Surprising supernova scars cover the Earth

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...

Is this likely? What is it a consequence of?

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.

"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

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?

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).

I think parent meant the kind of dinosaur that can eat you.

While birds are technically a kind of dinosaur, lizards are not.

At the time scales we're considering that's not even a rounding _error_.

Yes, the Cretaceous–Paleogene extinction is agreed to be 66 mya with some surprisingly tight error bars of about 50k years.

But for the purpose of discussion 100 mya is close enough in terms of orders of magnitude so there's not a need to be pedantic.

Not all of those explode eventually, rather it's a small amount. Only the most massive stars explode into a supernova. The majority of stars are smaller, and will have different lifetimes. For example, the sun, an unusually bright star (brighter than about 95% of stars) will eventually turn into a red giant, slough off material then collapse to a white dwarf. It's estimated that the majority of stars are brown dwarf (very small, some not too-too much larger than Jupiter), and less than 1% of stars are massive enough to go supernova. The problem is that only the big stars go super nova, and the big stars also have the short lifetimes because they're burning fuel so quickly.

to the point that probably all atoms once within your body are spread rather evenly far from each other, and not coming back

Also in Supernova Era if I remember correctly!

And in Charles Stross's Iron Sunrise.

>A supernova, seen from as far away as the Sun is from the Earth

GP and XKCD are talking about a supernova from the Sun, you're talking Alpha Centauri.

A DT fusion reactor with iron in its structure would produce a small amount of Fe-60, by double neutron capture on Fe-58. The amount would be limited because the half life of Fe-59 is 44.5 days.

It’s not so ridiculous once you learn that most of the earths crust gets recycled within 500 million years, and more than half gets recycled within a mere 100 million years.

That’s why we don’t find fossils everywhere. And if humanity goes extinct today, it would be fairly tricky to find evidence of us in a billion years.

It’s of course a non falsifiable hypothesis, so there’s not much we can do. But plenty of people believe in another non falsifiable hypothesis——invisible man in the sky.

It's ridiculous because a past civilization wouldn't have spread iron-60 all over the planet the way a supernova would have.

But a fairly advanced civilization could have existed in a fairly local part of the planet that we don't much explore (think of the Sahara desert) and so haven't found the remains of, or it could be buried or under quite a bit of water (if it developed during a glacial period).

I agree with this comment fully but I just wanted add a little on the subduction.

It’s a lot quicker than people think.

The vast majority of rocks we can find that aren’t of extra terrestrial origin are only around 200 million years old.

>A few seams of very old rock have been discovered, such as the billions of years old Nuvvuagittuq greenstone belt in Hudson Bay, Canada, as well as similarly ancient outcrops in Australia, China, Greenland and South Africa. But even this very old rock has had a complex history. “Exposure to high temperatures during past collision can change the chemistry,” notes Boyet. “This disturbs the isotopic system we use for dating rock.”

https://cordis.europa.eu/article/id/442712-are-all-rocks-on-...

> It would be really weird if a Silurian civilization randomly pumped out a bunch of radioactive iron and didn't do anything else.

We never know any data before interpreting it through theories. All observations are, as Popper put it, theory-laden, and hence fallible, as all our theories are.

  Deutsch, David. The Beginning of Infinity

Probably the best evidence that Fe60 is not "Silurian" in origin is that it still arrives on Earth [0].

0. https://webarchiv.typo3.tum.de/PH/gams/fileadmin/w00bjs/www/...

Addendum:

The Silurian Theory is sometimes an interesting way to explore ideas. I don't think that a large pre-human "civilization" need take the same form as what we think of as human civilization. Even some large human civilizations like that of the Indus River Valley or Harappan culture are less understood because they left less in the way of stuff analogous to current times: "In sharp contrast to this civilisation's contemporaries, Mesopotamia and ancient Egypt, no large monumental structures were built. There is no conclusive evidence of palaces or temples."

https://en.wikipedia.org/wiki/Indus_Valley_Civilisation