Douglas Adams's book Life, The Universe And Everything (the lack of a second comma is not a typo) has a section about time travel that talks about how history is so messed up as a result of time travel, but because of the rules of time, nothing was ever messed up, that's just how it happened in the first place because after all, in our minds, perception is reality. For example, I could tell you that the signing of the Declaration of Independance was actually a massive viewing of the movie Jaws and later someone went back in time, delayed the production of Jaws a few hundred years (I could also say that Jaws was originally made in 1346) and replaced it with the starting of an exceedingly boring country known as The Republic of People Who Like Jaws. However, then another person later went back and saw to it that the country was named The United States of America. How would you prove me wrong? After all, nobody would know what the past was like before time travel. However the very premise of time travel proves that none of this could have happened because of the lack of time machines in the past, present, and future, because with the implications of time machines, they all suddenly would be in complete contact with each other.
Here's why
Let's say that a person ten years in the future invents a time machine. But through a horrifying accident, he dies from a giant moustrap (because we all know that the earth in five years is going to be invaded by giant mice that find it humorous to use giant moustraps on humans) and his machine is destroyed with him. But taking the secular standpoint that time and the universe itself is infinite, someone after him would make another time machine. He would most likely also die, though it would be from an incident involving a fossilized tomato. So suppose that another person a few million years in the future makes a time machine and survives long enough to use it. He's suddenly going to have access to every point in time, and one of these infinite number of people who manages to make and use a time machine is going to have infinite opportunities to share the knowledge with some poor sap in the past. Eventually this infinite number of people, through the infinity of time would have visited the very beginning of time and given people the technology of time machines. So now people have always had time machines. However going back to the original point that perception is reality and history is perception, we would have no knowledge of time machines not existing. They would have always been there. Therefore we would have them now at this very moment and I would have seen my future self telling me to not waste my time writing this post because I'm not going to go back in time and have it happen. No, it would have already happened because anything that I do in the future that involves going into my past, I would experience as it happens in the past before I go to the future. But since we don't have time machines now, we never will because time travel just isn't possible since we don't and didn't always have the knowledge.
