What we still don't
know
Astronomer Royal Sir Martin Rees investigates ...
Are we alone? | Why
are we here? | Are we real?
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Are we alone?
Programme Contents:
1. Is there anybody out there?
2. Planets like Earth
3. Universal biology
4. Predicting evolution
5. Complexity assured
6. Is someone watching you?
But no longer. In Are We Alone?, Martin Rees puts paid to the flights of fantasy and takes us on a journey of unsettling consequence.
Seth Shostak is one of SETI’s (Institute for the Search for Extra Terrestrial Intelligence) leading investigators. He is utterly convinced that there is someone out there. The most compelling evidence is simply in the vast scales of space. There are 10,000 billion billion stars visible from Earth’s telescopes alone, and a conservative estimate places orbiting planets around one in ten of them. Would it not then be very strange if Earth were the only planet out of so many boggling billions to have been a cradle for life?
Peter Ward is a paleontologist at the University of
Washington in Seattle. He’s an expert biologist and not given to inventing
weird alien creatures. But even he has to admit that life elsewhere is more
than likely: ‘When you think there are 400 billion stars in our galaxy
alone, and there are billions of galaxies, we now think that virtually every
star has a planet, more than one planet, you’re going to have abodes for
life almost everywhere. It’s ridiculous to think it happened on this planet
and this planet alone. Life is definitely out there.’
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This is all very well but we only actually know of life in one place. If we are to search for other life in any meaningful way, life on Earth is our only reference point. Rees takes the trouble to point this out: ‘It makes sense to look at planets which we feel might have resembled the young Earth, because there, in principle, the same processes could have happened, which we believe happened here on Earth.’
One of the undeniable specialities of Earth that makes it a good home for life is that it has liquid water on its surface. Life is inconceivable without it. The chemical reactions that are believed to have originally sparked the evolution of life couldn’t have happened without liquid water. And no lifeform that we know of can live and reproduce if devoid of water.
But a planet can only maintain liquid water if it is just the right distance from its heater – its sun. Too close and water boils off, as it did on Venus. Too far away and it’s all locked up in ice, as it is on Mars.
There are thought to be one million million planets
that possess the necessary criteria for having liquid water. Endless potential
for life ...
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Well, although it was once fashionable, that idea is now losing ground. There is reason to believe that the materials of life are universal and inevitable, and produced as a by-product of cosmic processes. These materials are in meteorites, comets and even in interstellar space.
Nasa astrobiologist Lynn Rothschild explains: ‘There is a big overlap between these compounds found in interstellar space and what you would find if we took an earthworm and ground it up. Things like amino acids and the components that go into making nucleic acids. Things like DNA, which really defines life on Earth.’ All this leads scientists to suspect that life on other planets would have started from the very same chemicals as life on Earth did.
Indeed, there is tantalising evidence to suggest that life may be present on Mars. Gases that indicate the presence of living things have turned up in the Martian atmosphere. SETI scientist Seth Shostak can barely hide his excitement: ‘This methane is indicating to us that underneath that dreary, sterile surface, there are some bacteria living there. And that would tell you right away, hey, the next planet out also had biology. Biology is just really common place.’
Life on Mars would indeed suggest that life is everywhere.
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But Simon Conway Morris, a professor in the Department of Earth Sciences in Cambridge University, disagrees. He believes that there are some underlying patterns to the evolutionary process which ‘begin to suggest that we have, if you like, rules of engagement which allow us to predict what evolution will throw up almost anywhere.’
This is an important shift in thinking. Conway Morris has turned what others have ignored as life’s little coincidences into a powerful argument for the inevitability of certain structures.
Take the camera eye as an example. This has evolved separately up to seven times and the compound eye up to four times. What’s more, certain proteins of the eye, called crystallins, have evolved independently 20 to 25 times. To Conway Morris this is compelling evidence that the eye will always evolve. It’s inevitable. And the theory doesn’t just apply to eyes.
Biology is littered with examples of this so-called
‘convergent evolution’ – sex, photosynthesis, flight, crawling
on land, fur. All have evolved several times over. If life on other planets
is made of the same stuff as us, and we have reason to believe it is, then it
will follow the same patterns. We could be surprised to discover alien worlds
that are not that dissimilar to our own.
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Because natural selection, the engine of evolution, essentially fits life to its environment, one might expect that a single lifeform would come to dominate its home planet as the single best fit. But Ian Stewart has discovered a mathematical law that states otherwise. The diversity engine is best described by analogy to a pendulum.
A swinging pendulum can suddenly switch from one pattern of swing to a totally different one without apparent interference or warning. What’s going on is that invisible stresses have built up in the system causing rapid change. Similarly, evolution jogs along in the same way for a while, and then passes some threshold that causes it to change state. These state changes are the source of diversity in life, in a pendulum swing, or in just about any system.
What this actually means is that anywhere that life
evolves, it will diverge into a complex ecosystem, not unlike our own. ‘These
phenomena are universals, they are things that are going to happen anywhere
they can happen,’ explains Ian Stewart. The diversity engine is an inevitable
drive towards complexity that has other startling implications for alien lifeforms,
since, says Stewart, ‘some of them, surely, are going to go right through
to intelligent creatures and very intelligent creatures.’
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6.
Is someone watching you?
‘No one would have believed in the last years of the 19th century that
this world was being watched keenly and closely by intelligences greater than
man’s and yet as mortal as his own.’ These opening lines of HG Wells’
War of the Worlds have a prophetic ring to them.
In recent years, a conviction that alien life is inevitable has bubbled into scientific consciousness. If the conviction is right then there is reason to believe that life might have evolved in one or more of the solar systems that are much older than our own. These biospheres could have had well over a one billion-year or even a two billion-year head start on our own.
Furthermore, if complexity and intelligence are the products of natural universal laws, then at least some of the beings on planets older than our own will have superseded our intelligence. If they have done that, then you’d have thought that they’d know about us. And if so, why can’t we find them? Why aren’t they here? This was the question posed by the Italian physicist Enrico Fermi in 1950.
Professor Simon Conway Morris of Cambridge University has an unsettling take on the ‘Fermi Paradox’: ‘If we ever solve it, it will terrify us, because what will be out there will be so different, so strange, so weird, that I don’t think we’d possibly know how to deal with it. Though I find it a very interesting tension at the moment. Either we’re completely lonely, which is rather dispiriting, or we are surrounded by, for want of a better word, an over-mind, which I think is equally dispiriting.’
Which would you rather?
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Are we alone? | Why
are we here? | Are we real?
Find out more | Home
page | Graphical Version