[thrashh]

Another possibility is that energy is really hard to come by. Humans absolutely struggle to amass much energy. Think of the insane amount of energy required to lift things into space, and how many millions more amounts of energy we’ll need just to build something in space. Heck if you go drive off grid on Earth, you can barely bring any energy with you and you won’t really be able to generate an appreciative amount of energy to do anything major. Climate change is ultimately caused by our energy needs.

One day we might be able to harness the output of a whole star but the amount of energy we’d need to get to that point seems out of reach right now.

I wouldn’t be surprised if the lack of energy is a universal issue across the stars.

A huge game changer would be if we discovered some physical phenomenon to allow us to safely extract energy easier from mass. It would do to our progress like what the telephones and the Internet did to communication.

[pfdietz]

It actually doesn't require THAT much energy to get into orbit. The energy of a kilogram of mass in low earth orbit is about 9 kWh, although rockets will use a bit more than that (not enormously more, though). Fuel cost remains a minor fraction of launch cost, even with Falcon 9.

In comparison, the best aluminum plants in the world use 13 kWh to make a kilogram of aluminum. Yet no one says aluminum is out of reach because it takes too much energy to make it.

The per capita primary energy consumption in the US is about 10 kw; your share of this energy over your lifespan would be enough to accelerate 1 kg to 2% of the speed of light.

[shagie]

An interesting problem is "how much energy would it take to launch from a super-earth?"

https://www.space.com/40375-super-earth-exoplanets-hard-alie...

> To launch the equivalent of an Apollo moon mission, a rocket on a super-Earth would need to have a mass of about 440,000 tons (400,000 metric tons), due to fuel requirements, the study said. That's on the order of the mass of the Great Pyramid of Giza in Egypt.

We may be in a Goldilocks zone not only for distance from the primary star (lots of systems are binary which gets problematic), but also in terms of size of the planet (not to light to loose atmosphere, not to heavy to trap everything), and we've got a nice big moon to keep things sloshing around and stabilize the tilt.

I am of the opinion that life is rare because we live in a surprisingly boring solar system with a terrestrial planet in the right range, not to large and not too small, and with a massive moon.

[pfdietz]

A super earth would require exponentially more energy with chemical rockets, due to that darn rocket equation. Fortunately, Earth isn't that bad.

[foobarian]

> A super earth would require exponentially more

Polynomially, right?

[pfdietz]

No, exponentially. I used that word precisely, because the mass ratio in the rocket equation is exponential in (delta V)/(exhaust velocity).

[foobarian]

Thanks for the reply. Context: there are so few exponential processes in nature, especially around classical physics that it really stuck out here, so I made the comment. I should have searched and read up on it instead, but thought there is still some value in others seeing the conversation.

And lastly: that is really depressing :-(

[saiya-jin]

I agree with rare earth theory too, but even with it, the observable universe is so huge that even those tiny fractions of various probabilities should at the end materialize on a massive scale.

And its not like with higher G or some other singular aspect moving into more challenging territory, everything becomes suddenly impossible. Think about how many obstacles mankind could conquer in a relatively short amount of time, say a million years.

[GoblinSlayer]

We see only super earthes because they are easier to see. Small planets can be more numerous.

[shagie]

They can... but a challenge with a small planet in the habitable zone of a star is that it also has a weaker magnetic field and is more prone to having its atmosphere stripped away.

Consider that the moon had an atmosphere - https://en.wikipedia.org/wiki/Atmosphere_of_the_Moon#Ancient...

> In October 2017, NASA scientists at the Marshall Space Flight Center and the Lunar and Planetary Institute in Houston announced their finding, based on studies of Moon magma samples retrieved by the Apollo missions, that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions, was twice the thickness of that of present-day Mars.

http://time.com/4974580/nasa-moon-had-atmosphere-volcanoes/

Which brings us to

https://worldbuilding.stackexchange.com/questions/13583/what...

While smaller planets are certainly more numerous - many of them likely lack the mass and active magnetic field to retain an atmosphere in the habitable zone.

[hoseja]

Aluminium has been out of reach for much of history.

[pfdietz]

But not because it needed too much energy.

[zabzonk]

Then for what other reasons?

[pfdietz]

Well, it needs electricity. For most of history, we didn't have electricity. And, we didn't have cheap electricity until electromagnetism was understood and electric power could be made from rotating machinery. After that, there needed to be found a chemistry that would allow aluminum to be made directly, rather than from sodium or potassium reducing aluminum compounds.

The actual physical amount of energy needed to make aluminum would have been available since forever; it's the form of that energy that wasn't there.

[vbezhenar]

That's why it makes no sense to build something big by lifting heavy things from the Earth. Just mine asteroids, extract iron, melt it into chunks, then transport those chunks very slowly but with huge throughput from asteroids to the necessary building site in space and use them to build space ship. You can melt iron just by focusing enough sun light and you can build ships closer to sun for cheaper sun light. It's imaginable with current technologies, we just need industry to move into space.

Imagine that with all your knowledge you suddenly moved to the ancient times. You know how to make CPU but you can't even make a shovel because iron production is not there. You need to spend enormous amount of time and efforts to build all the industries required to build a factory to produce simple resistor. That's where we at when it comes to space right now. We need to spend lots of time and effort to build space industry. But once it's there, space ships will not be a big deal.

[pdfernhout]

Thinking through those interrelations for manufacturing processes was my hope for this: https://www.kurtz-fernhout.com/oscomak/ https://www.oscomak.net/ https://openvirgle.net/

And earlier, this: https://pdfernhout.net/princeton-graduate-school-plans.html https://pdfernhout.net/sunrise-sustainable-technology-ventur...

Still think it is all a good idea. Glad the "maker" movement is making some progress in that area. As I noted on the LibrePlanet mailing list a few weeks ago: https://lists.gnu.org/archive/html/libreplanet-discuss/2022-...

Someday after I "retire" I hope to have more time to work on all that.

Tangentially, on a super earth with more gravity, they would have an easier time going into orbit energetically using mass drivers or laser launch systems instead of rockets. And in any case, how big a seed do you really need to make a space infrastructure if you are patient? And the ground can communicate to space with radio or lasers (like for telepresence) which are not affected much by planetary gravity even for super earths.