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Cosmic Concerns

Writer's picture: Mishkat BhattacharyaMishkat Bhattacharya

This is a post to read in case you do not already have enough to worry about in your own life, including, but not limited to, what AI will bring in the near future. It lists some crises of astrophysical evolution - catastrophes that could come over our planet, our solar system, our Sun, our galaxy and our universe - in the future.


The Earth


The most immediate natural planetary-scale event of consequence is likely the next Ice Age. Originally scheduled to happen 50,000 years from now, there is now an expectation that human-made climate changes will delay it significantly.


The Solar system


Generally, we see that the planets in our solar system behave quite regularly. For example, Venus appears in the sky after sunset, and the Earth goes around the Sun once a year. But planetary motion is actually chaotic in the long term, as first indicated by Poincare. This means waiting for long enough will lead to irregular motion of the planets and increasing chances of collisions between them.


Initial research revealed 'long enough' to be about a million years. But some recent work has shown that over the expected 5 billion years of its total expected existence, the chance of collisions in our solar system, though not zero, is less than 1%. So don't sell those investments just yet.


The Sun


Which cosmic actuarial table does that 5 billion year solar system life expectancy come from? The answer to that question lies in the fact that the sun is actually a nuclear reactor. In about 5 billion years our Sun will run out of its nuclear fuel (Hydrogen). Its inner core, now consisting of Helium (produced when the Hydrogen fused), will begin to shrink. Its outer shell will begin to expand, due to radiation pressure from the core, and the Sun will become a red giant. The shell will heat up to thousands of degrees, evaporating the Earth's atmosphere, boiling way the oceans, and generally scorching the planet. This development will obviate any need to sue your neighbor.


The galaxy


I will now stop following the fate of the sun - it will go on to become a white dwarf - as around this time, about 5 billion years from now, the Milky Way (our galaxy) is scheduled to collide with Andromeda (the next galaxy over). A nice simulation of the collision can be found here. There is evidence that Andromeda already has some experience in colliding with other galaxies in the past, and we cannot guarantee that it will be more careful in the future.


The universe


As best as we know it, the universe came into being about 14 billion years ago and has been expanding ever since. What is going to happen to it in the future is a bit in the dark - that's a double pun, as you will see below.


That's because the expansion seems to be (we're not sure) driven by a substance we know so little about we call it dark energy. Depending on how strong the repulsive effect of dark energy is compared to gravity - which is attractive - the universe could see variety of outcomes.


If dark energy is strong enough to drive expansion forever, the universe will die a cold death. Space will become so dilute in matter that new stars will no longer form. They will become rare, as existing ones mostly turn into black holes, and evaporate away. The universe will become a largely empty and dark necropolis. If dark energy is strong enough to rip apart the fabric of spacetime itself, then it's anybody's guess what happens after that - just like all bets are off after we get a rip in our trousers.


If gravity overcomes dark energy, then the universe will contract and end up as it was at the Big Bang - as a single point. It might be possible that expansion can subsequently follow, repeating the whole process.


The end of the universe is estimated to occur, in the earliest scenarios, in about 20 billion years. So you have at least that much time to wrap up your social media conversations. For more details, here is an illuminating interview of Katie Mack. She wrote in detail about the gerontology of the universe in her book The End of Everything.






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