I have never met anyone travelling from the future to our time. If a time travel prototype (e.g., send a mouse back 15 seconds) were to be developed at some point in the future -- say 5100 AD --, by 5300-5500 AD travel back by thousands of years by human tourists would be probable.
If we haven't met such travelers, either time travel doesnt exist, or these "tourists" are a hulluva lot more disciplined than today's tourists anywhere, or they are out of quantum phase with us, and at most can look but not "touch" us in any way, shape, or form.
There could be lots of parallel universes. It's been theorized that there are 7 additional dimensions formed at the time of the Big Bang, but for various reasons, never grew to beyond Planck's length (10 exp minus 33 m or something like that) Thats a lot of permutations each of which may be spinning off a 4-dimensional universe -- some like ours, probably many more totally lifeless or without any form we'd recognize.