Two of my current favourite space facts 🌌

In a recent TikTok comment, I got asked what my favourite two facts about the universe were. Below is the answer that I gave:

"I really like this question, because space is so massive and so weird that almost every time I learn a new fact about it, that fact becomes my new favourite. My current two favourites are both courtesy of my cosmology lecturer, and they both involve "photons" (small packets [or quanta] of light) and "baryons"(subatomic particles made of three quarks [e.g. protons or neutrons]):

1. For every 1 baryon in the universe, there exists more than 1.6 billion photons!

As astonishing as this fact is on its own, it's also only a lower limit! This is because it only considers photons that originate from the cosmic microwave background [CMB] (the radiation leftover from the big bang) and not photons that come from stars.

(However, to be fair, photons from stars only really make up around 1/40th of the number of photons that come from the cosmic microwave background)

Map of the CMB

1. Per cubic metre of space (that's roughly the volume of 2 fridge freezers) there exists, on average, just one-quarter of a baryon!

Luckily for us, they cluster together under gravity. So there's a lot more per cubic metre where we are, and a lot less out in the voids of space."

So, those are my two current favourite space facts. What are yours?

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