Spend any time discussing metaphysics with a believer and eventually there will be a comment about having a "faith in science." It may seem like an absurd throw-away statement (especially for those who see faith as a virtue) but there may be a nugget of truth behind it. At a superficial level, there may be some validity to such a claim. No one person knows everything there is about reality as science reveals it, specialists in one field may have little more than a superficial knowledge of another. The sheer diversity of science means that no single person can know everything. So it seems like there's a strong argument for such a statement, right?
Science, it works!
Sitting in front of me now is a machine that can perform more calculations a second than the entire human race combined - and does so with startling accuracy. Hour after hour, day after day, month after month; a computer is the triumph of the scientific method. It's an incredibly complex device that is only made possible through rigorous scrutiny of the laws of nature. The precise nature of such a device speak wonders for the theoretical foundation on which it's based.
Coming back from my European adventure I flew halfway around the globe in under 24 hours, a plane flying higher than the tallest mountain was able to carry hundreds of people at 900km/h. Again, powered flight is an achievement of the scientific method with the principles of flight derived from observation and testing. Any modern transport for that matter has the same scientific underpinnings. Most of our modern-day conveniences are triumphs of the scientific method. Electricity in our houses, the ability to modify the room temperature, to cook and store away food, to have hot running water, talk to people around the world; it's an endless list of modern conveniences that are all a testament to the power of the scientific method.
To dismiss science while indulging in all modern conveniences is to be a hypocrite, yet there are many willing to commit this grave act of hypocrisy while basking in it's rewards. The victory of science is that while many are dedicated to unscientific nonsense and actively argue against the cold materialism that the scientific outlook has provided, those people at the end of their day will go home to an air-conditioned house where they cook store-bought food with electric appliances and sit down in front of the television. Science has won the battle of ideas.
Scientific knowledge is not absolutely certain, and any glance at the history of knowledge will demonstrate this notion. To use evolution as an example, what Darwin proposed first in 1859 has undergone serious revision. By gathering more evidence and by studying the natural world, scientists are able to research the mechanisms by which evolution works. As such, modern evolutionary theory is not the word of Darwin but modified to more accurately match the theory to current evidence and give it a greater predictive power.
In this respect, science is a tentative endeavour. Any confirming evidence prolongs the life of a hypothesis / theory, and any evidence that contradicts hypothesis means that the theory has to be modified to accommodate the new evidence; or even in some circumstances a hypothesis / theory is discarded completely. For this reason, despite all the confirming evidence for any particular model no model in science is regarded as certain. To fully understand this notion it is best to look back in time and see how knowledge derived from observation has led to a shifting insight.
It was only 500 years ago when the earth was the centre of the universe; the sun, moon the 5 planets and a backdrop of stars all revolved around what was only recently changed from flat to spherical. Copernicus proposed that the earth orbited the sun, and Galileo confirmed it - which in doing so led to a crime of heresy from the catholic church. Then over the next few hundred years, the discovery of other galaxies showed that the sun was not the centre of the universe, and now it stands that there is no centre of the universe. Over the course of only 500 years, Euclidean space-time of a geocentric universe has been replaced with a finite relativistic reality with the sun but an ordinary star - and the inadequacies of this view of reality is leading to further revision.
It's there where scientific knowledge is distinct from faith. Science changes over time, as more evidence comes to light and as great thinkers come up with new ways of interpreting it. Defending evolution is not defending the exact mechanisms of which evolution currently stands, rather it's defending the process by which those principles have arrived. Scientific knowledge is tentative and that is a good thing. This is what separates a scientific worldview from a faith-based one. The scientific method is based on evidence and defended with great zeal, but it's open to the notion that ideas can be wrong and gives several means to demonstrate that. Someone who doesn't understand the uncertainty and tentative nature of scientific knowledge will never be able to understand this distinction.
The bottom line
Ultimately one cannot know everything, and in science there's a certain level of trust in those who have done the experiments to verify hypothesises. But this is entirely different to what the religious call faith for the above reason. Science is testable, falsifiable, and ultimately an ever-evolving accumulation of knowledge. As a consumer of science, I believe in the results because I'm aware of the power and scope of the process. Turning on my computer is not an act of faith, just as believing that the science behind the process works. For the most part the endeavour of science is self-evident - even if the conclusions are very counter-intuitive. One doesn't have to understand how a computer works to use it, but it's downright dangerous for society not to recognise that it's the scientific method that is responsible for such a device.