"I wouldn't hire a contractor to build a new bathroom without finding out how much it would cost and how long it would take," Martin Harwit explained during a visit to Caltech in June. "So why should we astronomers go about exploring the universe without knowing how many new phenomena are left to find, how much it is going to cost and how long it will take us to finish the job."
In a recent article in the journal Nature, Harwit suggests that we know enough about the cosmos now to answer these questions.
Astronomy today, he believes, is where geography and zoology were a century ago, when explorers were still finding new rivers and mountain ranges and biologists puzzled over where to place the new species that seemed to be turning up almost daily on their taxonomic charts. Now the planet Earth has been mapped from outer space and, as far as animal life is concerned, the search for new species is not at the forefront of scientific interest. Occasionally a species thought to be extinct is found alive, but the rate of discovery is very slow. According to UCLA's Jared Diamond, there have been only 134 bird species discovered since 1934, and no new mammals since the Kouprey was found in Indochina 50 years ago.
But the whole star-filled universe is different, isn't it? The number of plant and animal species on the Earth is finite. But the universe . . . ?
The universe, according to Harwit, is not so different. Drawing an analogy from his son's collection of baseball cards, he pursued this line of thought. When the boy bought his first packet it contained eight or 10 different cards. But after about the fourth purchase duplicates began turning up. From that the boy knew that there was a finite number of baseball players. The more cards he collected, the more he could tell about the distribution pattern and without having to see the whole set of cards, he could estimate the total number.
This same principle explains how zoologists can say that there are still so many species of insects or fish yet to be discovered. After collecting butterflies for a while in a rain forest, a lepidopterist will begin to find duplicates. Although there are still occasional new finds, the duplicates outnumber the discoveries so that the collector can estimate the odds of making a discovery and project the proportion of familiar to unfamiliar species in the territory.
Using a form of mathematics called Poisson statistics, Harwit asserts that astronomers are already finding "duplicates," phenomena such as more double stars, galaxies, quasars and black holes. The rate of discovery in astronomy has increased sharply in recent years because of new instrumentation that has opened up not only the visible sky but the infrared, radio and X-ray sky as well. Each new technique, Harwit explains, is the equivalent of the purchase of a new packet of baseball cards.
Barring space travel, and accepting the limits put upon our explorations by both the nature of our own minds and the laws of the universe as we have come to know them, Harwit conjectures that we already know about a third of the phenomena that exist in space. At the moment he lists 45 different astronomical events including black holes and the new gravitational lens. If funds remain adequate, he suggests, we will have discovered 90% of all the phenomena of the universe by the year 2050.
After 2050, he believes, the rate of discovery will slow down, just as it has for the discovery of biological species, and it will be several thousand years before we know another 9% with the last 1% continuing to elude us, or perhaps ceasing to be of interest. This is the nature of scientific discoveries. They clump together, building on new technology and creating a mood of discovery that keeps scientists on the lookout--for a while. The 19th Century was a great age for the discovery of biological species. We are living in a golden age of astronomy.
Harwit thinks it only reasonable to seek a scale--decades, centuries or millions of years. Most people, he points out, don't start on a journey without believing they will finish. They usually want to know where they are going, so they can tell if they have gone half way, or have gone too far to turn back.
When his colleagues look askance at his predictions, he wonders about their motivations. Some people have made a religion of science and consider the quest for knowledge of the universe a reflection of the human spirit. Thus they find the possibility of completing the quest anathema--an equivalent to the end of the human race.
This does not trouble Harwit. When the universe is understood, which he anticipates will happen, there will be other goals for the human spirit. After all, we have mastered the geography of our own planet and are none the worse for it. Why should the possibility of mastering the more complicated geography of space provoke such distress? Perhaps it is because we have always located our Creator "out there," which makes the suggestion that we can understand the realms beyond our planet tantamount to blasphemy.