"So it may be technically possible, extremely expensive and utterly useless. Sounds like a gov't program."
It would be invaluable in determining cause. Terrorist attacks, crime...
Good point, but it would also obliterate privacy. I read a story once, might have been Bradbury. There was a machine that supposedly let you view the past. You could dial up, say Congress on July 4, 1776 and see what happened.
But it turns out that you could also dial up your neighbor's bedroom three picoseconds ago.
SD