Time travel could collapse (or build) a great number of bridges and buildings.
Nuclear physics, a comparatively trivial academic accomplishment, did collapse a great number of bridges and buildings, and stood a very real chance of collapsing all of the bridges and buildings. It still might.
It will, it's now simply a numbers game. Let's not kid ourselves, one day a two nuclear powers will escalate and then we'll get to see if our doomsday predictions were correct ;)
Nuclear physics, a comparatively trivial academic accomplishment, did collapse a great number of bridges and buildings, and stood a very real chance of collapsing all of the bridges and buildings. It still might.