Extremes in Perspective

If you've ever read any science, you might have noticed that it's impractical to really "feel" the scales for the objects being discussed.  For me, at least, they usually just fall into the categories of "really big", "really small", or (in the case of the speed of light): "really fast."

Sometimes, I try to paint these extremes in a manner that I can wrap my head around -- to try to make them as tangible as possible.  Most often, I can't come up with any particularly satisfying analogy -- but I've had a few that I really like.  ...And along the way, I had one really big revelation, which I'll describe.


Here are a few of the most satisfying analogies I've come up with, that make things a bit more conceivable.

Distance to the edge of the Universe:  You're probably aware that we live in the Milky Way galaxy, and that our closest galactic neighbor is Andromeda (part of the so-called "galactic group").  And likely you know that the universe itself is a lot bigger than even that.  But how much bigger?

If we shrunk the universe so that the Andromeda galaxy (our closest neighbor) were 1.5 miles away, the universe would be the size of the earth.  That's a hard one to let sink in, but try.  Andromeda is 2.5M light years away.  The distance to the edge of the observable universe is 46B light years, about eighteen thousand times farther away.

Size of the Universe:  If we shrunk the universe so that the Andromeda galaxy (our closest neighbor) were 1.5 miles away, the universe would be the size of the earth.

Speed of Light:  If you could fly around the world seven times in one second, you'd be going the speed of light.

Distance to Center of Earth:  To reach the Earth's core, you'd have to dig a hole (straight down, obviously) equal to the distance from Boston to San Diego, and then a third of the way back.  That'd be a pretty deep hole.

Distance from the atomic nucleus to an electron:  If we enlarged a hydrogen atom to be the size of the sun, its first electron (to the extent that we can treat it like a point particle) would actually be about the size of the Earth, but about 200 times farther away (about 22 billion miles away from the sun).