Saturday, March 18, 2017

Don't worry, you're almost certainly real (and so is everything else)

I've never been really taken with the idea that the universe is just a computer simulation running on some advanced intelligence's computer.   I don't know - just always seemed a bit redundant to argue that instead of looking at reality at every single level from quarks to galaxy clusters, we're looking at someone's super computer simulation that's good enough to make every single level from quarks to galaxy clusters look, feel and behave real. 

And I see that I'm in good company - physicist Bee at Backreaction has a ranty post complaining about the whole idea, too.   Here are some of her key paragraphs:
If you try to build the universe from classical bits, you won’t get quantum effects, so forget about this – it doesn’t work. This might be somebody’s universe, maybe, but not ours. You either have to overthrow quantum mechanics (good luck), or you have to use qubits.

Even from qubits, however, nobody’s been able to recover the presently accepted fundamental theories – general relativity and the standard model of particle physics. The best attempt to date is that by Xiao-Gang Wen and collaborators, but they are still far away from getting back general relativity. It’s not easy.

Indeed, there are good reasons to believe it’s not possible. The idea that our universe is discretized clashes with observations because it runs into conflict with special relativity. The effects of violating the symmetries of special relativity aren’t necessarily small and have been looked for – and nothing’s been found.

For the purpose of this present post, the details don’t actually matter all that much. What’s more important is that these difficulties of getting the physics right are rarely even mentioned when it comes to the simulation hypothesis. Instead there’s some fog about how the programmer could prevent simulated brains from ever noticing contradictions, for example contradictions between discretization and special relativity....
And this section made me smile:
Stephen Wolfram (from Wolfram research) recently told John Horgan that:
    “[Maybe] down at the Planck scale we’d find a whole civilization that’s setting things up so our universe works the way it does.”
I cried a few tears over this.

The idea that the universe is self-similar and repeats on small scales – so that elementary particles are built of universes which again contain atoms and so on – seems to hold a great appeal for many. It’s another one of these nice ideas that work badly. Nobody’s ever been able to write down a consistent theory that achieves this – consistent both internally and with our observations. The best attempt I know of are limit cycles in theory space but to my knowledge that too doesn’t really work.

Again, however, the details don’t matter all that much – just take my word for it: It’s not easy to find a consistent theory for universes within atoms. What matters is the stunning display of ignorance – for not to mention arrogance –, demonstrated by the belief that for physics at the Planck scale anything goes. Hey, maybe there’s civilizations down there. Let’s make a TED talk about it next. For someone who, like me, actually works on Planck scale physics, this is pretty painful.

To be fair, in the interview, Wolfram also explains that he doesn’t believe in the simulation hypothesis, in the sense that there’s no programmer and no superior intelligence laughing at our attempts to pin down evidence for their existence. I get the impression he just likes the idea that the universe is a computer. (Note added: As a commenter points out, he likes the idea that the universe can be described as a computer.)
So put away your Matrix movie DVDs (I never really got past the first one anyway - it might have them that put me off the simulation idea.)  Go out and smell the (real) roses.

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