Question about galaxies...?

Question

If you looked up at the night sky to find the Andromeda galaxy (the light entering your eyes as you look up to this galaxy traveled in space 2.5 million yrs before it hit your retina) If people in Andromeda were doing the same but looking at the milkyway what would they see? Could they know that we exist here in earth?

Answer 1

From Andromeda, they'd be seeing Earth as it was 2.5 million years ago.  No modern humans existed then.

Now let's say that they had a really big space telescope, perhaps doing interferometry over the size of a solar system.  We'll be doing this soon.  They might be able to detect oxygen on the 3rd rock from the Sun.  It'd be easier if they had an alignment that allows for transits - but Andromeda does not.

Answer 2

Aside from the fact that anyone that is potentially in the Andromeda Galaxy that might be looking at the Milky Way would be seeing it as it was 2.5 million years ago, I don't see any way that they would be able to resolve our arm of the galaxy sharp enough to even pinpoint our sun, let alone any of the planets orbiting it.  Unless, of course, they had some tremendous optics or some technology that is unfamiliar to us, all they would know about the Milky Way is that it's a large "nearby" galaxy.  

So no, not only would they not know we were here because they would be seeing us 2.5 million years ago, but they wouldn't even be able to detect that there is an earth!

Answer 3

Ah, no. You've kind of answered your own question. How would they know we exist? Light from our galaxy is 2.5 million years old before it reaches them - humanity hasn't really been around that long!

What would they see? Much what you see when you look at Andromeda - a bright spot in the sky.