this post was submitted on 11 May 2024
217 points (98.2% liked)
Space
8341 readers
1 users here now
Share & discuss informative content on: Astrophysics, Cosmology, Space Exploration, Planetary Science and Astrobiology.
Rules
- Be respectful and inclusive.
- No harassment, hate speech, or trolling.
- Engage in constructive discussions.
- Share relevant content.
- Follow guidelines and moderators' instructions.
- Use appropriate language and tone.
- Report violations.
- Foster a continuous learning environment.
Picture of the Day
The Busy Center of the Lagoon Nebula
Related Communities
🔭 Science
- [email protected]
- [email protected]
- [email protected]
- [email protected]
- [email protected]
- [email protected]
- [email protected]
- [email protected]
- [email protected]
🚀 Engineering
🌌 Art and Photography
Other Cool Links
founded 2 years ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
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.