(Not a rocket scientist or mathematician, but I spent 100s of hours playing KSP RP-1)

Just doing some estimates using data from the wikipedia page:

The dV (delta-V) needed to get into low Earth orbit is around 9.4km/s.
The dV for K2-18b might be around 19km/s, more than double that of Earth's.

It's practically impossible I think, you would need such a massive launch vehicle. For double the dV, you would need exponentially more fuel assuming current rocketry tech (fuel+oxidizer tanks and engines). There wouldn't be any single-stage or two-stage rockets that could do this. With a 3 or 4 stage rocket maybe? But you would be sending nearly 100% fuel off the launchpad with virtually zero payload.

Check out the "tyranny of the rocket equation". The more propellant you need to lift heavier rockets, the more propellant you need to lift that extra propellant and so on and so on.

I tried to factor in:

It's probably still a lot harder though. You're not just heavier, but also slower which means you'll spend more time fighting gravity. And all the extra fuel you bring for that makes the rocket heavier which means you need even more fuel to launch the fuel. Higher surface gravity likely means a thicker atmosphere too which is a big issue and a more massive body also has a faster orbital velocity. Although in this case the larger diameter might counteract that a bit because higher orbits have slower velocities.

My point is that this would probably still be a lot harder than just building a 50% bigger rocket. If you've ever tried launching from Eve in Kerbal Space Program you know the pain. Although in that case you also have to fly the entire rocket there first which is its own challenge.

It would actually be impossible for them to get to orbit using chemical rocketry, like we use. They could theoretically do it with nukes.

Chemical rocketry limits

Nuking your way to orbit

Have you read Hitchhiker's Guide to the Galaxy?

I wrote and tried publishing a short story about a species like that.

where only occasionally people on top of mountains see stars, and they chuck it as a consequence of low pressure. eventually they invented flight, and assume pilots going high enough to see stars are having cognitive issues due to lack of air.

They asked pilots to draw the stars they see, and they get different drawings (they sent pilots at different times of the year because they couldn't ever expect stars to shift) and assume its proof that thise stars are a cognitive artifact.

Eventually a pilot swears they are real and can actually use then to navigate, skepticism, he proves it. brand new research field emerges.

Although the story focuses more on deep DEEP time an omniengineering. (A term I just made up because mega engineering is a concept way too small compared to the one in the story).

If you want I don't mind putting that story in the conversation.

"Nightfall", by Arthur C. Clarke is a short story based on this premise.

Except in the story it's a complex multiple-star solar system that makes it very rare for all suns to set at once.

Edit: It's actually Isaac Asimov.

Well, the church threw us back about a millenia, so what's a few centuries.

Project Hail Mary has a bit about this, don't want to say more to keep it spoiler free.

Well, as soon as they invent radio and experience interferens radio astronomi will evolve... I guess?

Uhh, one stargate doesn’t go anywhere.

We really are in the Goldilocks Zone, aren't we?

Imagine humanity in 1000 years. We would be among the stars.

Now imagine humanity in 10000 years, 100000 years or even 1000000 years.

A million years is still a fraction in the cosmic timescale.

It would be nearly impossible to have other civilizations be on exactly the same technological level as us. They would indeed be either much less advanced, or much more advanced.

This is just arrogance.

We have only been announcing our intelligence for 100 years. It takes 100,000 years just to cross our galaxy. No-one knows we are here yet.

Maybe they just don't want to leave their planet because it's dope af

Apparently with 50% higher gravity it would be pretty much impossible with chemical rockets, but with the median of the estimate (so about 12.43 m/s^2^) it would be possible, you'd just need an incredibly large rocket, or non-chemical propulsion (e.g. nuclear).

A space program on that planet would definitely advance much slower than on Earth.

Yup, I wonder sometimes, all those sci-fi tales about a long lost ancient civilisation that spread throughout the galaxy before everyone else did, what if we’re set to become that, before space-faring life eventually emerges, then thrives and flourishes all over the galaxy?

One can dream anyway…