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Marcelo Gleiser on “absence of evidence is not evidence of absence.”


In “Dexter’s Killer Commentary On Science And Religion” (NPR, October 28, 2011), mostly about a TV show that features a killer who works for the police department (you have to read it), physicist Marcelo Gleiser opines,

Carl Sagan used to apply a similar logic to the question of extraterrestrial alien life when he said that “the absence of evidence is not evidence of absence.” Quite often his quote is misused to explain why science can’t say anything about God: the fact that we have no “evidence” cannot be used to disprove His existence.

There is, however, a very crucial difference between using science to prove the existence of aliens and using it to prove the existence of gods. Aliens, weird as they might be, still follow the laws of nature, being creatures with a biochemistry and metabolic rates. They can interact with our sensors and thus be detected. Gods, on the other hand, are, by definition, beyond the laws of nature: they don’t interact physically with sensors and other detecting devices scientists may use to find out what’s “out there.”

How does Gleiser know that aliens “weird as they might be, still follow the laws of nature”?

Once he walks that far on the wild side (we have zero evidence of any aliens’ existence), how does he know anything at all?

And, by the way, absence of evidence IS evidence of absence, if it goes on long enough. Why don’t we think the tyrannosaur is still alive? No law of nature says it can’t be; lots of “living fossils” (we prefer the term “durable species” here) are out there. We just don’t have evidence for that one.

Also, why doesn’t anybody apply that kind of reasoning to everyday life? Does the landlady say that the absence of evidence for the rent check is not evidence of absence? Does she ever even imagine thinking that way?

That’s trouble with people like her; they are just not scientific enough.

Hat tip: Pos-Darwinista

The books on formal logic teach that an exception to the argument from ignorance exists if we can conclude that any evidence for a proposition would have been found by now. F'rinstance, if there were an extant T. rex, a rather conspicuous predator by all accounts, some evidence would be available to us. In a like manner, if the rent had been paid, the landlady would be holding the check. The like cannot be conclusively argued for God, because there are reasons other than non-existence for a lack of observable miracles (such as, He hasn't decided to manifest any). EvilSnack
"Gods, on the other hand, are, by definition, beyond the laws of nature..." Just like the universe's origin at t=0 junkdnaforlife

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