Hi, everybody. And welcome to the first lecture in our
course Exploring Quantum Physics. Today, I will introduce the main
formulation of quantum theory using Schrodinger.
And I will also tell you a little bit about a fascinating history of the
subject. But before going to this main part, I
would like to talk about the process of learning quantum physics.
And about why I think, so many people find it difficult and frustrating.
And I hope that this brief discussion will help you avoid this frustration, and
make the process of learning quantum physics here more effective.
Richard Feynman doesn't really need an introduction.
He was one of the heroes and legends in physics, universally recognized as a
genius. He was also a great speaker and
enthusiastic popularizer of physics. In 1979, he gave a series of very
interesting lectures on quantum physics at the University of Auckland in New
Zealand. They're actually available on YouTube
online and I would encourage you to listen to them.
If you do so, you will see that Feynman spends 30 or so, minutes in the beginning
of his first lecture to prepare the audience for what they were going to hear
next. In one of the main messages of this
introductory part was that no matter what Feynman was to do, the audience wouldn't
be able to understand Quantum Mechanics anyway.
That he talks about physics students and physics professors and their level of
understanding of Quantum Physics. Let's listen to what Feynman had to say
in this regard. if I'm going to explain this theory, the
question is, are you going to understand it?
Will you understand the theory? When I tell you first that the first time
we really thoroughly explain it to our own physics students is when they're in
the third year graduate, graduate physics.
Then, you think the answer is going to be no.
And that's correct, you will not understand.
>> [LAUGH] .
>> But this business about not understanding
is a very serious one that we have between a scientist and an audience.
And I want to be at work with you, because I want to tell you something.
The students do not understand it either.
>> [LAUGH].
>> And that's because the professor doesn't understand.
>> [LAUGH].
>> This is not a joke, but very interesting.
>> So, what Feynman seems to be saying is
that nobody, not even professional physicists, not even himself perhaps,
really understand quantum physics. Well, this is probably the last thing you
want to hear before starting this course. But this is strictly not my intention to
give you the impression that you should give up without even trying.
On the contrary, I'd like to speculate what I think Feynmam might have meant
there. But why I think so many people find it
difficult to study quantum physics and other advanced physic subjects.
And I hope that this discussion will help us further down the road when we
encounter unusual counter intuitive quantum phenomena.
Let us look at quantum mechanics from the perspective of all major physics theories
out there. In this slide, I attempt to present all
these theories in a single diagram, which, of course, is an unrealistic sort
of silly task. And so, the result I should, I cannot, I
shouldn't be taken too seriously. What we have here are three axis,
labeling fundamental physics constants. So, here, I have an the inverse speed of
light. this constant G is the gravity constant,
which appears in the Newtonion gravity. And along the horizontal axis, I have the
Planck constant. We show, as we show, c is the most
important fundamental constant that appears in quantum mechanics and that it
relates the particle and wave properties. Now, the red dots in this diagram
represent, symbolically, major fields of physics.
For example, on this line, I have two red dots.
So, the one which has all, agree, responds to all physical constants being
zero is just kinematics or classical mechanics.
Essentially, 17th century physics. So this dot here, with the finite gravity
constant, but all other constant. 0 is the Newtonian Gravity.
Now, moving up, the vertical axis, to the finite speed of light, brings us to a
theory which takes into account this finite speed with which, with which
interactions propagate. And this is the celebrated Special
Relativity Theory of Einstein. Combining it with gravity results in
General Relativity, another celebrated, another very famous geometric theory of
Einstein. Finally, moving along the horizontal axis
to find a Planck's constant, brings us to, actually, the subject of our course,
non-relativistic quantum mechanics. So, the results of this part, which we
are not going to discuss too much in this course, which combines the relativistic
effects and the quantum mechanical effects.
And this is, so called Quantum Field Theory or Quantum Electrodynamics.
They are more complicated theory. Actually, I could have added here another
dot which has all fundamental physics constants.
This is this would be theory of everything.
It doesn't really exist yet but everybody wants to get it.
So, this has been one of the holy grails of physics for many years.
Now going back to learning quantum physics and what does it all have to do
with it. so let us discuss what theory governs our
everyday lives. What is sort of our comfort zone?
And I would claim that we are somewhere here in this area.
Certainly, the life skills that we encounter in our everyday lives are much
larger than atomic. The velocities are certainly much smaller
than the speed of light. And well, we do experience gravity on a
daily basis. So, we're somewhere here.
And here is also where our intuition works.
And if we say, we understand something, what we usually mean by that is that we
can relate a phenomenon to another phenomenon that occurs here in this area.
So, for example, if we were to say that we really understand quantum mechanical
effect, it would often times imply that we would have found a way to relate it by
something that we all ready know here. But the problem with all this advanced
physics subjects, especially with quantum physics, is that such a mapping, such a
relation is not always possible. In other words, it's not always possible
to meaningfully project quantum mechanical phenomena on this classical
axis. And if no classical analog exist, this is
what we call strange. And this is what we find difficult.
But on the other hand, if we were to imagine a fictitious civilization of tiny
species that lived on atomic scales somewhere in this area.
So, this guys would have had really a lot of problems understanding our classical
work. So, the problem is not really with the
quantum physics itself but with our centristic position on how we want to
understand it. But now, how do[UKNOWN] quantum physics
if we can't really regularly understand it at intuitive level.
Fortunately, there is a way to do so. By speaking in common language of all
physic theories, that is not rooted in and is independent of our classical
world. And this is, of course, mathematical
formalism that needs to be developed. And it may turn out that two seemly
unrelated phenomena, lets say, on the classical side and on the quantum side,
may be explained by similar differential equations or something like that.
And by studying those, we can develop intuition about something which is
otherwise, inaccessible to us. But after this discussion, you may ask,
why bother studying quantum physics if it's not really relevant to our everyday
lives? So, the modulation comes from
experiments. And more recently, also from ecological
advances that creates systems and devices, which operate further, on the
right of this axis. The take home message here, is that when
you study quantum physics or any other advanced physics subject, for this
measure, you should actually be prepared to encounter phenomena that may appear
bizarre at the first sight. And that you may find difficult to
understand. When it does happen don't panic and
certainly don't drop the course because of that, and don't assume that others
find these things obvious. It's certainly not the case.
so, I think the best way to understand such new concepts is first, understand
experimental data that support them. And then, develop or understand a
mathematical formalism and the proper theory that describes these phenomena.
So, when you use this theory again and again, you will develop your own
intuition and get the feeling about a deeper understanding of the subject.
So, speaking about the mathematical side, so I should mention that of course
quantum mechanics is a demanding subject. And it, we will have to use certain vast
mathematical techniques. But there will be lectures with different
sort of levels of mathematical sophistication.
Some of them will be pretty advanced, some of them actually won't use much math
at all. And so, I, I hope that all of you with,
with different backgrounds in different levels of mathematical preparation will
find something that is useful and interesting.