I was disappointed in the thin, banal issue of SciAm on "Time," but now there's a new special issue devoted to "The Once and Future Cosmos."
It's very good, filled with excellent illustrations of models of cosmology, key experiments, and what we currently know about the structure of the cosmos. Some of the graphics are so good that I am tempted to buy a second copy just so I can clip the graphics and put them up in places where I can ponder them. For this list, there's a little bit of discussion of the Rees/Linde/Vilenkin/Barrow/Smolin/Tegmark sort of model where new universes are created with slightly different laws of physics. This is mentioned in a fanciful figure showing such hypothetical pocket universes being formed: "Multiple universes are continuously being born, according to some cosmologists. Each universe is shown here as an expanding bubble branching off from its parent universe. The changes in color represent shifts in the laws of physics from one universe to another." [Figure on page 85] By the way, I'm reading Smolin's "Life of the Cosmos," where he makes a good case for his thesis that the cosmos we are in is one strongly rigged (basic laws, parameters) so as to have a very high production rate of black holes. The idea is similar to the Boostrum sort of Bayesian argument about assuming the world we find ourselves in is "typical." Smolin argues that if a universe creates few or no black holes (for example, it expands and collapses in a Planck time, or has no aggregations of matter worth mentioning, and so on), it leaves no (or just one) children. A universe which creates, say, 10^18 black holes, leaves 10^18 children, some of which may leave even more children, and so on. Thus, there's a fitness landscape with the x and y axes (in a simple diagram) being some set of parameters which affect black hole formation and the vertical or z axis being the number of black holes (and hence universes, a la Linde, others) created. While there is no "competition amongst the universes" directly, that we know of, differential reproduction is enough, in general, to produce evolutionary effects. After some number of "bounces or black hole formations with slightly different laws of physics" the result will be that nearly all universes in some multiverse are ones where black hole formation is commonplace. Smolin argues that we will be able to measure the number of black holes, from small (stellar masses) to larger (recently found, it is believed, 1000-sun mass black holes, to massive galactic core black holes, and, he thinks, reach the conclusion that we are in a universe which is "selected" for maximum ease of black hole formation. Maybe. By the way, it may also be the case that universes in which intelligence is possible are dominant. My notion, refecting some of the fantastical fiction of Steven Baxter and Greg Egan, is that advanced civilizations will be able to _make_ black holes, possibly in vastly greater abundance than astrophysical sources can. (Yeah, of much smaller mass. And presumably of very short duration. The weirdness of spacetime and the insides of black holes are enigmas, but it is speculated by some that even a microscopic black hole could have a "full cosmos" inside. We don't, at least, have any compelling evidence that a galactic core black hole with 10,000 solar masses is going to produce a richer or more complete "cosmos inside" than a microscopic black hole made up of a few grams or less of our matter.) Using the same kind of reasoning Smolin uses, a civilization which has special accelerators cranking out 10^30 black holes per second, say, is going to "outbreed" and thus be more represented, than universes where only astrophysical processes are making only a relatively paltry 10^18 or 10^25 black holes in the age of that universe. (And, even more speculatively, the difference is not great between the number of black holes a single civilization can make and the number a million civilizations can make, so it's more significant that a universe supports AT LEAST SOME advanced intelligence/civilization than that it supports UBIQUITOUS intelligence/civilization. But this reasoning is speculative and needs a lot more thought...maybe. Someone could probably write a nice Baxterian story with this theme.) --Tim May, Occupied America "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -- Benjamin Franklin, 1759.