The h Bar

8:30 AM

morning

David Z

@dmckee @SirCumference Indeed, very culture-specific. In the US it would be rather strange to address your lecturer as "Sir".

Q: Are the claims made by Indian Ministers / personalities regarding ancient Indian inventions true?

9:27 AM

What about "Doctor"

Herr Doktor Professor

user2723984

9:40 AM

I have a lecturer that insists to be called by a friendly abbreviation of his first name, I find it a bit awkward to be honest, I'm not used to it

GodotMisogi

@JakeRose The magnitude of a complex phase shift is 1, and its square is also 1.

@user2723984 what's the abbreviation?

GodotMisogi

9:58 AM

@Blue I just read about some prof from Jadavpur Uni's comments on virginity

Indian news is sometimes more entertaining than Trumposting

2 hours later…

Anonymous

12:21 PM

@GodotMisogi Sigh...some people are jobless.

Anonymous

That's why I've stopped reading the local news these days. :P

user129412

1:25 PM

Near the bottom of the third page this paper (journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.100502) writes that the superconducting gap Delta decreases with magnetic field as $\Delta(B) = \Delta(0) \sqrt{1-(B/B_c)^2} and gives Tinkham's intro to superconductivity as a reference. I tried looking in tinkham and couldn't find this equation. Does anyone know where in the book that would be?

Or perhaps you'd know of another reference that looks at this

The paper talks about Al, so it should be in type 1 part of the book, but I can't seem to locate it

It seems to mimic the phenomenological parabolic law discussed very early on in the book for Bc in terms of Tc, but beyond that I can't find much

I found it, I should have looked a little harder. Its equation 4-52, somewhere in the chapter on Ginzburg Landau

user129412

1:56 PM

What I wrote above is true for parallel magnetic fields. Anyone know where (in Tinkham, probably) I can find something on the field dependence of the superconducting gap for a perpendicular magnetic field?

Avnish Kabaj

2:08 PM

In the past couple of years, several Indian Ministers / personalities have made claims regarding existence of modern inventions in Ancient India. Prime Minister Modi claimed that genetic science and plastic surgery existed in Ancient India. Tripura Chief Minister Biplab Kumar Deb has claimed ...

medical-science history physics history-of-science

Anything for votes

1 hour later…

3:30 PM

It said, "In the distant past, the expansion rate was much larger, while today it's the smallest it's ever been." does it mean that the universe is decelerating?

Nobody recognizeable

@dmckee interesting is that in indian culture we call teachers or professors as sir.

What a bunch of squares

HDE 226868

3:49 PM

@SirCumference Are you back at school for the spring semester?

Anonymous

@Nobodyrecognizeable Nah. The interesting part is that we refer to every random stranger as "sir", irrespective of their gender (at least until they clarify or we get some visual proof) and normally folks don't take offense. A good strategy to avoid one of the most common interpersonal issues in academia. :P

Anonymous

@Student404Mus It seems to be well summarized in the Wiki article.

what my problem is this article which makes me confused
https://www.forbes.com/sites/startswithabang/2018/06/29/surprise-the-hubble-constant-changes-over-time/#147bd4bb9c9a

is the universe accelerating or decelerating in its expansion?

4:10 PM

@Student404Mus the expansion rate is currently increasing with time

ok this is proved observatory

what about theoretically

@Student404Mus the expansion rate depends on the density of matter and dark energy. When matter dominates the expansion rate lows with time i.e. the expansion decelerates. When dark energy dominates the expansion rate increases with time ie the expansion accelerates.

which equation says that?
because Friedmann equation predicts the first case you mentioned

The relevant Friedmann equation is (assuming no pressure):

$$ \frac{\ddot{a}}{a} = -\frac{4\pi G \rho}{3} + \frac{\Lambda c^2}{3} $$

Note that the term in the density $\rho$ is negative and the term in the dark energy $\Lambda$ is positive, so $\ddot{a}$ can be positive or negative (or zero) depending on whether dark energy or matter dominates.

I see. what proves in nowadays the domination of dark energy

4:23 PM

the accelerated expansion

We can't directly measure dark energy, but we can measure the expansion rate using type 1a supernovae. So we measure that the expansion rate in increasing ($\ddot{a} > 0$) and infer the presence of dark energy

I'm not sure what the proof of the accelerated expansion is, I'm sure it's in the PDT

Let's see

student

@Slereah adsabs.harvard.edu/abs/2013PhR...530...87W

4:27 PM

why in this article it wasn't showed that the universe is accelerating rather is decelerating as I understood forbes.com/sites/startswithabang/2018/06/29/…

probably relevant

Q: Reputation cap for highly-upvoted posts

i see

kartik c.p

4:44 PM

why space is black ? . i found two paradox , one by Gyuk and the other seemed complicated (2-one is about finite universe and finite speed of light )can anybody simplify the second one and understand me

Sir Cumference

4:56 PM

@HDE226868 Winter mini classes : )

Physics Meta

5:26 PM

Today I posted an answer on Physics SE which has received a fair amount of attention. However, the reputation increase stopped after about 20 upvotes. I’m not exactly sure how the reputation system works — is this an intended feature? It’d also be neat to see a general list of what actions corres...

support reputation

Q: Electrostatic potential of a point charge

weez

Avnish Kabaj

5:54 PM

From Wikipedia The electrostatic potential energy, UE, of one point charge q at position r in the presence of an electric field E is defined as the negative of the work W done by the electrostatic force to bring it from the reference position rref[note 1] to that position r.1[2]:§25-1[note 2]...

electrostatics potential-energy

Halp!

It probably has a one line answer

6:10 PM

I think it's generally discouraged to post your recently posted questions here in chat to ask for answers

HDE 226868

6:46 PM

@SirCumference Oh, nice. I've heard about things like that.

Anonymous

6:59 PM

@AvnishKabaj Please don't ask for answers to your recent Physics SE questions, in chat (your question was just a few minutes old; be patient). It sets a precedent for what might become an annoying trend in the future. Those who can answer are already watching the queue on the main site! However, if you don't receive sufficient response to you question on the main site (even after waiting for a couple days), then of course you can consider bringing it to the attention of the chat regulars.

Sir Cumference

7:40 PM

@HDE226868 How's life with you btw (been a while since I've seen ya here)?

dang, this roivant sciences is really trying hard to recruit right now...I've gotten calls from like 3 different recruiters about them lol

2 hours later…

9:23 PM

why the very distant galaxies we observe appear to follow straight-line relation?

10:15 PM

woot, posted a story-identification question in sci-fi and fantasy SE

let's see how good they are at identification :D

10:35 PM

@Student404Mus by "straight-line relation" do you meant he Hubble law?

1 hour later…