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2:49 AM
SCP
Secret's criteria of abnormality: A phenomenon that displays nonlocal classical causation without any involvement of rituals or other guiding context
A phenomenon is classically nonlocal if 1) there is no quantum correlation (duh), and 2) there are no causal sequence bounded by the speed of light that connects from the source to the occurrence of the phenomenon. In other words "it just is"
Thus a phenomenon displays nonlocal classical causation if every time event A happened, event B happened some time later but there is no causal chains that can connects the influence of A to B below the speed of light.
Timelike separated events that are causal, but not positioned next to each other in some phase space (including locally in spacetime) nor mediated by any fields is an anomally
A cup that change the color of the sky when rotated is an example of an anomalous object because no physical models can fully reproduce the causation it demonstrates
 
 
1 hour later…
3:56 AM
@Slereah whom did you email here about that thesis anyway
 
 
2 hours later…
6:06 AM
I'm trying to understand what is meant by "fractional timing precision" in the following: "Over the past year, the precision of optical lattice clocks has advanced dramatically, to a fractional timing precision of (∆t/t)∼10^−18"
I did a search but couldn't find any other uses of this term
I have only a basic understanding of atomic clocks but I have to write a summary of the paper this is from and want to understand as much of it as I can. Can anyone shed some light on this?
 
6:46 AM
@Simplex Suppose you measure some time T with your clock. T could be any time - a second, a year or whatever. The measured time T will have some error ∆T. The fractional timing precision is just ∆T/T. It's like a percentage error.
 
Ahh ok, thanks. I was thinking ∆t referred to the time difference between two events
 
Are photons absorbed instantly? Or is the a timescale over which absorption takes place?
 
@user400188 no, the interaction with the photon takes a measurable time. The interaction timescale is calculated by an equation called Fermi's Golden Rule.
 
Thank you @JohnRennie.
 
7:10 AM
Wow. This question from 2015 got bumped yesterday. I don't think it's answerable (as I implied in a comment) but it has a -5 answer that's non-mainstream.
 
7:57 AM
@JohnRennie I have a question
 
@Akash.B hi :-)
 
@JohnRennie hi
You know that in sun there occurs nuclear fusion and fission
Hydrogen fuses to give helium and helium decomposes to hydogen
@JohnRennie do you feel something fishy here?
Well hydrogen has no neutrons and helium has neutrons
 
Helium doesn't decompose to give hydrogen ...
 
???
One min let me google it to find more information
@JohnRennie you there?
 
@Akash.B hi
 
8:09 AM
Hi again
@JohnRennie so hydrogen fuses to give helium in sun
 
@Akash.B yes
 
It's only the process happening there, right?
So let me ask
Hydrogen has no neurons right?
 
Correct.
 
So where did the hell it get neutron to form a helium atom with two neutrons?
Is energy being converted to mass?
 
A proton can form a neutron by electron capture.
 
8:13 AM
Wow a new term
 
In the Sun two protons form a very short lived diproton state. This normally immediately falls apart again, but occasionally one of the protons will capture an electron and form a deuterium nucleus.
 
Hmm @JohnRennie so how's helium formed?
 
The proton–proton chain reaction is one of two known sets of nuclear fusion reactions by which stars convert hydrogen to helium. It dominates in stars with masses less than or equal to that of the Sun, whereas the CNO cycle, the other known reaction, is suggested by theoretical models to dominate in stars with masses greater than about 1.3 times that of the Sun.In general, proton–proton fusion can occur only if the kinetic energy (i.e. temperature) of the protons is high enough to overcome their mutual electrostatic or Coulomb repulsion.In the Sun, deuterium-producing events are rare. Diprotons...
 
Snap :-)
 
Great minds think alike... or fools seldom differ. :D
In the p-p chain, diprotium converts to deuterium by beta-plus decay (emission of a positron). Electron capture is possible, but it generally doesn't have time to happen. And the beta-plus decay itself is very rare, normally diprotium just splits into a pair of protons.
There are questions relating to this on Physics.SE & Astronomy.SE. Even forming diprotium is hard, due to the electrostatic repulsion between the protons: they have to get really close for the nuclear force to be strong enough to overcome that repulsion.
But even when a diprotium manages to be formed it nearly always falls apart. The odds of it converting to a deuteron are in the order of 1 part in $10^{26}$. So in the Sun's core, a proton has a mean lifetime of around a billion years before successfully being incorporated into a helium nucleus.
 
8:38 AM
@RyanUnger i used the form for outside people requestiing digitization of documentd
 
 
2 hours later…
11:07 AM
@PM2Ring oh I see
But what about nuetrons
Oh one of them undergoes beta plus decay I see
 
11:23 AM
6
A: Is there a useful way to visualize the symmetries of the relativistic Riemann curvature tensor?

knzhouYes, the method is called Young tableaux. For a rank $n$ tensor, give its $n$ slots names. Then the possible symmetries of the tensors may be classified by Young taleaux, arrays of $n$ boxes filled with the names of the $n$ slots. The rule is that one symmetrizes indices in rows, then antisymmetr...

@knzhou how did you know the vertical diagram doesn't contribute because of $R_{[ab,cd]} = 0$ and how did you know the first one is linked to it
 
12:31 PM
The biggest issue is knowing, just by looking at a diagram, that say $R_{[ab,cd]} = 0$
 
12:44 PM
@Slereah ok I don't see why it should be denied then
have you heard back from them?
 
@PM2Ring the version my collaborator likes: “great minds stink alike”
 
@RyanUnger not so far, but from what I've read it can take 2-3 weeks to process
 
1:07 PM
@JohnRennie old but still good
 
So Amerigo found out that South and North America are not part of Asia. Did Columbus think his whole life that what he found was just Asia?
 
2:01 PM
Columbus always insisted, in the face of mounting evidence to the contrary, that the lands that he visited during those voyages were part of the Asian continent, as previously described by Marco Polo and other European travelers. Columbus's refusal to accept that the lands he had visited and claimed for Spain were not part of Asia might explain, in part, why the American continent was named after the Florentine explorer Amerigo Vespucci and not after Columbus.
 
@PM2Ring Thx
How can the geocentric theory be wrong? Everything is relative, so geocentric and heliocentric are equally correct depending on which point of reference you use?
Am I stupid?
Ahh I'm confused now that I think about it
 
@NovaliumCompany Yes, in GR you can assume that everything goes around the Earth, but it makes the calculations uglier.
 
@PM2Ring I mean the same is true of all frames really
depending on what you're looking at
Heliocentric frame for the CMB is probably ugly
 
2:18 PM
@NovaliumCompany GR gives you a lot of freedom to choose weird & wonderful coordinate systems, but you normally choose coords that simplify the problem you're analyzing.
 
Oh ok, thx
 
bad news tho
for most problems, it will always be awful
 
@Slereah Agreed. But lets face it, doing GR on anything that doesn't have nice symmetries gets painful very quickly.
 
alas
 
3:08 PM
morning
 
3:41 PM
hello
 
4:03 PM
howdy
 
 
2 hours later…
6:12 PM
sup
I think I'm 2 hours late
 
 
1 hour later…
7:18 PM
2 hours late for nothing, it appears :P
 
7:53 PM
2
Q: Is there a magnetic attraction between two parallel electron beams?

ExocytosisI am refering to Ampere's force law, and to the beams accelerated after the cathode, so the deflection is not due to their respective cathode. In other words, do two electrons accelerating parallel to each other converge because of magnetic attraction? Does it apply to wires only or to a beam of ...

Ooooohhhh, c'mon, make HNQ please
=)
=P
 
8:15 PM
@EmilioPisanty no pretty pictures, no HNQ
 
@ACuriousMind ah, figures
 
figures, pictures, call them whatever you want ;P
2
 
 
2 hours later…
10:02 PM
Anyone use email notifications?
 
 
1 hour later…
11:13 PM
@ACuriousMind is the top-scored answer at physics.stackexchange.com/questions/505593/… accurate?
If it isn't, it probably needs attention from a subject-matter expert and I'm not quite close enough to the subject to jump in
 

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