For example, it’s possible for me to hear footsteps behind me and then imagine, vividly enough such that I believe what I’m imagining, that I’m seeing somebody walking behind me. That is, it’s possible for (a) my auditory sense, which is one of my sensory modalities, to pick up on what’s happening directly, (b) my visual sense to not pick up on what’s happening directly, and (c) my mind to use the auditory information, directly given in the present hypothetical example, in order to fill in the missing visual information. Ultimately, I associate certain auditory information so strongly with certain visual information that getting the auditory information is enough to assume the visual information.

The different sensory modalities (e.g., the auditory sense, the visual sense, the tactile sense) are different ways of learning about the same world. Whether I hear a burglar break into my house (without seeing him) and then I call the police or I see the burglar break into my house (without hearing him) and then I call the police, what (purportedly) happened in the world is the same: A burglar broke into my house, and then I called the police. The subjective experience of hearing something without seeing it is different than the subjective experience of seeing something without hearing it, but what’s objective is the same. That is, the mental experience is different, but what’s physical is the same.

Imagine that you hear something surprising without seeing it. What would you do? You’d probably try to corroborate the surprising auditory information with visual information, tactile information, etc. You’d also probably try to get other people to corroborate what you heard etc.

That’s a lot of redundant information: my visual sense, another person’s visual sense, my auditory sense, another person’s auditory sense, etc.

Physics, being the study of the physical world, is a radically corroborative system. There are deaf people, blind people, people who are both deaf and blind, men (who usually have a worse sense of smell), women (who usually have a better sense of smell), etc. Physics doesn’t study the different ways of learning about the world. It studies the world. Whether you’re deaf, blind, both deaf and blind, somebody with a bad sense of smell, or somebody with a good sense of smell, physics tells you about the same world. In that way, physics is one of the most radically universalistic systems. In fact, physicalism (which is the metaphysical position of a lot of people with a background in physics, understandably) is in effect a kind of universalism.

Physics studies not only “visible” but also “invisible” light, not only “audible” but also “inaudible” sound. The electromagnetic spectrum, for instance, which is a model in physics that I’ll take on faith for now—I haven’t looked into the relevant physics myself yet—is a lot wider than what we as humans can sense without technology. We use technology in order to “see” X rays, FM radio waves, AM radio waves, etc.

Even an illiterate farmer a thousand years ago, though, would take the first small step toward physics when thinking to himself that his bloodhound has a much better sense of smell than he does.