Just how long is 380,000 years after the big bang?

Deep Breadth
Feb 18, 2018 · 2 min read

Visualizing when the CMBR was released

Most people that know what the CMB is also know that it was an event that occurred about 380,000 years after the big bang.

But in the context of a universe that’s 13.8 billion years old, what does that mean exactly?

Maybe we can draw a timeline…

If we draw the timeline of the universe starting from the the big bang at the surface of the earth and ending at the present on the surface of the moon, where would the moment of the CMBR fall?

First, take a guess of where you might expect it to be...

Okay, let’s math.

If we marked the spot on our timeline where the CMB occurred, it would only be 10.58 kilometers (6.57 miles) above the earth’s surface.

That’s barely half way through the bulk of earth’s atmosphere, which can be thought of as the equivalent of a layer of varnish on a bowling ball.

And keep in mind that moon is actually much further away than our intuitions tell us…


So it’s pretty damn close to the beginning.

With the correct scale in mind, we’d have to draw our CMBR line like this:

Even if we drew our timeline to mars instead of the moon, the line for the CMBR would still be less than two percent of the distance to the moon.

So now it seems like the CMBR happened almost immediately, but really an awful lot happened in those 380,000 years…

Physicist today can tell a pretty compelling story about what happened allll the way up to approximately 10^-37 seconds after the big bang, when the spark of inflation seems to have ignited into the initial exponential expansion of space allowing the four fundamental forces to split off from one another and allowing for the creation of the first fundamental particles (including some exotic varieties that aren’t around anymore).

10^-37 seconds. Now that is hard to visualize. Details here.

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