The h Bar

12:43 AM

Why is the wave function times its complex conjugate also written as \$|\Psi$|^2 ? I am confused about the purpose of including the absolute value bars.

Is this just by the definition of the inner product in the hilbert space we're concerned with?

Silly Goose

12:55 AM

nvm got it but i have another question

what makes electrons emit a photon? i have seen this in two cases: 1) in griffiths qm, it says "the result is that a container of hydrogen gives off light (photons)", and when i was reading about Feynman diagrams, i read that electrons approach each other, exchange a photon, and this change in momentum propels the electrons in opposite directions, which can be represented by a Feynman diagram. however, in both cases, it's not clear to me why the electro would emit a photon

PM 2Ring

3:17 AM

How does this guy have 850+ points? physics.stackexchange.com/q/722428/123208 He hasn't posted many questions or answers, and I can't see a bounty on any of his answers. I find it a bit disturbing that someone with a physics PhD is working with a known anti-gravity / free energy crackpot.

antimony

what does sub quantum mean?

PM 2Ring

3:35 AM

@antimony It's not really a standard term. But it means a level of physics more fundamental than quantum physics.

antimony

ohh

PM 2Ring

The idea is that there's a simple subquantum layer that explains what we see at the quantum level. Like how the physics of protons, neutrons, electrons and photons explains the chemistry of atoms.

antimony

but it doesn't necessarily mean quarks and things?

or beyond quarks?

or that is what it means? deeper than quarks?

PM 2Ring

Yes, deeper than quarks. At the quantum level, we have quarks, which appear to be fundamental. But at the subquantum level, the quark is a complex entity. Think of the quark as a picture composed of subquantum pixels.

antimony

wow

thats a pretty cool idea tbh

but of course, being cool and being correct are not always the same thing haha

are there any experiments which prove these quark pixels?

PM 2Ring

3:46 AM

There's nothing wrong with looking for deeper levels of physics, in principle.

antimony

right

PM 2Ring

@antimony Right. Physics isn't just about pretty ideas. You need to be able to test those ideas, and see how well they explain what we can observe in the physical world.

Now it can be very difficulf to do effective experiments that explore the world at the quantum level. Generally, the smaller you go, the more energy you need. Which is why we build huge accelerators like the LHC.

antimony

oh good point

so noone has an accelerator powerful enough to get inside the quark?

yet

PM 2Ring

But we can also do simulated experiments: we create mathematical models, feed them into a computer, crunch the numbers and see if the model corresponds to what our empirical measurements say.

antimony

oh thats true

i wonder if you could do some of those experiments in space

PM 2Ring

3:57 AM

We've had a lot of success modelling the extreme particle physics that happens deep inside stars. That gives us confidence that our particle physics theories and our astrophysics theories are on track.

antimony

where there might be some high energy events from natural sources?

ahh yes, right

PM 2Ring

Indeed. Long before we had big accelerators we were trying to figure out the nuclear processes in stars. Obviously, we can't see deep inside stars, but we can get a good idea of what elements they contain from their spectra.

antimony

oh yes, good point

PM 2Ring

@antimony As far as we know, there isn't anything deeper than quarks. And if there is, it's impossible to get enough energy to see it. Due to color confinement we can't ever isolate a quark. If you try to separate the quarks in a proton it takes so much energy that you end up up producing more quarks & gluons, all bound to each other. We can't see the individual quarks or gluons, but we can see the patterns they make.

antimony

ohh wow

huh

thats very cool

PM 2Ring

4:11 AM

Jet (particle physics)

A jet is a narrow cone of hadrons and other particles produced by the hadronization of a quark or gluon in a particle physics or heavy ion experiment. Particles carrying a color charge, such as quarks, cannot exist in free form because of quantum chromodynamics (QCD) confinement which only allows for colorless states. When an object containing color charge fragments, each fragment carries away some of the color charge. In order to obey confinement, these fragments create other colored objects around them to form colorless objects. The ensemble of these objects is called a jet, since the fragments...

antimony

incredible

is this line of thinking at all reasonable: if we know approximately the energy which would be required, can we find the equivalent frequency associated with that energy and consider some temporal properties which might occur at that scale?

could it give some hints of the timescales these sub-quark properties might operate at?

PM 2Ring

Yes, that's reasonable. And that gives a timescale on the order of the Planck time. And energy densities similar to what the universe was like within a Planck time of the start of the Big Bang.

Even if you build a galaxy-sized particle accelerator, you probably won't have enough energy to explore the subquantum world... if it exists.

PM 2Ring

4:34 AM

We could do computer simulations of sub-quark stuff, but there are a few problems. It's hard enough to do that at the quark level: it takes huge amounts of computing power, and we have to make various approximations. Those calculations have improved in the last decade or so, due to clever mathematical tricks, but those tricks involve simplifications.

Subquantum theories claim that the subquantum level is simpler, so the calculations should be easier. OTOH, you probably need to perform a whole lot more calculations.

And that can lead to a combinatorial explosion: en.wikipedia.org/wiki/Combinatorial_explosion

antimony

sorry phonecall bbs

PM 2Ring

No worries.

A similar thing affects string theories. In those theories, a quark isn't a point, it's a tiny string. We can build mathematical models of those strings, and crunch them in a computer, but there are too many possibilities for the string parameters.

So even if some set of parameters lets us perfectly simulate all the known fundamental particles there are zillions of other combinations of parameters that will give the same result, so there's no way to decide which set of parameters is the correct one.

John Rennie

5:56 AM

@SillyGoose Do you mean an electron in hydrogen atom? or something like Compton scattering? Note that Feynman diagrams are a pictorial representation of an integral and do not show an actual physical process. The two interaction electrons do not emit photons towards each other.

John Rennie

6:38 AM

Deleted

RewCie

7:12 AM

Chad Afternoon

Is it possible to know the Jounal/Conference at which an ArXiv Paper was published?

I just wanted to know if there are any Journal where an ArXiv paper has been accepted or not, otherwise I would have to waste my time reconstructing my whole time that paper and comparing the results (which I think is highly misleading)

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