This is a really interesting video regarding time travel and how, more than likely, the government is already travelling back in time to promote their agendas. I'm not sure if I agree with everything, but it seems logical. Old movies and TV series often showed and still show things that were unthinkable back then. For example, touch-screen phones weren't a thing until 2006, however, the TV series Star Trek depicted them as early as the 1960s. So who is to say that this technology isn't actually older than 2006? And who is to say that this doesn't apply for time travel as well?
I have a really interesting book about time travel, which speaks about a lot of the time machines, including those that are often discussed on these forums like the HDR or Bajak's time machines.