How can something be 32 billion light-years away?

The Cosmic Stretch: How a Galaxy Can Be 32 Billion Light-Years Away

The universe is a vast and bewildering place. Statements like “GN-z11 is 32 billion light-years away” often leave people scratching their heads. After all, the light from this galaxy, the furthest currently observed, has only been traveling for 13.4 billion years – the age of the universe itself. How can something be farther away than the age of the universe suggests it should be? The answer lies in the relentless expansion of space itself.

The common misconception is that the distance stated (32 billion light-years) represents the distance the light has travelled. This is incorrect. The 13.4 billion light-years represents the comoving distance – the distance the light travelled at the time it was emitted. However, during the journey of that light, the universe has continued to expand. This expansion isn’t just galaxies moving through existing space; it’s the space itself stretching, carrying galaxies along with it.

Imagine a rubber band with two ants on it. One ant represents us, and the other represents GN-z11. If you stretch the rubber band (representing the expansion of the universe), the ants move further apart, even though neither ant has moved significantly along the rubber band itself. Similarly, the light from GN-z11 has travelled a certain distance, but the expansion of space during its journey has drastically increased the separation between us and that galaxy.

This “stretching” of space is described by the Hubble constant, a measure of the universe’s expansion rate. The further away an object is, the faster it appears to recede from us due to this expansion. For extremely distant objects like GN-z11, this recession speed is a significant fraction of the speed of light.

Therefore, the 32 billion light-years is the current proper distance to GN-z11. It represents the distance we would measure today, accounting for the expansion that has occurred since the light began its journey. This proper distance is significantly larger than the comoving distance because the expansion of space has added to the separation during the 13.4 billion years it took the light to reach us.

It’s crucial to understand that this isn’t a violation of the speed of light. The galaxy wasn’t moving through space faster than light; rather, the space between us and the galaxy expanded, increasing the distance between us. The light itself still travelled at the speed of light, but the fabric of spacetime itself expanded, resulting in a vastly larger separation than the light travel time alone would suggest. This concept, counterintuitive as it may seem, is a cornerstone of our understanding of the expanding universe and the vast distances within it.