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Comment by HJain13 | Hacker News Reader

So is rest of the earth; Youtube channel Vsauce covered this in one their videos https://youtu.be/mxhxL1LzKww?t=721

I recall Neil deGrasse Tyson mentioning that the whole earth would be smoother than the smoothest billiards ball if scaled down. I found that surprising.

Wow, that scale! Thanks for posting that!

If my calculations are right, Earth's diameter is about 12000km and its highest/lowest places are about 10km, so about 0.001 If a billiard ball is about 10cm, it's highest/lowest places equivalent to earth would be 0.1mm.

Not sure what are the standards for billiard smoothness, but that seems very smooth to me.

0.1mm is not very smooth. According to wikipedia, 150 grit sandpaper has average particle size of 90-100µm

edit: of course there is vigorous internet commentary about billiard ball smoothness compared to earth:

https://possiblywrong.wordpress.com/2011/01/03/is-the-earth-...

https://skeptics.stackexchange.com/questions/10763/is-earth-...

https://billiards.colostate.edu/faq/ball/smooth/

Which mostly seem to agree that earth definitely is not as smooth as a (new) billiards ball, but there is lots of debate about the details.

A billiard ball is about 50mm in diameter. I guess the question is to what tolerance they are made. I wouldn’t expect a small feature to stick up (you’d be able to feel or see those fairly easily) but the overall deviation from a perfect sphere could easily be that large.

Me too, I was going with "smoother than an orange", the billiard or bowling ball seem excessive - https://what-if.xkcd.com/46/ posted here

Tyson has pretty low standards for rigor and accuracy. Take everything he says with a grain of salt.

"So is rest of the earth" ... when taken as a whole, though. Switzerland is not flat as a pancake, for example.

From what I understood from the video, the surface irregularities a general pancake can have when stretched to dimensions of the earth would lead to 10km high feature; Given even Mt. Everest is <9km, I am not sure why Switzerland wouldn't fit the definition

edit: Typo

If you stretch the pancake only to the dimensions of Switzerland, the vertical features would be a lot less high. And Switzerland has quite some height differences within a small area.

Or a more extreme example: If you stretched the pancake to just the width of Everest clearly Everest would be less flat.

The peaks measure ~9km above sea level. The deepest portions of the ocean add another 3-4km.

Not sure how to read this, but have you heard of the Mariana Trench?

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