“And yet, even though useful quantum computers might still be decades away, many of their payoffs are already arriving. For example, the mere possibility of quantum computers has all but overthrown a conception of the universe that scientists like Stephen Wolfram have championed. That conception holds that, as in the “Matrix” movies, the universe itself is basically a giant computer, twiddling an array of 1’s and 0’s in essentially the same way any desktop PC does.

Quantum computing has challenged that vision by showing that if “the universe is a computer,” then even at a hard-nosed theoretical level, it’s a vastly more powerful kind of computer than any yet constructed by humankind. Indeed, the only ways to evade that conclusion seem even crazier than quantum computing itself: One would have to overturn quantum mechanics, or else find a fast way to simulate quantum mechanics using today’s computers.” http://www.nytimes.com/2011/12/06/science/scott-aaronson-quantum-computing-promises-new-insights.html?_r=1&ref=science&pagewanted=all

“Carson Chow Says:
Comment #2 December 5th, 2011 at 10:35 pm
Nice article but I am confused about this paragraph:

“For example, the mere possibility of quantum computers has all but overthrown a conception of the universe that scientists like Stephen Wolfram have championed. That conception holds that, as in the “Matrix” movies, the universe itself is basically a giant computer, twiddling an array of 1’s and 0’s in essentially the same way any desktop PC does.”

A quantum universe or a classical universe are both computable aren’t they? It’s just that the quantum universe is exponentially “bigger”. In principle, you could have a classical computer just chug away painfully slowly and simulate the quantum universe, no? There is nothing in the “Matrix” universe that says the computation must be efficient is there? There are still just a countable number of possible quantum universes right?”

“Scott Says:
Comment #5 December 5th, 2011 at 10:59 pm
Carson #2: Yes, as the tagline of my blog says, quantum computers can be simulated classically but with exponential slowdown.

What we learn from quantum computing is that, if both quantum mechanics and the prevailing conjectures in complexity theory are valid, then the physical universe can’t be feasibly simulated by a computer that “twiddles an array of 1’s and 0’s in essentially the same way any desktop PC does.”

(That last clause was meant to indicate that I was talking about efficient simulation by conventional computers — i.e., the Extended Church-Turing Thesis, or what Wikipedia calls the Feasibility Thesis. I wish I knew how to put the point more clearly within the constraints of this article, since you’re right that it might be misinterpreted!)

For what it’s worth, Stephen Wolfram, Ed Fredkin, and other believers in “digital physics,” have been very explicit in saying that they think the universe is a classical cellular automaton—basically, a three-dimensional array of pixels—and that their view would preclude exponential speedups from quantum computation. (Wolfram believes that quantum mechanics is wrong, whereas Fredkin believes that quantum mechanics can be efficiently simulated classically.) So, these viewpoints would indeed be ruled out under the assumptions I mentioned above.

A last remark: the Matrix movies aren’t very clear about what type of computer is being used, other than that it’s powered by human bodies! But since they never mention anything about quantum computing, and since the simulation clearly isn’t astronomically slow, it seems reasonable to assume that Keanu Reeves was trapped in some sort of classical simulation. So maybe he could’ve caused the simulation to crash by building a quantum computer and trying to run Shor’s factoring algorithm! For the version where Keanu is trapped in a quantum computation, we might need to wait for the followup trilogy, “The Unitary Matrix” (har, har).”

“Jiav Says:
Comment #8 December 6th, 2011 at 12:59 am
Nice essay Scott, but how could we know our simulation is not astronomically slow?

I’m curious to see if Greg Egan will comment this one ”

http://www.scottaaronson.com/blog/?p=871

Cf. http://theunitedpersons.org/blog/if-the-answer-is-42-what-is-the-question

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Conway’s Game of Life Extrusion “I wrote a script that takes the lifetime of the cellular automaton Conway’s Game of Life and extrudes it into a three dimensional object. [...]” http://www.qotile.net/blog/wp/?p=600

Cf. Instructions for turning Blender files into RepRap instructions http://objects.reprap.org/wiki/Using_Blender_for_making_print-sheets

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“[...] At least based on our current human characteristics, we’d expect that our technology would advance to the point where we can tool around the universe—and colonize it.

So why haven’t we met any extraterrestrials? It seems like it’d take only one instance to eventually fill the whole universe.

Well, maybe there just aren’t ones close enough to human-like. Or maybe we’ve got something wrong in our expectations for the future.

Perhaps exploration just isn’t terribly popular. I mean, there are lots of parts of the Earth—like the bottoms of the oceans—where we could in principle go, but we usually don’t bother.

But unless something kills off diversity in purposes, even if there wasn’t a giant cultural push towards exploration, one might still expect one solitary extraterrestrial to decide to do it. And that’d be enough.

Of course, what really is the point? Let’s assume we know the fundamental theory of physics; we know the program for our universe.

Well, there’s computational irreducibility, so we can’t make general predictions from it. But we can certainly use it to systematically search for possible technology that we can implement in our universe, and so on.

But in a sense we don’t need physical—starships and everything—exploration to find it.

We just need to be running computations.

Well, you might think surely it’d be good to do a giant, bizarrely modified version of SETI@home all over the universe. But, you know, there are a lot more orders of magnitude that can be achieved by making things smaller than by going out and co-opting other planets to turn into computers and so on.

Well, OK, so we have a sort of strange view of the limiting future.

We’re reduced to computations. But computations that in some absolute sense are nothing special; they’re just as sophisticated or unsophisticated as lots of other computations happening around the universe.

But what’s special about these computations is that they have evolved from us—with our various special features and purposes.

How will those purposes evolve? Perhaps they will in effect dissipate—and it will in a sense be the end of meaningful history.

But I have a slight—perhaps self-serving—guess.

That when our current constraints are all removed, our future selves will indeed have a difficult time knowing which of all possible purposes to pursue.

But that one of the most important guides will be to look at history. To look back at a time when there were constraints—like mortality and scarce resources—that pruned out possible purposes.

And perhaps there will be a desire to go back as far as possible—to understand the origins of purposes.

But one will need data—as much as possible—on what actually happened.

So here’s the funny thing: our times, these years, are the first times in history when a decent fraction of everything that happens is recorded.

And that will only increase over the next few years.

So from the future, as one tries to analyze history and purposes, one will potentially land right on our times in these years.

So that it’ll be our activities and purposes in these years that define the purposes for our whole future.

I don’t know if that’s actually how things will work. It’s perhaps satisfying to think so. Though it’s a big responsibility.

To think that our efforts at this time in history might not just be stepping stones to the future, but actually define all of it.

In effect, pulling from the computational universe that part which defines the future essence of the human condition.

Well, I think I should wrap up.

I hope you found this interesting, and that it didn’t get too abstract.

I find all this fun. But I also like to think more seriously about how it relates to things I actually do.

And for example to my own life projects.

Well, obviously NKS is trying to tell us about everything that’s out there, independent of our human condition—and giving us a paradigm to think about it all.

And Wolfram|Alpha is trying to capture the computable knowledge of our civilization—the stuff that in a sense defines what’s special about the human condition.

And Mathematica is in a sense the bridge between these two—a language that makes raw, formal, precise computation accessible to us humans.

I have my next big project picked out: trying to find the fundamental theory of physics.

But if I get the chance to do more projects, it’s this kind of thinking about the future that’s going to determine what they are.

It’s always fun at that moment when all the abstraction condenses into something very definite—and turns into something that helps us concretely define the future.

I hope I’ll be back in a few decades to talk more about what happened.

Well, I should stop now. I’d be happy to discuss both abstract and concrete things.

Thanks very much.”

http://www.stephenwolfram.com/publications/recent/hplus2010/

Cf. http://theunitedpersons.org/blog/if-the-answer-is-42-what-is-the-question

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Is the illustration of the ‘simplest universal cellular automaton’ at 4′ 25″ proved to be universal & uniquely the simplest?? We know that the simplest universal Turing machine is proven (2007), cf. http://blog.wolfram.com/?year=2007&monthnum=10&name=the-prize-is-won-the-simplest-universal-turing-machine-is-proved

But I never heard about the simplest universal CA.

What is more surprising, Google is at a loss as well (2010.04.27 10PM GMT):

If you find this exceptionally:) simple universal cellular automaton I’ll owe you a beer.

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Answer: “42″ (42 = 101010 = 0101010 = oxoxoxo)

Unfortunately, this answer does not tell us anything about the rules

of the cellular automaton with the initial state oxoxoxo.

But never mind: Stephen Wolfram and Jürgen Schmidhuber are working on it;)

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