Wednesday, July 12, 2006


Before you read the following excerpt, let me admit that much of the essay from which the excerpt is taken is way beyond my understanding. The only reason I pass this excerption is because it is a simple proof that I can understand, and so I pass it on expecting that you also will be able to understand it. Maybe some of you can go far beyond this. The passage reveals a series of considerations by which parallel universes can perhaps be predicted to exist. What I specially like about the passage is the same elegance of thought we’ve seen in other scientific lines of reasoning that I’ve copied into other posts. I hope you enjoy these paragraphs as much as I did. I’m always overjoyed when I my limited capabilities are able to follow an exemplary line of reasoning. My MFA in Creative Writing did not prepare me for the beautiful paths of reason these paragraphs reveal, though a beautiful poem has a logic of its own too. But I must also add that more than one scientist I've come across in my reading points out that these sorts of proof are more philosophy than science.

The following excerpt is an essay, “Parallel Universes”, by Max Tegmark (Dept. of Physics at Univ. of Pennsylvania) which appeared in Science and Ultimate Reality: From Quantum to Cosmos, Cambridge University Press (2003).

[OPEN QUOTE] Physicists dislike unexplained coincidences. Indeed, they interpret them as evidence that models are ruled out. In Section IC, we saw how the open universe model was ruled out at 99.9% confidence because it implies that the observed pattern of CMB fluctuations [cosmic microwave background—the stuff left over from the Big Bang] is extremely unlikely, a one-in-a thousand coincidence occurring in only 0.1% of all Hubble volumes [the volume of our universe made visible by the Hubble telescope].

Suppose you check into a hotel, are assigned room 1967 and, surprised, note that that this is the year you were born. After a moment of reflection, you conclude that this is not all that surprising after all, given that the hotel has many rooms and that you would not be having these thoughts in the first place if you'd been assigned another one. You then realize that even if you knew nothing about hotels, you could have inferred the existence of other hotel rooms, because if there were only one room number in the entire universe, you would be left with an unexplained coincidence.

As a more pertinent example, consider M, the mass of the Sun. M affects the luminosity of the Sun, and using basic physics, one can compute that life as we know it on Earth is only possible if M is in the narrow range 1.6 x 10 to the 30 power kg - 2.4 x 10 to the 30 power kg—otherwise Earth's climate would be colder than on Mars or hotter than on Venus [therefore uninhabitable]. The measured value is M ~ 2.0 x 10 to the 30 power kg. This apparent coincidence of the habitable and observed M-values may appear disturbing given that calculations show that stars in the much broader mass range M ~ 10 to the 29 power kg - 10 to the 32 power kg can exist. However, just as in the hotel example, we can explain this apparent coincidence if there is an ensemble and a selection effect: if there are in fact many solar systems with a range of sizes of the central star and the planetary orbits, then we obviously expect to find ourselves living in one of the inhabitable ones.

More generally, the apparent coincidence of the habitable and observed values of some physical parameter can be taken as evidence for the existence of a larger ensemble, of which what we observe is merely one member among many (Carter 1973). Although the existence of other hotel rooms and solar systems is uncontroversial and observationally confirmed, that of parallel universes is not, since they cannot be observed. Yet if fine-tuning is observed, one can argue for their existence using the exact same logic as above. Indeed, there are numerous examples of fine tuning suggesting parallel universes with other physical constants, although the degree of fine tuning is still under active debate and should be clarified by additional calculations—see Rees (2002) and Davies (1982) for popular accounts and Barrow & Tipler (1986) for technical details. [CLOSE QUOTE]

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