our future -- 12/16/20

Today's selection -- from Our Universe by Jo Dunkley. The future of our solar system, galaxy, and universe:

"All of our observations of the sky have told us that our moment in time, here for us humans on Earth, is almost 14 billion years into our universe's history, and about a billion years into the Solar System's history. We now have a well­ formed idea of when and how our planet got to be here, but it is also in our nature to wonder what will happen in the future. Luckily, the laws of physics are reliable enough to make pretty good predictions. We can be reasonably sure of some things. In the next hundred years or so there should be a supernova that explodes in our own Galaxy. It will be mag­nificent to watch and will be extremely valuable for under­standing the inner workings of these exploding stars. At some time in the next few hundred thousand years the red star Betelgeuse in Orion will also become a supernova, light­ing up the sky for days or weeks. Some of our lucky descend­ants might be around to see it.

"In about 200 million years the Solar System will complete another orbit around the Milky Way. By then the familiar constellations in Earth's night sky will have changed. Many of the same celestial neighbors will still surround us, but the Sun will not stay in an absolutely fixed position relative the backdrop of these nearby stars. It is certainly possible that during that time the Earth will also get hit by large rocky objects traveling through the Solar System.

"Further ahead, in 4 or 5 billion years, our Sun will eventu­ally run out of fuel at its core and will swell up to become a red giant. It will later end its days as a white dwarf. On a simi­lar timescale the Milky Way will also first consume the Ma­gellanic Clouds and then collide with Andromeda to create a brand new elliptical galaxy. Earth will be little affected by the collision with Andromeda, but strongly affected by the growth of the Sun. It will either be absorbed into the larger Sun or will be perilously close to the edge of it. It will be a seriously inhospitable place. Even before then, the Sun will become hotter over its lifetime, limiting the options for life on Earth.

"We do not yet know if, in the much more distant future, the universe will keep growing. At the moment it appears as if it will do, with all the galaxies separating on average ever further apart from each other. A time may come in the very distant future when an astronomer sitting in a galaxy like ours will no longer be able to see any other galaxies, as they will all have vanished from view, disappearing over the cosmic horizon as space grows and grows ever faster. Hap­pily, that time has not yet come, and the universe is still very much within our reach."

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Jo Dunkley


Our Universe


The Belknap Press of Harvard University Press Cambridge, MASS 2019


Copyright Jo Dunkley 2019


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