Can we make sense of the world without belief? This is the central question behind the faith and science dichotomy, and one that informs how an individual chooses to relate to the world. Contrasting mythic and scientific explanations of reality, we could say that at the extreme, religious myths attempt to explain the unknown with the unknowable, while science attempts to explain the unknown with the knowable. Much of the tension springs from the belief that there are two mutually inconsistent realities, one within this world (and thus knowable) and one without (and thus unknowable).
Perhaps surprisingly, both scientist and faithful believe, even if the nature of the belief is completely different for each.
In the sciences, this is most obvious when there is an attempt to extrapolate a theory or model beyond its tested limits, as in 'gravity works the same way across the entire universe,' or 'the theory of evolution by natural selection applies to all forms of life, including extraterrestrial ones.' The scientist feels justified in doing so, given the accumulated power of her theories to explain so much of the world. We can even say, with slight impropriety, that her belief is empirically validated.
Without this kind of belief in the power of extrapolation, science would not move forward. As David Deutsch wrote in The Beginning of Infinity, "The real source of our theories is conjecture, and the real source of our knowledge is conjecture alternating with criticism."
Here is an example. Newton's theory of universal gravitation, as explained in Book III of his masterful Mathematical Principles of Natural Philosophy, the Principia, should really have been called a theory of solar system gravitation, since by the late 17th century no tests were conceivable beyond its confines. Yet, Newton called Book III The System of the World, assuming that his description of gravitational attraction as a force proportional to the quantity of mass in two bodies and decreasing with the square of the distance between them would extend to the whole world, that is, the cosmos: "if it is universally established by experiments and astronomical observations that all bodies on or near the earth gravitate toward the earth, and do so in the proportion of matter in each body ... it will have to be concluded ... that all bodies gravitate toward one another."
Later, in a letter to the Cambridge theologian Richard Bentley, dated December 10, 1692, Newton used his extrapolation on the nature of the gravitational force to justify why the universe should be infinite. If gravity acted equally across a spatially finite universe, Bentley wondered, why wouldn't all matter be concentrated in a huge ball at the center? Newton agreed that this would indeed be the case if the universe were finite in extent. However, he went on, "if the matter was evenly diffused through an infinite space, it would never convene into one mass but some of it convene into one mass and some into another so as to make an infinite number of great masses scattered at great distances from one to another throughout all that infinite space." Newton's belief in the universal nature of gravity was strong enough to let him speculate confidently about the spatial extent of the cosmos as a whole. Einstein did something very similar, but we will have to leave it for another time.
In order to move forward, a scientist must have the courage to take the risk of being wrong. You stick your neck out so that you can perhaps see a bit farther than the others.