We can't. But he has to exist for all of this to work. The universe has a beginning point. All matter and energy began at this point. But what caused this singularity event to happen? Nothing just happens because it can. Everything needs to cause something. That's how the universe works. So what is it? Well, it can't be matter or energy because there was none before this point, so the only logical explanation IS a supernatural being. Maybe it's not God but something else. Let's call this being Bob. Bob needs to exist forever, be all-powerful, all-knowing, and care enough to make life and the universe as we know it and keep it running. If these weren't true, then Bob couldn't have started the big bang or wouldn't have. You may call him Bob, but I call him God.
This is The irony about their hate of the meme "loss". They hate it because it's about miscarriage, but are fine with abortion. So it's okay to kill the unborn baby if you want to, but if you don't want to kill the baby it's terrible that they are dying.