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Which of these events have a >1% chance of happening in the next thousand years?

If our rate of innovation continues, maybe we don’t have much to worry about on this front.

"our rate of innovation"

That's the most worrisome thing

Nuclear war.

This may sound positively retro and cold-warish, but IMO we've had way too many close calls in the 80 years nuclear weapons existed, and the quality of governance worldwide only seems to decline.

Neither the United States nor the Soviet Union treated each other with the vitriol that Russia and the US do today. Do you believe Putin and Trump are half the gentlemen Kennedy and Khrushchev were? I seriously believe we are closer now to nuclear deployment than at any time after 1945. During the Cuban Missile Crisis, Khrushchev was dreadfully worried about nuclear war and wrote many cables to Kennedy sorrowfully bemoaning the thought. While today, Putin airs propaganda to an increasingly uneducated audience treating a theoretical first nuclear use as unremarkable, and his ministers seem more concerned with the idea of whether or not they can ever beat MAD.[1] Trump liked to brag about the size of his "button" to Kim Jong Un like it was a WWE script. There's little hope I have that the world will escape, even a limited tactical deployment in the coming two decades, playing fiery chicken with the future of humanity.

[1]: https://www.bbc.com/news/world-europe-65119595

Nuclear war is not an extinction event, though. Most people would survive, and while they would face hardships, the "radioactive wasteland" thing is a fairly sloppy sci-fi trope.

OP didn't say extinction event.

That aside, if all nukes were launched, it's not about the directly irradiated areas. Imagine how much fallout will be launched into the upper atmosphere when 10,000+ nukes hit, with many in the multi-megaton range.

The sheer amount of material thrown into the air could virtually blot out the sun for potentially years. Given that a large portion will be radioactive, it could be raining death for years too.

Ehh the dust will fall out of the atmosphere within a few months. Large population centers will be craters proba ly. The 4 year nuclear winter will cause starvation and eating the "long pork" such that up to 90% of the population globally will die.

> Large icy or rocky bodies hitting the planet

Or comparatively tiny bodies hitting the planet at relativistic speeds

Is this likely? What is it a consequence of?

What would happen if you tried to hit a baseball pitched at 90% the speed of light?

https://what-if.xkcd.com/1/

Nice. Could a baseball pitched at 90% the speed of light from [anywhere that could produce such a speed] make it to Earth and impact? What can cause chunks of matter to travel this fast?

Could one make it to Earth and impact? The universe is very large, so it's a possibility, but space is very big and very empty, so we'd have to get very very very very unlucky for that to happen. But supernova explosions, pulsars and neutron stars, gamma-Ray bursts, supermassive black holes, and (theoretical) dark matter annihilation could all do it.

https://www.universetoday.com/145006/there-could-be-meteors-...

I wonder how often that happens. What's the fastest interstellar object we've ever detected? 0.01% of the speed of light, more or less? That's a few orders of magnitude shy of relativistic speed.

If you're thinking really long term, evolution should be considered an existential threat as well. If its not us doing the surviving, it's not us.

What is valuable life? What a philosophical question on HN! I think many will say "sentience". Many religious will say "if my religious leader said they are God's children". What is your definition?

> To survive in the really long term, we are going to have do something pretty drastic. Whatever we do (eg interstellar travel, moving the EArth--yes, this is possible)...

I'll bite. :-) Could you elaborate on what it might look like to transport the earth? Where would we move it to? How would life survive in transit without the sun?

Just move it further out, as the Sun expands. Just.

I think he might just mean moving the earth to a different (further out presumably) orbit in this solar system.

One proposal I've seen involves putting asteroids into an orbit such that their gravity pulls the Earth outwards a tiny bit each time they pass. Over an extended period of time (millions of years?) we could move the Earth outwards from the sun before the sun expands and cooks it. Obviously the Earth would pull the asteroid inward as well so we would have to adjust the asteroid's orbit after each pass. One proposal I've seen would be use Venus to keep the asteroid in a stable orbit. Essentially each pass of the Earth would slow the asteroid down a little bit, but each pass by Venus would speed it back up again, essentially pulling the Earth away from the sun while pulling Venus closer to the sun. In theory we could set up a system like this and just let it do its thing over a very long time, the change would be imperceptible over a human lifetime.

There are different froms of this and it depends on your goal.

For the 1-5 billion year range your issue is the Earth overheating because Solar output is increasing by about 10% per billion years. There are three basic ways of doing this:

1. Putting something between the EArth and the Sun to reduce the amount of radiation that hits the Earth. This is by far the easiest;

2. Move the Earth to an orbit further from the Sun; or

3. Removing mass from the Sun to extend its life or reduce its output. This is the hardest.

So how do you move the Earth to a different orbit? Well that's pretty easy actually. I mean "easy" in the sense that it requires no new hypsics, no negative energy or negative mass. It just ruses gravity.

The Earth interacts with any mass. A sufficiently sized mass will attract the Earth. So you just fly large bodies of mass past the Earth to slowly nudge it in the direction you want. The Earth is relatively heavy (~10^24kg) so the energy requiremetns are still immense but it can be done slowly (and probably should be).

Add "running out of CO2" and "the atmosphere thins too much" to the list. I don't know when those could happen, but they've been happening slowly for billions of years, and they will finish happening eventually, most likely well before the Sun's output gets too high.

Atmospheric loss is an interesting and not-entirely-understood subject [1].

But here's one aspect we do know that puts the scale in context. Any gas has a Boltzmann distribution of kinetic energies. You can calculate that a certain portion of that will have a kinetic energy high enough to escape gravity. This is called the Jeans escape energy [2].

For Earth this amounts to losing 60-100,000 tons of atmosphere every year, which is actually a complete non-issue.

I mention this because the idea of terraforming Mars is a popular sci-fi trope but really makes absolutely zero sense. Mars has lower gravity (and no magnetic field, although part this is fixable) so the atmospheric loss would be significantly higher if we wanted to produce 1 atmosphere of pressure at the surface.

So however we produced that atmosphere would have to be able to sustain a loss of 100,000+ tons of atmosphere every year as a rounding error. That's the scale of just one of the many problems in terraforming Mars. You also have to produce (or ship in) that atmosphere without boiling the planet. The scale combined with thermodynamics makes this a nontrivial problem.

And where is all this energy coming from? We return back to the Dyson Swarm.

[1]: https://sseh.uchicago.edu/doc/Catling2009.pdf

[2]: https://en.wikipedia.org/wiki/Atmospheric_escape#Jeans_escap...

I got a lot out of your comment, but I don't know that Mars and Earth are directly comparable.

- Earth has nearly 10x the surface area of Mars. This decreases the rate of escape.

- Mars has lower gravity meaning escape velocity is roughly 1/3 Earth's, or escape energy is 1/10. This increases the rate of escape.

- Mars has lower temperatures, which reduces what fraction of the atmosphere is at an escape velocity. This reduces the rate of escape. Though if we terraform it, maybe it warms up as well?

So Mars and Earth are not easily compared, and are likely off by an order of magnitude.

Still, it is worth thinking about what general scale we are talking about. Terraforming requires a civilization with access to resources many times our own.

This [1] may interest you. It estimated Mars's atmospheric loss at 0.1-0.5kg/s, which amounts to about 3-16k tons/year but that's also with Mars's current almost nonexistent atmosphere. Losses would be higher with a thicker stmosphere that would be ~1 atmosphere of pressure at ground level.

[1]: https://sci.esa.int/documents/33745/35957/1567258799920-Weih...

Do we need 1 atmosphere of pressure on Mars to survive? Cusco has 40% less oxygen than sea level and people there seem just fine.

Mars currently has less than 1% of Earth's sea level atmospheric pressure.

Cusco is roughly 0.6atm of pressure.

So Cusco is a lot closer to use. Mars is essentially the Moon. Actually, it's worse than the Moon. Because all Mars's atmosphere dos is blow really annoying dust all over your equipment. Everything about Mars is the worst [1] eg specifically about the problems of landing on Mars:

> “It’s like this annoyingly middle value,” he said. “The atmosphere is thick enough to cause you all the problems you have on Earth, but too thin to really stop you like on Earth.”

[1]: https://fivethirtyeight.com/features/everything-about-mars-i...

Right, but the idea is that if you had an atmosphere with a higher partial percentage of O2 you could get by with far less inert gas filler, which makes terraforming a bit less daunting. You could imagine an atmosphere with 35% O2 at 0.3 atm being possibly habitable and requiring many trillion less tons of material added to Mars.

Cody's Lab has a few interestig videos about burning things in pure oxygen. For example https://www.youtube.com/watch?v=JlSeHSDc-Do So it's no so simple becuae you can't just ignore the 80% of nitrogen and use only the 20% of oxygen.

(IIR/UC the problem is that the nitrogen absorbs heat, so the pure 20% of oxygens burn things too easily.)

I'm not arguing that Mars atmosphere is close to Cusco. I'm responding to the parent comment implying that 1 atmosphere off pressure would be lost very quickly on Mars. Would this be the same for 0.6 or 0.5 atmospheres? If we could create such an atmosphere is a whole different discussion

Jeans escape is not the only way an atmosphere can be lost.

If a planet doesn't have a magnetic field, the solar wind can directly erode the atmosphere (ionizing molecules and carrying away the ions and electrons in the magnetic fields of the wind.)

Even with a magnetic field the solar wind can erode the atmosphere, it's just slower.

A hundred million years for the terraformed atmosphere of Mars to escape would still mean that it's going to be useful.

I believe that the issue is the loss rate exceeds the creation rate, making a viable atmosphere a nonstarter - not that "an atmosphere suddenly appears and lasts 100,000 years"

The "plans" for Mars terraforming will probably include slamming comets into it (at low relative speeds), on the scale of 1000-10000 years. It's unlikely to involve slow-and-steady air production.

I looked into this a while ago, and a major problem with Mars terraforming is that if you add a bit of additional carbon dioxide (or water vapor), it'll mostly just get frozen and deposited onto the ice caps.

So you need to add something like nitrogen to "bulk up" the atmosphere to prevent it from freezing out. And there's just no nitrogen on Mars.