David Kipping

So the universe is expanding.

So therefore, if something is very far away from us and the universe is expanding, its light gets stretched more and more and more as it journeys over space.

And so we can use that redshift to kind of date how old these things are.

When we use those dates, we look at these images.

Again, they seem suspiciously too old.

You really shouldn't be able to form these things that early on in the universe.

And so that kind of puzzled us.

I think for the galaxy thing, there was a bit of a resolution there.

One of the resolutions is that we probably miscalculated how easy it is to form these galaxies in the first place.

So we had these models for galaxy formation.

We had these models for how stars should form, how quickly they should live.

But it was all essentially calibrated on what we see around us, like right here in this part of the universe, in the local universe.

And then we kind of realized that those same models probably need to be tweaked if you're going to apply them to the early universe where the density is so much higher, the gas temperature is much hotter.

Everything's just completely different in the early universe.

So when you kind of make those corrections, it actually looks like maybe it's actually possible to make those galaxies earlier than we thought.

So I think the galaxy problem is a bit easier to explain.

I think the quasar problem to me is more interesting.

How do you get those supermassive black holes so early?

There's a certain kind of maximum rate you can feed these things called the Eddington limit.

And that's sort of you throw mass into a black hole and so much energy is going in, some of it spews back out.