On this topic, I always thought that if time travel were possible we would know about it already because it wouldn't matter when it was invented. < g!>
Time travel is impossible, if for no other reason than everything in the universe is MOVING.
Let’s say that you actually have a working ‘Time Machine’.
You step in, turn it on and go back or forward in time to some point.
You exit the time machine and find that you are in empty space, far from the earth or even the solar system or possibly the entire galaxy. You immediately die from lack of oxygen and freeze solid as rock within a few minutes.
Because the earth and the sun and the solar system and the galaxy are moving constantly, but you did not, you just traversed TIME and not SPACE.....................
I actually haven't had time to read the article yet. Posted then ran off to eat dinner. But time travel, at least to the future, doesn't require infinite mass. I can't imagine what they mean by that. Will read now and see. And, as I mentioned at the top, it happens everyday, all around us, to an almost imperceptible degree (only high accuracy atomic clocks can detect it).
All the inventors of time machines would be fighting on the doorstep of the US Patent Office on the day it opened to get patent #1. First to file would be the rule because no one can sort out first to invent when dealing with a time machine.
How about localization? Maybe there is a way to create an artificial universe in which all of its mass is contained within.