Hi everyone. How was the last lecture?
Ok.· Today's lecture topic is, Heisenberg's Uncertainty Principle.
Seongho, How should we start?
Hmm· I think we should introduce what ﹒Uncertainty‧is, first.
Okay, can I get an A+ grade in this course? Is this uncertainty?
(No! It's clear.)
That's not what we are going to cover in this lecture.
This is today lecture plan.
Then, just consider a situation. You are going to measure some quantities of a particle.
Thanks to technologies, measurement errors are getting smaller....
However there is a FUNDAMENTAL limit of errors. That's why we call this uncertainty.
But I think some of you guys might got confused about this concept.
So, we'll introduce how to visualize this concept.
Heisenberg also tried to visualize it and designed a thought experiment. Like schrödinger's cat.
Look at this page. There is an imaginary microscope that can measure the position of electron.
To know the position of electron, there needs to be a ray coming back from electron.
The position is determined when the ray collides with the electron.
But that moment, the momentum of electron changes by compton scattering.
So at the moment, we can get the precise position value, but for the momentum, we cannot.
Precise position or precise momentum that is the question.
Error of position, delta x equals to lambda over sin e,
and delta Px approximately equals to h over lambda times sin e.
So we can get this equation, but it is just an approximate expression by Heisenberg.
As you can see, this equation is different with the one we used to learn.
Why does it happen?
This thought experiment can explain uncertainty principle very easily.
But it also has a limitation.
It's just heuristic argument and it is not a exact explanation.
Collision and energy exchange is not an important reason for uncertainty.
There is an intrinsic reason.
According to quantum approach, every measurable value is determined by observation.
Before an observation, we do not clearly know the measurable value of a particle.
Look at this picture, the states are not determined before an observation and finally states are determined after observation.
Well, it may not make sense, but that﹑s how the nature works!
In a Heisenberg's Microscope, position and momentum would be good examples of these.
Then how we get a exact, and generalized equation of uncertainty principle?
Using variance of measurement and some math techniques, and then..
BOOM! we can derive this equation.
We'll upload full process on KLMS so have a look!
Thanks for watching this lecture. See you on next lecture~^^
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