Beyond the Big Bang
6 August 2011
The cover story on this month’s issue of Scientific American is Does the Multiverse Really Exist?, and the BBC has also had a story on the same, ‘Multiverse’ theory suggested by microwave background. Here is the opening paragraph of the Scientific American story:
“In the past decade an extraordinary claim has captivated cosmologists: that the expanding universe we see around us is not the only one; that billions of other universes are out there, too. There is not one universe—there is a multiverse. In Scientific American articles and books such as Brian Greene’s latest, The Hidden Reality, leading scientists have spoken of a super-Copernican revolution. In this view, not only is our planet one among many, but even our entire universe is insignificant on the cosmic scale of things. It is just one of countless universes, each doing its own thing”
It is typical for contemporary scientific thought to present this as a new idea, notwithstanding several thousand years of philosophical tradition investigating the infinity of worlds, as it is equally typical to cite a recent book on the topic rather than to acknowledge the theoretical underpinnings of the idea that go back to the earliest works of the Western tradition. I mentioned similar considerations not long ago in a post about Conformal Cyclic Cosmology.
The BBC story ‘Multiverse’ theory suggested by microwave background by Jason Palmer references the paper First Observational Tests of Eternal Inflation by Feeney, Johnson, Mortlock, and Peiris. Here’s the abstract of the paper:
The eternal inflation scenario predicts that our observable universe resides inside a single bubble embedded in a vast inflating multiverse. We present the first observational tests of eternal inflation, performing a search for cosmological signatures of collisions with other bubble universes in cosmic microwave background data from the WMAP satellite. We conclude that the WMAP 7-year data do not warrant augmenting ACDM with bubble collisions, constraining the average number of detectable bubble collisions on the full sky Ns < 1:6 at 68% CL. Data from the Planck satellite can be used to more definitively test the bubble collision hypothesis.
First Observational Tests of Eternal Inflation by Feeney, Johnson, Mortlock, and Peiris
This is from the second paragraph of the paper:
Eternal inflation is ubiquitous in theories with extra dimensions (string theory being the primary example) and positive vacuum energy. However, testing this scenario is extremely difficult since eternal inflation is a pre-inflationary epoch: any signals from outside of our bubble would naively appear to be stretched to unobservable super-horizon scales. While this is in general true, one prospect for probing this epoch lies in the observation of the collisions between vacuum bubbles. These collisions produce inhomogeneities in the inner-bubble cosmology, raising the possibility that their effects are imprinted in the cosmic microwave background
I find these recent developments in cosmology both welcome and troubling. It is welcome because the time in long overdue to give serious consideration to theories that do not limit the universe to that generated from the Big Bang (as cosmologists once limited the universe only to the Milky Way galaxy, and before that to our solar system), and it is troubling because the way in which these developments are presented confirms much that I have written recently about Fashionable Anti-Philosophy in science.
From the origins of the Big Bang model up until very recently, it was commonplace among scientists to assert that space and time began with the big bang, and that it was meaningless to speak of the big bang singularity as existing in space or time (this was called the “container theory” of space and time), since space and time (actually, spacetime) was generated by the big bang. To insist upon any other account marked you out as a philosopher and a fool who simply couldn’t understand the scientific concepts involved and the mathematics behind them.
Truly enough, from the point of view of observational cosmology it is meaningless to develop theories of things that can’t be observed, like the interior of singularities, what lies outside the light cone, or what happened before the big bang. But cosmology is not limited to observational cosmology, and physicists routinely theorize about things that can’t be observed, on the hope that they might someday be observed. The “standard model” of particle physics has been looking for the Higgs boson for years, and is hopeful that it will be found soon. But this is why we formulate hypotheses: so we have a research program that can focus on finding mechanisms that might explain the things that we can see.
The great scientific and mathematical revolution that supposedly made all this both possible and rational was the idea of the finite and unbounded universe that was bent around on itself, like the surface of the earth, so that even though there is no edge to the cosmos, that does not mean that it is infinite. There is no edge because there is no boundary, and there is no boundary because the universe is finite and unbounded. The elliptical geometry of Riemann, adapted by Einstein as the setting for General Relativity, gave a precise mathematical expression to this idea. But the advocates of the finite and unbounded universe carefully avoided explaining the distinction between intrinsic and extrinsic curvature, and with a little bit of ambiguity they were able to pretend that the universe was expanding into nothingness without giving an account of this nothingness.
A typical expression of this attitude, in the form of an aside, comes from J. J. Callahan, in discussing his motivation for writing his frequently cited paper, “The Curvature of Space in a Finite Universe” (Scientific American, Volume 235, Number 2, August, 1976). Callahan said the paper grew:
“…out of an attempt to explain Einstein’s concept of a finite but unbounded space to my nonscientific colleagues at Smith. They found it tough going, and some simply dismissed a finite universe as impossible, because Kant had done so when he studied the question 300 years ago.”
Apart from a misrepresentation of Kant, Callahan’s “non-scientific colleagues” are caricatured as mere simpletons who can’t hack mathematical and scientific ideas (it was “tough going” for them), and not people who had genuine intuitions of the how the universe is put together but were unable to express them with the same blinding simplicity of the big bang model producing a finite and unbounded universe.
I am not the only one to have noticed this systematic ambiguity in recent cosmology. I found this amusingly acerbic quote in The Ontology and Cosmology of Non-Euclidean Geometry:
“The closest we seem to have come to a more open consideration of these matters is when both Stephen Hawking and Karl Popper [Karl Popper, Unended Quest, Open Court, 1990; p.16] point out that Einstein, whether or not he successfully answered Kant’s Antinomy of Space, did not answer the Antinomy of Time: despite decades of everyone glorifying in the philosophical revelation of a finite but unbounded universe, they simply didn’t notice that the solution proposed for space didn’t work with time. It is to Hawking’s great philosophical credit that he faces this question squarely.”
The author here has been more charitable to Hawking than I would be, as Hawking has been prominent among those who have ridiculed what he sees as the simple-mindedness of philosophers in insisting upon answers to their questions about a universe with this geometrical structure. Morevoer, I would maintain that the “philosophical revelation of a finite but unbounded universe” doesn’t even offer a solution to the problem of space, much less time, much less spacetime.
So I am happy to see cosmologists extending their scope and trying to get outside the confines of the big bang model, but I continue to be distressed that they continue to ridicule the philosophical underpinnings of their own ideas, and that they will go through a lot of needless duplication of labor in coming up with ideas that have been worked through time and again. But, if you’re aiming at research dollars to build the latest, greatest superconducting supercollider, or the biggest and most sensitive radio telescope, it isn’t going to pull much weight with the grant writing committees or the grant granting institutions themselves to tell them you’ll be spending the next few years in a library reading old books in order to refine your concepts to the point that they might suggest a research program.
Physicists and cosmologists seem to belong to the Field of Dreams school of thought, pursuing a “if we build it, they will come” strategy in research, with “they” being discoveries, suitably celebrated in the headlines of newspapers.
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