If science can't even disprove the existence of unicorns, how can it disprove the existence of God?
I often hear the comment, "Science has proved there is no God." Don't ever be bullied by such a statement. Science is completely incapable of proving such a thing.
I'm not saying that because I don't like science, but rather because I know a little about how science works. Science operates on induction. The inductive method entails searching out things in the world and drawing generalized conclusions about those things based on observation. Scientists can only draw conclusions on what they find, not on what they can't find.
Science, by its very nature, is never capable of proving the non-existence of anything.
For example, can science prove there are no unicorns? Absolutely not. How could science ever prove that unicorns don't exist? All science can do is say that scientists may have been looking for unicorns for a long time and never found any. They might therefore conclude that no one is justified in believing that unicorns exist. They might show how certain facts considered to be evidence for unicorns in the past can be explained adequately by other things. They may invoke Occam's Razor to favor a simpler explanation for the facts than that unicorns exist. But scientists can never prove unicorns themselves don't exist.
Since science, by its very nature, is never capable of proving the non-existence of anything, one can never accurately claim that science has proven God doesn't exist. That's a misuse of the discipline. Such a claim would require omniscience. The only way one can say a thing does not exist is not by using the inductive method, but by using a deductive method, by showing that there's something about the concept itself that is contradictory.
I can confidently say for sure that no square circles exist. Why? Not because I've searched the entire universe to make sure that there aren't any square circles hiding behind a star somewhere. No, I don't need to search the world to answer that question.
The concept of square circles entails a contradictory notion, and therefore can't be real. A thing cannot be a square and be circular (i.e., not a square) at the same time. A thing cannot be a circle and squared (i.e., not a circle) at the same time. Therefore, square circles cannot exist. The laws of rationality (specifically, the law of non-contradiction) exclude the possibility of their existence.
This means, by the way, that all inductive knowledge is contingent. One cannot know anything inductively with absolute certainty. The inductive method gives us knowledge that is only probably true. Science, therefore, cannot be certain about anything in an absolute sense. It can provide a high degree of confidence based on evidence that strongly justifies scientific conclusions, but its method never allows certainty.
If you want to know something for certain, with no possibility of error--what's called apodictic certainty in philosophy--you must employ the deductive method.
There have been attempts to use the deductive method to show that certain ways of thinking about God are contradictory. The deductive problem of evil is like that. If God were all good, the argument goes, He would want to get rid of evil. If God were all powerful, He'd be able to get rid of evil. Since we still have evil, then God either is not good or not powerful, or neither, but He can't be both.
If this argument is sustained, then Christianity is defeated, because contradictory things (the belief that God is both good and powerful in the face of evil) cannot be true at the same time. The job of the Christian at this point is to show there isn't a necessary contradiction in their view of God, that genuine love does not require that there be no evil or suffering, and that preventing such a thing is a non-function of God's power. I think that can be done, and I've addressed that issue in another place (see The Strength of God and the Problem of Evil).
So don't be cowed or bullied by any comments that science has proven there is no God. Science can't do that because it uses the inductive method, not the deductive method. When you hear someone make that claim, don't contradict them. Simply ask this question: "How can science prove that someone like God doesn't exist? Explain to me how science can do that. Spell it out."
Some take the position that if science doesn't give us reason to believe in something, then no good reason exists. That's simply the false assumption of scientism.
You can even choose something you have no good reason to believe actually does exist--unicorns, or leprechauns, for that matter. Make that person show you, in principle, how science is capable of proving that any particular thing does not exist. He won't be able to. All he'll be able to show you is that science has proven certain things do exist, not that they don't exist. There's a difference.
Some take the position that if science doesn't give us reason to believe in something, then no good reason exists. That's simply the false assumption scientism. Don't ever concede the idea that science is the only method available to learn things about the world.
Remember the line in the movie Contact? Ellie Arroway claimed she loved her father, but she couldn't prove it scientifically. Does that mean she didn't really love him? No scientific test known to man could ever prove such a thing. Ellie knew her own love for her father directly and immediately. She didn't have to learn it from some scientific test.
There are things we know to be true that we don't know through empirical testing--the five senses-- but we do know through other ways. Science seems to give us true, or approximately true, information about the world, and it uses a technique that seems to be reliable, by and large. (Even this, though, is debated among philosophers of science.) However, science is not the only means of giving us true information about the world; its methodology limits it significantly.
One thing science cannot do, even in principle, is disprove the existence of anything. So when people try to use science to disprove the existence of God, they're using science illegitimately. They're misusing it, and this just makes science look bad.
The way many try to show God doesn't exist is simply by asserting it, but that's not proof. It isn't even evidence. Scientists sometimes get away with this by requiring that scientific law--natural law--must explain everything. If it can't explain a supernatural act or a supernatural Being then neither can exist. This is cheating, though.
Scientists haven't proven God doesn't exist; they've merely assumed it in many cases. They've foisted this truism on the public, and then operated from that point of view. They act as if they've really said something profound, when all they've done is given you an unjustified opinion.