Quizzes & Puzzles29 mins ago
I Am Not Convinced, That There Are More Stars Than Grains Of Sand...
20 Answers
I have heard and read about this for many years, and I just cant see it.
When you think about how many coastlines there are around the world with sand, and what we dont see beneath the sea, how can scientist tell us this.
There must be millions of grains of sand in one houshold bucket, and if you multiply how many buckets you could fill, I find it impossible to beleive.
And finally, how do they know how many stars there are in the galaxys?
When you think about how many coastlines there are around the world with sand, and what we dont see beneath the sea, how can scientist tell us this.
There must be millions of grains of sand in one houshold bucket, and if you multiply how many buckets you could fill, I find it impossible to beleive.
And finally, how do they know how many stars there are in the galaxys?
Answers
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Given that stars are themselves utterly huge objects in comparison to sand grains (sand is to stars as we are to cells, roughly) then the fact that it is even possible for this statement to be correct says a lot about the size of the Universe. But it's not really meant to be a factual statement, for two reasons: the first is that the statement itself varies...
10:05 Sun 14th Jun 2015
I'm afraid we're in one of those endless, philosophical debates, woof… actually, infinite implies immeasurable… since the known universe had a beginning it is measurable… seen here:
The space that we can observe, on the other hand, does have a definite size. Because the universe was born 13.8 billion years ago, we can only observe objects whose light has traveled at most 13.8 billion years to reach Earth. This portion of the universe is called the observable universe, and it’s the only part of the universe we can know anything about.
But due to the universe’s expansion, the radius of the observable universe is not 13.8 billion light-years. Current estimates instead set its radius at about 46 billion light-years, an estimate made in co-moving coordinates, which account for the expansion of the universe. As the universe ages, the size of the observable universe will continue to expand… (Source: National Public Radio).
So… while we may not yet be able to measure the universe that lies beyond what we know… what we do know has and is being measured… so it can't fit the classical definition of infinite. Plus, the only reason it can be measured is we know it had a beginning at a point...
The space that we can observe, on the other hand, does have a definite size. Because the universe was born 13.8 billion years ago, we can only observe objects whose light has traveled at most 13.8 billion years to reach Earth. This portion of the universe is called the observable universe, and it’s the only part of the universe we can know anything about.
But due to the universe’s expansion, the radius of the observable universe is not 13.8 billion light-years. Current estimates instead set its radius at about 46 billion light-years, an estimate made in co-moving coordinates, which account for the expansion of the universe. As the universe ages, the size of the observable universe will continue to expand… (Source: National Public Radio).
So… while we may not yet be able to measure the universe that lies beyond what we know… what we do know has and is being measured… so it can't fit the classical definition of infinite. Plus, the only reason it can be measured is we know it had a beginning at a point...
-- answer removed --
It can not be infinite unless infinite acceleration & velocity is possible. We believe we know it was a small finite size at one time. Thus it can't be infinite now.
Simple maths tells us there are more stars. We define how small a grain can be. We know how large the planet is. We can make a good estimate of the maximum number of grains there could be. Do something similar to estimate stars in the universe and get a larger number.
Simple maths tells us there are more stars. We define how small a grain can be. We know how large the planet is. We can make a good estimate of the maximum number of grains there could be. Do something similar to estimate stars in the universe and get a larger number.
-- answer removed --
Given that stars are themselves utterly huge objects in comparison to sand grains (sand is to stars as we are to cells, roughly) then the fact that it is even possible for this statement to be correct says a lot about the size of the Universe. But it's not really meant to be a factual statement, for two reasons: the first is that the statement itself varies depending on who says it. The number of grains of sand is variously described as "on the beaches" or just "on Earth", for example. It is clear that the number of sand grains on the whole of Earth is many times larger than just the number of sand grains on beaches, so you have to decide how much sand you are going to count before you make the statement. I think the initial one referred only to sand on beaches, but I'd have to check this.
The second point is that the statement is really a comparison of two ballpark estimates, either of which could be wrong by as much as a factor of ten. If you wanted to check the statement for yourself, say, you might want to assume the following about sand grains:
- they are all (basically) the same size;
- beaches are all of the same average size and density;
- whether or not to include deserts, and what assumptions to make about them;
and so on. It's clear that all of these assumptions are in general wrong, so the figure you get at the end is also wrong, but it will also be reasonably close and saves you from having to do a more accurate count (which is probably impossible, or at any rate too much like hard work).
Then you do the same thing for the stars. Either count the total number of galaxies, or just count up the number in some smallish region of space and assume that the remainder are distributed evenly throughout the rest of the Universe (they are not, but it's a good average estimate), and that each contains essentially the same number of stars (they don't, but again it's going to be pretty close); or just divide the total mass in the Universe by the average mass of stars (again, giving a wrong answer, but it should be reasonably close).
The end result is that you are comparing two numbers, both of which are wrong, to each other. If your estimates are close enough to the true value then you can still say something fairly meaningful, which is that the number of grains of sand on earth (restricted to the beaches or not) and the number of stars in the Visible Universe are approximately the same to within some (potentially quite large) errors. Then it tends to be put as "there are more stars than grains of sand" because that sounds marginally more impressive.
The second point is that the statement is really a comparison of two ballpark estimates, either of which could be wrong by as much as a factor of ten. If you wanted to check the statement for yourself, say, you might want to assume the following about sand grains:
- they are all (basically) the same size;
- beaches are all of the same average size and density;
- whether or not to include deserts, and what assumptions to make about them;
and so on. It's clear that all of these assumptions are in general wrong, so the figure you get at the end is also wrong, but it will also be reasonably close and saves you from having to do a more accurate count (which is probably impossible, or at any rate too much like hard work).
Then you do the same thing for the stars. Either count the total number of galaxies, or just count up the number in some smallish region of space and assume that the remainder are distributed evenly throughout the rest of the Universe (they are not, but it's a good average estimate), and that each contains essentially the same number of stars (they don't, but again it's going to be pretty close); or just divide the total mass in the Universe by the average mass of stars (again, giving a wrong answer, but it should be reasonably close).
The end result is that you are comparing two numbers, both of which are wrong, to each other. If your estimates are close enough to the true value then you can still say something fairly meaningful, which is that the number of grains of sand on earth (restricted to the beaches or not) and the number of stars in the Visible Universe are approximately the same to within some (potentially quite large) errors. Then it tends to be put as "there are more stars than grains of sand" because that sounds marginally more impressive.
Here's my own back-of-the-envelope calculation:
1) To calculate the number of stars you can take the rough number of galaxies (170 billion or so) times the number of stars per galaxy (pretty much the same number) and end up therefore with a number that is as near as dammit to 1,000,000,000,000,000,000,000,000 (or 10^24). This is a lower bound as we've only considered the visible Universe, but took no real calculating at all.
2) To do the same thing for sand takes a bit longer, but looking up values for average mass of a grain of sand, and then the average size and density of beaches, and then using the following simple formula, doesn't take too long:
Number of sand grains on beaches = (Density of beaches) x (average Width of beaches) x (average depth of beaches) * (total length of world's coastline) / (mass of average sand grain)
reasonable figures for each of these can be looked up reasonably quickly, or guesstimated, eg:
- the world's coastlines are about 1.5 million km long (and aren't all beach, but let's pretend they are);
- the depth of beaches varies widely but it's probably reasonable to assume an average depth of somewhere around 10 metres or so;
-the density of beaches can be taken as somewhere between that of water (1000 kilograms per cubic metre) and that of sandstone (2000 kilograms per cubic metre) so let's call it 1500 kg/m^3;
- assume that all beaches are 100 metres wide;
- the mass of a grain of sand varies but is typically about 50 micrograms on average.
If you put these numbers in then you get something like 50,000,000,000,000,000,000,000, or 5*10^22 grains of sand on the earth's beaches. I have no idea how wrong this is but a comparison with the number of stars derived earlier shows that it is in fact smaller!
So there are (probably) more stars in the Universe than grains of sand on the Earth's beaches. If you include all sand from deserts, though, I think that the numbers would tip in favour of sand. But then if you included all stars in the invisible Universe, it might go back to stars again.
Bottom line, though, is that despite how tiny grains of sand can be, and how many of them must be on the Earth's beaches, the number of stars we can see is almost the same order of magnitude.
1) To calculate the number of stars you can take the rough number of galaxies (170 billion or so) times the number of stars per galaxy (pretty much the same number) and end up therefore with a number that is as near as dammit to 1,000,000,000,000,000,000,000,000 (or 10^24). This is a lower bound as we've only considered the visible Universe, but took no real calculating at all.
2) To do the same thing for sand takes a bit longer, but looking up values for average mass of a grain of sand, and then the average size and density of beaches, and then using the following simple formula, doesn't take too long:
Number of sand grains on beaches = (Density of beaches) x (average Width of beaches) x (average depth of beaches) * (total length of world's coastline) / (mass of average sand grain)
reasonable figures for each of these can be looked up reasonably quickly, or guesstimated, eg:
- the world's coastlines are about 1.5 million km long (and aren't all beach, but let's pretend they are);
- the depth of beaches varies widely but it's probably reasonable to assume an average depth of somewhere around 10 metres or so;
-the density of beaches can be taken as somewhere between that of water (1000 kilograms per cubic metre) and that of sandstone (2000 kilograms per cubic metre) so let's call it 1500 kg/m^3;
- assume that all beaches are 100 metres wide;
- the mass of a grain of sand varies but is typically about 50 micrograms on average.
If you put these numbers in then you get something like 50,000,000,000,000,000,000,000, or 5*10^22 grains of sand on the earth's beaches. I have no idea how wrong this is but a comparison with the number of stars derived earlier shows that it is in fact smaller!
So there are (probably) more stars in the Universe than grains of sand on the Earth's beaches. If you include all sand from deserts, though, I think that the numbers would tip in favour of sand. But then if you included all stars in the invisible Universe, it might go back to stars again.
Bottom line, though, is that despite how tiny grains of sand can be, and how many of them must be on the Earth's beaches, the number of stars we can see is almost the same order of magnitude.
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