Before we get started, just a note that I had an Op-ed in the New York Times about young men, science and the “Manosphere”.  This is something I’ll come back to soon, but I wanted to give a link here for those who hadn’t seen it.

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 Today’s topic is the end of the Universe. Might as well start Monday on an upbeat note, right?

I want to introduce you to a wild idea that comes from the overlap between Cosmology    - the study of the Universe as a whole – and Stellar Astrophysics.

Here’s one point to consider, the Universe had a beginning but to the best of our knowledge it won’t have an end. What we call the Cosmos (expanding Space-Time filled with Matter-Energy) began about 14 billion years ago. But to the best of our knowledge, the Universe’s expansion will go on forever and that means the Universe will go on forever.

Stars, on the other hand, have beginnings but also have a definite end. Stars are born and then they die. The lifetime of a star is determined by how much fuel for nuclear fusion it’s born with. A star like the sun will last about 10 billion years. Stars half as massive as the sun (the most common kinds of star) will last trillions of years.  While I could do a whole post just on the how-and-why of star death (and I will), today the point is simply that they do end.  And when they die, they go dark.  They stop pumping out light into the Universe.  That leads to a startling question.

What happens when all the stars in the Universe are dead?

If you work out the cosmological details what you find is that after about a trillion, trillion years in the future, all the stars in the Universe will have exhausted their fuel. Even more importantly, there won’t be enough interstellar gas around to make new stars.  When that happens, the Universe will have lost its most potent sources of illumination. There will still be the scattered corpses of dead stars, things like white dwarfs and neutron stars that will provide faint glows. There will also be black holes around too.  But overwhelmingly, the Universe will be dark and destined to go on that way forever.

That means we live in what it’s called the Stelliferous age of the Universe – the era when stars are possible.  But if the Universe has an infinite future ahead of it, then this Stelliferous period of light (and life since starlight is what powers biology) will be just a short blip in its overall history.  Most of cosmic history will be written in blackness.

I don’t know about you, but for me that’s a mind-blowing idea.

If it’s an idea that bums you out, I do have some good news… maybe.   I don’t have a huge amount of confidence in extrapolating cosmology into infinite futures. Our ability to tell the story of the Universe is pretty freaking amazing and we have done an incredible job of mapping out the last 14 billion years. Seriously, it's a triumph of the human intellect.

However, trying to push trillions of years into the future means stretching our models in ways that I’m willing to hold with a very big grain of salt. Still, the idea of Stelliferous age is pretty cool, and it forces us to reflect for a moment about our own place in the vast cathedral of time.

— Adam Frank 🚀