Ask Ethan #102: Is Everything In The Universe The Same Age?
Ethan Siegel

Disclaimer: Never 100% got my head around relativity

It occurs to me that we are in a Universe that has a 3x10^11 m/s speed limit, it is 13.8 billion years old, yet it is wider than 27.6 billion light years (I think that we have detected sources out to 40–50 billion light years in each direction). The standard explanation for this is “Inflation”, which kind of screams “very big fudge factor” to me. Assuming that the universe came from a point, the chances that we are close to the center (and therefore not moving at very high speeds) seems small. This explanation of the relativity effects implies that we would be seeing a universe that was 13.8 billion years old, but being surrounded by matter that would be a lot younger. Geological factors (the fact that we have a lot of heavy elements around) implies that the local area is pretty old. My question would be how do you measure how fast you are “traveling” relative to the CMB? Surely it moves at light speed, right?