Stars in a Young Universe

Episode 4 of the new “Cosmos” was titled “A Sky Full of Ghosts”.

In it, Neil deGrasse Tyson showed a map of the galaxy, then showed a small circle around our solar system and said (more or less) “If the universe were only 6,000 years old, this is the farthest we’d be able to see.”  The light from farther bodies wouldn’t have reached us yet.  

And I thought But how cool would that be?  If the world were only 6,000 years old?  To be constantly spotting new stars? Stars we’ve never gotten to see before?

Because, in such a universe, the light from more and more distant stars would reach us each year.  We would see new stars all the time.

Someone pointed out to me that our nearest neighbour is something like four light-years away. So really, you’d be getting only a handful of new stars over the course of your lifetime.

So I threw some math at it.

Some Assumptions

Assume that the universe snapped into existence, as it is now, in 4004 BC.  This is the figure provided by the Ussher chronology, and is a figure I usually see cited by young-earth Creationists.  This universe contains an Earth, and this Earth contains humans who are cognizant of the night sky.

Assume that the Milky Way galaxy is a sphere (which it isn’t) and that stars are uniformly distributed (which they aren’t). These are purely to make the math simpler.  Assume also that our solar system within the galaxy is at least 6,018 light-years from its edge (so that the horizon of visibility doesn’t reach the galaxy’s edge before the present day).

Assume the Milky Way galaxy has a volume of about 39 trillion cubic light-years.

Assume the Milky Way galaxy has about 400 billion stars.

That gives us one star for every 97.5 cubic light-years.

The History of the World

From this math, a narrative starts to emerge.

For the first three years, we expect to see no stars. The only lights in the sky are the Sun, the Moon, and the five planets that are visible to the naked eye.

Then, somewhere between year 3 and 4, a new light appears! Another night-time pinprick light, like the few we already see!  What does this mean?  Has the Sun had new children?  Are new gods being born?  Is Creation ongoing?

Somewhere between year 4 and 5, three more stars appear. Because guess what? The process accelerates.

The distance to our visible horizon increases linearly with time, but the visible volume increases with the cube of time.

By the end of year 7, we can see 13 stars, along with the Sun, Moon, and classical planets. By the end of year 10, we can see 42.

In year 100 – not by year 100 but in year 100 – we get 1,276 new stars.

That’s 3.5 new stars a day.

In year 1,000 we get 128,757 new stars.

Creation is Complete

Now, though the process accelerates, there’s a point where it rather suddenly peters out.  The visible horizon reaches the point where the “new” stars are too distant to see with the naked eye.  I’m talking individual stars; brighter objects, like galaxies, are visible much farther away.

I’ve found different answers as to how far away that would be.  This forum post provides a broken link, and a claim that it indicates about 4,075 light-years.  This site claims 16,300 light-years.

I’m going to pick a nice round 4,000.  4,000 years is the upper bound on this accelerating increase in visible stars.  After about the year 4,000, we mostly stop seeing new stars with the naked eye.

But in the year 4,000… we get 2 million new stars.

That’s 3.9 new stars becoming visible each second.  3.9 new stars every second, and then nothing more.

I want to world-build with this.  I mentioned it to some friends, and several said they want to poach it for their own writing.  (They’re welcome to it; I can’t be the first person to have thought of this.)

Having a long period where new stars are appearing – faster and faster – would be awesome for delimiting the Ancient Days – you know, that period where The Rules Were Different, and The Gods Routinely Meddled On Earth.

I don’t believe any of this is true, of course.  We have detailed astronomical records going back millennia, and we have all sorts of evidence that the universe is, y’know, not just 6,000 years old.  And I’ve made all kinds of simplifying assumptions that kind of sink it (the “uniform distribution” assumption in particular).

But.  This is neat.  I want to worldbuild with it.