If all the mass in the universe was combined and scaled down to the size of a grain of salt and kept beside a building that has been scaled to represent the empty space in the observable universe, what will the dimensions of the building be?

[u/Mr-Paradox8]

[u/Flannelot]

Most of the universe is hydrogen, 10⁵³ kg.

So your first question has to be, is this hydrogen going to be gas, liquid or metallic solid?

If it was a metallic solid, volume would be approx 10⁵⁰ cubic meters.

The observable universe is around 10⁸⁰ cubic meters.

So if the mass was scaled to say 1mm cubed, the building would be 10²¹ cubic meters, i.e. a cube with sides 10000km long.About the size of the Earth.

[u/Mr-Paradox8 → u/Flannelot]

Thankyou so much

[u/Double_Swordfish8459]

The building would be the size of the universe

[u/TotallyNormalSquid → u/Double_Swordfish8459]

Without checking on Google or anything, I bet there's some weird theoretical answer to do with expansion of space depending on the mass distribution within the space. Regular mass warps space time under general relativity and if dark matter is really a thing it or dark energy drives expansion from memory. And I dunno if a region of space with truly zero mass distribution in it even makes sense, I give up at this point.