# Tag Info

• 86
1 vote

### When will the particle horizon reach its limit of 63 billion light years?

The maximum particle horizon size is approached asymptotically over an infinite span of time. There is no particular time at which the light from distant objects stops reaching us. Rather, the ...
• 19.2k
1 vote

### How can you determine distances to obejcts further away than 13.72 billion light years?

It doesn't make sense to treat the light travel time times $c$ as a distance when the light travel time is large, because of spacetime curvature. In a comment you implied that you want to know the ...
• 19.2k
1 vote

### Varying energy density of photons?

For self-consistency, we need the energy to come from somewhere. For astrophysical sources, it of course comes from matter. In that case you can assume that there is some energy exchange rate $\Gamma$ ...
• 86
1 vote

### Energy from spacetime expansion?

General relativity, in an arbitrary spacetime, has local conservation of energy but not global conservation of energy. On practical scales, spacetime can be modeled as asymptotically flat. In an ...
• 11

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