I caught an interesting show on the Science Channel last night. It was Through the Wromhole
It was good presentation of current scientific thought on physics and astrophysics. Morgan Freeman did a great job in hosting it.
When it came to the topic of the search for alien life, it fell a bit short though. At least if I were to compare it to Carl Sagan's Cosmos.
In TTW, a few reasons were given as to why we haven't heard from any alien life forms. And in those explanations, the most important reason proposed by Carl Sagan was missing. Those alien life forms may not have the abundant energy to broadcast signals or create a technologically advanced civilization as we have done. Further, if they did, then like us, they are likely to exhaust in a geologically short time and then fall back to a more primitive state.
Essentially, it's possible that intelligent life could evolve on a planet that is too young to produce abundant fossil fuel reserves. That species might then never build a civilization based on an energy source that is anymore concentrated than wood or charcoal. This level of civilization persisted on Earth until the Middle Ages. Though vast civilizations like the Roman Empire could be powered by this kind of fuel, a civilization like ours could never be built. we uses thousands of times more energy than forests can provide.
In the second scenario, which fits us. A species learns has high quality fossil fuels available. The fuels make it possible to produce a hi-tech civilization and a lot of food for a growing population. But then fossil fuels are limited. A little over a hundred years later, the fuel begins to run out and the technology level and population drop fast. A civilization then would have only about a century to broadcast, then it would shut down.
Finding a civilization that was formed after a planet put down fossil fuel reserves and having the timing line up so that we can hear them in their 100 year window, reduces dramatically the odds that we'll ever detect ETs.
Carl Sagan proposed that few species would use fossil fuels to solve their societies problems, and leave their planet before they run out. He proposed that our example is probably the more common one, and we're going to revert back to the iron age without migrating to the stars.
Even the physicists barely touched on the energy problem in the program. One made a comment about a super brain organism of virtual processing space inside of a machine, going on happily without interest in the universe, so long as someone keeps paying the electric bill.
It was good program if I forget this important oversight. But the oversight does demonstrate this big hole in the thinking of our greatest minds. It does not bode well for our future.