# More sand or stars?July 23, 2006 7:03 PM   Subscribe

Are there more grains of sand on Earth or stars in the sky?

Is an answer to this question possible or is it merely philosophical?
posted by names are hard to Science & Nature (25 answers total) 4 users marked this as a favorite

posted by RichardP at 7:07 PM on July 23, 2006

Stars in the Universe, or stars that can be seen in the sky?
posted by tiamat at 7:07 PM on July 23, 2006

Answered here; scroll about 2/3 down under "How Many Stars and Planets.
posted by TedW at 7:07 PM on July 23, 2006

"The usual way to determine the number of stars in the universe is to consider how many stars there are in the Milky Way, and then to multiply that number by our best guesstimate at the number of galaxies in the universe. This FAQ suggests there are probably about 400 billion stars in the Milky Way, although "a 50% error either way is quite plausible." As for the number of galaxies in the universe, well that's a whole separate mathematical puzzle.

Other star enumerators we located on the Web offer numbers ranging from more than 200 billion stars in our galaxy to 3 thousand million billion stars (3 followed by 16 zeroes), in the universe. NASA alleges there are zillions of uncountable stars."

I'm going to go ahead and guess that there're more stars in the sky.
posted by Baby_Balrog at 7:08 PM on July 23, 2006

More stars in the universe by by by far, but more grains of sand on earth than stars in "our" night's sky.
posted by nintendo at 7:09 PM on July 23, 2006

This is the kind of question that physicists like to answer when they're drunk.

My order-of-magnitude estimate: Our best estimate is that there are 7 x 1022 stars in the Universe. If a grain of sand is spherical and 1 mm in diameter, then 7 x 1022 grains of sand would take up 3.7 x 1013 cubic metres. This would be enough to cover the entire surface of the Earth to a depth of 7.2 centimetres. Or about three inches, for you Yanks in the audience. I find it dubious that there would be enough sand on Earth to do this, given that the vast majority of the Earth is covered in water and the vast majority of the land is not covered in sand. But I could be wrong.
posted by Johnny Assay at 7:19 PM on July 23, 2006

If a grain of sand is spherical and 1 mm in diameter,

But many grains of sand are much smaller - I'd consider that a fairly coarse sand.

vast majority of the Earth is covered in water

Aah, but what's underneath that water? For an extensive part of the continental shelf, I think you'll find sand.

the vast majority of the land is not covered in sand

But a lot of it is - to quite a depth. Desert sand can be many metres deep. Then there's the whole issue of different soil types. Sandy loam soils are quite common. The problem is that when people are counting "grains of sand", they might be interpreted as "grains of a sand on a beach", when in reality a "grain of sand" is simply a soil particle of a particular size. I can step outside onto my back lawn, dig up some soil, and separate a significant volume of sand from it.
posted by Jimbob at 7:30 PM on July 23, 2006

For reference, if you want to recalculate:

1.0 - 2.0mm - Very Coarse Sand
0.5 - 1.0mm - Coarse Sand
0.25 - 0.5mm - Medium Sand
0.125 - 0.25mm - Fine Sand
0.05 - 0.125mm - Very Fine Sand
posted by Jimbob at 7:32 PM on July 23, 2006

I think that this question is answerable if you put suitable constraints around it...

For instance.. beach sand, only? Potential grains of sand (such as the un-broken mantle) or just actual? Sub-ocean sand? At what size does a particle cease to be sand and become a pebble for purposes of your query. (As Johnny Assay suggests, you can develop an estimate based on a virtual particle and a ballpark volume estimate of your desired sand quantities.)

Regardless of what your constraints are, however, you are dealing with what are practically different orders of near infinity... superbly large numbers.

In the contest between these two, my gut feeling is that stars win (if the constraint is the actual stellar population in the universe currently as viewed from here... remember some stars we can still see don't exist any more.)

I have no calculcations to support this, but could generate some in a few hours, as could you.

You may be interested to know that Archimedes made a calculation of the number of grains of sand that would fill the universe several thousand years ago. I was astounded to hear this, thinking that all geocentric universes were the normal conception until relatively modern times, but apparently not so! His paper is included in Newman's World of Mathematics, Volume 1, and it's called oddly enough, "The Sand Reconer". Make a good read for an evening.
posted by FauxScot at 7:36 PM on July 23, 2006

the number of grains of sand that would fill the universe

What did he consider "the universe" to be?
posted by RustyBrooks at 7:42 PM on July 23, 2006

Is an answer to this question possible or is it merely philosophical?

A reliable answer is not possible, because it isn't possible for us to see the majority of the universe to determine how many stars there are out there.

It's only possible to make estimates.
posted by Steven C. Den Beste at 7:47 PM on July 23, 2006

Consider that grains of sand on Earth is a finite number. Impossibly huge, but finite. Now consider that the universe is theoretically infinite. Therefore, there are probably more stars than sand.
posted by frogan at 8:35 PM on July 23, 2006

Now consider that the universe is theoretically infinite.

I'm not a cosmologist, but I was under the impression that the universe is most definately not infinite.
posted by Jimbob at 9:10 PM on July 23, 2006

I'm not a cosmologist, but I was under the impression that the universe is most definately not infinite.

Hence the term "theoretically." Nobody's really 100 percent, definitely, certain. Even models of the Big Bang Theory (there's that word again) consider an expanding universe idea.
posted by frogan at 9:25 PM on July 23, 2006

No currently respectable theory of cosmology includes the idea of an infinite universe. All of them require the universe to be finite in size. The fact that they include the idea of an "expanding" universe doesn't mean that they think the universe is infinite in size.
posted by Steven C. Den Beste at 9:34 PM on July 23, 2006

But even an expaning universe only has a set amount of matter in it, right? The matter is just getting cooler and more sparse as the universe expands. Stars don't pop into existence out of no-where, they are created from dense patches of matter condensing under gravity.

I'll be quiet now, we're getting off topic.
posted by Jimbob at 9:36 PM on July 23, 2006

And the "just a theory" argument represents a gross misunderstanding of how scientists use the word "theory". The common use is more congruent to how a scientist uses the word "conjecture" or "speculation". "Theories" are much stronger and more well grounded than that.
posted by Steven C. Den Beste at 9:36 PM on July 23, 2006

Yeah, what Steven C. Den Anime said.
posted by Jimbob at 9:36 PM on July 23, 2006

No currently respectable theory of cosmology

Wow, what a sweeping generalized statement. And I usually like your stuff, Den Beste.
posted by frogan at 9:46 PM on July 23, 2006

No currently respectable theory of cosmology includes the idea of an infinite universe

Again we fall back on definitions. When most cosmologists talk about Universe they do usually mean the visible universe which by various constraints does lead to a finite model. However, if you leave out the "visible" shorthand you have a Universe which may be infinite in extent - with all current cosmological theories being agnostic to this. The truth is that there is stuff that hasnt been in our visible universe since the big bang and there's no theoretical reason our Universe couldnt be flat and infinite in extent.

Den Beste, I've called you out in science threads before and its because you say stuff with an air of authority yet your statements are generally inexact or just plain wrong. I'd suggest you at least consult cosmology tutorials before commenting in cases like these...[feel free to email me or drag me to metatalk]
posted by vacapinta at 11:37 PM on July 23, 2006 [3 favorites]

Vaca, there are a whole bunch of problems that pop up with a literally infinite universe - I'm interested in any reasons you have to not exclude that possiblility out of hand.
posted by Optimus Chyme at 8:02 AM on July 24, 2006

This brings up Olber's Paradox. If there are an infinite number of stars in the universe, why is the night sky dark. An infinite number of stars implies that there would be a star at every line of sight and that the night sky would be as bright as the surface of the average star. The answer to the paradox if that even if the universe were infinite, it has a infinite age. Any stars that are farther away in light years than the age of the universe are beyond our event horizon and are invisible to us. The night sky is dark because the universe is not old enough for the light from more distant, infinite stars to reach us. One could argue that the only stars that matter to us are those that are within our event horizon, which just happens to be about as far as the Hubble telescope can see.
posted by JackFlash at 9:49 AM on July 24, 2006

Rather: The answer to the paradox if that even if the universe were infinite, it has a finite age.
posted by JackFlash at 9:51 AM on July 24, 2006

[offtopic] JackFlash, I thought the answer to that was dark matter. [/offtopic]
posted by po at 10:17 PM on July 24, 2006

Why not rephrase it this way: is there more information than stars in the universe?

The question is viable only if one agrees that information can be quantified. The size of the "infinite" universe is not necessarily related to the quantities described by numeration. or measurement.
posted by pwiener at 1:24 PM on July 28, 2006

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