Il senso delle proporzioni

SE IL SOLE fosse una moneta da un centesimo poggiata a terra davanti a noi, la prossima stella si troverebbe a 700 chilometri di distanza. La Via lattea avrebbe una larghezza complessiva di 30 volte la distanza tra la Terra e la Luna. L'universo è una cosa grande. Bel pezzo che rimette le cose nelle giuste proporzioni.

Money Quote: Scientists argue over the exact shape and size of the universe but they can calculate one thing with good precision: how far away we can see. Light travels at a specific speed, and because the universe is approximately 13.7 billion years old, we can’t see anything farther away than 13.7 billion light years away, right?

Wrong. The strange thing about space is that it’s expanding. And that expansion can occur at more or less any speed — including faster than light speed — so the most distant objects we can see were in fact once much closer to us. Over time, the universe has shuffled distant stars and galaxies away from us as if they were on an extremely rapid conveyor belt, and dropped them off in far away locations.

Strangely, this means that our observational power is sort of “boosted” and the furthest things we can see are more than 46 billion light years away. While we are not the center of the universe, we are at the center of this observable portion of the universe, which traces out a sphere roughly 93 billion light years across.

E nei commenti, ancora meglio:

It's easy. If the diameter of the solar system (kuiper belt) is 1mm. The nearest star is 3m (10 feet) away. At that scale the diameter of the galaxy is 64km (40miles).

Now if that 40mile galaxy (with the solar system being 1mm) was itself just a cm across (about half an inch) the nearest galaxy (andromeda) would only be 25cm away. The great Sloan wall would be 100m wide (300ft) at a distance of 100m, and the entire observable universe (if the galaxy was 1cm in diameter (half an inch) would only be 9 km (6 miles across).