The End of Everything (Astrophysically Speaking)

written on October 27, 2026, read April 2021

If astrophysics weren’t – as the name suggests – part of physics, and therefore full of formulas with letters and strange symbols, this science would have a clear advantage over the study of history. While in history you have to piece the truth together from many subjective and few objective data points,¹ astrophysics – assuming that physics works the same everywhere – means you only have to look into space with a suitable instrument to see whether all the calculations are actually right. And not only for the present, but for the past as well. And if you know how the past became the present, you can probably make a pretty good forecast about the future, too.

As a child, I found the thought that we only learn about everything concerning the Sun a good eight minutes later – that someone could long since have switched off the light without us, for all practical purposes, knowing it yet – a proper brainf*ck.

Incidentally, this is also one of the topics from my childhood that I can put to good use in my working life. Because if, against every safety instruction, I look into an optical fibre, everything I see there represents a state of the sending system from the past: 0.049 milliseconds in the past if I look into 10 km of fibre. 500 km of fibre means a look 2.45 milliseconds into the very recent past. That may not sound like much, but it really does matter in my day-to-day work.

The very same effect that makes my planning harder has an interesting side effect, though: an astrophysicist can see everything at once. A Sun from eight minutes ago – just look at our own Sun. A look 13.44 billion years into the past – point the telescope towards GLASS-z12 (plus four years, after all it’s been that long since this galaxy was discovered). And everything in between. At the same time.

And if you want to trigger the next brainf*ck, just think about the fact that we never see the present, only ever the past. Because even everything that happens right on the tip of our nose still needs time to reach our eyes. It just doesn’t matter, because our brain takes incomparably longer to process it than the light takes to travel: around 100 milliseconds for conscious perception. More when you’re being particularly slow on the uptake. But basically, not only can we not look into the future. We can’t even see the present. And that’s a really weird thought.

I wrote at the beginning about forecasting the future. And that brings us to a book I very much enjoyed reading. How does this whole shop (the cosmos, I mean, and all that) actually end? And when? And why, actually? That’s basically what Katie Mack’s “The End of Everything (Astrophysically Speaking)” is about.

So many mental bridges are built in this book. For example, we tend to imagine the Big Bang as an explosion in a space: a point, it explodes there, and the universe expands. But Mack describes this very nicely: the Big Bang happened at every point in space, because no space exists outside the Big Bang. It wasn’t an explosion, because that would mean it exploded into something. She explains that it is the expansion of everything. At least that’s how my brain understands it. Not that this is much more intuitive for me, but at least you can file away the question “Where did it explode to?” and put it aside. In exchange, you now have dozens of other questions. Thanks a lot, Ms Mack.

The possible endings of the universe don’t sound particularly pleasant either. Mack describes scenarios such as the “Big Crunch”, the “Heat Death” or “Vacuum Decay”. None of it sounds like a fun night out – unless you’re dining at the Restaurant at the End of the Universe. But the good thing is: it’s all so far off that it’s no longer my problem.²

Except for vacuum decay. That spreads at nearly the speed of light. So someone may already have switched off the light in the universe, and we just don’t know it yet. If that’s not weird enough for you, add the thought on top that the destruction will never reach you if it just starts far enough away – because there the universe is moving away from us faster than light can travel. “Doom crept after us, but it never caught up.” So: Don’t panic.

I don’t want to tell you any more about the book, so as not to spoil your fun of getting your brain twisted. I would be disappointed by a non-fiction book if I had fewer questions in my head after reading it than before. I want new questions that build on what I have learned. And here you have to say that the book really delivered. For me personally, that is one of the best things you can say about a non-fiction book.