Are there more stars in the Universe than grains of sand on Earth?

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Offline Harri

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Hi all,  a friend told me that there was more stars in the universe than there are grains of sand on the whole planet! Is this correct? If that were true just how many planets and moons would we be talking about?
« Last Edit: 16/10/2015 20:36:00 by chris »

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Offline chiralSPO

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Well, we don't know how many stars there are in the whole universe, but in the part of the universe we can see (the observable universe), there are about 1021 stars (that's 1000000000000000000000 stars).

How many grains of sand on the Earth? a quick google search offers 1018. Even if they are underestimating by a factor of 100, that's still 10 times as many stars that we could theoretically see.

As to how many planets and moons there are... Recent work looking for and studying exoplanets suggest that stars have between one and two planets on average (that we can detect). Many of these may be too close to their stars to have stable satellites, but I would hazard a guess that any given star would have around a dozen orbiting bodies that are large enough to pull themselves into spherical shapes (our own solar system has at least 32 confirmed spherical bodies https://en.wikipedia.org/wiki/List_of_gravitationally_rounded_objects_of_the_Solar_System)

So there could be 1022 worlds in the observable universe, a full 10000 times as many as there are grains of sand on Earth.

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Offline Harri

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Thanks for answering my question.

It's a lot for a small human brain to take in but you put have put it quite succinctly and I find it quite mind blowing!!!

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Offline chiralSPO

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Even more mind blowing (I think) is that there are >1000 times as many atoms in a glass of water as there are stars in the observable universe!

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Offline PmbPhy

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Hi all,  a friend told me that there was more stars in the universe than there are grains of sand on the whole planet! Is this correct? If that were true just how many planets and moons would we be talking about?
If the universe is flat then yes, that's true. If it's not true then it might still be true, I don't know.
« Last Edit: 18/10/2015 04:15:35 by chiralSPO »