One of my favorite columnists, Charles Krauthammer, has written a thoughtful lament concerning the apparent lack of other sapient civilizations in the universe (see: National Review Article) or at least, if there are such extraterrestials (E.T.s), why we don't hear from them? Basically, he states that, as we continue to find exo-planets within the habitable zone of "nearby" stars but are yet to see or hear any evidence of any life thereon, this suggests that "advanced civilizations destroy themselves."
I have a slightly different take. Yes, I do believe, like many renowned scientists, that the laws of probability suggest that there are perhaps many billions (maybe even trillions) of other stars with planets that could and should support life. However, when one unwinds the spans of time and distances involved in our universe, to me it is not surprising that we have not heard sapient coded message from afar.
Let me explain my logic:
- The universe is approximately 13 billion years old and our earth is about 1/10 of that age ... all back-end loaded. I would imagine that many of these other theorized exo-planets are either yet to be ... or have been burnt to a crisp when their suns became red giants. Let's estimate that this culling percentage is 50%. So automatically these billions of stars with habitable exo-planets is cut in half.
- Now, sapient life on our earth has existed for perhaps only a million years ... or 1/13,000 of this earth's existence and scientific advancement sufficient to understand our time and place in the universe has existed for, at most, 100 years ... or 1/130,000,000 of this planets existence. Let us (optimistically) imagine that this enlightenment age on earth will last for another 13,000 years. This would result in a sapient window for our planet to be about 1/1,000,000 (one-millionth) of its total existence ... which fraction I suggest should then apply to other exo-planets. Now these potential billions of habitable exo-planets with enlightened intelligent life is now reduced by 1/2,000,000 (1/2 x 1/1,000,000).
- As for distance spans, our universe is estimated to be 46 billion light years wide. Now, no communication can travel faster than the speed of light, so assuming that sapient communications was or will be sent out from another exo-planet during our current and predicted future enlightenment age, it must originate within a bubble of 13,000 light years from Earth. This reduces the number of habitable exo-planets from which we might ever receive a message by another factor of 3.5 million (13 thousand/46 billion). Or such potential messages from habitable exo-planets with enlightened intelligent life are reduced by a factor of seven trillion (1/2,000,000 x 1/3,500,000).. Now, assuming we want to get this message within the next 100 years, we then must multiply this fraction by 1/130 (100/13,000) ... resulting in a reduction of the number of eligible communicating exo-planets contacting us within the next 100 years by 910 trillion ... quite a bit larger than even the number of the estimated exo-planets.
- So, my conclusion is that, even if my calculations are off by one or two orders of magnitude, it is very unlikely that there is an exo-planet from which we might receive an intelligent coded message sometime within the next hundred years. That is assuming (and this is a huge assumption) that such an exo-planet has a power source large enough to radiate this coded message out over the vast distances of intergalactic space. This required power source has been estimated to be as large as the energy coming from our sun. Soooo ... I highly doubt that E.T. will be calling home anytime soon ... and that Charles Krauthammer should find solace in the assumption that our "civilization" could well last for at least another few thousand years without his doom-and-gloom conclusion being justified.
