Recent content by orienst

Must the ground state in an even potential of one dimension be the even parity?

Thanks for your reply.

Let f(x) be the following function: f(x)=\infty,if x<0 or x>a;f(x)=0,if 0<x<a. What’s the derivative of f(x) at x=0 and x=a? I know that the derivative of step function is \delta(x) , but what will occur if the jump is infinite?

Thanks! I think what you mean is that the measurement collapse the spin state. But what does the spin vector like before your measurement?

Thanks for your reply. I’ve read your story. But I want to visualize a vector in three-dimension!

Thanks, Demystifier !Perhaps I didn’t express clearly. When I say “a vector a which has the same projection in any direction and at any time”, I mean I’ve made a measurement in a random direction at some time. Certainly I will get \hbar/2 or -\hbar/2. So I say that the electron spin has...

If I have two point mass moving on a track, we say that this system has 2 degrees of freedom, because we need two independent variable to locate the point mass. But what’s the number of DOF if their (the two point mass) distance was determined? Is it one? If so, which variable can locate the two...

Can we always calculate the commutation relations of two observables? If so, what’s the commutator of P (momentum) and H (Hamiltonian) in infinite square well, considering that the momentum is not a conserved quantity?

How do you visualize the spin of electron in your head? I can’t imagine such a vector which has the same projection in any direction and at any time. Is it an understandable object in three dimension?

But t is not a dynamic observable.

Why we use arrow for vector? I think it’s only am instrument. Use the appropriate tools to make work clear, that’s what we should do when we learn physics. We mustn’t use operators, we can use matrix instead.

Anyone who majored experimental physics can tell me how to measure the momentum in the laboratory ?

Law of Gravity！Why？

You are calculating the velocity using the classical mechanics. I don't think you can use macroscopic objects to explain the microscopic phenomenon.

If a "particle" in a momentum eigenstate, then according to the uncertain principal, the particle’s position has the biggest uncertainty. It may appear everywhere. Then you say that the particle has an exact velocity… I can’t understand that.