# Thread: If our sun was the size of an atom, how big would the universe be?

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## If our sun was the size of an atom, how big would the universe be?

Just curious that's all. I guess it may make it easier to grasp the actual size of the universe.

2. Well i managed to pick this out of one of my books, not quite what you are asking but at least a start.

This is if the earth was the size of an atom, resulting in an approximation for the diameter of our galaxy.

Let's do the math.

22500 miles to 10^-30th in. is :
22500 * 5280 * 12 * 1/10^30 =
0.000 000 000 000 000 000 001 188 inches.

100,000,000 light years converted to inches...
37 246 890 974 515 200 000 000 000 inches...

Would make the Galaxy 44249.31 inches (or 3687.44 feet, or 0.70 miles) in diameter

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Originally Posted by cosmocrazy
Well i managed to pick this out of one of my books, not quite what you are asking but at least a start.

This is if the earth was the size of an atom, resulting in an approximation for the diameter of our galaxy.

Let's do the math.

22500 miles to 10^-30th in. is :
22500 * 5280 * 12 * 1/10^30 =
0.000 000 000 000 000 000 001 188 inches.

100,000,000 light years converted to inches...
37 246 890 974 515 200 000 000 000 inches...

Would make the Galaxy 44249.31 inches (or 3687.44 feet, or 0.70 miles) in diameter
That certainly puts things in persepctive. Not the universe but the size of our galaxy, I never thought our galaxy was THAT big!

I would've thought if the Earth was the size of an atom then our galaxy would've been more like the size of a football field or full size swimming pool, which is still, unbelievably enormous.

4. The diameter of the milky way is about 100,000 light years - not 100,000,000.

5. Originally Posted by Ross PK81
Just curious that's all. I guess it may make it easier to grasp the actual size of the universe.
Here's a way to think about it:
- The Sun is 6 light-seconds across.
- There are about 5 million solar diameters in a light year
(so if the Sun were 0.1 nanometers, a light year would be half a millimeter.

So:
- the galaxy would be about 50 meters across.
- M31 would be about a kilometer away.
- The most distant observed galaxies would be about 6000 kilometers away --- So the visible universe would be about the size of the Earth.

6. Originally Posted by Ross PK81
Just curious that's all. I guess it may make it easier to grasp the actual size of the universe.
It depends on ones grasp of how small an atom actually is. If someone has the idea that an atom is just a bit smaller than, say, bacteria, then this comparison will not help them much.

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Originally Posted by cosmocrazy
Would make the Galaxy 44249.31 inches (or 3687.44 feet, or 0.70 miles) in diameter
Wow.

Given the diameter ratio between the Milky way and the observable universe, that would put make the universe 651,000 miles in diameter - about 36% larger than the diameter of the Moon's orbit.

I'd be interested in seeing someone calculate how many atoms can be packed into this sphere at Earth-normal densities...

8. First, note my earlier post correcting your size conclusion.

Second, If there are 4x1024 nucleons per cubic centimeter (this would require converting about half the Hydrogen in the universe to neutrons), the roughly 1078 nucleons in the universe would take up about 2x1053 cubic centimeters, so they would have a radius of about 1012 kilometers. This would roughly be in a sphere centered on the Sun and going out to the aphelion of Sedna.

Please note that the effects of gravity would make this a black hole of colossal proportions, and it wouldn't look like a big sphere of dirt for very long.

9. Originally Posted by antoniseb
....
So:
- the galaxy would be about 50 meters across.
- M31 would be about a kilometer away.
- The most distant observed galaxies would be about 6000 kilometers away --- So the visible universe would be about the size of the Earth.
And no one would take the blindest bit of notice of that

10. Originally Posted by dhd40
And no one would take the blindest bit of notice of that
I made a lot of approximations there. The result could be off by a factor of four or more. No reason to ascribe subtle meaning there.

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Originally Posted by cosmocrazy
Let's do the math.

<SNIP>

Would make the Galaxy 44249.31 inches (or 3687.44 feet, or 0.70 miles) in diameter
That's manageable. Don't need a telescope now; I'm gonna go out to the kitchen now and look at Alpha Centauri...

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The universe would be even smaller if you reduce the sun to one Planck length in diameter, but that's not as useful for visualizing size scales.

13. Originally Posted by antoniseb
I made a lot of approximations there. The result could be off by a factor of four or more. No reason to ascribe subtle meaning there.
??? ??? My poor wording ???

What I wanted to say was that if everything shrinked (or expanded) by the same factor, no one would be able to recognize this

14. Originally Posted by Veeger
The diameter of the milky way is about 100,000 light years - not 100,000,000.
You know i have just checked the calculation in my book and it must be a mistake. It has def, got the diameter of 100,000,000 light-years for the galaxy which is wrong.

This means the actual approximation is more like 44.3 inches for the galaxy if the earth was atom sized.

sorry folks.

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Originally Posted by slang
It depends on ones grasp of how small an atom actually is. If someone has the idea that an atom is just a bit smaller than, say, bacteria, then this comparison will not help them much.
You're right, I do find it hard to imagine just how small an atom is. I do have an idea in mind (once heard that if a person was the size of an atom, then a raindrop would be a mile long), but I'm not sure how true it is.

16. http://en.wikipedia.org/wiki/Observable_universe

From the link above we can approximate the observable universe to be now at this time about 93billion light years in diameter.

so based on this approximation for the galaxy, if the earth was atom sized then the universe would be approx -1046Km in diameter

assuming any calculation was correct.

17. Originally Posted by Ross PK81
You're right, I do find it hard to imagine just how small an atom is. I do have an idea in mind (once heard that if a person was the size of an atom, then a raindrop would be a mile long), but I'm not sure how true it is.
If a raindrop is 1/20th of a ml then it is about ten million water molecules in diameter. If a person was the size of a water molecule, the drop would be a little bigger than the Earth.

18. Originally Posted by dhd40
What I wanted to say was that if everything shrinked (or expanded) by the same factor, no one would be able to recognize this
Or perhaps my poor listening. I thought you were saying that it was too big a coincidence to be mere chance... but rather was a sign of a mystical truth.

Of course now I know what you really meant, and I feel pretty dumb. sorry.

19. An atom is a million times smaller than the thickest human hair. The diameter of an atom ranges from about 0.1 to 0.5 nanometres (1 × 10-10 m to 5 × 10-10 m).

If the total atom was the size of a football field, then the nucleus would be the size of an apple in the middle of the field

20. Originally Posted by Ross PK81
Just curious that's all. I guess it may make it easier to grasp the actual size of the universe.

First of all you'd have to be able to grasp the size of an "atom". I don't beleive you can grasp the size of an atom any more than you can the size of the universe. At least, I can't.

But, since no one knows the size of the Universe ( we can only measure he viewable universe) it's safe to say that, if the sun were the size of an atom, the universe would still be too big to see.

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I have a link the OP might be interested in viewing, it's a little dated however.

There is also a nice write-up of relative sizes in this link.

http://fuse.pha.jhu.edu/~wpb/scale.html

22. Originally Posted by Gandalf223
That's manageable. Don't need a telescope now; I'm gonna go out to the kitchen now and look at Alpha Centauri...
Lucky you. I live in the wrong hemisphere to see it.

23. Hydrogen atom or uranium atom?

24. I agree that the comparison doesn't really help much because of two factors:

1: No-one can imagine the size of an atom... it is as 'little' as the universe is 'big' (not too scale... just as far as human imagination is concerned.)

2: We dont know how big the universe is. We know how much we can observe and its only 13.7 billion light years in any direction (ignoring inflation). So max of 30 billion lightyears across. (Spacetime is curved so this is getting unwieldy... but to continue...) Now the bit we can 'see' (the 30 billion lightyears worth) might no even be 1% of the universe... we dont know.

But I do understand the intent of the question... I have spent all my life wondering if I could ever understand our place in the universe but it just plainly boggles the mind.

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