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If the universe is infinite, and if the universe is homogeneous and isotropic on the largest scales, then there will be an infinite number of identical Earths in that infinite universe.
The universe may be infinite, but we can only see a finite section of it due to the finite speed of light. We can only see those parts from which light has had time to reach us since the beginning of the universe - which means we can (in theory) see a spherical universe with radius of about 47 billion light years.
According to the new analysis, a whopping 22% of sunlike stars have planets more or less the size of Earth in their habitable zones. That adds up to about 20 billion Earths in our galaxy alone, says lead author Erik Petigura, of the University of California, Berkeley.
The odds of an alien civilization coexisting with humans is often calculated by the Drake equation. It was first proposed by Frank Drake in 1961. Simply take the rate at which stars form in our galaxy and multiply it by the fraction of stars with planets, the average number of planets per star that could support life, the fraction of those that actually develop life, the fraction of life bearing planets that develop civilization, the fraction of civilizations that have detectible signals, and finally the length of time a civilization might last.
Crunch the numbers and you have the number of civilizations in our galaxy capable of communicating with us. When Drake first proposed the equation, the values for each term were largely unknown, but we now have good estimates for many of them. We know that most stars have planets, and the odds of a potentially habitable planet is actually quite high, possibly as high as 100 billion in our galaxy alone.
Unfortunately the really important factors of the Drake equation are still completely unknown. On how many potentially habitable planets does life actually arise? How many of those give rise to civilizations? How long does a typical civilization last? No idea. Depending on the answer to those questions the number of civilizations in our galaxy could range from hundreds of thousands to only one.
originally posted by: ColaTesla
I cant remember the exact equation, But its been worked out and its a mathematical certainty.
originally posted by: Blue Shift
Here's the math as of today:
Number of planets we know of with life on them: 1
Number of planets where we know how life "arose" or got on them: 0
Number of other planets out there with life on them that we know about: 0
originally posted by: Blue Shift
originally posted by: intrptr
You walk outside, see a garden and go, hey where'd that garden come from? Someone must have planted it. Where'd they get the seeds? From another garden.
But where did the seeds from the original garden come from?
As soon as the environment settled down to be relatively habitable, life appeared. Just half a billion years beyond the formation of the Earth. So how did life make the jump from raw chemicals to the evolutionary process we see today? The term for this mystery is abiogenesis and scientists are working on several theories to explain it.
One of the first clues is amino acids, the building blocks of life. In 1953, Stanley Miller and Harold Urey demonstrated that amino acids could form naturally in the environment of the early Earth. They replicated the atmosphere and chemicals present, and then used electric sparks to simulate lightning strikes.