K^2

Horizon is modeled as a potential in this paper. It's like if you shine a beam of light into a mirror. Physically, electromagnetic wave induces a change in the electrostatic potential on the metallic coating of the mirror, which influences electric field near it, generating a reflected wave. Mathematically, we describe this as an incident wave entering a mirror and a reflected wave exiting the mirror. Just because that's how the math works out, doesn't mean the beam physically entered some sort of a mirror dimension that happens to have an identical beam shining back out of it into ours. Light simply got reflected without going past the boundary. It's a bit more complicated here, because the boundary is asymptotic due to the expansion, but the end result is the same. We model it as outgoing waves reaching towards the horizon and inbound waves from it, because infinities are hard, and sometimes you have to do strange things with math to get useful predictions out. The whole paper just talks about the universe being a resonance cavity that's expanding, producing interesting effects in the wave spectrum. And this only works because there is a boundary that nothing can reach us from beyond. If gravitational waves could pass and go freely, there would be no resonance, and no amplification.

That the spectrum of the background gravitational waves is going to have features corresponding to the change in dominant mode of expansion of the early universe. It's all in the paper. I have no idea why you think this has something to do with propagation of waves from beyond the horizon, seeing how the paper treats the horizon as a boundary.

The source of the primordial waves isn't beyond the horizon. It's the early inflation of the universe itself. Meaning, the source is effectively local. The article merely talks about the fact that the observable universe acts as a resonance chamber. It's not allowing any waves or information from beyond the horizon to reach us.

No, that doesn't work this way. Gravitational waves obey locality, just like everything else. You can create a space-time in which you can traverse the distance faster, but you have to do so in advance, because the initial change has to propagate through the space-time with the initial speed of light. That's why a gravitational wave, despite being able to modify space-time behind it, can't reach you faster than a light beam would. Anything that's beyond Cosmological Horizon for light, is also beyond the horizon for gravitational waves. We cannot interact in any way with matter that's beyond that point, which means that whether or not it even exists is entirely academic unless entirely new principles are discovered. Within classical General Relativity, the Cosmological Horizon is absolute.

Theoretically, sure. There isn't really an upper bound on how much compression and temperature you can get from accelerating matter towards a common focal point, as in a perfectly spherical case, it is indistinguishable from the action of gravity, and we know stars work. Practically, that's another matter. There's only so much pressure you can generate in the chemical explosion stages, so you have to rely on inertia and hydrodynamics of materials you normally consider solid for the rest. That seems to be the direction the linked article suggests, but any imperfection will lead to a high pressure zone that's going to turn your perfectly focused explosion into a spray. It's a bit like balancing a skyscraper on a needle-point. I'm pretty sure that not only do your shaped charges and plates have to be flawless, you can't even rely on cylindrical symmetry, as the device's own weight will produce enough density variation to cause it to fail. Unless you're going to detonate it in space, you'll have to account for how this device sits on the ground. The fact that no nation has built one, despite the fact that it perfectly circumvents many of the nuclear treaties, is a strong indication that even with modern simulation methods, this is a little too precise.

Yes, it's called a supernova. Short of that, a particle accelerator works, but if you need more than a handful of atoms, you're out of luck.

I'm pretty sure Obsidian kept the rights to The Outer Worlds IP and Hades II is listed as published by the Supergiant, so they definitely kept the rights. I'm sure PD had a lot of IP besides KSP, but most of it wasn't all that big. That said, the fact that the buyer didn't share the news immediately suggests that PD properties will be sold off piece-meal, rather than used to publish games in the near future. So on the KSP front, we'd be waiting to see who picks it up next. If anyone. On the bright side, Unlike T2, who felt like they need to get back what they spent for KSP IP, whoever bought PD is probably not going to have any particular attachment, and will just try go get the best bid. So it's much more likely that the price will be more reasonable, making it more likely that somebody will pick it up, rather than IP just collecting dust.

At a scale height of 11km, it would take 56km before the pressure hits atmospheric. Of course, the temperature will be higher down there, increasing scale height, so call it ~60km. In contrast, you can dig down a few dozen meters and put in an airlock to achieve the same effect.

If you're going to be using ethanol for fuel, you should just have a normal turbofan engines. Ethanol makes for a crap fuel for a number of reasons, but nearly all of them are going to impact your fuel cells the same way as a turbofan.

Legend has it, the topic of reversibility of time is what drove Boltzmann insane. So if all you got is a headache, you got off easy.

Fine grain entropy is conserved. Coarse entropy is growing. In context of a system governed by quantum mechanics, it allows for chaotic observables while being entirely on rails. The easiest (though, not the only) way to interpret this is through the lens of MWI, where it's pretty easy to show that the fine grain entropy of the universe is simply fixed at zero (there is exactly one state), while any particular timeline becomes more chaotic over the course of evolution. The increase in available state-space as the universe inflates leads to significantly more entropy/chaos in the "future" direction, setting up the arrow of time. Consequently, there is no practical difference if our universe is expanding from a point due to a Big Bang, or if it's collapsing in on itself. The future universe is in the future because it's bigger. And all of the chaos is a consequence of observation, while all underlying physics is fully deterministic, because the universe as a whole doesn't have such silly notions as order or chaos or time or entropy. It's just a multi-dimensional manifold with some symmetries, and we're just too small to perceive it that way. Physics is the most depressing of sciences.

Honestly? Why? The KSP2 source isn't really worth working with. Whether it's restarting the project or making a fan game out of it, there isn't anything in KSP2 source worth keeping. Option 1, you want to stick to Unity, in which case, KSP had a lot of fixes that KSP2 never got based on when they branched. Just start with KSP and add KSP2 features. Option 2, forget all of that, and start with Unreal. That way you get a modern physics engine (no problems with bendy rockets, if you set it up correctly) and you get planet tech for free. But then you do have to implement all of the space stuff from scratch, but IMO, worth it. Either way, KSP2 is not what you want. As for the assets, while raw assets are a bit better to work with than ripping baked assets, odds are, you're either going to make small changes to them, or just add new stuff. In which case, ripping KSP2 assets is just as good. In other words, you have everything you need. The big problem is that recycling KSP2 assets is going to set you up for being sued by T2, who'll probably do it just on principle even if the game is fully abandoned. So realistically, if you think KSP2 had good ideas that should be turned into a game, the correct path is to make a new game. New engine, new art, the lot. Yeah, we are all going to miss the Kerbals, but I doubt it's going to make a critical difference to any good stab at the genre.

Ah, yes, landing. Nonetheless, it seems that because the problem happened as the engines were getting re-lit, NASA opted to ground the flights, presumably out of abundance of caution. https://www.npr.org/2024/08/28/g-s1-19934/faa-spacex-falcon9-grounded-polaris-dawn

Pressure isn't as big of a factor for fire risk as it is for, say, breathing. Most of the reduction of reactivity of oxygen in air isn't due to the partial pressure of oxygen being lower, so much as the ballast of nitrogen etc. While it's true that fire hazard of pure oxygen at 0.2 bar is going to be lower than at 1 bar, it is still way higher than for air at 1 bar. A lot of things that won't catch fire in an air mix will catch fire in O2 at 0.2 bar. Unrelated, at least in any direct way, due to the failure of the most recent Falcon 9 launch, NASA has temporarily grounded all F9 flights until further notice. As far as I can tell, nobody really knows how long the grounding is likely to be in effect, but the general consensus seems to be that we should expect Polaris Dawn to be further delayed.

Somebody said this mission gives Titan vibes, and I kind of agree. I have no reason to doubt the capsule itself, but everything about the spacewalk plan is sounding very flimsy.