# Nikolaj K.

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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.

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 Jan29 awarded Popular Question Jan28 comment Textbook on the Geometry of Special Relativity Relativity, Groups, Particles by Sexl and Urbantke will work. Jan25 asked What is a Nicolai map? Jan23 comment Are Newton's “laws” of motion laws or definitions of force and mass? @joshphysics: That wasn't supposed to be my theme, but I agree to some extent (while I still think axiomatizations are great fun and important to our understanding, if done carefully). The claim in your answer just caught my eye and something told me to point out the trouble I'm having with it. Just as now I feel I should point out that " If I say unicorns exist, then I'm saying something 'untrue,' because they have not been observed" isn't true, I'm sure people have seen them. "Believe to have seem them", if you will. It's appearently not reproducable anyhow. But okay, let's leave it at that. Jan23 comment Are Newton's “laws” of motion laws or definitions of force and mass? @joshphysics: "...how is any definition in physics a meaningful statement about the world if there isn't an existence statement underlying it?" In the logical sense: If $A$ and if from $A$ follows $B$, it follows $B$. I.e. axiom: $A\land (A\implies B)\implies B$. No need for existence. That's the example: the empty set is postulated to exist and then used to model numbers. I don't quite see where the existence of reference frames is used. We can say "If we see no change in $v$ (to some desired accuracy), then $B$", that's enough. I think your axiomatization just wantso make sense of Newton 1. Jan23 comment Are Newton's “laws” of motion laws or definitions of force and mass? @joshphysics: What is my sentiment that you share? I'm sure trying to axiomize stuff is helpful, specifically if one want to find flaws in the old mindset. It also clarifies "the status of our empirical knowledge" in some way, but I don't quite know how as this topic is difficult. If there is "empirical knowledge" about masses of particles, then we must recognize that this idea presupposes a physical theory (involving stuff like "mass"). "Also, existence statements tell us something about how the world actually is" How? If I say unicorn exist, does this give us info about how the world is? Jan22 revised Is the step of analytic continuation unavoidable or can you model around it? added 21 characters in body Jan22 comment Are Newton's “laws” of motion laws or definitions of force and mass? And the justification "These are frames of reference in which when an object is isolated from all other matter, it's local acceleration is zero. It is an empirical fact that such frames exist, and we'll take this as the first law" is problematic. Firstly, I don't quite know what an empiric fact is, but I have an engineering understanding of it. But then we can never know if some thing are or can be isolated and hence we can not test this concept. If my friend and I jump off a building, he will not accelerate next to me and so I'd not assume there is a force somewhere. Jan22 comment Are Newton's “laws” of motion laws or definitions of force and mass? What, would you say, is the aim of an axiomatization of Newtonian mechanics? And then regsrding the first axiom: How is an unconditional axiom of the form "there exists $X$" of any use? Is there anything constructively build on the inertial frame (analogous to, for example, the empty set, where you can model numbers in terms of set). I don't quite understand physics, so I might just not see the use, but I see potential harm in enforcing an axiomatization in terms of three sentences, just to conform to the frameworks history. Jan22 comment Is force a “real thing”, or a tool for explaining changes in measurable phenomena? Regarding your first line, What exactly is ment by "is simply a definition of force"? Jan14 revised In which field theories with fermions do string- and fivebrane structures not come up? added 16 characters in body Jan14 asked In which field theories with fermions do string- and fivebrane structures not come up? Jan14 revised Gupta-Bleuler Formalism langle rangle and some text changes, if you like Jan14 suggested suggested edit on Gupta-Bleuler Formalism Jan10 comment How to treat differentials and infinitesimals? Is the infinitesimal interval $D$ used to cheat new generalized elements into our space $X$, which aren't there in the classical formulations? Some of the links speak of $D$ as a subset of a ring. Is there always an ordering on the infinitesimal interval and does one think of this as a collection of different small things, equipped with some notion of size for distinguishing them? It also seems like the Kock-Lawvere axiom (a functional "$ϵ^2=0$"?) seems suitable for extension to infinitesimal calculi like Ito calculus etc., is that right? Do we do super-stuff directly by adding this object? Jan7 comment What are the practical applications of quantum foundations? Why bother painting? (Here "painting" to be understood as a metaphor for the intrinsically rewarding activity of working on foundations for physics. Incidentally, it's also a metaphor for FAPPing.) Jan6 comment The most general procedure for quantization +1, Informative answer (though OP likely doesn't know Kähler). / Does the same work if you view classical mechanics as a field theory over the $\mathbb R$ time axis? / You pop out one concise definition after the other and it seems to work. What are general obstacles to have injective and dense $K$? For computational purposes, this map seems essentially bijective. Does one need to know much about solving the classical equations of motion (Klein Gordon here, although it's never used in your answer as far as I can see) to find the right Hilber space of could one start ad hoc on the other side? Jan4 awarded Good Question Dec31 comment General relativity in terms of differential forms @gerardpc: (I was in doubt if I should use the term covariant) Yes, I mean forminvariant, valid in all coordinates you can come up with. Dec31 answered General relativity in terms of differential forms