The h Bar

1:51 AM

@Kaumudi.H I am around now.

I know Madras is Chennai. I just reproduced what was written in our notes

3:02 AM

So my siter brought some fufu and eru (some hard core cameroonian[sometimes Nigerian too] food) drive.google.com/file/d/…

I went full blown African on that food.

At any rate, back in my room now. My brother is going to be here in a bit

I don't drink alcohol so eh. . .

At any rate going to shower,

Presumably, my cousin will pop in too. Maybe he will bring his girlfriend, and they will make fun of my code.

Sid

3:22 AM

@Cows if they do, throw them out of your house.

vzn

3:41 AM

PHYSICS: SCIENTISTS REWRITE QUANTUM THEORY TO DO THE IMPOSSIBLE AND TRACK ‘SECRET’ PARTICLES / newsweek

user228700

4:39 AM

@Sid I...see.

user228700

When are you going to be in Chennai, again?

HsMjstyMstdn

5:07 AM

I HAS HAT

SO HAPPY

dmckee

5:35 AM

Jumpy Jeeebus on a Pogo Stick!

I'm out of touch for one measly travel day and the HNQ goes batgauno loco on a quicky answer I threw up to hold the place until a real expert came along!

Sid

@Kaumudi.H 28th and 30th

29th I will be in Puducherry

John Rennie

@dmckee 38 upvotes and counting for talking about hairy balls :-)

dmckee

@JohnRennie I always have a little trepidation when the situation calss for a discussion of that theorem.

Well. Most of me does. My inner thirteen year old is giddy at the opportunity.

But he's a insufferably little git.

John Rennie

5:51 AM

Embrace your 13 year old inner self. It is the path to true happiness and fulfilment in life!

I can say this from experience :-)

dmckee

Uhm. I might buy that of my sixteen or seventeen year old inner self. At thirteen I not only didn't know how to talk to girls, I still couldn't quite see why I would want to.

And I was a bit of a late bloomer on the whole empathy thing.

Secret

6:22 AM

@vzn arxiv.org/abs/1705.06574 uh, that's not what the actual paper is talking about. The paper is comparing two counterfactual schemes, and found that when the system undergoes some uncontrolled phase rotation, one of the schemes violates the requirement to be counterfactual, and thus under realistic conditions, that scheme used by the interferometer is not counterfactual, in that some uncontrolled interaction actually occurred during the operation

instead of having the quantum state not interacting with anything and yet still provide information on the system as counterfactuality would have suggest

---
hmm...

Interaction-free measurement

In physics, interaction-free measurement is a type of measurement in quantum mechanics that detects the position or state of an object without an interaction occurring between it and the measuring device. Examples include the Renninger negative-result experiment, the Elitzur–Vaidman bomb-testing problem, and certain double-cavity optical systems, such as Hardy's paradox. == See also == Counterfactual definiteness == References == Mauritius Renninger, Messungen ohne Storung des Messobjekts (Observations without disturbing the object), (1960) Zeitschrift für Physik, 158 pp 417-421. Maurit...

> The situation can be analyzed in terms of two simultaneous interaction-free measurements: from the point of view of the interferometer on the left, a click at d+ implies the presence of the obstructing electron in u−.

> Similarly, for the interferometer on the right, a click at d− implies the presence of the positron in u+. Indeed, every time a click is recorded at d+ (or d−), the other particle is found in u− (or u+ respectively). If we assume the particles are independent (described by local hidden variables), we conclude that they can never emerge simultaneously in d+ and d−. This would imply that they were in u+ and u−, which cannot occur because of the annihilation process.

This is so weird, this never occured to me when I read those paragraphs of the Hardy's paradox setup above this one

the way I think of this experiment is that: There are 4 possible routes to the detectors, if d+ clicks, it means u+ is obstructed by the electron. Therefore only the ampitude v+ reaches BSl^2 and give the destructive interference at d+ as expected. Similarly for d-. Thus when both clicks, the u paths are obstructed by the electron and positrons, leaving only the v paths to click both d detectors

> An article by Yakir Aharonov and colleagues in 2001[6] pointed out that the number of electrons or positrons in each branch is theoretically observable and is 0 in the w branches and 1 in the v branches. And yet, the number of electron–positron pairs in any combination is also observable and is not given by the product of the single-particle values. So we find that the number of ww pairs (both particles in their w path) is 0, each wv pair is 1, and the number in the vv combination is −1!

> They proposed a way that this could be observed physically by temporarily trapping the electron and the positron in the v paths in boxes and noting the effect of their mutual electrostatic attraction. They stated that one would actually find a repulsion between the boxes.

What does -1 number of electron-positron pairs mean?

Secret

7:06 AM

3

Q: Weak measurement and Hardy's paradox

How the notion of weak measurement resolves Hardy's paradox?

hmm makes sense

so I guess treating quantum states like vectors in rigged hilbert space will tell us exactly why projection operators don't necessary force the state vector (or density matrix for the mixed states) into some state independent to the order the operators are applied

The problem with Lubos Motl's proof is that it presupposes non-contextuality of the "realistic" theories. But dBB theory is contextual. That means, some "measurement results" are in dBB theory results of an interaction between the system and the measurement device. For such "measurements" the old remarks that measurements which have not been made have no results holds in dBB theory too. — Schmelzer May 31 '16 at 12:53

and then something to be careful when applying Bohm to this scenario, which makes the above vector space argument invalid

As for "negative occupation number", it seems that QFT does not allow any state to have that. Will read in more detail on why later but it suggests Yakir Aharonov analysis is strange

But suppose this concept does make sense, it will then be a good idea to figure out how to store negative occupation number of objects for some kind of applications...

@JohnRennie My 13 year old self is a boy, my mature self is a girl. I am currently somewhere in between

3

The goal is simple: Not to let the cruel reality to murder the boy, for it is the very reason of my dreams and all the weirdness and ideas you all knew about me

Sid

8:16 AM

Happy Boxing Day @JohnRennie England are getting boxed at MCG. :P

John Rennie

@Sid Not that anyone expected it :-)

Abcd

8:35 AM

@JohnRennie is the time period of the pendulum clocks in the houses $2s$?

John Rennie

@Abcd huh?

What clocks in what houses?

Abcd

Found it:

Seconds pendulum

A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 1/2 Hz. A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. When released, the restoring force combined with the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one...