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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.


Apr
14
comment Does anyone take the Wightman axioms seriously?
"The question sounds like this, for a classical physicist: Does anyone...". That should read: The question sounds (to an here not further specified referent, probably you mean yourself) like the following question sounds like to a classical physicist: Does anyone..."
Apr
10
comment Is $\langle k \vert k_1k_2\rangle=0$
Have you tried writing down the bracket with the annihilation/procreation operators in full, and permuted them inside the vacuum state according to the commutator rule?
Apr
9
comment Feynman propagators for scalar fields
Off-topic remark: I'd add $\left|_{J_1=0}\right.$ right after the operator. Btw. to force a good height of |, that reads "\left|_{J_1=0}\right."
Apr
4
comment Where do $L_+$ and $L_-$ live, if not in $\mathfrak{so(3)}$?
@user35952: My points is, e.g., if you study the multiplication of the number $7$ by the number $5$ in $\mathbb N$, there is no reason to write this as $7\mapsto(1-2i)\,7\,\overline{(1-2i)}$, if you think that's useful.
Apr
4
comment Where do $L_+$ and $L_-$ live, if not in $\mathfrak{so(3)}$?
I might be misunderstanding something here, so let me raise a point: Without judging if the operators do or do not lie in the algebra, why does your question arise anyway? In my ear, it sounds similar to "I want to study the properties of consecutive derivatives and people use abstract algebra to do it. How is that justified?" Why not? If you study how $a\mapsto\mathrm{e}^{i\phi}a$ affects elements of $\mathbb C$, is there a reason you would you restrict your study by demanding not to use complex conjugation on $\mathbb C$?
Apr
2
comment What are the spaces over spacetime points in which a field takes its values? Is it always the same?
What is the b-boundary approach? What objects are added to the frame bundle? And at those new fibers the direct sum of frame bundle and that new object then?
Mar
31
comment Why do we require manifolds to be a topological space?
What is $U$? Anyway, the Wikipedia article Metric space says in the fourth section how every metric space induces a topology. / The work I liked to is a little long. The main idea is to use topoi, which are frameworks which encompass the set paradigm, but generally don't need to play the same game/follow the same logical rules. This is related. And just for curiosity, lets me mention that the discussion in this question reminded me of Exotic R4.
Mar
31
comment Why do we require manifolds to be a topological space?
Just two comments: a) Doesn't a metric induce a topology anyway? If you want to have conventional spacetime, there will necessarily be some topology. b) There are doing physics in topoi, e.g. this, in which the notion of openness is a little broader (but not for manifolds, it doesn't start out with spacetime.)
Mar
30
comment Why is the Gibbs Free Energy $F-HM$?
@ChickenGod: You can use $\mathrm dV_1=-\mathrm dV_2$ to show equilibration of the intensive variables $P_1,P_2$, but it's not, I think, relevant in the proof to show that $T\mathrm dS\ge \delta Q = \mathrm d(U-\frac{\partial U}{\partial q}\cdot q)$, were $q$ is $V, M, \dots$.
Mar
28
comment Why is the Gibbs Free Energy $F-HM$?
@ChickenGod: I don't know what the first half of your response has to do with the question at the end, or what you set $E_2=TS_2$ for, but let me ask you something in return: How does "$V$" in the derivation of the extremal conditions for the various potential single out that it has to do with volume. If you have a proof for $V$ and $P$, why doesn't it work if you use the other $M$ and $H$ in their place instead?
Mar
27
comment Homogeneity of space implies linearity of Lorentz transformations
"some reference"... do you have little more background on what your thoughts on this are? Have you le asked this before somewhere?
Mar
27
comment S. Weinberg, “The Quantum theory of fields: Foundations” (1995), Eq. 9.2.15
Final value theorem.
Mar
26
comment Attraction and repulsion of charge?
@JohnRennie: Well, the question has 3 electromagnetism tags. Yes, I start with the point of view that there is the experimental observation that there are repelling objects and non-repelling objects.
Mar
26
comment Attraction and repulsion of charge?
@JohnRennie: I don't know how you can justify using quantum field theory other than by that it works, which is the same argument that I use. I agree that a quantum field theory explanation has great appeal. It also has the merit that it explains it in terms of some other structures which relate to many other things, which I don't do. Not sure how I'd classify "fundamental" though. Maybe by "part of current research", then it works.
Mar
26
comment Attraction and repulsion of charge?
@JohnRennie: Mhm, I just point out why the inverted variant doesn't work. I'd even say it's a better answer than the one given in 'Why do same/opposite electric charges r...' where he sets up a huge framework and then argues "Unlike charges attract each other, because if we model the world with this math then there is just no other way." We arrived at this math because the conclusions from the other math doesn't agree with what we see, and the $AB$-repel alternative doesn't either. If you want charges, better to it the $AB$-attract way.
Mar
23
comment What are type system examples of local gauge transformation- and field strength-like objects?
Thanks for the response. 1) Adding $\pm 1$ is again global as it doesn't see the types, but I get this now. 2) I want to see why gauges should be seen as identity types. You said "Notably when the homotopy type theory is equipped with the additional axiom of differential cohesion, then one can "differentiate" identity types." Is there something we get from HoTT, which we don't have if we, even more directly, set up a suitable topos for our physics? I.e. is there a reason why types actually are an advantage here, apart from the meta advantage that many different people are interested in it now?
Mar
23
comment Are identity types interpreted physically in an infinity-topos formulation of equations of motion?
Thanks for the answer, I'm working to understand it. I imagine you'd like to see my follow-up question, which is more concrete.
Mar
21
comment How did the scientific community receive Einstein's theories when he published them?
There are Wikipedia articles on these sorts of things, see e.g. wiki/History_of_special_relativity#Early_reception.
Mar
18
comment What is the scientific view of creation?
Who is "we" and what's the range of "nobody" in the first sentence? Everybody has access to gravity, the big bang theory is much harder to defend. I couldn't do it, in any case. Like with the existence of chromosomes, I can only appeal to authorities who at this point in time are of the opinion that it's a better model than the others. If they change their mind in the next years about it, I'd give another answer. Hence it's easy to doubt it.
Mar
16
comment How rigorous can conservation of energy be made?
In physics you try what has worked before until it doesn't. Conservation of energy is a showpiece of the cookbook, hard to get rid of. And people like it, it's tasty. I also asked a related question, and see the related links posted by Cmechanic.