Wednesday, October 03, 2018

The Boltzmann brain paradox

Last Thursdayism is a famous thought-experiment by Bertrand Russell:

There is no logical impossibility in the hypothesis that the world sprang into being five minutes ago, exactly as it then was, with a population that "remembered" a wholly unreal past. There is no logically necessary connection between events at different times; therefore nothing that is happening now or will happen in the future can disprove the hypothesis that the world began five minutes ago.

Of course, most folks, including most philosophers and scientists, don't think those skeptical scenarios are realistic. However, Last Thursdayism has a counterpart in modern physics: 

It could be the weirdest and most embarrassing prediction in the history of cosmology, if not science.

If true, it would mean that you yourself reading this article are more likely to be some momentary fluctuation in a field of matter and energy out in space than a person with a real past born through billions of years of evolution in an orderly star-spangled cosmos. Your memories and the world you think you see around you are illusions.

This bizarre picture is the outcome of a recent series of calculations that take some of the bedrock theories and discoveries of modern cosmology to the limit. Nobody in the field believes that this is the way things really work, however. And so in the last couple of years there has been a growing stream of debate and dueling papers, replete with references to such esoteric subjects as reincarnation, multiple universes and even the death of spacetime, as cosmologists try to square the predictions of their cherished theories with their convictions that we and the universe are real. The basic problem is that across the eons of time, the standard theories suggest, the universe can recur over and over again in an endless cycle of big bangs, but it’s hard for nature to make a whole universe. It’s much easier to make fragments of one, like planets, yourself maybe in a spacesuit or even — in the most absurd and troubling example — a naked brain floating in space. Nature tends to do what is easiest, from the standpoint of energy and probability. And so these fragments — in particular the brains — would appear far more frequently than real full-fledged universes, or than us. Or they might be us.

Lately, Sean Carroll has tried to debunk the Boltzmann brain paradox, but his solution is questionable:

This poses quite a dilemma for atheists–if naturalism and modern physics commits them to a scientific version of Last Thursdayism. 

From a traditional Christian standpoint, one way to relieve the dilemma is to deny physicalism. Minds aren't brains.

In addition, why would a benevolent God make ephemeral conscious beings? Beings with our mental complexity, emotional life, and memories–if that's a trick? False memories–like the malevolent aliens in Dark City. But atheists don't have those countervailing resources. 

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