# Is absence of evidence evidence of absence? **URL:** \ **Category:** Great Debates\ **Created:** [February 20, 2010, 1:18am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720 "2010-02-20T01:18:27Z")\ **Posts on this page:** 20\ **Page:** 7
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 8, 2010, 10:46am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/121 "2010-03-08T10:46:56Z")
> [@cmosdes](#): > > But we don’t know that is true or not. That is the entire point of this metaphor. In logic, you can make a statement like “X is true,” and then show that “Y is true,” is a natural consequence of that statement. Example: (of a logical argument, and not representative of previous arguments) 1. There is a _blank_ in the room. 2. We have searched the entire room, except in the box, and the _blank_ is not anywhere we have searched. 3. Therefore, the _blank_ is in the box. I said, “And let’s say that’s true.” for the sake of argument, let’s say we know something from outside the system that the participants don’t know. I didn’t say that the “you” who went to look in the room knew this to be true. I was using a logical argument that you obviously didn’t get. As common as it is. [QUOTE=cmosdes] Others seemed to be arguing that looking and not finding tells you nothing. [/QUOTE] We’re not quite on the same page, yet. You have to know when not finding anything is evidence, and when it isn’t. Or, what it’s evidence of. When there is no reason to expect poo in the yard, whether the dog exists or not, then the absence of poo is an absence of evidence, (for the existence of a dog somewhere else.) When there is a reason to expect poo in the yard, an absence of poo says something. Looking in the room is evidence of what’s in the room. Not what’s in the box. Not finding something in the room says nothing about what’s in the box. We need other evidence for that. It’s evidence of absence in the room, but it’s an absence of evidence for what’s in the box. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 8, 2010, 3:59pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/122 "2010-03-08T15:59:30Z")
> [@ch4rl3s](#): > > I admitted it wasn’t going to be compelling to you. I said there was more of it you had to ignore to believe your point of view. I don’t even have to ignore the evidence to discount the FSM. > > And that isn’t the point of the FSM. The point is to redefine the debate to be about something, (usually inside the universe,) that’s ludicrous and try to convince someone that it’s still the same debate. It isn’t. Although, some people can be convinced that it is; you were. And as long as you think it is the same debate, you have your eyes closed, your fingers in your ears, going “la la la la,” and you’re trying to convince me to do the same. So, there’s no point me addressing any other point of that post. It’s a hijack of this thread, anyway, and belongs elsewhere. You keep claiming you have more evidence for JCG than for the FSM. Show it. Until you can show something that makes JCG more compelling than the FSM, it _is_ the same debate. You seem to be missing that point. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 8, 2010, 4:50pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/123 "2010-03-08T16:50:43Z")
> [@ch4rl3s](#): > > In logic, you can make a statement like “X is true,” and then show that “Y is true,” is a natural consequence of that statement. > > Example: (of a logical argument, and not representative of previous arguments) > > 1. There is a _blank_ in the room. > 2. We have searched the entire room, except in the box, and the _blank_ is not anywhere we have searched. > 3. Therefore, the _blank_ is in the box. Yeah, yeah.. If P then Q. I get it. But the only time you know anything about Q is if P is true. If P is not true, you know _nothing_ about Q. In your case, the _blank_ is only in the box if we _know_ that _blank_ is in the room (Your “X” = _blank_ is in the room = P). Therefore, your “Y” (my Q, “_blank_ is in the box”) only follows if “X” is true. This may or may not be true. We usually don’t know, with certainty, that _blank_ is in the room. Typically there is an assumption, that _blank_ exists _somewhere_. Then the search begins, usually in the most likely places you expect to find it. Eventually, you start looking in unlikely places. Then you start looking in even unlikelier places. Pretty soon, with no sign of _blank_ anywhere, you might start to reassess if “X” is true. If “X” is that a coin contains a head and a tail side, then “Y” is that eventually the coin will show a tail side when flipped. After 1,000,000,000 times of it coming up heads, most people would conclude there is no tail side. Sure, there is still the “box” of not having actually looked at both sides of the coin, but is that really a bet you are willing to make? > [@ch4rl3s](#): > > We’re not quite on the same page, yet. You have to know when not finding anything is evidence, and when it isn’t. Or, what it’s evidence of. When there is no reason to expect poo in the yard, whether the dog exists or not, then the absence of poo is an absence of evidence, (for the existence of a dog somewhere else.) When there is a reason to expect poo in the yard, an absence of poo says something. > > Looking in the room is evidence of what’s in the room. Not what’s in the box. Not finding something in the room says nothing about what’s in the box. We need other evidence for that. It’s evidence of absence in the room, but it’s an absence of evidence for what’s in the box. If someone is going to claim that the room contains dead mice, and I look in the room and don’t see any dead mice, only a box, you are correct that I haven’t proved the room doesn’t have dead mice. However, the fact the room doesn’t contain dead mice is some evidence for what is and isn’t in the box. If the room contained dead mice there is a greater chance the box would also contain dead mice. If the room is the size of Russia and the box is shoebox sized, then completely searching an area the size of Russia and not finding any dead mice makes me pretty sure that the only area left, a shoebox, probably doesn’t contain a dead mouse. Even if the room is the size of a normal room, there is no reason to believe that what is in the box is appreciably different than what is outside the box, given no other input or information. If you are told _nothing_ about the room and walk into it without any knowledge or preconceived ideas, there is no reason to assume the box has something different than the rest of the room. Especially if you detect nothing special about the box at all. No smells, or movement or anything else. Some people want to claim the box contains magic fairies or dog poo, when outside the box there is absolutely no indications whatsoever that the anything like that is inside the box. Unless you have some other proof that there is something remarkably different about what is in the box, I will assume that whatever is in the box is unremarkable. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [March 8, 2010, 5:56pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/124 "2010-03-08T17:56:24Z")
> [@cmosdes](#): > > Given 1,000,000 boxes we might find 1 with a dead mouse. I’d call that probability 1 in a million. Each box either has a mouse or doesn’t have a mouse, but that doesn’t mean we can’t assign a probability to each of the boxes. As pTerry says, million to one shots happen nine times out of ten. But how do you know that one box in a million has a mouse? Why not two, or ten, or 500,000? Given no data, we know nothing. If someone told you the probability of a dead mouse being in the box, then that’s another story. Some people fallaciously claim that the probability of something for which there is no data is 50%. One in a million isn’t any better supported. > [@](#): > > I’ve lost track. What are the two cases we are talking about? Case 1 is an empty room with no box? And case two is a room with only a box? You seem to be arguing that until we have looked everywhere there is still a possibility there is a dead mouse. And I agree with that. I’ve said that all along. However, if you start with a room the size of Russia and search that entire room, save for one shoebox, and don’t find a single dead mouse, I’d be inclined to believe there isn’t a dead mouse in the room. I don’t need to search every dark corner to be sure. The probability the box contains a dead mouse is the same before and after we searched, but the more we look for something and don’t find it the less likely it exists anywhere. I’m assuming the box doesn’t fill up the entire room, so we need to look in the non-box part of the room, just like in case 1. But I agree - searching outside the box doesn’t say anything about what is inside the box, and it is still possible that the mouse is there. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [March 8, 2010, 6:03pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/125 "2010-03-08T18:03:12Z")
> [@ch4rl3s](#): > > Just to reiterate what I’ve already said previously… Strictly from the definition… “Absence of evidence” can never be “evidence.” if you have “evidence” it can’t be an “absence of evidence.” There is no way around it. If you have something that is evidence of absence, then whatever it is that is indicating absense is by definition evidence. > > It does seem hopeless based on the number of people who can’t understand that if you have something that can be used as evidence, it is evidence. It isn’t a lack of evidence, even if your evidence is a lack of something else. > > A lack of expected poo is a lack of poo. and it’s evidence, not a lack of it. it’s a lack of what you expected. If you didn’t expect poo in the first place, the lack of it tells you nothing. > > You want to know if your neighbour has a new dog. They’ve had one before, and always cleaned up after it. You never saw any poo. You look over the fence now and see no poo. Ah ha!!! That proves it… Oh, right, that proves nothing either way. I used “evidence of absence” in the thread title because that was being used in the thread which was arguing about this. It might be better to say “absence of expected evidence is grounds for falsifying a hypothesis” instead. That is really what is going on here. ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [March 8, 2010, 7:10pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/126 "2010-03-08T19:10:08Z")
> [@ch4rl3s](#): > > I admitted it wasn’t going to be compelling to you. I said there was more of it you had to ignore to believe your point of view. I don’t even have to ignore the evidence to discount the FSM. > > And that isn’t the point of the FSM. The point is to redefine the debate to be about something, (usually inside the universe,) that’s ludicrous and try to convince someone that it’s still the same debate. It isn’t. Although, some people can be convinced that it is; you were. And as long as you think it is the same debate, you have your eyes closed, your fingers in your ears, going “la la la la,” and you’re trying to convince me to do the same. So, there’s no point me addressing any other point of that post. It’s a hijack of this thread, anyway, and belongs elsewhere. Who ignores the bible? We look at the bible and explain it. Just like we did with lightning - lightning used to be evideince for God’s smiting wrath, but it ain’t anymore, since we explained it. All of the so-called “evidence” for the JCG evaporates similarly, leaving it in a similar boat to the FSM. That said, there’s a lot of wrongness about the FSM floating around here, starting with the fact that the _actual_ point of the FSM was to give a third controvery to teach as long as we were going to be adding religion to science classes. (Perhaps y’all were thinking of the IPU? Or perhaps that teapot.) The nifty thing about the FSM in this discussion is, it’s actually _immune_ to disproof by lack of evidence, by definition! This is because whenever you might hope to find evidence of it, the evidence _is_ there, but He reaches our His noodly appendage and conceals it from you, changing your perceptions so you literally don’t see evidence when you stare right at it. (Except when he doesn’t do so, as with the obvious correlation between pirates and global warming.) The JCG is not being portrayed as being such a cheerfully habitual liar, and is thus _less_ likely to be real than the FSM, because with the JCG the fact that all the supposed evidence evaporates when examined is actually a meaningful abscence of evidence. You have to invent some closet outside the universe to stuff him in to even _pretend_ he exists - whereas the FSM could be standing right in front of you holding your feet down and pretending it’s gravity doing it, and you can’t argue otherwise. ---
**Author:** ![SteveG1](https://avatars.discourse-cdn.com/v4/letter/s/bb73d2/32.png) [@SteveG1](https://boards.straightdope.com/u/SteveG1)\ **Post date:** [March 8, 2010, 7:19pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/127 "2010-03-08T19:19:48Z")
So why then, must a person accept and believe in the JCG, when there is no hard concrete evidence, and discount any other deities, who also suffer from a lack of hard evidence? Why should anything that lacks compelling evidence be believed? Faith. Either you have faith in it or you don’t. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 8, 2010, 7:36pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/128 "2010-03-08T19:36:56Z")
> [@Voyager](#): > > As pTerry says, million to one shots happen nine times out of ten. But how do you know that one box in a million has a mouse? Why not two, or ten, or 500,000? Given no data, we know nothing. If someone told you the probability of a dead mouse being in the box, then that’s another story. > Some people fallaciously claim that the probability of something for which there is no data is 50%. One in a million isn’t any better supported. Right. Just because there are two choices doesn’t make them equally likely. > [@Voyager](#): > > I’m assuming the box doesn’t fill up the entire room, so we need to look in the non-box part of the room, just like in case 1. But I agree - searching outside the box doesn’t say anything about what is inside the box, and it is still possible that the mouse is there. I’m saying the opposite, actually. Examining outside the box can and does tell you about what is inside the box. It is possible a mouse is in there, but without some further evidence to suggest why I should conclude that, I’m not going to conclude that. Finding mice outside the box could be an indication there are mice in the box, and similarly not finding mice around, anywhere around, could be an indication there isn’t a mouse in the box. This is just like finding a cockroach scurrying across your kitchen floor. Finding one is a good indicator you have more of them under the cupboards. However, if I search my floor, the cupboards, behind food boxes and every other accessible place in the room and find no sign of a cockroach, I’m likely to conclude there aren’t any in the places I can’t see or get to. And even if they are in there, who cares? They obviously aren’t making their way into my kitchen. ---
**Author:** ![whorfin](https://avatars.discourse-cdn.com/v4/letter/w/6f9a4e/32.png) [@whorfin](https://boards.straightdope.com/u/whorfin)\ **Post date:** [March 8, 2010, 7:45pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/129 "2010-03-08T19:45:59Z")
ETA: **Csmodes** makes the point I’m making in a more compact fashion–the existence of [mice]/[cockroaches]/[creatures that ignore the laws of physics] outside a box is not entirely irrelevant to the existence of same inside the box. It’s not proof, and it’s not conclusive, but it is relevant, and in some cases (as in searching all of russia except for one shoebox), it can be incredibly convincing evidence–that is to any reasonable person proof (even if it is not absolute proof to a mathematician or a philosopher) > [@Voyager](#): > > I’m assuming the box doesn’t fill up the entire room, so we need to look in the non-box part of the room, just like in case 1. But I agree - searching outside the box doesn’t say anything about what is inside the box, and it is still possible that the mouse is there. I disagree that it doesn’t say anything about what’s inside the box. Looking at the outside of the box, or at a million similar boxes is only “no data” about the box we’re now looking at in a very narrow set of circumstances–where the probabilities are truly independent. While a strict mathematical viewpoint of independent probability does mean that one outcome has no influence on the next, so that how a coin lands the first time does not affect the probability it will land that way the second time, a box and a room are not two flips of a coin. The probability of a mouse being in a box is not independent of the probability of a mouse being in the room in which the box is found. If you find a mouse in one room of your house, does that change the probability that there is a mouse in another room? Sure–offhand, there are two ways it does. First, it suggests your house has mice in it. (that your house is an environment in which mice can live, that there are mice in the local environment, and that they have infested your house. That makes it more likely to find a mouse in another room. Second, it removes one mouse from your house. That makes it less likely to find a mouse in another room as well. Similarly, the fact that we have no evidence that god-like creatures can exist–that (for example) the rules of physics can be broken, that makes it less likely that there is a god. Imagine I hand you a box with holes in the lid, and ask you what the chance is there are live mice in it. We don’t know. However, now imagine we are in outer space, on a spacewalk. We find no mice in outer space, because we know mice can’t survive zero pressure. I hand you a box with holes in the lid. Now, does the fact that there are no live mice outside the box change the probability that there are no live mice inside the box? Obviously yes. This is even true with the coin example. If we flip a coin a thousand times, and get heads every time, do those flips affect the probability of the next flip? No. They are not “proof” that the next flip will be a head. Do they tell us something about that probability? Yep. if it always comes up heads, it is more probable that it is a weighted coin than the also-possible, but much less probable alternative that it is just an incredibly unlikely chain of events. > [@Voyager](#): > > I used “evidence of absence” in the thread title because that was being used in the thread which was arguing about this. It might be better to say “absence of expected evidence is grounds for falsifying a hypothesis” instead. That is really what is going on here. This is very true–but people are often mistaken about what “expected evidence” is–as in the mouse/box example, we’re often not dealing with truly independent probabilities–and even if we are, we can often learn something about what that probability is from the lack of evidence of a certain outcome. I agree completely that that is properly thought of as affirmative evidence, not lack thereof. That goes to my next point: when we say something “exists,” that has an inherent meaning–that it is something detectable, tangible, and (generally) physical. Similarly, the thing that is claimed to exist often has attributes implicit in its definition. For example, when I say “is there a live mouse in the box,” you implicitly understand that I’m talking about a regular mouse, not a super-mouse that can live in zero pressure. As many have pointed out, but it bears repeating, the same is true of saying a god exists–the terms “god” and “exist” have meaning, such that absence of evidence usually is affirmative evidence of absence–as we would expect to see such evidence, given what is understood by “god’ and “exist”. Now, could we redefine those terms so that “god” is a totally noninterventionist, or a being that can hide any evidence of its existence, and “exist” includes " but not in this universe”? Sure, but that is a different argument. > [@begbert2](#): > > The nifty thing about the FSM in this discussion is, it’s actually _immune_ to disproof by lack of evidence, by definition! This is because whenever you might hope to find evidence of it, the evidence _is_ there, but He reaches our His noodly appendage and conceals it from you, changing your perceptions so you literally don’t see evidence when you stare right at it. (Except when he doesn’t do so, as with the obvious correlation between pirates and global warming.) > > The JCG is not being portrayed as being such a cheerfully habitual liar, and is thus _less_ likely to be real than the FSM, because with the JCG the fact that all the supposed evidence evaporates when examined is actually a meaningful abscence of evidence. You have to invent some closet outside the universe to stuff him in to even _pretend_ he exists - whereas the FSM could be standing right in front of you holding your feet down and pretending it’s gravity doing it, and you can’t argue otherwise. Exactly. The JCG, given its description by those claiming it exists, is not the kind of noninterventionist god existing on a different plane for which lack of evidence is not evidence of absence. It’s a god that destroyed cities, wiped out civilizations, caused miracles, often as a result of the affirmative requests or bad conduct of the faithful. Even if there was a god for which lack of evidence was not affirmative evidence of absence, it’s not this one. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [March 8, 2010, 8:34pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/130 "2010-03-08T20:34:17Z")
> [@cmosdes](#): > > I’m saying the opposite, actually. Examining outside the box can and does tell you about what is inside the box. It is possible a mouse is in there, but without some further evidence to suggest why I should conclude that, I’m not going to conclude that. Finding mice outside the box could be an indication there are mice in the box, and similarly not finding mice around, anywhere around, could be an indication there isn’t a mouse in the box. This is just like finding a cockroach scurrying across your kitchen floor. Finding one is a good indicator you have more of them under the cupboards. However, if I search my floor, the cupboards, behind food boxes and every other accessible place in the room and find no sign of a cockroach, I’m likely to conclude there aren’t any in the places I can’t see or get to. And even if they are in there, who cares? They obviously aren’t making their way into my kitchen. What’s your model of the situation? If the box is not sealed, then I agree that evidence of mice (or no evidence) has some relevance to whether a dead mouse is in the box. If, however, the box is sealed, the mouse would have to get in there through some other mechanism - cat food manufacturer, perhaps. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [March 8, 2010, 8:56pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/131 "2010-03-08T20:56:32Z")
> [@whorfin](#): > > ETA: **Csmodes** makes the point I’m making in a more compact fashion–the existence of [mice]/[cockroaches]/[creatures that ignore the laws of physics] outside a box is not entirely irrelevant to the existence of same inside the box. It’s not proof, and it’s not conclusive, but it is relevant, and in some cases (as in searching all of russia except for one shoebox), it can be incredibly convincing evidence–that is to any reasonable person proof (even if it is not absolute proof to a mathematician or a philosopher) I think you are going back to basics a little too much here. We’d have a different discussion if we were talking about a dragon in the box. We are saying “given that mice exist, what does the lack of evidence for the mouse in the box say about the statement that a mouse is in the box?” If we don’t know that mice exist, I agree that evidence for them outside the box is more relevant, unless there is some special reason for thinking it is more likely to be in the box - canned dodo, maybe? > [@](#): > > Similarly, the fact that we have no evidence that god-like creatures can exist–that (for example) the rules of physics can be broken, that makes it less likely that there is a god. The argument could be that only god creatures can break the laws of physics, so not seeing them broken when no god creatures are around is not evidence for the absence of god creatures - since both theists and atheist predict the same thing when no gods are around. Deists only go this far. Theists, on the other hand, claim that god creatures have and continue to interact with us, and make specific claims about the historical record and the efficacy of prayer. The absence of evidence for these claims is a good reason to conclude that the god creature supposedly doing this does not exist - or, rather, it falsifies the god creature hypothesis, as stated. > [@](#): > > Imagine I hand you a box with holes in the lid, and ask you what the chance is there are live mice in it. We don’t know. > > However, now imagine we are in outer space, on a spacewalk. > We find no mice in outer space, because we know mice can’t survive zero pressure. I hand you a box with holes in the lid. > > Now, does the fact that there are no live mice outside the box change the probability that there are no live mice inside the box? Obviously yes. Actually we can deduce that no live mice are in the box from the properties of mice and space. We don’t need to examine thousands, or in fact any, boxes to draw this conclusion. If the question was whether there was a live mouse in our hermetically sealed box, we wouldn’t need to examine the box to get the answer either. > [@](#): > > This is even true with the coin example. If we flip a coin a thousand times, and get heads every time, do those flips affect the probability of the next flip? No. They are not “proof” that the next flip will be a head. Do they tell us something about that probability? Yep. if it always comes up heads, it is more probable that it is a weighted coin than the also-possible, but much less probable alternative that it is just an incredibly unlikely chain of events. What we actually should be doing is constructing a hypothesis that the coin if rigged. We do the experiment, and we can state the p value that the results were due to chance, not the falsification of the null hypothesis (that the coin is fair.) The value we get is far lower than the usually accepted values for rejecting the null hypothesis, so we can reasonably conclude that the hypothesis is verified. Which is more or less what you said, but I think it is important to put some rigor behind it. We are of course assuming the existence of coins! ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 8, 2010, 11:15pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/132 "2010-03-08T23:15:51Z")
> [@Voyager](#): > > What’s your model of the situation? If the box is not sealed, then I agree that evidence of mice (or no evidence) has some relevance to whether a dead mouse is in the box. If, however, the box is sealed, the mouse would have to get in there through some other mechanism - cat food manufacturer, perhaps. As I understand it the box represents the unknowable. Asking the state of the box is is akin to asking why can’t we know what is in the box. That does have some bearing on what we might conclude about what is in the box, to be sure. However, under the present hypothetical I can’t really answer that. All I know is that I can’t see in the box. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [March 9, 2010, 1:02am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/133 "2010-03-09T01:02:58Z")
> [@cmosdes](#): > > As I understand it the box represents the unknowable. Asking the state of the box is is akin to asking why can’t we know what is in the box. That does have some bearing on what we might conclude about what is in the box, to be sure. However, under the present hypothetical I can’t really answer that. All I know is that I can’t see in the box. I think unknown at the moment is just as good as unknowable. To get back to the aliens, it is certainly knowable if aliens live on some other world, but since at the moment we have no evidence, and expect none, we can’t say anything about it. Right now it is the same as speculating about aliens living beyond the event horizon, who are unknowable. In the future the cases will be different. Of course even if a probe doesn’t find aliens, it is not proof. About the time of the first Mars fly-by probes, our MITSFS fanzine had a cartoon showing the Mariner near Mars, with a Martian in a flying saucer holding up a picture or craters to its camera. ---
**Author:** ![cmosdes](https://avatars.discourse-cdn.com/v4/letter/c/a587f6/32.png) [@cmosdes](https://boards.straightdope.com/u/cmosdes)\ **Post date:** [March 9, 2010, 2:16am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/134 "2010-03-09T02:16:43Z")
> [@Voyager](#): > > I think unknown at the moment is just as good as unknowable. To get back to the aliens, it is certainly knowable if aliens live on some other world, but since at the moment we have no evidence, and expect none, we can’t say anything about it. Right now it is the same as speculating about aliens living beyond the event horizon, who are unknowable. In the future the cases will be different. > > Of course even if a probe doesn’t find aliens, it is not proof. About the time of the first Mars fly-by probes, our MITSFS fanzine had a cartoon showing the Mariner near Mars, with a Martian in a flying saucer holding up a picture or craters to its camera. There has been some discussion about whether or not we should expect evidence of aliens (Fermi’s paradox). That aside, as I’ve stated before, absence of evidence does not mean evidence of absence if no evidence is expected and has not been attempted to be found. I think we both agree on that, no? In the case of aliens, I have two thoughts. On the one hand, SETI did hope (expect might be too strong) to find evidence of alien life. As did all those people looking at Mars and the canals. As have lots of people in various other ways. They never found anything (save for the “wow” find), so we do have an absence of evidence despite looking. On the other hand, we really haven’t looked in many places, so there is still lots of opportunity to find alien life. Most importantly of all, though, we have proof that life is possible in this universe which raises the possibility of other life much, much higher. ---
**Author:** ![Voyager](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voyager/32/133_2.png) [@Voyager](https://boards.straightdope.com/u/Voyager)\ **Post date:** [March 9, 2010, 4:37am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/135 "2010-03-09T04:37:50Z")
> [@cmosdes](#): > > There has been some discussion about whether or not we should expect evidence of aliens (Fermi’s paradox). That aside, as I’ve stated before, absence of evidence does not mean evidence of absence if no evidence is expected and has not been attempted to be found. I think we both agree on that, no? I said that in the OP, what seems like years ago. > [@](#): > > In the case of aliens, I have two thoughts. > > On the one hand, SETI did hope (expect might be too strong) to find evidence of alien life. As did all those people looking at Mars and the canals. As have lots of people in various other ways. They never found anything (save for the “wow” find), so we do have an absence of evidence despite looking. > > On the other hand, we really haven’t looked in many places, so there is still lots of opportunity to find alien life. Most importantly of all, though, we have proof that life is possible in this universe which raises the possibility of other life much, much higher. That’s right, we know that it is not impossible for there to be alien life. The absence of radio waves is evidence of the absence of civilizations which broadcast lots of radio signals between stars. That’s a far cry from evidence of absence of aliens in general. In other thread, btw, aliens were defined specifically as non-technological civilizations living around certain stars. They do qualify for the absence of evidence is not evidence of absence category. As I said then, aliens buzzing us in UFOs are another matter altogether. ---
**Author:** ![ch4rl3s](https://avatars.discourse-cdn.com/v4/letter/c/c4cdca/32.png) [@ch4rl3s](https://boards.straightdope.com/u/ch4rl3s)\ **Post date:** [March 20, 2010, 5:08am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/136 "2010-03-20T05:08:10Z")
> [@cmosdes](#): > > But you see, you have no evidence about JCG that is any more compelling than evidence for the FSM. 1. You’re looking in the wrong place: If I hand you a superball and say that the creator of this superball was a man, do you slice it into a trillion pieces and look for him? Do you then claim he can’t exist because he wasn’t trapped in the superball? It’s ridiculous to assume he must have trapped himself. (sure, if you find him, it’s validation, but if you don’t it means nothing.) 2. There’s a distinct lack of understanding of what would be possible outside the universe: [QUOTE=begbert2] You have to invent some closet outside the universe to stuff him in to even pretend he exists [/QUOTE] Everytime I suggest a god may have created the universe and isn’t bound by it’s rules, I keep getting “arguments” back that assume it’s either still in the universe or still bound by its rules. This “closet” grossly underestimates both what might be possible outside the universe, and what rules it might follow. 1. You’re looking for the wrong thing: Ok, we have to look inside the observable universe. So, what could we expect? I usually see ridiculous expectations. Like one person on this board, (some time ago,) suggesting that a good god couldn’t exist because we have free will to harm one another, that a good god must prevent all suffering. [QUOTE=begbert2] Who ignores the bible? We look at the bible and explain it. [/QUOTE] The best explanation I’ve seen yet in this thread is this: [QUOTE=cmosdes] Eyewitness testimony given 40+ years after the fact is unlikely to be highly accurate. [/QUOTE] And yet, if you were a defence attorney and that was your best defence in a 40 year old murder case with multiple witnesses, your client is likely to be convicted. (and it’s quite clear that even though the books were written 40+ years after the fact, they had been telling those stories since the beginning.) 1. You’ve made up your mind and are not looking: The FSM is just a smokescreen to redefine the “debate.” There is no scientific evidence for god. I don’t expect any. Move on. Atheists keep trying to move the issue back to that, and wonder why that doesn’t sway me. [QUOTE=begbert2] Who ignores the bible? We look at the bible and explain it. [/QUOTE] Back to this one. I haven’t seen that done. I’ve seen it dismissed with a statement. Both sides can expain anything… Even when that explanation is wrong. Deists: God is responsible for everything. Athiests: devise a natural explanation for everything. For example: Athiests used to claim that if god existed, we should naturally feel a desire to believe. They don’t claim that much anymore. (except someone on this board tried to use that argument on me a month or so ago.) They’ve moved away from that, because it’s become clear, even to scientists, that it’s true… So, do they now say, “well, that requirement is fulfilled?” No, they don’t. They say, “well, there must be a god gene to do that. It’s natural.” And so what if it is? Why would it matter how a god did this? It’s still a requirement fulfilled, but, now they still try to use it as an argument against a god. I have just as much disagreement with deists who reject science as with atheists who think _they_ haven’t seen any evidence, so _no one_ has any reason to believe. Especially when both sides look to me like they’re closing their eyes, plugging their ears, and going, “la la la la la,” in order not to see any evidence for the other side. Back to explanations. They can be wrong, even if they explain things nicely. Luminiferous Ether: even as the properties of this supposed material became more and more bizarre, (stiffer than steel, but resisted movement not at all,) it explained things nicely and scientists kept saying they had no doubt in it’s existence. Atoms and Energy: scientists were deeply and viciously divided on whether atoms existed. There was a perfectly good thermodynamic explanation for chemical reactions and no sign that atoms would ever be detectable. Everything could be described with energy. (and I find it funny that even though atoms won the debate, we once again can think of everything as energy.) Quantum Mechanics: Einstein ended both those previous debates, and then started new ones with the proponents of quantum mechanics, which, although it is the best predictive tool ever, gives us no underlying picture of reality… i.e. what is “really” happening. And now, the only way to explain every interaction in this universe, may be to propose things that exist outside it that may be forever unknowable. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [March 20, 2010, 6:09am UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/137 "2010-03-20T06:09:38Z")
> [@ch4rl3s](#): > > [QUOTE=cmosdes] > But you see, you have no evidence about JCG that is any more compelling than evidence for the FSM. 1. You’re looking in the wrong place: If I hand you a superball and say that the creator of this superball was a man, do you slice it into a trillion pieces and look for him? Do you then claim he can’t exist because he wasn’t trapped in the superball? It’s ridiculous to assume he must have trapped himself. (sure, if you find him, it’s validation, but if you don’t it means nothing.) [/quote] Except that there’s no evidence that the universe was manufactured at all. And your statement doesn’t invalidate **cmosdes** ’s point in any way; there IS no more evidence for JCG than the FSM existing outside the universe than there is for them existing in it. > [@ch4rl3s](#): > > 1. You’re looking for the wrong thing: > Ok, we have to look inside the observable universe. So, what could we expect? I usually see ridiculous expectations. Like one person on this board, (some time ago,) suggesting that a good god couldn’t exist because we have free will to harm one another, that a good god must prevent all suffering. That’s a distortion of the Problem Of Evil Argument. An omnimax god, the all good/all powerful/all seeing god the believers normally say they believe in would indeed prevent all suffering, because there could be no good purpose for it. Anything that could be accomplished with it, could be accomplished without it by an omnipotent. > [@ch4rl3s](#): > > 1. You’ve made up your mind and are not looking: > The FSM is just a smokescreen to redefine the “debate.” No, it’s to make a point. The point being, that the FSM is no less implausible than your god. Believing in the FSM is silly yes - but for the same reasons believing in your god or any other god is silly. > [@ch4rl3s](#): > > I have just as much disagreement with deists who reject science as with atheists who think _they_ haven’t seen any evidence, so _no one_ has any reason to believe. Atheists feel that, because no one ever has. Not in all of human history. Which is why you and your fellow believers can’t come up with such evidence; you just stomp your feet and insist it exists without providing it, or you try to provide it and it gets torn to shreds because it was never evidence at all. > [@ch4rl3s](#): > > Especially when both sides look to me like they’re closing their eyes, plugging their ears, and going, “la la la la la,” in order not to see any evidence for the other side. No atheist in history has ever done that, because there has never been a need. That no-evidence thing again. Even the most fervent atheist can’t go around “_closing their eyes, plugging their ears, and going, “la la la la la,” in order not to see any evidence for the other side_” when no such evidence exists. ---
**Author:** ![Cheshire\_Human](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)\ **Post date:** [March 20, 2010, 7:06pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/138 "2010-03-20T19:06:31Z")
> [@Anduril](#): > > The LACK of evidence is being acknowledged as evidence of a lack of elephants in the room. :rolleyes: Actually, you DO have evidence of absence. As soon as you open your eyes, you are employing an “elephant sensor”. If you direct your elephant sensor to **every** place an elephant can be, you have performed an exaustive search for the elephant. Performing an exaustive search for something produces concrete evidence for it’s absence, rather than an absence of evidence for it. If you have not performed an exaustive search for something, however, then all you have proved is that the elephant is not anywhere you looked. It does not prove that there is no elephant anywhere you did **not** look. Therefore, the elephant in the room is a bad example to use in answering the question.:rolleyes: ---
**Author:** ![Cheshire\_Human](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)\ **Post date:** [March 20, 2010, 7:20pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/139 "2010-03-20T19:20:36Z")
> [@Superfluous\_Parentheses](#): > > How large does the area have to be before you switch to the position that there is now suddenly no evidence at all (for or against)? Just large enough to preclude an exaustive search. ---
**Author:** ![Cheshire\_Human](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)\ **Post date:** [March 20, 2010, 10:23pm UTC](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720/140 "2010-03-20T22:23:00Z")
> [@Dan\_Norder](#): > > … if there’s anyone who this thread and \*still \*doesn’t understand they are hopeless. It’s not that they fail to understand your argument, it’s that you are insisting on a nonstandard definition of the words “absence of evidence”. They refuse to accept your definition because it’s **less useful** than the standard definition. It expands the number of things that qualify as “absence of evidence”, without giving any value from that expansion. I understand your explanation of your position perfectly, I just refuse to accept the definitions it relies on, because they do not improve my understanding of the universe. They just muddy the water. [Previous page](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720.md?page=6) [Next page](https://boards.straightdope.com/t/is-absence-of-evidence-evidence-of-absence/529720.md?page=8)