送交者: morningstar 于 January 25, 2002 02:09:06:
I hope Xiaosha's Buddha is the same as Einstein's God. Or else this Buddha must be a great one since he cares about a quantum mechanical representation.
Seriously, quantum mechanics presents a strange picture that is so different
from our daily experiences such that we do not even have adequate languages to describe it.
If one does not find quantum mechanics strange, one does not understand it.
Uncertainty Principle is the corner stone of quantum mechanics. In one form, it simply
states that one cannot accurately and simultaneously measure the position and
momentum of a particle. The product of the uncertainty of the two measurements is at least
the Plank constant h which is extremely small. This quantum phenomenon has to do with
the dual nature of particle and wave-Matter is neither particle nor wave. Quantum mechanics
would not exist if it were possible to measure the momentum and the position simultaneously
with much greater accuracy. In microscopic world, everything is a gamble - you can only
predict what the particle will do in a probabilistic way.
Of course Einstein was not happy about such state of affairs. In later years he
admitted that quantum mechanics describes things correctly, but its description is no
way closer to the truth. "God does not play dice" was his famous answer. Of
course we now know God does. But why?
The exclusion Principle is another matter. This has to do with how the wave function
of a collection of identical particles changes signs when two particle exchange
their position. The particular type with half-integer spin, called Fermions,
produces a negative sign when you do that. This makes it impossible to have two
particles to occupy the same quantum state. The reason for this is much deeper.
Pauli was the first to use relativitistic quantum mechanics to prove this is
the case - hence his name is forever linked with the principle. This is one of
the principle that did not find any elementary explanation so you have to take it
as it is.
It is scaring to think what would be the consequence if the Plank constant suddenly
becomes large.
I apologize for typing in English. Just want to share some thoughts.
大布苏，
I don't quite recall the experience. Perhaps I was crazier at that time than I realized.
Those were fun times, won't you say?
量子同学：
Your question on the definition of force is a common one. The apparent tautology in a way is unavoidable with any fundamental concepts. In math, in language, in logic, you face the same
difficulty. The fundamental concept is difficult to define when there is nothing else to rely
on. Define force as God is OK, as long as you can measure God and manipulate God,and put God
in a mathematical form to precise its relationship with other Gods. Language is always limited, but understanding is not. So don't feel discouraged when the fundamental concept is not crystal
clear. Certain tolerance for vagueness perhaps is necessary in order to move forward. After all,
you need infinite amount of words to precisely define a concept - another reflection of the uncertainty principle. Have fun! Thanks for all the thought-provoking messages.