The h Bar

Specter Prophet

6:03 AM

(removed)

user434058

This question is pure gold. Marijuana really makes you an exceptional physicist :P

Specter Prophet

I will not read it.

user434058

STRING THEORY - R C SQUARED - TAU FUNCTION U - INTEGRAL CALCULUS - SYMMETRY R4 - DIMENSION 26

user434058

> As crazy at it sounds, this phrase came to me during an altered state of consciousness. At the risk of sounding silly, I am from California where recreational marijuana is legal. Last night, I tried it for the first time, and for some reason, I had an odd mystical experience that subjectively seemed enlightening, insane, and terrifying all at the same time.

user434058

> Information seemed to be overloading my mind, so I actually jotted down some of it during my experience of being high. I guess I am just curious if altered states of consciousness can unlock genuine knowledge about reality or if they merely lead to temporary psychological delusions of grandeur.

user434058

6:15 AM

> From reading the popular science books of Michio Kaku, I am familiar with the strange story of the mathematician Ramanujan who apparently learned many of his math discoveries through dreams. Oddly enough, after googling it after the experience, I discovered that Tau Function is one of Ramanujan's discoveries.

user434058

(For those who might not be lucky enough to see the question before it's deleted)

Specter Prophet

how do u prove entanglement is true

user434058

Hypothesis proven: Ramanujan did drugs.

user434058

@SpecterProphet Damn, your timing is messed up :P

Specter Prophet

|:<P

user434058

6:30 AM

Is it just me, or is the homepage really flooded with more HW questions than ever?

Specter Prophet

I didn't post homework I surrender

John Rennie

@FakeMod the frequency of HW questions waxes and wanes. I think we're just seeing natural variation.

user434058

@JohnRennie Hmm... Right!

Captain Bohemian

7:52 AM

why has ergodicity never been taught in my statistical mechanics textbooks?

user434058

10:43 AM

Did MathJax just stop working, or is it just me?

PM 2Ring

When you're in such a state of information overload you may notice patterns & connections that are not normally apparent, but your mind may attribute greater significance to those patterns & connections than they warrant. So dreaming (like Ramanujan) or being high can be inspirational, but you need clear rational reasoning to investigate those patterns to see if they're actually useful, or whether they're merely the product of you're mind's pattern matching abilities going overboard. ;) — PM 2Ring 56 secs ago

user434058

@PM2Ring True.

user434058

MathJax is definitely broken.

PM 2Ring

@FakeMod It's working on the main site for me.

But the ChatJax script I use on my phone in here isn't working: it can't load several files.

user434058

@PM2Ring Not for me :(

ACuriousMind

10:57 AM

both work for me

Balarka Sen

hi ACM

ACuriousMind

yo @BalarkaSen

Balarka Sen

whats the avatar this time

ACuriousMind

what's up?

Balarka Sen

not much admittedly

ACuriousMind

11:05 AM

@BalarkaSen Kim Kitsuragi from Disco Elysium

Balarka Sen

hmm i see

user434058

MathJax's back for me.

Balarka Sen

nice artstyle

user434058

Don't know what happened...

Balarka Sen

@CaptainBohemian yeah i would like to learn the physics POV

user434058

11:10 AM

@BalarkaSen You mean the gravatar?

Balarka Sen

that was to ACM sorry

user434058

Lol, yeah, his display pic is... Interesting.

ACuriousMind

@BalarkaSen It's a pretty game and a good one.

One of the rare games clearly recognizable as an RPG that doesn't have any dedicated combat mechanics.

Balarka Sen

I see, I'll have to try it out. looks very cool

PM 2Ring

@FakeMod Me too.

Emilio Pisanty

11:14 AM

@FadedGiant fair enough

what I don't get is the hydrogen

I keep hearing of all of these hydrogen problems associated with the zirconium

or is that mostly a generic feature that would also occur with other materials?

having looked at Wikipedia, the reaction they give (Zr + 2 H2O → ZrO2 + 2 H2) sounds like a simple "steals the oxygen from the water" which is probably true for anything that's hungrier for electrons than hydrogen, so maybe it is generic

then again, it sounds like what that is saying is that zirconium will happily burn in water (in the sense of using it as oxidant)

much like titanium will burn in sand

PM 2Ring

Also, check out all those lovely stable (or almost stable) zirconium isotopes in a row, from A=90 through to 96, apart from 95. So it takes a lot of neutrons to make natural zirconium radioactive. en.wikipedia.org/wiki/Isotopes_of_zirconium

Emilio Pisanty

(a friend recently told me of working in a workshop with a lathe for titanium. They had to keep it in a tank with a bunch of argon bottles on top, ready to dump the gas in case there was a fire.)

PM 2Ring

@EmilioPisanty Yes, any metal will split water, if it's hot enough. The alkali metals do it rather spectacularly at low temperatures. ;) Magnesium takes a bit more heat, but water hitting molten magnesium would be pretty scary. OTOH, it's not easy to melt magnesium in the presence of oxygen.

Emilio Pisanty

> OTOH, it's not easy to melt magnesium in the presence of oxygen

@PM2Ring yes, I would imagine

user434058

@PM2Ring Magnesium will form MgO before melting, right?

Emilio Pisanty

11:23 AM

lighting magnesium strips was one of the highlights of chemistry class in junior high school

PM 2Ring

When you burn magnesium in air, some of it even reacts with the nitrogen, creating magnesium nitride, which has a distinctive yellowish tinge that's easy to spot against the white magnesium oxide.

@FakeMod Definitely.

user434058

@PM2Ring So does Lithium (only Lithium of all the group 1 metals does this).

user434058

Diagonal relationship.

PM 2Ring

One of my school buddies bought a 30 metre roll of magnesium ribbon.

user434058

Though, idk how Li3N looks.

Emilio Pisanty

11:27 AM

@PM2Ring that sounds... deeply, deeply alarming

user434058

@PM2Ring Did he burn it? :P

Emilio Pisanty

OK, no, maybe not so much

amazon.co.uk/Magnesium-ribbon-pure-roll-about/dp/B00K86XY9U

25g, 15m

PM 2Ring

Well, we didn't burn it all at once! But it did keep us entertained for several years. :)

Emilio Pisanty

I guess it makes a good chemistry exercise to work out just how much energy would be released by burning the whole roll, and what it compares to

a hand grenade, maybe?

PM 2Ring

Another friend "borrowed" some sodium metal from the school lab, and gave small chunks to a few of us who had chem "labs" at home. I handled it pretty carefully, most of the time...

@EmilioPisanty The fun thing to do with burning magnesium is to use it as a fuse to ignite a thermite reaction, eg aluminium + iron oxide, which produces aluminium oxide + molten iron.

But we never got around to doing that. Thank goodness. ;)

Emilio Pisanty

11:34 AM

@PM2Ring that does sound like a hand grenade

ACuriousMind

Iirc thermite doesn't explode, it just melts through most things it comes in contact with

PM 2Ring

@EmilioPisanty It doesn't have a lot of explosive force, but it does put out a fair bit of heat. It has been used in firebombs, though.

ACuriousMind

Still, I never really understood why some people consider it "fun" and not "keep that away from me what are you doing I'm out of here" :P

PM 2Ring

They used to use thermite for spot-welding stuff like tram tracks, before modern gas & electric welding was developed.

Emilio Pisanty

@ACuriousMind I guess you're with Derek Lowe in thinking that the best tool to deal with those situations is a good pair of running shoes?

ACuriousMind

11:39 AM

yeah, definitely

every time I begin to wonder why I'm not a chemist I go back and read his blog ;P

Emilio Pisanty

@PM2Ring Well, yes, I guess. But then again 17% is Zr-94, and if you give that one two neutrons then it will happily plow through four beta decays in a matter of hours

PM 2Ring

I found chemistry fascinating, but I was never a huge fan of explosions, probably due to a fire cracker exploding near me when I was a baby. In my baby carriage.

2

Emilio Pisanty

Thermite in the act of not-exploding

PM 2Ring

@EmilioPisanty Yeah. And it's probably very expensive to make isotopically pure zirconium, even just getting rid of the Zr-94.

Emilio Pisanty

@ACuriousMind tbf the quote is probably originally from John D Clark

PM 2Ring

11:42 AM

@EmilioPisanty That sounds right.

Emilio Pisanty

anyways, fellas

lovely chat, but I'm off to lunch

catch you later

don't burn any of youse houses in the meantime

PM 2Ring

See you, Emilio.

One of the members of a now-defunct science forum I used to inhabit was using isotopically pure sodium chloride, that had (virtually) no Cl-37, only Cl-35. I can't remember what she was using it for, but it cost 300 dollars (Australian) per gram, 15 or 20 years ago.

Slereah

12:07 PM

Still cheaper than LSD

PM 2Ring

12:19 PM

True, but a gram of LSD goes a long way.

Slereah

just take it all

you will meet Jesus

Because you died, mostly

bolbteppa

1:30 PM

Imagine being smart enough to have figured out the necessity of kappa symmetry

Slereah

"What is called κ\kappa-symmetry in string theory/M-theory is a certain fermionic symmetry of Green-Schwarz action functionals for super p-branes whose effect is to gauge away half of the spinorial sigma-model fields."

Well, there it is

I don't even know what the Green-Schwarz function does rly

There's apparently four different actions for the susy brane???

PM 2Ring

1:55 PM

I'm sure we had someone several months ago who claimed that time dilation is BS, and that atomic clocks simply malfunction due to changes in gravity & speed. Maybe it was this guy using another name, or maybe not. physics.stackexchange.com/a/572529/123208

Slereah

Well the question is

What is the difference

If you say "Time doesn't slow down, clocks slow down because of these effects", you have to explain what time is then

If it's a quantity you can't measure it's not a very physical idea

bolbteppa

It's just a Nambu-Goto or Polyakov action which is invariant under supersymmetry, defined on superspace so that both $X^{\mu}$ and $\Theta^{Aa}$ are treated as actual coordinates of your space

PM 2Ring

@Slereah Well, his answer to that is that time is a fiction. And he doesn't explain why all clocks malfunction the same way. OTOH, I guess nobody's tried testing a whole bunch of different clocks for relativistic effects, partly because most clocks aren't precise enough to show those effects in the small gravity & speed regimes that we currently have access to.

abhas_RewCie

@Slereah time is defined by distance divided by speed of light.

Slereah

@PM2Ring Are you kidding

abhas_RewCie

2:07 PM

^very rough one

definition

Slereah

There's a whole thing about testing clocks

abhas_RewCie

@PM2Ring damn!

Slereah

There's a whole book about clocks in GR

sigh

bolbteppa

The 'problem of time' apparently tries to say time is a fiction so... :p

Slereah

"time is a fiction" is a pretty big red flag

PM 2Ring

2:09 PM

Well, we can easily test things like particle decay times at ultrarelativistic speeds in particle accelerators. But he'd probably class them all as variations of atomic clock.

You can't exactly send a Timex, Rolex, or a sandglass for a spin around the LHC.

ACuriousMind

→ 8 messages moved to Trash

@abhas_RewCie Please refrain from annoying other users with nonsensical interjections. Jokes are fine, nonsense is not.

abhas_RewCie

Okay... Bad jokes then

Avyansh Katiyar

2:34 PM

hi

@JohnRennie don't start doors of stone hasn't been released and god knows when

John Rennie

@AvyanshKatiyar hi :-)

@AvyanshKatiyar Did you like The Wise Man's Fear?

Avyansh Katiyar

3:12 PM

@JohnRennie Yes

It was great

Captain Bohemian

3:42 PM

How strong we fear of something depends on whether our heart is in systole or diastole.

user434058

4:21 PM

It feels like Christmas, man. We've got two awesomely entertaining questions today :P

Charlie

"will there be a change in the direction of the sun" lol

Faded Giant

4:55 PM

@PM2Ring You never did a thermite reaction? We already had it as a teacher demonstation in school; and we did it ourselves in the first year at university.

@EmilioPisanty Yes, a similar reaction would occur with other metals, too, even at much lower temperatures.

The Zr water reaction becomes a problem at high temperatures, i.e. during core melt accidents, i.e. when already many things must have gone wrong.

The first problem is that the reaction releases a lot of energy, so it adds to the residual heat of the reactor that has to be removed first from the fuel and then from the containment.

John Duffield

@Slereah : time is just a cumulative measure of local motion. Don't overthink it, just look hard at what a clock actually does. A clockwork clock isn't like a gas meter. There's gas flowing through a gas meter. A gas meter measures the flow of gas. A clockwork clock doesn't measure the flow of time. It just "clocks up" the motion of the cogs and sprockets. It's similar for a quartz wristwatch, but that features the piezo-electric motion of a crystal, plus electronics.

Faded Giant

The second problem is that the reaction releases hydrogen, which could create an explosive atmosphere in the containment.

The first problem has to be taken into account when designing the containment heat removal system.

The second problem is solved with autocatalytic recombiners.

PM 2Ring

5:21 PM

From en.wikipedia.org/wiki/… It is estimated that the hot zirconium fuel cladding-water reaction in Reactors 1–3 produced 800–1,000 kg (1,800–2,200 lb) of hydrogen gas each. The pressurized gas was vented out of the reactor pressure vessel where it mixed with the ambient air, and eventually reached explosive concentration limits in Units 1 and 3.

Rule #1 when venting hydrogen: don't let it mix with air in a confined space.

Faded Giant

@PM2Ring That cannot be avoided.

In only partly related news: We pulled out our old core barrel and lower core support yesterday.

It's now sitting in the pool and there are still 75 cm of water above it, so I can sleep again tonight.

Charlie

is that the inside of the reactor @FadedGiant?

Faded Giant

Not exactly. That's a part that was taken out of the reactor.

Charlie

:o

PM 2Ring

@FadedGiant Ok, but surely it can be minimised, with proper design. Of course, autocatalytic recombiners would be a good idea, but I suppose they wouldn't be able to do much if the Zr gets too hot & you get a whole lot of hydrogen in a short span of time.

@FadedGiant How "hot" is it?

Faded Giant

5:30 PM

@PM2Ring The modern autocatalytic recombiners in the containment are designed for that case. Of course, it would be difficult to test that under realistic conditions.

@PM2Ring The reactor was shut down in 2011. So it's not so hot anymore. About 20 Sv/h in the middle of the core barrel.

mainly from Co-60

about 25 µSv/h at the water surface

PM 2Ring

For comparison, 1 mSv is typical adult background radiation, per annum. 20 mSv is roughly a full-body CT scan. 25 µSv is like, 250 bananas.

Faded Giant

And note that there is no "milli" in "about 20 Sv/h in the middle of the core barrel" ;-)

PM 2Ring

I should memorise some of those numbers so I don't have to keep looking them up.

Yeah, I noticed that there was no milli.

Faded Giant

So after one hour in that spot, you would be dead in less than 5 days because of damage to nervous system.

You would never experience the damage to the gastrointestinal tract or to the bone marrow.

PM 2Ring

5:45 PM

Cobalt-60 has a scary reputation. I guess it's all those gamma rays...

Faded Giant

There are about 1E14 Bq of Co-60 only the cylindrical part of that thing in the picture.

PM 2Ring

When I was a kid, in the 60s & 70s, growing up in the Cold War era, the scariest bombs were the cobalt bomb, and the semi-mythical neutron bomb.

Faded Giant

And yes, it's about the hard gammas. One at 1.17323 MeV and one at 1.33249 MeV.

But we don't think it's scary. It's actually nice because it's easy to measure.

And it has a half-life of 5.2713 years; so we can wait and the values go down.

PM 2Ring

Good point. Beta emitters that don't emit gammas can be much harder to detect.

Faded Giant

If you ask people in the plant what they think is scary, they will tell you about the alphas.

Difficult to measure and high inhalation dose coefficients.

PM 2Ring

5:58 PM

A solid chunk containing Co-60 is definitely less scary than a bunch of loose Cs-137 salt, as in the Goiânia accident. But back in the 60s & 70s, we didn't hear much about caesium. The bad guys were plutonium, cobalt, strontium, and iodine. There were some very dirty tests done by the British in the Australian desert that spread quite a bit of plutonium around. We didn't hear about that until decades later. en.wikipedia.org/wiki/British_nuclear_tests_at_Maralinga

@FadedGiant Okay. I guess radon & polonium would be near the top of that list. Oddly, although polonium is a solid it can readily volatilize at temperatures much lower than its melting point. But I think I've mentioned that here before.

Faded Giant

The first alpha-radionuclide you would encounter here is Am-241. Because that's the one that you can still see in the gamma spectrum.

And then you start to think about it and you find that, if there is Am-241, there is also Pu-238,239,240 and Cm-244.

The problem is contaminated dust, for example when you cut things into smaller pieces.

The inhalation dose coefficient for Am-241 as 5 µm dust at the workplace is 1.7E-5 Sv/Bq.

So let's say you inhale dust with 1000 Bq Am-241, that's 17 mSv.

That's almost your annual limit.

JingleBells

6:14 PM

I has learnt to be well olequently spoken on england

PM 2Ring

Right. A few weeks ago, I was reading about how they mill plutonium for bombs. I expect the machinist copped quite a dose, especially in the early days. And Pu dust has a nasty tendency to ignite...

@JingleBells How many languages do you know? When you aren't being an idiot, you're English is very good, although you do make a few mistakes from time to time. Of course, native speakers make mistakes too, but non-native speakers tend to make certain kinds of mistakes that native speakers wouldn't. :)

Faded Giant

@PM2Ring yes, inhalation of Pu-239 dioxide, 5 µm AMAD: 2.5E-5 Sv/Bq

PM 2Ring

One of the Python ROs is Finnish, and married to a woman from Vietnam. His English is fairly good, but he sometimes makes bizarre choices when using prepositions.

Earlier today, I noticed a question from Chemistry in the HNQ about radioactivity, mostly concerning Chernobyl. One of the answers is great, but I think some of the answers contained some dubious stuff.

Faded Giant

@PM2Ring They call it "rally english" in Finland. :-D

@PM2Ring I try to avoid such questions. Maybe it's because I have to answer too much of this stuff at work, so I don't want to do it during my free time. Or maybe it's because the gap between the public media amateur level and the professional level is too wide, so it can actually be more difficult to answer an amateur question than answering a professional one.

Unfortunately, my trip to Chernobyl this year was canceled because of Corona. Maybe we will try again in November.

PM 2Ring

6:34 PM

@FadedGiant Fair enough. It would be nice if someone who actually knows about this stuff could correct the errors on that HNQ. ;) But I guess other people can do that.

Faded Giant

I actually answered a Chernobyl question on movies.stackexchange.com once. :-D

PM 2Ring

Ha. :)

Faded Giant

found it:

6

A: Magic behind 3.6 roentgen/hour in Chernobyl TV series

The measuring instrument used for the first ambient dose rate measurements on site was a Russian DRG3-02 (ДРГЗ-02) scintillation counter. Similar devices are still available today (picture taken from zapadpribor.com; I am not affiliated with that site). You can see that it has two scales: 0–3 ...

Charlie

7:55 PM

If i could ask a question specifically about the action of the Jacobian. Would I be correct in saying that given a map between manifolds $$f:M\rightarrow N$$ if I define a curve $\gamma$ on $M$, for which the map $f$ gives an image curve $f(\gamma)$ on $N$, and I then push-forward the entire set of tangent vectors to the curve through $f$, the pushed-forward vectors on $N$ are such that they are the tangent vectors to the image of the curve ($f(\gamma)$)?

assuming $M$ and $N$ and $f$ are all differentiable etc.

If this is true then I completely get how the push-forward isn't arbitrary, because then $f_*\vec v$ on $N$ has to be aligned such that any curve generating $\vec v$ as its tangent on $M$ always in some sense generates $f_*\vec v$ as its tangent on $N$.

Captain Bohemian

8:42 PM

What is $sigma$-algebra designed for? What is its application in physics?

bolbteppa

8:56 PM

@Charlie yes, these notes are good on it, specifically pages 32 and 137

@CaptainBohemian they are used to define probability spaces, i.e. they are everywhere in QM even though people ignore it, c.f. the Kolmogorov axioms

Probability axioms

The Kolmogorov axioms are the foundations of probability theory introduced by Andrey Kolmogorov in 1933. These axioms remain central and have direct contributions to mathematics, the physical sciences, and real-world probability cases. An alternative approach to formalising probability, favoured by some Bayesians, is given by Cox's theorem. == Axioms == The assumptions as to setting up the axioms can be summarised as follows: Let (Ω, F, P) be a measure space with P being the probability of some event E, denoted P ( E ) {\displaystyle...

Charlie

ty @bolbteppa, btw I went carefully through those notes you linked on visualising forms and they were really good, idk where you find these but tyvm

bolbteppa

cool

julien surel

hello guys

I was here a few days ago.

Do you think it's a good idea that I spend a little time with Feynman's path integral book in order to begin to learn QFT?

bolbteppa

9:25 PM

Probably better to just read a book like Peskin and Schroeder

julien surel

11:30 PM

I have a basic question about quantizing fields. Let's say we have a scalar field \psi, by quantizing the field we are going to write it down as a series of creation/annihilation operators. Do these operators vary from point to point or are they fixed for psi? in other words do they depend on coordinates?

ACuriousMind

They depend

or rather, you get the c/a operator by Fourier transform, so they depend on momentum, not on position

julien surel

So at each point we get a pair of operators right?

ACuriousMind

No, as I just said the c/a operators depend on momentum, not on position

julien surel

that's what I saw as well they are written as a_p, but why do they depend on momentum?

ACuriousMind

Because you get them as the Fourier coefficients of the field

julien surel

11:34 PM

okay thank you

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