Equipped with his five senses, man explores the universe around him and calls the adventure science.
-Edwin R Hubble, 1948
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."
Apologies to Edwin P. Hubble, but his words at the top of this essay, while poignant and poetic, should have read more like this:
Equipped with our five senses-along with telescopes and microscopes and mass spectrometers and seismographs and magnetometers and particle accelerators and detectors sensitive to the entire electromagnetic spectrumwe explore the universe around us and call the adventure science.
Imagine how much richer the world would appear to us and how much earlier the nature of the universe would have been figured out if we were born with high-precision, tunable eyeballs: Tune into the radiowave part of the spectrum, and the daytime sky is as dark as night, except in some choice locations, such as the center of our galaxy (visible behind some of the principal stars of the constellation Sagittarius). Dial up microwaves, and the entire cosmos is aglow with a remnant from the early universe, a wall of light that hails from 300,000 years after the big bang. Flip the dial to X rays, and the locations of nearby black holes, with matter spiraling into them, pop immediately into view. Tune into gamma rays, and see titanic explosions scattered throughout the universe at a rate of about one per day. Watch the effect of these explosions on the surrounding material as it heats up and glows in other bands of light.
If we were born with magnetic detectors, the compass would never have been invented, because we wouldn't need one. We could just tune into Earth's magnetic field lines (as some bacteria do), and the magnetic north pole would call to us from beyond the horizon. If we had gas analyzers within our retinas, we wouldn't have to wonder what was in the air we were breathing. We could just check the analyzer to see whether the air contained sufficient oxygen to sustain human life. And we would have learned thousands of years ago that the stars in the Milky Way contain the same chemical elements found here on Earth.
If we were born with big eyes and built-in Doppler motion detectors, we would have seen immediately, even as grunting troglodytes, that all distant galaxies are receding from us-that the entire universe is expanding.
If our eyes had the resolution of high-performance microscopes, nobody would ever have blamed the plague and other illnesses on divine wrath. The bacteria and viruses that make us sick would be in plain view as they crawled on our food or slid through open wounds on our skin. With simple experiments, we could easily tell which bugs were bad and which were good. And, of course, the problem of postoperative infection would have been identified and solved hundreds of years earlier.
If we could detect high-energy particles, we would be able to spot radioactive substances from great dislances-no Geiger counters necessary. You could even watch radon gas seep through the basement floor of your home and not have to pay somebody to tell you about it.
Honed from infancy, our senses allow us as adults to pass judgment on events and phenomena in our lives, to determine whether or not they "make sense." Problem is, hardly any scientific discoveries of the past century flowed from the direct application of our five senses. They flowed instead from sense-transcendent mathematics and hardware. This simple fact explains why relativity, particle physics, and ten-dimensional string theory make no sense to the average person. Neither do black holes, wormholes, and the big bang. Actually, these things don't make much sense to scientists either. At least not until they acquire a new and higher level of "common sense" from long study of the math and physics of the universe. This allows for creative thinking and enables us to pass judgment in the unfamiliar underworld of the atom or in the mind-bending domain of higher-dimensional space. The German physicist Max Planck, who won a Nobel Prize in 1918, made a similar observation about the discovery of quantum mechanics:
Modern Physics impresses us particularly with the truth of the old doctrine which teaches that there are realities existing apart from our senseperceptions, and that there are problems and conflicts where these realities are of greater value for us than the richest treasures of the world of experience.
Our five senses even interfere with sensible answers to stupid metaphysical questions, such as "If a tree falls in the forest and nobody is around to hear it, did it fall?" My best answer is, "How do you know it fell?" But that just gets people angry. So I offer a senseless analogy: "Q: If you can't smell the carbon monoxide, how do you know it's there? A: You drop dead." (Natural gas, too, is odorless to the human nose. For our protection, a pungent smell is added so that gas leaks can be safely identified and located.) In modern times, if the sole measure of what's out there flows from your senses, then a precarious life awaits you.
New ways of knowing are new windows on the universe, new detectors we can add to our growing list of nonbiological senses. Whenever this happens, a new level of majesty and complexity in the universe reveals itself to us, as though we were technologically evolving into supersentient beings, always coming to our senses.
Neil de Grasse Tyson is the Frederick P Rose Director of New York City's Hayden Planetarium. This semester he is teaching astrophysics at Princeton University.…