The Finely Tuned Universe Preliminaries: Is Earth Finely Tuned? The conditions for intelligent life are extremely difficult to achieve. Benign conditions must exist for a very long period of time. If Earth froze over, or the oceans evaporated, or life were obliterated by impact from a large space object any time over geologic history, intelligent life wouldn’t be here. Earth is a finely tuned environment for intelligent life to develop. It is the right size: enough gravity to keep its atmosphere, but not so much that substantial creatures have a hard time moving about, or so much that the atmosphere is too dense. It is the right distance from its star, so that we have plentiful liquid water. It orbits around the right size star: much larger and the Sun would not last long enough for intelligent life to develop here. Much smaller, and we’d have to be much closer to the star. Smaller stars have large flares that could kill life on Earth. Earth has plenty of carbon and oxygen needed for life, as well as heavier elements that are so essential to our well-being. Earth’s plate tectonics recycles carbon and other elements, keeping the climate relatively stable. Jupiter, a large planet slightly further out in the solar system, helps to protect Earth from being impacted a lot more often by large objects, due to its significant gravity. It acts like a catcher’s mitt in most cases. Our relatively large Moon keeps Earth’s rotation axis stable over very long periods of time; advanced life might not be feasible without this, and it is most likely rare. Here’s more: Scientific American, August 2012: Black holes, such as the four-million-solar-mass lurker at the center of our galaxy, are not simply consumers. They also radiate copious amounts of energy as they devour nearby matter. Supermassive black holes are at the center of nearly all large galaxies. A black hole’s feeding habits can have a surprising influence on the galaxy. Too much black hole activity, or too little, and stars with the right conditions for life as we know it could be scarce. It appears that if there is too much black hole activity (too much material falling in), the fierce ultraviolet and x-ray radiation would propel so much windlike heated gas outward that there would be little new star formation. (Astronomy magazine also says—September 2012—that stellar growth quickly drops off in galaxies with the most active black holes.) If there is too little black hole activity, it appears that either environments might be overly full of young and exploding stars (large galaxies) or too little stirred up to produce much of anything (if the galaxies are small). Change the balance at all, and the whole pathway of star and galaxy formation changes. The Milky Way occupies a galactic sweet spot, with a black hole that appears to act out just often enough to stir things up and keep the galaxy’s stellar population at a perfect simmer. Our galaxy’s central black hole seems to have made numerous contributions to our ability to exist at this place and time. There are hundreds of billions of galaxies (in the portion of the Universe we can see), each with typically a hundred billion stars. We have recently started discovering planets around other stars, and it appears there are at least as many planets as stars, probably more. So even if things have to be finely tuned for there to be complex life, there are lots of opportunities for it to happen somewhere. There are several places in our solar system (besides Earth) where we think life might have, or still does, exist—Mars (there is a lot of evidence that water existed and still exists), Europa, and possibly (maybe less likely) 1
Ganymede, Enceladus, and Titan. With the huge number of planets and the wide variety of conditions, the Universe is probably teeming with life. Of course we have no proof of that; we don’t really know how hard it is for life to get started although we have theories. We do know that life on Earth is extremely tenacious; we find it in extremely cold places, extremely dry places, the bottom of the oceans, in volcanic vents, in rocks, pretty much everywhere.
Mars (combination image from NASA)
Enceladus ice geysers (NASA) 3
Sun glint off Titan lake (methane)
Titan lakes from Cassini radar data (NASA) Intelligent life is much more difficult, as described above. It shouldn’t surprise us that we are on what appears to be a finely tuned planet. If all the details in the paragraph above are necessary for intelligent life, and if stars and planets are of random size and distances from each other, eventually with enough of them one will be ideal. Since we are here, obviously we are on one of these ideal places. They probably are rare, although we don’t know how rare. It could be that there are many planets in our galaxy that could harbor intelligent life. On the other hand, maybe we are the only ones in our galaxy. Even with the ideal conditions being very rare, with hundreds of billions of galaxies, there may be a very large number of extraterrestrial civilizations. (Personally, I find it hard to imagine that God created this huge, wonderful Universe, and we are the only intelligent life.) So there isn’t evidence that Earth was in particular designed specifically for life. It appears that it is simply the result of a Universe that generates every kind of star and planet. But what about the Universe itself that led to the possibility of intelligent life on Earth? It appears that the Universe is very finely tuned for life, that the physical laws are perfect for generating more and more complexity. In the book Just Six Numbers, Sir Martin Rees covers how the choice of six numbers leads to the Universe being what it is. What he doesn’t cover is why the laws are such that choosing these six numbers the way they are makes all this amazingness possible. Why are there even protons, neutrons, and electrons? He also doesn’t cover how amazing it is that with these few important laws and parameters set, everything works together so well that we get to where we are, with complex, intelligent life. Just Six Numbers by Martin Rees Rees won the Templeton Prize, was Astronomer Royal for Great Britain, Royal Society Research Professor at Cambridge University, and was president of the Royal Society from 2005-2010. The book is a perspective on how a single ‘genesis event’ created billions of galaxies, black holes, stars and planets, and how atoms have been assembled – here on Earth, and perhaps on other worlds – into living beings intricate enough to ponder their origins. Our emergence and survival depend on very special ‘tuning’ of the cosmos. Chapter 1: The Cosmos and the Microworld Mathematical laws underpin the fabric of our universe – not just atoms, but galaxies, stars, and people. Six numbers seem especially significant. N, the ratio of the strength of the electrical forces that hold atoms together to the force of gravity. 1036, a few less zeroes and we wouldn’t be here. , 0.007, defining how firmly atomic nuclei bind together and how all the atoms on Earth were made. If it were 0.006 or 0.008, we would not be here. , the relative importance of gravity and expansion energy in the universe. Too high and the universe would have collapsed long ago; too low and no galaxies or stars would have formed. 5
, the dark energy effect. It is very small (surprising to theorists). Otherwise galaxies and stars would not have formed. Q, the ratio of two fundamental energies, about 1/100,000. If it were smaller, the universe would be inert and structureless; if much larger, it would be a violent place where no stars or solar systems could survive. The number of spatial dimensions in our world, 3. Life couldn’t exist if it were 2 or 4. So far, we can’t predict any of these from the values of others. Each plays a crucial and distinctive role in our universe. Together they determine how the universe evolves and what its internal potentialities are. If any one were ‘untuned’, there would be no stars and no life. Rees lists three options: just a brute fact or coincidence, the providence of a benign Creator, or just one of an infinity of universes. In the others the numbers may be different and not tuned. [Hawking (A Brief History of Time) suggests that if the initial event occurred in just the right way, maybe the explanation of the rate of expansion just falls out and so did not have to be carefully set. He doesn’t address the other parameters, but one could imagine that if we get a deeper knowledge of the laws of physics, we could find that these parameters had to be this way and were not set independently to amazing values. (Of course, there is still the question of why the laws were such as to make all this so perfect).] It is astonishing that a universe whose starting point is so ‘simple’ that it can be specified by just a few numbers, can evolve into our intricately structured cosmos. Lengths spanning sixty powers of ten (such an enormous range) are actually a prerequisite for an ‘interesting’ universe. A universe that didn’t involve large numbers could never evolve a complex hierarchy of structures: it would be dull, and certainly not habitable. There must be long timespans as well. Processes in an atom may take a millionth of a billionth of a second to be completed; the complex processes that transform an embryo into blood, bone and flesh involve a succession of cell divisions, coupled with differentiation, each involving thousands of intricately orchestrated regroupings and replications of molecules. It has taken 4.5 billion years for the emergence of human life here on Earth. Even before our Sun and its planets could form, earlier stars must have transmuted pristine hydrogen into carbon, oxygen, and the other atoms of the periodic table. Creatures like us require special conditions to have evolved. Einstein expressed amazement that the laws of physics, which our minds are somehow attuned to understand, apply not just here on Earth but also in the remotest galaxy. All parts of the Universe seem to be evolving in a similar way, as though they shared a common origin. Without this uniformity, cosmology would have gotten nowhere. [The simplest approach is to assume that all the Universe created in the Big Bang is the same, just like the large part we can see, and was created in this single event, not that there are an infinity of them.] There are no theoretical bounds on the extent of our Universe. It may stretch not just millions of times further than our currently observable domain, but millions of powers of ten further. It may itself be just 6
one of a possibly infinite ensemble. This ‘multiverse’ concept, although speculative, is a natural extension of current cosmological theories. The physical laws and geometry could be different in other universes [but we know of no way to observe this]. Chapter 2: Planets, Stars, and Life Because there are so many stars and so many planets, we should not be surprised that we developed near a stable, long-lived star on a planet with the right conditions. Likewise, there may be innumerable other universes that we cannot observe because the light from them cannot reach us. In most of them, the six numbers could be different, and only a few would be ‘well tuned’ for life. *In this class, we’ll discuss additional amazing things besides these six numbers.] Chapter 3: N Gravity is amazingly feeble compared with the other forces that affect atoms. The gravitational attraction between protons is 36 powers of 10 more feeble than the electrical forces. Gravity gains in larger objects because electrical positive and negative forces are balanced. Even when we are ‘charged up’ so that our hair stands on end, the imbalance is less than one charge in a billion billion. It is because gravity is so weak that a typical star like the Sun is so massive. If gravity were much weaker, it would not compete with the pressure and could not squeeze the material sufficiently to ignite nuclear fusion. [Bigger stars would be necessary to get fusion going. If huge mega stars were needed to provide fusion like the Sun does, for a long life, it is hard to imagine how mega mega stars could produce the elements necessary for life and then to have these mix with the gas that is needed for the life-producing stars.] What would happen if gravity were, say, ‘only’ 1030 times feebler than the electric forces? Objects would not need to be so large before gravity became competitive with the other forces. The number of atoms needed to make a star would be a billion times less in this imagined universe. Planet masses would also be scaled down by a billion. Insects would need thick legs to support them, and no animals could get much larger without being crushed by gravity. Galaxies would be much tinier, and stars would be densely packed. This would preclude stable planetary systems, because the orbits would be disturbed by passing stars. Even worse for complex ecosystems, instead of living for ten billion years, a typical star would live for about 10,000 years. [If gravity were significantly stronger, stars the size of the Sun would be much more compressed, and so rather than burning hydrogen for a long time, they would be like massive stars that quickly generate more complicated elements and live short lives. Then the only stars available for life would be much smaller stars than the Sun, but they would not live very long as they would not have much material for long-term fusion burning. ] Nothing as complex as humankind could have emerged if N were much less than 1,000,000,000,000,000,000,000,000,000,000,000,000. Chapter 4:
Without supernovae, we would never have existed….The place of each atom in the periodic table depends on the number of protons in its nucleus. Carbon is number 6 in the table; its nucleus contains 6 protons. The most common form of carbon, 12C, contains 6 neutrons as well. Isotopes with 7 or 8 neutrons are designated by 13C and 14C . Helium nuclei have twice the electric charge of hydrogen (two protons), so they need to collide faster to overcome the fiercer electric repulsion, and this demands a higher temperature. When the star’s central hydrogen has all been converted into helium, the core is pulled inwards and is squeezed until it is much hotter. When the helium is used up, the star contracts and heats up still more. The Sun won’t get very far with this, but in the center of more massive stars, temperatures can reach a billion degrees. They release energy by producing carbon, oxygen, neon, sodium, silicon, etc. Iron, which has 26 protons, is very tightly bound, and energy must be added (rather than being released) to build up still heavier nuclei. So when the core is iron, the star reaches an energy crisis. The star implodes, and then rebounds. The star is like an onion skin, with different elements in layers progressing outward. A supernova is the result, and the debris from the exploded star is thrown into space. Oxygen is the most common element generated, followed by carbon, nitrogen, silicon, and iron. The calculated proportions agree with those observed on Earth. In the intense heat of the supernova collapse, the rest of the observed elements are formed. So carbon and oxygen are common here on Earth, but gold and uranium are rare. The Earth, and we ourselves, are the ashes from ancient stars. Our galaxy is an ecosystem, recycling atoms again and again through generations of stars. Hydrogen and helium are by far still the most dominant atoms, but heavier atoms are overrepresented on Earth because hydrogen and helium are volatile gases that escaped from the inner planets [most of it]. Accounting for the proportions of the different atoms, and realizing that the Creator didn’t need to turn 92 different knobs, is a triumph of astrophysics. The essence depends on just one number: the strength of the force that binds together the particles (protons and neutrons) that make up an atomic nucleus. The number, , means that when hydrogen fuses into helium, 0.7% of the mass goes into energy, mainly heat. The nucleus of the helium atom has 99.3% of the mass of the two protons and two neutrons that go to make it. So the Sun converts 0.007 of its mass into energy when it fuses hydrogen into helium. This number determines how long stars can live. What if the nuclear ‘glue’ were weaker, so that was 0.006. A proton could not be bonded to a neutron and deuterium would not be stable (used in the path from hydrogen to helium). The path to helium formation would be closed off. Stars would have no nuclear fuel, and would deflate and cool. What if was 0.008? We couldn’t have existed, because no hydrogen would have survived from the Big Bang. In our actual universe, two protons repel each other so strongly that the nuclear ‘strong interaction’ force can’t bind them together without the aid of one or two neutrons (which add to the nuclear ‘glue’, but, being uncharged, exert no extra electrical repulsion). If was 0.008, two protons would have been able to bind together directly. This would have happened readily in the early universe (that was very dense), and no hydrogen would remain to provide the fuel in ordinary stars, and water could never have existed. 8
So any universe with complex chemistry requires to be in the range 0.006-0.008. It’s actually even more restrictive than this. English theorist Fred Hoyle stumbled on this when he was calculating exactly how carbon and oxygen are synthesized in stars. Carbon is made by combining three helium nuclei. There isn’t much chance of all three coming together simultaneously, so the process happens via an intermediate stage where two helium nuclei combine into beryllium (four protons and four neutrons) before combining with another helium nucleus to form carbon. The beryllium nucleus is unstable. It would decay so quickly that there is little chance of the third helium nucleus combining. So how does carbon ever arise? It turns out that a special feature of the carbon nucleus, namely the presence of a ‘resonance’ with a very particular energy, enhances the chance that a beryllium will grab another helium nucleus in the brief interval before it decays. (Hoyle predicted this resonance before it was found). This seeming ‘accident’ of nuclear physics allows carbon to be built up, but no similar effect enhances the next stage in the process where carbon captures another helium nucleus and turns into oxygen. A shift by 4% in the nuclear force would severely deplete the amount of carbon that could be made. Hoyle said that our existence would have been jeopardized by a change of a few percentage points in . [A 4% variation means could vary between 0.00672 and 0.00728 (if 0.007 is the exact right number)]. Chapter 5: Beyond our Galaxy The texture of our universe on large scales is important. It might not seem to matter whether our galaxy contained a quadrillion stars, or ‘only’ a million, rather than the hundred billion that we observe; or whether it belonged to a cluster containing millions of other galaxies rather than just a few. But a universe much rougher than ours wouldn’t be hospitable to stars and planets. And a universe that is too smooth would be blandly uninteresting: no galaxies and no stars, with the material thinly spread. Our universe is expanding. Astronomers used to think that the universe was static, but a static universe doesn’t work because it would immediately start contracting due to gravity. Our universe is like a cubic lattice where all the rods lengthen at the same rate. All the vertices recede from each other in accordance with Hubble’s law. Space stretches as light travels through it, and we see a Doppler effect. It is possible to date the oldest stars in the Milky Way, and in other galaxies, by comparing their properties with the outcome of computations of how stars evolve. The oldest are about 10 billion years old, consistent with the view that the universe has been expanding for a bit longer than that. We see distant regions not as they are now but as they were a long time ago, when the universe was more compressed. The gravitational pull that everything in the universe exerts on everything else causes deceleration; another force may be at work that tends to speed up the expansion. The best evidence that everything really emerged from a dense ‘beginning’ is that there is an ‘afterglow of creation’, the cosmic microwave background. This background radiation matches what is expected if the universe began in this way. It is a really hot, high-energy, emission, stretched to the microwave part of the spectrum by the universe’s expansion over such a long period of time. Measurements of the cosmic microwave background confirms beyond reasonable doubt that everything in our universe was once a compressed gas, hotter 9
than the Sun’s core. The intense radiation from the original fireball, although cooled by expansion, still pervades the whole universe. Why weren’t the primordial nuclei of hydrogen all transmuted to heavy elements during the Big Bang? Fortunately, the first few minutes of expansion didn’t allow enough time for nuclear reactions to ‘process’ any of the primordial material into iron, nor even into carbon, oxygen, etc. The reactions would turn about 23% of the hydrogen into helium and a trace of lithium, but nothing higher up on the periodic table. Some deuterium (‘heavy hydrogen’) is also produced. And in fact we do observe the expected percentage of hydrogen, helium, and deuterium in the various stars and galaxies. Chapter 6:
and Dark Matter
, the ratio of actual universe density to the critical density, is a crucial number. The critical density is the difference between a universe that expands forever and one that falls back into a ‘big crunch’. With just what we can see, the universe would be open (expand forever). We’ve discovered dark matter, because the motion of stars around their galaxies requires much more mass than we observe, and because the bending of light from behind galaxies implies much more mass than we see (about 10 times as much). We don’t know what dark matter is. But another puzzle is: why are there any atoms? Why isn’t our universe solely composed of dark matter? Also, why does our galaxy consist of matter and not antimatter? The simplest universe one might imagine would have started with particles and antiparticles mixed up in equal numbers. Our universe luckily wasn’t like that. If it had been, all the protons would have annihilated with antiprotons during the dense early stages. No atoms, no stars, no galaxies. This was first pointed out by the Soviet physicist Andrei Sakharov. Physicists have discovered that particles and antiparticles aren’t exactly mirror images of each other (but close), so it may be possible to explain the difference in particles versus antiparticles. Here is another fine tuning, but one we understand less (more of a conjecture). We, and the visible universe around us, may exist only because of a difference in the ninth decimal place between the numbers of quarks and antiquarks. (This is not one of the six numbers discussed in this book because we know less about it.) It turns out that had to be very, very close to 1.0 in the early Universe. If it were slightly less than 1 in the early Universe, eventually kinetic energy would completely dominate. The Universe would expand forever, but there would be no chance for life. If much more than 1, gravity would soon get the upper hand and bring the expansion to a halt, leading to a Big Crunch. It turns out that the initial cannot have differed from 1.0 by more than one part in a million billion (1015) in order that the Universe should now, after over 10 billion years, be still expanding and with a value that has not departed wildly from 1.0.
Chapter 9 will discuss an explanation (inflation) for why the expansion and the universe look the same in all directions, and for the fine tuning of in the early universe. Chapter 7:
Is the Expansion Slowing or Speeding?
We observe the speed of expansion by measuring the spectrum of the light, and by having some idea of how far away the object is. Type 1a supernovae are regarded as ‘standard candles’. In addition, the brightening and fading of a supernova is like a clock, and the slowdown of this ‘light curve’ is proportional to the redshift, which is what we expect if it is receding. In 1998, two separate teams had discovered about a dozen distant supernovae and announced that the expansion seemed to be speeding up. The case for a nonzero is strong but not overwhelming. [There is more evidence for this today.] So there must be an extra force that causes a ‘cosmic repulsion’ even in a vacuum, an ‘antigravity’. Einstein 11
had a term like this, labeled , because he felt the universe should be static, with a repulsion force counteracting gravity. He removed this term later because he knew of no reason for it. But it is back. Empty space is not simple, but we don’t understand it on a tiny scale. String theory says that empty space is a seething tangle of strings, manifesting structures in extra dimensions. is very small. It is much smaller than theories accounting for it predict (based on string theory), by many orders of magnitude. It is weak enough that it only competes with the very dilute gravity of intergalactic space. This cosmic number describes the weakest and most mysterious force in nature. A much higher value of would have had catastrophic consequences: gravity would have been overwhelmed early on, and there would have been no galaxies. Our existence requires a small . It seems likely at this point that the expansion will continue indefinitely [a beginning, but no end!]. Chapter 8: Primordial ‘Ripples’; the number Q “The Universe was brought into being in a less than fully formed state, but was gifted with the capacity to transform itself from unformed matter into a truly marvelous array of structure and life forms.”-St. Augustine. If our Universe had started off completely smooth and uniform, it would have remained so throughout its expansion. No galaxies, no stars, no periodic table, no complexity, no people. Slight irregularities make a crucial difference, because density contrasts amplify during the expansion. If we look at galaxies and clusters of galaxies, and ask how tightly they are bound together, that is how much energy would be needed to break up and disperse them, the answer is about one part in a hundred thousand (as a proportion of their ‘rest-mass energy’, mc2). This is the number Q. This number is small, and means that gravity is actually quite weak in galaxies and clusters. In the microwave background radiation, slightly overdense regions, expanding slower than average, are destined to become galaxies or clusters of galaxies. The expected effect is about one part in 100,000 (same as Q). NASA’s COBE satellite and follow-up measurements showed that non-uniformities in the microwave background temperature are at a level of one part in 100,000. This is really remarkable; if a stone was spherical to one part in 100,000, you would be perplexed by the overall smoothness. Inflation (Chapter 9) is our best theory of this. The starting point of the expanding universe is described by , , and Q. The outcome depends sensitively on these three key numbers, imprinted (we are not sure how) in the very early universe. If Q were smaller (and the other numbers were the same), galaxies would be anemic (smaller and looser) structures in which star formation would be slow and inefficient. Processed material would be blown out of the galaxies rather than being processed into new stars and planets. If Q were smaller than 1 in a million, gas would never condense into gravitationally bound structures at all. If Q were substantially larger, the universe would be a turbulent and violent place. Instead of stars, we’d have vast black holes. Even if some stars formed, they would be packed so tightly that they wouldn’t be able to form stable planetary systems (similar to near the center of our galaxy). 12
[From the Goddard Space Flight Center “7-year WMAP [Wilkinson Microwave Anisotropy Probe] Results”; results obtained after the book was written: “The newly-released WMAP data are now sufficiently sensitive to test dark energy, providing important new information with no reliance on previous supernovae results. The combination of WMAP and other data** limits the extent to which dark energy deviates from Einstein's cosmological constant. The simplest model (a flat universe with a cosmological constant) fits the data remarkably well. The new data constrain the dark energy to be within 14% of the expected value for a cosmological constant, while the geometry must be flat to better than 1%. The simplest model: a flat universe with a cosmological constant, fits the data remarkably well.”
** Includes: the current expansion rate of the universe (the Hubble constant) and the large-scale galaxy distribution (the baryon acoustic oscillations).]
Chapter 9: What Lies Beyond Our Horizon? “Then assuredly the world was made, not in time, but simultaneously with time.” -St. Augustine. Defenses of the Big Bang theory: --No objects discovered with helium much less than 23% of the hydrogen abundance. --The background radiation matches the expected spectrum. --Nothing discovered about neutrinos that is incompatible with the Big Bang. --The deuterium abundance is in line with the amount expected. --The value of Q is compatible with the current structure of the universe [and of course, the expansion of the universe]. At the beginning, the mysteries of the cosmos and the microworld overlapped. We don’t understand these mysteries because we haven’t figured out how to combine quantum mechanics (microworld) with general relativity (cosmos). The Large Hadron Collider will not be able to attain energies at the levels that existed in the universe in the first 10-14 seconds. Lots happened during that short time. Why does our huge Universe have such uniformity, and physical laws that appear to be the same everywhere we can observe? Why is the Universe expanding in the special way we’ve discussed? If all parts of our present Universe had synchronized very early on and then accelerated apart, this could explain it. This is called ‘inflation’. There was a very rapid expansion, a repulsion, that occurred when the entire Universe was a microscopic size. The fierce repulsion that drove inflation must have switched off 13
[at just the right moment!], allowing the Universe, having by then enlarged enough to encompass everything we now see, to embark on its more leisurely expansion. At the moment, this offers the only credible explanation for why our Universe is so large and so uniform. If a wrinkled surface is stretched by a huge factor, then the curvature reduces until any deviations in flatness are imperceptible. The analog of ‘flatness’ in cosmology is an exact balance between gravitational energy and expansion energy. Also, microscopic ‘vibrations’, imprinted when our Universe was smaller than a golf ball, inflate so much that they now stretch across the Universe, constituting the ripples that develop into galaxies and clusters of galaxies. By studying ‘gravity waves’, we may eventually be able to learn more about this early period. Theorists may, some day, be able to write down fundamental equations governing physical reality. But physics can never explain what ‘breathes fire’ into the equations, and actualizes them in a real cosmos. The fundamental question of ‘Why is there something rather than nothing? remains the province of philosophers. What about beyond our observable Universe? A drastic change only just beyond our horizon would be unlikely; on the other hand, we have no warrant to extrapolate all the way to infinity. Inflation dramatically enlarges our perspective on the Universe. The Universe may be so much larger than what we can see, that a succession of views of factors of 10 in size (beyond what we can see) may require millions of frames before reaching the end. Even this colossal Universe might not be everything; the Big Bang could be one event in an infinite ensemble. This gets pretty quickly into speculation. Chapter 10. Three dimensions One consequence of our 3-dimensional universe is that forces like gravity and electricity obey an inverse square law. If we were in four dimensions, they would obey an inverse cube law, and orbits would not be stable (no Sun, no planets, no galaxies, no stable electrons in atoms). Two dimensions doesn’t work either: there could not be a complicated network without the wires crossing; or an object with a channel through it (like a digestive tract for example) without dividing it in two. There are other reasons a 2-D universe wouldn’t work. *Rees discusses this, but doesn’t call it out as a separate fine tuning, the rate of expansion of the universe.] If our universe had remained at a temperature of a billion degrees for a long time, or if nuclear reactions had happened faster, all the atoms would have been processed into iron. Fortunately, the expansion was fast enough to quench nuclear reactions before they could do more than convert 23% of the hydrogen into helium. [no long-lived stars otherwise] A perspective on string theory: “In the present era Edward Witten, the currently acknowledged intellectual leader of mathematical physics, has said that ‘good wrong ideas are extremely scarce, and good wrong ideas that even remotely rival the majesty of string theory have never been seen’.” *Note the intuition physicists have that the theories should be ‘elegant’—why?] There are other reasons for being optimistic about string theory. Einstein’s theory of general relativity is inescapably built into superstring theory. The long-sought synthesis between gravity and the quantum principle should thus 14
naturally emerge. The calculated entropy of black holes agrees precisely with that calculated from superstring theories. Chapter 11. Coincidence, Providence, or Multiverse? Our universe is governed by laws that permit immensely varied consequences. For example, it is a straightforward consequence of their size that stars have lifetimes that are enormously long, allowing time for evolutionary processes to unfold on suitable planets in orbit around them. We’ve already discussed a number of aspects of the various universal laws. This chapter talks about some of the amazing complexities of our Universe. Everything may be the outcome of processes at the subatomic level, but even if we know the relevant equations governing the microworld, we can’t, in practice, solve them for anything more complex than a single molecule. Even if we could, the resultant explanation would not be enlightening. To bring meaning to complex phenomena, we introduce new ‘emergent’ concepts. For example, the turbulence and wetness of liquids, the textures [and strength] of solids, which arise from the collective behavior of atoms. [The turbulence and wetness of water is necessary for life.+ There are lots more of these ‘emergent’ concepts, for example natural selection. [Amazing that, from the simple rules of the subatomic world, all these complex things necessary for life can emerge.] [In his book, “The Creator and the Cosmos”, Hugh Ross gives a table, pp. 118-121, with 26 items that he characterizes as evidence of the fine-tuning of the universe. I am somewhat suspicious of this, however, since the whole book is about proving the God of the Bible is needed (unlike Rees’ book) because everything is just too unlikely without God stepping in. Besides, later he explains why Earth had to be designed specifically by God because it is just too perfect. That argument is fallacious, however, because with hundreds of billions of planets in this galaxy and hundreds of billions of galaxies, some of them are surely good ones. It’s not surprising that we are on one of the good ones. (He wrote this before scientists started finding planets around other stars and conjectured that there are probably not very many.) Regardless, among his 26 items, there are many more than the 6 mentioned by Rees. Some of these are no big deal, but many are probably legitimate. I suspect that Rees would say that some of these are simply consequences of the more fundamental laws and numbers. But in that case why should the few fundamental good numbers lead to a bunch of other consequences that are needed for life? Alternatively, maybe some are not as clear or as restrictive. Still, it is an amazing thing that the laws fit together in such a way as to allow for all the amazingness that is our Universe.] Here is Ross’s list. Many of these are valid; many follow from Rees. Most make sense. He got this list from a large list of sources. No. 12 is certainly not valid. I suspect 25 is probably just conjecture (it relates to how many Type 1A supernovae there are, although certainly if the differences were huge we’d be in trouble).