Comment by gavinray | Hacker News Reader

Comment by gavinray | Hacker News Reader

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Is there anyone present who understands this?

I'd like to ask a question:

My view on life is that it's deterministic. The mental analogy I've come up with is this:

"If you were to roll a set of marbles down a hill, the outcome and trajectory would be identical no matter how many times you repeated the experiment given the same marble shapes and initial force."

Where the marbles here are an analogy for our genetics, and the hill + initial force our environment.

Reading the thought experiment it sounds like a similar analogy:

  > "Run a bath, then dump a bunch of floating bar magnets into the water. Each magnet will flip its orientation back and forth, trying to align with its neighbors. It will push and pull on the other magnets and get pushed and pulled in return. Now try to answer this: What will be the system’s final arrangement?"

  > "This problem and others like it, it turns out, are impossibly complicated."

Can someone explain why this is "impossibly complicated?"

Isn't it deterministic and calculable?

> Isn't it deterministic and calculable?

The classical version is deterministic, but "deterministic" does not necessarily mean "calculable". There are plenty of deterministic problems that are not calculable (at least not in any reasonable time frame, where "reasonable" means "not of a much greater order of magnitude than the age of the universe") because they are so sensitive to precise conditions that miniscule differences quickly become unmanageably huge. And since we can never measure a system's state to exact precision, nor can we calculate things to exact precision, our model of a system is always imprecise, and for many systems, "imprecise" means "not calculable" even though the underlying laws are deterministic.

The quantum version is not even deterministic when measurements are involved.

There are interpretations of quantum mechanics in which it is deterministic as well (google search term: block universe).

Yes, there are (the many worlds interpretation and the Bohmian "pilot wave" interpretation are the two that come immediately to mind). I don't see what that has to do with "block universe", however, since that is an interpretation of relativity, not quantum mechanics.

We must be talking about different things. Block universe is the theory that the universe is fixed in advance (deterministic) as a 4 dimensional “block” (more dimensions to include many worlds, I suppose?) and we’re just exploring one probabilistic trace through it.

> more dimensions to include many worlds, I suppose?

There is no spacetime model of many worlds at all, as far as I know. Many worlds as an interpretation of QM is based on non-relativistic QM.

The "space" in which quantum states "live" is not spacetime but Hilbert space. "Many worlds" is really a misnomer in the sense that there is only one quantum state in Hilbert space. But quantum states in Hilbert space can have relationships to ordinary space that are not at all like those in classical physics: for example, a single quantum state can describe a system containing multiple entangled particles that are spatially separated; in such a state no particle by itself has any definite state at all (which is impossible in classical physics). That is true regardless of which QM interpretation you adopt.

Block universe, as a theory, is based on classical (non-quantum) relativity, and its model of 4-dimensional spacetime. It is not based on QM. Non-relativistic QM does not even use spacetime. Relativistic QM, aka quantum field theory, does use it, but is not a deterministic model and does not treat spacetime as fixed in the sense of all events within it being determined in advance.

> we’re just exploring one probabilistic trace through it

There is no such thing as a "probabilistic trace" through a deterministic 4-dimensional spacetime in which all events are fixed in advance.

So how does the universe itself “calculates” things in real time. How do so many operation “render” on the quantum/classical scale. Forces adapt in real time?

No one knows.

Even the idea that anything is being calculated is a supposition. There appear to be relationships between entities and some of them can be modelled using human math on human-accessible time scales.

But although some of the models have potentially infinite precision the universe itself clearly doesn't on any scale.

Or if it does, it's not accessible to us. So whatever is happening may use some other paradigm to manage relationships, and the entities and relationships we see are emergent and not at all fundamental.

It's not necessarily real time, you only experience time at the same rate, no matter how fast the universe is calculating in meta time. Or maybe time is a 4th spacial dimension, then the universe would be a finished, static thing, no more calculations needed (you would experience time in the sense that characters in a movie experience time, even though the film roll already contains all the frames)

the universe doesn't calculate anything. it just happens.

this is also why I think that artificial consciousness (big difference to intelligence) is a whole lot harder than many people think. a stack of papers where someone has manually written the neural net (or whatever technology) computation and results is unlikely to have a subjective experience. because there is an indirection between a simulation and the real world. the simulation is a computation. the real world happens.

Could we devise a process, which makes things "just happen", so that consciousness results? I think that is the question. I don't see, why it should be impossible to do so.

What you are saying aligns a lot with the “emergent consciousness” line of thinking. It means that consciousness appears out of the complexity of our wiring.

Perhaps consciousness is not one single 'flavour', but comes in lots of different varieties?

Physics is a model for us to estimate and in some way explain phenomena we see in the universe, it isn't the way that the universe itself produces phenomena

It’s interesting to ponder how phenomena come about : energy, matter, dimensions, consciousness that can reflect on phenomena.

no haya banda! Its all a tape recording! https://youtu.be/oJDlipYYaFQ

Small differences in the initial conditions can bring big differences in the final result. This is the main postulate of chaos theory started with one Edward Lorenz and giving birth to stuff like the butterfly effect.

https://en.wikipedia.org/wiki/Chaos_theory

This is part of the answer. The other part being that there seems to be fundamental non determinism in our universe.

Most likely but it depends on your interpretation of quantum mechanics. I believe in non determinism but that’s mainly a hunch

I agree - it is obvious to me that free will = non-determinism. But we are getting into metaphysics and unprovable thought experiments

Deterministic, yes. Calculable, no, because you can never know the precise initial conditions, either for statistical mechanics reasons (classical) or uncertainty limits (quantum).

https://en.wikipedia.org/wiki/Quantum_indeterminacy

This is similar to nondeterminacy, and is why we end up with all sorts of “interpretations” (Copenhagen, …). Indeterminacy makes the math really hard. I would like to say more, but I can’t do so and be correct. If you’re really interested, pick up all three volumes of “The Theoretical Minimum”, and come to your own opinion after learning the physics.

Actually the probabilistic interpretations of quantum mechanics are far easier to use than the deterministic ones

  > Isn't it deterministic and calculable?

Your quest for knowledge should include examining the Double Pendulum. It is an extremely simplified device, easily explained and understood, whose motion is chaotic.

[1] https://en.wikipedia.org/wiki/Double_pendulum

There are three categories of theories relevant here:

Deterministic classical mechanics

Non deterministic interpretations of quantum mechanics (most popular among physicists)

Deterministic interpretations of quantum mechanics (eg Bohmian mechanics)

In the first case, the future is calculable in principle, but probably not in practise (too complex)

In both of the other two cases, it is incalculable in principle, even though the latter is deterministic

You left out non-deterministic classical mechanics, e.g., Norton’s Dome: https://en.m.wikipedia.org/wiki/Norton%27s_dome

Whenever you introduce fluids into this sort of experiment, any turbulent flow will add indeterminism to outcomes - this applies to air as well.

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