You cannot physically travel backwards in time. You can see into the past--one does that every time one looks up at the night sky--but you can never physically go there.

And the reason is obvious. Say you are looking at a star that is ten light-years away. Now, say someone travels eleven light-years into the past and obliterates the star. How could you have seen it if it was never there? Or what if someone traveled into the past and prevented your parents from meeting. You would never have been born. How could you have observed the star if you weren't around to see it?

So, sorry, but physically traveling into the past is impossible. We can look into the past, and with sufficiently powerful telescopes we can detect everything there is to know about it, but that's all. The past will only tantalize.

As for the future, well, we're traveling into the future all the time! But that's not what people mean when they talk about traveling into the future. They mean traveling way into the future.

Now that is possible. But it's a relative rate that is changing. Traveling at nearly the speed of light, you could get to the Andromeda Galaxy in thirty years. To people back on Earth, who are traveling more slowly, millions of years will have passed.

If you went back to tell them about what you found, sixty years would have passed for you (thirty years out to the galaxy and thirty years back to Earth) but they would be long dead. You would have to travel into the distant past to see them, but as demonstrated earlier, that is impossible.

None of this is particularly original, of course, but it seems to me that, like it or not, it's the way things stand.