Even a Dyson sphere, which is technically unlikely anyway, would be possible to spot. You would look for something very bright in the infrared spectrum with almost no light in the visible spectrum. It would also be larger than a normal star of the same energy, but that would be hard to tell given all the other issues.
A partial swarm is easier because it will have variability towards more infrared and then back to a more normal spectrum.
And, of course, all this is speculation until we find a candidate and determine it doesn’t have a natural source for that behavior.
Why would there necessarily be strong infrared emissions? Since a Dyson Sphere is meant to harvest all energy produced by a star, any leakage would be unnecessary inefficiency, wouldn’t it?
Thermodynamics says that energy can’t be destroyed (mass-energy, but generally that won’t matter). So after the work of running your stellar civilization is done, you will radiate out waste heat. There is no real way around this without breaking thermodynamics or having a handy black hole to dump all your waste heat into. Therefore, the energy of the star will still be released, but it will be released as infrared.
If you’re using the Dyson sphere purely as a power plant and e.g. charge batteries, the thermal radiation will be distributed over the whole area covered by the civilization.
A solar panel, or any other power generator we use, doesn’t radiate away all the generated energy either. It’s radiated from the point of use.
So you heat habitats, which radiate heat. And run computers, which radiate heat. And move objects around, which radiates heat (among other things). And if you merely absorb energy from your star…it radiates as heat. This is the whole idea of entropy. Unless your lasers are particularly efficient and you use them to beam the energy elsewhere, your Dyson swarm is going to radiate heat equivalent to the energy your star puts out.
You’re ignoring my example - what if you charge up batteries at the Dyson sphere, and use the energy anywhere else? There’s no physical reason the energy must be used around the Dyson sphere.
So all you need is a perfect charging system. We don’t have those, and physics doesn’t allow for them. This would be no different than the laser example I gave, and this only makes sense after you have a second Dyson swarm.
Why perfect? As long as the efficiency is high enough, you wouldn’t see the sphere itself as very bright, it would be quite dim. Do we know any hard, physical limitations for this, like we do for speed?
A partial answer to your question is that there’s a minimum amount of heat necessarily radiated when doing computation, given by the Landauer principle.
Furthermore, I also do not think that we will detect dyson spheres, because if a civilisation wishes to hide, they won’t radiate heat uncontrollably by extracting all possible energy, but rather send that energy elsewhere, for example by dumping it into a black hole. But I could be wrong and such a civilisation might care more about energy than remaining undiscovered.
I don’t think you have any appreciation for just how much energy even a dim star provides. A Kardashev 2 civilization has access to a billion times the energy we (Earth) have, and we only use about 70% of the energy we have access to. Even if you use all that energy, there will still be waste heat. Now you’re proposing that this hypothetical civilization has a second star (at least) that it’s importing energy from, which means it will be a larger area emitting infrared in their home system, because thermodynamics still has to be obeyed.
And yes, the laws of thermodynamics have to be obeyed. They are as rigid as the speed of light, meaning there might be shortcuts but they are very advanced. To put it in perspective, we are almost capable of starting a Dyson swarm, and we have no options for bypassing the laws of thermodynamics and only have the barest ideas of how to bypass the speed of light.
But you would still be radiating heat from that star system unless you’re proposing wireless energy transfer over Interstellar distances. So the entire system would still give off an unusually high infrared signature.
I’m not proposing that - I literally wrote my idea in the comment you replied to: a potential alien civilization could charge up batteries at their Dyson sphere, and use the energy anywhere else in the galaxy. You know, the way EVs work.
Sure, you won’t reach 100%. But say you reach 99.9% - the Dyson sphere should radiate infrared at 0.1% of a normal star, right? It wouldn’t necessarily be bright.
Even if that level of efficiency were possible, 0.01% of a star’s output is still a substantial amount of heat. You would still have to radiate it away otherwise it would melt your mega structure, and you would have to radiate it out equally in all directions otherwise you’d knock it off its orbit with the thrust generated from the radiating of the heat on one side.
Even a Dyson sphere, which is technically unlikely anyway, would be possible to spot. You would look for something very bright in the infrared spectrum with almost no light in the visible spectrum. It would also be larger than a normal star of the same energy, but that would be hard to tell given all the other issues.
A partial swarm is easier because it will have variability towards more infrared and then back to a more normal spectrum.
And, of course, all this is speculation until we find a candidate and determine it doesn’t have a natural source for that behavior.
Why would there necessarily be strong infrared emissions? Since a Dyson Sphere is meant to harvest all energy produced by a star, any leakage would be unnecessary inefficiency, wouldn’t it?
Thermodynamics says that energy can’t be destroyed (mass-energy, but generally that won’t matter). So after the work of running your stellar civilization is done, you will radiate out waste heat. There is no real way around this without breaking thermodynamics or having a handy black hole to dump all your waste heat into. Therefore, the energy of the star will still be released, but it will be released as infrared.
If you’re using the Dyson sphere purely as a power plant and e.g. charge batteries, the thermal radiation will be distributed over the whole area covered by the civilization.
A solar panel, or any other power generator we use, doesn’t radiate away all the generated energy either. It’s radiated from the point of use.
So you heat habitats, which radiate heat. And run computers, which radiate heat. And move objects around, which radiates heat (among other things). And if you merely absorb energy from your star…it radiates as heat. This is the whole idea of entropy. Unless your lasers are particularly efficient and you use them to beam the energy elsewhere, your Dyson swarm is going to radiate heat equivalent to the energy your star puts out.
You’re ignoring my example - what if you charge up batteries at the Dyson sphere, and use the energy anywhere else? There’s no physical reason the energy must be used around the Dyson sphere.
So all you need is a perfect charging system. We don’t have those, and physics doesn’t allow for them. This would be no different than the laser example I gave, and this only makes sense after you have a second Dyson swarm.
Why perfect? As long as the efficiency is high enough, you wouldn’t see the sphere itself as very bright, it would be quite dim. Do we know any hard, physical limitations for this, like we do for speed?
A partial answer to your question is that there’s a minimum amount of heat necessarily radiated when doing computation, given by the Landauer principle.
Furthermore, I also do not think that we will detect dyson spheres, because if a civilisation wishes to hide, they won’t radiate heat uncontrollably by extracting all possible energy, but rather send that energy elsewhere, for example by dumping it into a black hole. But I could be wrong and such a civilisation might care more about energy than remaining undiscovered.
I don’t think you have any appreciation for just how much energy even a dim star provides. A Kardashev 2 civilization has access to a billion times the energy we (Earth) have, and we only use about 70% of the energy we have access to. Even if you use all that energy, there will still be waste heat. Now you’re proposing that this hypothetical civilization has a second star (at least) that it’s importing energy from, which means it will be a larger area emitting infrared in their home system, because thermodynamics still has to be obeyed.
And yes, the laws of thermodynamics have to be obeyed. They are as rigid as the speed of light, meaning there might be shortcuts but they are very advanced. To put it in perspective, we are almost capable of starting a Dyson swarm, and we have no options for bypassing the laws of thermodynamics and only have the barest ideas of how to bypass the speed of light.
But you would still be radiating heat from that star system unless you’re proposing wireless energy transfer over Interstellar distances. So the entire system would still give off an unusually high infrared signature.
I’m not proposing that - I literally wrote my idea in the comment you replied to: a potential alien civilization could charge up batteries at their Dyson sphere, and use the energy anywhere else in the galaxy. You know, the way EVs work.
Because all that energy contains heat as well, and you’ll need to balance the heat from your star along with the energy absorbed.
You’re never going to get to 100% efficient conversion, so you’ll have to radiate away the heat so your sphere doesn’t melt or something.
Sure, you won’t reach 100%. But say you reach 99.9% - the Dyson sphere should radiate infrared at 0.1% of a normal star, right? It wouldn’t necessarily be bright.
They must be mining a lot of bitcoin to need 99.9% of a star’s energy.
Or else to power one of those Kurtzgestat space lasers that will melt us anyway.
Maybe they are just fabricating matter. That takes a surprising amount of energy!
Even if that level of efficiency were possible, 0.01% of a star’s output is still a substantial amount of heat. You would still have to radiate it away otherwise it would melt your mega structure, and you would have to radiate it out equally in all directions otherwise you’d knock it off its orbit with the thrust generated from the radiating of the heat on one side.
Yeah, it’s interesting to think about IR powered thrust.
I wonder if moving a star by cooling one side could ever happen? Like in a some weird future tech way obviously.
Not all heat can be converted to work by the second law of thermodynamics. Now the question is, how hot can the star be for it to sustain life? Can most of its light be UV with very little visible? https://courses.lumenlearning.com/suny-physics/chapter/15-4-carnots-perfect-heat-engine-the-second-law-of-thermodynamics-restated/