Coming to Our Senses

Natural History, March, 2001 by Neil de Grasse Tyson

Equipped with his five senses, man explores the universe around him and calls the adventure science.

-- Edwin P. Hubble

Our eyes are special organs. They allow us to register information not only from across the room but from across the universe. Without human eyesight, the science of astronomy would never have been born, and our capacity to measure our place in the universe would have been hopelessly stunted. Think of bats. Whatever bat wisdom gets passed from one generation to the next, you can bet that none of it is based on the appearance of the night sky.

When thought of as an ensemble of experimental tools for exploring the world, our senses have an astonishing acuity and range of sensitivity: Your ears can register the thunderous launch of the space shuttle, yet they can also hear a mosquito buzzing a foot away from your head. Your sense of touch allows you to feel not only a bowling ball dropped on your big toe but also a one-milligram bug crawling up your arm. Some people enjoy munching on habanero peppers, while other people can taste (and rebel against) the habanero on the level of parts per trillion. And your eyes can register the bright, sandy terrain on a sunny beach yet have no trouble spotting a lone match, freshly lit, hundreds of feet away in a darkened auditorium.

Before we get carried away in praise of ourselves, note that we gain in breadth what we lose in precision, because we register the world's stimuli in logarithmic rather than linear increments. For example, if you increase a sound's energy by a factor of two, you will barely take notice. Increase it by a factor of ten, and the change will be apparent. Our eyes perceive light the same way. If you have ever viewed a total solar eclipse, you may have noticed that the Sun's disk must be at least 90 percent covered by the Moon before anybody comments that the sky has darkened. The magnitude scale of stellar brightness, the well-known acoustic decibel scale, the seismic scale for earthquake severity--each is logarithmic, in part because of our biological propensity to see, hear, and feel the world that way.

What, if anything, lies beyond our senses? Does there exist a way of knowing that isn't limited by these biological connections with our earthly environment?

Consider that the human machine, while good at decoding the basics of the immediate environment (if it's day or night, if a creature is about to eat us), has very little talent for decoding how the rest of nature works. For that, we need the tools of science. If we want to know what's out there, then we must resort to detectors other than the ones we are born with. The job is to extend and, when we can, transcend the breadth and depth of our senses.

Some people boast of having a sixth sense, professing to know or see things that others cannot. Fortune-tellers, mind readers, and mystics top the list of those who lay claim to these mysterious powers. In so doing, they elicit widespread fascination in others, especially book publishers and television producers. The questionable field of parapsychology is founded on the belief that at least some people actually possess this talent. To me, the biggest mystery of all is why so many fortune-tellers choose to work the phones on TV psychic hotlines instead of becoming insanely wealthy futures traders on Wall Street. Apart from this inexplicable fact, the persistent failure of controlled, double-blind experiments to support the claims of parapsychology suggests that what's going on is nonsense rather than sixth sense.

Modern science wields dozens of "senses" yet scientists do not claim to have special powers, just special hardware. In the end, of course, the hardware converts the information it gleans into simple tables, charts, diagrams, or images that our innate senses can interpret. In the original Star Trek sci-fi series, the crew that beamed down from their starship to an uncharted planet always brought with them a "tricorder," a handheld device that could analyze the basic properties of anything they encountered, living or inanimate. As you waved the tricorder over the object in question, it made a spacey sound that was interpreted by the user.

Suppose a glowing blob of some unknown substance were parked right in front of you. Without some diagnostic tool like a tricorder, you would be clueless about the blob's chemical or nuclear composition. Nor could you know whether it has an electromagnetic field or whether it is strongly emitting gamma rays, X rays, ultraviolet radiation, microwaves, or radio waves. If the blob were far out in space, appearing as an unresolved point of light in the sky, your five senses would offer no hint of its distance, its velocity through space, or its rate of rotation. You would have no capacity to see the spectrum of colors that compose its emitted light, nor could you know (as bees do) whether or not the light was polarized. Without any hardware to help your analysis--and lacking the urge to lick the stuff--all you could report back to the starship would be, "Captain, it's a blob."