Post by rmarks1 on Aug 19, 2018 13:27:04 GMT -5
Years ago, I saw a cartoon (I think it was "Nancy") where she was watching a professor on tv who said that according to his calculations, the Sun would burn out in 5 million years, Then he looked at his papers and said he made a mistake. It would only take 2 million years for the sun to burn out. Nancy panicked.
Keep that in mind as you read this article.
Bob
Keep that in mind as you read this article.
The Universe Is Disappearing, And There's Nothing We Can Do To Stop It
But this picture, which held sway from the 1920s onward, has been recently revised. It's been only 20 years since we first realized that this expansion was speeding up, and that as time goes on, individual galaxies will appear to recede away from us faster and faster. In time, they'll become unreachable, even if we journeyed towards them at the speed of light. The Universe is disappearing, and there's nothing we can do about it...
But there's an inevitable conclusion that this leads to that's even more disturbing. It means that, at a particular, key distance from us, the expansion of the fabric of space itself makes it so that a photon either leaving our galaxy towards a distant one or leaving a distant galaxy headed towards ours will never reach us. The expansion rate of the Universe is so great that distant galaxies become unreachable to our own, even if we were to move at the speed of light!
At present, that distance is "only" about 15 billion light years away. If you consider that our observable Universe is some 46 billion light years in radius, and that all regions of space contain (on average and on the largest scales) the same number of galaxies as one another, it means that only about 3% of the total number of galaxies in our Universe are presently reachable by us, even if we left today, and traveled at the speed of light.
It also means that, 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.
www.forbes.com/sites/startswithabang/2018/08/17/the-universe-is-disappearing-and-theres-nothing-we-can-do-to-stop-it/#4676cca7560e
But this picture, which held sway from the 1920s onward, has been recently revised. It's been only 20 years since we first realized that this expansion was speeding up, and that as time goes on, individual galaxies will appear to recede away from us faster and faster. In time, they'll become unreachable, even if we journeyed towards them at the speed of light. The Universe is disappearing, and there's nothing we can do about it...
But there's an inevitable conclusion that this leads to that's even more disturbing. It means that, at a particular, key distance from us, the expansion of the fabric of space itself makes it so that a photon either leaving our galaxy towards a distant one or leaving a distant galaxy headed towards ours will never reach us. The expansion rate of the Universe is so great that distant galaxies become unreachable to our own, even if we were to move at the speed of light!
At present, that distance is "only" about 15 billion light years away. If you consider that our observable Universe is some 46 billion light years in radius, and that all regions of space contain (on average and on the largest scales) the same number of galaxies as one another, it means that only about 3% of the total number of galaxies in our Universe are presently reachable by us, even if we left today, and traveled at the speed of light.
It also means that, 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.
www.forbes.com/sites/startswithabang/2018/08/17/the-universe-is-disappearing-and-theres-nothing-we-can-do-to-stop-it/#4676cca7560e
Bob
