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A duck walks into a bar. Animal control is promptly called and the duck is released into a near by park.

My email is to be found on my website.


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.
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
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
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.
Oct
18
comment Where did Schrödinger solve the radiating problem of Bohr's model?
To answer the question in the title: At the university of Vienna.
Oct
16
comment What is divergence?
@DanielSank: Add one, don't complain.
Oct
16
comment Does velocity determine a geodesic?
I remember making this point here.
Oct
13
comment Laplace operator's interpretation
@jinawee: Yeah, I know, I can't quite remember what it was - probably just a screencap of that second section on Wikipedia I speak about.
Sep
11
comment How can we say that a wave function follows schrodinger equation using operators?
If by energy operator you mean that it's a function value of $H$, i.e. $Â=F(H)$, for example $Â:=4H+H^4$, then $Â$ and $H$ have the same eigenfunctions. (I'm pretty sure about this, certainly in the common cases, but not in general. Look up the spectral theorem. Maybe there are pathological functional analysis scenarios I can't think of right now, it happens sometimes. You know, such that if $F$ is ill-behaved, the domain of $H$ and $F(H)$ is different etc.)
Sep
6
comment Difference between Hamiltonian in classical Mechanics and in quantum Mechanics
@Wingonafly: Regarding your response to the second point, what you derive from what is a matter of choice. Usually the Schrödinger equation isn't taken to be derived from anything but taking as a starting point. I don't know what you mean by "How do you answer the question about..." because your initial post didn't even include specific questions. A main difference is that classical observables always commute.
Aug
19
comment How much energy would the Human Torch need?
Joke's on you, The Human Torch is pretty far from being human.
Jul
28
comment Is this really a golden ratio spiral?
Do you know what the object of your interest actually is? If no, search the web for a definition. Once you understand it, there will be no barrier to take the picture and test it yourself.
Jul
10
comment How can blackbody radition be explained by quantization?
Maybe this question relates as well.
Jul
8
comment Laplace operator's interpretation
@mcodesmart: don't worry.. it was fun!