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The entropy of the observable universe is mainly in supermassive black holes.

Next comes star-sized black holes.

Then comes the cosmic background radiation: photons, neutrinos and gravitons.

Everything else is a tiny correction - probably even dark matter, if it exists.

(1/n)

Photons and neutrinos beat gravitons, because gravitons decoupled from other matter earlier and have had more time to cool down!

If you want to see how these estimates are done, see Chas Egan and Charles Lineweaver's paper:

(2/n)

arxiv.org/abs/0909.3983

These estimates are rough! Egan and Lineweaver's estimate is 100 times that of this earlier paper, because they assume more supermassive black holes: black holes at least 10 million times heavier than the Sun, living at the centers of galaxies.

(3/n)

arxiv.org/abs/0801.1847

For more fun facts about entropy and information, check out this page of mine:

math.ucr.edu/home/baez/informa

For example: a 1-gram black hole would have entropy equal to 4.78 gigabytes!

(4/n, n = 4)

I'm going to delete these tweets. I copied the data from a webpage of mine. Reviewing the original paper I see that I'd forgotten to convert entropy from boltzmanns to bits.

This means all my numbers should be multiplied by 10²³.

Ahem. 🥴

Carry on....

I'm going to delete these tweets. I copied the data from a webpage of mine. Reviewing the original paper I see that I'd forgotten to convert entropy from boltzmanns to bits.

This means all my numbers should be multiplied by 10²³.

Ahem. 🥴

Carry on....

(5/n)

@johncarlosbaez
as a comparison:
a mini-SD (memory) card is about 2 g. How many GB of memory in your mini-SD card in your phone?

@johncarlosbaez C'mon, what's a 1023 error between friends?

It's not too late to consider an accounting career!

@johncarlosbaez
what's an order of magnitude, or 23, among friends?

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