The h Bar

1:23 AM

Gaussian 16 quote:

THE BEST WAY TO CONVINCE A FOOL THAT HE IS WRONG
IS TO LET HIM HAVE HIS OWN WAY.

JOSH BILLINGS

My addendum:

The best way to convince a crank with a fatal idea that he is wrong
It to let him have his own way
and be perished by nature in the process

Or more simply:

> The best way to convince someone is (most likely) fatally wrong, is to let nature to murder them

Reference:

3

Q: How are beliefs restricted by an objective reality?

Consider the following belief A human can survive if they don't drink water for 1000 days We knew from biology that this is practically improbable as there are very few people who can survive for 18 days without water (Andreas Mihavecz in 1979). However, there are also beliefs that are unr...

Now this may sound very brutal, but it turns out Nature is quite a gentle being, because most false beliefs are not maladaptive

user400188

5:22 AM

Hmm itemize doesnt appear to work

If Hilbert space is described by $\mathbf{H}=\mathbf{C}^n$, and contains $n$-dimensional complex vectors [1], what is its dimensionality when describing a system of only two possible states?

I know the following things already:

-The state of a system can be described with a vector in Hilbert space [1]
-A single complex number can be thought of as a vector in the complex plane [2]

If I only two states are possible in some quantum mechanical system, what is the minimum dimensionality of the Hilbert space used to describe it?

References:
[1] http://users.cecs.anu.edu.au/~trumpf/LSslides/Matt\_James.pdf
[2] https://socratic.org/questions/what-the-difference-between-cardinality-and-dimension-of-a-set-for-example-for-r
[3] https://physics.stackexchange.com/questions/78519/dimensionality-of-hilbert-space

John Rennie

@EmilioPisanty Yes! August is a long time away so there's no great urgency to arrange anything. I'll mail you my mobile number nearer the time so we can arrange a meetup.

What brings you to Chester?

Slereah

7:12 AM

$\mathbb C^n$ is $n$-dimensional

A two-particle Hilbert space is $\mathbb C^2$

Which is two complex dimensions or four dimensionals

parvin

7:38 AM

hi

I've got a question, why is it easier to put your elbow on the table to lift a box compared to just lifting it?

is it even true? is it like some kind of torque or fulcrum and lever?

John Rennie

@parvin Hi Parvin. Basically, when your elbow is on the table some of the upwards force needed to lift the box is provided by the table so your muscles don't need to produce as much force.

A really detailed answer would involve the exact geometry of your bones and muscles, and it would get rather complicated.

parvin

thank you ! I'm trying to give some idea for a robot arm for being able to move heavier objects, I was thinking this could be a way, using a table and the elbow as a fulcrum, do you thing that's right?

I mean do you thing it's gonna work?

John Rennie

7:55 AM

Yes, essentially it's all just levers.

@DavidZ @ACuriousMind @rob @Qmechanic migrate this? I would have flagged it but you've blocked from flagging. Thanks for that.

Anonymous

@JohnRennie Blocked from flagging? Why?

John Rennie

@Blue Apparently three declined flags bars you from flagging, though I think it only lasts for 24 hours

Anonymous

Ehh. Strange. Those look like legitimate flags from your side. Moderators are usually supposed to mark flags which are made in good faith as "helpful" and not "decline" such flags. They're later free to decide whether to act on them or not

Anonymous

I guess you need to talk to the Physics SE mods about this

John Rennie

It's happened to me before. I tend to err on the enthusiastic side when flagging what I consider to be answers to homework questions so I regularly get them declined. It's just bad timing to get three declined in a row. I'll survive the experience :-)

Anonymous

8:15 AM

Heh. Anyway, in my opinion, flagging is a good habit. It helps to regulate the quality of posts on the site. Discouraging it would be against that philosophy. :)

Qmechanic

@JohnRennie : I migrated it.

David Z

@Blue Eh, not so much. The way we do it here (or at least the way I do it), we approve flags to send the message "please continue to cast this flag for this reason" and decline flags to send the message "please don't use this flag for this reason".

But we also try to really push the message that a few declined flags is not a big deal, and getting the occasional flag declined shouldn't discourage a person from flagging.

(also, if I notice a run of declinable flags from a single member, I'll often ask them about it rather than just declining the flags directly, since I'm not eager to drop people into flag bans)

Anonymous

8:33 AM

@DavidZ If a user has a habit pattern of flagging for wrong reasons it might be more effective to superping them in chat. In my experience, most users don't even know where to look for their previous accepted/declined flags :P So what you want to convey - " this flag X is not suitable for Y" might not be reaching that individual

Anonymous

But then, I guess the size of Physics SE is rather big and it might not be scalable to send a chat message to all those whose good-faith flag you're declining. So I sort of understand your position

David Z

Yeah, there are enough flags that it would make things quite a bit more difficult on us if we followed up on a significant fraction of them. Declining is easy; pulling people into chat, not so much.

John Rennie

8:59 AM

@Qmechanic thanks :-)

Slereah

10:01 AM

DiFrancesco's book arrived!

Secret

11:32 AM

history:

"We set up a telephone connection between us and the guys at SRI ...", Kleinrock ... said in an interview: "We typed the L and we asked on the phone,

"Do you see the L?"
"Yes, we see the L," came the response.
We typed the O, and we asked, "Do you see the O."
"Yes, we see the O."
Then we typed the G, and the system crashed ...

Yet a revolution had begun" ....[32]

> October 30 – The first transatlantic fiber optic cable TAT-8 fails, causing a slowdown of Internet traffic between the United States and Europe.[32]

Daily reminder that for every world changing success, there are numerous unsung failures

Slereah

12:46 PM

hello gent

s

Federico

12:59 PM

I have a question about the new kilogram definition. If suitable for the main site I will happily ask it there. From the description that I got from newspaper, I understand this is basically a method to measure a kilogram-force, not a kilogram-mass. Is this correct?

John Rennie

@Federico yes

@Federico See:

3

Q: Watt (Kibble) balance and the kilogram - how does the dependence on $g$ get eliminated?

The standard ${kg}$ is now in the process of being redefined by the watt balance (rather than the lump of metal in Paris) A watt balance is very simple, you measure the force needed to support a mass against gravity (by accurately measuring the current/voltage in an electromagnet). But in orde...

newtonian-gravity mass si-units metrology

Federico

ok, gonna read and come back, thanks :)

Slereah

I mean using $g$ in it is pretty bad, but it beats "that kilogram we have at home"

John Rennie

At least $G$ isn't changing with time. Or is it?!!!

Federico

ok, measuring g through other means answers my follow-up question, thanks :)

John Rennie

1:08 PM

@Federico Cool. I guessed that was what you were going to ask next :-)

Federico

engineers are predictable :P

Slereah

also that is assuming the equivalence principle!

lılostafa

2:25 PM

when setting the time for an interview, is it a good idea to ask (the professor) what subjects you can review to get better prepared?

Captain Bohemian

3:25 PM

I feel so cold, not knowing it's really cold in temperature or it's the desolate effect.

the weather website says it's 21.3 C around now here.

Anonymous

@lılostafa Worth a try :P Worst case: they'll say no

lılostafa

@Blue I've already answered (and asked this too :)

Anonymous

@lılostafa They answered?

lılostafa

@Blue yes; "It will be just an informal chat"

:)

Anonymous

Heh, they always say that

Anonymous

3:36 PM

Interview for PhD position?

lılostafa

@Blue yes

BTW, congrats for the Diamond

The days of ACM's hegemony in this room are over

Slereah

@CaptainBohemian 21 Coulombs???

Anonymous

@lılostafa Thanks :P

Anonymous

@lılostafa LOL

lılostafa

Finally we The People have a voice

Anonymous

3:38 PM

@lılostafa IIRC, photonics PhD, right?

lılostafa

@Blue Photonics. yes

Anonymous

Nice! :D

Anonymous

@lılostafa We can at least delay the AI world-dominance for a while ;)

Captain Bohemian

@Slereah I think you are joking with me. Celsius.

photonics. No wonder you get interview opportunity so soon.

Anonymous

@CaptainBohemian How do you know it was "so soon" for Mostafa? :P

Shing

3:48 PM

I dont get the joke: why hamburger is in the ground state?

Captain Bohemian

@Blue not long ago I saw he talked about writing to professors for PhD opportunity.

Anonymous

@Shing rebresearch.com/blog/yet-another-quantum-joke

Slereah

@CaptainBohemian That would be $^\circ C$

Captain Bohemian

4:03 PM

@Slereah I can't quite know LaTeX commands if there is not a screen keyboard showing icons with corresponding commands.

Anonymous

$℃$

Anonymous

\circ looks a bit abnormal

Anonymous

> The \degree command is provided by the gensymb package, so if you add:

\usepackage{gensymb}

to your preamble, that should enable the command.

Another alternative is the \textdegree command, which is provided by the textcomp package. And, finally, ∘ is another way of obtaining roughly the right symbol.

Anonymous

For MathJax \circ suffices :P

Captain Bohemian

I don't install mathjax actually.

Anonymous

4:10 PM

@CaptainBohemian There exist screen keyboards which show LaTeX commands?

Anonymous

@CaptainBohemian You should! It's quite helpful, especially in math-based chats like these

Captain Bohemian

@Blue yes, if you use WinEdt.

Anonymous

Ah, nice. I didn't know

Anonymous

Usually people just memorize them over time

Captain Bohemian

I think memorizing the commands for Latin letters may be easier for westerners.

our school never teaches us those Latin letters. They automatically appear in our science textbooks so I sometimes even don't know how to pronounce them.

but I can recognize them.

John Rennie

4:17 PM

Is $[\hat{L}^2, \hat{L}^2_z] = 0$ ?