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user301074

3:53 AM

heyo

vzn

4:58 AM

Nasa's New Horizons: 'Snowman' shape of distant Ultima Thule revealed / bbcnews

Secret

5:20 AM

A perceptual question:

How long is one hour?

what I mean is the following context: we knew that we can visualise some large sum of money like 100000 by saying how many cars we can buy

Is there something similar that can give us some intuitive notion of the length of a time interval as well, assuming we don't have a watch available?

1 hour later…

John Rennie

6:39 AM

@Secret 3600 heartbeats

Captain Bohemian

7:12 AM

@Secret You also have the problem of managing time? I have long had that problem. I feel time just slips crazily fast, having no much feeling for a year.

MartianCactus

7:57 AM

can anyone link me to chem stack exchange?

John Rennie

MartianCactus

8:13 AM

oh sorry I mean link to the chem stack exchange chat, I cant seem to find it..

Captain Bohemian

The period table

MartianCactus

cant find lol

Captain Bohemian

The Periodic Table

Haikus are awesome / Chemistry's even better / So pull up a chair

2 hours later…

Shing

9:55 AM

hey guys

I am thinking

for quantum mechanics, given a simple harmonic oscillator,

supposed that I measure a photon with $\hbar \omega$,

given any $n$, the energy of an emitted photon between state $n$ and $n-1$ is always $\hbar \omega$, do I have anyway to tell what exactly the state is, given the photon I measured?

GodotMisogi

@Shing wouldn't you have measured the emission of a photon, so the state should be $n-1$?

1 hour later…

Shing

11:27 AM

@GodotMisogi yes, I was thinking if I can be sure which $n-1$ state exactly it was before.

say, the photon emitted from 4 to 3 is $\hbar \omega$, so is from 2 to 1 or from 100 to 99.

can I be sure which one exactly it was before?

1 hour later…

MartianCactus

12:49 PM

i have another question

Anonymous

@Arjun @MartianCactus Please ask your homework (okay, mechanics and kinematics) questions in the problem solving room; not here. That room was made for discussing high school level physics problems, so you'll find more users interested in your questions there.

MartianCactus

alright

but that wasnt a homework question

the one before

Anonymous

→ 7 messages moved to Problem Solving Strategies

bolbteppa

1:50 PM

'Apparently, Landau considered the ghost state a hallmark of quantum field theories. He reportedly calculated the β‐ function of Yang ‐ Mills theory (on which QCD is based), but made a sign error, and missed asymptotic freedom.'

ACuriousMind

2:45 PM

@Shing No, you can't (but pure harmonic oscillators rarely emit photons anyway...)

Shing

2:57 PM

@ACuriousMind thanks, but why pure harmonic oscillators rarely emit photons?

ACuriousMind

@Shing I simply can't think of any real-world example of that

bolbteppa

3:17 PM

@vzn Have you come across the Abraham-Lorentz force?

Abraham–Lorentz force

In the physics of electromagnetism, the Abraham–Lorentz force (also Lorentz–Abraham force) is the recoil force on an accelerating charged particle caused by the particle emitting electromagnetic radiation. It is also called the radiation reaction force or the self force. The formula predates the theory of special relativity and is not valid at velocities of the order of the speed of light. Its relativistic generalization is called the "Abraham–Lorentz–Dirac force". Both of these are in the domain of classical physics, not quantum physics, and therefore may not be valid at distances of roughly...

"Inclusion of self-fields leads to problems in physics such as renormalization, some of which are still unsolved, that relate to the very nature of matter and energy."

"The self-fields in quantum electrodynamics generate a finite number of infinities in the calculations that can be removed by the process of renormalization. This has led to a theory that is able to make the most accurate predictions that humans have made to date. (See precision tests of QED.) The renormalization process fails, however, when applied to the gravitational force. The infinities in that case are infinite in number, which causes the failure of renormalization.

Therefore, general relativity has an unsolved self-field problem. String theory and loop quantum gravity are current attempts to resolve this problem, formally called the problem of radiation reaction or the problem of self-force. "

1 hour later…

Slereah

4:24 PM

Happy new year

Anonymous

@Slereah Hey, happy 2019! How're things goin'? :)

vzn

4:38 PM

@bolbteppa hadnt heard. reminiscent of Lorentz contractions. hence the name?

Slereah

5:21 PM

Finally home

Pretty tired

danielunderwood

6:13 PM

@Slereah the elusive GMT-40 time zone?

Slereah

@danielunderwood I was fairly busy 'round the new year

danielunderwood

6:30 PM

I prefer the ridiculous time zone scenario

Jake Rose

7:00 PM

What’s the difference between free spectral range and resolving power?

it seems to be they both say the same thing?

rob

7:55 PM

Filed for later: static friction doing nonzero work, kinetic friction doing zero/negligible work.

David Z

8:07 PM

@Blue No need to kick those questions out of this room. They're within the scope of what is okay to discuss here. You can certainly suggest that people may get a better response there, and move messages if their posters would like them moved, but I wouldn't go any further than that.

Anonymous

@DavidZ Oh, I thought we had an unwritten rule about keeping this room free from the high school physics and JEE stuff. I should have asked them whether they were interested in having their messages moved to the other room first. Sorry for that.

David Z

Ah, no such rule exists as far as I know.

No worries though.

Anonymous

8:27 PM

@DavidZ If it's not a rule already, then it would be more of a feature-request from my side. :P

Anonymous

(Partly joking :)

Anonymous

I've had some personal concerns about this room not being able to attract sufficient number of subject experts from the main site, for some time now (taking off my mod-cap). Not exactly sure what we can do about that but I believe they'd get interested in chat only if they notice interesting physics discussions here.

David Z

9:11 PM

@Blue Hm, well I'm not personally concerned about that but feel free to make a meta post about narrowing the scope of this room.

I suspect that a dearth of interesting physics discussions is not the main thing keeping experts away from chat, but I can't be sure.

Anonymous

@DavidZ Okay, I might do that in sometime in the near future. Tbh, the chat feels a bit different from before when we used have several interesting math and physics discussions. Many of the knowledgeable members and previously active participants don't seem to be around these days. Probably it's just the inevitable "change" and "real life" happening, and I'm worrying too much. :)

Anonymous

@DavidZ Might help to advertise chat a bit more. :P

David Z

9:39 PM

@Blue I haven't had that same feeling myself, but it could be. I definitely spend less time in chat than I used to because of the demands of real life.

danielunderwood

9:59 PM

@DavidZ I'm not an expert, but I didn't even know this chat existed for quite a while

I suspect others may be the same, expert or not

David Z

Yeah... actually we should check whether we have a community ad for chat

danielunderwood

I think I saw it on the right side bar at one point. I think that's where community ads are?

Anonymous

@DavidZ None for 2018:

Anonymous

Q: Community Promotion Ads - 2018

It's almost February in 2018, which isn't supposed to be the proper time to cycle these, but for this year it'll be once again, so we'll be refreshing the Community Promotion Ads for this year now! What are Community Promotion Ads? Community Promotion Ads are community-vetted advertisements tha...