Have you ever noticed, though, that how long ago and how far, far away are never actually specified?
Well, by default, it can’t have been longer than 13.8 billion years ago; that’s how long the Universe has been around. And after the Universe was formed, it took a bit of time for galaxies to begin forming, so we can now narrow it down to sometime in the last 13.1 billion years and less than 30 billion light-years away.
How? Good question…
On October 24th, 2013, Bahram Mobasher and Naveen Reddy announced the discovery of z8_GND_5296, the oldest and most distant galaxy discovered to date. Believed to be formed in the first 700 million years after the creation of the Universe, z8_GND_5296 is known to be about 30 billion light-years from Earth.
Now, before I go on, the answer is yes, I see the problem. If the Universe is expanding at the speed of light and it’s only 13.8 billion years old, how could another galaxy possibly be farther than 27.6 billion light-years away?
The answer is a concept called “comoving distance”, which essentially means that the measured distance between the observer and the object being observed doesn’t take the expansion of the Universe into account.
It’s also important to note that the expansion of the Universe isn’t limited to light speed. That’s right – even though it’s 13.8 billion years old, the Universe has a diameter of about 150 billion light-years, at a minimum.
It’s enough to make one’s brain hurt.
What it comes down to, though, is that it’s the oldest galaxy we know of – for now.
But given that we’re seeing z8_GND_5296 as it was 13.1 billion years ago, I wonder what it looks like now, and if there’s life there. Sadly, as things are now, it would take another 13.1 billion years to find out, and neither the Earth nor even our Sun will still be around by then. For that matter, humans won’t exist as we know them now either. We may have moved on and we certainly will have gone through some evolutionary changes by then.
So what can we do for now?