“They say the universe is expanding. That should help with the traffic.” -Steven Wright
Look out at a nearby object in our Universe, and you’ll find that the amount of time you look back (in years) is pretty much exactly equal to the object’s distance (in light years). But look far away, and these two numbers start to diverge. In our 13.8 billion year old Universe, in fact, we can see back up to 46 billion light years in any direction. If you think this number seems absurd, you’re not alone.
If the Universe were full of material everywhere and that material emitted light that was limited by c, you’d only be able to see for 13.8 billion light years. If you added in that the material could also be moving away from you at up to c, perhaps it could reach twice that: 27.6 billion light years. Yet the figure we have, 46 billion light years, only comes about because the fabric of space itself is stretching, a unique property of general relativity.