Over at her blog, BackReAction, physicist Sabine Hossenfelder has written a cogently argued article titled, No, we probably don’t live in a computer simulation (March 15, 2017). I’ll quote the most relevant excerpts:
According to Nick Bostrom of the Future of Humanity Institute, it is likely that we live in a computer simulation…
Among physicists, the simulation hypothesis is not popular and that’s for a good reason – we know that it is difficult to find consistent explanations for our observations…
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. [Note added for clarity: You might be able to get quantum mechanics from a classical, nonlocal approach, but nobody knows how to get quantum field theory from that.]
Even from qubits, however, nobody’s been able to recover the presently accepted fundamental theories – general relativity and the standard model of particle physics…
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.
I have in the past criticized the theory of the multiverse on several grounds (see here and here), one of them being that the existence of the multiverse appears to imply the existence of a great multitude of intelligently designed universes, as well as making it overwhelmingly likely that we are living in a “fake universe” or simulation. After reading Dr. Hossenfelder’s article, I feel compelled to withdraw this argument.
Another alleged problem with the multiverse hypothesis is that if we live in a multiverse, then we would expect biological life-forms like ourselves to be vastly outnumbered by “Boltzmann brains.” But this argument presupposes that the evolution of a Boltzmann brain is statistically more likely than that of a carbon-based life-form like ourselves. I now believe this is not the case. The formation of a self-aware brain as a result of a random fluctuation in the entropy of the cosmos is a fantastically unlikely event, akin to Fred Hoyle’s Boeing 747 forming from a tornado in a junkyard. The reason why it is so unlikely is that it has to take place over a very, very short time period, since a brain-in-the-making that formed gradually would be destroyed by the forces of nature long before it became self-aware. A stand-alone, self-aware brain might seem easier to generate than a complex organism possessing a brain, but one has to consider the pathway as well. An evolutionary pathway permits trial-and-error testing and cumulative improvements; a sudden random fluctuation that gives rise to a brain does not.
There are, however, other problems with the multiverse hypothesis as an explanation of fine-tuning: a multiverse capable of generating even one life-supporting universe would still need to be fine-tuned (as Dr. Robin Collins has pointed out); the multiverse hypothesis predicts that a universe containing intelligent life should be much smaller than the one we live in; and the multiverse hypothesis cannot account for the fact that the laws of physics are not only life-permitting, but also mathematically elegant – a fact acknowledged even by physicists with no religious beliefs.
That doesn’t mean there is no multiverse, of course. But what it does mean is that it can’t be invoked to explain away fine-tuning.
What do readers think?