Two of the largest holes in the Earth’s atmosphere are in those LIGO beam tubes, just there beyond the double doors of the control room. There’s less stuff in those tubes than there is in the empty space between galaxies, which has a very little bit of stuff known as the intergalactic medium. Two of the biggest holes in the atmosphere and eight times less stuff than parts of outer space. (Although the emptiest regions of outer space are emptier still.)
