Time's Arrow Prevents Reciprocal Images
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by
Damon22
I take it that one cannot assume that there may be someone on the lensed galaxy viewing our galaxy as a lensed galaxy via the same lensing galaxy, owing to the fact that the relative ages of the three galaxies involved are so vastly different.
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Tom_Collett
scientist
If none of the us, the source or lens were moving, in principle an alien on the source galaxy could 'look the other way', but they would be seeing the Milky Way as it was billions of years ago.
Because everything in the Universe is moving, the galaxies will eventually move out of alignment. I'm not sure how long the gravitational lens alignment lasts for, but I've just estimated a ballpark figure of about 100 million years. (Assuming galaxies move at about 200 km/s, which seems reasonable)
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by
Damon22
So, it is simply the alignment that matters, not the relative ages of the three galaxies involved. So we are in a 4.568 BY old solar system viewing a galaxy or Quasar maybe 13 BY old via a gravitational lens comprising a cluster of galaxies maybe 5 BY old and could have theoretically done so during any favourable 100 MY period for the past 4.568 BY. Why do I get the feeling that everything that has ever happened is happening now!
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Tom_Collett
scientist
The ages don't matter; as long as the source is sufficiently well aligned and emitting enough light, then we'll see it being gravitationally lensed. You don't need to worry about us living at a 'special time' 1BY ago you'd still have been able to see gravitational lenses, they just wouldn't have been the ones we see today! In a BY time the strong lenses will have changed again.
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