# Tag Info

### Bound states between neutrinos using Schrödinger's equation?

A quick back-of-the envelope estimate, in the style of Fermi: For a neutrino mass of m ~ 1 eV, and a Planck mass M ~ $10^{27}$ eV, and supplanting the newtonian potential $(m/M)^2/r$ for the Coulomb ...
• 64.1k
Accepted

### Negative kinetic energy on a step potential

I'm having trouble with the explanation of the kinetic energy on the classically forbbiden region on a step potential ($V=0$ for $x<0$, $V=V_0$ for $x>0$ and $E<V_0$). ... On the classically ...
• 21.8k
Accepted

### Does this double well potential contradict the fact that there is no degeneracy for one-dimensional bound states?

If you take $V_0$ infinite, the wave function solution of SchrÃ¶dinger's equation $\psi(x)$ is forced to vanish on the barrier. So it seems reasonable that the solution on either side of the barrier is ...
• 428
Accepted

### Time-evolution operator in QFT

Maggiore is assuming there that the field interacts with itself or with other fields in a stationary way. In other words, there is no direct appearance of time in the total Hamiltonian. This is a ...
• 73.4k
Accepted

### How to get a lower bound of the ground state energy?

It depends a lot on the specifics of the Hamiltonian and system being examined. One approach that works sometimes is to cast the computation as a semidefinite program and use the duality theory there ...
• 549

### Does this double well potential contradict the fact that there is no degeneracy for one-dimensional bound states?

No, there is no contradiction. For any finite height of the barrier, the splitting between eigenvalues remains small but nonzero, and the result holds. If you truly want to think of the barrier as ...
• 134k
Accepted

### Is Schrodinger's cat a problem of how we define identity?

Early versions of quantum theory (called the "Copenhagen Interpretation") contained a (subjectively) weird thing called the "Heisenberg cut" the idea of the Heisenberg cut is (...
• 549

### I need to find the state of the system at a general time, knowing the Hamiltonian and the state at $t=0$

For this particular initial state, you do not need to diagonalize the Hamiltonian. The reason is that this particular initial state is an eigenstate of the Hamiltonian, and as a consequence you can ...
Accepted

### Determining the Sign of $E$ When Solving the Time-Independent Schrödinger Equation

Normally, if the potential is finite at infinity, one often set this potential to be $0$: $V(\infty)=0$. In this case, bound states have $E<0$. Thus, for hydrogen, all $E<0$ for bound states. ...
• 46k

### Negative kinetic energy on a step potential

Negative kinetic energy is absurd, right? What's wrong with this calculation? Kinetic energy value we assign to the particle, based on measurement or the psi function, cannot be negative. When you ...
• 39k
Accepted

### Time derivative of complex conjugate wave function

Is $\Psi^*$ a wavefunction? Depends on what you mean by that: $\Psi^*(x,t)$ is certainly a function, it has the property that $\int dx\, |\Psi^*|^2 = 1$ for all $t$ (assuming that $\Psi$ does), so you ...
• 28.3k

### Is Schrodinger's cat a problem of how we define identity?

The idea that the property of being alive is emergent doesn't mean it is an illusion. There is a real objective difference between a cat being alive and a cat being dead. A living cat breathes in ...
• 8,474