4 ms·

I'd be curious about the source. Is that one He in the actual vacuum, or is that one He by dividing known matter by known space. If its the latter, that's very

• wongarsu 6y ago
  It depends on where we are talking about. Inside the solar system is the heliosphere [1] with lots of particles from solar wind. As you leave the solar system you get the interstellar medium [2], which is about 90% hydrogen and 10% helium, most of it about half a particle per cm^3. Between the galaxies there's the intergalactic medium [3], which is speculated to contain about half of (normal, not-dark) matter in tendrils with a density of about 1-10 particles per cm^3 (and a lot less outside those tendrils). The best vacuums we can produce artificially on earth have a couple billion particles per cm^3. 1: https://en.wikipedia.org/wiki/Heliosphere https://en.wikipedia.org/wiki/Heliosphere 2: https://en.wikipedia.org/wiki/Interstellar_medium https://en.wikipedia.org/wiki/Interstellar_medium 3: https://en.wikipedia.org/wiki/Warm%E2%80%93hot_intergalactic_medium https://en.wikipedia.org/wiki/Warm%E2%80%93hot_intergalactic...
• amadsen 6y ago
  Perhaps not as different as you think! Most of the "known matter" is indeed H and He drifting in otherwise "empty space". Stars, while very dense, are few and far between on cosmic scales. In terms of mass, the ratio is about 4:1. So you'd get quite similar answers from both calculations.