But don’t panic. At the end of the day there are good reasons to reject the radically narrow worldview of scientism.

I have to give Rosenberg credit for this: he is radically consistent in his logic. Because for anyone who adopts scientism, since science is restricted to investigating the measurable, testable, and observable things of the world, the existence of anything immaterial or “spiritual” is speculative. Rosenberg recognizes that things like free will, purpose, objective morality, and immortality cannot exist under his worldview and rejects them as illusions.

In his book The Atheist’s Guide to Reality , philosopher Alex Rosenberg defends his conviction that “the methods of science are the only reliable ways to secure knowledge of anything.” His philosophy is called scientism and is held by many of the world’s skeptics. In the spirit of his anti-supernaturalist leanings, Rosenberg asserts that “science provides all the significant truths about reality, and knowing such truths is what real understanding is all about.” In other words: if science can’t prove it, it’s not worth believing.

Scientism is self-refuting

The statement “science alone is the only reliable way to secure knowledge of anything” is itself a philosophical statement and cannot be proven by the scientific method. To test this, we might ask which scientific experiment has proven—or even could prove—that scientism is true? Of course, on deeper reflection this question is meaningless. It is like asking which mathematical equation proves that Napoleon existed in the eighteenth century.

To determine whether scientism is the true basis for determining reality, the skeptic must be willing to go beyond the scientific method. He must be willing to use philosophy—but scientism rejects the epistemic value of philosophy by definition. It is also important to note that science is impossible to do without first making certain philosophical assumptions. Science cannot prove ethical truths, the objective reality of the external world, that the laws of physics will hold in the future, or even that our cognitive faculties give true accounts of reality—and yet these sorts of assumptions serve as metaphysical underpinnings to science, holding it up and rendering it possible and potentially fruitful. You cannot do science coherently without first opening the door to philosophy.

Science cannot describe everything in the physical world

Science cannot provide a complete description of the real world, even if the natural world was all there is. The scientific method prides itself in giving us quantitative data. But as atheist philosopher Bertrand Russell acknowledges, science has boundaries when it comes to describing how physical entities are: “All that physics gives us is certain equations giving abstract properties of their changes. But as to what it is that changes, and what it changes from and to—as to this, physics is silent” (My Philosophical Development).

Rosenberg claims that all sciences can be reduced to the quantitative domain of physics. But our ordinary experience of the material world goes beyond the quantitative: it also includes the qualitative. Rosenberg and others want to reduce the nature of reality to “whatever physics says it is.” But there are no good reasons to believe that our sensory perceptions of, say, sight and sound are any less real than the physics equations that describe the particles, forces, or synapses that cause them. In fact, we rely on these qualitative experiences to do science in the first place. Edward Feser writes:

Now our ordinary experience of nature is of course qualitative through and through. We perceive colors, sounds, flavors, odors, warmth and coolness, pains and itches. . . . Physics abstracts from these rich concrete details, ignoring whatever cannot be concretely expressed in terms of equations and the like and thereby radically simplifying the natural order (Scholastic Metaphysics).

Although our sensory experiences are private, we know them to be real and intimately correlated with the natural world. In fact, qualitative perception is where the scientific method begins. Yet no one can see what I see or hear what I hear. Measurements of sound waves can be taken and mathematically analyzed, but the actual sound I hear cannot be heard by anyone else but me. My sense experience is inaccessible to others yet is still very real.

Science cannot explain everything about the physical world

Thomas Nagel, a prominent philosopher and an atheist, admits that “the physical sciences, in spite of their extraordinary successes in their own domain, necessarily leave an important aspect of nature unexplained” (The Core of Mind and Cosmos).

One thing that science cannot explain is why nature exists at all. The consensus among scientists today is that the best evidence in physics and astronomy points toward an absolute beginning to the universe. But whether or not science suggests that the universe had a beginning, science will never be able to tell us why there is something rather than nothing. Science cannot get off the ground until the physical universe exists. Whether the universe began to exist or not, science cannot give an absolute explanation for the existence of the sum total of time, space, matter, and energy—assuming it instead.

Thomas Aquinas argued, even if the world was eternal in the past, it still needs an explanation. The universe, he argued, does not explain itself and is therefore contingent (S.T. I:2:3). Just as a red brick wall is red because all of its bricks are red, in the same way a contingent universe is contingent because all of its components are contingent; and anything that is contingent needs an explanation for its existence. When it comes to explaining the universe itself, this is an explanation that science is impotent to give.

Furthermore, Aquinas showed that science is sterile when it comes to explaining why the universe is perpetual state of change or “motion.” He showed that the universal phenomenon of change must also be approached philosophically rather than scientifically. And contrary to popular rumor, Newton’s law of inertia has not put this argument to rest since Newton’s law is only concerned with local motion (motion from one place to another), and not metaphysical change such as in Thomas’s argument.

Finally, some scientists have suggested the existence of a multiverse in an attempt to avoid the theological implications (not to mention the poor consequences for skeptical worldviews like scientism) of a finite universe. But this is a metaphysical theory—a philosophical hypothesis—that cannot be proven by science; because science is restricted to this universe. So the multiverse hypothesis itself cannot be argued by anyone who holds to scientism.

Scientism is not enough

Not only does scientism refute itself, it cannot describe nor explain everything about physical reality. There is clearly more to reality than scientism allows. Our intuitive human experience of things like free will and morality suggest that the real world is not how skeptics like Rosenberg claim it is. But in the final analysis the scientific method itself is not sufficient to support scientism, because it is only equipped to give us a bare bones reading of reality for the sakes of description, prediction, and control. Because of the very limits it sets for itself, it is incapable of giving a complete description of reality.