Comments on: Stars and Sand Grains

By: George Whaley

George Whaley — Fri, 02 Oct 2009 16:57:03 +0000

I take your point about considering only beaches. It is clearly an important difference as many instances of this question being discussed do fail to make the distinction.
In any case the visible universe is only a fraction of the (unknowable?) total so the universe may well win out.

By: Ben Burress

Ben Burress — Fri, 02 Oct 2009 14:50:20 +0000

There are many ways to slice and dice this calculation. In my own, I was confining my example to only the sand of Earth's beaches (not deserts), and taking every opportunity to use conservative estimates for the variables. But the point of my estimation was not so much to try to calculate how many grains of sand there are, but demonstrate the number of stars in the Universe. Even if you regard my conservative beaches with their coarse sand grains, the fact is, that's a heck of a lot of sand! And if my (maybe unrealistically) conservative sand sum is in the ballpark of the Universal star-sum, as long as I've achieved mind-boggledom, I'm satisfied….

By: George Whaley

George Whaley — Fri, 02 Oct 2009 12:32:39 +0000

This longstanding issue has been discussed again recently (on BBC)and notwithstanding many web pages giving calculations I am deeply distrusting of the maths. I have just measured (roughly) some garden sand and reckon it at 100 grains per mm^3. 10^22 (stars) = 100×1000^3×1000^3×100 =100 km^3 of garden sand.
The sandy region of the Sahara desert (alone) is some 2.5 million km^2 which is 2500 km^3 or 25 universes per metre depth.
As to the rest of the world's deserts, beaches…

Or have I missed something?

By: Ben Burress

Ben Burress — Mon, 27 Apr 2009 22:32:02 +0000

And even after doing the math, part of me still can't believe it. This was reinforced recently as I sat on a beach in Half Moon Bay, surveyed all that sand, and just could not get my belief in gear.

There's another sand and star scale mind game that goes like this: If all the stars in the sky that we can see with our eyes (without a telescope) were stand grains, they would fill a thimble. All of the stars in the Milky Way Galaxy would fill a wheelbarrow. To represent all the stars in the visible universe this way, you would have to haul in the sand with a train, one boxcar-ful per second, 24 hours a day for 3 years….

By: Jim Fisher

Jim Fisher — Tue, 10 Feb 2009 05:10:56 +0000

I've been meaning to calculate this ever since I first read the "sand in the beaches" statement in Carl Sagan's "Cosmos." Thanks for saving me the time.

By: Jonas Kulland

Jonas Kulland — Wed, 04 Feb 2009 21:35:35 +0000

Mindblowing indeed!
Thanks for the perspective.

By: A Long and Winding DNA | QUEST Community Science Blog - KQED

A Long and Winding DNA | QUEST Community Science Blog - KQED — Mon, 02 Feb 2009 22:58:05 +0000

[...] is an awful lot of DNA stuffed into every cell.Ben's blog on stars and grains of sand got me to thinking about DNA. How long would the DNA from every living [...]

By: austin

austin — Wed, 28 Jan 2009 06:36:56 +0000

amazing. this blew my mind

thanks for doing the math.