Three Big Bangs Read online

  Martin Rees continues, two decades later:

  Perhaps a fundamental set of equations, which may some day be written on T-shirts, fixes all key properties of our universe uniquely. It would then just be an unassailable fact that these equations permitted the immensely complex evolution that led to our emergence. But I think there would still be something to wonder about. It is not guaranteed that simple equations permit complex consequences. (Rees 2001:162)

  Stephen M. Barr puts the point this way, with emphasis:

  Even if all the physical relationships needed for life to evolve were explained as arising from some fundamental physical theory, there would still be a coincidence. There would be the coincidence between what that physical theory required and what the evolution of life required. If life requires dozens of delicate relationships to be satisfied, and a certain physical theory also requires dozens of delicate relationships to be satisfied, and they turn out to be the very same relationships, that would be a fantastic coincidence. Or, rather, a series of fantastic coincidences. (Barr 2003:145)

  A Biogenic/Anthropic Universe

  Paul Davies, a cosmologist, claims that we hit “the cosmic jackpot,” a universe “just right for life” (Davies 2007). Phrased more technically, “virtually no physical parameters can be changed by large amounts without causing radical qualitative changes to the physical world. In other words, the ‘island’ in parameter space that supports human life appears to be quite small” (Tegmark 1998:6). The range of values of some quantity that is life-permitting (such as the strength of the force of gravity) is small compared with the range of values that physical theory might otherwise allow. Although physics finds such a jackpot universe just right for life, theories in physics, as we were noticing, nowhere require that there be such a universe. The question now is not so much whether cosmologists can explain “everything” as whether they can explain how there comes to be “anything”—especially anything as interesting as (in Davies’ metaphor) “a cosmic jackpot.”

  In the last half-century cosmologists have found dramatic interrelationships between astronomical and atomic scales that connect to make the universe “user-friendly.” These discoveries are commonly gathered under the name “the anthropic principle,” a term introduced by Brandon Carter in 1974, though it could better have been named “the biogenic principle.” Nor is this even a “principle” in any familiar sense. Rather the reference is to a series of observations about the values of the fundamental constants, the fundamental forces, the properties of particles, such as charge and mass, the nature of dynamic processes, the initial conditions. When these are figured into the theories of physics, the result in our universe appears to be “fine-tuned” so as to enable the development of complex chemistries, which are requisite for life (the second big bang) and self-conscious mind (the third big bang).

  How the various physical processes are “fine-tuned to such stunning accuracy is surely one of the great mysteries of cosmology,” concludes Paul Davies. “Had this exceedingly delicate tuning of values been even slightly upset, the subsequent structure of the universe would have been totally different.” “Extraordinary physical coincidences and apparently accidental cooperation… offer compelling evidence that something is ‘going on.’… A hidden principle seems to be at work” (Davies 1982:90, 110).

  Physicists cannot do experiments revising the universe, but they have been doing thought experiments to see whether another one would be more congenial. Such “if-then” experiments conclude that the universe is mysteriously right for producing life and mind. We next turn to some half dozen of these considerations, among fifty or sixty that have been variously explored (Barrow et al. 2008; Davies 2007; Rees 2000, 2001; Barr 2003; Denton 1998; Barrow and Tipler 1986; Leslie 1989).

  (1) The rate of expansion of space in the universe depends on the cosmological constant, usually symbolized by the Greek letter lambda (λ), which is quite small (nearly zero but not zero) (Vilenkin 2006). The cosmological constant is a term that Albert Einstein introduced into his theory of general relativity when applied to the universe, thinking thereby to allow the universe to remain static (nonexpanding, nonshrinking). Lambda is related to the acceleration of the universe. If this constant is positive, the universe expands. If negative, the universe contracts. Over a decade later Edwin Hubble discovered that, despite any effects of gravity, the universe was in fact expanding, based on observations of redshift in starlight from distant galaxies (the Doppler effect).

  Interestingly, the expansion rate of our “user-friendly” universe depends rather precisely on this minute constant. Expressed in natural units, it is less than 10-120. Written as an ordinary decimal, this would be:

  0.0000000000000000000000000000000000000000

  0000000000000000000000000000000000000000

  0000000000000000000000000000000000000001

  The small but positive cosmological constant can be thought of as a pressure, associated with an energy in empty space, that overcomes gravitational tendencies toward contraction and results in accelerating expansion. “Empty space” in cosmologists’ terms is empty of ordinary matter; they may call it a vacuum, but it is not really nothing. It is a sort of energy possibility space. Empty space is supposed to have latent particles that can pop into and out of existence, perhaps to contain dark energy and have other activities. Cosmologists speak of a space-time “quantum foam” or of microscopic quantum fluctuations in empty space-time. The cosmological constant permitting expansion arises from spatial features such as these. In theoretical accounts, the early dense inflationary universe has to settle in on this small quantity soon after the big bang, some 10120 times lower than the ultra-early density (Rees 2000:97).

  Even more interestingly, within conventional big bang cosmology, it has proven to be very difficult to understand why the constant is so tiny. Many different factors contribute to its strength; cosmologists would otherwise expect it to be quite large—so large the universe would fly apart. By some accounts the expected value today is 1060 to 10120 higher than its tiny life-permitting value. Some mechanism cancels out the contributing factors to nearly but not quite zero. Despite various proposals, at present there is no generally accepted way to derive the minute cosmological constant from particle physics or astrophysics.

  Even if such an account is found, the interactions that produce such a minute constant that figures so significantly into the expansion rate, continuing from the explosive big bang, will be remarkable. Martin Rees finds this puzzling:

  Fortunately for us (and very surprisingly to theorists), λ is very small. Otherwise its effect would have stopped galaxies and stars from forming and cosmic evolution would have been stifled before it could even begin…. The cosmic number λ—describing the weakest force in nature, as well as the most mysterious—seems to control the universe’s expansion and its eventual fate…. Our existence requires that λ should not have been too large. (Rees 2000: 3, 98–99; cf. Graesser et al. 2004)

  Stephen Hawking asks:

  Why is the universe so close to the dividing line between collapsing again and expanding indefinitely? In order to be as close as we are now, the rate of expansion early on had to be chosen fantastically accurately. If the rate of expansion one second after the big bang had been less by one part in 1010, the universe would have collapsed after a few million years. If it had been greater by one part in 1010, the universe would have been essentially empty after a few million years. In neither case would it have lasted long enough for life to develop. Thus one has either to appeal to the anthropic principle or find some physical explanation of why the universe is the way it is. (Hawking 1996:89–90; Penrose 2005:462–464, 772–778)

  If we cut the size of the universe from 1022 to 1011 stars, then that much smaller but still galaxy-sized universe might first seem roomy enough, but it would run through its entire cycle of expansion and recontraction in about one year! If the matter of the universe were not so relatively homogeneous as it is, then large portions o
f the universe would be so dense that they would already have undergone gravitational collapse. Other portions would be so thin that they could not give birth to galaxies and stars (Wheeler 1975). The universe is immense, but it could hardly be any smaller if life were to appear in it at all.

  If the universe were not expanding, then it would be too hot to support life. If the expansion rate of the universe had been a little faster or slower, then connections would have shifted so that the universe would already have recollapsed or so that galaxies and stars could not have formed. The explosive expansion, extent, and age of the universe are not obviously an outlandish extravagance. If it were not vast, lonely, and dark, we would not be here—as we earlier heard John Barrow conclude (Barrow 2002:113). Indeed, this may be the most economical universe in which life and mind can exist—so far as we can cast that question into a testable form in physics.

  (2) Astronomical phenomena such as the formation of galaxies, stars, and planets, which depend critically on the expansion rate of the universe, also depend critically on the microphysical phenomena. In turn, those midrange scales where the known complexity mostly lies depend on the interacting microscopic and astronomical ranges. The human world stands about midway between the infinitesimal and the immense on the natural scale. The size of a planet is near the geometric mean of the size of the known universe and the size of the atom. The mass of a human being is the geometric mean of the mass of Earth and the mass of a proton (Carr and Rees 1979:605). A person contains about 1028 atoms, more atoms than there are stars in the universe, and that number puts us mid-scale. “The human scale is, in a numerical sense, poised midway between atoms and stars” (Rees 2001:183).

  Planets and persons, at mid-scale ranges, equally depend on the structure and processes at the astronomical and atomic ranges. Change slightly the strengths of any of the binding forces that hold the world together, change critical particle masses and charges, and the stars would burn too quickly or too slowly, or atoms and molecules (including water, carbon, and oxygen) or amino acids (building blocks of life) would not form or remain stable. The charges on the light electron and on the vastly more massive proton are exactly equal numerically. “Heaven knows why they are equal,” wondered George Wald, “but if they weren’t there would be no galaxies, no stars, no planets – and, worst of all, no physicists” (quoted in New Scientist 60, no. 871 [Nov. 8, 1973]: 427). A fractional difference and there would have been nothing.

  (3) Those four fundamental forces that hold the world together range over forty orders of magnitude; some involve repulsion as well as attraction, but the push as well as the pull is used to hold things together. The mix of forces is both remarkable and complex.

  (3a) Gravity is the weakest of these forces, and only positive. Gravity affects the expansion rate of the universe; without it there would be no galaxies or stars. Since it is the weakest by far, although it does operate at long distances, we might ask why it is so weak. But if gravity were much stronger, the solar system as we know it would not exist. On Earth, most of the structural features of living organisms would be upset (such as bones or brains). Large terrestrial organisms would be impossible. If gravity were much weaker the formation of galaxies and stars would be upset, including the supernovae explosions on which life depends.

  (3b) Owing to the electromagnetic force, positively charged protons and negatively charged electrons are attracted. The electromagnetic force is essential to chemistry; think of chemical bonding or the atomic table. Protons repel protons by the same force. John D. Barrow and Joseph Silk calculate that “small changes in the electric charge of the electron would block any kind of chemistry” (Barrow and Silk 1980:128).

  (3c) At short ranges, however, the strong nuclear force is stronger and keeps the protons (and neutrons) together in an atom. Without the strong nuclear force there would be no atoms other than hydrogen. If these forces are much changed, basic atomic structures and chemistries are radically altered. When we consider the first seconds of the big bang, writes Bernard Lovell:

  It is an astonishing reflection that at this critical early moment in the history of the universe, all of the hydrogen would have turned into helium if the force of attraction between protons—that is, the nuclei of the hydrogen atoms—had been only a few percent stronger. In the earliest stages of the expansion of the universe, the primeval condensate would have turned into helium. No galaxies, no stars, no life would have emerged. It would have been a universe forever unknowable by living creatures. A remarkable and intimate relationship between man, the fundamental constants of nature and the initial moments of space and time seems to be an inescapable condition of our existence…. Human existence is itself entwined with the primeval state of the universe. (Lovell 1975:88, 95)

  The value of this strong nuclear force (∈) as figured into equations is 0.007. What if it were a little different? asks Martin Rees. His answer: “If ∈ were 0.006 or 0.008, we could not exist” (Rees 2000:2, 48–51).

  (3d) The weak nuclear force (a billion times weaker than the strong force) is involved in the relative proportions of protons and neutrons in stars. An aging star may end in a huge explosion, a supernova, which is how the elements it has forged get distributed into space and form planets. First the star collapses and the implosion results, on account of the weak force, in protons turning into neutrons, emitting neutrinos, which, in the dense stellar core, drive the rebounding explosion. These processes would fail if the weak force were much weaker, or stronger. Also, if the weak force were much different there would be only helium stars (with a short lifetime) and no hydrogen stars, in which the heavy elements form.

  In this universe at least, these forces, and the particle masses and charges involved, have to be about what they are, if anything more complex is to develop.

  (4) Carbon is basic to life as we know it, and there are considerable difficulties in envisioning any alternatives to carbon-based life (Pace 2001; cf. Bains 2004). Likewise, oxygen, required to form water, is vital to life (Finney 2004). Both are produced in stars in abundance by a series of quite precise steps. Hydrogen is converted to helium (helium 4) and the helium subsequently converted to carbon and oxygen. In an intermediate step, helium nuclei collide to form unstable beryllium 8, which is quite short-lived, capturing another helium nucleus to produce carbon (carbon 12). (Beryllium 9 is the stable form, a light metal.) Some of the carbon collides with helium nuclei to produce oxygen (oxygen 16) (Clayton 1983). These transformations are rather surprisingly adjusted so that abundant amounts of both carbon and oxygen are produced. If not, there would be mostly carbon or mostly oxygen.

  Fred Hoyle, an astronomer, was quite startled by his discovery of these critical levels through which carbon just manages to form and then only just avoids complete conversion into oxygen. If the strong force had varied by a half a percent, the ratio of carbon to oxygen would have shifted so as to make life impossible.

  Would you not say to yourself… “Some supercalculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of nature would be utterly minuscule”? Of course you would…. You would conclude that the carbon atom is a fix…. A common sense interpretation of the facts suggests that a superintellect has monkeyed with the physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question. (Hoyle 1981:12)

  These synthesis processes involve what are called “resonance states” in carbon and oxygen, which depend on the strong nuclear force and the electromagnetic force. Compare how a radio has to be tuned right on frequency to get the desired station—the origin of the “fine-tuned” metaphor. Astrophysicists have made quantitative analyses of the effects of changes in these forces on the amount of carbon (C) and oxygen (O) produced. “We conclude that a change of more than 0.5% in the strength of the strong interacti
on or more than 4% change in the strength of the Coulomb force [of electromagnetic attraction and repulsion] would destroy nearly all C or all O in every star” (Oberhummer et al. 2000: 90).

  The six elements especially important for life are hydrogen, carbon, oxygen, nitrogen, sulphur, and phosphorus. Hydrogen is everywhere, and of the heavier elements, four are produced in relative abundance. But phosphorus (phosphorus 15), quite vital to life, is not common, because its synthesis requires many complex nuclear reactions, which can only take place in a minor subset of massive stars, and these produce little (Maciá et al. 1997). Though uncommon on Earth, phosphorus is, fortunately, concentrated in minerals such as apatite, from which it, with its distinctive chemical properties, becomes available in sufficient amounts for the energies and structures of life. In the form of phosphates, conversions from ATP to ADP are the energy currency of life. Phosphate groups with sugars form the backbone links in DNA and RNA; phosphates are important in the synthesis of biological molecules (such as phospholipids in lipid bilayers) and in vertebrate skeletons. As part of the molecule NADP, phosphorus is essential in electron transport and oxidation-reduction reactions (Westheimer 1987; Williams 2000; Skinner 2002).

  There are as well several metallic ions required, often in only trace amounts, for key metabolic processes—magnesium, iron, and zinc, in the structures of chlorophyll, cytochromes, hemoglobins, and some enzymes (Williams 1953, 2000). These elements too are sufficiently available. So in sum, the nucleosynthesis of the biogenic elements, with their remarkable structural and metabolic possibilities, is both fortunate and impressive. As a result of the stellar physics and chemistry, the building blocks are in place. The carbon-oxygen synthesis seems exactly and singularly fine-tuned, but other syntheses are more plural and diverse, cooking up about a hundred elements, with varied nuclei and electron shells and subshells, those grappling hooks with such immense possibilities for constructions. A dozen of these elements have possibilities that are biologically tantalizing. Still, in the nucleosynthesis in the heavens above, there is not a shred of any cybernetic know-how to engineer the much more complex hookups that launch and sustain life. That came about in the second big bang on Earth.