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Comment by empath75 | Hacker News Reader

On observers creating the universe, I’ve sometimes wondered if given the simulation hypothesis, that simulating quantum mechanics is so computationally expensive that it isn’t done unless we’re looking at it, and that the high energy levels required to probe smaller and smaller length scales is an artifact of the computational requirements of simulating it.

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That's an interesting thought. It it's true, it seems to have some implications:

* Whoever is running the simulation cares about whether we're looking.

* They had a good reason for going with quantum mechanics rather than something that would be easier to simulate.

I know some people would say that's because they're interested in simulating conscious life and quantum mechanics is essential for consciousness. However, I find it very implausible that quantum mechanics is essential for consciousness so I'd prefer a different hypothesis for why they went with a difficult-to-simulate physics in their simulated universe. Any ideas?

Idea: their reality is much more computationally complex than quantum mechanics, so much so the difference between classical and quantum is irrelevant from a cost point of view and matters only from a results point of view.

Another possibility is simply that they've got wildly more resources than we can imagine. It's ferociously expensive to run the universe on a classical simulation of QM, but finite. We have no particular reason to believe this "higher reality" doesn't have this level of resources. I've often pondered our universe as the moral equivalent of an elementary school demonstration; what if we're some metaphorical elementary kid's homework, because our physics is relatively simple (assuming some ToE that may actually be simpler than meets the current eye) and produces interesting results?

We can reasonably discuss the feasibility of simulating our universe using our universe. We can do some reasonable discussion of "universes that run something like ours but with some differences". We are profoundly ignorant about everything else.

I can't help but find it unsettling listening to a subject of the universe describe it as "relatively simple". Simple relative to what?! Some arbitrary more complex system? Well Sure!

Frankly, I don't think it's a question of complexity, or even expressivity, but more one of encapsulation and information hiding.

The fundamental laws of the universe, at present, seem to be a whole lot simpler than many of the things that arise from them. That's as much of a statement in that direction as I think can be supported.

"I can't help but find it unsettling listening to a subject of the universe describe it as "relatively simple". Simple relative to what?!"

For one, simple relative to every universe we've ever created, such as Minecraft, World of Warcraft, Second Life, etc., all of which are megabytes upon megabytes (if not gigabytes) of ad-hoc rules, specifications, hard-coded geometry, etc. Even if we ignore the visualization aspects, they are all very complicated.

It is very likely that whatever the ultimate Theory of Everything is would fit comfortably into kilobytes. Very dense kilobytes, kilobytes you could spend your entire life understanding, but kilobytes. Certainly the entire Standard Model could be packed into kilobytes even starting from a fairly simple axiomatic mathematics, with a half-decent encoding. Its complexity comes from the number of particles interacting under its rules, and the fact our human brains aren't particularly suited to running QM calculations and confuses that difficulty with "complexity", since very few people have a grasp on what complexity truly is [1]. Most of the complexity of the Standard Model would actually be building up from the simple axioms and defining imaginary numbers and the other basic mathematic operations; once that was done, the fundamental equations to evolve state and the table of constants would not be very large. (Assuming that the parameters are not infinitely complicated real numbers, and that we can cut them off safely aften 40 or 50 decimal places without noticing a difference.)

The real universe's complexity does not appear to stem from its core building blocks necessarily, but from the staggering amount of space it occupies and the amount of computation it does, with both the Planck space and Planck time constants being staggeringly low on the one end, and the age of the universe and the expected age it should be able to survive staggeringly large on the other.

[1]: Defining it correctly is way beyond the scope of this post. But to get an idea, go here, look at the initial state, and then hit "start": http://pmav.eu/stuff/javascript-game-of-life-v3.1.1/ It looks like all sorts of complicated stuff is happening, right? However, the rule set is a small rule about what cells live or die based on neighbors, that small initial state, and if we're getting really technical, the iteration counter. What is on your screen may be visually complicated, but mathematically, it's very, very simple.

What's really shocking is that the Life rule set is probably sufficient to describe our universe. It's Turing Complete, and there's a sense in which any TC set of rules is equivalent to any other. However, it is also very likely that running our universe on Life rules would also require a massively complicated initial state, making it an unappealing theory to explain the real universe for that and several other reasons. We'd like to see something where the sum total of the complexity of the rule set and the initial state isn't that great, or is at least proportional to the amount of "stuff" the universe seems to have started out with.

Maybe because quantum mechanics has interesting dynamics and produces interesting results?

Hey, there's a seed for a hard sci-fi novel: we live in a simulation (or pocket universe), the laws of which were intelligently designed to produce aggressive life forms in order to make entertaining viewing for the builders and their clients. So all the wars we decry actually saved our universe by keeping it 'interesting'.

(I find it interesting that I'm willing to allow that evolution as we know it is just a quirk of our universe's dynamics, but I assume that commerce is universal...)

Watch South Park's "Canceled".

Perhaps our bodies are a shell for their consciousness. That's why they're so interested in "our" observations. We are the VR headset for them.

There is a theory that says that everytime somebody is close to understanding the structure and mechanics of the universe, the universe would immediately be replaced by something even more strange and incomprehensible. Another theory says this already has happened several times.

This would explain both our progress in physics and the strangeness of QM, and give credence to the idea that we are in a simulation.

You could make a humorous extension to that theory re: a priorly flat earth.

Whoever is running the simulation cares about whether we're looking. They had a good reason for going with quantum mechanics rather than something that would be easier to simulate.

The power running the Universe doesn't have infinite CPU/GPU/RAM resources at their disposal, any more than a game developer at this level of reality does. Some optimizations (or hacks, to be less charitable) are necessary. Quantum behavior is one of those hacks, part of the code that manages the potentially-visible set. It would be wasteful to render or run physics on particles that nothing is interacting with.

The only questions are whether God is an Nvidia fanboy or an AMD die-hard, and if He signed an exclusive deal with Sony or Nintendo at some point in the future.

> that simulating quantum mechanics is so computationally expensive that it isn’t done unless we’re looking at it

This is a common misconception. It's more difficult to simulate a quantum system than a classical system. To simulate a classic system you have to simulate one posible state. To simulate a quantum system you must simulate all possible path.

This is the advantage of quantum computers. With the hardware for only N qbits, you can calculate 2^N states (for some very specific problems that are quantum-computer-friendly).

I'm by no means an expert, but how about using Pilot Wave Theory to do the simulation? As I understand, you wouldn't need to simulate an exponential number of states, you just simulate the pilot wave.

See also (very accessible): https://www.quora.com/Why-dont-more-physicists-subscribe-to-...

You must simulate the value of the wave at every point of the universe, or at least a grid that has enough points to have the correct precision. It's even more work. Imagine simulating all the waves in all the ocean in the Earth, but worse because there are some nonlocality effects.

You can probably do some kind of smart representation of the wave, were you decompose it in some smart functional base of smooth waves. With a very optimized representation the calculations would be equivalent to the usual quantum mechanics calculations. With a not smart enough representation you would get something that needs more calculations.

> You must simulate the value of the wave at every point of the universe

Maybe I'm not getting it, but that still sounds simpler than simulating an exponential number of states for the entire universe.

Take a look at https://en.wikipedia.org/wiki/Pilot_wave_theory#Mathematical...

The problem is that if you have five particles then the function ψ(r1, r2, r3, r4, r5, t) is a function on 3*5+1=15 coordinates. If we assume that for each particle we use a 100x100x100=1000000 grid, then for the 5 particles we need a grid of (1000000)^5=1000000000000000000000000000000 points. The space were the wave is defined grows exponentially. (As a rule of thumb, with a current notebook, you can do up to 1000000000 or 1000000000000 calculations in a few seconds/minutes/hours.)

I was wondering how this article would read from a Bohmian perspective. It would seem to be an alternative to creating the universe as a result of perceptions in the modern era. (Damn Copenhagen interpretation)

I was also wondering about entropy as the arrow of time -- positrons are just as subject to entropy, no?

The equations are not simpler, there is no “just”.

I find it funny how people are so ready to believe the universe must be computing the same way our models must. The universe simply exists - it's not necessary for it to adhere to our human perceptions - not be a long shot. There's a vast gulf between the model and the modeled. That our theories quickly become uncomputable says more about their unfitness than the universe's functioning. To say otherwise is to negate the fundamental autonomy of the universe. We should be humbled by the universe precisely because our best models to understand it quickly diverge to where our minds and tools may not.

What autonomy does the universe possess?

For one, it exists before any of our feeble explanations of how it works. It's always correct and we try to play catch up.

Simulating the Mandelbrot set is also awfully computationally expensive. Unless you know the trick.

So you're saying the Universe is Lazy-Evaluated[0]?

[0]https://en.wikipedia.org/wiki/Lazy_evaluation

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