B00B7H7M2E EBOK, page 30
But the expanding number of people and projects also bears witness to the fact that the coast of our island is growing. There is more room on the shoreline every day, and people are eager to fill it. We’re aware of so many more questions than our ancestors thought to ask, so many more areas that need investigation, so many more trails of evidence to be followed, anomalous details to make sense of, complexity to be unravelled, paradoxes to get our stubbornly intuitive minds around. Ptolemy, Copernicus, Galileo had no idea how mysterious this universe would turn out to be!
If the mystery isn’t lost, perhaps the simplicity and single-mindedness of earlier science is? Has the coastline become too long? Too many names, too many teams, too much specialization, too many directions to go? Has it become nothing else but the exponential accumulation of arcane knowledge – more than anyone can ever fit together in a coherent picture?
Nature herself has made certain it isn’t like that. We have learned that this reaching into the unknown, while it certainly encounters bewildering complications, always seems to grasp simplicity. The story appears to work backwards: at the end of the Hellenistic era, Ptolemy’s explanation of the heavens was as complicated as the mechanics of Disneyland. Copernicus’s description was a move towards simplicity. Kepler’s more so. Newton’s understanding was even more concise. Einstein’s, simpler yet. Observations like those Galileo made with his telescope and those we are making with the Hubble telescope can be puzzling, can seem almost beyond possibility of explanation. Human genius searches for and often finds the beautiful symmetry that underlies and makes sense of the confusion.
We began this book by measuring a windmill, but nine chapters have shown us something subtly different from what my father, my brother and I did that day in Texas. We measured the windmill in an old-fashioned way, with hindsight, if you will. We knew that there were ways to measure it more directly, that its height was a number that could be found out precisely. We were not pushing our mathematics and technology to the limits by any means. The men and women in this saga of cosmic measurement have been doing that and more.
It is a particular fascination of mine to try to put myself in the place of those in earlier centuries who didn’t know what was coming next. When we try to do this with the characters in this book, we are immediately reminded that at every stage of history, it was impossible for them to anticipate that what they could not do, their descendants would be able to do. Perhaps that’s why they were so often willing to go out on a limb, to build on shaky assumptions, to fashion a precarious ladder, to put their faith in ill-understood calibrators . . . because they had no way of knowing whether it ever would be possible to stand on firmer ground.
Whatever the motivations, we have been an impatient and irrepressible lot . . . measuring the parallax of Mars in full knowledge that the uncertainty of the measurement would imperil the results . . . scrambling up the scaffolding to a giant telescope before it was safely braced . . . battling to measure stellar parallax long before the technological moment arrived . . . grasping at Cepheids as handholds into the universe without knowing the distance to even one of them . . . devising a formula for omega while our understanding of what goes into the formula is still worse than vague. In each epoch we have hoped that the impossible would later become easy. But we couldn’t know, and we weren’t willing to wait.
It might all have been less messy had we waited. It might in fact have more resembled what we would like to think the history of cosmic measurement has been. Many accounts give the impression that after Copernicus we ‘knew’ the arrangement of the solar system. After Cassini we ‘had’ the measurements to the planets and ‘were sure of’ the length of the base line afforded by Earth’s orbit. In the 1950s we finally ‘discovered’ the size of the universe. It all moved by solid increments.
It hasn’t been like that. We have groped, guessed, doubted one another, made missteps, built the rungs of the ladder too close together, felt it buckle beneath our feet, fought for a hold. In this book we’ve ended our tale not on the coastline of the island of What We Know but on jetties built far out from shore . . . even on small, frail craft almost out of sight of land . . . at sea in a sieve. But that is nothing new. Indeed that is precisely where we have been in every chapter of this book, at every stage of this history.
The nature we’ve striven to understand has fought back by showing us our place. Sometimes that’s been a severe comeuppance, but it isn’t all bad news. To be sure, human beings are not the centre of the universe, and they are not large by universal standards, but they aren’t small either. Not the largest nor the smallest things around by a long shot. Draw a line from the smallest to the largest, and from our vantage point the ends of the line stretch in both directions to numbers beyond our ability to comprehend. As far as we can tell, we are somewhere near the midpoint of the line, approximately equidistant from the ends as we now perceive them.
There’s another way to measure us. If we draw a line from the simplest to the most complex, we are not sitting at the midpoint. We’re at one end. We are the most complex thing we have yet discovered in the universe. The human mind is still largely unexplained. The human situation is unfathomable. How paradoxical that with motives and longings and limitations rooted in the confusion of who we are, we probe the depths and heights, often with complex mathematics as our only tool . . . on a quest to discover not more complication, but simplicity!
‘Who hath stretched a measuring line across it?’ God taunts Job in the scriptures. Shall we raise a timid hand and venture, ‘I think . . . well . . . actually . . . we have’? Maybe. Maybe not. For it is still a great mystery how large our island is – this treasured, hard-won, incalculably valuable, perhaps tiny island of human knowledge – compared with the sea.
ADDENDUM (2012)
The age of the universe, its shape, its expansion rate, its composition, its density . . . when a satellite called the Wilkinson Microwave Anisotropy Probe, better known as WMAP, took to the heavens in June 2001, the hope was that it would settle most of these issues once and for all. WMAP lived up to its promise. In February 2003, after the decades of research and debate that you’ve read about in the later chapters of this book, WMAP nailed down the age of the universe: 13.7 billion years.
WMAP was the result of a partnership between the Goddard Space Flight Center and Princeton University, and its primary mission was to produce a map of the cosmic microwave background radiation that was more precise than had ever before been possible. WMAP could detect and measure temperature differences of a millionth of a degree. Being a satellite rather than a land based instrument, it could take these measurements over the entire sky.
In addition to determining the age of the universe, WMAP data showed that the patterns in the CMBR froze into place when the universe was 380,000 years old. WMAP results also showed that space is flat (Friedmann’s third model, see Chapter 6), and that most of the energy in the universe today is ‘dark energy,’ also called “missing energy” (see Chapter 8). WMAP measurements showed that the variations in temperature and density in the CMBR, observed across the sky – the variations that seeded the formation of galaxies -- all had roughly the same amplitude regardless of their length. The distribution of the variations was random and all forms of energy had the same variation, just as predicted by the standard Big Bang inflationary model. As John Barrow summed it up, ‘The growing observational evidence for the distinctive pattern of temperature variations in the microwave background radiation means that we take very seriously the idea that our visible portion of the universe underwent a surge of inflation in its very earliest stages.’
Fine tuning the “standard model,” different versions of inflation theory had been presenting slightly different scenarios of precisely how inflation happened, and they were making different predictions about what pattern of temperature variations we should expect to find in the incoming CMBR if we compare its temperature in different directions. WMAP data gave scientists ways to test the different inflation stories. The temperature of the CMBR is dispersed extraordinarily evenly, but it does vary slightly from point to point in the sky. Warmer areas are assumed to correspond with denser regions in the very early universe.
WMAP results released in 2008 showed that the data was placing tight constraints on inflation, supporting some versions and not others. WMAP principal investigator Charles Bennett expressed his astonishment “that bold predictions of events in the first moments of the universe now can be confronted with solid measurements.” A results summary in January 2010, when the WMAP mission was preparing to wind down, confirmed that the large-scale temperature fluctuations in the CMBR are slightly more intense than the small-scale ones (a subtle but key prediction of many inflation models), and the universe is indeed flat – a conclusion supported in part by the randomness of locations of hot and cold points in the CMBR.
Other important issues remained unresolved. One important piece of evidence was missing: Inflation theory predicts what the patterns and characteristics of gravitational waves originating from the Big Bang should be like as they show up in the CMBR. WMAP failed to detect these gravitational wave footprints. Nor was it determined whether the “dark energy” (or “missing energy”) was due to the cosmological constant –“vacuum energy” – or “quintessence.”
When the WMAP satellite went into “graveyard orbit” in October 2010, the torch was handed on to a new satellite from the European Space Agency. The Planck satellite had been launched in May 2009, when the WMAP mission was preparing to wind down. Planck’s detectors were designed to operate at a temperature of minus 273.05C, just a tenth of a degree above absolute zero. The project’s first goal was to study some foreground sources that make studies of the CMBR tricky, but a formal release of fully prepared CMBR images, analyses, and scientific papers is expected, at the earliest, in 2013. Watch also for results coming from projects known as LIGO and LISA, which use a technique called laser interferometry to detect gravity waves, for these waves potentially offer the most direct opportunity we are likely ever to have to probe what the universe was like during the first split second of its existence.
1. A 15th century woodcarving of Ptolemy (second century AD), in the Ulm Cathedral: ‘When I trace at my pleasure the windings to and fro of the heavenly bodies, I take my fill of ambrosia, food of the gods.’
2. Drawing from Nicolaus Copernicus’s book De revolutionibus (1543), placing the Sun at the centre with the planets orbiting it. Beyond them is the ‘immobile sphere of the fixed stars’. The Moon orbits the Earth.
3. Johannes Kepler (1571–1630), discoverer of eliptical orbits: ‘Don’t sentence me completely to the treadmill of mathematical calculations – leave me time for philosophical speculations, my sole delight.’
4. Aristotle, Ptolemy and Copernicus on the Frontispiece of Galileo’s Dialogo (1632). The title page assures that this ‘discourse concerning the two chief systems of the world, Ptolemaic and Copernican,’ discusses ‘without prejudice one view, then the other, on the basis of philosophy and natural law’.
5. Woodcut showing the Octagon Room at the Royal Observatory in Greenwich as it looked in Flamsteed’s time, in the 17th and early 18th century.
6. One of the earliest photographs ever taken: Sir John Herschel’s 1839 photo of his father’s great 40-foot telescope.
7. Edmond Halley (1656–1742): ‘There remains but one observation by which one can resolve the problem of the Sun’s distance, and that advantage is reserved for astronomers of the following century.’ He left instructions for studying the transit of Venus across the Sun in 1761.
8. Sir William Herschel, astronomer and composer (1738–1822): ‘I used frequently to run from the harpsichord at the theatre to look at the stars during the time of an Act and return to the next Music.’
9. Caroline Lucretia Herschel, in a drawing made when she was 97, in 1847. A friend wrote that it does not ‘do justice to her intelligent countenance’.
10. The ‘Leviathan of Parsontown’, built by Lord Rosse in the 1840s and through which he observed the spiral nebulae. It remained for more than half a century the largest telescope in the world.
11. Henrietta Swan Leavitt (1868–1921). Her discovery of Cepheid variable stars and how to use them as stellar yardsticks led to the first measurements of distances outside the Milky Way Galaxy.
12. Before and after photos of Supernova 1987A in the Large Magellanic Cloud. The image on the left was taken in 1969; that on the right in February 1987, about a week after the supernova appeared.
13. The Andromeda galaxy, dominant spiral galaxy of the Local Group, with two companion galaxies – M32 (the bright dot close to Andromeda on the left) and NGC 205 (the bright dot on the right).
14. Albert Einstein visits Edwin Hubble at Mt. Wilson in 1930. Hubble’s astronomical observations and Einstein’s theories both indicated that the universe must be expanding.
15. Grote Reber’s radio telescope in Wheaton, Illinois (1937). Reber spent $4,000 of his own savings on designing and building this device in his mother’s back yard.
16. This image of the Milky Way Galaxy in ‘near infrared’ wavebands, from observations of the Cosmic Background Explorer (COBE), clearly shows the thin, flattened disk and central bulge.
17. The Hubble Space Telescope, NASA’s orbiting observatory, linked to the Space Shuttle Endeavour during the December 1993 repair mission.
GLOSSARY
absolute magnitude: How bright a star looks from a distance of ten parsecs (32.6 light-years). More technically: The amount of light received from a star that is ten parsecs away. The absolute magnitude of a star doesnʼt change with distance. Just as a 100-watt light bulb is still a 100-watt light bulb no matter how much its brightness appears to change with distance, a starʼs absolute magnitude remains the same no matter how much its apparent magnitude changes with distance.
absolute zero: The lowest possible temperature, at which a substance contains no heat energy.
absorption lines: Dark lines in a spectrum produced when light from a distant source passes through cooler gas closer to the observer.
acceleration: The rate at which the speed of an object is changing.
action at a distance: The phenomenon of an object exerting a force on a second object across empty space, without the intervention of anything physical.
aether: Aristotleʼs fifth element, of which he thought stars and planets were made.
angular size: Astronomers describe the apparent size of an object in the sky in terms of its angular size. For example, if two lines are drawn from an observer on the Earth to the opposite edges of the Moon, the angle formed by the two lines where they meet at the observer is about ½ degree. Another way of putting that is to say that the Moon “subtends” an angle of ½ degree; or that it has an angular size of ½ degree. The angular size of an object canʼt be converted into its true physical size unless the distance to the object is known.
In calculating angular size: A circle has 360 degrees; each degree is divided into 60 minutes of arc or arcminutes; each minute of ark is divided into 60 seconds of arc or arcseconds.
apparent magnitude: How bright a star looks as viewed from the Earth. More technically: The amount of light received from a star as observed from the Earth. The apparent magnitude of a star changes with distance.
apparent size: As opposed to true size, apparent size is the size of a heavenly body as viewed from the Earth. The apparent sizes of the Sun and Moon are the same; their true sizes are not.
arcminute: See angular size.
arcsecond: See angular size.
astronomical telescope: A telescope based on an optical system first described by Kepler that uses only convex lenses. Keplerʼs telescope inverted the image, but after that problem was sorted out, the astronomical telescope replaced the so-called Dutch telescope (the kind Galileo had used) in most serious astronomical work by the mid-seventeenth century. It provided a much larger field of view at equal magnifications.
atom: A unit of ordinary matter. The center of the atom is the nucleus, made up of protons and neutrons. Electrons orbit the nucleus.
bender: A massive body or galaxy or cluster of galaxies that is responsible for the bending of paths of light passing near it.
Big Bang: The state of enormous heat and density in which the universe probably began, and from which the universe has expanded and cooled to its present state; not necessarily a singularity.
Big Crunch: The collapsed state in which the universe might end.
binary star (or binary system): Double star system in which the two stars are bound together gravitationally and orbit their common center of mass.
black hole: The classical definition is a region of space-time from which nothing can escape unless it can travel at a speed greater than the speed of light.
blueshift: Displacement of the spectral lines in light coming from distant stars and galaxies that are moving toward Earth.
brightness fluctuation method: Technique used to calculate the distances to galaxies by measuring the unevenness in the brightness of the surface of the central bulge or near the center.
Cepheid variable: Pulsating variable star whose period of brightness variation is directly related to its absolute magnitude.
