that's a little more conceptual is an really underappreciated is this thing I just
eluded to which is, in 1907 he really said energy is really quantized. And I told you that Planck
fudged it. He really didn't want to say that at all. He didn't say it tell after Einstein. So the idea
that energy is quantized really came from Einstein in 06, 07. Then this is also what TS Kuhn, the
famous historian in science says. So I'm not the only one saying this. And so that thing which
sounds very kind of mundane, specific heat of solids turns out to be something that absolutely
clearly should've won the Nobel Prize. And when people write about Einstein, see, I'm the only,
they are mostly astrophysicists or high-energy physicist. They probably don't know that much
about the specific heat of solids but that's my field. That's big, so you know it's
underappreciated. So those two I would think.
>> Amy Draves: I must make this last question.
>> Audience: As you were researching his life, was there a big surprise or something that you
misconception that you had about him that turned around.
>> Douglas Stone: That is a great question. Well I think, I expected it to be harder to follow his
reasoning. I expected the kind of stereotype of this is the genius and you can't understand him,
he just has these leaps to be the case. And what I've found was he was completely compatible
with the way I think about physics that very logical and just someone that you could really get
inside his head and see him thinking about it and appreciate it. So I think the kind of you know
incomprehensible genius thing, even I as a theoretical physicist, I thought I would encounter
more of that. So maybe that would be one thing. The fact that he was so popular with his
friends and so liked, because there are these stereotypes. Another one, I'll give you two. You
know that maybe he was a little bit cold or a little bit, you know even there is this aspergers
rumor which clearly cannot be true. But it was actually just this kind of life of the party guy who
loved puns and jokes and had a little bit of a dirty mouth. That's another quote. Okay my last
quote may be not be the best one, was when he finally gets his first job in 1909. I mean it's
taking people four years after 1905 to actually give him an academic job in Switzerland and he
writes to his friend, " I am finally an official member of the guild of whores".
>> [laughter]
>> Douglas Stone: So that's the kind of joke that. And I actually told that to a German who's this
friend of mine and he absolutely refused to believe it. He said, oh it's mistranslated it must be
mistranslated. I don't really speak German so, I went, I got the German thing and the word is
poen, which sounds a lot like whore to me so I think it wasn't mistranslated. So the fact that he
was sort of, even more of the life of the party as opposed to this kind of gentle philosopher
particularly as a young man was the other thing on the personal side. Those two things I guess.
>> Amy Draves: Thank you so much.
>> [applause]