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1d
revised Can interacting Hamiltonians always be written in second quantized form?
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1d
revised Can interacting Hamiltonians always be written in second quantized form?
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1d
revised Can interacting Hamiltonians always be written in second quantized form?
added 12 characters in body
1d
answered Can interacting Hamiltonians always be written in second quantized form?
Dec
16
comment Total divergence term and corresponding Feynman Diagram
>Isn't that disturbing...pun intended?
Dec
15
comment Akin to gauge field, why GR's lagrangian is not $R_{abcd}R^{abcd}$? What's the mathematical or physical meaning of $R_{abcd}R^{abcd}$?
There are 50 or so variations in the Wikipedia article Alternatives to GR, maybe you find more information why they are dismissed or set aside. The term pops up e.g. Lovelock and Gauss-Bonnet gravity (which don't seem to live in 3+1 dimensions) and I guess in $f(R)$ variants.
Dec
4
revised The index of a Dirac operator and its physical meaning
computed the index
Dec
4
suggested approved edit on The index of a Dirac operator and its physical meaning
Nov
12
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
@DavidZ: Of course, you make me look it up.
Nov
12
comment How to derive the two-term approximation for the Boltzmann equation?
Thanks, yeah I know the BOLZIG+ reference - everyone cites it when they use the electron collision cross sections that come with it :)
Nov
7
comment What is the difference between $|0\rangle $ and $0$?
Consider the vector $v:=(-5,3,7)$ in ${\mathbb R}^3$. It can be written as $v=-5\,e_1+3\,e_2+7\,e_3$. The object $e_3$ is a vector like $|0\rangle$. The number $3$ is a coefficient, like $0$.
Nov
4
comment Formal definition of an observer?
You say you've seen a few formal definitions. What do you mean by "actual definition", then? Seems like there are several.
Nov
4
comment Are identity types interpreted physically in an infinity-topos formulation of equations of motion?
Or let me say: I get the need for path spaces, but do we need "equality proper" before we define equivalence and by this obtain the desired notion of equality?
Nov
4
comment Are identity types interpreted physically in an infinity-topos formulation of equations of motion?
Why do we need types "$=$" to begin with? After all, weak category theory can do without. Can you point me to why, in HoTT, we start out with an identity type and then impose $(A=B)\simeq(A\simeq B)$? Say we start out with a dependently typed theory (with $\prod, \sum$ in particular) and then define "$\simeq$" as is done in the HoTT book. If the principle of equivalence${}^{TM}$ is to be implemented with this axiom, why do we consider a theory with identity in the first place. It appears all we really want is "just" equivalence anyway. Btw. I lurk the nForum - is there a question section?
Oct
30
revised Renormalization, integrating out high momenta Wilson way
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Oct
30
suggested approved edit on Renormalization, integrating out high momenta Wilson way
Oct
27
comment Why quantum mechanics?
Can you, for a concrete simple example in quantum mechanics, follow this procedure (take classical geometry, choose circle group bundle with connection, write down the expression which amounts to the integration "in the $i$-direction") and express the observables $\langle H\rangle, \langle P\rangle, \dots$ in therms of this. Is there the harmonic oscillator, starting from the classical Hamiltonian, worked out with emphasis on exactly those bundles?
Oct
22
revised What exactly is $\hat{\psi}^\dagger(x)$? An operator or a function?
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Oct
20
awarded  Popular Question
Oct
19
comment Is there any physical quantity that does not have uncertainty?
@CarlWitthoft: I suspect you have two, but I'm not certain about it.