Absence Of Evidence

[chrisgel]

I have often heard the argument from theists that Absence of Evidence is not Evidence of Absence in relation to the amazing lack of any concrete evidence of their god.
I watched this video last night which claims to mathematically prove that indeed Absence of Evidence IS Evidence of Absence.
I am by no means a competent mathematician but I think I got the gist of what he was saying and it seemed logical to me.
I would really appreciate it if anyone with a reasonable maths aptitude could take the time to watch this and let me know if it is mathematically sound,

http://www.youtube.com/watch?v=qiNiW4_6R3I&list=FLlGTL1Mok477ZMO1Xll3bzQ

[chrisgel]

Thanks birdie. That's the sort of thing I was looking for. I don't quite see it as directly comparable to the search for aliens as that, by it's nature, is an extremely difficult thing to do given our current level of technology.
I think the logic works for other things such as ghosts, fairies, leprechauns etc. which you would expect to find on earth if they existed. So I'm not going to discount this just yet.

[jim360]

The maths is sound -- I'm not sure that the theology he uses is rational though.

More simply, his argument is an extension of the logical equivalence between A implies B and "not B" implies "not A" -- where we might imagine A being the existence of God and B being signs of His existence. The problem with the extension is that it then makes grandiose statements about the probabilities of God, and evidence, that are speculative at best.

I don't see that there's a problem with invoking Scientific or mathematical arguments in discussing God and faith. I do see that there's a problem if you prove an end result, and then massage the figures to give the conclusion of God. Theists would argue that the evidence is out there. I've not seen it myself -- but I'd argue that a further part of the maths would need to account for the person's own opinion as to how they perceive that evidence, if it exists! By which point yet more assumptions pile in and the exercise is essentially menaingless.

It would have been better to stop after having shown that absence of evidence is evidence of absence.

[chrisgel]

Thanks Jim360 - I'll watch this again with your comments in mind. I admit that I got a bit excited on first viewing and probably wasn't as dispassionate as I should have been.

[ll_billym]

I watched all of it and I have to take his and jim360's word for it that the maths are good but it struck me that the inputs to the equation contain value judgements about likeliness and how extraordinary an event is supposed to be. This adds a human element and it is then no longer purely mathematics.

[jim360]

Yes, I think that's a fair assessment.

The "proof" is conditional on the Bible story being unlikely (probably true, but not certainly) and there being no evidence for it (depends on whom you ask, doesn't it?). On another set of inputs the balance is reversed.

And, even then, if we reach the conclusion that the existence of God is "less probable", that only justifies rational scepticism, rather than outright rejection. Probabilistic arguments are always bounded by the fact that it's only probability, rather than necessarily truth -- the extraordinary may well have happened.

[jim360]

It suddenly occurred to me that I ought to add this too -- to measure the probability of any event X it is also vital to know what exactly makes up "not X". So what is the probability that there is no God, or what is the probability that the Universe spontaneously emerged unaided? Since we don't really know that either, you can't estimate the probability of X -- even if X is the overlap of a set of "unlikely events" you still can't say that it is small if you don't know anything about P(not X) -- which could also be the overlap of a set of equally unlikely events.

Again, everything is sound until he starts feeding his personal feelings about God, and (lack of) evidence for Him, into the equation.

[mibn2cweus]

Am I alone in finding the assertion "Absence of Evidence is not Evidence of Absence", inherently self contradictory? I don't suppose it should come as a great surprise that an idiot is devoid of any capacity to fathom the depths of his own idiocy.

Meanwhile, back at the ranch, the One with the alleged wherewithal to settle the question of His disputed existence once and for all remains conspicuously silent. But then, given the nature of those who declare themselves a product of His creation, I don't suppose I'd exactly be doing back flips for the opportunity of exposing myself for such ridicule either.

Perhaps the crucial question to ask oneself regarding this video is whether is was intended as an assertion of 'fact' or as a refutation of a fallacious 'logic'.

[naomi24]

//Am I alone in finding the assertion "Absence of Evidence is not Evidence of Absence", inherently self contradictory?//

I don't know if you're alone, but I don't find that contradictory. We have no evidence of intelligent life existing elsewhere in the universe, but that doesn't mean it doesn't exist. Having said that, God's reputation for interacting on a regular basis with the lives of human beings precedes him, and since there is no evidence to support that, I do think that, in his case, absence of evidence is likely to confirm evidence of absence.

[chrisgel]

Birdie - // I honestly don't think that the answer to the existence or non-existence of a creator deity is going to be found in a mathematical formula.//
But then you say //Yet the likelihood of extraterrestrial life is considered to be very high by the vast majority of scientists. //
Isn't this itself based on mathematical formula and probabilities. e.g. Drakes formula. Whilst not disagreeing with you, I don't see the problem in using maths to support an idea.

Jim - After watching again a couple of times I have to agree that he went a bit too far with his assertions.

II_Billym - As above re Drakes equation which has to have value judgements input to work.

[jomifl]

'Absence of evidence ' just means you haven't looked for it hard enough. 'Absence of evidence' in this case being absence of evidence of the non-existence of god. That's made it all much clearer............?

[jim360]

It's all very subjective, anyway. In the case of "is there intelligent life anywhere else?" really we do not have enough evidence so that this proof holds, P(¬E) is still small because we've barely begun to search; while P(X) is assumed to be fairly large -- so that P(aliens given no evidence) is still relatively unconstrained.