[api]

2.4% is not bad given how new this still is and how extreme the speeds and energies are.

Note that all the fatalities have been launch or landing related, not in space itself. Clawing out of this gravity well is tough. Make Earth a bit larger and you’d never get off it without something like NERVA or nuclear pulse Orion.

I wonder sometimes if that’s another thing to toss in the Fermi paradox bucket. Many rocky planets might be much more massive than Earth. On one with 3X our gravity a space program might never get going.

[m4rtink]

NERVA as envisioned had terrible thrust to weight ratio, not really usable to launch from a Super Earth. Nuclear lightbulb, orion or heck NSWR would likely work though. And bonus points for not having to think about landing systems for the return trip. ;-)

[api]

In that case aliens from a super Earth would be unable to get off it unless they decided to salt their biosphere with fissile waste. NERVA is at least contained if it works properly.

So no space program from a super Earth until they figure out not just fusion but compact high density fusion that could fly. You’d need stuff like in The Expanse, or at least in that rough ballpark.

Using fission is something they probably wouldn’t do unless they faced an existential reason forcing them to go to space, like deflecting an asteroid.

[m4rtink]

I think a launch loop would still work, even on a Super Earth:

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

Or potentially beamed power for launch, so you don't kug a power source. But in any case, indeed much harder. :)

[api]

Yeah.

I’m a little obsessed with Orion though. The fact that the math works on that lunacy. The good old devil’s pogo stick.

If you could make pure fusion bombs it would be maybe politically viable, especially if you also use superconducting magnets to make it less just brute force. You’d still induce a little radioactivity from neutrons but it would be short lived and not even close to fissile fallout bad.

To see that thing launch. From somewhere very remote though, probably Antarctica. And from many miles away, and probably with welders glass. But damn. That would be epic.

[Shitty-kitty]

The lack of plate tectonics is a much bigger obstacle on Super-Earths, then g.

[api]

Yeah the more I learn the more I buy the rare Earth explanation.

Life may not be that unusual but it might be mostly just goo: little extremophile type bacteria and maybe very tiny creepy crawlies living in deep seas, underground, in liquid mantles in ice moons, etc.

But to get stuff even as sophisticated as frogs and bunnies, let alone something that can try space flight, requires a place that is all of: big, stable, with abundant energy, with high enough metallicity, and in an environment well shielded from flares and impacts.

There may not be a lot of places like this.

[Shitty-kitty]

Stability is definitely good but excessive stability leads to stagnation. A perfect example of this is what's been coined as the "boring billion"

"In 1995, geologists Roger Buick, Davis Des Marais, and Andrew Knoll reviewed the apparent lack of major biological, geological, and climatic events during the Mesoproterozoic era 1.6 to 1 billion years ago (Ga), and, thus, described it as "the dullest time in Earth's history"

[BuyMyBitcoins]

You might enjoy reading about theorized “Superhabitable” planets. A super earth with about twice the mass of Earth would likely have plate tectonics and even more internal heat. Plus, if it orbits a K-type star that’s about 85% of the mass of the Sun, it could remain habitable for tens of billions of years.

By comparison, Earth may be barely habitable. It is amusing to think that we may be living on the galactic equivalent of Australia.

Perhaps the upside is that our gravity well is low enough to make routine spaceflight possible.

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

[antonvs]

> I wonder sometimes if that’s another thing to toss in the Fermi paradox bucket

Here we are, half a century after the first moon landing, doing a flyby of the moon in preparation for landing and supposedly for establishing a base there that makes no sense. We’re not even close to being able to send humans to the nearest planets, and even if we did send people to Mars, in one of the most pointlessly dangerous and expensive missions in history, it’d be extremely unlikely to lead even to a base, let alone a settlement.

Yet with all that, people still talk about the Fermi paradox as though it’s a mystery.

It makes me think we’re really dealing with a kind of religious belief. Religion backfills reality with comforting fantasies, like life after death. In this case, the fantasy that there are much more advanced, interstellar spacefaring civilizations than ours elsewhere in the galaxy. This implies that humans too could one day become an interstellar species (with enough grit and determination and pulling back on the control stick and yelling, I suppose!) But somehow, mysterious effects prevent us from ever observing any evidence of this belief.

[api]

It’s a logical extrapolation if you think life is a natural phenomenon. It would be exceedingly weird to see no evidence for it, but of course we have not been looking long or far.

And yes, space flight is brutally hard. Look up the history of sailing. Look up the Polynesian indigenous peoples and how long that took, through multiple waves of exploration, or the people who walked across a land bridge to North America during the ice age. Space flight is easier and safer than some of those feats, given the tech they did it with at the time.

If there is a fantasy it’s the idea that we’d have bases on the Moon and Mars by now. What we are doing today is the equivalent of early Polynesians hollowing out some logs and going fishing.

[card_zero]

Natural doesn't mean likely. Say life rarely gets started, because it requires some kind of accidental evolutionary engine involving rivers and clay crystals, some unusual conditions of weather and geology. Then say life rarely gets complex and big, because mats of bacteria can be the dominant species indefinitely. So the universe is mostly dead, and the living parts are mostly slime. Then say actual human-like intelligence, the kind that tries really hard to imagine new things to meddle with and new spaces to explore, such as exploring the space space, is a freakish mutation and is unlikely to be adaptive at first. So it rarely happens and then usually dies out straight away. The rare instances of complex life, then, are mostly just floating around in oceans wiggling their complex limbs fecklessly. So those are two terms in the Drake equation, with an extra one about complexity added in the middle, and they multiply together to make things very unlikely by an unknown amount. We don't know what the numbers are. It might be natural that there isn't any sign of life out there, if the small probability of spacefaring life is smaller than space is big.

[api]

Ultimately we don’t know. We have not been looking far or long.

SETI BTW is kind of a joke. The only way we would hear anything is if someone was very close or was intentionally blasting a signal at us at incredible transmit power (like terawatts or more). Radio signals fade pretty quickly.

[antonvs]

> It’s a logical extrapolation if you think life is a natural phenomenon.

No, it really isn't. Taking life on Earth as an example, almost all of our technological signatures are effectively undetectable as little as 5 light years away. See e.g. the paper "Earth Detecting Earth" (https://arxiv.org/pdf/2502.02614). The maximum detectable distance for unintentional signal leakage is 4 light years - about the distance to Proxima Centauri, the nearest star. So if we're looking for that kind of signal, we have a population of exactly one star system that we might be able to detect something from, at the maximum end of the detectable range.

The paper also lists a couple of exceptions, which are the highly directional Deep Space Network and planetary radar, theoretically detectable at 65 ly and 12,000 ly respectively. But these only cover small parts of the sky for short periods, making interception of such signals extremely unlikely. Also, signals like that have only been transmitted for decades at most, so there are at most a few thousand star systems that could conceivably have intercepted one of these signals.

All in all, while the probabilities involved can't be calculated with certainty, they do certainly lean towards it being very unlikely for us to have detected another technological civilization. Which is consistent with what we actually observe.

Detecting non-technological signs, like atmospheric gases, is more feasible but also not necessarily definitive. E.g., the recent evidence for dimethyl sulfide in the atmosphere of K2-18b is considered a tentative candidate for a biosignature, but is in no way definitive.

In short, the Fermi "Paradox" mainly confirms what we now know about the difficulty of detecting life beyond our solar system.

As for spaceflight vs. sailing, at some point extrapolation from analogies just breaks down, and interstellar travel is certainly one of those cases. The energy demands, distances, timescales, technological limitations, radiation issues, economic and political issues, etc. all combine to make it an effectively impossible project.