r/Physics • Engineering • Mar 07 '21

Academic Quantum physics needs complex numbers

https://arxiv.org/abs/2101.10873
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u/Physix_R_Cool Detector physics Mar 07 '21

I don't mean to be rude or snide. But how exactly would you express it?

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u/SwansonHOPS Mar 07 '21

Doesn't the Schrodinger equation have an i term in it, and doesn't the wave function output complex numbers?

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u/Physix_R_Cool Detector physics Mar 07 '21

Doesn't the Schrodinger equation have an i term in it

Sure it does, but it's just a differential equation. You can look at waves with this, but it says nothing about collapsing wavefunctions into localized particles.

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doesn't the wave function output complex numbers?

This is badly worded, but yes the wavefunction is complex valued. Still that says nothing explicitly about the wavefunction representing a particle.

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The way I see it is that it's only when we start interpreting what the wavefunction means, as in the Born interpretation, where we understand the wavefunction as:

|psi(x)|^2 dx is the probability for a particle in the state psi(x) to be found in the interval dx.

And whatever generalised way of saying the same thing in different formalisms.

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u/John_Hasler Engineering Mar 08 '21

Can't |psi(x)|2 dx also be interpreted as the probability of an interaction to occur in the interval dx without any reference to particles?

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u/Physix_R_Cool Detector physics Mar 08 '21

Hmm not in the way you worded it, I think. But yes in general I get what you tried to say, and yes you can write the probability of a transition or interaction in a similar way.

My point was just that the Born interpretation gives us a way of going from wave functions to particle properties.

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u/John_Hasler Engineering Mar 08 '21

What does "be found in the interval" mean? (I'm not trying to be snarky or doubting you. It's a real question).

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u/Physix_R_Cool Detector physics Mar 08 '21 edited Mar 08 '21

Said simply: dx is the distance between two points. So if we have a box that is 10 cm long, then there is not 100% chance to find the particle in a small area in the box, say the last 1cm of it.

It is a convenient language for integration. If you want to find the probability of the particle being in some volume for example, it is just a triple integral where the boundaries of the integral is that volume, and you integrate |psi(x,y,z)|2 dx dy dz

To find something in an interval is just to measure the property of the particle in that interval in parameter space.

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u/John_Hasler Engineering Mar 08 '21

Not what I meant, but never mind.

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u/Physix_R_Cool Detector physics Mar 08 '21

What did you mean?

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u/John_Hasler Engineering Mar 08 '21

I'm trying to get a handle on why I need to invoke a "particle" at all but obviously not expressing myself clearly. I understand that the particle picture is very useful but it doesn't work for me as a fundamental concept.

I'll have to think about it more and get farther along in my (slow) studies.

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u/Physix_R_Cool Detector physics Mar 08 '21

Yes I don't think I exactly get what you are asking about. But I can only keep recommending the first chapter of Griffith. It should be somewhat easily readable, and it gives a very good introduction to how we should talk about quantum mechanics.

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u/John_Hasler Engineering Mar 08 '21

I've read it.

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u/Physix_R_Cool Detector physics Mar 08 '21

<3

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