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Why does the Universe appear to be made for us? |
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(or: why are our legs just long enough to reach the ground?) |
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| Then There Were Eight Pluto's demotion made us angry, confused, dismissive, and sad. We'd broken the cardinal rule--we'd gotten emotionally involved. by Jonah Lehrer January 21, 2007 Illustration by Adam Billyeald At first, it seemed like Pluto might pull through. On August 15, when word leaked out that the Planet Definition Committee had proposed letting Pluto persist as a bona fide planet (and not just as a "dwarf planet"), it looked like a victory for the cosmic underdog. Pluto, the runt of our solar system, was going to be okay. |
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The astronomers admitted that this act of generosity wasn't particularly scientific. After all, if Pluto were discovered today, it would be classified as just another frozen rock trapped within the orbit of Neptune. But the committee decided to overrule the cosmological facts: Pluto should remain a planet because everybody already thinks it's a planet. As one scientist lamented, "There could be a public relations disaster if we just throw out Pluto, especially if we don't even give it a tip of the hat." For the most part, astronomers were simply a victim of their own success. Their old model of the solar system had become a sturdy cultural icon. The nine planets, all of them anthropomorphized and named for Roman and Greek gods, were now affixed to T-shirts, posters, screensavers and mobiles. Odd mnemonics were invented so that their order could be remembered ("My Very Efficient Metal Jaguar Sometimes Uses No Petrol"). Astrologers used the planets to forecast the future. (Pluto, for example, rules Scorpio.) In a universe full of dark matter and hungry black holes, our genteel neighborhood had become a source of reassurance, a suburb of space that seemed ordinary and safe. Beyond Pluto lay nothing but interstellar emptiness, the nameless sprawl of the Milky Way. Unfortunately, all it takes is a single new observation—a faint orangeish dot slowly moving against a quilt of stars—and a scientific model taught to generations of schoolchildren can come crashing down. In July 2005 Mike Brown, an astronomer at Cal-Tech, announced that he had found a "planet-like object" that was bigger than Pluto. This object resided in the Kuiper Belt, a swath of icy debris left over from the formation of the solar system. Brown called this new object Eris, after the Greek goddess of discord and strife. The name was prophetic. The discovery of Eris (its technical name was 2003 UB313) started an astronomical brawl. If Eris isn't a planet, then why is Pluto? After all, Pluto is smaller than Eris. Either the solar system had to be expanded, or Pluto had to go. For astronomers, the debate was embarrassing. Why was there no rigorous way to distinguish Pluto from its Kuiper Belt cousins? Shouldn't astronomers know what a planet is? Just where does our solar system end? This dispute led the International Astronomical Union (IAU) to form the Planet Definition Committee, which decided that Pluto and Eris, in addition to more than 40 other Kuiper Belt objects, were genuine planets, since they were "spherical objects that orbit the sun." Mike Brown called it the "No Ice Ball Left Behind" policy. Alas, most astronomers didn't agree with the committee. At the 2006 IAU meeting held in Prague this past summer, the scientists voted that every planet must also have "cleared the neighborhood around its orbit." Since only spheres with a large mass can achieve such orbital dominance, Pluto was no longer a planet. The scientific bureaucracy had spoken; our solar system had shrunk. Reactions were swift and plentiful. Disney pledged not to rename the cartoon character. The American Federation of Astrologers defiantly announced that "Pluto is still an effective energy source whose influence is felt on this earth." Gerry Wheeler, executive director of the National Science Teachers Association, struck a reassuring tone: "Pluto's still the same Pluto. It's still up there doing exactly the same thing." Planetarium gift shops were suddenly stocked with shelves of obsolete merchandise. Legions of disappointed children—"Pluto has the best name!"—organized a letter-writing campaign demanding that the IAU decision be overturned. The Smithsonian's Pluto marker became the site of a makeshift memorial, complete with melancholy condolence notes. On the one hand, demoting Pluto was an easy scientific decision. Our cultural kitsch should have no bearing on the reality of the universe. We should strive to see the cosmos as it is: just a swirl of dust and gravity, in which our sun is only a minor star. Sometimes, new knowledge requires us to redraw the celestial lines, to alter the maps that we project onto the dark. But nothing has really changed. Pluto doesn't care what we call it. The pitiless truth is that we aren't at the center of anything, let alone the center of everything. And yet, we can't comprehend all this vastness without seeing it from our particular point of view. There are more stars than grains of sand, which is why every star and planet that we happen to know seem so precious. Scientists might see Pluto as a mass of frozen methane, but we have given that mass a name. We have taken that cold speck of rock and emblazoned it on placemats. The universe certainly doesn't care about us, but we have learned to care about the universe, to invest in it the same emotional meaning that we invest in everything else. It is how we keep ourselves from feeling so alone. So what's the moral of the Pluto affair? Even when it comes to the obscure reaches of our solar system, our science and our culture remain awkwardly entangled. There is no clear line telling us where one ends and the other begins. Our dreams of outer space are drawn from the Hubble telescope and Star Trek, from the equations of cosmology and the bad artistic renderings of the Martian surface. We can't help but think this way, to imagine the galaxies as we would like them to be, full of personable Greek gods and interesting aliens. The public was upset that Pluto is no longer a planet because Pluto was never just a planet: It was also a cartoon character and a zodiac symbol and a small purple dot on our solar-system T-shirt. Amid the vast cosmic vacancy, this, surely, was a speck of light that wasn't anonymous, a spot in the heavens that we pretended to know. It turns out that we didn't know it after all. The place we thought was Pluto is only dwarf planet 134340. |
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| The following points are made by Robin L. Poidevin
(citation below): 1) You are presented with a large urn containing, you are told, 100 table-tennis balls. Removing one of these balls you discover, much to your surprise, that one of them has your name on it. Can you conclude anything about the rest of the balls in the urn? Precisely 100 hypotheses fit the rather limited data, ranging from the hypothesis that only one ball has your name on it (this being the one you happened to pick out) to the hypothesis that all the balls have your name on them. Clearly, you would be unwise to come to any fixed conclusion at this stage, for any of these hypotheses could be true. But are they equally likely? The probability of your picking out a ball with your name on it depends on the proportion of such balls in the urn. So, were there just one ball with your name on it, the probability of your picking it out first time would be 1/100, a rather small probability. In contrast, if all the balls had your name on them, the probability would be 100/100, i.e. 1, making it absolutely certain that your first choice would result in a ball with your name on it. This, surely, makes it more likely that all the balls have your name than that only one does. To put it in more general terms, you would be wise to prefer a hypothesis that makes the observed result very likely to one that makes that result very unlikely. Of course, this judgement is only provisional. As you continue to take balls out of the urn, and observe whether or not they have your name on them, your preferences may change. The point is, however, that your first observation gives you some reason for supposing that the ball you drew out is not unique. 2) Consider another example. You are examining a page of printout from a computer whose function is to generate a completely random sequence of numbers. Your eye is caught by the first line of numbers: 314159265358979323846. They seem oddly familiar. After a moment, you realize that they are the first 21 digits in the expansion of pi. Intrigued, you check the rest of the numbers on the page and discover that they all match the expansion of pi. Now, you do not know whether this is the one and only page that the computer has produced, or whether it is one of millions of pages, the computer having been producing its numbers non-stop for years, and this page has been deliberately selected by someone for your attention. What are you going to assume? If this is indeed the only page of numbers the computer has produced, then it is the most remarkable and unlikely coincidence that it matches exactly the first part of the expansion of pi. On the other hand, if this is just one of millions of pages (and perhaps taken from the printout of one of millions of computers, all generating random numbers simultaneously for years), then it becomes less improbable. So, given the general principle appealed to a moment ago, that we should choose the hypothesis that makes our observation more, rather than less, likely, we have reason to suppose, just on the basis of what we have before us, that this page is not unique -- that it is one of many such pages. As before, our assumptions may change with more data. 3) Now consider a third case, this time not a fictional one. For life to evolve, certainly in anything like the form in which we are familiar with it, the Universe had to have certain features. For example, there had, at some stage, to be carbon available in significant quantities. There also had to be water. The temperature of at least some parts of the Universe had to be relatively stable, and within a certain narrow range (defined by the freezing and boiling points of water), requiring a source (or sources) of warmth that was both stable and remained neither too distant from nor too near to the emerging life-forms. There had to be a significant variety, both of atoms, and of ways in which atoms could combine to form molecules. Both atoms and molecules had to be relatively stable, and yet capable of undergoing reactions with other atoms and molecules to form novel molecules without requiring extraordinary conditions. These features in turn required more fundamental conditions concerning both the internal structure of the atom, forces between objects, and conditions obtaining in the early stages of the universe after the Big Bang (supposing the Big Bang to have actually occurred). Even a slight difference in any of the fundamental physical features of the Universe, such as the forces that bind the components of atoms together, electromagnetic forces, the masses of particles, and the rate of expansion in the early Universe, would have made it impossible for life to have evolved. Some of the details of this story are, it would be fair to say, still in dispute. Yet, even if only part of it is right, the existence of life depends on what has been called the /fine tuning/ of the Universe. That life exists is an indisputable fact. Yet, when we contemplate the huge variety of possible ways in which the Universe could have been physically constituted, and the very narrow range within these possibilities that are compatible with life, that particular outcome -- the emergence of life -- seems almost unimaginably improbable. Are we content with this conclusion? Or do we, as with the cases of the urn and the page of numbers, look for hypotheses that make our observations less improbable? 4) The best-known hypothesis that transforms the probabilities is, of course, that of the existence of God. If the Universe were the outcome, not of blind chance, but of divine design, then it is no longer a remarkable coincidence that the physical constitution of the Universe lies in the very narrow band of possibilities that is compatible with life. Of course a benevolent God would have constituted the universe so that it was compatible with life. Given the existence and nature of God, the emergence of life in the Universe ceases to be almost vanishingly improbable and becomes certain. Some people see the fine tuning of the Universe to be a new argument (or, perhaps, a new variant of an old argument) for the existence of God. But there is another hypothesis that changes the probability of life, one that does not involve a creator, and which some cosmologists are taking seriously: the multiverse hypothesis. 5) According to the multiverse hypothesis, ours is just one of a number -- perhaps a vast number -- of universes, each of which exhibits different physical conditions. Given enough of these universes, a wide range of possible atomic, electromagnetic, and gravitational forces can be realized. Some universes have a Big Bang somewhere in their history, some do not. In some, the expansion of the universe after the Big Bang is very slow, and leads to a Big Crunch. In others, it is very rapid. In some, there are no stable atoms. Others are composed almost entirely of helium. Some may contain only two-dimensional spaces, others four-dimensional. Very possibly, others just consist of empty space and time. The more such universes there are, and the greater the range of physical constitutions realized, the less unlikely it becomes that one of them will contain just the right set of circumstances to permit life. In other words, postulating a multiverse is like postulating that the page of random numbers that just happens to match the expansion of pi is just one of many such pages, produced by many machines, running over many years. As long as our Universe is unique, the fact that it contains life is (the hypothesis of a creator aside) remarkable. But once we see it as one of billions of universes, each with a different physical make-up, the fact becomes less remarkable. Indeed, we may even be tempted to say that, given enough universes, it was inevitable that one should contain the conditions necessary for life. Adapted from: Robin L. Poidevin: Travels in Four Dimensions: The Enigmas of Space and Time. Oxford University Press 2003, p.186. |
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| What chemical formula would accurately
describe an adult human being, in terms of the relative distribution of
elements (including pollutants)? And what might be the formula for the first
alien life form we encounter? New Scientist Dec 05 One's "chemical formula" depends on a number of factors, most notably whether we're talking about a he or a she. Male bodies contain more water than female bodies, which have extra lipids. By weight, oxygen amounts to about two-thirds of the body, followed by carbon at 20 per cent, hydrogen at 10 per cent and nitrogen at 3 per cent. Elements originating from pollutants would only be present in trace amounts. If a human body were broken into single atoms, we would arrive at an empirical formula H15750 N310 O6500 C2250 Ca63 P48 K15 S15 Na10 Cl6 Mg3 Fe1. The relative numbers of atoms in this differ from the composition by weight because atoms have different masses. The composition of an alien life form would depend on two key factors. First, the element that forms the "skeleton" of its macromolecules. All life discovered so far is based on carbon, which can form long chains to which other elements bind. The most likely alternative building blocks for macromolecules would be silicon, phosphorus or nitrogen. Second, the solvent for the biochemical reactions that drive the body. The most likely alternative to water is probably ammonia (NH3) because it can dissolve most organic molecules. It is also liquid well below water's freezing point and is prevalent in space. So an alien life form might be silica and ammonia based. Lauri Suoranta, Espoo, Finland The chemical elements in an adult human are distributed in various molecular and atomic species. An accurate formula could be expressed in the standard form: 7×1025H2O+9×1024C6H12O6+2×1024CH3(CH2)14+ ... and so on. However, such a series would fill a bumper edition of New Scientist and we cannot possibly identify all species. Metabolism, defined as the chemical and energy exchanges in a living body, means that any such chemical formula is continually changing. Having a chemical formula for a process can be useful. If we find all the elements and determine all the mathematical expressions applying to them, the whole process can be determined. But this is not the whole story. Life is characterised by extensive, adaptive self-regulation of its own structural order, and utilises feedback control. An organism uses its resources in its own emergent way. The chemical reactions work, but how they are brought together is a matter of emergent control systems. This means that not only is it impossible to write an accurate formula for a human being, it is unnecessary and can be misleading to try. Life is what it does with chemical species, not just which ones it is made from. I guess the same would go for any alien life form we might encounter. We spend considerable time searching the electromagnetic spectrum to detect their signals, and we receive a lot of signals. But how will we know if any of them are life? Only, I suppose, if they show the characteristic of life: I'm in control, and I'm not solely a bottom-up deterministic chemical process. John Walter Haworth, Exeter, Devon, UK |
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