supplied to a simulated Titan atmosphere. When we analyze what this stuff is made of we find many of the essential building blocks of life on Earth. Because Titan is so far from the Sun, any water there should be frozen—and so you might think it is at best an incomplete analog of the Earth at the time of the origin of life. However, occasional impacts by comets are capable of melting the surface, and it looks as if an average place on Titan has been underwater for a millennium, more or less, in its4.5 billion year history. In the year 2004, a NASA spacecraft called
Cassini
will arrive in the Saturn system; an entry probe built by the European Space Agency called
Huygens
will detach itself and slowly sink through the atmosphere of Titan toward its enigmatic surface. We may then learn how far Titan has gone on the path to life.
3. Is There Intelligent Life Elsewhere? Radio waves travel at the speed of light. Nothing goes faster. At the right frequency they pass cleanly through interstellar space and through planetary atmospheres. If the largest radio/radar telescope on Earth were pointing at an equivalent telescope on a planet of another star, the two telescopes could be separated by thousands of light-years and still hear each other. For these reasons, existing radio telescopes are being used to see if anyone is sending us a message. So far we have found nothing certain, but there have been tantalizing “events”—signals recorded that satisfy all the criteria for extraterrestrial intelligence, except one: You turn the telescope back and point at that patch of sky again, minutes later, months later, years later; and the signal never repeats. We are only at the beginning of the search program. A really thorough search would take a decade or two. If extraterrestrial intelligence is found, then our view of the Universe and ourselves is changed forever. And if after a long and systematic search we find nothing, then we may have calibrated something of the rarity and preciousness of life on Earth. Either way, this is a search well worth doing.
4. What Is the Origin and Fate of the Universe? Astonishingly, modern astrophysics is on the verge of determining fundamental insights on the origin, nature, and fate of the entire Universe. The Universe is expanding; all the galaxies are running away from each other in what is called the Hubble flow, one of three main pieces of evidence for an enormous explosionat the time the Universe began—or at least its present incarnation. The gravity of the Earth is strong enough to pull back a stone thrown up into the sky, but not a rocket at escape velocity. And so it is with the Universe: If it contains a great deal of matter, the gravity exercised by all this matter will slow down and stop the expansion. An expanding Universe will be converted into a collapsing Universe. And if there is not enough matter, the expansion will continue forever. The present inventory of matter in the Universe is insufficient to slow the expansion, but there are reasons to think that there may be a great deal of dark matter that does not betray its existence by giving off light for the convenience of astronomers. If the expanding Universe turns out to be only temporary, ultimately to be replaced by a contracting Universe, this would certainly raise the possibility that the Universe goes through an infinite number of expansions and contractions and is infinitely old. An infinitely old Universe has no need to be created. It was always here. If, on the other hand, there is insufficient matter to reverse the expansion, then this would be consistent with a Universe created from nothing. These are deep and difficult questions which every human culture has one way or another tried to grapple with. But only in our time do we have a real prospect of uncovering some of the answers. Not by guesses or stories—but by real, repeatable, verifiable observations.
—
I think there is a reasonable chance that startling
Cassini
will arrive in the Saturn system; an entry probe built by the European Space Agency called
Huygens
will detach itself and slowly sink through the atmosphere of Titan toward its enigmatic surface. We may then learn how far Titan has gone on the path to life.
3. Is There Intelligent Life Elsewhere? Radio waves travel at the speed of light. Nothing goes faster. At the right frequency they pass cleanly through interstellar space and through planetary atmospheres. If the largest radio/radar telescope on Earth were pointing at an equivalent telescope on a planet of another star, the two telescopes could be separated by thousands of light-years and still hear each other. For these reasons, existing radio telescopes are being used to see if anyone is sending us a message. So far we have found nothing certain, but there have been tantalizing “events”—signals recorded that satisfy all the criteria for extraterrestrial intelligence, except one: You turn the telescope back and point at that patch of sky again, minutes later, months later, years later; and the signal never repeats. We are only at the beginning of the search program. A really thorough search would take a decade or two. If extraterrestrial intelligence is found, then our view of the Universe and ourselves is changed forever. And if after a long and systematic search we find nothing, then we may have calibrated something of the rarity and preciousness of life on Earth. Either way, this is a search well worth doing.
4. What Is the Origin and Fate of the Universe? Astonishingly, modern astrophysics is on the verge of determining fundamental insights on the origin, nature, and fate of the entire Universe. The Universe is expanding; all the galaxies are running away from each other in what is called the Hubble flow, one of three main pieces of evidence for an enormous explosionat the time the Universe began—or at least its present incarnation. The gravity of the Earth is strong enough to pull back a stone thrown up into the sky, but not a rocket at escape velocity. And so it is with the Universe: If it contains a great deal of matter, the gravity exercised by all this matter will slow down and stop the expansion. An expanding Universe will be converted into a collapsing Universe. And if there is not enough matter, the expansion will continue forever. The present inventory of matter in the Universe is insufficient to slow the expansion, but there are reasons to think that there may be a great deal of dark matter that does not betray its existence by giving off light for the convenience of astronomers. If the expanding Universe turns out to be only temporary, ultimately to be replaced by a contracting Universe, this would certainly raise the possibility that the Universe goes through an infinite number of expansions and contractions and is infinitely old. An infinitely old Universe has no need to be created. It was always here. If, on the other hand, there is insufficient matter to reverse the expansion, then this would be consistent with a Universe created from nothing. These are deep and difficult questions which every human culture has one way or another tried to grapple with. But only in our time do we have a real prospect of uncovering some of the answers. Not by guesses or stories—but by real, repeatable, verifiable observations.
—
I think there is a reasonable chance that startling
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