The h Bar

Emilio Pisanty

16:00

@ACuriousMind did you delete the third answer before migrating?

Semiclassical

Right. Part of what makes it tricky, as I understand it, is that neutrinos in the standard model are known to be 'left-handed'

ACuriousMind

@EmilioPisanty yes

no point in migrating that :P

Emilio Pisanty

@ACuriousMind yeah, that'd explain why I can't see it

did you comment on it before deleting?

nasil

why does left handedness create a problem

Emilio Pisanty

@ACuriousMind wow

Semiclassical

16:01

Here's how the story goes, as I understand it.

nasil

left handedness is the spin vector of a particle being in the opposite direction with its momentum vector

Semiclassical

First, the left-handedness of neutrinos is an experimental fact: no one has ever observed a right-handed neutrino.

Right. Helicity.

Now, if neutrinos were massless, then this would (apparently) have an easy explanation.

nasil

so helicity = left handedness

Semiclassical

left-handed helicity = left-handedness

nasil

for massless particles ?

Semiclassical

16:04

the line from Wikipedia is: "Experimental results[81] show that (nearly) all produced and observed neutrinos have left-handed helicities (spins antiparallel to momenta), and all antineutrinos have right-handed helicities, within the margin of error."

...that nearly makes me wonder a bit

nasil

so what is exactly helicity

In particle physics, helicity is the projection of the angular momentum onto the direction of momentum.

Semiclassical

direction of linear momentum

nasil

so if a particle is left handed helicity is zero

nooo

Semiclassical

no.

nasil

negative

Semiclassical

16:05

I think so.

nasil

yeah it makes sense for it to be negative

Semiclassical

anyways. apparently if neutrionos were massless than the helicity always being left-handed would have an easy explanation

quoting from another page (t2k-experiment.org/neutrinos/in-the-standard-model): "if neutrinos have exactly zero mass, then their handedness (or helicity) is a permanent property, and there is no way for a neutrino created as an electron-neutrino to change into any other type. "

nasil

so left handed helicity means that the projection of angular momentum onto the direction of linear momentum is negative

Semiclassical

yeah, antiparallel

nasil

and angular momentum of a particle is orbital momentum plus spin

Semiclassical

16:08

So the observed left-handed helicity would evidently follow if the neutrino was massless.

And the construction of the Standard Model assumed that that was the resolution.

But then neutrino oscillations were observed, and from that (and other stuff) people concluded that they indeed have mass

so that means that the Standard Model's resolution of it doesn't suffice.

nasil

orbital momentums projection along linear momentum is always zero

so helicity is actually the projection of spin along the direction of linear momentum

Semiclassical

I guess?

nasil

but if neutrinos did not have mass then they could not be left handed because their linear momentum does not have any direction because they do not have mass

Semiclassical

false.

a photon is massless, but it can certainly carry momentum.

nasil

ohhh

ok got it

Emilio Pisanty

16:15

btw @ACuriousMind that's a new one, for sure

dmckee

@nasil As @Semiclassical says reconstructing the detailed underpinnings of the standard model in the wake of neutrino mass is an open question, though people aren't very hot under the collar about it because the standard model is known to be an effective theory anyway.

Likewise dark matter—whatever it is—is not included in the current unifying framework.

Dark energy may be as "simple" as an Einsteinian cosmological constant, but if it is not then it has to fit in somewhere as well.

Emilio Pisanty

@dmckee how massive a change would the SM need to accommodate neutrino oscillations once they're well characterized?

Semiclassical

Dark matter pheno is a bit different than neutrino pheno, though, since in the latter case we have actual particle physics phenomenon as a reference point

Emilio Pisanty

I mean, obviously we can't know until we do, but in principle it can deal with it by just adding some mixing angles?

dmckee

QCD perturbative-hadronic transition regime is still poorly understood theoretically, though experimental exploration continues to reveal a lot.

Semiclassical

16:20

in the case of dark matter, the evidence for it is astrophysical in nature.

dmckee

Exotic hadronic states (tetra-quarks and penta-quarks) are still poorly understood.

Semiclassical

so with dark matter it's indirect

we could explain what we see in the universe if certain kinds of particles existed, but we haven't actually managed to observe them

dmckee

@EmilioPisanty There is no obvious or well understood change to the underlying group structure that would accommodate it. Figuring that out and keeping the clean structure of the standard model would probably net a Nobel.

Semiclassical

whereas we certainly have observed neutrinos, even if we don't understand how it all works

Emilio Pisanty

@dmckee hmmmm, ok

Semiclassical

16:22

(philosophically I'm a lot fonder of neutrino physics than I am of dark matter physics, as you can probably tell)

Emilio Pisanty

I hope we can keep it to one shared Nobel between experimentalists and theorists, to keep the field open to all that interesting not-particle-physics physics =P

dmckee

@EmilioPisanty I don't hand out with that kind of theorists but I'm not aware of a big push in that direction. I suppose no one wants to spend a huge amount of effort on what would still be an effective theory where you're done. Or something.

Emilio Pisanty

@dmckee I guess that's a reasonable reason for being lazy

Semiclassical

Neutrino physics also just doesn't seem as exciting as stuff like extra dimensions / supersymmetry etc.

I'd personally be happiest if the neutrino turned out to be a Majorana fermion, if only because condensed matter people also love looking for Majorana fermions

dmckee

@Blue Hmmm ... I'm a narrow gauge expert in certain aspects of experimental particle physics. Certainly not a generalized expert in the whole field which covers a lot of ground.

Emilio Pisanty

16:28

dammit, mathematica, what did I say?

Semiclassical

"I reject your reality and substitute my own"

0ßelö7

@skullpatrol I did not see it coming, in fact I never think I will be flagged.

The chat always amazes me with what it is willing to punish for

skullpatrol

Live & learn pal @0ßelö7

2

0ßelö7

this book writes $0.6\times 10^6$

I don't think they understand the concept of scientific notation

Abcd

@0ßelö7 What's the proper way to write it then?

0ßelö7

16:43

$6\times 10^5$

Abcd

Okay.

skullpatrol

That's engineering notation.

0ßelö7

@skullpatrol never heard of it

skullpatrol

You will.

0ßelö7

When?

And how would you know?

skullpatrol

16:46

Engineering notation

Prathyush Poduval

@BalarkaSen Are you watching Republic TV now? There's a commie who's wearing an apple watch, might get on you're nerves :P

Emilio Pisanty

@0ßelö7 'cause he can ensure that you hear of it, by hounding you to the ends of the Earth if need be

@skullpatrol mobile link? ugh

de-.m. your wikipedia links, people

=P

0ßelö7

@PrathyushPoduval your

Prathyush Poduval

Sorry, typo :P

skullpatrol

@EmilioPisanty I tried, but it was too tough to do on mobile :P

Talking about Apple @PrathyushPoduval the appleX starts at $999 US

0ßelö7

16:57

why would one talk about that

Prathyush Poduval

@skullpatrol Gonna cost much higher in India, (around $1,500 )

skullpatrol

Boredom, perhaps @0ßelö7

Prathyush Poduval

Anyone planning on buying that?

0ßelö7

learn some string theory if you're bored

skullpatrol

yes sir

Prathyush Poduval

16:59

@0ßelö7 Any suggestions (For books)?

0ßelö7

nothing for string theory

I'm not into it

I have lots of other books I like though

skullpatrol

...and nobody can ban you from reading a book...

0ßelö7

stop

why do people want to get me banned?

Semiclassical

I think the problem there was not so much reading but writing...

0ßelö7

what have I done to you

Semiclassical

17:06

dude. you're the one who wrote it.

0ßelö7

@Semiclassical the Nazis burned books

@Semiclassical and it gets starred and then people see it and flag it

Semiclassical

ah. misunderstood your analogy

so if you write something that'll get you banned, and someone stars it....it's their fault for starring it?

0ßelö7

yep

skullpatrol

Fahrenheit 454?

Semiclassical

I don't think I have anything to add, then.

0ßelö7

17:08

do you know fluid mechanics?

Anonymous

@skullpatrol C'mon. Just stop with the indirect references to moderator actions. It's irritating and doesn't really help make things better.

0ßelö7

fighting words

skullpatrol

Nah, I'm done.

Slereah

Hello ladies and germs

skullpatrol

Hi pal.

How's the book coming along?

Slereah

17:20

Not much lately!

what with school and whatnot

also making a website and all

How goes the skull patrolling

found any skulls?

2

skullpatrol

Not yet.

Slereah

is that good or bad

i'm not sure

skullpatrol

It's all good in da hood.

John Rennie

Seen on Facebook :-)

Slereah

a ripoff of the classic

3

skullpatrol

17:25

All the girls like big biceps.

Slereah

I want to be a famous scientist with big biceps

the true ubermesnch

Prathyush Poduval

@Slereah You're writing a book?

Slereah

On general relativity, yes

John Rennie

@skullpatrol why would a girl want to have big biceps?

Prathyush Poduval

@Slereah Nice, best of luck!

skullpatrol

17:28

To cuddle with? @JohnRennie

Anonymous

Sid

@Slereah Excellent! All the best! Send us a copy when you are done. :P

Prathyush Poduval

The Ideal Man

Slereah

Good old Rich Piana

he died recently

Can you guess of what

Prathyush Poduval

tatoo-inie

Sid

17:29

Cancer?

Slereah

It's STEROIDS

skullpatrol

:O

What a surprise!

Sid

So, that's the secret of his muscles. :P

Slereah

Who could have seen it coming!

Well, not just steroids

But it is part of the recipe, yes

Steroids don't actually give you magic muscles

You still have to work out

Sid

My shoulder muscles are probably the same width as his wrists. :P

Anonymous

17:31

Big muscles don't necessarily look visually appealing me. But then, I'm not a girl.

skullpatrol

Having a team of PhD tutors doesn't make you smart, you still have to study :P

Slereah

Imagine that guy as a PHD student

Bench pressing the cyclotron

0ßelö7

I have dreams about rappers becoming great mathematicians

Anonymous

We have a quantum computing seminar tomorrow at college. I don't know if I should attend it. It seems to be directed towards the general public without math/physics experience.

0ßelö7

there's a magical limit when cough syrup gives you amazing proof powers

@Blue So perfect for you

skullpatrol

17:35

fighting words

Slereah

Heyooooo

Anonymous

@0ßelö7 Well, if it doesn't turn out to be a pop-sci seminar. :d

0ßelö7

@Blue but seriously, for an intro you don't want all the details and they can't put all the details in an hour talk anyway

Prathyush Poduval

@Blue If it has no maths, It's pop-sci

Anonymous

@0ßelö7 Exactly. That's why I think I'll not go. Better start learning it rigorously from next semester.

0ßelö7

17:37

@Blue you might get some of the high level (big picture) ideas

skullpatrol

^

Anonymous

@0ßelö7 Hmm, true. Okay, I'll think tomorrow. Thanks for your suggestion.

vzn

@Blue lol thats freaking disgusting. its not a real image is it?

Anonymous

@vzn Only God and Google would know. And I'm not sure if the former exists.

Sid

@Blue When are your mid sems?

Anonymous

17:40

@Sid Oct

0ßelö7

*midterm

vzn

@Blue anyway reminds me of a silly book read recently. "the game". it has an amusing quote, that evolution has shifted, and instead of survival of the strongest its now "survival of the smoothest" :P

Anonymous

@vzn Yeah, you mentioned it earlier :P

0ßelö7

@vzn yep $C^\infty$ is the best

vzn

@skullpatrol lol maybe look into the book to find out what "girls really like" :P en.wikipedia.org/wiki/…

skullpatrol

17:45

Oookaay...looks like a con game to me :P

vzn

@skullpatrol found it entertaining, didnt take it entirely seriously... reminded me of some of the banter in here at times etc... o_O

skullpatrol

That's what I meant pal.

vzn

@skullpatrol we could talk about physics instead but not sure youre interested in that either :P

@Blue whats the title anyway

Sid

@0ßelö7 is semester=term in the US?

Anonymous

Just got this mail: "Hi there,

We are having the <sci | Φ> v1.0 on Friday, September 15 at 5:30 pm.
The venue is TEQIP 101.

The topic of the first this series is 'Quantum Computation'. Do Come.
No prerequisites necessary.

Cheers,
JUSC."

Sid

17:53

You have received the institutional e-mail?

Anonymous

@Sid Nah, personal email

skullpatrol

Semester @Sid

Anonymous

I had given it to them while signing up for the Science Club.

Sid

Yeah, well in that case, mid sem!=mid term

skullpatrol

A midterm is a test given halfway through the semester.

0ßelö7

18:01

@Sid nope

ACuriousMind

@EmilioPisanty Oh, for your 30k proposal? Nice.

0ßelö7

@Sid what is a mid sem then?

Anonymous

@Sid mid term=mid sem for colleges which follow the semester system

skullpatrol

"Sem" is not a word.

Anonymous

@skullpatrol Semester=Sem

Anonymous

18:05

Common lingo

skullpatrol

There is also the trimester system.

ACuriousMind

@Blue I have literally never heard anyone refer to a semester as "sem" :P

skullpatrol

Would it be "midtri" then?

Anonymous

@ACuriousMind Oh, "mid-sems" is a very common abbreviation here. At least in my college.

ACuriousMind

Well, that can't be a common abbreviation here because the concept of midterms/midsems whatever doesn't exist here, but I've never heard anyone shorten the word "semester" in any context

Prathyush Poduval

18:09

@Blue also an abbreviation in these parts

Anonymous

I see. It depends on the place you live in I suppose. Indians have their abbreviations for several English words.

Anonymous

Hehe. Look here: iitk.ac.in/doaa/exam-schedule

Emilio Pisanty

@ACuriousMind that and a couple of others on the Shiny New Top Bar® thread

12

A: New top bar is coming to the Stack Exchange network

If you want me to review, then don't light up the review icon if there are no actionable tasks The number-one complaint I have with the current top bar is the fact that the review counter lights up even when there's nothing at all I can do to make it go away: So, what's the main outcome o...

^ in particular

pls support

bloody review blinker, uslessest thing on the UI

hmmmm. "Uselessest" isn't in either British or American English corpora. It's high time it goes in there.

One of the usefuler words in the English language.

skullpatrol

Why not just "unusable"?

"Uselesser" sounds funny too :P

Emilio Pisanty

18:30

@skullpatrol that's a very different word. Nothing wrong with it, but uselessest is usefuler in that context.

skullpatrol

Useless, uselesser, uselessest?

ACuriousMind

@EmilioPisanty Ugh, don't get me started on that bar :P

Emilio Pisanty

6 hours ago, by Emilio Pisanty

::sigh::. Again?

way ahead of you

skullpatrol

You should get the "sniper" chat badge :P

dmckee

@Slereah We actually have a guy here who finished his chemistry degree but stayed on for a bit of advanced work who is heavily into body building (in a natural and healthy way, I believe) who walks around the place looking like his muscle shirt is about to tear off of its own accord.

Balarka Sen

18:37

some interesting conversation that happened since i was gone

skullpatrol

welcome back pal

dmckee

Nice guy. Soft-spoken, thoughtful, studious, disciplined (of course!), and very able.

Emilio Pisanty

@skullpatrol there's a sniper chat badge?

skullpatrol

If there was one @EmilioPisanty :-)

Balarka Sen

sniper no sniping

skullpatrol

18:40

sniper

Jasper

Hiii

skullpatrol

hello

Emilio Pisanty

Looking Back On The Cassini-Huygens Mission to Saturn

►

Jasper

@Blue I don't like muscles that are too big. This guy doesn't look human anymore, lol. I think the ideal amount of muscle would be someone like Brenton Thwaites in the movie Blue Lagoon, lol.

Emilio Pisanty

::facepalm::

skullpatrol

18:45

::palmface::

Emilio Pisanty

so... they're saying that a software timing issue because they were sloppy with Doppler shifts made them squander $\Delta v$ that could be used right this week to keep Cassini alive?

skullpatrol

RIP Cassini

Emilio Pisanty

has it actually died yet?

> The spacecraft's descent into Saturn's atmosphere occurred on September 15, 2017

> ─ Wikipedia

uh.... when exactly?

Balarka Sen

oh that saturn spacecraft suicided

didn't know that

Anonymous

It was an unintentional murder. Not a suicide. :P

dmckee

18:51

@EmilioPisanty Don't know. I understand that they have finished the de-orbit burns and couldn't save it now if they wanted to.

Emilio Pisanty

@dmckee this seems to be it: saturn.jpl.nasa.gov/mission/grand-finale/for-media/…

there's to be a mission control video stream, it seems

tomorrow at 4am PD(?)T

Anonymous

vox.com/science-and-health/2017/9/14/16306996/…

Anonymous

On Friday, September 15, around 7:55 am EDT, NASA will tune in to watch its 20-year-old, $4 billion-plus Cassini spacecraft crash into Saturn.

Balarka Sen

"The planned deorbiting is necessary to mitigate the risk of the spacecraft eventually colliding with and contaminating one of Saturn's moons." I don't understand what contaminating means.

Anonymous

@BalarkaSen "Biological"

Anonymous

18:54

"Biological Contamination"

Emilio Pisanty

^ that

dmckee

@BalarkaSen The main spacecraft has not been comprehensively sterilized (and expensive and painstaking process) and could harbor Earth-native bacterial spores or biological molecules.

Balarka Sen

Ah

dmckee

They don't wnat those confusing possible future search-for-life missions.

Emilio Pisanty

14

Q: How can Cassini be a source of potential biological contamination?

In Wikipedia they mention that the Cassini spaceship will be destroyed in by sending it into Saturn's atmosphere: However, due to the spacecraft's dwindling fuel resources for further orbital corrections, it is currently planned to be destroyed by diving into the planet's(Saturn) atmosphe...

I'm unsure whether Cassini and Huygens were sterilized to different standards

but in any case

7

Q: Why are we concerned about Cassini contaminating Saturn's moons when we landed Huygens probe on one of them?

Cassini is scheduled to crash land into Saturn later in 2017. The reason stated was that they did not want to risk contaminating any of Saturn's moons. However, during the Cassini mission, we landed the Huygens probe on Titan. If we're concerned about bacteria onboard Cassini surviving, why are...

cassini planetary-protection

Balarka Sen

18:56

So that moon's atmosphere is suitable for potential biological growths?

Anonymous

@BalarkaSen It could be. We don't know. Microorganisms can exist in unimaginable conditions.

Balarka Sen

Ok, that's fair

nasil

why does smashing accelerated protons to metal create anti matter?

Balarka Sen

@EmilioPisanty Oh nice, it's an ocean world.

dmckee

@nasil Because it can. --Totalitarian principle.

nasil

18:58

i mean how

skullpatrol

7 hours ago, by Secret

https://saturn.jpl.nasa.gov/

Emilio Pisanty

hmmmm, no, it seems they were both sterilized to Category II standards

dmckee

@nasil That's sort of the point of the totalitarian principle: having suitable quantum numbers is the process. THat's all there is to it. No cogwheels.

nasil

so what is the answer to why does cherenkov effect happen

is it also because it does

dmckee

@nasil That's a shockwave in the electromagnetic field. Very similar to a sonic-boom actually.

nasil

19:03

so why didnt you say because it does happen

because it does happen

how are the two questions different from each other

dmckee

One of the philosophical difficulties of studying physics is in recognizing that there are 'based on underlying principles' explanations for some phenomena and not for others.

We go looking for ever more basic explanations, but at any given time, at the bottom of the stack the best we can do is 'because this is observed to be the way it works'.

As yet there is no more fundamental explanation for quantum mechanics.

nasil

so why do you bother in the first place if there is a dead end

Emilio Pisanty

so... anybody wants to put up bets on whether any NASA engineers will be wearing inappropriate articles of clothing this time around?

dmckee

Same reason you climb a mountain, but also because if you look hard enough it might turn out not to be a dead end.

But you don't find that out by asking in a chatroom. You have to climb to the cutting edge and figure it out for yourself.

nasil

so why do you call it a dead end

dmckee

19:06

@EmilioPisanty I don't know the story behind that question. Have I missed something juicy?

nasil

that last line makes sense

he used it

he accepted it

why remove?

@dmckee let me sum it up

Emilio Pisanty

@dmckee nothing recent

Matt Taylor (scientist)

Matthew Graham George Thaddeus "Matt" Taylor (born 1973) is a British astrophysicist employed by the European Space Agency. He is best known to the public for his involvement in the landing on Comet 67P/Churyumov–Gerasimenko by the Rosetta mission (European Space Agency)'s Philae lander, which was the first spacecraft to land on a comet nucleus. He is Project Scientist of the Rosetta mission. == Education and early life == Taylor was born in Manor Park, London. He was born in 1973, and is the son of a bricklayer and worked alongside his father, on building sites, during his summer breaks ...

@nasil because it was inaccurate

nasil

@dmckee What I wanted to ask in the first place was what happens in between the time interval of a proton smashing on a metal target and anti-protons flying away that the interaction of accelerated protons and a metal target produce anti-protons. I assume that this question is not one of those which are near "the cutting edge". But you may do as you please.

Emilio Pisanty

@nasil It's not a matter of whether it's cutting-edge or not. It's a question that's been studied thoroughly enough and the answer is that there's not really an answer.

nasil

So nobody knows why smashing a proton onto a metal surface creates anti-protons

Emilio Pisanty

19:15

There are some mechanistic explanations for the process, based on perturbation-theory pictures, but they rely too heavily on concepts (including e.g. virtual particles) that fall on the side of the mathematical model rather than on the physical ontology

@nasil That depends on what you mean by "why"

if you mean "can we calculate the results of the process accurately", then yes

nasil

that meaning is out of the scope of the meaning of "why"

Emilio Pisanty

if you mean "can we map the internal workings of that calculation onto things that physically happen", then no

nasil

i meant the second one

Emilio Pisanty

then the answer is no

nasil

and i am pretty sure that you cannot understand "can we calculate the results of the process accurately" from a "why?"

Emilio Pisanty

19:18

@nasil well, from where I sit, the natural answer to "why" is that the relevant transition matrix element of the evolution is nonzero

but that is a technical understanding of the question

(and it's synonymous with dmckee's "it's not forbidden" as regards the totalitarian principle)

dmckee

@nasil We can draw Feynman diagrams and group the possible reaction in various useful ways, but in each case the verticies that allowed (or not allowed) are those the the right (wrong) quantum numbers.

nasil

@EmilioPisanty I agree that you clearly have the potential to show your mathematical capacities.

Emilio Pisanty

@dmckee but it's important to note that the Feynman diagrams rely on virtual particles that are mathematical constructs and not physically present, so they don't constitute an explanation as to the "why" the process happens

dmckee

Introducing the (moderately complicated) rules of the strong and weak interactions to show which reaction can and can't happen doesn't illuminate the underlying processes any. It just gives you a catalog of rules to use in figuring out which combination of matter and anti-matter can (or can't) come out.

nasil

@EmilioPisanty AM NOT ASKING WHY THE PROCESS HAPPENS!!!

Emilio Pisanty

19:22

@nasil ah. what are you asking, then?

dmckee

@EmilioPisanty But they do a very nice job of organizing the application of the rule for the the various interactions into a discussable hierarchy.

nasil

what is that process

Emilio Pisanty

@nasil what process?

dmckee

And the answer is that no one knows of a more fundamental explanation than: it is seen to happen.

Welcome to the fact that science is descriptive.

nasil

A process describes how an input condition spits out an output condition

it describes the phenomena

Emilio Pisanty

19:25

btw @dmckee in this link, when it says "Sept. 15 4 a.m. PT", I take it that means PDT rather than PST?

nasil

so what I am asking is not out of the reach of science

i am asking for the description of the event

dmckee

@EmilioPisanty I would assume so. And I come to hate daylight savings time more every year. And it's worse because congress keeps extending it so that our deliberate very clocks are wrong more often than they are approximately right. Gawh!

@nasil The description is "a proton beam hits the metal and anti-matter is observed among the ejecta". Or we can look at it at an atomic scale on order of "a proton appears to have hit a nucleus in there and anti-matter was among the stuff that came out".

nasil

how can I block users?

dmckee

The time and space scales involved are attoseconds or less and femtometers. You can't 'watch' it happen.

Emilio Pisanty

@nasil here's a description of the event: a proton approaches a nucleus, it evolves under the Standard Model hamiltonian, and after the event there is a nonzero probability that there is antimatter present.

nasil

19:29

ok thats what i want

0ßelö7

What is the standard model Hamiltonian anyway

nasil

i mean wasnt the question clear

skullpatrol

@0ßelö7 did you see my wiki link to Fahrenheit 451 was removed?

Emilio Pisanty

@nasil Maybe this is a good time to accept that your question might involve subtleties that you're unaware of, or that many other people have asked similar questions that require different answers, and that it wasn't clear to us which version you were asking?

You might hope for a more detailed description - there isn't one. Quantum mechanics explicitly forbids you from asking questions about measurements that were not performed. (More accurately, you can ask, but some questions might not have answers.) Those questions are called counterfactual.

Counterfactual definiteness

In quantum mechanics, counterfactual definiteness (CFD) is the ability to speak "meaningfully" of the definiteness of the results of measurements that have not been performed (i.e., the ability to assume the existence of objects, and properties of objects, even when they have not been measured). The term "counterfactual definiteness" is used in discussions of physics calculations, especially those related to the phenomenon called quantum entanglement and those related to the Bell inequalities. In such discussions "meaningfully" means the ability to treat these unmeasured results on an equal footing...

For some processes, any explanation of the mechanistic details would involve counterfactual questions, so there's no such explanation. Pair production is in that class.

For other processes, there are parts of the mechanistic details that don't involve counterfactual questions, so we can say more about the details. Cherenkov radiation is in that class.

0ßelö7

@skullpatrol lmao

skullpatrol

19:36

>8(

"WE" are not amused.

0ßelö7

@skullpatrol how will we talk when one of us gets deleted?

it's a matter of time

@ACuriousMind Ok, I just went to a talk that was "too technical" but "not technical enough"

The results were very technical in nature but he didn't spend enough time defining all of the terms

skullpatrol

@dmckee was Fahrenheit 451 required reading when you went to school?

dmckee

@skullpatrol Yeah. It was OK, but it didn't fire my imagination on the level that Pohl and Niven and Le Guin did.

skullpatrol

Yup, those are classics :-)

dmckee

In retrospect I understand why literature people like it Bradbury better: he plays to their way of reading things. Evocative. Lots about the narrator's inner life.

skullpatrol

19:48

1984 was cool.

Emilio Pisanty

does twitter oneboxing show pictures?

Depositing books due at the library, the grad student takes a humiliating whirlwind tour of everything his past sel… https://twitter.com/i/web/status/907660392318459904

Tweeted by legogradstudent on September 12, 2017 at 5:41 PM

damn

Depositing books due at the library, the grad student takes a humiliating whirlwind tour of everything his past self had planned to read.

skullpatrol

What does Gell-Mann have to say about the future of nuclear physics? @dmckee

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