August 25, 2018

Time is precious even on cosmological timeframes

The Universe Is Disappearing, And There’s Nothing We Can Do To Stop It

...on average, twenty thousand stars transition every second from being reachable to being unreachable. The light they emitted a second ago will someday reach us, but the light they emit this very second never will. It’s a disturbing, sobering thought, but there’s also a more optimistic way to view it: this is the Universe reminding us how precious every second is. It’s the Universe telling us that if we ever want to travel beyond our own local group — beyond the gravitationally bound set of objects made up of Andromeda, the Milky Way and about 60 small, satellite galaxies — that every moment we delay is another opportunity being lost.

Of the estimated two trillion galaxies in our Universe today, only about 3% of them are still reachable from the point of view of the Milky Way. This also means that 97% of the galaxies in our observable Universe are already out of humanity’s reach, owing to the accelerated expansion of the Universe caused by dark energy. Every galaxy beyond our local group, as time goes on, is destined for that same fate.


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