We spend our nights observing distant places. Most of these celestial bodies lie so far away and existed so long ago that they’ll never be touched by human feet.
Nonetheless, we’re not truly separate. Interactions between Earth and the cosmos are continuous. In fact, everything is so interconnected, the links so intimate, that the universe’s emissaries pay continuous courtesy calls on our bodies.
The obvious ambassador is light itself, whose particles (photons) bring the electromagnetic force here from distant places. The night sky would be dark if photons created in remote empires weren’t continuously touching our retinas. Air’s near-total transparency to electromagnetic radiation at visible wavelengths lets us see these objects. Our atmosphere dims stars by a barely-perceptible one-third of a magnitude compared to their brightness in space. Translation: What we view from an unpolluted site is a true representation of the cosmic energy flux at visual wavelengths.
Even though it’s invisible to our eyes, some of the universe’s infrared energy can be detected by sensory receptors in our skin — as heat. The Sun’s warmth is obvious and welcome, while the Moon directs infrared our way as well. Thanks to its hot sunlit surface, each Full Moon temporarily warms our lower atmosphere by 0.04° Fahrenheit — like a giant bathroom heater whose rays are beamed in our direction.
Heat from beyond the solar system is measurable but harder to perceive. Raise your palm toward Arcturus, the brightest springtime star. Feel anything? Well, at least you tried. This giant yellow-orange sun warms your hand to the same extent as a candle located 3 miles (5 kilometers) away.
Some of the incoming material from space does not stop at our retinas or skin. Neutrinos, omnipresent fundamental particles, originate from nuclear fusion inside stars and travel at near light-speed. They have no problem passing through solid objects. It would take a lead wall 1,000 times thicker than the Earth-to-Pluto distance to stop the average neutrino. A trillion pass through your body each second. At night, most come up from below your chair and exit the top of your skull after having zipped through the entire planet in 1/20 of a second. By day, they mostly radiate down from the Sun, enter your head, and exit the soles of your feet.
The same can’t be said for muons. They originate 30 miles (48 km) up when cosmic rays from supernovae and other violent events strike air molecules. An average of 240 muons penetrate your body per second, each equaling the weight of 207 electrons. They damage material in cell nuclei and are responsible for some of the spontaneous tumors that have forever plagued the human race.
Other potential troublemakers include magnetars, which we’ll explore this summer. One of these tiny stars, lying on the far side of our galaxy, sent a huge burst of energy our way December 27, 2004, followed by a lesser outburst November 3, 2005. Both released more power in a quarter of a second than the Sun emits in 100,000 years.
The resulting gamma rays swept past Earth, knocked spacecraft detectors off-scale, caused an aurora, and interfered with radio communications. If you got a sudden yen for chicken with broccoli last November, it was from the extra particles that flashed through your brain.
Most theorists now believe dark matter passes through us in the form of neutralinos — a theoretical type of weakly interactive massive particle that almost never hobnobs with Earth’s baryonic material (the stuff that composes your body). Nonetheless, particles like neutralinos exert a gravitational influence and make our galaxy spin as if it were a solid disk. They glue clusters of galaxies together. Neutralinos may explain why Andromeda and the Pinwheel, our two spiral galaxy companions, don’t partake of the universe’s expansion and leave us for the wild black yonder.
Astronomers back away from the “independent Earth” paradigms that dominated 19th- and 20th-century thought. No longer are we sure our oceans arose without external help from impacting comets, or that amino acids — the precursors to life — developed independently on Earth rather than coming from visiting meteors and comets. We now attribute life’s evolution to periodic impacts and space radiation that leaks through our helpful, but not impenetrable, magnetosphere.
Bottom line: Island Earth isn’t that much of an island after all. Emissaries from distant places have always been with us. And they are with us, each of us, now.