@CrazyBuddy My sleep schedule is pretty random these days, depends on when I have lab work. For example, today I got up at 4 PM (I'd slept at 5AM). But the day before, I'd gotten up at 12.
Note that as you accelerate a spaceship towards the speed of light you will blue shift the microwave radiation and increase it's temperature. Eventually you'll roast the ship and all aboard! This is actually happening for the Earth (well, not the roasting bit) as the microwave background is sligh...
let's say there is a star every unit of distance, then as time gets closer to 0 (big bang), these stars get closer and closer until they are touching. So when t is very close to 0, all of the stars are pretty much touching. So this means we have an infinite universe of enourmous density
@Chris We don't know if the universe is infinite in size, but assuming that it is, it remained infinite down to and including the Big Bang, at which point the density was infinite.
yeah that's probably right john, but just the idea of an infinite universe with such a large density everywhere is definitely not how i immagined the big bang
@Chris the balloon analogy only works for a finite universe with positive curvature. The curvature of our universe has been measured to the flat to within 2% i.e. the critical density is 1.02 +/- 0.02
The universe isn't expanding through a fourth spatial dimension. It's common to visualise a curved manifold by embedding it onto a space of one higher dimension, but this is a purely mathematical operation to make it easier for our 3D brains to grasp. There is no sense in which the universe aroun...
Note I was looking at wolframs definition: A curvature such as Gaussian curvature which is detectable to the "inhabitants" of a surface and not just outside observers. An extrinsic curvature, on the other hand, is not detectable to someone who can't study the three-dimensional space surrounding the surface on which he resides.
@Chris extrinsic curvature can be detected by inhabitants of the embedded universe. For example two ants on the balloon could set off walking in parallel straight lines and they would find their paths converged.
The greater question is what is the most elegant framework to describe GR and everything else in the universe. It's true, thinking of curvature as going into the next dimension gets you squat
I had been saying I was planning on leaving the site, and the reason was that our community had become too unfriendly and too tolerant of rude behavior. After the election, that seems like it may have changed, and if that's the case, my initial reason for leaving is no more. So I wanted to get a sense of whether the current community really wants to require civility.
and if so, if I should stick around.
and I have to log off for a few minutes but I'll be back
@Chris dark energy causes distant parts of the universe to accelerate away from us. Go far enough and the acceleration gets so great that even light can't keep up.
but the time taken (according to Earth) for you to get to far away points diverges to infinity at a finite location, beyond that you can't reach even going to t=infinity
This is all getting a bit confused. I don't think the chat format makes it easy to discuss this sort of thing. Really you need to look back through the site for answers that go into it.
And to be fair my experience is that it rarely does. Only on a couple of occasions have I been personally criticised, and since the critic subsequently went quiet I suspect they knew they'd overstepped the mark.
I posted some genuine questions that get grilled instantly by wanna be moderators. In particular one question, then a higher rep guy said my questionw as great, and the wanna be moderators all changed their minds. My question now has 11 up votes
Suppose when a train is at rest, it has a length of $L$. Let the position of the back of the train at any time be $A$, and let the position of the front of the train at any time be $B$.
Now assume a stationary observer on the Earth, O, observes point $A$ to be accelerating at a constant rate, ...
If a ball is simply dropped, each time a ball bounces, it's height decreases in what appears to be an exponential rate.
Let's suppose that the ball is thrown horizontally instead of being simply dropped. How does the horizontal distance travelled change after each bounce?
Context behind ques...
these sites are stricter than most online forums, and new members get confused when what they think are good questions get grilled and downvoted instantly
Hi, John, and welcome to Physics Stack Exchange! Please see our homework policy. We expect homework problems to have some effort put into them, and deal with conceptual issues. If you edit your question to explain (1) What you have tried, (2) the concept you have trouble with, and (3) your level of understanding, I'll be happy to reopen this. (Flag this message for ♦ attention with a custom message, or reply to me in the comments with @Manishearth to notify me) — Manishearthyesterday
@Chris you could argue that it should be called something other than "closing," and that has been brought up on MSO, but bottom line is that it is not an insult
@DarenW well, we generally don't allow open-ended questions, especially questions which can have a host of different answers (like this one--there probably are hundreds of good textbooks that qualify). I'll close it for now, if you edit it into a much more specific question, I'll be happy to reopen. Otherwise, you may ask this question on Stack Exchange Api V2 Chat. — ManishearthSep 21 at 4:14
For some reason the link title says "SE API V2", that's a bug
I checked the FAQs to look for an answer without any luck. Forgive me if it is there and I overlooked it. I recently asked a question with the title: Causality in a gedanken experiment on the hydrogen atom, and John Rennie commented on it. In my response I simply put his name in the text. I mean ...
@DavidZaslavsky I have just read the chat session and your preconditions for sticking around confuse me. I got the impression that you'd like to exchange the crew of members that was here (long ago) before the elections and contributed interesting and high level stuff against new more polite users. This seems exactly what has happend at the expence of the level of the content of the site. Things look still mostly homeworky to me,
and the few people who ask higher level advanced questions, such as Luscher, RamanujanDirac (or how he is called), and others interested in similar things have troubles getting good answers.
@Nemo well, I never really got to finish making that point, which is why you are confused
but now that you've brought it up: my precondition for sticking around is basically that the community does not tolerate or encourage rudeness.
it doesn't matter whether the community is made of the same people from before and they change their behavior, or whether it is mostly new people
it doesn't matter whether they ask high or low level questions
On a separate point, perhaps at this moment (i.e. the last couple of hours) there are a few more homework-like questions than usual. But in general, I still do not agree at all with your assessment that the level of content of the site has dropped.
So you are really willing to sacrifice the nice good high level content we had before the election to achieve a site that has more polite conversations? Would you really be happy with just a homework level site as long as strict politeness is ensured?
Look at Luscher's question and similar questions, they are hardly getting answered now.
I'll say this: I am willing to participate in a site where rudeness is not tolerated, whether or not that site has high-level questions. I'm not willing to participate in a site where rudeness (of the sort we have seen here) is tolerated, whether or not that site has high-level questions.
It's always been the case that high-level specialized questions were less likely to receive answers.
Why is it that when you look in the mirror left and right directions appear flipped, but not the up and down?
Suppose when a train is at rest, it has a length of $L$. Let the position of the back of the train at any time be $A$, and let the position of the front of the train at any time be $B$.
Now assume a stationary observer on the Earth, O, observes point $A$ to be accelerating at a constant rate, ...
