“There’s No Evidence For The Existence of God”

27 Aug


I used to think that the title-quote of this blog post was a good rejoinder when people asked me why I didn’t believe in any sort of god. Nowadays, I sort of grimace a little when I hear atheists use that phrase. Because now I consider myself a Bayesian. And for Bayesians, “no evidence” means something a lot different than how other people use “no evidence”.

As a Bayesian, if I say there is evidence for some hypothesis, then this means that P(H | E) > P(H). If I say there is evidence against some hypothesis, then this means that P(H | E) < P(H). Most importantly, as a Bayesian, I don't just update once; I update on multiple pieces of evidence to arrive at a provisional posterior probability about some claim. And it’s provisional because there’s always new evidence to discover. In this sense, and in my opinion, agnosticism is probably the closest mainstream or Traditional Rationality analog to being a Bayesian.

But what could it mean if I say there is no evidence for some claim? And does this apply to the concept of god?

Let’s compare two conditional probabilities: The probability of having some datum given that god exists and the probability of having some datum given the nonexistence of god. P(D | G) and P(D | ~G). So, assuming god exists, what would the most basic evidence be, and would this be more or less likely given the nonexistence of god?

Some axioms of probability to remind you of: P(E | H) + P(~E | H) = 100%. That is, the probability of the evidence given the hypothesis is true plus the nonexistence of (or existence of some other) evidence given the hypothesis is true must exhaust all possibilities. Meaning they add up to 100%. This is how you know that you have a 1/6 chance of rolling a 4 given a fair die. P(Roll 4 | Fair Die) + P(Roll Other Number | Fair Die) = 100%.

Given that, most simplistically, stories about the existence of god are more likely than no stories about god given that god exists. Meaning that P(D | G) > P(~D | G). And the opposite for the alternative: stories about the existence of god are less likely given that no god exists than no stories about god given that god doesn’t exist. Meaning, also, that P(D | ~G) < P(~D | ~G). If I can say this another way, if god did exist we would have more stories about him than if god didn’t exist: P(D | G) > P(D | ~G). Think about it. There are more non stories of things that don’t exist than there are stories of things that don’t exist. Sure there are stories of unicorns and unicorns don’t exist. But what about the trillions of things that don’t exist that we concurrently don’t have stories of? They are legion.

Basically, anecdotes about the existence of god are evidence that god exists. I go over this in the post Logical Fallacies as Weak Bayesian Evidence: Argument from Anecdote. This all might seem a bit counterintuitive, but relying on intuition to make decisions is just another way of saying that the decision conforms to your biases. Which is usually not a good thing.

So what does no evidence look like? To me, this would be some conditional probability that is equal to all alternatives. One where Bayes Factor is 1. In other words, the evidence exists independently of the hypothesis.

This all being said, I think there is evidence for the existence of god. I actually concede a little bit of relatively strong evidence for the existence of god. But, there is so much more evidence against the existence of god because god, as defined by laypeople and sophisticated theologians alike, is unfalsifiable. For most other data besides morality, god is the equivalent of a trillion^trillion sided die and expecting to roll a 3, and comparing that to the probability of rolling a 3 given normal die. This is what happens when one conceives of an all-powerful god; there’s nothing an all powerful god can’t explain.

So yes, there is evidence for the existence of god. But it is underwhelming in comparison to the orders upon orders of magnitude of the evidence — Bayesian evidence — against the existence of god.


5 responses to ““There’s No Evidence For The Existence of God”

  1. Koray

    August 27, 2014 at 7:48 pm

    No, there is not any evidence. But, you hit the pedantic nerve. The exact hypothesis in question is not god, but:

    “There are reports of past incidents about a being superior to man communicating to some men. Are these reports true?”

    Nobody is contesting the existence of the reports. But, for the accuracy of the reports, there’s zero evidence. (Someone simply making a claim doesn’t constitute evidence for it.)

    • J. Quinton

      August 27, 2014 at 8:04 pm

      You are using “evidence” in the colloquial sense. I’m using it in the technical sense.

      Ironically that’s exactly what creationist do; they use “theory” in the colloquial sense while scientists use “theory” in the technical sense.

      • Koray

        August 28, 2014 at 6:52 pm

        No, I am not. (And if you admit to using the term differently, then you have no right to grimace.)

        Firstly, the hypothesis is intimately tied to the story: before the story was first told, the hypothesis didn’t even make sense. Consider this: what do you think of the current probability of QUUX, or the smell that is closest to blue? I will tell you what the hell these mean later, at which point you will also have to recognize my stories as nonzero evidence.

        Your line on “we have more stories on things that do exist than stories on things that don’t exist” is simply naïve. For everyday subjects, perhaps that is true. But, policemen will tell you that most stories they hear are false. So, why should hearing about another cult be surprising? It’s exactly what I expect from people

      • J. Quinton

        August 29, 2014 at 10:32 am

        That’s all nice, but you haven’t actually demonstrated anything. You’ve just asserted it; you’re doing the equivalent of claiming that modus tollens is an invalid logical inference because it doesn’t match up to your intuitions about what an “inference” means (and then calling anyone who disagrees with you “naive”).

        Let’s try something out. Let’s say there are two types of blood found at a crime scene. The blood groups of the two traces are found to be of type O (a common type in the local population, where 6 out of 10 people have it) and of type AB (a rare type, with frequency 1%). A suspect, Oliver, is brought in for questioning about the murder and his blood type is found to be type O. Is Oliver having type O blood evidence that he was at the crime scene? Yes or no?

  2. mikespeir

    August 28, 2014 at 3:47 am

    I would never say, “There is no evidence for the existence of God.” What I say is, “I don’t see any good evidence for the existence of God.”

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