Hacker News Reader

Comment by ConcernedCoder | Hacker News Reader

So if I shoot a beam of, let's say, a movie or live feed of myself typing this comment around a black hole some 50 light years away precisely enough to have it land back here on earth 100 years in the future, would an observer see back into the past 100 years? ...in the same thread if I observe precisely enough a position near a black hole some N light years away could I see what was happening on the earth N*2 years in the past?

View on HN

Yes, but there's an easier way: use a mirror. Depending on how far you place it, you're looking at yourself in the past.

Based on other comments, and my own very limited knowledge of the relevant physics, there's no way to do this from Earth; all of the black holes (and binary block hole systems) are too far away for us to reliably aim a laser beam to slingshot around the black hole as is being described.

But the general form of what you're describing isn't any more outlandish than a time capsule, i.e. 'transmitting information into the future'.

But no, sorry, you can't see the past with the paucity of black holes near the Earth (and ignoring all of the other impediments to such a thing happening).

Yes, this is just a special case of the fact that when you look at something N light years away, you're seeing the object as it was N years ago. You're always seeing the past, never the present! Most of the time in everyday life it's infinitesimally close to the present, though.

Reply on news.ycombinator.com