[khafra]

The mind-blowingly relevant picture: http://proto-knowledge.blogspot.com/2011/02/human-radio-bubb...

Of course, light goes really, really fast compared to anything physics says we can possibly manage for things with more rest mass than photons. Although there could be aliens on another spiral arm, or Andromeda, communication would take longer than the lifetime of our civilization; and material trade would take longer than the lifetime of our species.

[barisme]

Yes. Why do people assume you can just make a phone call to Andromeda? 'Ya, hi ET, what's new?' If Andromeda disappeared into a black hole 1 million years ago, we wouldn't even know yet. We have to wait 2.5 million years for news from Andromeda, assuming the news can't transcend the speed of light.