@JohnRennie But the even horizon is the black hole's boundary where no causal curve can escape towards infinity and that's just the light cone, isn't it?
@JohnRennie OK. You are right that the hypersurface $T=\pm X$ is just the light cone of the origin of the KS diagram, not the light cone of the whole KS diagram while the event horizon is the hypersurface $T=\pm X$. So what does that all curves $r\neq r_s$ approach the event horizon $T=\pm X$ when t approaches $\pm \infty$ mean? All test objects stationary on the KS diagram would approach the event horizon when t approaches $\pm$? Why is so?
They don't really approach the event horizon of course, it's just the result of the non-linear mapping between Schwarzschild and KS coordinates that makes it look as if the lines of constant $r$ are approaching the horizon.
@JohnRennie so the KS coordinate system is not ideal in that it may lead to the misunderstanding that all test particles stationary on the KS diagram will approach the event horizon when t approaches $\pm \infty$?
All diagrams have their uses. The KS diagram is very useful for understanding the behaviour of objects crossing the event horizon. It's not so useful for distances large compared to the event horizon radius.
@JohnRennie OK. In addition, I also find another strange place on the KS diagram: the curve $r=r_s$ is at the origin at whatever finite $t$ but runs across $T=\pm X$ when $t=\pm \infty$.
Hi there! Is $n$th order degenerate perturbation theory contained as a limit in $n+1$th order non-degenerate PT? Is there a concise way to form this limit?
I imagine I have some symmetry breaking parameter $\delta$ which allows me to control $E_1 - E_2$ such that I can bring the gap the zero in a controlled way.
@ZeroTheHero Well, yes I understand the first part if your message. For the second part, IMO, there's no reason to not "invite" any user who wants to contribute in keeping the site clean. And I don't know why that room should be even made a gallery room. I can cast close votes, so I could be of some help to the community. I don't see what's the point in stopping me from doing that.
user434058
@ZeroTheHero And if you are under the impression that the chatroom (that I proposed) is a "cabal" or, in any way, secretive, then you are misunderstanding my proposal. I only wanted an open and visible to all chatroom. It is in no way any special group of sword-yielding elite users :-)
$v(t) = t^2$ <-- velocity-time graph where $\frac{dv}{dt} = 2t$ therefore at exactly 3 seconds after I have started running, my instantaneous velocity (my velocity at exactly the 3rd second) would be $6m/s$ right?
user434058
8:21 AM
@JingleBells No! Just find $v(3)$, in this case $3^2=9\:\rm m/s$. What you've found by putting $t=3 \: \rm sec$ in $\mathrm d v/\mathrm dt$ is the instantaneous acceleration at $t=3 \:\rm sec$, which is $6 \:\rm m/s^2$.
So in this example I want to find the extension produced in the spring. The two methods are given in the image.( First one is by force method and the other one is energy method). The two yield different results. Where did I commit the mistake?
In the second method I have assumed that kinetic e...
@FakeMod What you're proposing would primarily affect new users, and not every user can access chat (even if the rep threshold is low). Moreover, the chat feature is not used much expect by a small subset of users, so it would de facto have a selective reach. Given the controversy around this CURED room, you should at least stand up and make the suggestion on Meta about this: I hope to be the first to downvote this foolish idea.
However frustrating it is to run out of close votes, the reality is that concerted action to work around that limitation would IMO be harmful.
user434058
2:26 PM
@ZeroTheHero Yeah, I was thinking of making a Meta post, but seeing lesser support than I expected, I suppose making a post on Meta would not make any difference as to the creation of the room. I have satisfactorily convinced myself that the room should not be created, and that's why I do not intend to push this further :-)
user434058
@BioPhysicist I was quite sure that this would have beenasked before (since it's really common), but I couldn't find any dupes. So after 10 minutes of searching, I decided it to answer it myself :-)
@ACuriousMind From more of a teaching / tutoring perspective I enjoy Newtonian mechanics in the sense that it is (should be?) used to teach students how to start thinking more like a physicist.
I just asked a question about how to figure out how fast a room will cool, and what the name for this type of problem is, so I can do more research, and potentially find the answer to it in the responses, or if someone tells me what type of problem it is, by searching Google for the right phrases...
@BioPhysicist Sad :-( Space SE folks say, had they 10 minutes more, they chould have launched. Next try about 2 days later ($\approx$ 22:30 saturday in CET)
So in this example I want to find the extension produced in the spring. The two methods are given in the image.( First one is by force method and the other one is energy method). The two yield different results. Where did I commit the mistake?
In the second method I have assumed that kinetic e...
