3 ms·

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.

gregoriol 5y ago
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.
- zokier 5y ago
  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-like-a-billiard-ball-or-not/ https://possiblywrong.wordpress.com/2011/01/03/is-the-earth-... https://skeptics.stackexchange.com/questions/10763/is-earth-as-smooth-as-a-billiard-ball https://skeptics.stackexchange.com/questions/10763/is-earth-... https://billiards.colostate.edu/faq/ball/smooth/ 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.
- aardvark179 5y ago
  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.
B1FF_PSUVM 5y ago
Me too, I was going with "smoother than an orange", the billiard or bowling ball seem excessive - https://what-if.xkcd.com/46/ https://what-if.xkcd.com/46/ posted here
HopDavid 5y ago
Tyson has pretty low standards for rigor and accuracy. Take everything he says with a grain of salt.

gregoriol 5y ago

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.

zokier 5y ago
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-like-a-billiard-ball-or-not/ https://possiblywrong.wordpress.com/2011/01/03/is-the-earth-... https://skeptics.stackexchange.com/questions/10763/is-earth-as-smooth-as-a-billiard-ball https://skeptics.stackexchange.com/questions/10763/is-earth-... https://billiards.colostate.edu/faq/ball/smooth/ 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.
aardvark179 5y ago
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.

B1FF_PSUVM 5y ago

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

HopDavid 5y ago

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