Are there more planets than grains of sand?

Are there really more stars in our universe than there are grains of sand on all the beaches on Earth?

Table of Contents Show

So what about grains of sand on Earth?
Are there more solar systems than grains of sand?
Is there really more stars than grains of sand?
Are there more galaxies than grains of sand on Earth?
How many grains of sand are there in the world?

It may hurt your brain to think about it, but it seems that the answer is likely to be yes, or at least the numbers are roughly in the same ballpark.

Astronomers actually set out to answer this question about a decade ago. It's a tricky problem to solve, but it's slightly easier if you throw in a couple of qualifiers — that we're talking about stars in the observable universe; and grains of sand on the entire planet, not just the beaches.

The scientists started by measuring the luminosity density of a section of the universe — this is a measurement of how much light is in that space.

They then used this measurement to estimate the number of stars required to create that amount of light. This was quite a mathematical challenge!

"You have to assume that you can have one type of star represent all types of stars," says astronomer Simon Driver, Professor at the International Centre for Radio Astronomy Research in Western Australia and one of the scientists who worked on the question.

"Then let's assume, on average, this is a typical mass star that gives out the typical amount of light, so if I know that a portion of the universe is generating this amount of light, I can now say how many stars that would equate to."

Now equipped with an estimate of the number of stars within a section of the universe, the next challenge was to work out the size of the universe.

Given we know that the universe is 13.8 billion years old, we can assume that we exist in a sphere 13.8 billion light years in volume. But there's a catch: the universe is potentially infinite in size.

"We know that it has a finite age — we know it started 13.8 billion years ago — but spatially, in terms of its extent, it could be infinite," Driver says. However we also know that because of its age, we exist in a bubble within that infiniteness, and that bubble is called the 'observable' universe.

After all these calculations and caveats, Driver and colleagues came up with a figure of seven followed by 22 zeros, or 70 thousand million, million, million stars in the observable universe.

That's 70,000,000,000,000,000,000,000 stars!

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So what about grains of sand on Earth?

"That was almost harder to work out than the number of stars," Driver says.

Luckily, someone suggested starting with the Sahara Desert, which is home to around half of all the grains of sand on Earth.

"That made it easier; I then just had to work out how many grains of sand are in the Sahara, and I didn't have to worry about every beach on the planet," Driver recalls.

He found the total size of the Sahara, the average depth of sand across the Sahara and from that was able to calculate the approximate number of grains of sand in the Sahara.

"Once I got all that I could put all those numbers together and got a number that was remarkably close to the figure for the number of stars, but just a little bit less," he says. "It was about a factor of 10 smaller, but there's easily a factor of 10 error in both of those estimates so it could just as easily be the other way around."

That's 70,000,000,000,000,000,000,000 stars versus 7,000,000,000,000,000,000,000 grains of sand!

So even though it's an impossible question to answer definitively, it seems that the mind-bending possibility of so many stars existing in the universe is actually true.

Professor Simon Driver spoke with Bianca Nogrady

Be a citizen scientist

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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.

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Are there more solar systems than grains of sand?

Our universe contains at least 70 septillion stars, 7 followed by 23 zeros. Astronomers estimate there exist roughly 10,000 stars for each grain of sand on Earth.

Is there really more stars than grains of sand?

The numbers pretty much matched. There are about the same number of stars in the observable universe as there are sand grains in all of Earth's beaches.

Are there more galaxies than grains of sand on Earth?

Considering that, 300 billion galaxies with 100 billion stars each gives us 30,000,000,000,000,000,000,000, or 30 followed by 21 zeroes worth of stars in the universe. Now that is more than grains of sand on the Earth.

How many grains of sand are there in the world?

Assuming an average size, calculating how many grains are in a teaspoon, then multiply by all the beaches and deserts in the world, Earth has very roughly 7.5 x 10 to the 18th power grains of sand, or seven quintillion, five hundred quadrillion grains.