User Quantumwhisp

35 votes

6 answers

3k views

Must observables be Hermitian only because we want real eigenvalues, or is more to that?

asked Apr 24, 2021 at 8:40

14 votes

3 answers

877 views

Justification of the Least Action Principle using conservation of information

asked Dec 18, 2017 at 11:22

13 votes

1 answer

2k views

Is the usage of the Fock space a postulate in QFT?

asked Jun 23, 2016 at 11:59

11 votes

3 answers

2k views

Is the vacuum state a coherent state?

asked Sep 8, 2017 at 11:53

11 votes

5 answers

564 views

Does an Operator that neither commutes with $\hat{X}$ or $\hat{P}$, nor can be expressed as a "function" of $\hat{X}$ and $\hat{P}$ make sense?

asked Oct 2, 2019 at 12:48

10 votes

3 answers

1k views

Is a canonical transformation equivalent to a transformation that preserves volume and orientation?

asked Dec 18, 2017 at 10:06

10 votes

2 answers

810 views

Can we always express the EM-Field Hamiltonian as (possibly time dependent) pair of annihilation and creation operators?

asked Sep 29, 2017 at 10:01

8 votes

2 answers

2k views

Derive canonical commutation relations from Schwinger's principle

asked Jul 8, 2017 at 13:57

8 votes

1 answer

565 views

Can any symplectomorphism (1 Definition of canonical transformation) be represented by the flow of a vectorfield?

asked Mar 9, 2018 at 19:04

8 votes

1 answer

497 views

Where does it become apparent in real scalar QFT that the field has to be an operator-valued distribution, as opposed to an operator-valued function?

asked Aug 28, 2022 at 15:04

7 votes

3 answers

567 views

(Coming from Wigner's Theorem): What is a Symmetry in QFT?

asked Nov 7, 2019 at 6:49

7 votes

2 answers

759 views

Ehrenfest Theorem and boundary Conditions

asked Jul 13, 2016 at 11:32

7 votes

3 answers

1k views

Rigorous mathematical definition of vector operator?

asked Apr 19, 2017 at 0:16

6 votes

0 answers

367 views

Is there a modified Least Action Principle for nonholonomic systems?

asked May 8, 2017 at 23:03

6 votes

1 answer

690 views

Entropy of subsystem maximized?

asked Nov 3, 2016 at 11:00

6 votes

0 answers

541 views

Hamiltonian formulation of the semiclassical Model of electrons

asked Jul 9, 2016 at 10:42

6 votes

1 answer

817 views

Definition of matrix elements of an operator in the path integral formalism wrong?

asked Jun 24, 2017 at 16:40

6 votes

2 answers

1k views

Contradiction between Rabi oscillation and energy shifts in AC Stark effect

asked Apr 8, 2017 at 9:05

6 votes

1 answer

302 views

Locality in the coulomb gauge of classical electrodynamics

asked Oct 16, 2017 at 23:15

6 votes

2 answers

601 views

Formulation of an Action-Principle in a general Phase Space (No Cotangent-Bundle)

asked Apr 6, 2018 at 19:13

6 votes

2 answers

393 views

Why is time-evolution unitary? - The Heisenberg-picture Version

asked Oct 15, 2019 at 16:06

6 votes

1 answer

676 views

Does Haags Theorem forbid Time-Evolution?

asked Nov 6, 2018 at 18:18

6 votes

1 answer

322 views

Momentum operator ambiguous?

asked Aug 18, 2018 at 5:31

6 votes

1 answer

122 views

Spectral theorem in QFT

asked Sep 1, 2022 at 23:22

6 votes

2 answers

177 views

Are Grassmann numbers always "under the hood" if we deal with fermionic ladder / field operators?

asked Jun 18, 2022 at 20:19

6 votes

1 answer

357 views

Definition of the $S$-Matrix in Schwartz QFT-Book: Why is $\langle f, t_f | i, t_i \rangle$ in the Schroedinger picture, and not Heisenberg-picture?

asked Jun 28, 2021 at 23:04

5 votes

1 answer

568 views

Does the LSZ-Reduction Formula work for Photons?

asked Jul 2, 2021 at 11:29

5 votes

1 answer

70 views

Can we assign an Entropy-value to physical systems without modelling them by an ensemble / classical probabilities?

asked Apr 13, 2021 at 0:14

5 votes

3 answers

231 views

Why is it said that it takes more energy to let a house cool down and heat up again, compared to keeping the temperature constant? [duplicate]

asked Oct 12, 2021 at 11:37

5 votes

2 answers

335 views

Derivation of Schwingers action principle from Heisenberg Equation and CCR - Why does it work with Anticommuting variations?

asked Oct 24, 2017 at 0:19

Stack Exchange Network

165 Questions

Must observables be Hermitian only because we want real eigenvalues, or is more to that?

Justification of the Least Action Principle using conservation of information

Is the usage of the Fock space a postulate in QFT?

Is the vacuum state a coherent state?

Does an Operator that neither commutes with $\hat{X}$ or $\hat{P}$, nor can be expressed as a "function" of $\hat{X}$ and $\hat{P}$ make sense?

Is a canonical transformation equivalent to a transformation that preserves volume and orientation?

Can we always express the EM-Field Hamiltonian as (possibly time dependent) pair of annihilation and creation operators?

Derive canonical commutation relations from Schwinger's principle

Can any symplectomorphism (1 Definition of canonical transformation) be represented by the flow of a vectorfield?

Where does it become apparent in real scalar QFT that the field has to be an operator-valued distribution, as opposed to an operator-valued function?

(Coming from Wigner's Theorem): What is a Symmetry in QFT?

Ehrenfest Theorem and boundary Conditions

Rigorous mathematical definition of vector operator?

Is there a modified Least Action Principle for nonholonomic systems?

Entropy of subsystem maximized?

Hamiltonian formulation of the semiclassical Model of electrons

Definition of matrix elements of an operator in the path integral formalism wrong?

Contradiction between Rabi oscillation and energy shifts in AC Stark effect

Locality in the coulomb gauge of classical electrodynamics

Formulation of an Action-Principle in a general Phase Space (No Cotangent-Bundle)

Why is time-evolution unitary? - The Heisenberg-picture Version

Does Haags Theorem forbid Time-Evolution?

Momentum operator ambiguous?

Spectral theorem in QFT

Are Grassmann numbers always "under the hood" if we deal with fermionic ladder / field operators?

Definition of the $S$-Matrix in Schwartz QFT-Book: Why is $\langle f, t_f | i, t_i \rangle$ in the Schroedinger picture, and not Heisenberg-picture?

Does the LSZ-Reduction Formula work for Photons?

Can we assign an Entropy-value to physical systems without modelling them by an ensemble / classical probabilities?

Why is it said that it takes more energy to let a house cool down and heat up again, compared to keeping the temperature constant? [duplicate]

Derivation of Schwingers action principle from Heisenberg Equation and CCR - Why does it work with Anticommuting variations?