I was recently reading an old scifi classic called The Door Into Summer by Robert Heinlein (quite good, by the way) and came across a passage in which the main character is talking about a time-traveling guinea pig.
The thought came to me that time travel provides a neat illustration of the Christian doctrine of the Trinity, which, if you are not familiar with it, is essentially this mind-bending statement: There is only one God; the Father, the Son and the Holy Spirit. Each of them is wholly God but none of them is the other.
If you are confused, you are hardly alone. This doctrine was not proposed because it is easy to understand, but because the Bible teaches it.
So anyway, Heinlein's story got me thinking of this illustration.
Let's pretend that the genius scientist who lives next door to you has just invented a time machine, which you get to test. You step into the machine and it sends you back to last week. You walk home, open the door and stand face to face with ... you.
Hmmm. Now here is an interesting situation. Which of these two quite distinct, quite solid and quite real individuals is you?
So does that means there are two of you?
Wellll, there are two individuals that are you, but - I know it sounds weird - there's just one you.
Does that mean that each of the individuals in the room is only part of you?
Noooo. Each of the individuals in the room, by himself, is completely and wholly you.
(Notice also that the "you" who went back in time came from the "you" who inhabited the past, and therefore the "you" in the past could - in a way - be said to be the source or "creator" of the future "you," but that doesn't mean the "you" from the future is younger than the "you" from the past. You are the same age as you.)
Similarly, the Father can be completely and wholly God and the Son can be completely and wholly God, but the Son is not the Father and the Father is not the Son (or the Holy Spirit, but I tried to keep it simple). The illustration also shows how a father-son type relationship could exist without the father existing before the son.
Big caveat: I'm not suggesting that this is how God is triune; I'm just trying to illustrate how it might be so in a situation we can imagine.
Some other things I've written on the Trinity:
Thoughts on the Trinity