The h Bar

« first day (3061 days earlier) ← previous day next day → last day (1851 days later) »

1:07 AM

Q: Has the "osmium spheres" gravity example ever been done?

Calculating the force of gravity between two dense spheres is a classic physics problem that has come up numerous times. Has any real-world space mission ever performed a demonstration of small body gravity? Set up an effectively weightless environment in high vacuum, nudge a pair of spheres ver...

5 hours later…

Physics Meta

5:40 AM

Q: An Issue with Detecting Identical Titles

I was editing a question titled "newton's law of restitution" and I edited the title to "Newton's law of restitution" (There were latex issues in the body of the question and I was not editing the question just because of obsessing over the title as it might seem from my recent behavior :P). When...

discussion bug questions moderation search

7 hours later…

bolbteppa

12:30 PM

Is there a super fast hand-wavey way to see that $R_{kl} \approx \sqrt{\frac{2}{\pi}} \frac{\sin(kr - \frac{1}{2}l \pi + \delta_l)}{r}$

2 hours later…

Emilio Pisanty

2:08 PM

Q: What is a singular continuous spectrum?

I read some answers about this and the wikipedia page that basically always say that a spectrum can be decomposed into: $$\mu = \mu_{ac} + \mu_{sc} + \mu_{pp}, $$ where $\mu_{ac}$ is absolutely continuous, $\mu_{pp}$ is a pure point spectrum, and $\mu_{sc}$ in singular continuous... What does...

quantum-mechanics mathematical-physics hamiltonian mathematics

@Qmechanic sounds like your cuppa tea

Either yours or Valter's

ACuriousMind

2:24 PM

@EmilioPisanty String comparison that does not test for exact equality but some fuzzier notion is annoyingly hard and usually not very fast. If the text is guaranteed to be ASCII you can just cast both strings to upper- or lowercase and condense whitespaces, but once Unicode is involved it gets messy

Imagine: Every time you type a question title, you see several seconds of "Searching for similar question titles..." before it lets you post.

Actually...that might not be entirely bad :P

4 hours later…

Sir Cumference

6:42 PM

@bolbteppa I like how the quantum field theory book shows a literal field

danielunderwood

I don't seem to understand the cover of his GR book

I always get a chuckle out of the QFT one though

ACuriousMind

@danielunderwood It symbolizes that "Oh, the walls are melting again" feeling you get when you do too much GR

2 hours later…

pp.ch.te

8:32 PM

Hi everyone! This is a problem from a entrance exam for a phd in geometry and mathematical physics. Just out of curiosity, what would you say for the first question?

First of all, how would one go in finding H?

Because i thought considering the L as a classical lagrangian, legendre transforming it and quantize canonically. What is bothering me is that \mathcal L that resembles a lagrangian density

ACuriousMind

@pp.ch.te You mean because many write $L$ for the Lagrangian and $\mathcal{L}$ for the Lagrangian density? That's not an iron-clad rule, and your $\mathcal{L}$ there is pretty clearly an ordinary Lagrangian.

danielunderwood

9:06 PM

What exactly are entrance exams? Do you take them between admission and officially starting or along with the application? Are they the same as qualifiers?

1 hour later…

Captain Bohemian

10:29 PM

@danielunderwood Entrance exams are exams held to select applicants.

I hate waking up without feeling refreshed.

1 hour later…

Captain Bohemian

11:37 PM

I find managing time very difficult. How nice if I can do whatever I want to do without considering the time constraint. Actually when I concentrate on my engagement, I don't have the track of how much time has elapsed. I can only keep track of time when my attention is lost and think of to check the clock.

« first day (3061 days earlier) ← previous day next day → last day (1851 days later) »

all rooms