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Sha Vuklia

00:15

@user2723984 hey thanks again, yea I found it in the book indeed!

we (as in, in my year at uni) haven't worked with the measurement operator, but apparently it's part of the postulates (at least in this book), so that was worth looking up:)

5 hours later…

Physics Meta

05:25

Q: a hole in the question and answer system, when the question has a drastic edit after answers have been provided

In this post is an example where the editing by the OP has made a drastic difference and makes nonsense of the answer provided before the edit. This has happened to me again after edits by moderators and others, but usually I return to look at the questions I answer, to see what others have mayb...

feature-request

3 hours later…

Slereah

08:30

morning

David Z

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

Slereah

09:27

What about "Doctor"

Herr Doktor Professor

user2723984

09:40

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

09:58

@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

@GodotMisogi Sigh...some people are jobless.

Anonymous

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

user129412

13:25

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

13:56

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

14:08

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

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…

Student404Mus

15:30

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.

Slereah

What a bunch of squares

HDE 226868

15:49

@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.

Student404Mus

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?

John Rennie

16:10

@Student404Mus the expansion rate is currently increasing with time

Student404Mus

ok this is proved observatory

what about theoretically

John Rennie

@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.

Student404Mus

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

John Rennie

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.

Student404Mus

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

Slereah

16:23

the accelerated expansion

John Rennie

Student404Mus

John Rennie

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

Slereah

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

Student404Mus

16:27

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/…

Slereah

probably relevant

Student404Mus

i see

kartik c.p

16:44

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

16:56

@HDE226868 Winter mini classes : )

Physics Meta

17:26

Q: Reputation cap for highly-upvoted posts

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

enumaris

weez

Avnish Kabaj

17:54

Q: Electrostatic potential of a point charge

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

enumaris

18:10

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

HDE 226868

18:46

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

Anonymous

18:59

@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

19:40

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

enumaris

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…

Student404Mus

21:23

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

enumaris

22:15

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

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

enumaris

22:35

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

1 hour later…

enumaris

23:44

anyone know if it's possible in pandas for a column to have elements of different types?

I'm getting an error when trying to tokenize text in a pandas column that's saying expected str, got float but it works for a bunch of rows and then fails at some row number...I didn't think that should be possible...

hmmm

oh...pandas saved the text column as an "object" type...hmmm...odd

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