The reasoning of Rees in his Nautilus article seems to go like this:
- In the first Copernican
revolution, we found that our planet isn't special in the solar
system.
- In the second Copernican
revolution, we found that our solar system isn't special in our
galaxy.
- In the third Copernican
revolution, we found that our galaxy isn't special in the universe.
- So now it's time for the
fourth Copernican revolution, in which we realize that our universe
is just an ordinary universe among many.
There's nothing original about this line of reasoning, since the same type of reasoning was made six years ago in an article by scientist Marcelo Gleiser, the main difference being that Gleiser's article was “Welcome to the Third Copernican Revolution.” Gleiser made no mention of the discovery that the solar system was ordinary, so the third Copernican revolution listed by Rees is the second Copernican revolution listed by Gleiser. Gleiser stated the following: “As Earth became just another planet in the First Copernican revolution and the Milky Way just another galaxy in the Second, our Universe would become just another universe among countless others, each with its properties, private histories, and creation events.”
There's a reason why we should be very suspicious of multiverse fantasists trying to insinuate that they are kind of the new Galileos in the same class as Copernicus. The reason is that Copernicus and Galileo advanced the doctrine of heliocentrism (that the sun is the physical center of the solar system) because it was compelled by observations. Once Galileo started using his telescope, the observational evidence for heliocentrism started piling up. But there are no observations favoring the idea of the multiverse. We have zero observations of other universes. I certainly do not count as evidence for the multiverse Penrose's recent claims that very faint specks in the cosmic background radiation support his theory of previous cycles of the universe. Such claims are subjective “Jesus in my toast” type of claims. Observations of the cosmic background radiation can only tell us about the state of our universe about 380,000 years ago, and do not tell us anything about either other universes or previous states of our universe before the Big Bang.
So when scientists try to grab some of the glory of Copernicus and Galileo when doing mere speculation, we should treat them rather like someone trying to suggest that he's like Babe Ruth or Hank Aaron because he can imagine himself hitting 700 home runs in a career. And one reason for rejecting the type of reasoning listed above is that one or more previous revolutions do not imply any need for a future revolution. For example, there was an American revolution, but that fact does nothing to imply the need for a second American revolution.
There's another reason why the type of reasoning in Rees' essay fails. It is that there could never be the “fourth Copernican revolution” he imagines. Our universe has many incredibly unlikely fundamental constants and laws that combine to allow the existence of living things. It has been speculated that this is merely an accident that occurs once in 1,000,000,000,000,000,000,000,000,000,000,000 universes because of blind luck. We cannot realistically imagine any observations that would ever back up such a speculation. But let's imagine that such a speculation were to be somehow substantiated. Then it would still be true that our universe was an incredibly special universe. It would not at all be proven that our universe (with life-favoring conditions so improbable) was “just an ordinary universe.” So it seems that there is no way in which the “fourth Copernican revolution” imagined by Rees could ever occur.
There's still another reason for rejecting the line of reasoning Rees suggests in his essay. It is that in a very real sense the first three Copernican revolutions in the list above did not actually occur.
Let us consider the first Copernican revolution. It has been said countless times that after Copernicus and Galileo, it was proven that the Earth is not the center of the universe. But there are three ways in which Earth might be the center of a universe:
- Earth might be the
physical center of the universe.
- Earth might be the
biological center of the universe.
- Earth might be the
intellectual center of the universe.
Given the “organization explosion” needed for life to appear from chemicals, apparently requiring mountainous amounts of luck all over the place, possibilities 2 and 3 listed above are not at all remote possibilities. If scientists are ever able to synthesize a living thing from some experiment reproducing early conditions on Earth, using some mixture of chemicals that started out sterile, then possibility 2 (that Earth is the biological center of the universe) might be removed (for it might be shown that the chance of extraterrestrial life appearing by chance is not very low). But scientists have done no such thing. And scientists have had no luck in all of their efforts to detect extraterrestrial intelligence by looking for radio signals from alien civilizations. So possibility 3 stands as something that could well be true.
I can now restate the type of reasoning made above, along with some statements in parentheses rebutting each point.
- In the first Copernican
revolution, we found that our planet isn't special in the solar
system. (Not really, because after Copernicus and Galileo, Earth was
still the only known planet with life and minds, so it was still the
biological and intellectual center of the solar system.)
- In the second Copernican
revolution, we found that our solar system isn't special in our
galaxy. (Not really, because while we have found that there are
many solar systems in the galaxy, we have not discovered any other
solar system in our galaxy with living things or minds.)
- In the third Copernican
revolution, we found that our galaxy isn't special in the universe.
(Not really, because while we have found there are many other
galaxies, we have not discovered any other galaxy with living things
or minds.)
- So now it's time for the fourth Copernican revolution, in which we realize that our universe is just an ordinary universe among many. (Why should we “realize” something not supported by observations? And if there were a million billion trillion other universes, each with random conditions, our universe would still be something very special – not ordinary -- because our universe is habitable, but 99.9999999999999999% of those random universes would not be habitable.)
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