Let’s assume it’s physically possible to travel backwards in time…
Every one forgets the earth is a spaceship traveling through the heavens..
Some Astrophysics 101:
The earth is orbiting the sun at a fast speed.
The Sun is orbiting the Milky way galaxy at an even faster speed.
The Milky Way galaxy is moving relative to the center of the known universe at an even faster speed…
So relative to any point in time and space in the universe – you are currently traveling at at least thousands of miles every minute..
If you traveled back in time just a few seconds, without teleporting to where the earth was, actually traveling when you go back in time… Going back in time one second – you’d end up miles away from where you stared.
Travel back in time a couple hours or more? You find yourself in the exactly same place, but in the past, before the earth / sun / milky way system got there, you’d have to wait in the dark cold of space until the earth happened to run into you (if for some reason, when you travel back in time your momentum doesn’t come with you; actually the earth probably wouldn’t catch up to you because you would be moving yourself..)
So if you want to go back and see the first black president of the USA inaugurated – you would not only have to go back in time to 2008, but also travel a millions of miles into space where the earth was in 2008.
Time travel is probably the easy part, compared to calculating exactly where you need to land and actually getting there as you travel through time.
There is a reason why Einstein and numerous science fiction writers call it space/time.
Of course, it could be that time travel is not really possible.
Or it could be that people from the future are time travelling to our period, but before they worked out how to time travel they also worked out that (a) letting us find out they were doing it would be a really bad idea, and (b) how not to let us find out, so they don’t.
And we think they are ‘people’ because? Perhaps intelligent life in the future looks a lot like a virus, and it does travel through time.