What is the most distant object humans have ever seen in the known Universe? The latest record-holder is a galaxy that is about 13.4 billion light-years away! Or, is it? Something screwy is going on when we talk about distances in an our ever-expanding Universe.
The Universe itself is roughly 13.8 billion years old, so this distant galaxy (MACS0647-D) is indeed old, since its light has been traveling to us for 13 billion years.
In comparison, our Solar System is only about 4.6 billion years old. (Our Solar System consists of our Sun and the orbiting planets and objects. Our Sun is one of many stars in the Milky Way Galaxy which is one among the billions of galaxies in what makes up the total known Universe!)
The object that we see, however, is very young, since it took so many years to travel to us. It’s from the time when the Universe itself was still an infant, just 420 million years old or 3 percent of its present age! So, we can look back into the very formation of the Universe.
The Crab Nebula, a six-light-year-wide remnant of a star’s supernova
Is it really 13.4 billion light-years away?
So, is the farthest object in the Universe really 13.4 billion light-years away, as the news articles claim? Well, when the image we now see left that galaxy, we were much closer together because the entire expanding Universe was much smaller back then.
Since those very first minutes of the Universe, it has been expanding. In 1998, the Hubble Space Telescope revealed that the expansion of the Universe is actually accelerating due to dark energy, which is still a mystery.
Since it was only 3 billion light-years away when its light started toward us, that galaxy should logically look large, since a photograph’s dimensions don’t change just because it took a long time to get delivered here. Amazingly, that galaxy does look four times larger than we’d expect for something so far away. It appears much closer than it is!
In size, that is. But its brightness is the opposite. It’s far dimmer than we’d expect a 13.4 billion light-year object to be. Space has been stretching all the time that this image traveled, dramatically reshifting it. It now exhibits the ultra-faintness of a galaxy at the impossible distance of 263 billion light-years!
Kepler’s Supernova Remnant is a cloud from an exploded star in our Milky Way galaxy
Could things get any weirder? You bet. Science articles say that it’s 13.4 billion light-years from here—but that’s merely how long its light took to reach us. During all that time, that farthest-of-all galaxies has meanwhile been madly receding in this expanding universe. It is now actually 30 billion light-years away. Got all that?
Anyway, it’s clear that the simple question, “How far is it, really?” has no simple answer. Don’t ask! You can’t get there from here!