Your iphone would also be worthless if you physically took it back to 1/1/70 in your time machine.
Quite seriously and if-and-only-if there was even such a thing as Time Travel.....my preferred destination would likely be 1 Jan 1963.
1970 was about six months AFTER I'd finished active duty, 1966 was about the time that I realized that I had screwed up when I'd enlisted, 1964 was when I actually did the deed and that second semester in '63 was when I goofed off and put myself in the position where I had to enlist or get (shudder) drafted.
Still, if all of those things had not occurred, I'd never have met Grandma and.....
Hell, Time Travel would probably require most of the energy involved in the collision of two Black Holes anyway, so screw it.
School will be out in a few minutes and the grandkids are supposed to come over and play. I can live with that.
Siri no workie. Of course that is the case now.