If the universe is 13.8B years old, how can we see 46B light years away? (2018)

Re:If the universe is 13.8B years old, how can we see 46B li... by rhinokungfu on Saturday December 07, 2019 @12:26PM (#21731408)

Some of the confusion is, I think from referring to speed of light as "speed of light". When it really is speed limit of causality between 2 points in space. And light (em waves) just happen to be able to hit that limit. Now since expansion of space is itself not going to allow one point in space to cause any effect on another, it (the expansion) can be faster than speed of causality.

PBS space time has a good video on this - https://www.youtube.com/watch?v=msVuCEs8Ydo

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Re:If the universe is 13.8B years old, how can we see 46B li... by nuccy on Saturday December 07, 2019 @03:15PM (#21732316)

It is also peculiar that the energy conservation law is not applicable on cosmological scales, the light is redshifted due to expansion of the Universe and the energy difference between emitted and received light is "wasted", i.e. it doesn't feed the expansion in any way.

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Re:If the universe is 13.8B years old, how can we see 46B li... by cygx on Saturday December 07, 2019 @03:28PM (#21732366)

I don't know if 'feeding expansion' is necessarily the right way to think about this, but by the first Friedmann equation, loss of photon energy will in fact be balanced by the increased expansion rate...

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Re:If the universe is 13.8B years old, how can we see 46B li... by nuccy on Saturday December 07, 2019 @03:43PM (#21732428)

Sure, though the first Friedmann equation, or any other equation, where terms are balanced, e.g. a + b = 0, doesn't tell you anything about causality, though redshifting of light is exactly caused by expansion, so it is not strange that both are "balanced".

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