The Expanding Universe
About four thousand years ago, at a place called Stonehenge in England, people placed some huge stones in a large circle.
We think at least part of the plan was to keep track of the seasons. We do know that by sighting along mathematical arcs defined by the stones today, you can tell the precise calendar dates when spring, summer, fall and winter begin-called the spring and fall equinoxes, and the winter and summer solstices.
Early knowledge of astronomy was not special to England. In Babylonia, Egypt, China; in North and South America, India and Africa; just about every human culture has discovered important facts about our sun, earth and star cycles.
Just about every human culture has searched for a better understanding of the cosmos, and of how earth and human life fit in.
This better understanding has always had two sides.
First, as at Stonehenge such knowledge can help people cope with practical problems caused by night and day, by the seasons, by the cycles of plant, animal and human life. It can also help travelers navigate in strange lands and on chartless seas.
The second reason for understanding the cosmos is just as powerful. For the sheer wonder of it. Who has not looked out at the starry sky and wondered. What are the stars? How far away are they? How did the stars and the sun and the planets get to be the way they are?
These are some of the same questions that Huck Finn and his friend, Jim, asked and wondered about as they floated down the Mississippi River on their raft. Huck put it this way.
"We used to lay on our backs and look up at the stars, and wonder whether they was made or just happened. Jim, he allowed they was made. I allowed they just happened. I judged it would of took too long to make so many. Jim said the moon could a laid them. "Well, that sounded kind of reasonable so I didn't say nothing against it, because I've seen a frog lay most as many, so of course it could be done. We used to watch the stars that fell too, and see them streak down. Jim allowed they got spoiled and was hove out of the nest."
Two thousand years before Huck and Jim, other humans sat on the hills overlooking Ionian Greece and asked some of these same questions. These men lived in the ancient city of Miletus, then a Mediterranean port city.
Often looked on as the world's first natural scientists, these men built new models of the universe in their minds. Some of these models were fantastic, others were startling in their imaginative accuracy.
Thales, for instance, imagined the world was a giant disc that floated on a cosmic sea of water. Anaximander said the world was curved, not flat, and pictured it as a giant cylinder, surrounded by crystal spheres that held the sun and the stars. Pythagoras was the first to teach that the earth is spherical. All this around 500 B.C.
A few years later in Athens, Greece, Democritus (the laughing philosopher) invented the world's first atomic theory. He also claimed that all the specks of light in the Milky Way were stars just like our sun. And that the moon was an earthlike body with mountains and deserts.
Born about the same time that Democritus died, the most famous of all scientists of antiquity was Aristotle. His vision of the universe was as beautiful as it was influential for centuries to come.
Aristotle pictured the earth as spherical in the center of a series of fifty-six concentric spheres. These spheres held the sun, the moon, the planets and the stars. The heaviest part of the universe, said Aristotle, was the center-earth. That was why things always fell "down." Next heaviest was water. Then came air. Still lighter was fire, which was always rising up. And finally, highest and lightest of all, were the crystal spheres of the sky, which held the eternal stars.
In fact, Aristotle thought these crystal spheres were a fifth element of no weight at all. An unchangeable aether. Aristarchus had the earth and the sun switch places, and built the first helio-centric (that is, sun-centered) universe.
But how could this be, argued critics. If the earth were not the center of the universe, there would be no gravity. Instead of falling down, things would go flying every which way. A few years later another Greek astronomer, Eratosthenes, actually measured how big the earth was!
By carefully measuring the angle sunlight made in southern Egypt with the angle it made at Alexandria on the day of the summer solstice, and applying a little mathematics, he estimated the diameter of the earth itself with astonishing accuracy.
In the second century A.D., Ptolemy, a Greek astronomer living in Egypt, simplified the picture first created by Aristotle and refined by later Greek astronomers.
It was this picture, the famous Ptolemaic System, that all educated people in the Western World held to throughout the Roman Empire and the Middle Ages, a period of over one thousand five hundred years.
That Ptolemaic System was challenged in the early sixteenth century by a Polish astronomer named Nicholas Copernicus.
Copernicus went back to the helio-centric system of Aristarchus, gave it a mathematical base, and started a revolution in science and society! A revolution that in its methodical way is still changing the world today. The revolution sparked by what we call modern science and technology.
Copernicus, of course, was not conscious he was starting such a major revolution. He wanted to improve the calendar, to be more accurate than Ptolemy in predicting the positions of the planets, and more reasonable in explaining the strange "backward" motion of the planets that the Ptolemaic system had to imagine.
Why not, said Copernicus, simplify things by putting the sun at the center of those spheres, and have the earth and other planets revolve around the sun. With that assumption, indeed, the motion of all the planets did become more understandable.
And Copernicus was a good enough mathematician to improve upon Ptolemy by making tables that could predict the positions of the planets, the equinoxes and the calendar adjustments with more accuracy than the old model.
Copernicus's book On the Revolution of the Celestial Spheres was published in 1543, as Copernicus himself was dying. It became popular with scholars throughout Europe, though more often for its usefulness in calendar reform (and even in astrology) than for the literal picture it presented of sun, earth and planets.
This idea, that the earth was not at the center of the universe, was very hard for people to accept then. (As it still is today!)
A German astronomer, Johannes Kepler, took the next step forward when he revised the Copernican picture by pointing to the need for elliptical rather than circular orbits for the planets. A brilliant mathematician, Kepler had available the most accurate observations yet made, those of the Danish astronomer Tycho Brahe.
Using Brahe's figures he formulated the first laws of planetary motion.
At the same time Kepler was working in Austria, a young university professor named Galileo Galilei was sitting in a church in Pisa, Italy, timing the back-and-forth movement of an altar lamp. He was timing it with the only instrument available for measuring short units of time, his own pulse. Which was good enough to discover the law of the pendulum. Far more important, Galileo's simple experiments with the altar lamp were the first in a series of breakthroughs that brought together the motion of altar lamps, cannon shells, falling bodies and the motion of the earth around the sun!
By that time, conflicts had heated up between the new scientific scholars like Galileo, and the Church authorities, determined to uphold traditional views.
Galileo was cautioned many times to take greater care in how he presented his new views, lest he give offense to the Church and contradict Holy Scripture. Galileo was not a cautious man, however. Instead of taking greater care not to give offense, he boldly published a new book, Two New Sciences. In it he argued aggressively and persuasively for a Copernican universe. To make matters worse, the book was in the form of a dialogue and Galileo put the Pope's words into the mouth of a simpleton named Simplicio, a characterization the Pope did not appreciate.
Galileo was arrested and brought to trial in Rome. He was convicted in 1633 of disobeying the Church's orders. An old man now and almost blind, his only punishment was house arrest in his villa near Florence- on condition he take back his view that the earth was not the center of the universe.
He did so.
Though the Church won this battle, it lost the war. The evidence for the Copernican universe was too strong to keep down.
And when Isaac Newton came along in the seventeenth century, the scientific revolution was well on its way to change the world more rapidly than it had ever changed before.
Isaac Newton escaped the plague of London in 1665 by retiring to his parent's farm in Woolsthorpe. He was not a very good gentleman farmer. He was a difficult man to get along with. But some think he was the greatest scientist who ever lived.
Looking out his bedroom window, Newton himself tells us he saw an apple fall, and it gave him an idea. Could the force that makes the apple fall to the earth be the same force that makes the earth fall around the sun? The answer he gave was, yes.
And he proceeded to invent a whole new kind of mathematics, calculus, to prove his new laws of motion and of universal gravitation. Laws that were the foundation stones for much of science for almost three centuries to come. And laws which still today do service in astronomy, physics, chemistry and technology. Newton's discoveries not only confirmed the truth of the Copernican sun-centered system, but they made it much more precise, elegant and simple. Now there could be no doubt. The earth and the planets all move at high speeds around the sun. They keep moving by inertia. They are bent into their elliptical paths by a universal force of gravitation, continually "falling" around the sun.
All this in just the same way that three centuries later humanmade satellites obey the same universal laws first discovered by Isaac Newton.
But what about the other stars? The stars besides our sun? Were they really "fixed" in the distant sky, as earlier astronomers had supposed? And was our sun really the center of the universe?
About the time of the American Revolution, a hundred years after Newton's stay at Woolsthorpe, a German-English brother and sister team found answers to these new questions. Sir William Herschel and his sister, Caroline Herschel, lived in the English resort town of Bath. William played the organ at the Octagon, a church for the aristocracy. To keep body and soul together, he was also a music teacher, tutoring up to thirty-five pupils a week. With his sister Caroline, however, his real passion was for telescopes and for astronomy.
Together William and Caroline spent hour upon hour, week upon week, grinding the best telescope lenses ever made. They assembled these lenses into the finest telescopes ever made and used these telescopes to gaze into the night sky and learn.
Over the next fifty years they found thousands of new stars in the sky. They found a new planet, Uranus. And most important of all, they drew a new map of the universe.
Copernicus, Galileo and Newton had dethroned the earth from center spot. The Herschels dethroned the sun. They found that our sun was only one medium-sized star in a whole galaxy of stars, a galaxy they called the Milky Way. Our whole proud solar system, they said, was itself only one insignificantly small part of a much much larger star system, a galaxy. Our view of the universe was, indeed, expanding.
And this was only the beginning.
After the Herschels, throughout the nineteenth century, telescopes did improve, of course. As the catalog of known stars grew larger and larger, The Herschels speculated there might be other galaxies besides our Milky Way, but their instruments were not good enough to see that far. Such instruments would not be built for another 150 years.
The big picture, however, was not radically altered until a young man named Albert Einstein began his work in Berne, Switzerland around the beginning of the twentieth century.
Just when people had adjusted to the Newtonian world, Einstein replaced it with a new world of relativity. Until now, time and space had been taken for granted. Einstein took away this taken-for-granted time and space. Until Einstein there was here and now, there and then. Events unrolled neatly as though in a motion picture, or a scheduled trip.
But that is all an assumption, pointed out Einstein, and nature does not need to follow our rules and assumptions. If we assume, instead, that time and space themselves are relative, and not necessarily the same to some other observer at some other spot in the universe, then all our scientific laws take on quite a different shape.
The shape Einstein suggested was his special theory of relativity, later to be expanded into the general theory of relativity. It is one thing to propose a new theory, another to prove it right.
Who was right, Newton or Einstein?
It turned out there was a way to test. Eventually many ways to test.
And in every case, it was Einstein's universe that passed the tests.
Since Einstein, our view of the universe has expanded still more.
Edwin Hubble, a former lawyer, worked at the large new telescope at Mount Palomar in California. He discovered that our Milky Way galaxy was not the whole universe. In fact, it was itself only an infinitesimal part of a truly gigantic universe. A universe that was itself expanding continuously at enormous speeds. Even Einstein was astounded!
But if that were so, and the evidence was strong, what was the universe expanding from? Had it once been closer together? How close?
A Catholic priest at the University of Louvain in Belgium, the Abbe Lemaitre, proposed an answer to this puzzle. The universe had once been all one tiny "cosmic egg." There had been an explosion, a "big bang," and in an instant, matter and energy moved outward faster and faster. And stars and planets were born. And galaxies and clusters of galaxies. And all moved faster and away from each other. And still farther away, and that is just what is still happening today in our expanding universe. ..
Was this just another wild idea? Where was the evidence?
Some of the evidence came from Hubble himself. He found that the distant galaxies were indeed all moving away from our own galaxy at very high speeds. In fact, the ones farthest away (and there are not just a few, but billions on billions of these far away galaxies!) were also moving the fastest. Just what you would expect if there had been a big bang.
On careful checking with geologists, the time scale seemed to make sense. It all happened, the Big Bang that is, about fifteen billion years ago. That would fit with the age of rocks on earth, and on the moon. Then very recently, from a surprising new source, came independent evidence of such a beginning.
In 1964 two scientists at Bell Telephone laboratories, Arno Penzias and Robert Wilson, aimed a horn-shaped radio antenna at the sky and detected a faint radio noise that was not coming from any individual star or galaxy or black hole. It seemed to be coming equally from all directions. After taking great precautions to eliminate all possible sources of error, including pigeon droppings in the antennae, they came to the conclusion that this radio noise was left over from the Big Bang explosion of fifteen billion years ago.
They were listening in on the birth of the universe!
Their eavesdropping won them a Nobel Prize in 1978.
So today we stand on the threshold of what new surprises as we venture into outer space ourselves? As we put new telescopes on our space vehicles to hear and see new mysteries. Quasars, pulsars, black holes, who knows what next? And yet, with all that space out there we need to remind ourselves once in a while that there is an equally large space in here. In the brains and minds of each and every one of us.
As a poet said long ago, "It is not the immensity of space that should command our wonder, but rather the man who measured it."
When puppies are born, their eyes are sealed shut. The limit of their world is their mother's warm body. Before many weeks pass, however, not only do their eyes open, but their neighborhood expands, their muscles and senses begin to work together and days of exciting exploration begin.
Humans are similar.
Moving away from our own warm mother earth, already we have come upon as many surprises as puppies in a backyard.
And we have only just begun our exploration of the universe.
Let's look around and see just what we have found out so far.
First, how big is our universe?
Put it this way. If you tried to go from one end of the universe to the other in the fastest of present day spaceships, it would take you so long numbers would lose meaning. Trillions on trillions of years. If you managed to build a spaceship that could go at the fastest possible speed in the universe, the speed of light, it would still take not years, or hundreds of years, or thousands, or millions-- but billions of years to make the trip. And even then, there might be billions of more years to go once we got into parts of the universe we have never seen or suspected before.
Here the answer can be more definite, or at least we think so today. About fifteen billion years old, give or take a few billion. Both of these estimates of distance and time come from careful study of stars and galaxies we can see through light telescopes, and more recently from new giant radio telescopes like the one at Joddrell Bank near Manchester, England.
By analyzing the light and the radio signals we receive from these far away stars, we can make pretty accurate estimates of their size, their distance from us and the speed with which they are moving. What we find is a surprise. All of the far-off stars and galaxies are moving away from us at very high speeds. And the ones farthest away are moving the fastest.
The logical assumption is that a long time ago they were all much closer together, perhaps very close together, and ever since a cosmic explosion they have been moving away from each other. Counting backwards now, knowing present day distances and speeds, we find that this Big Bang must have happened about fifteen billion years ago.
A Belgian priest and astronomer, the Abbe Lemaitre, first put forth this theory of the origin of the universe with a Big Bang.
One of his students, George Gamow, described it this way.
"The evolution of the world can be compared to a display of fireworks that has just ended. Some few red wisps, ashes and smoke. Standing on a cooled cinder, we see the slow fading of the suns and try to recall the vanished brilliance of the origin of worlds."
A long way from puppies.
What do we know of what's inside this expanding universe?
First of all, we have to watch that word "inside." Since Einstein we have a good idea that the universe is finite, but unbounded. We live, in other words, not in three, but in four dimensions. And the fourth dimension is time. And this fourth dimension of time makes all of space "curved."
To get some idea of what this might be like, imagine a balloon that is expanding. If you lived on the surface of the balloon (in just two dimensions) you would see all around you expanding, but there would be no boundaries. And yet the total space would be limited, finite. So, too, in our three dimensional world, when you add the fourth dimension, the geometry becomes curved, unbounded, yet finite.
Having said all that, we still yearn to get a mental picture of what it's like out there, curved space or not.
If we switch from the largest possible view out there to a more comfortable view in here, maybe it will take a more sensible shape. Earth, we are sure by now, is a spherical planet that is rotating on its own axis once every twenty-four hours, and moving in a large elliptical orbit around the sun once every 365 1/4 days. It is one of nine planets that are doing the same thing at differing distances from the sun and differing speeds of rotation on their own axes.
By now we have actually visited most of these planets in person. (Well, by proxy at least, with our humanmade spaceships.)
The one nearest to the sun is Mercury. Our spaceship Mariner 10 visited Mercury a few years ago and reported that its surface was similar to the moon with many meteor craters and a heavy iron core.
Next out comes Venus. It is about the same size as earth, but not nearly as comfortable. It's surface temperature is over nine hundred degrees Fahrenheit. We know there are volcanoes on that surface, but they are deep beneath gloomy storm-driven clouds of carbon dioxide and sulfuric acid. Venus may be a planet where the "greenhouse effect" (carbon dioxide in the atmosphere reflecting heat back to the ground and warming the planet) has made a catastrophic difference. Venus may have had life in the past, but today it is certainly not a very promising spot for life.
Then comes Earth, blue white and alive. Earth is medium size as planets go, bigger than Mercury and Mars, but much smaller than Jupiter or Saturn. All the planets, of course, are much much smaller than stars like our sun. In fact, to get a picture of how much small!er, imagine that you were trying to fill a big star like Epsilon Aurigae with Earths. You would need about 35 thousand billion Earths to do the job! Close to Earth, and moving around it in a monthly orbit is the moon. Our moon. The only other body in the universe that has been walked upon by human beings.
Next planet out from the sun is Mars. For many years Mars was thought to be the only one of the planets besides Earth that might have life. Numerous probes of the Martian surface have so far failed to provide any evidence of life. What we have found are unweathered craters where meteors have hit in past ages, extinct volcanoes fifteen miles high and dry river beds! These do suggest that in ages past Mars may have had water, or some kind of liquid on its surface.
Next out is Jupiter, the largest of the planets (larger than all the other planets put together). Jupiter is probably not solid anywhere. Most astronomers now believe it is made of mostly hydrogen, liquid inside, gas on the surface. On the surface of Jupiter is a very large red spot, thirty thousand miles long by six thousand miles wide. A surface area larger than our earth! This red spot we know is a great whirling storm, though why it should persist so long we don't know. Jupiter was the first of the planets besides Earth that was known to have moons. Galileo found the first four moons around Jupiter back in 1610. Today we know that Jupiter has at least fourteen moons.
Saturn comes next, certainly one of the most beautiful sights you can see in a telescope with its impressive rings. Voyager II traveled through these rings taking spectacular photos and gathering new data on the chemical composition of the rings, and of the thick atmosphere on one of Saturn's moons, Titan. It turns out that this atmosphere is made of nitrogen, ammonia and many simple organic compounds-the very same chemicals that life is made of on Earth! We are just at the dawn of planetary exploration now. Future probes will no doubt give us more insight into not only how the solar system..was formed, but also how life began. Uranus is next, though it is almost twice as far out as Saturn.
Still farther out is Neptune, and finally Pluto. Besides these nine planets, the solar system has an assortment of many other heavenly bodies, all orbiting our sun.
Among the most important are asteroids. Asteroids are miniplanets really-that is, large chunks of rock ranging in size from a mile to a hundred miles in diameter. There are somewhere between thirty thousand and one hundred thousand asteroids revolving in orbits around the sun just beyond Mars.
Some space pioneers think that these asteroids will provide the raw materials for building huge space colonies of the future. All of the planets, including some asteroids, comets and zillions of particles of space dust and our own new space satellites are themselves moving along with their parent sun through dark space. And more and more dark space. And more and more and more dark space.
Our entire solar system is but one of many possible solar systems in a giant group known as the Milky Way galaxy. Just about all the stars you can see outside on a clear night with the naked eye are other suns within this Milky Way galaxy. If you put even a small telescope to the sky you will see many thousands more Milky Way stars. Each star itself a sun to who knows how many planets.
Very recently radio astronomers have picked up the first bits of evidence that one of the brightest stars in our summer sky, Vega, some twenty light years away, may indeed have a solar system. And a solar system in an early stage of evolution since Vega is only about one billion years old, in comparison to our own sun's age of 4.6 billion.
Here is an outside view of another galaxy (we can't get a picture of the Milky Way galaxy from outside, since we are inside it). We think our Milky Way would look something like this if we could see it from outside.
Our own solar system would be a tiny speck somewhere out on the edge of one of those pinwheel-like rays. Our Milky Way galaxy is only one of many billions of galaxies in the known universe.
The best known and first to be discovered is the great galaxy in Andromeda, which you can just barely see with the naked eye.
In a high powered telescope you can sometimes see more than one galaxy in the same view.
And remember, each of these galaxies has billions of stars making it up.
Billions of stars in billions of galaxies.
Each one billions of miles apart and billions of years ago.
That is what is "inside" our universe. And "outside" too. And all around and all about.
And yet not quite all.
Very recently we have begun to discover still new surprises. Radio astronomers were the first ones to suspect space was not quite as simple as we once thought. From some spots in space we could see no light with our eyes, but we could pick up strong sources of other electromagnetic waves with our electronic ears. What was causing these signals?
We could also see pulsating sources, and sources of radiation and energy far in excess of even the largest galaxy! Institutes with large radio telescopes on earth are actively investigating these new quasars, pulsars and black holes. NASA is launching a new space telescope that once outside the earth's atmosphere will let us see ten times clearer than any telescope on earth's surface.
What new insights will come from this research is impossible to predict. We are also sponsoring projects to try to communicate with possible civilizations on other planets, if there are any. The theory is, if life evolves the way we think it does, given the right chemicals and the right environment, there must be thousands, millions, even billions of other earths out there with intelligent life on them.
We should someday be able to say hello.
And to hear and understand their answer.
It happens routinely in our science fiction.
When the day comes that it happens in our science reality, perhaps, like the newborn puppies, our eyes will begin to open and our adventure in space will have truly begun.