> Let's also assume that somebody had a reason to travel into the past, say to kill Hitler. Our timeline would record that an Austrian artist was murdered in the 1920s.
This would prevent World War 2 and the associated advances in technology, possibly including those leading to the time travel being possible in the first place.
You could also imagine the converse, where someone from the future brings back all scientific knowledge, thus reducing the time it takes scientists of the past to invent time travel, which in turn leads to that person bringing back all scientific knowledge sooner, perpetuating onwards until massive amounts of knowledge are acquired in small amounts of time. Such is the nature of the grandfather paradox.
This would prevent World War 2 and the associated advances in technology, possibly including those leading to the time travel being possible in the first place.