Science's first objective, contends Nicholas Maxwell in his book, Is Science Neurotic?, is to use reason "to learn about the world and ourselves". Its second objective is "to promote wisdom by rational means" and thereby "make humanity more civilized". As for the first objective, science has been remarkably successful. As for the second, it has provided us with the capability to nearly wreck the planet.

Perhaps science should not be blamed if its creations are used by humanity's failings for destructive purposes. But, as a discipline, science presents itself as a way of thinking that is supposed to benefit ourselves and the planet on which we must learn to live sustainably. Indeed, if the purpose of science were otherwise, it would not be a practice worthy of our respect and promotion. So most of us believe in science.

This issue of belief comes close to explaining the title of Maxwell's book. In his words, "Science pretends to be more rational than it really is, and therefore prevents itself from being truly rational." According to Maxwell, for science to fulfil its second objective of making humanity wiser and more civilized, it must examine itself with brutal honestly.

Science could begin, Maxwell suggests, by asking some fundamental questions. If scientific knowledge is true, then what is it for? Does scientific truth have value? And what is that value? And are its uses ultimately destructive or beneficial?

In one important respect, science is already extremely self-critical. This has been pointed out by Professor Karl Popper, Maxwell's mentor and one of the world's most famous philosophers of science. According to Popper, science does not verify theories, it can only falsify them. All scientific knowledge is reached by this process of falsification. Theories stand because they cannot disproved. So we learn what is, by being certain of what is not. This is what Popper called "critical rationalism". Science is really based on doubt, disagreement, continual testing and perpetual refinement. Truths stand because they cannot be proven false.

This method of reaching truth, together with the question of its value, has created misunderstanding and tension with other ways of seeking knowledge. One of the most obvious examples is the conflict between science and religion, and one of its most dramatic instances was the collision in the 16th century between Galileo and the Catholic Church.

Galileo's heliocentric view of the universe was rejected by the Church because his science contradicted the prevalent theology and philosophy of the day that placed humanity at the centre of Creation. Furthermore, the evidence that Galileo obtained through his telescope required the Church to accept that observation — scientific evidence — be given preference over the established truths of theology and philosophy that were the existing standards of verification. Science was asking the Church to believe in a reality of facts that was independent of human reference and our human sense of meaning.

Science creates a body of evidence, acquired through careful measurement and strict method, that attempts to create an objective reality independent of us. It discovers truths that are disconnected from a personal framework of meaning, and we are expected to adjust our sense of meaning to fit this scientific evidence, not vice versa. This succinctly explains the science-religion conflict.

This, too, answers Maxwell's question about science's failure to make humanity wiser and more civilized. As a discipline, science has essentially separated itself from everything but itself in order to be true to its own principles — searching for truth for truth's sake

But this may be changing. We now live in a more secular world whose very ecological stability will likely be determined by our response to deteriorating environmental conditions. If we can summon the power of science to address this critically important challenge, then we may find for science a utilitarian purpose that wholly concurs with its own methods and principles — and a use that serves our needs, as well as nature's.

We already see the beginnings of this process. Science is being used to track the health of the planet from space: everything from temperatures, flora distribution, atmospheric composition, radiation levels, pollutants, topography, tectonic movement, weather, ice covering and ocean currents to algae blooms. Science is being applied to the challenges of cleaning up old energy systems and of finding new and sustainable alternatives. It is rehabilitating ecosystems. It is identifying and saving endangered plants and animals. It is cataloguing existing species and assessing their ecological values. It is studying soils and forests, water systems and air currents, biochemistry and biosystems. Indeed, almost every branch of science is wrestling with the twin tasks of understanding our planet and directing us toward sustainable behaviour.

Avoiding or ameliorating the emerging environmental crisis is becoming science's new cause, providing direction and meaning to a discipline that for 500 years has been wandering wherever its curiosity led. The prospect of a planet in ecological distress has given science a focus and an imperative — and its biggest challenge. Many issues are becoming matters of life or death. The very world that science once tried to understand dispassionately, now demands passionate advocates. And scientists everywhere are rising to this new call of purpose.