This question comes from Sheldon Grimshaw.
"I've heard that there are more stars in our
Universe than there are grains of sand on
all the beaches on Earth.
Is this possible?"
Awesome question, and a great excuse to do
some math.
As we learned in a previous video, there are
100 to 400 billion stars in the Milky Way
and more than 100 billion galaxies in the
Universe - maybe as many as 500 billion.
If you multiply stars by galaxies, at the
low end, you get 10 billion billion stars,
or 10 sextillion stars in the Universe - a
1 followed by 22 zeros.
At the high end, it's 200 sextillion.
These are mind bogglingly huge numbers.
How do they compare to the number of grains
of sand on the collective beaches of an entire
planet?
This type of sand measures about a half millimeter
across.
You could put 20 grains of sand packed in
side-by-side to make a centimeter.
8000 grains in one cubic centimeter.
If you took 10 sextillion grains of sand,
put them into a ball, it would have a radius
of 10.6 kilometers.
And for the high end of our estimate, 200
sextillion, it would be 72 kilometers across.
If we had a sphere bigger than the Earth,
it would be an easy answer, but no such luck.
This might be close.
So, is there that much sand on all the beaches,
everywhere, on this planet?
You'd need to estimate the average volume
of a sandy beach and the average amount of
the world's coastlines which are beaches.
I'm going to follow the estimates and calculations
made by Dr. Jason Marshall, aka, the Math
Dude.
According to Jason, there about 700 trillion
cubic meters of beach of Earth, and that works
out to around 5 sextillion grains of sand.
Jason reminds us that his math is a rough
estimate, and he could be off by a factor
of 2 either way.
So it could be 2.5 sextillion or there could
be 10 sextillion grains of sand on all the
world's beaches.
So, if the low end estimate for the number
of stars matches the high end estimate for
the number of grains of sand, it's the same.
But more likely, there are 5 to 10 times more
stars than there are grains of sand on all
the world's beaches.
So, there's your answer, Sheldon.
For some "back of the napkin" math we can
guess that there are more stars in our Universe
than there are grains of sand on all the beaches
of Earth.
Oh, one more thing.
Instead of grains of sand, what about atoms?
How big is 10 sextillion atoms?
How huge would something with that massive
quantity of anything be?
Pretty gigantic.
Well, relatively at least.
10 sextillion of anything does sound like
a whole lot.
If you were to make a pile of that many atoms...
guess how big it would be.
It'd be about.... (gesture big then gesture
small) 4 times smaller than a dust mite.
Which means, a single grain of sand has more
atoms than there 
are stars 
in the Universe.
