# Is it logically possible to prove that something does not exist?

Asked by

nebule (

16436)
July 4th, 2009

I’m not entirely sure I know what I’m talking about here but… Surely it is possible to prove that something *does* exist but *not* possible to prove that it does *not*? Because that would require knowing everything about everything would it not? Of course hypothetically if you did know everything and everything then it would be possible to prove that something does not exist… but…

it isn’t humanly possible to know everything is it?

Does that make sense?

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## 45 Answers

No. You can never prove a negative.

It is possible to prove that something **cannot** exist. Usually this is done by showing that if it existed, it would contradict another fact known to be true.

@AstroChuck I thought as much…were the reasons I stated *sound* ones for this conclusion?

No. Nobody knows everything there is to know and if they did know everything how would they know they know everything. Make sense??

Absence of evidence is not evidence of absence.

@lynneblundell I’m relatively certain it was a phrase I heard in 2003 regarding the accusation that Iraq had weapons of mass destruction.

AH yes…that rings a bell! x

Actually, scientifically speaking it’s a matter of “Matter”, and as one studies and breaks matter into it’s smaller parts one finds that it’s really made up of a lot of ‘space’ and smaller bits… Of matter.

All the down to something which is neither a wave nor a particle (string theory)...

So one can surmise that actually nothing exists! by that reasoning….

I can prove that there’s not a pink horse dancing on my computer desk.

I cannot prove that there’s not an invisible, intangible, pink horse dancing on my computer desk.

To prove *anything*, you must make assumptions, chief among which is the assumption that experience is accurate. Once you have made this assumption, you can just as easily prove that there is no pink horse tangoing on your desk as that there is one such horse; there is no real difference between the two. You can prove that something does not exist *in a certain place and time*, if you can prove that it would be detectable. There are also certain conditions under which you can prove that something does not exist anywhere. You can prove that there is no invisible pink horse anywhere because you can’t be invisible *and* pink; the item in question is internally inconsistent, and therefore cannot exist.

What you cannot do is prove a theory true, because it is always possible that there is another explanation that you haven’t thought of yet. You can disprove a theory, if it is contradicts itself. If the theory makes predictions that are not borne out, this is proof that the theory or its implications are at least incomplete, if not necessarily false.

Of course. One can prove, for example, that there is no integer between 4 and 5.

Simply put, only Truth exists. Because it is True. Any idea other than Truth is just untrue.

Therefore, any Untruth can be proven to not exist,due to the Fact that Truth (Only) does.

@lloydbird, Since you cannot observe everything, even if you assume that all observations are reliable, it is still not possible to prove all truths.

@AstroChuck I thought I just did. But if you know otherwise, tell me how I haven’t.:)

@lloydbird truth is relative, like the color blue. What you perceive as blue cannot be proven to be exactly the same shade of blue that I perceive, due to differences in the cones and rods in each of our eyes due to individula makeup, as well as other factors like light, radiance, and the overall health of each of our eyes.

You can prove something does not exist if given the proper constraints. e.g. Does water exist in this cup?

But I assume you’re thinking much grander.. as in: “Can we prove that X does not exist at all anywhere in the universe”.. to which you can only logically respond “no”. Even if we think X conflicts with something known to be present.. it does not preclude X from existing outside of our rule set.. or outside of the bubble in which our constants lie.

@evelyns_pet_zebra “truth is relative”, is that true? Might it not be more accurate to say that ‘Truth is Actual’ or that ‘Truth’ just ‘Is’ ?

It is possible to prove there is no pink horse dancing on your computer at a certain point in time,

HOWEVER

You cannot prove the pink horse does not exist, you cannot prove the computer does not exist, you also cannot prove that there will never be a pink horse dancing on a computer.

I’m glad I’ve got people talking…but I’m really confused :-)

it depends on whether or not the universe is infinite. If it’s finite then yes, it’s *possible* but if it has no end, then it’s impossible.

@lloydbird – Imagine this.

A man stole something from a store. It’s true that he’s bad.

A man stole something from a store to feed his hungry children, when there was no other way to do so. Is it true that he’s bad?

Truth is relative sometimes.

Doing something wrong for the right reason, does not make it right.

@laureth The ‘Truth’ in your scenario is that the ”..man stole something from a store”. The man’s reasons for doing so are open to interpretation, as far as their ‘badness’ or otherwise. Also, the actual reasons for his actions are based in ‘Truth’, although he could offer ‘False’ reasons for his having done so. This, he is only able to do because of the existent ‘Truth’ of the situation.

Until it is proven to exist it does not exist. And, theory, is just that.

@ChazMaz What, do you mean like a black swan?

In a way. Even things beyond the realm of normal expectations. Still have to be proved.

Now if after proved you still do not want to believe.

@ChazMaz “Now if after proved you still do not want to believe” Somewhat like ‘Religion’ ?

Somewhat like Religion?

Somewhat like anything.

I made that statement, “Now if after proved you still do not want to believe.”

It insinuate you understand what was meant.

Meaning ignorance then applies.

If you do not believe there is a God. That is one thing. If you have no proof, then it is probable. Till proven otherwise.

@lloydbird – if he had not stolen from the store, the ‘Truth’ would be that he let the kids starve, although he could have done something about it. That, too, is bad. Poor guy can’t win! ;)

@laureth But that doesn’t alter the fact (According to your scenario) that he did steal from the store.

I’m beginning to feel sorry for this poor guy as well. I hope his luck changes.

He stole from the store. To feed his children.

It was not an act of theft for pleasure and/or self profit.

It was to feed his children. Becoming survival. If the store owner still wanted to press charges, (that then making it theft) knowing what the reason was. That is tyranny.

Once survival comes into play the rules change. Becoming perception of view.

Wrong is wrong, even if it helps you.

@DrBill is it though? what if you’ll never be punished or looked down upon for it? right and wrong is not objective what so ever.

Right is right, wrong is wrong, no matter why.

You may “justify” why you did a wrong thing, but it is still wrong even if you had a good reason for doing it.

@DrBill- Oh, come on. Sometimes a little wrong is right. Best of all, sometimes what feels right is a little wrong. Right?

So the the Revolutionary War was wrong? We were wrong, we should not have messed with the Kings property?

@AstroChuck – You can never prove a negative? Sorry, but you’re wrong. I’m amazed how this widespread myth has survived for so long, especially in atheist communities.

It is possible to prove a negative. Here’s an example: Does a computer program exist that can determine whether computer programs will terminate or not? The answer is: Such a computer program does not exist. It is a negative and we can prove it.

Here’s a sketch of the proof:

http://en.wikipedia.org/wiki/Halting_problem#Sketch_of_proof

@mattbrowne: But that is not a proof that such a program does not exist—it is a proof that it is impossible for such a program to exist. Those are two very different statements, even though one logically follows from the other.

What about a proof that it is impossible for a deity to exist? Another proof of a negative? There’s the catch. In some cases we can prove a negative in other cases we can’t. We can’t prove that God doesn’t exist. Neither can we prove that He or She exists. We can believe it or we can not believe or we can remain undecided what to believe.

It’s entirely possible to prove a negative. It just depends on the particular negative. For instance, I can prove that there are no positive even prime numbers greater than 2—I do this by proving that it is impossible for such a number to exist.

Proving that something does not exist without proving that it is **impossible** for such a thing to exist is rather difficult, and that’s where the popular canard that it is impossible to prove a negative statement comes from.

once we have arrived at a definition of ‘thing’ then we may begin our journey towards the answer

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