Speed often provides clues to an object’s nature. For example, our planet travels at 18.5 miles (29.8 kilometers) per second. Interestingly, every solar system body must move at this same speed when it’s our distance from the Sun. Therefore, anything that collides with us, like Quadrantid meteoroids on January 4, zooms at this velocity, too.
But are they traveling alongside us like adjacent horses on a carousel, or meeting us head-on like in a game of chicken? Because comets and their debris can orbit in any direction, some do barely catch up to us from behind while others, like December’s Geminids, hit us nearly sideways, which makes them impact at around 22 miles (35 km) per second. August’s Perseid meteors slam into us head-on with a ferocious combined speed — theirs plus ours — of exactly twice our orbital velocity, 37 miles (59 km) per second. Suddenly, it makes sense that meteors are generally much faster after midnight. Those are the ones hitting us head-on as our part of Earth then faces forward in the direction we’re traveling.
Once in a Blue Moon, something hits us with a seemingly impossible speed. Then we know it must have been freshly whipped like a slingshot by an encounter with Jupiter, or else it’s an intruder from beyond the solar system. Cosmic rays are like that. They’re too fast to be from around here. But even within our galaxy, there’s some sort of speed limit. It’s probably 600 miles (1,000 km) per second — three-thousandths the speed of light. If anything were to go faster, it would escape the Milky Way.
That’s the cosmic speed limit within a couple of million light-years of here, except for a few recently discovered stars slung outward by a massive black hole. But we can access an even faster realm by observing other galaxies. The universe’s expansion means that for every million light-years of distance, galaxies rush away from us 14 miles a second faster. This is called the Hubble Flow, even though Edwin Hubble was a haughty control-freak who reportedly never flowed with anything. Just remember 14. Any galaxy 100 million light-years away whooshes at 14×100=1,400 miles per second. Simple. If you prefer kilometers, use 23.
Do the math, and galaxies 13.3 billion light-years away must apparently zoom away at about the speed of light — 186,282 miles (299,792 km) per second. Do they?
Absolutely. But how can anything go faster than light? It is here that we invoke our Einsteinian escape clause. We say the galaxies barely move. Rather, space itself is inflating. The galaxies just sit inertly like Scrabble players waiting for a vowel.
But how can space expand? Isn’t space simply nothingness? How can nothingness do anything?
Turns out, space is not nothing. There’s no such thing as nothing. (Meditate on that one, grasshopper.) Space has properties. Virtual particles pop in and out of it. An inconceivably powerful “vacuum energy” pervades its every nook and cranny. Space is no medium for sound, but it is a medium for quantum phenomena like tangled particle information, which makes the trip from Disney World to space’s farthest ZIP codes in exactly zero time. More germane to this article, space is also expanding wildly.
Back in our local sandbox, where we cannot blame squirmy space for the perceived motions of things, any increase in speed also boosts an object’s mass. Einstein insisted that a hurled baseball is a bit heavier than one sitting at home in a drawer. This is why we only compare objects when they’re all at rest in a lab. A quick brown fox is heavier than a lazy dog.
But a photon of light is a special case. You often hear that light weighs nothing. What physicists mean, however, is that photons have no “rest mass.” Like a habitual knee-shaker, a photon is never at rest. It can’t stop moving. Each photon’s high speed endows it with an “equivalent mass” that is nowhere near zero. That’s why bits of light can damage atoms and human genes. If they were truly massless, they wouldn’t harm a fly.
Moreover, all moving objects have “kinetic energy.” Make anything stop, and it suddenly releases this energy, as the dinosaurs noticed when a giant meteor slammed into their favorite Mexican beach. But when we discuss the kinetic energy of moving atoms, we call it heat.
The fact that everything is moving, spinning, or jiggling means stupendous energies are everywhere. And because the universe’s total energy never decreases in the slightest, it means the cosmos must exist forever. It surely also means it never had a true birth. (The Big Bang is merely the earliest event we know about or can date.) This strongly suggests that the universe is eternal.
Yes, on all levels, there’s much we can infer from the endless varied motions that pervade Earth and the heavens.