According to what I found on Wolfram Alpha…
Earth and Venus (our nearest planetary neighbor) don’t get much less than 0.3 AU apart. In kilometers, that’s 45 million. Earth’s diameter is 12,735 kilometers, so the ratio of that distance to Earth’s diameter is about 3500/1.
Huge, right? Well, let’s take it into interstellar overdrive. The Sun’s diameter is 1.4 million kilometers. The closest star, Proxima Centauri, is 4.2 lightyears away (3.97 x 10^13 kilometers). The ratio of distance to diameter is about 28,360,000/1.
Repeat the exercise for other heavenly bodies–finding diameter-to-distance-ratios–and you’ll find the same result. Things in space are really, really far apart compared to how big they are.
The big exception, it turns out, is galaxies. The Milky Way is 100,000 lightyears across. The Andromeda galaxy is even bigger. But check the distance between the two: 2.6 million lightyears! The diameter-to-distance ratio is a staggeringly small 26! And some small galaxies are even closer to the Milky Way.
When you get up to a large enough scale, things seem more crowded.