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Not Crazy Enough

Entry 1458, on 2012-11-06 at 22:31:27 (Rating 1, Science)

The great physicist, Niels Bohr, once commented that he was unsure about a new quantum theory idea by using the following phrase: "Your theory is crazy but is it crazy enough to be true?". In fact, the exact quote was "We are all agreed that your theory is crazy. The question that divides us is whether it is crazy enough to have a chance of being correct", but I don't think that's quite as snappy!

Anyway, there is no doubt that many theories at the frontiers of modern physics, especially in quantum theory and relativity, are so crazy that it must be difficult for many people to take them seriously. The idea that a photon is both a particle and a wave, that two particles separated by a great distance are entangled, that a system can be in two states simultaneously until that state is observed, that a clock will run more slowly as its speed increases, that two objects approaching each other at a particular speed don't actually pass each other at double that speed, etc. It's all crazy yet according to careful observation it's also true!

Not only is it crazy but, as your knowledge of physics becomes greater, it becomes more crazy! A totally naive person might not notice the craziness immediately but as their knowledge of classical systems increases they will see how quantum and relativistic physics is mad! But also when you reach a particular level of knowledge all of this suddenly starts making a sort of odd sense!

So that is my introduction to crazy physics. The idea I want to explore in detail here is really crazy: it's the idea that our whole universe might just be a simulation in a computer! Yeah, I know, that really is crazy. But as Bohr would ask: is it crazy enough to be true?

Before I go any further I do have to say that craziness is not a guarantee that something is true. Obviously in many cases the opposite is true. There are different types of craziness and some are just simply disconnected from reality. It's similar to the situation when someone invents a new perpetual motion machine and is ridiculed by real engineers and scientists. They often say something like "well they laughed at [insert well known scientist here] too, and he was proved right!" Yes, being laughed at is not sufficient in itself. I agree that some people laughed at the Wright Brothers, but they also laughed at Bozo the Clown!

Back to the "universe in a computer" idea. A research team recently simulated a small part of the universe in a computer. I don't mean they made an imitation of it, as far as we can tell they genuinely exactly recreated it. OK, I have to admit this was a very small part of the universe, in fact it was an area a few femtometers across (a femtometer is one thousandth of a trillionth of a meter). But it shows that this type of simulation isn't impossible.

Now some philosophers have come up with the following argument: at least one of the following is true: the human species will probably become extinct before reaching an advanced "posthuman" stage, or a posthuman civilisation will not run simulations of their past, or we almost certainly live in a simulation. The justification for the third statement goes something like this: if statement one is false and humans survive to become far more advanced then other civilisations must have done that already, if statement 2 is false and advanced civilisations do run simulations then there must be many of those simulations running now. If there is only one real universe but many simulations then the greatest chance is that ours is one of the simulations.

So in summary: either humanity will die out soon, or we won't create advanced simulations of the universe, or we almost certainly live in a simulated universe.

The argument all seems to make sense but it does make some assumptions. First, that there are many advanced civilisations in the universe. Given how big the universe is and how late humans evolved (almost 10 billion years after the Big Bang) then that isn't unreasonable. Second, that advanced civilisations will be able to and will want to create simulated universes. With the rate of progress in information management over the last 50 years it seems almost inevitable that after a few thousand or even million years of similar progress that such a simulation would be created. Third, that there is only one "real" universe. Actually that doesn't matter because the ratio of simulated to real universes is likely to be high irrespective of the number of real universes.

But I can't help feeling the same way about this argument as I do about many other philosophical discourses. It seems more like sophistry than a genuine argument. It's not quite as blatantly bad as the ontological proof of god (for example) but it still seems pretty bad. What we really need is some empiricism to sort the truth from the supposition. But that's not possible. Or is it...

Some scientists think that it should be possible to tell if we do live in a simulation. A simulation could not have infinite resolution - there would have to be a limit just like there is with simulations we can run today. We should be able to detect these "pixels" in the universe. They have proposed an effect which should be visible in the path of cosmic rays.

I also think it's interesting that our universe does indeed seem to have a more basic "resolution". The Planck length could be a resolution in space and the Planck time could be the resolution in time. Both of those numbers are ridiculously small. The Planck distance is about 1 billion trillion trillionth of a millimeter and the Planck time is about 5 billion trillion trillion trillionths of a second. So if this universe is a simulation it must be an extremely detailed one!

So the simulated universe theory is an interesting one and it's also a crazy one. But is it crazy enough to be true? Or is it just too crazy...

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Comment 1 (3373) by Anonymous on 2012-11-16 at 15:36:44:

I agree, this argument is too convenient to be taken seriously. It's not possible to discover deep meaning from this sort of argument.

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Comment 2 (3374) by OJB on 2012-11-17 at 15:44:11:

I think it's important to distinguish between real scientific theories and interesting speculation. I would put this into the second category. Note that "interesting speculation" should not be confused with "useless speculation" which many other groups indulge in, and that speculation can be promoted to theory once some related facts are discovered.

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