Is it possible that with just the right alignment and gravitational lensing for the light of our galaxy to bend and curve back to us, so that we can directly observe our past?
Joachim,
The reference poses a curious conjecture - no one has successfully demonstrated this procedure in the past 11 years... I think its not practical to think that astronomers could find a nearby black hole and precisely aim a laser to intersect the BH gravitational field such that it encircled the BH before returning to its point of origin. That would be a real trick!
At any rate, the only information that could be derived from such a signal would be the delay in its propagation, its dispersion, etc. Not much like viewing the Earth of the dinosaurs!
In the spirit of the question - I think asking whether we could view the events of the Earth's distant past, in practical terms, I think the answer is a resounding no. Gravitational lenses generally produce a highly distorted image of a distant background object - closely linearly aligned with both the foreground lensing object and the observer. See http://en.wikipedia.org/wiki/Gravitational_lens.
You don't need anything fancy like a black hole for this. Just place a large enough mirror in deep space. If you had a mirror 10 light years from the Earth, you could use it to view ourselves as we were 20 years in the past. Of course for this to work, you need a really big mirror! (Maybe like the size of the Earth's orbit or something.) On the plus side, you might as well make the surface of the mirror curved, so that it also magnifies things and you won't need nearly as big a telescope to observe ourselves.
And somehow, I am now reminded of Italo Calvino's short story "The Light Years" (from his Cosmicomics) about a sign appearing on a distant galaxy with the words, "I saw you"...
More seriously though, with a black hole, it is possible to find trajectories for light that pass near the event horizon that circle the black hole as many times as you want before escaping back to infinity. So it is certainly possible to find trajectories where a ray of light returns in the same direction where it came from. One problem with this is that nearby rays of light will diverge, i.e., the black hole will make things appear smaller, not bigger, as we try to watch ourselves... another reason to opt for a mirror instead!
- Badges
- Science topic