I wrote about my reasons for converting to someone in a private message, and then figured that reading over them might help other people who are in the process of converting so here they are:
The message was also way too long to post at once, so I’ll post the whole thing by way of replying to myself.
—The first step in my conversion process was the realization that science can’t explain everything in principle. For the scientific method to be valid two things have to be true: 1) Events in the universe are understandable, they aren’t arbitrary or completely random, and 2) The laws of science are the same everywhere in the universe. From my understanding these assumptions limit real science to the observable universe, which, in order for science to work, has to be deterministic in that the same laws of physics would apply in all places all the time.
I think this limits science to studying the material universe that exists. It means that science in principle cannot address the questions of why there exists something instead of nothing and of how it came to be. (It also means that speculations on the part of some scientists about an infinite number of worlds existing somewhere “out there” forever and without cause are unscientific because they can never be tested by experiment. Replacing cause and effect with randomness is also unscientific because the scientific method needs consistent cause and effect throughout time to have validity.)
What the best of modern science tells us is that the universe had a definite beginning, a moment when time itself began. At that moment the laws of nature were born and from then until now the universe evolved according to them. If we understand the laws of physics we can explain how the universe developed reasonably well, but we can never use science to answer the question or how or why it began because neither the laws of physics nor time existed then!
At the same time, everything that we know suggests that it did have a beginning. And from how I see it, there needs to be a reason why there exists something instead of nothing, and why it exists this way and not another way. This way of thinking brought me to the “first cause” argument, which goes along these lines: 1) Since everything in the universe has a cause of its existence, 2) the universe itself has a cause of its existence, and 3) the first cause of a chain of causes must be necessary (i.e. not needing a cause itself) otherwise nothing could exist.
While this isn’t a conclusive proof of God, from my perspective it is a very strong case for there to be a need for something outside the material universe that gives it a reason for existing.