Bounded in an Inflatable Nutshell

Thirty years ago, big bang cosmology faced a problem. Actually, it faced a trinity of problems. It couldn't account for the uniformity of the observable universe, the near-perfect flatness of the universe, and the absence of certain particles that theoretically ought to exist. These three birds were taken down with one big stone when Alan Guth realized that a brief period of superluminal expansion early in the universe's history could account for all of these observations. The notebook pages on which he scribbled his historic calculations--with "Spectacular Realization!" written triumphantly at the top--are on display at Chicago's Adler Planetarium.

But inflation--now a cornerstone of modern cosmology and supported by additional observation evidence--comes with some heavy ontological baggage. It implies that what we know as the universe, a vast expanse bordered by distant quasars and gamma-ray bursts, is not the totality of existence. Instead, this observable universe is a merely a pocket of a much larger Universe, a bubble in an endlessly larger cosmic sea. And there are other bubbles in that sea, pockets of the Universe that have inflated or are inflating. Each one is a universe in its own right, some subject to different physical laws than our own observable universe. The bigger Universe (with a capital U) containing all the bubbles is likely infinite but one question worth exploring is how many types of other bubble universes exist beyond the horizons of our own. The arXiv blog has a post up detailing a new paper from one of the pioneers of inflationary cosmology, Andrei Linde, where he explores the question and comes up with an answer: 10¹⁰¹⁰⁷:

How many of these could we actually see? What's interesting here is that the properties of the observer become an important factor because of a limit to the amount of information that can be contained within any given volume of space, a number known as the Bekenstein limit, and by the limits of the human brain.

Linde and Vanchurin say that total amount of information that can be absorbed by one individual during a lifetime is about 10¹⁶ bits. So a typical human brain can have 10¹⁰¹⁶ configurations and so could never disintguish more than that number of different universes.

10¹⁰¹⁶ is a big number but it is dwarfed by the "humungous" 10¹⁰¹⁰⁷.

"We have found that the strongest limit on the number of different locally distinguishable geometries is determined mostly by our abilities to distinguish between different universes and to remember our results," say Linde and Vanchurin

This is a bit like the human eye distinguishing shades of a given color--how many shades are "really" there is less relevant than the number of shades the human eye/brain can distinguish. Two bubble universes might be slightly different in some physical sense but if you plop a human in first one then the other and he can't find a way to distinguish between them, then it doesn't really matter how different they are. That's why the number of possible types of universe they calculate is reduced to the vastly smaller (but still enormous) 10¹⁰¹⁶ number.

This reminder of the vastness of the inflationary Universe makes me think of an argument I once read that inserts anthropic reasoning into an inflationary universe and finds that something's got to give:

Anthropic reasoning often begins with the premise that we should expect to find ourselves typical among all intelligent observers. However, in the infinite universe predicted by inflation, there are some civilizations which have spread across their galaxies and contain huge numbers of individuals. Unless the proportion of such large civilizations is unreasonably tiny, most observers belong to them. Thus anthropic reasoning predicts that we should find ourselves in such a large civilization, while in fact we do not. There must be an important flaw in our understanding of the structure of the universe and the range of development of civilizations, or in the process of anthropic reasoning.

The argument is pretty simple. Start with the assumption that of all the sentient observers in all the multiverse (the collection of bubble universes in the sea-Universe), you're not particularly special. The majority of civilizations in the multiverse will be relatively small but imagine that a handful of "supercivilizations" exist that spread across a galaxy in their universe (and perhaps on to other galaxies) and pack individual star systems a billion times more densely than we do. Then there's a very good chance that the majority of sentient beings exist in such a supercivilization. To take a real-world example that might make this a little clearer: in the United States, only 0.4% of firms have more than 100 employees, yet employees of these big firms account for 63% of paid employees in U.S. firms. The reason, of course, is that even if there are lots and lots of little firms, the big firms are the ones that have lots of people. So if I picked a worker at random from the working population of the U.S., it would be a smart guess that he works for a big firm and not a small one (even though big firms are rarer than small ones).

The same logic applies here, except the numbers are significantly more exaggerated. Whereas all but about 2 in 5 U.S. private employees work for a large firm in our example, the authors in that paper calculate that "all but one individual in a hundred million belongs to a large civilization." So if you pick a sentient observer at random, it would be a very good bet that he belongs to one of those supercivilizations because that's where most of the sentient beings are. But we Earthicans are in the curious position of not finding ourselves in such a supercivilization. So is our starting assumption that we're not special (i.e. that if we pick someone at random out of the multiverse we're free to pick ourselves) wrong? Is inflation--with its untold numbers of other bubble universes--wrong? Is there some general principle that forbids or nearly rules out the development of supercivilizations?

Ultimately we don't know but the author does offer some suggestions. In addition to the ones I just mentioned, he suggests maybe we are part of a supercivilization but just don't know it (paging Agent Mulder!), maybe some sort of selection bias is going on here, or perhaps even "the idea of 'individual' will be different in the future. That last one is particularly interesting:

Perhaps civilizations more advanced than ours consist of only a single individual, or only a single individual per planet, in whatever sense of individual is necessary for anthropic reasoning. In that case, even though the civilization is very widespread, the number of individuals is small. A similar idea is that individuals of those advanced civilizations are so different from us that they cannot be considered part of the same reference class, and we should not reason as though we could have been one of them.

Does this remind anybody else of the Kurzweil predictions we talked about in What Lies Ahead? Particularly the bits like:

● Individual beings merge and separate constantly, making it impossible to determine how many “people” there are on Earth.
● This new plasticity of consciousness and ability for beings to join minds seriously alters the nature of self-identity.

Something to mull over.