The h Bar

danielunderwood

12:10 AM

I've never even heard of The Mouse that Roared

Sounds interesting though

Sir Cumference

12:31 AM

Fast is done, just had three bagels. It tastes so good ;-;

vzn

1:36 AM

in theory salon, 1 min ago, by vzn

Reimagining of Schrödinger's Cat Breaks Quantum Mechanics—and Stumps Physicists / SciAm

:( o_O no luv for bohmianism reddit.com/r/Physics/comments/9h69dn/…

Jack Clerk

2:01 AM

Good night/morning/evening for everyone!

Is the Wronskian a example of second order tensor?

John Rennie

4:40 AM

@JackClerk The Wronskian is a determinant isn't it? So it's a scalar.

Jack Clerk

4:52 AM

@JohnRennie how are you? Yeah, but it's a multilinear map

Sir Cumference

5:06 AM

@JackClerk You mean the matrix that the Wronskian is the determinant of?

Jack Clerk

@SirCumference I mean the Wronskian Determinant:

W(f,g)

My point is:

Consider the whole world of multilinear functions,right?
So, by the construction of Tensor Product vector space we earn something really special:

These multilinear functions are isomorfic to tensors (elements of tensor product).

Then multilinear functions are Tensors

Now I'm asking if my statements are correct (at least in conceptual/intuitive level)

Sir Cumference

Sorry, I don't know jack about tensors. But you could try asking in Math's chat too

Jack Clerk

Actually it seems that the authors in physics books (like General Relativity, Robert Wald),define tensors just to call everything multilinear in the text a Tensor.

It seems also that, the components of a multilinear function and a tensor are the same and then by the tensor product you can write the multilinear function in a very compact form....

Secret

5:24 AM

Last night dream, went to a drink shop and ordered a mixed drink called United Nations:

The lady (black curly haired, dark skinned, 160 cm something in height) first poured some blue lemonade into a small shot cup. Meanwhile, two other staff were placing whole papaya and a half cut giant mango into a blender and blend it so it becomes puree

After that, a quarter of the shop is capped under a plastic transparent box, as the lady then place some kind of mask like object on a cup, turned it on and the whole place become very foggy with liquid nitrogen vapor

After the fog cleared, the drink is completed, with 7 colored layers of liquid. 3 potatoe fries were then placed next to the straw followed by 5 slices of steak

As I drink it, the color easily mixed and then the whole drink became translucent yellowish, and then some areas becomes chocolate brown, as well discs of instant noodles floating up of it followed by some chicken soup and pieces of chicken breast

It has a weird sweet sour taste

Secret

6:53 AM

nature.com/articles/s41534-017-0055-x

Ok I have also finished reading this. So basically the way it works is that given a very large entangled state, choose POVMs such that local measurements were performed on each subsystem (thus will not break the entanglement) and then the final result can be made to one if it is the target state with the required quantum correlations. Thus in a way, even a single copy behaves like many copies in parallel as the correlations were exploited to ensure only for a target state will give the required

success

So in a way, quantum correlations represents an extra computational resources besides the traditional size of the system and number of replicates (hence time of computation)

I think it is safe to say that large entangled state essentially behaves like a generalised form of parellel computing with each subsystem holding infomation of the whole system

user55789

8:24 AM

Hi, a little question too small for a full "thread" on the physics.SE front page

I stumbled upon this notation

...where the effective velocity $v^\text{eff}$ itself depends on the local distribution of quasi-particles $p(. ; x; t)$ through the "dressed" functions..."

where $p(\theta,x,t)$ normally had a $\theta$ instead of the "dot"

Is this normal notation?

I can't help but to say, this dot means nothing to me

David Z

8:37 AM

Huh. It's not very typical but I believe I've seen that used a few times to indicate a parameter which doesn't matter in that particular context.

But it might also be a typo or something.

Maybe if you link to where you found it, we could be more specific.

user55789

It's ArXiv 1711 00873 bottom of page 2, left column between (3) and (4)

Hold on while I get a link

David Z

(to the abstract page!)

Thanks

user55789

Does this work? arxiv.org/pdf/1711.00873

David Z

arxiv.org/abs/1711.00873 would be better

but yeah

it works

user55789

Saves 1 click off your mouse's lifetime ;)

David Z

8:41 AM

I am much more interested in not unexpectedly downloading (potentially large) PDF files than about saving mouse clicks

as are many other people

Anyway, I don't see any reason for the dot. Maybe it means something to someone who is familiar with that particular topic, but my guess would be just a typo, and it should be $\theta$.

Anonymous

10

Q: What is the meaning of expressions of the type $f(\cdot)$ (function (dot))?

Simple question, fully expressed in the Title line. Is the dot within the parenthesis intended to mean, "any possible function"?

Slereah

8:57 AM

Hello my droogs

Anonymous

Morning :)

user55789

@Blue Cheers, yes I guess that makes sense in this context

Anonymous

I am...playing truant today

Anonymous

(more like got bored and came back home :P)

Mithrandir24601

9:17 AM

@Slereah mornin'

Slereah

How's life

Secret

> Once I created the interfinite, I will be able to break down the very foundation of all creation and noncreation: Hoerarchy and their stupid rules

nonsense!

Hierarchy are there for a reason

Mithrandir24601

@Slereah sitting waiting to get a flu jab... Great times...

Slereah

@Mithrandir24601 Beats having the flu

Two years ago I was the only one who had the flu shot at a family Christmas

Everyone got the flu but me

Dodged a bullet there

Mithrandir24601

@Slereah most definitely going to agree there - I got it really bad last year

faheemahmed400

9:36 AM

a

The above diagram is of Coulomb's torsion balance from yesterday's question

0

Q: Coulomb's law: Torsion balance experiment

I have read about Coulomb's torsion balance experiment for the first time from an online pdf article. I interpret it as follows: Black ball $-$ neutral Red ball $-$ positive charge Blue ball $-$ negative charge At point $P$, there is no spring force and the positive charge is...

forces electrostatics experimental-physics coulombs-law

User Peter says the following:

The problem is that the equilibrium will not be stable. It is like balancing a pencil on its tip. If it begins to move away from the upright postion gravity will pull it further away. In this case if the charge on the torsion balance moves away from the fixed charge, even as a result of microscopic vibrations, the electrostatic attraction will reduce, and the torque from the torsion balance will pull it further away, reducing the electrostatic attraction even further, etc, etc. There is also the problem that air is not a perfect insulator, so charge will leak from one to the other. — Peter 19 hours ago

It says the equilibrium won't be stable if we use opposite charges.

John Rennie

@faheemahmed400 I think Peter has misunderstood the experiment. In Coulomb's experiment the charges are the same and that is stable.

faheemahmed400

What if we use opposite charges? Why it will not work?

In my question, I use opp charges

John Rennie

Because the torsion force varies linearly with distance while the electrostatic attraction varies as $1/r^2$.

faheemahmed400

Then how does same charges (repulsion) work?

John Rennie

Suppose we find the distance where the two forces are exactly equal. Now move the ball on the torsion balance closer to the static ball by a very small amount. The attractive electrostatic force will increase more then the repulsive torsion force increases. So if you move the ball closer than the equilibrium distance it is attracted towards the static ball and moves until it hits it.

faheemahmed400

9:51 AM

I see.

faheemahmed400

10:03 AM

Is it like this for same charges? Suppose we find the distance where the two forces are exactly equal. Now move the ball on the torsion balance away from the static ball by a very small amount. The repulsive electrostatic force will be less than the attractive torsion force.

Do I understand correctly sir?

John Rennie

@faheemahmed400 What you need to do is graph the force for the two cases. You'll find that for same charges there is a minimum in the force-distance curve, and this is a stable point. For the opposite charges there is no minimum so there is no stable point.

faheemahmed400

Ok, tks... Let me see

Secret

10:45 AM

While vzn covered the groundbreaking ones, I felt this one need to deserve more attention:nature.com/articles/s41586-018-0503-6

So with the jump able to be timed, what else previous unmeasurable is now possible to be reassessed

pentane

11:03 AM

9

Q: Only sea water appears blue in color, why this is not happening in river water?

Is the salt in the water the reason for scattering sunlight into blue?

visible-light water material-science scattering atmospheric-science

faheemahmed400

@John Rennie: I am totally confused in the graph. Can you show me a rough sketch graph.

pentane

The most upvoted answer and the answer that was selected by the OP states (paraphrasing here) that "water is blue because it absorbs red light." If like me you disagree with this notion please offer feedback to the poster of the question directly :)

Mithrandir24601

@pentane whoever asked that doesn't seem to have seen the sea on a grey and rainy day :P

user 2646

12:13 PM

2

Q: Are snide remarks allowed here?

I asked a question about dots on jerseys and got the following comment: Funny thing is, I saw the photo on a news website and a headline about how the Orioles were wearing dots (admittedly, I didn't read that article, which would have brought me to my answer, but not everyone knows the headqua...

Transcript for