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Comment by phkahler | Hacker News Reader

But if someone makes a conscious choice to choose one that preserves locality, shouldn't they change their mind when "spooky action at a distance" starts happening? Non-locality is staring them in the face and they refuse to adopt a formalism that makes it explicit. They seem to like things that appear strange and non-intuitive.

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There is no spooky action at a distance. When you measure one member of an EPR pair, nothing actually happens to the other member.

See https://www.youtube.com/watch?v=dEaecUuEqfc or http://www.flownet.com/ron/QM.pdf for a detailed explanation.

I had a look at part of that pdf and I don't think the author really gets it. The essence of most nonlocality experiments is that if you send entangled photons off to two separate detectors with polarising filters in front of them then the correlation between the two photons getting through varies dependent on the angle between the two polarisers in a way that can only be explained by photon 1 kind of knowing what the angle of photon 2's polariser is or visa versa. How do they know that when far apart? See Bell's Theorem for more details.

Your parent is the author ...

Really it boils down to the fact that (to quote a very insightful comment I can no longer recall the author of) “if I flip a coin and look at it whilst hiding it from your sight, the outcome is perfectly deterministic for me but it is still perfectly random for you” (and, I'll add, the maximum speed at which I can “de-randomise” the outcome for you is by telling you what I measured (at the speed of light)).

No, there really is a difference between a flipped coin and an unobserved particle: the latter can interfere with itself. A coin will not interfere with itself after you flip it even if you don't look at the outcome.

Fair enough: single-particle-at-the-time double-slit-experiment is relevant here, but I didn't have it in mind when I was thinking of remote entangled particles being measured. My bad.

This is just getting at the basic insight that probabilities are most usefully thought of as being subjective. The coin will land on either side depending on the torque applied and air resistance and whatnot. 50% is only a measure of our subjective uncertainty. This isn't about quantum mechanics.

I'm the author, and I assure you I am (and was) aware of Bell's theorem, notwithstanding that I didn't actually mention it in the paper. Bell's theorem in no way invalidates what I said. It is in fact a theorem of its own that measuring one EPR particle cannot affect the outcome of any experiment performed on its partner.

https://en.wikipedia.org/wiki/No-communication_theorem

I've argued that for years. If "collapsedness" is property of a particle, then measuring one branch of a stream of entangled particles would modulate the collapsedness of the other branch and could be used for FLT communication. The bottom line is that nobody can tell the difference between a particle whose wave function collapsed and one that didn't. The conclusions from that is that wave function collapse is fiction. That video makes the same point in a more formal way.

How convenient that this supposed "spooky action at a distance" can't actually send information ftl. Locality is very important for coherent laws of physics. Many worlds is still the most parsimonious explanation which is why it enjoys the most support from theoretical physicists. It's literally just extrapolating what we already see in small scale experiments to the macro scale, it's staring you in the face!

Could you touch on why many worlds is more parsimonious than pilot wave? I'm not sure that I understand that reasoning. Is it because a given "universe" is locally simpler? Would it be accurate to describe the comparison as an infinite number of universes (separated via some higher dimension) vs. a single universe that is holistically connected throughout spacetime?

Many worlds is parsimonious in some ways in that all the stuff allowed by the equations happens and that's it (sort of in theory at any rate - not sure it really gives the Born rule). With pilot wave or Copenhagen you have to tack on a wave or observer respectively. On the other hand all the stuff is a lot of stuff.

The theory is more parsimonious. Whether it generates untold amounts of parallel universes is immaterial to its own Kolmogorov complexity.

Many worlds basically says "the wave function is real". You just take what the math says at face value, and the math says there's a blob of amplitude where the cat is alive, and another blob of amplitude where the cat is dead, and those blobs do not interact.

Copenhagen adds something on top of the math: a kind of "collapse" where the blob you did not observe gets mysteriously zeroed out. There's only one universe, which looks simpler, but the theory itself is more complex, because you just added that collapse.

Pilot Wave (of which I know nothing) seems to add a similar complexity. There's no collapse, but there's this additional non-local "wave" that's laid out on top of everything, and determines which of the blobs is real (the dead cat blob or the live cat blob).

Think Chess vs Go. Chess has rather complex rules, with an initial position, moves for 6 different pieces, and a couple special cases. Go's rules on the other hand can fit on one page. So, Go is simpler. However, in terms of possibilities, the universe generated by the Go rules is orders of magnitudes bigger than Chess'. Simpler rules can lead to more diverse possibilities. Quantum physics interpretations are similar: Many Worlds have the simplest rules, but it also describes the biggest universe.

However, doesn't many worlds also necessarily require one or more dimensions for separating the universes from each other?

Actually, configuration space have an infinite number of dimensions. Current physics, (or at least QM) doesn't describe our universe as having 3 spatial dimensions. That's a projection, the classical illusion —which is a logical consequences of the underlying physics of course.

Imagine 2 pearls on a thread. You have 2 ways to represent them: the obvious one is 2 points on a line. A less obvious (but just as valid) is a single point on a plane: the X axis would represent the first pearl, and the Y axis would represent the second pearl. Similarly, 2 billiard balls on a billiard can be represented by a single point in a 4 dimension configuration space. And the entire universe require many many more dimensions than that.

There are many more subtleties. I suggest you read the Quantum Physics Sequence for a comprehensible explanation of all this mess. http://lesswrong.com/lw/r5/the_quantum_physics_sequence/

Can I just say this was very beautifully laid out. Much simpler and more convincing than what I could have done. Thank you.

The complexity of a theory is in how long the theory itself is, not how big the objects it generates are. The peano axioms are extremely simple, despite generating an Infinity of numbers.

Nope, you can get around that with superselection rules (which give you a mathematically rigorous thing that sort of looks like many worlds). Pilot wave and Einselection are the two most promising avenues into making sense of apparent wavefunction collapse, in my opinion.

I agree. I thought that the scientific world already gave up on the idea of locality, since entanglement has been experimentally demonstrated.

Furthermore, I don't have a problem with accepting non-locality from a theoretical perspective either, now that I know about the Holographic Principle. If the universe is a hologram, then the apparatus that is projecting the hologram can be connected in ways that aren't obvious in the hologram.

It's not that kind of a hologram... all the hologram idea says is that all of the information in our universe can be represented on a 2 dimensional surface. It doesn't claim there is literally a hologram projector somewhere projecting a hologram of our universe. Such a thing would be nonsensical. If the projector were outside our universe it would, by definition, be causally disconnected from our universe and thereby never capable of influencing it in any way. If it were capable, it would, again by definition, be part of our holographic universe.

Just because something is outside something else does not mean it is causally disconnected.

The computer program runs inside the computer. The computer is outside the program. But nevertheless the computer's hardware is causally connected to the program. Further still, the programmer is outside the program, but he very much can influence it. Indeed, he brought it into being.

The idea is that to be outside the universe is to be causally disconnected from it, not to be outside of some arbitrary system. A "universe" is not an arbitrary system -- it is the whole of reality.

A computer program is not a universe independent of the programmer. They both exist in the same universe because they are causally connected. If they were in different universes, they must be causally disconnected. You're whole argument rests on the assumption that the program and the programmer reside in different universes, which is clearly not the case.

You can reproduce entanglement in a number of local theories. I always mention Einselection in these sorts of threads, because it's a very clean way to get something that looks like many-worlds but isn't hand-wavy and can reproduce entanglement via local mechanisms. In particular, contradictory measurements may take place, but they are forbidden from interacting via superselection rules (such that <x|A|y> = 0 for any observable A for contradictory states x and y). The math isn't as developed as Pilot Wave theory, but it's at least as aesthetically pleasing (deterministic, local, etc.). I guess it gives up definiteness, but in a less objectionable way than many worlds.

Are you implying that Many-Worlds is hand-wavy? It's not.

A large fraction of working physicists subscribe to the Many-Worlds Interpretation, which preserves locality even though it has entanglement.

Field theories like QED have the concept of a field, which is something that permeates all of space, which makes it non-local. Electrons all have the same electric charge because they are all different excitations of the same electric field. Does that in some way mean they are all the same particle? They are all connected by the same electric field and have the same charge.

"Spooky action at a distance" does not violate locality in the sense that information does not travel faster than the speed of light.

You should be very suspicious if your theory claims non-locality, but in a way that does not allow any transfer of information.

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