A

　　I give two examples as to why intelligent life may not actually exist，though I admit that for me，or even for a physicist who devoted his or her entire life to researching and studying the universe，it’s shocking to claim that completely no life exists elsewhere.

　　Keeping that in mind，I’d just like to consider conditions elsewhere in the known universe.You really only need to look at our own solar system or the Earth at certain periods in its own history to appreciate that most places are much worse and much less suitable for life than our mild，watery globe.

　　So far，space scientists have discovered about seventy planets outside the solar system.But it appears that if you wish to have a planet suitable for life，you just have to be very lucky，and the more advanced the life is，the luckier you’ll have to be.I’m by no means a space observer，but I can recognize some particularly fortunate breaks we’ve had on the Earth.For example：

　　We are，to a degree，at the right distance from the perfect type of star，the one that is big enough to radiate a huge amount of energy，but not so big as to burn itself out quickly.Had our sun been ten times as huge，it would have burnt out completely after only ten million years，instead of ten billion and surely we would not exist.Too near，everything on the Earth would have boiled and withered away；any further，everything would have frozen over.

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