Comment by denniskane | Hacker News Reader

Comment by denniskane | Hacker News Reader

Instead of invoking the idea of action-at-a-distance and then reflexively prepending the "spooky" tag to it, why doesn't anyone ever ask what a purely local physical description would entail, and then prepend something like "spooky" to that?

A purely local description would consist of a universe filled with nothing but [zero-dimensional] mathematical points that somehow affect each other in some bizarre way. But the physics involved would be entirely unknown, because mathematical points have precisely zero extent, with the side effect being that two mathematical points either a) occupy the same location, making them physically indistinguishable, or b) occupy different locations, making them absolutely disjoint (ie, "infinitely apart").

Let's think about 2 points approaching each other in a classical Newtonian universe. Now they are a meter apart and now they are a millimeter apart and now they are a nanometer apart. In each of these cases, they are perfectly disjoint, and have no possible way of communicating to each other. But now they both occupy the same location, and all possible classical physical descriptions have broken down!

The only rational solution is that the universe can only have a fundamentally nonlocal description. That is, the fundamental units of reality are spatially extended fields that do not suffer from the same requirement of pure mutual exclusivity that naive Bohr-esque classical models suffer from.

Abandoning this requirement is what gave de Broglie the impetus to develop his own theoretical model that would soon thereafter inspire Schrodinger to develop a mathematical infrastructure, which, when combined with Heisenberg's matrix mechanics via Dirac's new algebraic formalism, would become the modern, canonical quantum theory that we have today.

Edit: downvotes land me in negative territory for this :( ... Any explanation as why this reply is so bad? I am honestly curious!

Edit #2: I guess I should have just said "Hey, Schrodinger's cat!" or "Wow, how about that Many Worlds Interpretation!", then I would have inspired the peanut gallery to jump into some pseudo-philosophical discussion that has been repeated time and again. But alas, I have resorted to a thoughtful consideration of the deeper ideas of QM, and have found myself relegated to the footnotes of the "Hackernews-iverse" :P!!!

A purely local description is generally understood to be field-mediated interaction, where field can be at the same place as the particle it acts on, without being the same thing.

There is a semantic quibble at play here that actually makes all the difference in the world when it comes to discussions about QM that inevitably end up in pseudo-intellectual balderdash. A strictly local physical description can only involve classical Newtonian pictures, such that all of the nonlocal effects are superadded onto these pictures and were elegantly explained away by Newton as such: "Hypothesis non fingo" -- in other words, "Hehe, your guess is as good as mine".

In modern times, when we observe nonlocal effects between objects (such as with gravity), we first measure the effect, and only later do we invent something called a "field" whose definition consists of nothing other than the observed measurements themselves.

This is still nothing other than the same "Hypothesis non fingo" as before, except that now, the question of whether fields can possibly be explained in terms of classical physical pictures does not exist anywhere in the entire physics profession. That is, those kinds of hand-waving, natural language questions just don't have any place in the discourse of those who can rightfully be called credentialed, working physicists.

To such physicists, a particle is simply a set of quantum numbers that exists in n-dimensional Hilbert space (or "mathspace"). Again, whatever field is said to exist at the particle's location is nothing more than the measurement that is recorded by some apparatus that exists in [classical] spacetime. So, it is of course necessarily true that the particle and the [part of the] field [that affected it] must exist at the same location.

But to then say that this is therefore a meaningful account of something called "local physics" is, IMO, fairly absurd, because the entire point of the inventions called fields is to say: "Hey, I have no idea what accounts for instantaneous, space-bridging forces like gravity, so I am just going to leave it to the philosophers to offer up speculations so that the masses may be entertained."

Of course, this can be countered by the argument that gravity is fundamentally different from the electromagnetic force, because electromagnetism necessarily depends on the supposed propagation of things called photons. But this argument depends crucially on the notion that our mathematical shorthand for the quantization of the EM field (ie, photons) is at the same time a meaningful physical description that exists in the framework of a classical spacetime picture that is based fundamentally on the quality of locality.

However, QED (quantum electrodynamics; the quantum description of electromagnetism) in no way exists in any such classical framework. It is all rather the very same "mathspace" previously mentioned. The "field" is nothing but whatever bit of data that some classical measuring device recorded there.

p.s. Thanks for the upvotes :)... sometimes it pays to complain, I guess!!!

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