In this day and age we are awash in a sea of information overload -- much of it good and much more of it utter nonsense. It pervades TV, social media, and cellphones. Much of it panders to people's faint wishes rather than sticking to the facts, and nowhere is this better illustrated than the garbage pseudoscience programs catering to UFO enthusiasts.
A significant part of the population in many countries believes that UFOs have visited Earth. No matter that none has plopped down in the middle of Central Park and asked to be whisked off to dinner at Tavern on the Green. These supposed encounters and sightings typically occur in the middle of nowhere where large numbers of witnesses don't exist.
It's really a central part of being human, the longing to not feel alone in the universe. And who could blame us? Our Milky Way Galaxy contains something like 400 billion stars, of which the Sun is just one. (We don't know exactly how many stars the galaxy holds because dwarf stars are very faint and can't be observed over long distances.) And astronomers know of approximately 125 billion galaxies. By back-of-the-envelope calculations, that's roughly 50,000 billion billion star systems that could host life. What are the odds we're the only one with sentient beings -- intelligence -- civilization? Not very high.
But the fact that life, even civilizations, could be common in the cosmos is very different from asking whether other beings have traveled to see us. What UFO proponents and sci-fi story writers too often fail to appreciate is the distance scale of the universe. It is HUGE. REALLY HUGE.
To begin to understand it, get some sheets of paper and a ruler with metric measurements (yes, the one everyone else in the world uses except Americans). Tape together five 8-1/2" by 11" sheets end to end and draw a long line along the bottom. Now you can start drawing a picture of the solar system, just the tiny region around our Sun and planets.
Draw the Sun on one end of the line and, 1 centimeter away from it, mark a dot to represent Earth. On the scale of 1 cm = 1 Astronomical Unit (the distance between Earth and Sun), you can now fill in some of the other planets. Mercury and Venus lie between the Sun and Earth. Mars gets plotted at 1.4 cm from the Sun, and Jupiter at about 5 cm. Plot Saturn at around 9.5 cm, Uranus at about 19 cm, Neptune at 30 cm, and Pluto (yes, a dwarf planet) a little shy of 40 cm.
The main asteroid belt lies between Mars and Jupiter, and the Kuiper Belt, the disk of icy comets and asteroids, lies between 30 and 50 cm from the Sun. The so-called Scattered Disk, a thin population of comets that have been knocked into strange orbits, extends to about 120 cm, near the edge of your drawing.
Now consider where we have been in terms of solar system exploration. Our most ambitious planetary spacecraft have all been concentrated on Mars, Jupiter, and Saturn, close to Earth on this scale. All of the space missions that have carried humans have extended to the Moon, a barely perceptible distance away from the dot representing Earth.
Look at the overall diagram you've put together. On this scale, the Oort Cloud, the enormous shell of 2 trillion comets that surrounds the solar system and in some ways marks its edge, extends to a distance of 1,000 meters -- 10 football fields end to end. The distance to the nearest star would be more than 2-1/2 times farther away. The scale of the Milky Way Galaxy on this chart would stretch 1/6th of the way to the Moon.
The point is that the distances between objects in space are incredibly vast, even in our solar system -- let alone between stars in our galaxy or in other galaxies. Yes, I know technology is an ever-improving thing for any given civilization, and that someday we may be able to travel far faster than we now believe.
Yet physics is physics, regardless of how technology changes. Light can travel at the fastest known speed because it has no mass; anything with mass takes an incredible amount of energy to start moving at any impressive speed. With an ion propulsion engine, the best technologically feasible idea we now have, we could travel to the nearest star in something like 75,000 years.
But that's only if the world's politicians had an unlimited budget to offer up for such a project. And there are serious logistical problems too. How do you stock a spacecraft with enough munchies for a 75,000-year trip?
When it really comes down to understanding the physics of space travel and the vast distances between stars, it's pretty discouraging for the idea of flitting about throughout the galaxy. And black holes acting as wormholes don't help, either. (An old sci-fi idea is that you could travel through a wormhole and end up in a different part of the universe, in a flash. But if you're first pulled into a string of protons 10 kilometers long, it doesn't really matter where you come out. It's pretty much going to ruin your day.)
So the idea of interstellar travel is, at least for now, awfully, incredibly, naïvely, amazingly, staggeringly optimistic.
It's far more likely that the universe is teeming with life -- even intelligent life -- but that dreams of standing beside beings from other worlds are just that -- dreams.
David J. Eicher is Editor-in-Chief of Astronomy magazine, author of 16 books on science and history, and president of the Astronomy Foundation. His book COMETS! Visitors from Deep Space will be out in October from Cambridge University Press.
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