ooliAstronomers are on the Hunt for Dyson Spheres
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?
BlóðbókA 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.
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.
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.
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.
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.
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 reason an observer doesn’t experiencing 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.