 undisturbed, and eventually reach our eyes, redshifted even farther into the infrared, so far that it’s almost (but not quite) into the microwave region of the spectrum!
It’s good that we’re not in the microwave region of the spectrum, to be honest, because there’s a cosmic microwave background that would make this light totally undetectable.
But, could we see this far-infrared light from the early Universe?
Unfortunately, there is a cosmic infrared background, too, and right now we don’t know how to technically deal with it.
Where does this infrared background come from? Believe it or not, the same neutral hydrogen that’s so transparent to infrared light is also very good at absorbing UV and optical light.
Well, like all matter, it’s going to re-radiate that energy away again, and when it does so — just like the Earth does — it radiates it away in the infrared. So the same neutral hydrogen that’s transparent to infrared light is also a tremendous source of infrared light.
And right now, we don’t know — even in principle — how to extract a signal from the truly first stars against this cosmic infrared background.
So when I hear about the newest big news from the distant Universe, or someone asking how far away the farthest galaxy is, it’s great that we’re taking another step forward in our understanding. But let’s not pretend we’ve got the very first one of anything; we’ve still got a long way to go to get there! The most distant galaxy in the Universe is out there, but we’re going to have to really make an investment if we want to find it!