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Comment by quadcore | Hacker News Reader

from a catalog of 1 million galaxies

For a lay person, reading that number is mind blowing. Quick question: how many do we think there are? Or rather, do we have some sort of a number for the total energy there is in the universe compared to that of our sun?

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Estimates place the number of galaxies at around 200 billion, give or take an order of magnitude.

The total energy produced by our sun during its entire lifetime is insignificantly miniscule compared to all the energy emitted by every star in the universe for a single nanosecond.

In the observable universe.

Depending on various theories of universe formation the universe could have a radius anywhere from at least 10x the observable universe to even infinite.

Some more recent studies estimate two trillion galaxies. Mind blowing either way.

Definitely. That's why this is basically the only context where it makes sense to say something like "give or take an order of magnitude" lol

2-6 trillion is the new postulate that now includes smaller dim galaxies proximate to larger galaxies.

https://bigthink.com/starts-with-a-bang/galaxies-in-universe...

Ofc they are smaller, so its a classification problem.

Can all stars go extinct at some point in the future - does the universe has a life expectancy?

They can, and they will. Fusion will stop once all the elements have been converted to iron. Many black holes will form, protons will probably decay, black holes will evaporate, and nothing but smooth radiation will remain.

It's called the heat death of the universe.

https://en.wikipedia.org/wiki/Timeline_of_the_far_future

This is assuming the cosmic concordance model describes reality. There are other models where some sort of reverse expansion will occur. They call it either Big Crunch or Big Bounce.

Similar in scale the number of neurons in a brain: 86 billion neurons [1].

One neuron might seem insignificantly miniscule, but just one neuron may encapsulate you recognizing a specific face of someone important to you.

[1] https://bionumbers.hms.harvard.edu/bionumber.aspx?id=106322

...and yet I remain very bad at putting names on faces.

About as many galaxies in the universe as there are stars in the galaxy: hundreds of billions, ~10^11

That's a neat symmetry. Another symmetry I like, in the other direction, is a fist is to the Earth as a carbon molecule is to a fist sized rock (I might be off by a magnitude or two, but by charitable interpretation it's accurate enough). That's a lot of molecules.

The number of stars in the observable universe is roughly of the same order as the number of grains of sand on earth, and the number of atoms in a human eye.

Estimates are: 10^19 grains of sand, 10^22 atoms in the human eye and 10^23 stars in the observable universe.

I just saw that estimate for atoms in an average human body is on the order of 10^27. I didn’t expect that the whole body is 100,000x atoms compared to the eye.

By weight (68kg/28g) the body is only about 2500x the size of an eye.

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