The h Bar

10:24 AM

I hate rainy days at hometown.

We had Storm Deirdre blow in from the Atlantic over the weekend. The worst of the strong winds are past now, but it has been raining on and off since Friday. Lovely.

10:52 AM

11:10 AM

I've read 1Q84 and quite enjoyed it, but I'm not a huge fan of Murakami's books. I am not a fan of aphorisms, his or anyone elses.

I don't Murakami at all. But I find these text reflects what I experience.

1:46 PM

you should be ready for upcoming possible storms.

bolbteppa

2:32 PM

I don't know why every set of string notes does not do what Rebbi does, push NG the full way first

Even the normalization of the wave equation is completely obvious this way

No ghost is still driving me nuts

Q: Consider two electrons a distance d apart. What is the maximum kinetic energy obtained NOT neglecting energy lost to radiation if released?

2:51 PM

@JohnRennie hmmmmm.

is that coming our way?

I sure hope not

Avnish Kabaj

Kafka on the shore was very disturbing for me in 6th grade

danielunderwood

We have our own storm over here. Though it's more of snow and ice much earlier than usual than a large storm

dmckee

3:10 PM

OK, this

0

Two electrons d apart have potential energy. Release them, they will be repelled according to Coulomb's law. But accelerating charges radiate, producing radiation, resulting in breaking action. How much energy us lost instead of becoming kinetic?

electromagnetic-radiation

obviously runs afoul the homework policy, but it's gotten it's hooks into me and I want to answer it.

Or at least to talk about how you would approach answering it and then look at someone else's work.

The way I figure it you would find the multi-pole expansion of two identical point charges as a function of $q$ and separation and figure the radiation from the evolution thereof. Maybe.

It has been two decades since graduate E&M for me, after all.

I'd feel better about that question had they done something as simple as note what the result would be if you didn't worry about radiation

(i.e. what's the potential energy of that scenario)

I also question whether it makes sense to do that problem using classical E&M, since we're talking about two electrons specifically

@dmckee this is nowhere near obvious to me

I really can't picture any EM course that would ask this question

it's ridiculously hard

it puts you in all sorts of tricky Abraham-Lorentz situations

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...

including (i) the EOM is third-order in time, not second order, and (ii) if you're not careful, you get some extremely ugly runaway solutions

3:32 PM

a variation on that would be: suppose you have two identical particles which start from $x=\pm \infty$ with speed $v$. If you ignore radiation, they'll move towards each other until their mutual repulsion brings them to stop, then they'll move apart and ultimately exit at $x=\pm \infty$ with speed $v$.

What happens if you include radiation? (My supposition would be that it's an absolutely miserable calculation.)

@EmilioPisanty I don't think so. It's moved off to the north now. But the pressure charts for the next week don't look good. There are a couple of deep Atlantic lows headed our way.

I think one can at least anticipate that KE will be lost along the way, so the distance of closest approach will be larger and the exit speeds will be smaller than $v$.

But that's not a calculation :S

I suspect at least some version of this problem is treated in Jackson...which is a pretty good reason for me to not want to touch it

@EmilioPisanty it's an interesting question and I've voted to reopen it. I think David might have been a bit hasty in closing it.

It's an interesting question, but I'd be hard pressed to say that the OP has presented it well

Akash. B

Hi

4:02 PM

@JohnRennie good.

@JohnRennie @dmckee @DavidZ now reopened.

@EmilioPisanty now we just need someone to answer it :-)

'ndeed