Authors: Kitty Ferguson
B00B7H7M2E EBOK
About the Book
Suppose you and I still wondered whether all of the pinpoints of light in the night sky are the same distance from us. Suppose none of our contemporaries could tell us whether the Sun orbits the Earth, or vice versa, or even how large the Earth is. Suppose no one had guessed there are mathematical laws underlying the motions of the heavens.
How would – how did – anyone begin to discover these numbers and these relationships without leaving the Earth? What made anyone even think it was possible to find out “how far,” without going there? In Measuring the Universe we join our ancestors and contemporary scientists as they tease this information out of a sky full of stars. Some of the questions have turned out to be loaded, and a great deal besides mathematics and astronomy has gone into answering them. Politics, religion, philosophy and personal ambition: all have played roles in this drama.
There are poignant personal stories, of people like Copernicus, Kepler, Newton, Herschel, and Hubble. Today scientists are attempting to determine the distance to objects near the borders of the observable universe, far beyond anything that can be seen with the naked eye in the night sky, and to measure time back to its origin. The numbers are too enormous to comprehend.
Nevertheless, generations of curious people have figured them out, one resourceful step at a time. Progress has owed as much to raw ingenuity as to technology, and frontier inventiveness is still not out of date.
Contents
Prologue: Tilting at Windmills
6. The Demise of Constancy and Stability
To my brother, David, who made himself ill as a child and caused a family crisis, worrying about the size of the
universe
Acknowledgements
The author wishes to thank the following, who have read portions of the manuscript, answered her questions, supplied background material and information, and made suggestions and corrections. Without this help,
Measuring the Universe
could not have been written:
Judy Anderson, Boyd Edwards, Caitlin Ferguson, Yale Ferguson, Carlos Frenk, Wendy Freedman, Margaret Geller, Owen Gingerich, Stephen Hawking, Jill Knapp, Helen Langhorne, P. Susie Maloney, Robert Naeye, Saul Perlmutter, Barbara Quinn, Allan Sandage, Bill Sheehan, Patrick Thaddeus and David Vetter.
Credits for plate section photographs
3 Sternwarte Kremsmünster; 5 Engraving attributed to Francis Place; 6, 10 Royal Astronomical Society Library; 7, 8, 9 Yerkes Observatory; 11 Harvard College Observatory; 12, 13 Victor Blanco, Wendy Roberts/CTIO/NOAO/AURA/NSF; 14 Henry E. Huntington Library; 15 NRAO/ AUI; 16 COBE Science Team, NASA, Goddard Space Flight Center; 17 NASA/Space Telescope Science Institute.
PROLOGUE
Tilting at Windmills 1951
WHEN I WAS
nine years old, my father suggested one morning that he and my brother and I go out and measure the height of the windmill on my grandparents’ farm. My brother and I agreed that was a fine idea.
How would we do it? Climb the windmill, of course . . . at least my father would. My brother and I wouldn’t be allowed to try anything so dangerous as that. When my father reached the top, there would still be the problem of how to measure the height. We didn’t have a measuring tape that long. Would he take a yardstick and mark off the yards on the windmill as he climbed? Maybe he would drop the end of a long rope from up there and cut it off, and we would stand clear while the cut-off piece fell, and then we would measure it. That must be the plan, for he’d said my brother and I would help him.
My brother suggested that my father wouldn’t need to climb the windmill at all. We could throw something over the top, just clearing it. Yes, I interrupted, attach a rope to the thing we threw, a rope with inches and feet marked on it, and then pull back on it gently so it would catch on the top of the windmill, and see what the measurement was to the ground! No, no, said
my
brother, who was two years younger than I but already very mathematically minded, we would measure the curve the object followed through the air. Good thinking, said my father, but, practically speaking, more difficult than the original problem of measuring the height of the windmill.
I asked whether we might walk away from the windmill and measure how much smaller it looked as we got further away. More good thinking, said my father, but there was a better way.
He gave us a hint. He’d thought it was a wise idea to wait for a sunny day . . . and no one would have to climb the windmill or take a walk or risk wrecking the windmill with a bad throw . . . and the only tools we’d need would be a yardstick and our eyes and brains and a pencil and paper to do some calculations. And although at this latitude it would be possible to measure the windmill precisely at noon, it would be easier at another time of day.
Neither my brother nor I was clever enough to see where this was leading until my father said, ‘The windmill does more than just pump water, you know. It casts a shadow, and so does a yardstick,’ and then we began to understand how the trick could be done. We would stand the yardstick upright and measure its shadow. Then we would measure the windmill’s shadow. If a shadow
this
long went with a three-foot stick, then a shadow
that
long went with a windmill of thus-and-so height. My brother and I didn’t know how to make the comparison. My father taught us how and then pointed out that there was actually a more primitive way to find the answer. Wait for the time of day when the three-foot yardstick cast a three-foot shadow. At that moment the length of the windmill’s shadow would be the same as the height of the windmill. We decided to use our newly acquired mathematics first, and then we checked our answer by sitting out in the Texas sun, watching the shadow of the yardstick creep along the ground.
That’s how we measured the windmill, while above our heads the giant structure thrummed and creaked with the
watery
, metallic sounds windmills in central Texas made in those days, doing its work, turning and pumping, adjusting its angle to catch a stronger breeze, not paying any attention to the mental exertions of three little people below who had captured its shadow.
I was elated. It seemed we had outwitted the windmill without so much as touching it, and now we knew a wondrous secret: Not the height of the windmill, but how to find it out. None of us thought to ask: why are we doing this? There was no need whatsoever for any of us three to know the height of a windmill that wasn’t even our own.
Measuring is one of the more practical uses for mathematics, but our ability and desire to measure isn’t always wrapped up with the need to know useful answers. Going with numbers where we can’t go in person – whether that’s to the top of a windmill or to the origin and borders of the universe – has been and still is one of humankind’s favourite intellectual adventures. By the beginning of the twenty-first century it had outrun our practical requirements by billions of light years.
Compared with the adventure of finding them out, the actual measurements often seem dry as dust: The Sun is 149.5 million kilometres away (mean distance). The nearest star is 4.3 light years. The ‘Local Group’ of galaxies covers an area about 3 million light years in diameter. The distance to the edge of the observable universe is 13.7 billion light years. We shake our heads at how large these numbers are or admit their largeness makes them meaningless, remember them for a day or maybe long enough for a school exam . . . and then forget them. Science trivia.
Not trivial at all when you realize how hard-won these numbers are and what ingenuity it took and still takes to find them out. Can we even begin to imagine what it would be like if no one knew them? The night sky sparkles with pinpricks of light. Are these all the same distance from us? Suppose we
didn’t
know. Suppose none of our contemporaries knew whether the Sun orbits the Earth, or vice versa, or even how large the Earth is. Suppose no one had guessed there are mathematical laws underlying the motion of the heavens. How would – how did – anyone begin to discover these numbers and these relationships without leaving the Earth? What made anyone even think it was possible to find out ‘how far’? Without going there. Without climbing the windmill.
In the pages to come we’ll take many steps back, forget we know the measurements or how to make them, and join our ancestors as they tease this information out of a sky full of stars. The laboratory isn’t a neat, sterile room where carefully controlled experiments take place. Events in the heavens happen in their own good time and not before, and they are often not repeatable. We have learned to take what’s on offer and make the best of it.
Our human point of view is sorely limited. Until recently we had no ground on which to stand and take our measurements, no possible viewing platform, other than here on Earth. In the twentieth century we travelled to the Moon and looked back at our planet from space and sent probes out into the far reaches of our solar system. But by universal standards, by the standards of the distances we’ve learned to measure and still hope to measure, how pitifully close to home that is.
This book is a chronicle of how men and women over the course of two and a half millennia have built a ladder of measurement from our doorsteps to the borders of the known universe, and how the adventure has changed our ideas about the shape and nature of the universe and our place in it. It is not a history of all astronomy. There are fascinating discoveries, both in Western astronomy and in other cultures, that I have had to remind myself have no direct bearing on our knowledge of distances, size and shape. With regret, I have left them out, though the temptation to embark on long digressions from the main theme of the book has been almost irresistible.
We shall however broaden our focus in another direction to examine the context in which the discoveries have taken place, for this is a story inextricably bound up with the rest of social, political and intellectual history. One of our tasks will be to look for reasons why a particular discovery or measurement happened when and where it did. What was it about that time and place, that society, that mindset or intellectual milieu, the available technology, the chain of previous discovery, the way some random occurrences fell out . . . perhaps most interesting of all, what was it about a specific individual that precipitated this advance in knowledge?