Space is empty… almost. When we say vacuum, we mean space that is devoid of matter, but interestingly, creating a real vacuum on earth in a laboratory has been impossible. Just how empty are different degrees of vacuum? How empty are the depths of space? Between planets? Between stars? Between galaxies? We can go through a quick scale of emptiness. As it turns out, space beats out our best efforts by a longshot.
| Pressure (Pa or kPa) | Pressure (Torr) | Mean Free Path | Molecules per cm3 | |
|---|---|---|---|---|
| Standard atmosphere, for comparison | 101.325 kPa | 760 | 66 nm | 2.5×1019[60] |
| Vacuum cleaner | approximately 8×10+4 | 600 | 70 nm | 1019 |
| Steam turbine exhaust (Condenser Backpressure) | 9 kPa | |||
| liquid ring vacuum pump | approximately 3.2×10+3 | 24 | 1.75 μm | 1018 |
| Mars atmosphere | 1.155 kPa to 0.03 kPa (mean 0.6 kPa) | 8.66 to 0.23 | ||
| freeze drying | 100 to 10 | 1 to 0.1 | 100 μm to 1 mm | 1016 to 1015 |
| rotary vane pump | 100 to 0.1 | 1 to 10−3 | 100 μm to 10 cm | 1016 to 1013 |
| Incandescent light bulb | 10 to 1 | 0.1 to 0.01 | 1 mm to 1 cm | 1015 to 1014 |
| Thermos bottle | 1 to 0.01 [1] | 10−2 to 10−4 | 1 cm to 1 m | 1014 to 1012 |
| Earth thermosphere | 1 Pa to 1×10−7 | 10−2 to 10−9 | 1 cm to 100 km | 1014 to 107 |
| Vacuum tube | 1×10−5 to 1×10−8 | 10−7 to 10−10 | 1 to 1,000 km | 109 to 106 |
| Cryopumped MBE chamber | 1×10−7 to 1×10−9 | 10−9 to 10−11 | 100 to 10,000 km | 107 to 105 |
| Pressure on the Moon | approximately 1×10−9 | 10−11 | 10,000 km | 4×105[61] |
| Interplanetary space | 11[1] | |||
| Interstellar space | 1[62] | |||
| Intergalactic space | 10−6[1] |
Table borrowed from http://en.wikipedia.org/wiki/Vacuum
There are some surprising conclusions. The commercial vacuum is ironically not much of a vacuum at all; it only reduces pressure by about 20%.
Mars’ atmosphere is 1/100th the density of Earth’s.
The moon does have an atmosphere, and it gives about the same surface pressure as our BEST vacuums on earth.
Interplanetary space is densely populated in comparison to the cold, dark space between stars and galaxies.
The quantum description of the vacuum is quite different, but we can save that for later.
Öpik, E. J. (1962). “The lunar atmosphere”. Planetary and Space Science 9 (5): 211. Bibcode:1962P&SS….9..211O. doi:10.1016/0032-0633(62)90149-6.
Chambers, Austin (2004). Modern Vacuum Physics. Boca Raton: CRC Press. ISBN 0-8493-2438-6. OCLC 55000526.[page needed]
University of New Hampshire Experimental Space Plasma Group. “What is the Interstellar Medium”. The Interstellar Medium, an online tutorial. Retrieved 2006-03-15.
