Light from edge of the observable universe has travelled 13.8 billion light years so far. And, that edge itself has travelled 32.2-33.2 billion light years (that's why actual radius of observable universe is roughly 46-47 billion light years). So, edge of the observable universe has won the race of traveling distance against light.

Before anyone knocks me for FLRW metric, I want to be clear that any metric won't change the distance light needs to travel. Meaning, light from the current actual edge of the universe will reach us after 46-47 billion years despite general relativity calculates the edge is expanding slower than light or such expansion isn't defined. So, better calculate it classical way...

The edge of the universe is roughly 2.33 times faster than $c$. Assuming it's constant (accelerating universe is worse, but you can use that data), we should definitely black out. After 0.1 second, a source 0.1 light seconds away would be 0.23 light seconds away and for next 0.23 seconds we won't receive any light from it. Now, we can go down to nanoseconds for the same thing or smallest possible scale for space and time. I suppose it's planks constant as space and time are continuous, but lower limit can be average duration between consequent photon quanta emissions when the difference would look significant.

Also, expansion is more apparent if the object is farther away. Combining this, with what fraction the average duration between consequent photon quanta emissions increased for the observer? Can I have a formula for that?


closed as unclear what you're asking by Rob Jeffries, Colin McFaul, Brandon Enright, JamalS, John Rennie Nov 24 '14 at 7:24

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  • $\begingroup$ I can't tell if this is a dupe of physics.stackexchange.com/q/67412 or not. $\endgroup$ – Brandon Enright Nov 24 '14 at 0:18
  • $\begingroup$ No, it's not a duplicate.. $\endgroup$ – Schrödinger's Cat Nov 24 '14 at 3:44
  • $\begingroup$ I've read through this several times, but I'm afraid I still can't work out exactly what you're asking. $\endgroup$ – John Rennie Nov 24 '14 at 7:24