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The red sky paradox is a difficult problem for astronomers. On the one hand, we know for certain that life exists here on Earth around a G-type yellow dwarf star. On the other hand, this type of star is not that common. M-dwarfs, which are red stars, are far more common, making up between 60-70 percent of all the stars in our galaxy, and that is likely true in other galaxies as well.
David Kipping, the associate professor of astronomy at Columbia University, has published a study, which is available in preprint on arXiv, trying to explain this situation.
In the paper, he says:
“Most stars in the universe are red dwarfs. They outnumber stars like our Sun by a factor of 5 and outlive them by another factor of 20 (population-weighted mean). When combined with recent observations uncovering an abundance of temperate, rocky planets around these diminutive stars, we are faced with an apparent logical contradiction – why do we not see a red dwarf in our sky?”
The fact that there is just one proven sample of life, much less intelligent life, leaves scientists with very little data to work from.
One piece of data, however, is enough to at least start thinking about things, and in this case, it is leaving Kipping puzzled.
“As a general principle of statistics, a random sample drawn from some unknown distribution is unlikely to be a tail-end outlier. This reasoning informs the Copernican Principle, which argues that amongst all observers, our experience is not privileged and should thus be a representative sample; an idea which has become a cornerstone of modern cosmology.”
He came up with three possible explanations for why we are here, spinning around a yellow star and not a red one.
The first explanation is what he calls the desolate M-dwarf hypothesis, which simply says that the red stars don’t produce life, or at least that they don’t produce intelligent life.
The second option is what is known as the truncated window hypothesis, which says that intelligent species don’t last long enough to develop interstellar travel or communication. Whether they wipe themselves out or some unknown force eliminates them, they just don’t survive long enough to be detected.
The last option is just dumb luck. We are here, and if we weren’t here, we wouldn’t be able to ask why we are here. So, even though it may be astronomically unlikely, just sheer luck has us where we are to ask the question.
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This last option is one that Kipping actually thinks can be basically eliminated because, according to the calculations, it is unlikely by a Bayes factor of about 1600. He explains how unlikely it is:
“That is huge. Usually we would say that anything above 10 to one is classified as strong evidence and anything above 100 to one is typically called decisive evidence. We literally don’t have words to describe numbers which are higher than 100 to one. So at 1,600 to one, we really just don’t have a leg to stand on.”
So, that leaves the two other options as possibilities. He goes on to say:
“Two plausible explanations remain: M-dwarfs do not develop observers and the window for observers is truncated to some maximum timescale. We have found that the latter is untenable in isolation, rejected at a Bayes factor of ∼33, although it may contribute in collaboration with the desolate M-dwarf hypothesis.”
He thinks the most likely is that the M-dwarf stars just don’t support life (or not intelligent life, anyway). He explains:
“I think that the solution presented that low mass stars do not develop observers provides by far the best explanation as to our existence. But barring interstellar colonization, M-dwarfs should be very quiet places. That’s my best bet. I think it is rigorously the most likely position based on the available data.”
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Of course, this is just his theory. Nothing can be proven at this point.
It is also possible that there is a lot of life out there, but their technology (or other abilities) simply aren’t at all compatible with our own. They may be sending something they use for communication right to us, and we just never see it.
The difficult part of trying to figure out life in the universe is that the universe can be very weird, and so can life. Trying to come up with answers that make sense is sometimes all but impossible.
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