We are in the home stretch of our tour of the Drake equation:
N = R* × fp × ne × fl × fi × fc × L
In this equation,
- N is the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy
- R* is the rate at which new stars are created in our galaxy
- fp is the fraction of stars that have planets
- ne is the average number of planets per star that might support life
- fl is the fraction of life-supporting planets that actually develop life
- fi is the fraction of developed life that becomes intelligent
- fc is the the fraction of intelligent life that sends signals into space
- L is how long a signal-sending civilization survives and sends those signals
So far, we have estimated R* = 2 per year, fp = 0.99, ne = 0.35, fl = 0.75, and fi = 0.75. Now we turn our attention to fc, the the fraction of intelligent life that sends signals into space.
I’ll start with a couple of blanket assertions: it is difficult to imagine a civilization that doesn’t advance its technology over time, and it is even more difficult to imagine a civilization advancing its technology without eventually arriving at the ability to transmit signals through the air (and therefore space). On Earth, the advancement of technology is part of what led to the rise of our species – the use of tools, the discovery of fire, and so forth. Over time these activities even defined the names of the ages we now apply – the Stone Age, the Bronze Age, the Iron Age, and similar names across different cultures and locations. Even during the Dark Ages, we gradually got better at things over time, and although there was a long stretch of suppression, eventually folks like Galileo, Copernicus, Kepler, and Newton broke through with new understandings of the world and universe around us. At least on Earth, curiosity seems to go hand in hand with intelligence. Maybe I’m biased. Well of course I am. Whose blog is this, anyway?
Once a civilization heads down the path of ever advancing technology, it is bound to discover the workings of electromagnetism. The electromagnetic force is actually a great deal stronger than gravity. We just don’t notice all that much, because it is a force between oppositely charged particles, and most of the objects we deal with on a daily basis have an equal amount of positive and negative charge. But examples of the strength of electromagnetism are still fairly familiar to all of us. A magnet will pick a nail up off a table despite the entire Earth pulling from the other side. Voltages in power lines can move electric current across vast distances at breakneck speeds. And during a thunderstorm, the charge buildup in the clouds and on the ground leads to a sudden electric current (a.k.a. lightning) that momentarily makes the air hotter several times hotter than the surface of the Sun.
In the early 1860’s, the brilliant physicist James Clerk Maxwell developed a set of equations that revolutionized our understanding of the world around us. Maxwell showed us that electricity and magnetism are two aspects of the same fundamental force – electricity can generate magnetism and vice versa. He further showed that what we now call electromagnetic radiation (radio waves, X-rays, microwaves, and so on) is really just the propagation of electric and magnetic fields through space – each field generating another one like an insanely fast game of leapfrog. These particular frogs move through space at the speed of light, which leads to the final stroke of brilliance – Maxwell showed us light is just a form of electromagnetic radiation. The only fundamental difference between light and radio waves is their frequency – the same type of difference between the signals from neighboring radio stations. Give that man a scotch.
It didn’t take too long for others to seize on Maxwell’s equations – in the 1880’s we learned how to purposely transmit signals through the air, and radio broadcasts and communication took off in the early 20th century. Television followed, then satellite communications, then cell towers, and, well you get the picture. Our modern world is awash in electromagnetic signals – and for the last century or so, those signals have found their way out of our atmosphere and into space. Our ability communicate with each other over large distances has gone hand in hand with our ability to advance in so many other ways – so again, it is difficult to imagine that we wouldn’t have stumbled on this kind of technology at some point. We just needed one Scotsman to put it all together for us, and we were off and running. The price of this technology is that we have been sending these signals into space whether we wanted to or not. Since they travel at the speed of light, our signals have reached a distance of over 100 light years in virtually every direction – so there is an ever-expanding bubble of space in which another civilization could theoretically detect our existence. By the time you get to the edge of that bubble, the signal is pretty weak and probably quite garbled, but it is still there.
In moments of boldness, we have also sent some purposeful and targeted messages into space, to let any potential alien folk know we are here. One of the earliest and most famous attempts was the Arecibo message, sent in 1974 toward a distant star cluster. Its content was fairly basic information about our home and our species, but it won’t arrive at its target until around 25974. Among the other messages we have sent, the earliest arriving one will reach the planetary system Gliese 581 in 2029, 21 years after it was sent – and meaning even an immediate response would not arrive back here until 2050. Some among us, including the late Stephen Hawking, have been less than thrilled that we are revealing our presence and location to strangers. But the proverbial cat is out of the bag at this point.
Given the discussion to this point, you can probably guess that I think fc should be quite high – and I am indeed leaning toward decidedly optimistic. To leave some room for civilizations that simultaneously do not want to be found and have also developed some sort of technology to shield their signals from the rest of us, I’m going to set it at 0.9. Which brings our newly updated Drake equation to:
N = 2 × 0.99 × 0.35 × 0.75 × 0.75 × 0.9 × L
In other words, around once every three years, a star forms in our galaxy which will eventually see the beings on one of its planets send signals into outer space. In the next post, we will complete the equation with the final estimate: for how long does a typical civilization do that?