Or why atheists try to hijack science to bolster their religion, and how this shows that they don't understand science.
When I was young, and first studied science, I came to hear about something called ball lightning. Now ball lightning was widely accepted in the scientific community in the nineteenth century, as phlogiston was widely accepted in the eighteenth, but by the latter part of the twentieth century it was dismissed as so much bunk, along with sea-monsters and the like. So when I was young, and asked about ball lightning, I was told that it was superstitious nonsense.
Now, of course, ball lighting is accepted by scientists. There is lots of wrangling over the theories: burning gases; plasma; burning silicates; lots of ideas. Some of these theories are potentially quite fruitful: if plasma can be contained for many seconds in the atmosphere, there's a lot of fusion researchers who might be interested in knowing more.
The cautionary aspect is this: in the early 1970s, when I was learning about science, I was told that ball lightning was disproved by science. But since then that proof has been overturned. The moral is this: Absence of evidence is not evidence of absence.
There is a reason why science will always fall at this hurdle, though. That reason is one of the two pillars upon which science is built: a thing called Occam's Razor.
Sometime around the turn of the fourteenth century, a Franciscian monk named William of Ockham stated pluralitas non est ponenda sine neccesitate. A more modern equivalent might be when seeking explanations, choose the simplest that fits the facts. This guiding principle is used in science to avoid getting entangled in how many angels can dance on the head of a pin discussions, and instead reduce the world to simple explanations, that can in turn be used to predict future events. This sort of thing is good for questions like why do bridges fall down, which in turn can be used to predict that bridges built this way won't fall down.
Now compare these two principles:-
Absence of evidence is not evidence of absence.
When choosing explanations, pick the simplest that fits the facts.
Can you see the problem? Can you see what happens when there is a phenomenon which hasn't shown itself to you yet? Very few people have seen ball lightning as eyewitnesses, but thanks to the appearance of cheap and widespread video cameras, more and more people are seeing pictures of it. But before the video cameras came along, what do our principles have to say?
The only way to square the two principles is to take the stand, as a scientist, that you won't say anything scientific about a phenomenom unless you have seen evidence. The only way to avoid the problem is to do just that - avoid the problem - and to refuse to be drawn into the discussion as a scientist.
So, with this in mind, what can a scientist say about God? There is no scientific evidence to support the hypothesis of a God, so by Occam's Razor we should not include God in our scientific theories. But, don't forget, the absence of evidence for God is not evidence of the absence of God. All that science can say is that there is no evidence. Science cannot say there is no God. The statement there is no God is not scientific, it is religious. A scientific statement about God is science has no proof that God exists.
So, if you hear someone say there is no God, even if that person claims to be a scientist, remember Occam's Razor. That person is not speaking as a scientist. They are making a religious statement: one for which they have no proof.
The corollary of this, of course, is that atheism is a religious faith like any other, and should be treated like any other. A good scientist will have as little time for atheism as for any other religion.