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Is the universe fine-tuned for intelligent life?
David H. Bailey
9 Apr 2017 (c) 2017
Some of the most remarkable findings of modern physics and cosmology are the "cosmic coincidences," namely indications that our particular universe and its laws seem remarkably tailored for the rise of intelligent life. For example, the expansion of the universe is finely tuned to the long-term existence of the universe -- if gravitation had been very slightly stronger in the early universe, the expansion would have stopped and even reversed long ago, ending the universe in a big crunch long before any sentient creatures would have arisen. On the other hand, if gravitation had been very slightly weaker, stars and galaxies might not have formed until matter was too dispersed, leaving the universe a cold and lifeless place.
A few of these cosmic coincidences that have been noted in previous years now have reasonable explanations. For instance, the knife-edge balance of gravitation and expansion may be explained by the "inflation" theory of cosmology, wherein the early universe underwent an incredible expansion in the first microscopic instances of time. However, the inflationary theory is now being questioned by many in the field, and may have to be substantially revised or even discarded [Steinhardt2011].
Many other of these cosmic coincidences remain inexplicable, and, if anything, recent developments in physics and astronomy have compounded these mysteries. Such paradoxes have even led some leading scientists to resurrect the "anthropic principle": the reason that we see these cosmic coincidences is a selection effect of our very existence. In other words, they propose that if the universe weren't constructed in an exceedingly special way, neither humans nor any other conceivable sentient beings would be around to discuss the issue [Barrow1986]. However, other scientists are extremely uncomfortable with the multiverse-anthropic approach, and view the mere fact that scientists would even suggest such solutions as an indictment of the entire enterprise of modern physics [Smolin2006]. For additional discussion on the anthropic principle, see
Some cosmic coincidences
Here are just a few of the cosmic coincidences that have been noted in the scientific literature:
Additional examples and details are presented in books by Paul Davies, Geraint Lewis and Luke Barnes, among others [Davies2007; Lewis2016].
- Carbon resonance and the strong force. Although the laws of physics can readily explain the abundances of hydrogen, helium, lithium and beryllium (they were formed in the first 100 seconds or so after the big bang), the synthesis of heavier elements, beginning with carbon, was a deep mystery until 1951, when astronomer Fred Hoyle hypothesized and then discovered a resonance that is just energetic enough to permit a triple-helium nuclear reaction to produce a carbon nucleus. If the strong force were slightly stronger or slightly weaker (by just 1% in either direction), then the binding energies of the nuclei would be different, and this resonance would not work. In that case, there would be no carbon or any heavier elements anywhere in the universe, and thus no carbon-based life forms to contemplate this intriguing fact [Davies2007, pg. 133-138; Lewis2016, pg. 114-120; Chown2016].
By the way, although one can imagine living organisms based on other elements, carbon is by far is the most suitable element for the construction of complex molecules, as required for any conceivable form of living or sentient beings [Lewis2016, pg. 268]. In any event, nuclear chemistry precludes any heavier elements (i.e., elements beyond hydrogen, helium, lithium and beryllium) if carbon cannot form.
- The weak force and the proton-neutron balance. Had the weak force been somewhat stronger, primordial neutrons produced in the first few seconds after the big bang would have decayed faster, and there would be little if any carbon or heavier elements in our universe. On the other hand, if the weak force had been somewhat weaker, the amount of hydrogen in the universe would be greatly decreased, starving stars of fuel for nuclear energy and leaving the universe a cold and lifeless place [Davies2007, pg. 142-143].
- The electromagnetic-gravitational strength ratio. In 1974, Brandon Carter noted an interesting relationship between the ratio of the strengths of the electromagnetic and gravitational fields, which is roughly 1040, and the properties of stars. If gravity were slightly stronger (so that the ratio is lower), all stars would be radiative rather than convective, and planets might not form. But if gravity were somewhat weaker (so that the ratio was higher), then all stars would be convective and supernovas might not happen. Since all elements from carbon on up are synthesized in stellar explosions, we might not be here to discuss the issue [Carter1974; Davies2007, pg. 144].
- The proton-to-electron mass ratio. The ratio of the mass of the proton to that of the electron is approximately 1836.15, according to latest measurements. The ratio of the mass of the neutron to the mass of the proton is approximately 1.0013784. In other words, the neutron's mass is slightly more than the combined mass of a proton, an electron and a neutrino. As a result, free neutrons (neutrons that are not tied up in the nucleus of an atom) spontaneously decay with a half life of about 10 minutes. If the neutron were very slightly less massive, then it could not decay without energy input. If its mass were lower by 1%, then isolated protons would decay instead of neutrons, and very few atoms heavier than lithium could form [Davies2007, pg. 145].
- Uniformity of the cosmic microwave background. For many years after the discovery of the cosmic microwave background radiation, measurements indicated that it was isotropic (constant in all directions), except for a well-understood effect resulting from our galaxy's motion. In 1992, scientists discovered that there is a very slight anisotropy in this radiation, roughly one part in 100,000, which is just enough to ensure the formation of stars and galaxies. If this anisotropy had been significantly smaller, the early universe would have been too smooth for stars and galaxies to have formed. It it had been significantly smaller, galaxies would have been denser, resulting in numerous stellar collisions, so that stable, long-lived stars with planetary systems would have been very rare [Davies2007, pg. 146]. In sharp contrast, planetary systems are plentiful in our universe [Clery2017].
- The cosmological constant. The cosmological constant paradox derives from the fact that when one calculates, based on known principles of quantum mechanics, the "vacuum energy density" of the universe, one obtains the incredible result that empty space "weighs" 1093 grams per cubic centimeter (since the actual average mass density of the universe is roughly 10-28 grams per cc, this is in error by 120 orders of magnitude) [Susskind2005, pg. 70-78]. Stephen Hawking quipped that this is the most spectacular failure of a physical theory in history [Davies2007, pg. 147]. Physicists, who have fretted over this discrepancy for decades, have noted that calculations such as the above involve only the electromagnetic force, and so perhaps when the contributions of the other known forces are included, all terms will cancel out to exactly zero as a consequence of some heretofore unknown physical principle. These hopes were shattered with the 1998 discovery that the expansion of the universe is accelerating, which implies that the cosmological constant must be slightly positive [Panek2011]. But this means that physicists are left to explain the startling fact that the positive and negative contributions to the cosmological constant cancel to 120-digit accuracy, yet fail to cancel beginning at the 121-st digit. Curiously, this observation is in accord with a prediction made by physicist Steven Weinberg in 1987, who argued from basic principles that the cosmological constant must be zero to within one part in roughly 10120, or else the universe either would have dispersed too fast for stars and galaxies to have formed, or would have recollapsed upon itself long ago [Susskind2005, pg. 80-82; Weinberg1989]. Numerous "solutions" have been proposed for the cosmological constant paradox (Lewis and Barnes mention eight [Lewis2016, pg. 163-164]), but they all fail, rather miserably. For additional discussion of the cosmological constant, see
- Mass of the Higgs boson. A similar cosmic coincidence has come to light recently in the wake of the 2012 discovery of the Higgs boson at the Large Hadron Collider. Higgs was found to have a mass of 126 billion electron volts (i.e., 126 giga-electron-volts or Gev). However, a calculation of interactions with other known particles yields a mass of some 1019 Gev. This means that the rest mass of the Higgs boson must be almost exactly the negative of this enormous number, so that when added to 1019 gives 126 Gev, as a result of massive and unexplained cancelation. Supersymmetry (the notion that each known particle has a "superpartner" with different properties) has been proposed as a solution to this and the cosmological constant paradox, but no hint of these other particles are seen in the latest experiments at the LHC [Wolchover2013].
- The flatness problem. General relativity allows the space-time fabric of the universe to be open (extending forever, like an infinite saddle), closed (like the surface of a sphere), or flat. The latest measurements confirm that the universe is flat to within 1%. But looking back to the first few minutes of the universe at the big bang, this means that the universe must have been flat to within one part in 1015. As mentioned above, the cosmic inflation theory was proposed by Alan Guth and others in the 1970s to explain this and some other phenomena [Guth1997], but recently even some of inflation's most devoted proponents (e.g., Paul Steinhart) have acknowledged that the theory is in deep trouble and will have to be either substantially revised or discarded altogether [Horgan2014]. See Inflation for more details.
- The low-entropy state of the universe. The overall entropy (disorder) of the universe is, in the words of Lewis and Barnes, "freakishly lower than life requires" [Lewis2016, pg. 126]. After all, life requires, at most, a galaxy of highly ordered matter to create chemistry and life on a single planet. Physicist Roger Penrose has calculated the odds that the entire universe is as orderly as our galactic neighborhood to be one in 1010123, a number whose decimal representation has vastly more zeroes than the number of fundamental particles in the observable universe [Penrose1989, pg. 341-344]. Extrapolating back to the big bang only deepens this puzzle.
What does it mean?
In short, numerous features of our universe seem fantastically fine-tuned for the existence of intelligent life. While some physicists still hold out for a "natural" explanation, many others are now coming to grips with the notion that our universe is profoundly "unnatural," with no good explanation other than the anthropic principle -- the universe is in this extremely improbable state, because if it weren't we wouldn't be here to discuss the fact [Wolchover2013].
While some religious-minded writers conclude that these "cosmic coincidences" constitute iron-clad "proof" that our universe was designed by a supreme being, others recommend caution. For example, the search for "design" in the creation of the universe is reminiscent of the search for "design" in the evolution of life on earth. And long experience has taught us that claims that one can "prove" God via arguments based on apparent design or other inexplicable phenomena in the natural world are likely to disappoint in the long run. Furthermore, invoking a Creator or Designer every time unexplained phenomena arise is a "thinking stopper," burying the grand questions of science and religion in the inaccessible, inscrutable mind of some transcendent being.
Along this line, the recent emergence of the "multiverse" cosmology (see
Multiverse) have led some theologians, who once were fond of the big bang cosmology, to reconsider what their theology means in the context of the multiverse. As Catholic philosopher John Haught notes [Haught1995, pg. 109]:
And although it may seem for the moment that big bang physics is smoothing over some of the friction between science and religion, we know that science will continue to change. And if the big bang theory is eventually discarded as premature or inaccurate, then on what ground will those theologians stand who now see it as a vindication of theism?
And while such discussions may be engaging and intriguing, it is not clear that they relate in any substantive way with what most religious believers experience. Is the "God of the big bang" the same being that inspired Albert Schweitzer, Mohandas Ghandi and Mother Teresa to surrender their careers and fortunes, and instead devote their lives to the poor and downtrodden? Did Johann Sebastian Bach have the "God of the big bang" in mind when he composed the Mass in B Minor, the Christmas Oratorio and over 1,000 other sacred works? Probably not!
For additional details and discussion, see
Cosmological constant ,
Big bang theology and