The simple answer is that spiritual is that which is not physical. Which doesn’t help us much, unless we can define “physical.”

Some people will tell you that “physical” means anything they can see, hear, smell, taste or touch. That’s problematic. I can’t perceive radio waves with any of my five senses—or any other form of electromagnetic energy outside of the light spectrum. Does that mean that my phone calls are being transmitted by spiritual means, and my microwave oven is cooking using spirituality?

On the other hand, I can see a rainbow. Is a rainbow physical? Are colors physical? Are the colors that appear to the eye by optical illusion (such as the green band that appears when blue and red are placed contiguously) physical?

Perhaps a better definition of physical, then, is that which can be given discrete measurement. We can’t see radio waves, gravity or nuclear forces. We can’t hear infrasound (sounds at very low frequencies) or ultrasound (sounds at very high frequencies). We can’t feel thin air with our sense of touch. But all of these can be measured, at least theoretically.

Spirituality is that which eludes discrete measurement.

“Spiritual,” then, is that which eludes discrete measurement. Have you ever tried to rate degrees of love? Or precisely categorize an idea? We can see the symptoms and effects of all of these, even measure those to a degree, but we cannot measure emotions and ideas themselves. Not because we do not have the tools, but because they inherently elude measurement. They are among those things that, sociologists and psychologists bemoan with exasperation, “count the most, but can’t be counted.”

If you are reading this, you are probably alive. Life is inherently elusive. When we say something is alive, we mean just that: it will not be the same this moment as it was the moment before. It is constantly eluding definition, transcending itself. A plant is alive because it grows. An animal is yet a higher quality of life, because it moves about deliberately, by its own reason. A human being is yet more elusive, escaping his or her own self through communication with others.

It is for this reason that the most common metaphor for the spiritual is light. Of all the physical phenomena, light is the most elusive. We don’t see light—we only see the objects off which it reflects. We can’t grasp it in our hands, hear it with our ears, taste it or smell it.

Light is our closest physical metaphor for the spiritual.

Most fascinating, even our best technology is incapable of providing a perfectly discrete measurement of light. Quantum mechanics, perhaps the most successful physical theory ever developed, determines that it is impossible to provide both the position and velocity of a photon of light (or any particle of energy). Not because we don’t have good enough tools to do so, but because that measurement simply does not exist. A photon of light has a discrete velocity without a discrete position, or a discrete position without a discrete velocity, but it does not have both.

Light, we must say, is still physical. But it’s the closest we get in our common experience to a spiritual form.

Is spirituality scientific?

If spirituality is such an essential element of the human experience, why is it that contemporary science appears to ignore it (some scientists will even deny that there is such a thing)?

Modern science is all about those things that can be measured. We haven’t yet developed tools to deal scientifically with those things that elude measurement. That creates major problems for us, because attempting to understand the universe with tools that measure only quantities but not qualities is extremely limiting.

We can speak of time in metric terms. But what about the quality of the flow of time as a human being experiences it?

We can speak of colors in terms of frequencies of light waves and their combinations, but that is still quite distant from the human experience of color, which changes throughout the day according to mood and other factors.

We can speak of neurons transferring data to be electrochemically imprinted in our brains. But what about the experience of perceiving that image in our mind? What about the “qualia” of human consciousness? How can we possibly begin to say we understand the universe we observe, when we have no scientific way to discuss the act of human observation? How can we say we understand anything at all, if we find in it no relationship to the inner experience of being human?

The things that count the most are those that can’t be counted.

Although we don’t know what spirituality is, we all experience it constantly. The deep knowledge we do have of the spiritual is through those special individuals who are capable of vivid experiences of that which eludes the rest of us. We can compare these experiences to one another, analyze them, and attempt to construct our ideas from them.

The Kabbalah contains much of this discussion, and the classic Kabbalists developed rigorous systems by which to study these ideas. The Jewish tradition, similar to that of science, is tightly accumulative, slowly and carefully building upon the confirmed knowledge of the past.

At some time, perhaps in the near future, we will find ways to include the non-physical within scientific study. Until then, it would be foolish to believe that that which cannot be counted simply doesn’t count.