5 ms·
It might be better to replace the link with this [1] article from yesterday that digests the argument: > The authors of this new paper don’t think so. “We sugg
by cletus 4y ago
It might be better to replace the link with this [1] article from yesterday that digests the argument:
> The authors of this new paper don’t think so. “We suggest, following the hypothesis of Hansen & Zuckerman (2021), that an expanding civilization will preferentially settle on low-mass K- or M-dwarf systems, avoiding higher-mass stars, in order to maximize their longevity in the galaxy,” they write.
I figured longevity would come into it. Remember systems like Trappist will live for trillions of years. There are three main problems with this argument:
1. Once you have the technology and the erngy to travel to different star systems, the energy output of a star is way more important than longevity. Bigger stars might burn out faster but they will produce a ton more total energy in their much shorter lifespans.
2. It is technically possible to extend the lifespan of stars. This is a whole futurism topic in and of itself but basically there are means of extracting mass from stars and you can greatly increase their longevity by removing Helium; and
3. While I agree with the paper that SETI is pretty much a waste of time, this paper seems to not address the main way a K2 civilization will be detected: by the IR signatures of Dyson Swarms.
The only way to get rid of waste heat in space is to radiate it away. People will often suggest that heat could be recycled. While true, this simply makes the system more efficient (ie less waste heat). It won't eliminate it. And even 1% of a normal star's waste heat is significant.
Thermal radiation radiates at a predictable wavelength based on the temperature of the radiating material. This means any significant Dyson Swarm has an IR signature that will stand out like a shining beacon, particularly to IR sensitive instruments like JWST.
So even if aliens only colonize long-lasting smaller systems, we'd still be able to detect their inevitable Dyson Swarms if they were a significant presence.
[1]: https://www.universetoday.com/158287/maybe-we-dont-see-aliens-because-nobody-wants-to-come-here/ https://www.universetoday.com/158287/maybe-we-dont-see-alien...
- Sharlin 4y ago> The only way to get rid of waste heat in space is to radiate it away. People will often suggest that heat could be recycled. While true, this simply makes the system more efficient (ie less waste heat). It won't eliminate it. And even 1% of a normal star's waste heat is significant. Any construction around a star in thermal equilibrium must necessarily radiate away exactly 100% of the energy output of the star, not 1% or 10% but 100%. Otherwise the structure will just heat up until it does. The only known way around that would be using a black hole as a heat sink, or somehow radiating the heat in tight beams rather than uniformly in all directions to make detection less likely (hopefully nobody gets in the way!)
- renewiltord 4y agoIs that true? It could transform the energy into useful output, right? For instance, if I get sunlight and put it into photovoltaic and then use that electricity to push an object 1 m and I am forced to radiate that outwards then I have just done work for free?
- naasking 4y agoDoing that work will also release heat, but yes, you're correct that the heat wouldn't necessarily emanate from the star like any other. Firstly it would have a very unique emission spectrum in IR. Secondly, the energy could be transported elsewhere first. For instance, focus the star's energy into coherent beams for millions of light sails moving away from it. That would transport the point of partial heat emission out into space where the light sail is.
- renewiltord 4y agoOkay, but it can't release all the energy as heat, surely, because otherwise I've just doubled the energy. I have moved something against gravity to create a gravitational potential difference and I have all the heat radiated. So now when I let the thing fall, I will generate at least some small amount of heat and so I will have 1+\eps heat as arrived. I am making energy.
- Sharlin 4y agoThat is true, but you can’t keep on doing that forever, you run out of things to store potential energy in.
- zokier 4y agoYou could bind up energy into matter though? Fuse iron into bismuth or something
- Sharlin 4y agoYes, but why collect it in the first place then? Unless you're thinking of using the stored energy later when stars are dead, which might in fact be something an advanced civ might want to do... You'd likely need some form of direct energy-to-matter conversion more efficient than mere fusion to be able to use even a small fraction of a star's energy output.
- pencilguin 4y agoAny civilization so primitive as to depend for its energy on radiation from a star is hardly worth detecting, never mind visiting.
- rendall 4y agoWhat are realistic alternatives? You're not talking about zero-point energy are you?
- pencilguin 4y agoAnybody not stony-planet primitive will have worked out aneutronic fusion. There is plenty of helium-3 in Neptune's atmosphere. And that is just stuff even a stony-planet primitive knows about.
- rpastuszak 4y agoHere's our solution to Fermi's paradox then. We're just so uninteresting, we're being ghosted by the entire universe! (come to think of it, this does sound like one of the proposed solutions, so we won't be able to call it "the pencilguin's theorem")