The h Bar

Nah just some FB goblin

CooperCape

poor goblins

12:39 AM

Goblins grow-up to become trolls.

Alex Jones' and the Literal Potbelly Goblins $^{copyright_Phase}^{(circa 2017)}$

Huh

guess you cant do that

You need a base.

Base^exponent

Fug

12:55 AM

@Phase 1) it's massless, 2) what?, 3) pretty much? That's "not even wrong"

On the other hand, global warming is a hoax

How isn't it wrong?

It's nonsense

Just because something has energy doesn't make it energy, otherwise a basketball is just vibrating energy too. Particles have other properties than just energy

Impossible color

Impossible colors or forbidden colors are supposed colors that cannot be perceived in normal seeing of light that is a combination of various intensities of the various frequencies of visible light, but are reported to be seen in special circumstances. == Types == These impossible colors are of two types: Colors that would be seen if the output strengths of the human eye retina's three types of cone cell (red, green, blue) could be set to values which cannot be produced by exposing the eye in normal seeing conditions to any possible combination of strengths of the frequencies of visible light....

1:22 AM

@0ßelö7 have heard from Chris White?

@skullpatrol not in a while

He's at Berkeley, right? @0ßelö7

maybe

How's the temp on your new computer?

no idea

1:44 AM

If I measure $\overline{R} = 7.924556 \Omega$ and $\delta R = 0.054322\Omega$, how do i properly report this measurement in the form $X = \overline{X} \pm \delta X$ ?

@georg Is $\overline R$ an average of multiple measurements of a resistance?

yeah

What's wrong with just taking the two numbers you have and putting them in the slots you've made?

http://courses.physics.ucsd.edu/2012/Summer/session1/physics2bl/Lecture1.pdf
page 34 of that makes me think i must truncate..?

But I'm not sure..

@georg I agree. Truncation is appropriate.

After you remove the insignificant digits, what's left?

1:49 AM

So.. $$R = (7.92455 \pm 0.05432 )\Omega$$
?

@georg Here you have very many significant digits on your uncertainty. Do you believe them all?

Assuming I do, is my value of R correct?

@georg Well, I don't believe all the digits in your uncertainty are significant. Truncate more.

The recipe you linked to is pretty simple in this case.

It's a theoretical exercise to make sure i understand

Even those of us in the precision measurements business, who are sometimes just as interested in the uncertainty as in the central value of a measurement, only rarely report an uncertainty to more than two significant figures.

1:55 AM

I think I'm meant to apply this rule:

The uncertainty in any measurement, 𝜹𝑿, can never be smaller than the half the smallest
division on the measurement device.

But, I'm not sure

Sorry, actually this:

@georg You haven't mentioned a measurement device (and 0.05 Ω is a pretty impressive precision for a resistance).

Rule 4: The measured value, 𝑿̅, must be rounded to the precision of the uncertainty.
To find 𝑋̅ from a minimum and maximum we can use:
𝑋̅ =1/2*(𝑋𝑚𝑎𝑥 + 𝑋𝑚𝑖𝑛)

Where we must round to exactly the same digit as the uncertainty.

So, is the \overline{x} value rounded the same digit as uncertainty?

I believe the original numbers needn't be truncated based on that.

@georg Yes, that is the correct rule. But in this example your uncertainty is not yet rounded correctly.

How can i fix?

This stuff is elementary but really confusing for me

@georg Follow the guidance you linked to already: truncate the uncertainty to one significant figure, keeping extra figure if the first significant figure is a one.

Well, round rather than truncating, but it winds up being the same half the time :-)

2:03 AM

The linked pdf isn't my classes. So i don't think i should follow it

The Rule 4 is from class

@georg In my professional opinion, the linked PDF is giving you good advice.

So, it is saying this:

Rule 3: When writing the lab report, the uncertainty in any value, 𝜹𝑿, must have exactly ONE
“significant figure.”

The correct way to write your uncertainty is 0.05 Ω.

Yes, that's the rule.

To find 𝛿𝑋 from a minimum and maximum we can use:
𝛿𝑋 =
1/2*(𝑋𝑚𝑎𝑥 − 𝑋𝑚𝑖𝑛)

Where we ALWAYS ROUND UP so there is one non-zero digit.

So I should apply both Rules 3) and 4)

3) for \delta X and 4) for \overline{X}

The caveat about an extra digit if the first one is something that starts to make sense after you've dealt with uncertainties for a while

2:05 AM

You mean 𝜹𝑿, must have exactly ONE
“significant figure.” ?

@georg This is a fine rule.

What does that mean, can you give an example

2 mins ago, by rob

The correct way to write your uncertainty is 0.05 Ω.

How is 0.05 \ohms only one sig fig

why not 0.5\ohms

20 mins ago, by georg

So.. $$R = (7.92455 \pm 0.05432 )\Omega$$
?

2:10 AM

Oh aha

0.05 and 0.5 are different numbers, by a factor of ten.

i see

yeah

lol

So rule 3) says only use exactly one sig fig =? \delta R = 0.05

@0ßelö7 It happens.

2:11 AM

@rob tl;dr

So then \overbar{R} = 7.92.

@georg Yes. Well, δR = 0.05 Ω -- you need the unit.

@georg The level of rounding is correct. Tie it together?

R = (7.92\pm 0.05) \omega

@georg Gold star.

Wow. That was really helpful

My ta's are more confusing than anything

2:13 AM

TAs are the worst.

Especially since last semester my ta wasn't sure about uncertainty

@georg Uncertainties are tricky.

Agreed.

I think physics 2 lab will be a lot of fun

It wasn't required but I bought

amazon.com/Rigol-DS1054Z-Digital-Oscilloscope-Channels/dp/…

@georg You ... bought yourself an oscilloscope?

yeah

i've been watching a lot of cool shit on youtube

I wanna get more into it

2:18 AM

That's pretty cool.

Yeah cool.
Unusual, but definitely cool.

Do you plan on going into engineering?

I wanna build stuff

i did the applied math thing, but it got too abstract

Too much functional analysis :/

Robotics just seems cool

Idk if i'll actually persue that in school,
but it's defs a major interest i want to nurture

2:34 AM

@0ßelö7 please elaborate

@ııııııııııııııııııııııı it's clear

I don't like a lot of ta's because a lot of them aren't prepared for grad school academically, can't teach, or both

some are really great and i end up learning more from them than the professors

guys what is the technical term for the following: We can always add a constant to a gravitational potential without having an affect on the equations of motion. Is tht called translational invariance or?????

LegionMammal978

Just curious, when literature refers to "years" or "days" in nuclear half-lives, which definition of the terms is implied? ("Hours" and "minutes" are likely just 3600 s and 60 s respectively.)

@LegionMammal978 one day = 24 hours, one year = π * 10^7 seconds

LegionMammal978

2:47 AM

@rob Where does the year figure come from?

Most nuclear half-lives aren't measured with enough precision that you care about the difference between 365 days vs. 365.24 days

The π*10^7 s = 1 year approximation is good to 0.3%.

LegionMammal978

Was wondering, as π·10⁷ s ≈ 363.61 days

@LegionMammal978 Hmm, closer to 0.5% from the actual value. Pretty deep in who-cares territory for most purposes, though

How did your concert go? @rob

@skullpatrol Oh, the concert was in May. Sunday night was the radio broadcast.

2:56 AM

I see.

I was quite pleased with the sound.

Sir Cumference

You guys ever wonder how humans would go about life if they couldn't understand math, beyond very simple arithmetic?

3:12 AM

@SirCumference More than a handful of times :-)

Sir Cumference

@rob Yeah, it's so weird to imagine.

@rob I went to rough talk today

the advisor was a total ass

I had him for a class -- good to know he treats undergrads and grads equally badly

he then interrogated me at the end because I asked a question

told him I had his class, he told me he has better things to do than remember me

@SirCumference If you read Watership Down, there's a footnote about how none of the characters can count past five, and so use "five" to mean "uncountably many"

@0ßelö7 Wow. What an unpleasant interaction.

@rob Actually he put it very strangely. He said "the longer I live in America, the less I remember such things"

@0ßelö7 Have I met this person?

3:17 AM

@rob Have you ever gone to topology seminars?

@0ßelö7 Yes, but not recently.

Not sure I want to badmouth him by name, but I can't imagine anyone actually liking this guy

pls mod abuse delete when you see it

@0ßelö7 I actually had him as an undergrad. He was nice at that point.

@rob On the other hand, I think he said I should keep coming to the seminars

It was such a strange interaction

@rob he taught my linear algebra class online even thought it was a normal class

we saw him in class maybe a few times

@0ßelö7 How bizarre. I had him for abstract algebra/group theory and it was a treat; I remember him fondly.

I remember the linear algebra class being kind of a slog with a lot of unhappy engineering students in it. Maybe he just didn't enjoy teaching it.

3:25 AM

@rob Oh, he's also very political now

@0ßelö7 Aren't we all.

he also made fun of his grad student for not liking football

it was such a strange seminar

@rob like he talks about it in lectures

@rob I met the two new faculty after the seminar who are working in my area, they seem really nice

so at least one good thing came of it

they invited me to talk at the new geometric analysis seminar

@0ßelö7 Well, that's a win.

@rob Engineers hate linear algebra for some reason

@rob I kind of have to, the time slot was moved so I could attend it :)

@0ßelö7 This is a pretty surefire way to get someone to attend a seminar :-)

3:29 AM

@rob did you take the 400 level algebra?

or the 300 intro?

@0ßelö7 I think the 300-level one --- but since it was in 1999, I'm not 100% sure.

@rob dang, that guy has been around for a while

I think the situation was that after everything I needed for physics, two upper-level math courses got me a minor.

user84215

@ACuriousMind Please note that my question is about the importance of attending physics workshops, not advertising my room (Only at the end of the question I have mentioned that room). Why do you disagree on posting that question on the Meta?

@rob I see

3:35 AM

@0ßelö7 Hmmm, looking at the faculty page, there are several folks that I had as an undergrad. Tenure has that effect on people.

I took a fabulous math modeling course from Collins.

user147690

@MathematicsAminPhysics Are you the user 'twink'?

@rob Don't know him

user84215

@AlexClark No.

@rob Mengesha is my new favorite person. Know him?

@0ßelö7 I don't think so.

3:39 AM

@AlexClark lol, there's no way he's "twink"

The initial question at the top of this post may be suitable for Academia. It's unclear what you think the subsequent rant will accomplish. — Emilio Pisanty 15 hours ago

@skullpatrol eyebrow raise

Sofia was right

@MathematicsAminPhysics We answer questions here about physics on the main site, and about the main site on the meta site. But questions about career advice aren't really a good fit for our format.

Sir Cumference

I remember back in high school geometry a kid somehow got an answer with more than one decimal point

@rob if you want to look at the finished poster just refresh the link I emailed you

3:41 AM

@0ßelö7 Will do this tomorrow. About to hop off.

@rob ok, I'm presenting tomorrow

hopefully I can make someone understand something

Cya

@skullpatrol CPU: 36, GPU: 43, SSD: 37

@0ßelö7 Sophie was "nice."

@skullpatrol and look what it got her

3:43 AM

True dat, pal.

@skullpatrol are you happy with those temps

Not 43

for a massively overclocked GTX 1080? You don't know what you're talking about then.

@0ßelö7 Are those temperatures?

@rob yes

3:45 AM

Oh yeah, I forgot you over clocked @0ßelö7

@0ßelö7 I think they're not temperatures.

@rob what is that supposed to mean?

43 C is a temperature. 43 is a number.

oh for fuck's sake

you're not my physics TA

Sorry: start of term unit pedantry :-)

user84215

3:46 AM

@rob So, I should repeat my announcement here everyday?

@rob the fact that you knew it was C proves the point

@MathematicsAminPhysics Please don't use the chat room for periodic announcements about your personal projects.

If a student wrote x + 43 would you mark it wrong

@MathematicsAminPhysics If you make an announcement in here and people think it is interesting, it'll get starred and featured over on the right side for a while.

@0ßelö7 In what sense is it a hoax? Isn't it global? or there's no warming at all? or both? (or...?)

3:49 AM

@ııııııııııııııııııııııı there is warming

everything else is a lie by the reptiles

@MathematicsAminPhysics The line between "hey I'm doing this thing" and "I'm going to spam you about this thing of mine all the time" is a little murky. Try to stay on the correct side of it.

2

@skullpatrol What is x?

lol

@0ßelö7 and why is there warming? is it the CO2 released by us? (and can we stop the warming if control the CO2 release?)

Length @rob

@ııııııııııııııııııııııı Why? Only God knows for certain. Humans probably only contribute an infinitesimal amount.

3:52 AM

@skullpatrol So your expression takes some length x and increases it by 43? That takes you out of the solar system.

no units --> natural units

43 light seconds

@0ßelö7 So you mean human activities aren't the main cause. Then what about the green house effect and all the stats?

not out of the solar system @rob

@ııııııııııııııııııııııı I'm not having an actual debate on athropogenic global warming at midnight

Hi @MathematicsAminPhysics

in fact, I don't really care at all

both sides are probably faking data

not much I can do about it

3:55 AM

@0ßelö7 But the radius of Neptune's orbit is only 30

This is a typical word problem found in any high school @rob

@rob I thought we were like 8 light minutes away from the sun

Right, but the "natural" unit for describing solar system orbits is the astronomical unit.

^

user84215

@ııııııııııııııııııııııı Hi.

3:56 AM

I default to GR units

Always use units.

@JohnRennie and I had some fun with those the other day

How about a ratio of two quantities of the same kind and units? @rob

@skullpatrol It's frequently the case that ratios are dimensionless.

user84215

@rob Where can I post questions about the process of learning physics?

3:59 AM

@MathematicsAminPhysics quora

Aha! So not always :-)

user84215

I mean in the SE

I've got to bow out for the night, folks --- take care

night

Cya

Do you see my point? @0ßelö7

4:04 AM

no

43 could be the ratio 43C/1C

it could also be 43apples/1apple

Yes, but we are talking about temp

Avantgarde

@rob Wow, terrible wastage of hard work, time and money!

4:34 AM

@JohnRennie morning

Morning

@JohnRennie I'm presenting tomorrow

tips?

Relax and have fun.

You're talking about something really interesting and if you relax into it that interest will show.

That's an interesting use of "into"?

relax into it

I don't think that's a controversial use of English ...

4:48 AM

Must be BrEng

Not "controversial" :-)

Ok getting some sleep

Cheers

Good luck for the presentation

Cya, good luck pal.

"relax into it"

:-)

@Hippalectryon The surface of glass reacts with water so exactly what's on the surface depends on the history of the glass. If you clean the glass with alkali the surface will have a lot of SiOH groups. If you flame it these will dehydrate and you'll be left with very few SiOH groups.

As a general rule flaming the glass will make the surface less polar and lower surface energy.

Did you watch the fight on Saturday night? @JohnRennie

5:03 AM

No. It's not something I'm interested in.

McGregor made Ireland proud

5:24 AM

@Rumplestillskin that is called a gauge freedom

Q: Does entropy increase or decrease as our Universe is expanding?

[Random]

> A 2011 paper argues that the Big Bang itself is a white hole. It further suggests that the emergence of a white hole, which was named a 'Small Bang', is spontaneous—all the matter is ejected at a single pulse.

> Thus, unlike black holes, white holes cannot be continuously observed—rather their effect can only be detected around the event itself. The paper even proposed identifying a new group of gamma-ray bursts with white holes.[14] The idea of the Big Bang being produced by a white hole explosion was recently explored in the framework of a five dimensional vacuum by Madriz Aguilar, Moreno and Bellini in the paper.[15]

localised in both space and time, hmm...

13

Q: What is a White Hole?

White holes are purely hypothetical at this point and are considered only because it is assumed something like it could exist as the balance to black-holes. Reading this article seems mostly writers taking liberties with the information but poses an interesting question. What is a White Hole?

white-hole

Ok, I know that energy momentum is not conversed globally, but really, does it allow such degree of fluctuation :?

4

Scientists say that entropy of our universe is increasing as it is expanding and our universe is cooling down gradually from the time of its birth. If something is getting cooler and cooler, then how can it become more random (entropy increase) with the passage of time? According to laws of therm...

thermodynamics entropy space-expansion big-bang

>

But, beware! Thermodynamics are built assuming there are not long distance interactions, but the evolution of the universe is controlled by gravity, that has infinite range. Therefore, you cannot naively apply any thermodynamical theorem to the universe as a whole. You can physically argue the correctness of many of the postulates, but you are on shaky ground there.

bleh...

10

Q: Can entropy of Universe be constant?

If I understand entropy correctly, then for example two objects orbiting a centre of mass have lower entropy than when said objects eventually crash into each other and form a new one. So let's say that a typical galaxy spirals around its centre of mass and eventually objects within it will fall...

gravity entropy space-expansion

And then, it gets complicated...

Perhaps I should add one extra item to my shopping list of exotic objects: 5 grams of micro white holes

[The Shopping list]

* 3 micro black holes
* 125 micro CTCs
* -6g negative mass
* 5g antihydrogen
* 1 nL QGP
* 45g Dark matter
* 8Pa Dark energy
* 5g neutronium
* 5g micro white holes

and this is why, I have no desire for buying things, because the things I want to play with is simply too expensive for even the richest billionaire to get

(I will let you figure out why I need that many CTCs)

7:08 AM

@MathematicsAminPhysics Because meta is for questions about the site, not for general discussion about physics related things.

@ACuriousMind No, physics workshops are important.

They build character.

So?

surely you realize my ironic tone

Periodic reminder that while I might, others may not. Using dry irony where other people might act in earnest as you do is a recipe short disaster.

TRIBULATION - The Motherhood Of God

I suppose that's fair. I think most of the regulars would realize in this case that I'm being memetic about the academic musings of the user in question.

But that's entirely fair; I'll desist.

Avantgarde

7:25 AM

@balarka stop following Jake Paul and embrace black/death metal

►

Oh wait, I actually have something that you might like. It's one of my favorites. Do you like spacey metal music? If yes, then this is one of the best things in that category

Arcturus - Kinetic

►

^No growling in that one. Clean, and one of the best in metal

@Avantgarde Let me check that out. (JP rocks tho)

Hi, by the way

Avantgarde

Oh hi

But now I gotta go. Bye Jake fanboy

seeya

I'm currently listening to the Queens of the Stone Age

7:40 AM

@JohnRennie Heh, I've listened to them rather often in the background because for some reason they're always in the play list when I play cards with friends

8:05 AM

@JohnRennie Hi JohnRennie thanks for that. I didn't realise that was what gauge freedom was. I always thought it was some complicated monster and always avoided anything with the word gauge associated :P I might one day get the hang of this physics mallark!!!

@Rumplestillskin gauge freedoms can be more complicated. For example in GR there is a gauge freedom due to the Bianchi identities which is a lot more complicated. Also QFT uses local gauge freedoms, which are a very different beast.

@JohnRennie so we have a gauge freedom in Newtonian mechanics also? The field equations are $nabla^2 U$ = -4 pi G rho so we can add a constant here to the potential U and then remains unchanged??

@Rumplestillskin yes, that's the type of gauge freedom you referred to in your original post.

Is Binachi identity the usual thing about the curvature tensor, $R(X, Y)Z + R(Y, Z)X + R(Z, X)Y = 0$, here?

Yes

8:14 AM

Interesting. How does a gauge freedom appear from this?

@JohnRennie Ahhhh okay. Does this mean that you can also add any linear function to the field equations of Newtonian gravity and they remain unchanged? Because all second derivatives will be zero in the Laplacian?

Does it?

I don't think the Bianchi identity is really related to gauge freedom

it's more related to conservation of energy

Hmm, Google says Ricci discovered them first. They should be the Ricci identities.

@JohnRennie but

Stigler's law of eponymy

Stigler's law of eponymy is a process proposed by University of Chicago statistics professor Stephen Stigler in his 1980 publication "Stigler’s law of eponymy". It states that no scientific discovery is named after its original discoverer. Examples include Hubble's law which was derived by Georges Lemaître two years before Edwin Hubble, the Pythagorean theorem although it was known to Babylonian mathematicians before Pythagoras, and Halley's comet which was observed by astronomers since at least 240 BC. Stigler himself named the sociologist Robert K. Merton as the discoverer of "Stigler's law"...

So when you say the gauge freedom in GR - - You are referring to the choice of metric tensor is that right?

8:17 AM

@Rumplestillskin I'd have to think about that. It certainly means you can add any constant to the potential energy.

@Rumplestillskin the gauge freedom in GR is the freedom to choose any coordinate system

Gauge freedom in GR is complicated

There's a gauge freedom and a diffeomorphism invariance

which are not quite the same thing

:: John realises he might be out of his depth now ::

A lot of physicists say diffeomorphism is a gauge invariance but others say no because it's not quite that

@JohnRennie see my answer at physics.stackexchange.com/a/346812/50583

@JohnRennie and in Newtonian gravity it is the freedom associated with the potential and an arbitrary constant.

... maybe a linear function

On a different is anyone here doing OR has obtained a PhD in maths/physics?

8:23 AM

The freedom to add a constant to potential energy is not a gauge freedom in the technical sense, although it sort of serves as an archetype for the idea that we can change certain functions in certain ways without changing the physics

yeah I was actually having trouble connecting that to the mathematical notion

user84215

8:50 AM

@ACuriousMind Why can I not post question about the process of learning physics? The MSE accepts such questions.

[Updated shopping list]

@MathematicsAminPhysics Because our site has decided that we only allow objective questions about physics itself, not the lives of physicists or the study of physics. What is on topic at math.SE has no relevance to us (as also evidenced by e.g. the homework policy.

* 10Pa dark energy
* 50g dark matter
* 10000 neutrinos
* 5 micro black holes
* 5 micro white holes
* 400 micro CTCs
* 1 nL QGP
* 5g antihydrogen
* 1 tonne neutronium
* -10g negative mass
* 3 grandfather paradoxes
* 1 higgs boson

O and almost forgot:

* 5g elementary (dirac) magnetic north poles and magnetic south poles each

user84215

@ACuriousMind Creating the physics workshops room is a good idea. Right?

NB: Given that dark energy often behave like a pressure, pascals seemed to be a reasonable unit for dark energy

8:57 AM

@MathematicsAminPhysics I think we already do ad hoc workshops here. I'm not sure having a separate workshop room adds much.

and QGP is a perfect liquid

@MathematicsAminPhysics it's not detrimental but currently I don't see any benefit to it, either

Does anyone think there is a lack of questions or lack of interest for the Post-Newtonian approximation on PSE?