@Danu One thing you can do to "use" fewer package is use a class that either replaces them or includes them itself. For instance memoir for large documents or revtex4-1 for dense technical document.
The thing is that I just want a lot of special looking characters, and combine both mathematical things and physics (so I need things like braket and siunitx and slashed but also tikz-cd for commutative diagrams, extarrows for special arrows etc)
an instance of a package that I'm not really happy with but don't see how to avoid is dsfont for a nice-looking unit matrix symbol (the \mathbb-style 1)
It seems overkill to load a package just for that, but meh, I want a nice-looking unit matrix!
@0celo7 Again, I'm guessing they expect you to treat it as a constant for the purposes of the problem. A lot of intro physics makes these kinds of simplifying assumptions.
@dmckee : This flag. The mod timeline yields the following info: yesterday flag AnswerNotAnAnswer user36790 not an answer yesterday cleared Community♦ Disputed.
@dmckee Well, that is more convenient than crawling though the queue histories, which is what we normal users have to do to access specific review items.
I do it only when I stumble across some post I voted to close but that is still open to find out whether people thought differently or the review just hasn't been completed.
@Qmechanic Only by going into the review queue. We users cannot "handle" them in the way moderator do, and we cannot see pending flags on the posts themselves at all
@0celo7 I don't think that is a well-defined thing to ask for. GR is a physical theory that uses differential geometry. Whether you take the classic approach to defining all the diffgeo objects or the synthetic approach does not make one bit of difference.
@0celo7 Well, I mean, there's nothing specific to GR that you would have to do. You do synthetic differential geometry and at the end you have a model of classical differential geometry in it, which you then use to do GR. But, "doing GR" is precisely the same as "doing diffgeo".
In a very specific sense, whether you do classical or synthetical differential geometry is "just" the difference between using the limit definition of a derivative or using infinitesimals.
That "just" is...not a just, but after you've constructed all the diffgeo objects, the physical theory GR doesn't really care if you used the classic or the synthetic approach
@0celo7 I think you're "too restrictive" to say "GR". The strength of categorial approaches lies precisely in not focusing on a specific application, but in revealing general principles. Once you specialize to a specific application, it is often not worthwhile to pursue the categorial viewpoint further.
@0celo7 Seriously, how the hell am I supposed to remember what $t$ or its kernel is? :P
I seen in a string theory book them map a tree diagram, showing 4-point scattering (i.e. a big X), to a 4-punctured sphere as representing it's conformal equivalent, and at each puncture they insert a 'vertex operator' to somehow translate the incoming/outgoing information from the X to the sphere, is that the whole point of a vertex operator in CFT & ST?
@bolbteppa Yes, by the operator-state correspondence, the inserted vertex operator corresponds to a state in the CFT, and hence inserting it (togehter with other operators) into the partition function gives the transition amplitude between it and the states represented by the other operators
Interesting, he calls the vertex operator a wave function, I vaguely remember in Senechal he exponentiated something and then calls it a vertex operator because of a singularity, looking at it now I'm guessing they even bother to define it because it's useful as the operator $e^{ipX}$ since locally acts like $1 + pX$ for some reason?
@bolbteppa imo, t's just the simplest operator with conformal weight 1 you can write down, and the physical string states are precisely those with unit conformal weight.
Since $t : \mathbb{R}^4 \to \mathbb{R}$ is a map between vector spaces, we have a projection $\pi : \mathbb{R}^4 \to \ker(t)$ (by rank-nullity, essentially)
The first line should be "Consider a hausdorff second countable connected manifold equipped with a (1,n-1) signature section of the symmetric (0,2) tensor bundle"
@Slereah The latter part is just a silly way of saying that you are performing a reduction $\mathrm{GL}(n)\to\mathrm{SO}(1,n-1)$ for the structure group of the frame bundle ;)
