Why is there life? - Martin Rees The Universe is unlikely. Very unlikely. Deeply, shockingly unlikely.
"It's quite fantastic," says Martin Rees, Britain's Astronomer Royal, waving a hand through the steam rising from his salmon-and-potato casserole...
In his newest book, Just Six Numbers, Rees argues that six numbers underlie the fundamental physical properties of the universe, and that each is the precise value needed to permit life to flourish. In laying out this premise, he joins a long, intellectually daring line of cosmologists and astrophysicists (not to mention philosophers, theologians, and logicians) stretching all the way back to Galileo, who presume to ask: Why are we here? As Rees puts it, "These six numbers constitute a recipe for the universe." He adds that if any one of the numbers were different "even to the tiniest degree, there would be no stars, no complex elements, no life." ...
Faced with such overwhelming improbability, cosmologists have offered up several possible explanations. The simplest is the so-called brute fact argument. "A person can just say: 'That's the way the numbers are. If they were not that way, we would not be here to wonder about it,' " says Rees. "Many scientists are satisfied with that." Typical of this breed is Theodore Drange, a professor of philosophy at the University of West Virginia, who claims it is nonsensical to get worked up about the idea that our life-friendly universe is "one of a kind." As Drange puts it, "Whatever combination of physical constants may exist, it would be one of a kind."
Rees objects, drawing from an analogy given by philosopher John Leslie. "Suppose you are in front of a firing squad, and they all miss. You could say, 'Well, if they hadn't all missed, I wouldn't be here to worry about it.' But it is still something surprising, something that can't be easily explained. I think there is something there that needs explaining."
Meanwhile, the numbers' uncanny precision has driven some scientists, humbled, into the arms of the theologians. "The exquisite order displayed by our scientific understanding of the physical world calls for the divine," contends Vera Kistiakowsky, a physicist at the Massachusetts Institute of Technology. But Rees offers yet another explanation, one that smacks of neither resignation nor theology. Drawing on recent cosmology- especially the research of Stanford University physicist Andrei Linde and his own theories about the nature of the six numbers- Rees proposes that our universe is a tiny, isolated corner of what he terms the multiverse.
The idea is that a possibly infinite array of separate big bangs erupted from a primordial dense-matter state. As extravagant as the notion seems, it has nonetheless attracted a wide following among cosmologists. Rees stands today as its champion. "The analogy here is of a ready-made clothes shop," says Rees, peeling his dessert, a banana. "If there is a large stock of clothing, you're not surprised to find a suit that fits. If there are many universes, each governed by a differing set of numbers, there will be one where there is a particular set of numbers suitable to life. We are in that one."
A review of the book to name the six numbers:
So what are the six numbers? One is the number of dimensions we live in: three. The rest are, at least at first sight, more obscure. For the record, they are N, the ratio of the strength of gravity to that of electromagnetism; epsilon, the ratio of mass lost to energy when hydrogen is fused to form helium; Omega, describing the amount of dark matter; lambda, the cosmological constant; and Q, related to the scale at which the universe looks smooth.
Here’s another set of constants from my http://sparc.airtime.co.uk/users/station/cosmic.htm There are quite a few constants in physics which have values that look to have been plucked out of thin air, seemingly with no reference to anything else. It is interesting to see how a small change in one or other of them would make life totally impossible on Earth, or anywhere else in the universe. It almost seems as though the laws of physics themselves are precisely 'tuned' so as to favour the appearance of life somewhere...
Gravity. Suppose gravity was stronger or weaker than it is.
The forces show a very wide spread of strengths, which our Universe depends on to greater or lesser degrees. Suppose gravity was stronger, by a factor of 10^10. This seems quite a lot, but it would still be the weakest force, just 10^-28 of the strength of electromagnetism. The result would be that not as many atoms would be needed in a star to crush its core to make a nuclear furnace. Stars in this high-gravity universe would have the mass of a small planet in our Universe, being about 2km in diameter. They would have far less nuclear fuel as a result, and would use it all up in about one year. Needless to say, it is unlikely that any life would evolve or survive long under such conditions. Make gravity substantially weaker on the other hand, the gas clouds of hydrogen and helium left after the Big Bang would never manage to collapse in an expanding universe, once again leaving no opportunity for life to emerge
Water. What if ice was denser than water, as are most solids compared with their liquids?
These and other odd features of water are a consequence of the hydrogen bond - the attraction of the electron-rich oxygen atoms of water molecules for the electron-starved hydrogen atoms of other water molecules. This in turn is a function of the precise properties of the oxygen and hydrogen atoms, which also determines the H-O-H bond angle of 104.5 degrees - only slightly less than the ideal tetrahedral angle of 109.5 degrees. It is (incidentally) the hydrogen bond which holds together the two strands of DNA. It is also the hydrogen bond which is responsible for the crystalline structure of ice, which is in the form of an open lattice: this makes ice less dense than the liquid. As a result, ice floats. If ice was denser than its liquid form (as is the case with most other substances) then it would collect at the bottom of lakes and oceans, and eventually build up until the world was frozen solid. As it is, it forms a thin insulating sheet which prevents evaporation and keeps the waters below warm.
Carbon Resonance. A "put up job" according to Professor Sir Fred Hoyle.
A carbon-12 nucleus is made from the near-simultaneous collision of three of these helium-4 nuclei [within stars]. Actually, what happens is that two helium-4 nuclei merge to make beryllium-8, but beryllium-8 is so unstable that it lasts only 10^-17 of a second, and so a third alpha particle (which is what a helium nucleus is) must collide and fuse with the beryllium nucleus within that time. Not only is this triple encounter a relatively unlikely event, but any such unstable beryllium nuclei ought to be smashed apart in the process. Therefore, it should be expected that carbon itself (and consequently all heavier elements) would be rare in the Universe. However, the efficiencies of nuclear reactions vary as a function of energy, and at certain critical levels a reaction rate can increase sharply - this is called resonance. It just so happens that there is a resonance in the three-helium reaction at the precise thermal energy corresponding to the core of a star...
So if there was another resonance at work here all the carbon would be quickly processed into oxygen, making carbon very rare again. In fact, it turns out that there is an excited state of oxygen-16 that almost allows a resonant reaction, but it is too low by just 1%. It is shifted just far enough away from the critical energy to leave enough life-giving quantities of carbon untouched.
Supernovae. How critical are the properties of neutrinos in dispersing a star's heavy elements through space?
This ejection of rich material into space is carried by an enormous flux of neutrinos generated in the explosion. The neutrino is normally such a ghostly particle that it could pass right through many light-years of solid lead, unaffected. In blasting apart a supernova, its precise interactivity (or lack of it) is such that it should have enough time to reach the stellar envelope before dumping its energy and momentum, but not so much time that it should escape. This property is partly a function of the weak force in a complex relationship which must be just as we observe it, to one part in a thousand. If the star's matter was not so effectively redistributed, it would simply collect about the dead star or fall back. It would not be available for new stars to make planets capable of bearing life. A universe without our particular kind of neutrinos would be a dead universe.
Strong Nuclear Force. What would have happened if the strong nuclear force had been different by just a few percent?
If the strong force had actually been just 13% stronger, all of the free protons would have combined into helium-2 at an early stage of the Big Bang, and decay almost immediately into deuterons. Then pairs of deuterons would readily fuse to become helium-4, leaving no hydrogen in the Universe, and so no water, and no hydrocarbons… An increase in the strong force of just 9% would have made the dineutron possible. On the other hand a decrease of about 31% would be sufficient to make the deuteron unstable, and so remove an essential step in the chain of nucleosynthesis: the Universe would contain nothing but hydrogen, and again life would be impossible.
Flatness. What if the Universe was not so precisely balanced between ultimate collapse and unending expansion?
The Universe has been expanding for 15 billion years at a rate fantastically close to a knife-edge line between recollapse and ultimate dispersion. Even at this point in time we can not tell for sure which side of the line we are on: whether Big Crunch or Heat Death is the ultimate fate of the Universe. It is lucky for us that the Universe is flat in this way since the tiniest deviation from its initial value (which must have been exact to one part in 10^35) would have led to a rapid Big Crunch or cosmic dissipation. And, as usual, no life.
Proton-Neutron Mass Difference. Suppose protons and neutrons were not almost equal in mass.
The difference in mass between a proton and a neutron is only a little greater than the mass of the relatively tiny electron (which has about 1/1833 the mass of a proton). Calculations of relative particle abundances following the first second of the Big Bang, using Boltzmann's statistical theorem, show that neutrons should make up about 10% of the total particle content of the Universe. This is sensitive to the proton:neutron mass ratio which is (coincidentally) almost 1. A slight deviation from this mass ratio could have led to a neutron abundance of zero, or of 100%, the latter being most catastrophic for the prospects of any life appearing. Even if there were 50% neutrons, all of them would have combined with the remaining protons early in the Big Bang, leading to a Universe with no hydrogen, no stable long-lived stars, and no water. And no life
Antimatter. Why is there any matter in the Universe at all, but no appreciable quantities of antimatter?
In the colossal energies of first millionth of a second of the Big Bang, particles and their anti-particles would have been created and destroyed in pairs, equally. Once the temperature fell sufficiently, photons could no longer be readily converted into particle-antiparticle pairs, and so they annihilated each other. The present ratio of photons to protons, 'S', is 10^9, which suggests that only one proton (and one electron) per billion escaped annihilation
Dimensionality. What if there were more or fewer than three dimensions of space and one of time?
One consequence of having a three-dimensional space is the inverse square law of forces. In particular, only in such a space are stable planetary orbits possible: more or fewer dimensions introduce instability. By a series of complex arguments it can also be shown that stable atoms and chemistry also require three dimensions of space, and the distortion-free propagation of any wave-based signal also requires exactly three dimensions of space.
Of course if our Universe was actually hostile to life, we couldn't be here to remark on the fact. This is the basis of the Anthropic Principle. To put it another way: without the right kind of physics you don't get physicists. http://www.spacedaily.com/news/life-01o.html
Moreover, the Sun's circular orbit about the galactic center is just right; through a combination of factors it manages to keep out of the way of the Galaxy's dangerous spiral arms. Our Solar System is also far enough away from the galactic center to not have to worry about disruptive gravitational forces or too much radiation. When all of these factors occur together, they create a region of space that Gonzalez calls a "Galactic Habitable Zone." Gonzalez believes every form of life on our planet - from the simplest bacteria to the most complex animal - owes its existence to the balance of these unique conditions.
Because of this, states Gonzalez, "I believe both simple life and complex life are very rare, but complex life, like us, is probably unique in the observable Universe."
Going back to the Martin Rees article, there are basically three reactions to these stunning improbabilities: As a #1 – I consider #3 to be giving up. Conversely, as a #3 you might consider #1 to be giving up. But perhaps we can both agree that #2 ought to be pursued?
