How did they come to the conclusion that there are more stars in the universe than grains of sand on Earth?
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Imagine you have a really big jar full of candies, and a small jar full of marbles. You want to find out which jar has more items without counting each candy and marble one by one, because that would take forever!
So what you can do is, first, take a small cup and scoop out some candies from the big jar. You count how many candies are in that cup. Let’s say you count 100 candies.Next, you do the same thing with the marbles. You scoop out some marbles with the same cup and count them. This time, let’s say you count 10 marbles.
Now, you can estimate how many candies and marbles are in the jars. If the big jar is 100 times bigger than the small cup, and the small jar is 10 times bigger than the small cup, you can guess that there are about 10,000 candies (100 candies x 100) and 100 marbles (10 marbles x 10) in total.
Scientists used a similar idea to estimate the number of stars in the universe and the number of grains of sand on Earth.For stars, they looked at a small patch of the sky using telescopes and counted the number of stars in that patch. Then they figured out how many similar patches would cover the entire sky and multiplied the two numbers to estimate the total number of stars in the universe.
For the sand, they took a handful of sand and counted the grains. Then they estimated how many handfuls would make up all the beaches and deserts on Earth and multiplied the two numbers to get the total number of grains of sand.
When they compared the two numbers, they found out that the number of stars in the universe is much, much bigger than the number of grains of sand on Earth!
Statistics and estimation of quantities. Does depend on what one calls “sand” a bit, because there are a lot of sediment particles smaller than sand (silt and clay), and particles larger than sand (pebbles/cobbles/boulders) that we ignore when talking about sand.
We geologists have studies sands a lot, like everywhere even sandstone rocks, so we have a decent idea of the average number of sand grains that exist per unit volume in sand. You could even calculate it using basic geometry, imagining a sand grain of 1 mm diameter (or whatever size you decide would be good for the estimate) and how many you could fit into a cubic meter.
Then we look at how much sand there actually is on earth. Not sandstone, because that is rock, but just sand as beaches, delta sediments, and so on. This gives us a volume, and we know how many grains exist in any specific volume, so it is a simple arithmetic problem: We have X cubic meters of sand, and Y grains fit on average in X cubic meters, so just multiply. You get a very big number, and it might be off by a couple zeroes, but not by a lot more than that. We won’t get a great number, a “precise” number for the volume, and our number of grains per unit volume might be a bit off, but it will be in the right ballpark.
Then you turn around and do the same thing for stars: come up with an average number of stars per galaxy, and multiply by how many galaxies are out there that we can see or at least assume based on what we can see. This is also a very big number, with maybe some question as to how accurate it is (maybe off by a couple-few zeroes), BUT it is way bigger than the same number we got for sand grains. Not close.
If it were close, within several orders of magnitude (the amount of error in our estimation), then we couldn’t say with much certainty that more stars exist than grains of sand on earth. We would have to conclude that the numbers seem to be about the same.
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Important note…. It’s not a FACT. It’s a speculation, as neither every star nor every grain of sand on earth has been counted.
Because the universe is infinite and the earth is finite. Infinity > any countable quantity.
Apart from other estimations, the way they can say these things are because even with uncertainties, you can tell if something is obviously bigger than the other. Example:
I dont know how many grains of sand there are in the Sahara, I’ve never been there or seen it in person.
I also don’t know how many socks I own, kept in my drawer.
I can still confidently say there are more grains of sand in the sahara than socks in my drawer.
Similarly, the lowest estimates for the numbers of stars in the universe is so much bigger than any number we could get for grains of sand on the earth.
Isn’t the universe is infinit and earth is finite? That’s my understanding.
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