this post was submitted on 11 May 2024
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Okay, so the title is a bit off. They're hunting for partial Dyson spheres using infrared and optical.
I was confused on how they would detect something completely blocking a sun from millions of light-years away.
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?
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.
We also have no idea what such large amounts of energy could be practically used for. Just as one possible example, the recent approach for warp drives would consume large amounts of energy - and it would cause the energy to be used over a large area, going against your assumptions. Of course there are many other options, e.g. creating matter from energy.
Yes, and as I keep repeating, the waste heat would not necessarily be produced at the location of the Dyson sphere.
First: why must there necessarily be a second star? They could live inside ships in-between solar systems, which would only need one star to import energy from, and no more. And my whole point is that this would make the Dyson sphere itself much dimmer than you're assuming it to necessarily be.
You haven't shown that the laws of thermodynamics actually pose limits here. Nothing I'm proposing goes against the laws of thermodynamics.
Sorry, all I'm seeing are reasons how you could take all the energy from a given star and move it elsewhere without a reason to do so, even to the point where virtually none of that energy is being used locally. This is the classic solution looking for a problem idea.
There are plenty of resources on the internet that have already responded to all your questions. Feel free to look it up.
Yes, I was only focusing on the "physically possible" part. I don't think it makes sense for us to inherently limit our search for such things to the most obvious solution - focus on that first, sure, but don't rule out that non-physically based assumptions are wrong. We can't assume that a civilization capable of producing a Dyson sphere would exactly follow what we assume to make the most sense.
But I can gladly provide some possible reasons:
You're writing as if the assumption of local energy usage is physically given and can't be wrong, but we simply can't know for now. It could be right, or it could be wrong. Again, I agree that it makes sense to assume it to be correct, as it would be a much more easily recognizable marker, but that doesn't mean it's the only option.
Yeah, if you're going dark forest and AI, you could do a lot with even a K1 civilization, which makes a Dyson swarm kind of silly, anyway. Unless you put the effort into it, in which case it would be difficult to effectively fight a K2 civilization, especially a multi-system one, because the power, numbers, and capability to spread make options other than hiding not make much sense, anyway. Throw in some Von Neumann probes for good measure and the only winners will be the ones who spread faster.
The Bobiverse gives some ideas about what some good probes can do, and the Culture gives some ideas of just the kind of power an advanced civilization can have. Darwin's Radio has some good ideas about the dark forest and interstellar wars/genocide, and some interesting ideas about the nature of reality and matter itself.
I'd argue that the Dyson sphere is a method of hiding your whole solar system if done right - you put out your torch, which reduces the likelihood of visual detection, while also being able to safely expand your civilization throughout your solar system. Von Neumann probes would probably be a terrible idea in a dark forest scenario, since their communication should come back to you, spreading your position far and wide.
Thanks for the recommendations!
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.
It's not a given that Landauer's principle is an absolute threshold - the Wikipedia article describes challenges, and there are attempts like Reversible Computing which can potentially work around it.
Fully agree that such an advanced civilization will most likely want to hide, and stop any infrared radiation to the largest part.
Reversible computing can not work around it because one simply can not extract information without irreversibly affecting the system. This is a fundamental constraint due to how, in quantum mechanics, once an observer entangles themselves with a system they can never unentangle themselves. I believe that from that single fact one can derive the impossibility of reversible existence.
Better go tell the theoretical computer scientists who waste their time writing papers on the topic! Could save them a lot of trouble if they had just asked you.
This comment tells me that you do not fully understand reversible computing, thermodynamics, nor what I am trying to say. The snark does not motivate me to be patient or pedagogical, but I'll still give it a shot.
By interfering with a closed system as an entity outside of that system (for example by extracting information by performing a measurement on any of its component subsystems such as the position or momentum of a particle), you are introducing a dependency of that formerly closed system's state on your state and that of your environment. Now, by state I mean quantum state, and by interfering I mean entangling yourself (and your environment) with the system, because our reality is fundamentally quantum.
Entanglement between an observer and a system is what makes it appear to the observer as if the wave function of the system collapsed to a (more) definite state, because the observer never experiences the branching out of its own quantum state as the wave function of the now combined system describes a superposition of all possible state combinations (their (and their environment's) preceding state × the system's preceding state × the state of whatever catalyst joined them together). The reason an observer doesn't ever experience "branching out" is because the branches are causally disconnected, and so each branch describes a separate reality with all other realities becoming forever inaccessible. This inaccessibility entails a loss of information, and this loss of information is irreversible.
So there you have it. You can never extract useful work from a closed system without losing something in the process. This something is usually called "heat", but what is lost is not merely "heat": it is the potential usefulness of the thing of interest. But it really all boils down to information. Entropy increases as information is lost, and this is all relative to an observer. Heat dissipation represents "useless information" or "loss of useful/extractable energy" as it concerns an entity embedded in a quantum wave function.
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/
Dyson swarms are more likely. We even have a tiny one with our satellites using solar power in a heliocentric orbit. (Dyson spheres are basically impossible.) But we could theoretically detect either in infrared since if it doesn’t give off waste heat, it’d all heat up and melt.
That being said, I’m personally of the opinion this is a waste of time. Not to get all Fermi Paradox but it’s pretty sci fi brained to think any other species out there is as dumb as we are. Space sucks. You die super fast there. Everything had to align just right for Earth to make a bunch of dumb fuck apes willing to strap themselves onto rockets, have a planet small enough that the rocket could even overcome gravity to enter orbit using chemical rockets, and a World War and Cold War to accelerate things.
Time will always be the great filter. Even if we did spot a Dyson swarm, we have no feasible way to contact anything on a practice timescale. Any speck of civilization we detect will be hundreds of thousands of years out of date at best, billions at worst. Life in the universe, imo, is basically guaranteed. If it happened once, it can happen again. Meaningful contact between separately evolved concurrent sapient species? Not likely.
Given the estimated number of planets in this galaxy alone, it's particularly guaranteed that very similar events have occurred on multiple worlds. Unless you're proposing that all theoretical alien races are Vulcan level logical then tensions and interstate conflicts will always exist that will advance technology. This is practically an inevitability unless the race question is a hive mind species.
I think my Fermi Paradox explanation is that space is really fucking big and hostile and protecting the planet you evolved on is the only real option.
Not to mention the problem of what life is even supposed to do beyond a certain point of development. The depressing fact is that there is a finite amount of knowledge to be gained, a finite amount of resources to harvest, a finite diversity of life to contend or thrive alongside with. Once a pocket of life in this massive universe begins to run out of things to do and stagnates, then what? What is there to think about; to feel; to experience?
There's little point in exploring space if one know how this universe works. One knows the rules, knows all the ways it can play out, and there's no surprise waiting on the other end of any venture one can imagine embarking on.
That's my theory. The Great Filter is just depressive boredom. We don't see other life because by the time a civilisation is able and ready to spend thousands of years travelling through deep space, they'll have already lost any motivation they might have had to do so.
I suspect that there's at best a very short window wherein a species is both knowledgeable enough to dream of space exploration and technologically capable of sending any significant amount of artificial constructions out there.
Not to mention that anything an alien species might send into interstellar space is unimaginably unlikely to be recorded exactly at precisely the moment they pass another lump of matter - especially if the window is as short as I fear.
If it was actually completely enclosing a star that would be impressive. It would also be a bit pointless, since It would result in your spear heating up to stupid temperatures, Which would cause it to glow in the infrared, so you would detect it by that infrared.
Isn’t the idea that the sphere would have a circumference the size of earths orbit? Not sure it would heat up all that much to be noticeable.