October 21, 2015
Most Earth-like worlds still to come in future
See: Most earth-like worlds have yet to be born, according to theoretical study
Earth came early to the party in the evolving universe. According to a new theoretical study, when our solar system was born 4.6 billion years ago only eight percent of the potentially habitable planets that will ever form in the universe existed. And, the party won't be over when the sun burns out in another 6 billion years. The bulk of those planets -- 92 percent -- have yet to be born.
So we have one of the early entrants in the Earth-like world history of the universe. Suppose Earth-like worlds have much higher chance of giving birth to intelligent creators that create industrial civilizations. Seems plausible. That means most of our intelligent competitors haven't come into existence yet. If we manage to keep our species alive for a long time we are going to come up against many new intelligent species.
Randall Parker, 2015 October 21 07:44 PM
Earth might have come along early out of the total number of "earth like" worlds that will exist, but given that the first stars formed about 13.4 billion years ago, other life may have really jumped the gun on us. If 4.4 billion years pass from star formation to the first space faring intelligent species then they would have a 9 billion year jump on us. They may have had to spent at least the early part of their evolutionary history as aquatic life due to the hard radiation environment of the early universe, but that doesn't appear to be a problem. If they expanded at 1% the speed of light they could have expanded 90 million light years by now. Actually a bit further, because everything used to be closer together because space itself hadn't expanded so much back then. That's a huge chunk of sky. The Virgo Supercluster, which our Milkyway is part of, is 110 million light years across and contains maybe one and a half thousand galaxies. If they expanded at 50% the speed of light, which should not be impossible for a sufficiently advanced civilisation, they would have spread about 5 billion light years in all directions from their origin.
So maybe the universe looks the way it does to us because an early bird species started expanding a long time ago and they like the universe the way it looks now. Sure, it seems improbable that a species could have started interstellar travel 9 billion years ago, but the number of stars and planets within 90 million light years, or 5 billion light years, of where we are now even 9 billion years ago would have been, well, astronomical.
And if a 9 billion year head start still seems too implausible, a 5 billion year head start gives much the same result from our point of view.
Unless we colonize their planets before they ever have a chance to evolve, which this scenario would permit us to do.
Or you have an explanation for "central casting syndrome"; The Old Ones seeded the galaxy's potentially habitable planets with species that were just variations on a theme, with them being the theme. Though why they only varied the foreheads is beyond me...
Ronald, life can't form around the first generation stars, as they're too deficient in heavy elements. Can't form rocky planets, for instance. The Sun is a third generation star, built out of material heavily enriched in heavy elements by nucleosynthesis during the deaths of earlier stars. Maybe you could end up with intelligent plasma instablities within the stars themselves, or something like that. But nothing remotely like us, and thus a competitor.
Brett, if we are considering trillions of population II stars, then some of them are going to have higher than average metalicities by chance as a result of local supernovas supplying a greater than usual amount of heavier elements. If elements from a type Ia supernova are required, which certainly may be the case, then 50 million years might be enough time for them to begin to occur after initial star formation. And we don't know that worlds like earth are required for advanced life. Could a warmer Titan like world with a density one third that of earth support a rich biosphere? We don't really know at the moment. So out of the vast number of stars in a 100 million or 5 billion light year radius, maybe some got lucky. And if that still seems too improbable then, as I mentioned, a 5 billion year head start by an alien civilisation would give much the same result from our point of view, and the oldest population I stars are about 10 billion years old.