Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Does quantum theory imply the universe is preordained?

nature.com

Post reply on HN
Print view View original

31–40 of 180 posts

Re: Does quantum theory imply the universe is preordained?

#31

Post by digging »

PheonixPharts wrote: post #24
danbruc wrote: post #22

Earlier quoted context omitted.

"Random" is a property of your mind, not of the world. Limited information about the initial state is one source of randomness but not necessarily the only one. Whether there is true randomness in the universe is at very least an open question.

Can you clarify what "true randomness" means out side of the context of human agency and perception? Can you also give an example where "true randomness" would differ from the randomness I describe on the actions a human would take? That is to say, if a my internal model of the world tells me a coin landing on heads is 50/50 how does "true randomness" or not of the resulting coin toss impact how I should gamble on co…

In basic interpretations of quantum events, quantum properties are not defined until measured. It's not just that we can't see the other side of the card; the card is blank until we flip it.

Re: Does quantum theory imply the universe is preordained?

#32

Post by Jensson »

PheonixPharts wrote: post #15

"Random" is a property of your mind, not of the world. If I shuffle a deck of cards in a way that you don't know about, then the next card I pull is "random" to you even though, obviously, if one were to turn the cards face up nothing would have changed about the order of the cards, but now the next card would be fully deterministic. I could likewise sort the deck with an algorithm completely unknown to you. I could…

> Heisenberg uncertainty principle is more a statement about the limits of knowledge than about "God throwing dice".

This isn't what physicists believe though, Heisenberg uncertainty principle is about a wave not having both a well defined position and velocity. They either drift apart (undefined velocity) or they are spread apart (undefined position). Then the wave collapse keeps the wave together over time by randomly removing parts of it, we have no theory where that isn't random even "many world" means you randomly select one of the branches to follow.

We do know for sure that particles are waves that spread out and exist in all of those parts, it isn't just that it represent a point particle with unknown location. And we know for sure that those waves under certain circumstances withdraw from parts and just keep other parts, ie wave collapses. Both of those are easily observed in experiments and not up for debate.

Re: Does quantum theory imply the universe is preordained?

#33

Post by EA-3167 »

PheonixPharts wrote: post #24
danbruc wrote: post #22

Earlier quoted context omitted.

"Random" is a property of your mind, not of the world. Limited information about the initial state is one source of randomness but not necessarily the only one. Whether there is true randomness in the universe is at very least an open question.

Can you clarify what "true randomness" means out side of the context of human agency and perception? Can you also give an example where "true randomness" would differ from the randomness I describe on the actions a human would take? That is to say, if a my internal model of the world tells me a coin landing on heads is 50/50 how does "true randomness" or not of the resulting coin toss impact how I should gamble on co…

> Can you clarify what "true randomness" means out side of the context of human agency and perception?

Depending on your Interpretation of QM, randomness is a fundamental aspect of reality. How does a quantum superposition of two states resolve? The canonical view is wavefunction collapse, which is ultimately random, and attempts to find some pattern underneath it all generally fail. Look at the Bell Inequalities, which demonstrate that any theory which attempts to reproduce the successful predictions has to either be non-local, or non-realistic, and must be incompatible with local hidden variables.

Now does that mean nature is random? I don't know, no one does, because we're sure that QM isn't a complete theory. It is a really good theory though, in some domains such as QED it's been tested to more than 11 decimal places and found to hold. The difficulty of making a new theory that matches that precision and represents a paradigm shift can't be overstated. The result is that a lot of time is spent on those aforementioned Interpretations, you've probably heard of some, such as "The Many Worlds Interpretation" aka parallel universes. After all if everything happens, and we just happen to only perceive a part of it, then there is no randomness... no hidden variable. When a quantum state collapses, part of it doesn't just vanish, it's just out of our site.

The problem with that is... there's no evidence to support it, probably no way to even test it. Anyway, the bottom line is that maybe there is real randomness, and maybe there isn't, we just don't know.

Re: Does quantum theory imply the universe is preordained?

#34

Post by Guvante »

PheonixPharts wrote: post #24
danbruc wrote: post #22

Earlier quoted context omitted.

"Random" is a property of your mind, not of the world. Limited information about the initial state is one source of randomness but not necessarily the only one. Whether there is true randomness in the universe is at very least an open question.

Can you clarify what "true randomness" means out side of the context of human agency and perception? Can you also give an example where "true randomness" would differ from the randomness I describe on the actions a human would take? That is to say, if a my internal model of the world tells me a coin landing on heads is 50/50 how does "true randomness" or not of the resulting coin toss impact how I should gamble on co…

Do you count wave particle duality as randomness?

Certainly the dual slit experiment makes hidden variables very hard to preserve.

Additionally several tests have shown that hidden variables don't work to explain quantum mechanics, there aren't possible coins the allow the kind of probabilities we see.

Re: Does quantum theory imply the universe is preordained?

#35

Post by digging »

voxl wrote: post #14
digging wrote: post #12

Earlier quoted context omitted.

A good quip, lol. But of course they would, because they must, because the feeling of control (that is: the unconscious belief in control) is just as intrinsic as the actual absence of control.

which in other words makes superdeterminism unfalsifiable, because any attempt to do so can be met with "it must have been that way"

Absolutely. I find it an interesting thought experiment and nothing more unless and until we determine some way to actually see through the veil and identify these extra-universal hidden variables. (At which point our conception of the universe may expand to include these variables and whatever else exists in that outer layer.)

Re: Does quantum theory imply the universe is preordained?

#36

Post by nyssos »

PheonixPharts wrote: post #21
__turbobrew__ wrote: post #10

I have yet to see a subscriber of superdeterminism not look both ways before crossing the road.

Does believing that gravity exists mean a person will not roll down a hill? Why would belief that we are just agents responding predictably to stimuli imply that one would not respond predictably to stimuli ? The fact that ones behavior does not change when one acknowledges that all behavior is deterministic and predetermined seems evidence in favor not against that hypothesis.

> Why would belief that we are just agents responding predictably to stimuli imply that one would not respond predictably to stimuli?

This is determinism, not superdeterminism.

Superdeterminism claims that the state of any system you measure is always already correlated with the measurements you perform on it: photons emitted a billion years ago encode information about where someone is going to choose to point a telescope tomorrow. Not because of any interaction between the two, but because the initial conditions of the early universe just happened to be set up that way.

Re: Does quantum theory imply the universe is preordained?

#37

Post by simiones »

PheonixPharts wrote: post #15

"Random" is a property of your mind, not of the world. If I shuffle a deck of cards in a way that you don't know about, then the next card I pull is "random" to you even though, obviously, if one were to turn the cards face up nothing would have changed about the order of the cards, but now the next card would be fully deterministic. I could likewise sort the deck with an algorithm completely unknown to you. I could…

If QM is correct and there is no "deeper" hidden variable theory that explains the movement of all particles, then you're wrong.

Heisenberg uncertainty as it exists in QM today is not a statement about your knowledge, it is a statement about the possible interactions between particles. It tells you that if a particle collides with another at a specific point in space, then their trajectories after that collision can't depend on the momentum of either particle, for example, because that would violate the inequality.

This indeed does not necessarily imply randomness per se. But it is much more than a statement about precision of measurements at a human scale: it is a statement about the possible interactions at even the lowest scales.

Re: Does quantum theory imply the universe is preordained?

#38

Post by digging »

DebtDeflation wrote: post #6

I think, ultimately, there are only 3 possible explanations for the paradoxes of the quantum world. 1) superdeterminism (everything including our choices in quantum experiments today were fully determined at the instant of the Big Bang), 2) something "outside" our observable reality acting as a global hidden variable (whether something like the bulk in brane cosmology or whatever is running the simulation in simulati…

Actually, how are 1 and 2 different? If 2 simply refers to another layer of reality, don't we still have to figure out if it's deterministic or not? I suppose if it has its own completely different (or slightly different[1]) physics, we'd be starting over, but we'd still work our way back to the question of top-level determinism eventually).

[1] Referring to cosmological natural selection as a theory of the "fine-tuned" universe: https://en.wikipedia.org/wiki/Cosmological_natural_selection (a fun favorite of mine but not looking likely)

Re: Does quantum theory imply the universe is preordained?

#39

Post by [deleted] »

PheonixPharts wrote: post #15

"Random" is a property of your mind, not of the world. If I shuffle a deck of cards in a way that you don't know about, then the next card I pull is "random" to you even though, obviously, if one were to turn the cards face up nothing would have changed about the order of the cards, but now the next card would be fully deterministic. I could likewise sort the deck with an algorithm completely unknown to you. I could…

[deleted]

Re: Does quantum theory imply the universe is preordained?

#40

Post by simiones »

digging wrote: post #30
PheonixPharts wrote: post #15

"Random" is a property of your mind, not of the world. If I shuffle a deck of cards in a way that you don't know about, then the next card I pull is "random" to you even though, obviously, if one were to turn the cards face up nothing would have changed about the order of the cards, but now the next card would be fully deterministic. I could likewise sort the deck with an algorithm completely unknown to you. I could…

Not sure I agree fully in the case of Uncertainty. To the best of our knowledge, an undetermined quantum property is actually undefined. Whether we go with the simple Many Worlds or the Copenhagen wave function collapse or even Pilot Wave theory, when the value becomes defined it is randomly selected (or our World is a random selection of all of them) according to the wave function. I believe what you're saying is th…

I don't think you're right about the many worlds interpretation here.

In the most popular "simple" many worlds interpretation, the whole universe is a QM system described by the universal wavefunction. The "worlds" are just "branches" of the wavefunction that are not entangled with one another.

The Schrodinger equation (and the more advanced QFT versions) are fully deterministic differential equations: the state of the universe at time T is fully determined by the state of the universe at time T-x, for any x. This remains true even if x is negative: there is no "arrow of time" in QM, there is no distinction between the past and the future in any QM equations.

The only "non-determinism" in Many Worlds is thus of the knowledge kind: you don't know which "world" you happen to be in, so you don't know which result you'll notice. But this is like being spun around a coin: you don't know which face you'll end up looking at, but you know both faces actually exist. All the possible outcomes of any QM event are realized in "some world", there is 0 uncertainty.

Post reply on HN