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Given these two constraints: 1. The speed of light is a hard speed limit. This means there's also no cheating with warp drives, other forms of FTL, crossing di

by cletus 5y ago

Given these two constraints: 1. The speed of light is a hard speed limit. This means there's also no cheating with warp drives, other forms of FTL, crossing dimensions, parallel universes or time travel; and 2. The laws of thermodynamics as we understand them hold true. then the outcome of spacefaring civilization I believe is generally inevitable. That is, the ultimately limiting factor is energy and mass. The easiest way to get both is with Dyson Swarms. This requires no new physics and no exotic materials. If so, then a galaxy-spanning civilization is going to be completely obvious from a million light years away from the spectrum. Why? Because a full Dyson Swarm would have a very unique spectrum, specifically very little visible light and a lot of IR. That's just basic physics. The only realistic way to get rid of heat in space is to radiate it away and the wavelength of that is a function of temperature. This is discussed in the context of the Fermi Paradox, which has the advantage that you don't need to determine what every alien civilization does, you just need to know if there are any exceptions. Example: if there were 1000 spacefaring civilizations in the Milky Way, what are the odds that all 1000 of them (assuming they were within out light cone) would remain quiet or hidden? Couple that with mass and energy ultimately being limited then there is a strong incentive and advantage in becoming as large as possible. So even if 99% of civilizations remain quiet, the 1% will still make themselves visible. Additionally, on the notion of hidden civilizations in particular, it's essentially impossible to remain hidden to a K2 or K3 civilization so there's really no point. This is what gives me confidence that the Milky Way isn't teeming with spacefaring life. In fact I consider it much more likely we're the only such civilization in the Milky Way (within our light cone).

mattmanser 5y ago
Seems like a good theory, but when I read something like this it always makes me think about any of the sci-fi I've read that was written 50-75 years ago. They're also full of what were at the time good theories, but that are now so wrong it often makes reading the story difficult, even with my fairly rudimentary modern astrophysics knowledge. In all honesty I think it's more likely any sufficiently advanced civilization capable of interstellar travel has probably descended entirely into virtual reality or a singularity. I mean, what would you prefer? Being the star of your own personal VR space, the next Malcolm Reynolds, space cowboying around where you are the entire focus of that reality. Or schlepping it over to another star in a generation ship or whatever where even if you were somehow still alive when it arrived, you'd be landing on a planet that will probably instantly kill you.
- cletus 5y ago
  There are several differences between these old predictions and now: 1. We're now assuming based on the limits of known physics rather than the expected limits of technology. My father told me he once read a book that said it was impossible to go to the Moon because it would take 750 years to get there. The speed of light was known at that time but assumptions were made about the limits of acceleration and velocity that weren't grounded in science; 2. Things like the rocket equation are important. Specifically, the reaction mass problem. Even more specifically, the only way for an independent body to accelerate in space that we know of is by expelling mass (or energy). You need to carry that mass and this quickly becomes inefficient. A good example of this is how people have recently started to say "if we just accelerate at 1G we can get to Alpha Centauri in a few years". 1G acceleration sounds easy but it's not. So how would you travel between stars? I think it most likely that you'd use a ton of energy to accelerate (or decelerate) a vessel with lasers on a solar sail. Why? Because energy from a star is abundant and cheap and it doesn't require carrying reaction mass. If you accept that, then the need for Dyson Swarms becomes more obvious. 3. Breaking the 2 assumptions I listed makes spacefaring life more common not less. By this I mean we only really need to consider a million light years (of light cone) because of the speed of light. If FTL or even time travel were possible, then you need to consider a volume of spacetime orders of magnitude larger.
  - Calavar 5y ago
    > My father told me he once read a book that said it was impossible to go to the Moon because it would take 750 years to get there. A bit of a tangent, but that seems absurd even based on knowledge from hundreds of years ago. The moon is about 250,000 miles away, so the 750 years figure assumes a speed of less than 1 mile/day. And a quick google search suggests that we've had reasonable estimates of the distance to the moon since about the 2nd century BCE.
  - mattmanser 5y ago
    I think it's more that we don't know what we don't know. That's the thing that usually trips us up. Also, on a more human level, who's going to even pay/bother with these swarms? What will they achieve?
openasocket 5y ago
Are we sure we aren't seeing signs of alien life? I mean so much of astronomy is based on just observation, is it possible some phenomenon we observe is actually the result of an alien civilization and not natural? Sure, we haven't seen a Dyson swarm, but it's not like we've been looking super hard, and we're assuming that a Dyson swarm/sphere is practical to make and build. If a civilization were to develop a way to, say, directly convert matter to energy, the Dyson sphere/swarm is actually the less efficient option.
- goatlover 5y ago
  It's possible of course, and every so often some new weird anomaly is detected, and aliens are suggested. But mostly a natural explanation is found. The WOW signal and Oumuamua are one of the few exceptions, but natural explanations have been suggested for both. The thing is we know about natural phenomenon. We don't know whether aliens exist and are detectable. Occam's razor would favor existing natural explanations. Stars, planets, comets and what not are common throughout the universe.
  - betwixthewires 5y ago
    I think what he's getting at (I'm not the one you're responding to) is that something we see in space that appears more fundamental is evidence that we are so far from understanding that it just looks normal to us. Imagine ants walking on concrete. It is probably indistinguishable from naturally occurring ground to them. They probably don't even realize people make it. We could look up at the sky every day and see something that is evidently made by a civilization, at least to them and others on par with them, and think "that's pretty." We really don't know what sort of activities they'd be up to to even know what is and isn't evidence of their existence, if they were sufficiently advanced.
  - openasocket 5y ago
    > The thing is we know about natural phenomenon. We don't know whether aliens exist and are detectable. Occam's razor would favor existing natural explanations. That's kind of my point though. We have tons of astronomical data, but except for neighboring systems it isn't precise enough to unambiguously detect an extraterrestrial civilization. So we go with the natural explanation for what we see, because Occam's razor would seem to suggest that. But by definition that means that if the universe has alien civilizations producing megastructures we would first assume those were natural phenomena. And then we would try to find explanations for these phenomena, and build models, which would be incorrect, but would provide a natural explanation for these megastructures. So, ironically, if the galaxy really was teaming with alien life and alien megastructures, we would likely just categorize it as natural phenomena, and wonder why we aren't seeing any signs of alien life. I agree that just stars and planets and such are very common and thus unlikely to be alien megastructures. And I don't think there are any objects we've documented that are unique in all the universe. Any potential candidate would have to be something relatively rare in the universe (but wouldn't have to be unique) and would have to be poorly understood (something where we haven't directly observed its formation, or it has properties that aren't explained by physical laws/phenomena that we've been able to validate in a laboratory setting) to be a candidate. As a stab in the dark, consider pulsars. Fairly few known in the galaxy, from reading the wikipedia page it seems like they have some particularly weird and poorly-understood properties. They rotate and emit radiation very precisely, precise enough you can sync atomic clocks to it. It's been proposed that you can use multiple pulsars as reference points to very accurately determine your location, like GPS (https://en.wikipedia.org/wiki/Pulsar-based_navigation https://en.wikipedia.org/wiki/Pulsar-based_navigation ). They emit huge amounts of radiation and are very small, meaning it would be much, much easier to extract energy from it Dyson-swarm-style. To be clear, I don't know much about astronomy, and I think that pulsars are almost certainly NOT alien megastructures, but I'm just pointing to it as an example.
jjk166 5y ago
> Couple that with mass and energy ultimately being limited then there is a strong incentive and advantage in becoming as large as possible. Unless you can transmit power over infinite disctance without loss, you get diminishing returns as you expand. Eventually the amount of energy you can beam back from a new dyson swarm does not justify the cost of building a new dyson swarm. There is no incentive to expand beyond that point. For reasonable engineering estimates, such a range is still very small on galactic scales.
merpnderp 5y ago
It's not impossible that something like solving the cosmological constant problem could lead the way for harvesting zero point energy. If supersymmetry exists, which is a big if, physics would become a whole lot more exciting. This would make Dyson Spheres unnecessary for advancement on the Kardashev scale.
- T-A 5y ago
  > harvesting zero point energy Even if that were possible, it's only 6e-10 J/m^3 [1]. Want to keep a 10W LED light on? That's 10 J/s, so you need to extract all dark energy from 17e9 m^3 of space (roughly a cube with a side of 2.5 km) every second. [1] http://www.astronomy.ohio-state.edu/~ryden/ast162_10/notes41.html http://www.astronomy.ohio-state.edu/~ryden/ast162_10/notes41...
- dogma1138 5y ago
  If you can get to an infinite / near infinite source of energy then why would you need to expand? You’ll be able to create all the matter your want. We can already create W bosons from photon collisions at particle accelerators on earth.
JakeTheAndroid 5y ago
> Example: if there were 1000 spacefaring civilizations in the Milky Way, what are the odds that all 1000 of them (assuming they were within out light cone) would remain quiet or hidden? Couple that with mass and energy ultimately being limited then there is a strong incentive and advantage in becoming as large as possible. So even if 99% of civilizations remain quiet, the 1% will still make themselves visible. I am not sold on this math necessarily. When you ask "what are the odds?" what is that based on? How do we derive these odds at all? We know nothing about how these civilizations would evolve or what their values would be. So how can we assume that out of 1000 that 1% would be visible based on the odds? This sort of assumes that the Drake Equation is accurate, when the last few parts of that equation are complete guesses. > Additionally, on the notion of hidden civilizations in particular, it's essentially impossible to remain hidden to a K2 or K3 civilization so there's really no point. And maybe this is the difference. Maybe all 1000 are visible to K2 or K3's because it doesn't matter. But equally all 1000 aren't visible to K1's. We are so far away from K2 that I see no reason to speculate on the likelihood of this since we have literally no basis for this other than some fun thought experiments. And all of this is based on how we view ourselves and apply those same traits to beings we have never met and possibly can't even imagine. This is simply so far out of our grasp to intelligently speculate on, I tend to just avoid doing it.
- genghisjahn 5y ago
  I think it was Michael Crichton who said something like, "An equation whose variables can mean anything, means nothing."
  - genghisjahn 5y ago
    Here it is: As a result, the Drake equation can have any value from “billions and billions” to zero. An expression that can mean anything means nothing. Speaking precisely, the Drake equation is literally meaningless, and has nothing to do with science https://stephenschneider.stanford.edu/Publications/PDF_Papers/Crichton2003.pdf https://stephenschneider.stanford.edu/Publications/PDF_Paper...
rthomas6 5y ago
> very little visible light and a lot of IR. That sounds just like a brown dwarf. How would a Dyson swarm look different?
- wolfram74 5y ago
  TLDR: a bright infrared source is differentiable from a dim infrared source. If (big if) you can be confident about the distance of the object, that'll help tell you the total power output. If you have total power output and the black body spectrum, you can gauge it's size. A brown dwarf is, notably, small. If you took Sol and put a dyson swarm around it, the eventual power output would stay the same, just shifted colder as the light is now the waste product of all the industrial activity we did with it (minus any anti matter or magic matter fabrication we did) as opposed hot plasma collisions.
  - lrem 5y ago
    How can you get that kind of confidence? I imagine a slightly more advanced civilisation than ours can send a telescope far enough to use parallax. Are there better options?
    - PeterisP 5y ago
      It's not about measuring "size" by looking at width, but rather by looking at the total power emitted (for which you need essentially just the brightness and distance) which gives you the size (mass) of the star. So the OP's point seems to be that a Sol-mass star with a Dyson sphere may have the spectrum like a brown dwarf, but it would have the total emission quantity many, many times larger than a brown dwarf can have.
      - lrem 5y ago
        > for which you need essentially just the brightness and distance Parallax, which I mentioned, can be used for measuring the distance. I'm asking if there are better alternatives for getting the distance. For objects that are sufficiently far or slow moving, we can use Earth's natural movement to get some 2 AU of parallax base. Simply wait half a year before pointing the telescope at the object again. But, for things that move fast enough and are close enough to get some arc offset, we'll get wrong results. Which maybe isn't a problem, because we can detect such movement outright? I literally have no intuition how the math here works out. Hence asking.
jstanley 5y ago
> The only realistic way to get rid of heat in space is to radiate it away and the wavelength of that is a function of temperature. Then why would it definitely be IR? Couldn't a different form of intelligence thrive at a completely different temperature, and rely on elements that have phases that are useful to them at different temperatures?
- cletus 5y ago
  So the wavelength of black body radiation is called Wien's Law [1]. If you look at the electromagnetic spectrum [2], the IR spectrum is 25 μm to 2.5 μm. Compare those two and you'll see pretty much any reasonable range of temperatures has a heavy IR element. Some things to consider: 1. Tungsten has probably the highest melting point at ~3700K. It seems unlikely that complex matter of any kind can realistically survive at such extreme temperatures; 2. Heat above a certain level can itself be used to generate energy in a straightforward fashion. This itself will generate waste heat, most likely at a much lower temperature. As an aside, recycling heat is often raised as an objection to the IR signature issue with Dyson Swarms but that ignores thermodynamics. Let's say heat recycling for a star like the Sun is 90% effective then that's still 10% energy lost and 10% of the Sun's output is still massively significant. If there's perfect recycling, well that ignores entropy. [1]: https://en.wikipedia.org/wiki/Wien%27s_displacement_law https://en.wikipedia.org/wiki/Wien%27s_displacement_law [2]: http://labman.phys.utk.edu/phys222core/modules/m6/The%20EM%20spectrum.html http://labman.phys.utk.edu/phys222core/modules/m6/The%20EM%2...
  - jstanley 5y ago
    Good info, thanks!
  - raducu 5y ago
    What if that IR is not radiated in the orbital plane of our Galaxy, but up and dow
jandrese 5y ago
How can we be sure that something we have classified as a Red Dwarf star isn't a Dyson Sphere? All of the energy of the star has to be vented eventually, so a Dyson Sphere should glow like an end of life star that has expanded to the diameter of the Sphere. Also, how do you tell the difference between a solar system full of orbitals vs. a young solar system that has not had the orbital lanes cleared by planets?
- cletus 5y ago
  I don't believe that any Red Dwarf could be mistaken for a full Dyson Swarm. Some people more knowledgeable than me have put a lot of thought into the science of this. You can probably find a more satisfying answer. As for the second part, that's easy. There are two key differences: 1. Young solar systems are around young stars and young stars are... young. We can typically age stars, particularly those close by; and 2. A protoplanetary disk is, well, a disk. A full Dyson Swarm is a sphere. To be clear, it's not a rigid sphere, it's just a collection of orbitals that end up occluding the star they orbit in the same way as small water droplets form a cloud or fog. Alsos I suspect that a protoplanetary disk, even if we're directly on its plane, won't be as dense as a Dyson Swarm.
- PeterisP 5y ago
  I don't know if we can tell it for any particular star, but we can reason about large numbers of stars. We have a decent model of how stars must age, given their mass and composition; we have a decent model of how that composition must have evolved as the universe ages, so if there were many Dyson spheres around then I think that should be observable as there being "far too much" red dwarfs compared to how many we should observe.
rsynnott 5y ago
So I think where this idea runs into problems is assuming that people actually want or need a Dyson swarm. The sun puts out 3.846×10^26W. Let's assume a Dyson swarm manages 10% capture efficiency, and a future population of 100 billion. That would result in every person having access to 384TW, or about 25 times Earth's total power consumption. Clearly, that's far too much power for any reasonable use-case, so at that point you're talking about either a far higher population (quadrillions) or far smaller collection area. Earth's population seems to be destined to cap out at about 9bn, and the trend away from population growth is most pronounced in highly developed energy-hungry countries. So _we're_ probably never going to need a Dyson swarm, anyway...
- cletus 5y ago
  First, you'd be surprised how many people we can support. Like we could likely support more than a trillion people on Earth. The population of a full Dyson Swarm around our Sun likely caps out in the quadrillions, possibly quintillions. Second, it's entirely valid to ask the question of whether we'd ever reach such populations. This is of course unknown. As a solution to the Fermi Paradox, the idea of reaching a steady state (or even shrinking to a fragment) seems unsatisfying as a 100% outcome. Once again, it only takes 1 to keep growing and become detectable. A lot of things are likely to change in the next millenium, for example: 1. I expect we will live much, much longer than we do now; 2. Automation will increase to the point where labour is highly unlikely to be the limiting factor in any kind of industrial output. That leaves resources and energy as the limiting factors. Well, resources are just a proxy for energy. There are several rocky bodies in the Solar System that could, given enough energy, provide unimaginable amounts of raw materials; 3. Despite the wealth of developed nations, we are still living in an era of relative resource scarcity. Individuals in developed nations are certainly generally more prosperous than those in developing nations but it's expensive to raise children in developed nations the way most parents want to raise them: paying for education, housing, etc. I'm not comfortable making the prediction than the modern trend of having relatively few children per individual in the developed world will continue into an era of longer lives, far more abundance and being freed from the need to work their entire lives to set up those children. Lastly, there are some very obvious applications for huge amounts of energy, for example: 1. Extracting resources; 2. Vast amounts of computing power. What would you do with this? We haven't been good at predicting this other than to say that more bandwidth and more computing power has thus far always found applications that people want. One obvious one is I suspect we'll have VR worlds that people will basically live in on a scale we can't possibly yet imagine; 4. Interstellar travel; and, of course 5. Cryptocurrency mining. :)
jdkd8 5y ago
Or every species consumes its planets resources on phones and cars, imploding the environment before the necessary engineering feats to get them to the stars come along. My money is on it being too infeasible engineering wise due to resource exhaustion just building the infrastructure to get there. The carbon feedback loop creating disposable junk is destabilizing stable human climate. I lean towards the idea we’ll have to move away from industrialism at the scale we apply it today. Perhaps synthetic drugs can grow neuron structure that mimics the experience. Or helps acquire muscle memory from skills based work. Trip balls on the couch for 20 minutes and live life believing I just got from Mars Base 1 and have Zappa opening for me wouldn’t be so bad.
peakaboo 5y ago
I think it sounds daft to think speed of light is a hard speed limit, and there is absolutely a way to "cheat". Because aliens are here, and they certainly didn't travel at the speed of light to get here. That doesnt work at all. It's way too slow. My bet is they are extracting energy from space itself, what we call vacuum and we think there is nothing there. And I also think the speed of light only applies to things in our physical universe. Frequently these alien ships blink in and out of our reality. There is much we don't understand as humans.
krapp 5y ago
>This is what gives me confidence that the Milky Way isn't teeming with spacefaring life. Bear in mind that we humans are a spacefaring species. It seems entirely feasible to me that there could be a multitude of intelligent but "quiet" species limited as we are to probes and at best inter-system rockets, even that 100% of spacefaring civilizations thus far remain so, simply because getting to the "Let's Dyson swarm our sun and become Vorlons" stage is far, far more difficult than it appears on paper.
raducu 5y ago
> This requires no new physics and no exotic materials. It could be that Dyson Swarms are possible, but we have 0 examples of space industries so far. It could be an economical impossibility, it could be that the means to easily convert matter into energy is discoverable before the means to economically produce a Dyson Swarm, thus a Dyson Swarm is not necessary to orbit that close to a Star. It could be that the means to capture dark matter is right around the corner, so there's no need to estinguish stars to preserve them. It could be that the means to capture dark energy is also around the corner and there's no need to bother with altering the universe in any way, in fact, it would be a shame to do so. It could be that once a species is advanced enough to transcend its own biology and once it becomes kind of immortal, it no longer reproduces. I'm just pointing out counter arguments, I'm on the opinion that we are completely alone in our Milky Way and most likely the entire Universe. As in there is no bacteria outside our Solar System, anywhere, but there is no way to know yet.

by cletus 5y ago

mattmanser 5y ago

Seems like a good theory, but when I read something like this it always makes me think about any of the sci-fi I've read that was written 50-75 years ago. They're also full of what were at the time good theories, but that are now so wrong it often makes reading the story difficult, even with my fairly rudimentary modern astrophysics knowledge. In all honesty I think it's more likely any sufficiently advanced civilization capable of interstellar travel has probably descended entirely into virtual reality or a singularity. I mean, what would you prefer? Being the star of your own personal VR space, the next Malcolm Reynolds, space cowboying around where you are the entire focus of that reality. Or schlepping it over to another star in a generation ship or whatever where even if you were somehow still alive when it arrived, you'd be landing on a planet that will probably instantly kill you.

cletus 5y ago
There are several differences between these old predictions and now: 1. We're now assuming based on the limits of known physics rather than the expected limits of technology. My father told me he once read a book that said it was impossible to go to the Moon because it would take 750 years to get there. The speed of light was known at that time but assumptions were made about the limits of acceleration and velocity that weren't grounded in science; 2. Things like the rocket equation are important. Specifically, the reaction mass problem. Even more specifically, the only way for an independent body to accelerate in space that we know of is by expelling mass (or energy). You need to carry that mass and this quickly becomes inefficient. A good example of this is how people have recently started to say "if we just accelerate at 1G we can get to Alpha Centauri in a few years". 1G acceleration sounds easy but it's not. So how would you travel between stars? I think it most likely that you'd use a ton of energy to accelerate (or decelerate) a vessel with lasers on a solar sail. Why? Because energy from a star is abundant and cheap and it doesn't require carrying reaction mass. If you accept that, then the need for Dyson Swarms becomes more obvious. 3. Breaking the 2 assumptions I listed makes spacefaring life more common not less. By this I mean we only really need to consider a million light years (of light cone) because of the speed of light. If FTL or even time travel were possible, then you need to consider a volume of spacetime orders of magnitude larger.
- Calavar 5y ago
  > My father told me he once read a book that said it was impossible to go to the Moon because it would take 750 years to get there. A bit of a tangent, but that seems absurd even based on knowledge from hundreds of years ago. The moon is about 250,000 miles away, so the 750 years figure assumes a speed of less than 1 mile/day. And a quick google search suggests that we've had reasonable estimates of the distance to the moon since about the 2nd century BCE.
- mattmanser 5y ago
  I think it's more that we don't know what we don't know. That's the thing that usually trips us up. Also, on a more human level, who's going to even pay/bother with these swarms? What will they achieve?

openasocket 5y ago

Are we sure we aren't seeing signs of alien life? I mean so much of astronomy is based on just observation, is it possible some phenomenon we observe is actually the result of an alien civilization and not natural? Sure, we haven't seen a Dyson swarm, but it's not like we've been looking super hard, and we're assuming that a Dyson swarm/sphere is practical to make and build. If a civilization were to develop a way to, say, directly convert matter to energy, the Dyson sphere/swarm is actually the less efficient option.

goatlover 5y ago
It's possible of course, and every so often some new weird anomaly is detected, and aliens are suggested. But mostly a natural explanation is found. The WOW signal and Oumuamua are one of the few exceptions, but natural explanations have been suggested for both. The thing is we know about natural phenomenon. We don't know whether aliens exist and are detectable. Occam's razor would favor existing natural explanations. Stars, planets, comets and what not are common throughout the universe.
- betwixthewires 5y ago
  I think what he's getting at (I'm not the one you're responding to) is that something we see in space that appears more fundamental is evidence that we are so far from understanding that it just looks normal to us. Imagine ants walking on concrete. It is probably indistinguishable from naturally occurring ground to them. They probably don't even realize people make it. We could look up at the sky every day and see something that is evidently made by a civilization, at least to them and others on par with them, and think "that's pretty." We really don't know what sort of activities they'd be up to to even know what is and isn't evidence of their existence, if they were sufficiently advanced.
- openasocket 5y ago
  > The thing is we know about natural phenomenon. We don't know whether aliens exist and are detectable. Occam's razor would favor existing natural explanations. That's kind of my point though. We have tons of astronomical data, but except for neighboring systems it isn't precise enough to unambiguously detect an extraterrestrial civilization. So we go with the natural explanation for what we see, because Occam's razor would seem to suggest that. But by definition that means that if the universe has alien civilizations producing megastructures we would first assume those were natural phenomena. And then we would try to find explanations for these phenomena, and build models, which would be incorrect, but would provide a natural explanation for these megastructures. So, ironically, if the galaxy really was teaming with alien life and alien megastructures, we would likely just categorize it as natural phenomena, and wonder why we aren't seeing any signs of alien life. I agree that just stars and planets and such are very common and thus unlikely to be alien megastructures. And I don't think there are any objects we've documented that are unique in all the universe. Any potential candidate would have to be something relatively rare in the universe (but wouldn't have to be unique) and would have to be poorly understood (something where we haven't directly observed its formation, or it has properties that aren't explained by physical laws/phenomena that we've been able to validate in a laboratory setting) to be a candidate. As a stab in the dark, consider pulsars. Fairly few known in the galaxy, from reading the wikipedia page it seems like they have some particularly weird and poorly-understood properties. They rotate and emit radiation very precisely, precise enough you can sync atomic clocks to it. It's been proposed that you can use multiple pulsars as reference points to very accurately determine your location, like GPS (https://en.wikipedia.org/wiki/Pulsar-based_navigation https://en.wikipedia.org/wiki/Pulsar-based_navigation ). They emit huge amounts of radiation and are very small, meaning it would be much, much easier to extract energy from it Dyson-swarm-style. To be clear, I don't know much about astronomy, and I think that pulsars are almost certainly NOT alien megastructures, but I'm just pointing to it as an example.

jjk166 5y ago

> Couple that with mass and energy ultimately being limited then there is a strong incentive and advantage in becoming as large as possible. Unless you can transmit power over infinite disctance without loss, you get diminishing returns as you expand. Eventually the amount of energy you can beam back from a new dyson swarm does not justify the cost of building a new dyson swarm. There is no incentive to expand beyond that point. For reasonable engineering estimates, such a range is still very small on galactic scales.

merpnderp 5y ago

It's not impossible that something like solving the cosmological constant problem could lead the way for harvesting zero point energy. If supersymmetry exists, which is a big if, physics would become a whole lot more exciting. This would make Dyson Spheres unnecessary for advancement on the Kardashev scale.

T-A 5y ago
> harvesting zero point energy Even if that were possible, it's only 6e-10 J/m^3 [1]. Want to keep a 10W LED light on? That's 10 J/s, so you need to extract all dark energy from 17e9 m^3 of space (roughly a cube with a side of 2.5 km) every second. [1] http://www.astronomy.ohio-state.edu/~ryden/ast162_10/notes41.html http://www.astronomy.ohio-state.edu/~ryden/ast162_10/notes41...
dogma1138 5y ago
If you can get to an infinite / near infinite source of energy then why would you need to expand? You’ll be able to create all the matter your want. We can already create W bosons from photon collisions at particle accelerators on earth.

JakeTheAndroid 5y ago

> Example: if there were 1000 spacefaring civilizations in the Milky Way, what are the odds that all 1000 of them (assuming they were within out light cone) would remain quiet or hidden? Couple that with mass and energy ultimately being limited then there is a strong incentive and advantage in becoming as large as possible. So even if 99% of civilizations remain quiet, the 1% will still make themselves visible. I am not sold on this math necessarily. When you ask "what are the odds?" what is that based on? How do we derive these odds at all? We know nothing about how these civilizations would evolve or what their values would be. So how can we assume that out of 1000 that 1% would be visible based on the odds? This sort of assumes that the Drake Equation is accurate, when the last few parts of that equation are complete guesses. > Additionally, on the notion of hidden civilizations in particular, it's essentially impossible to remain hidden to a K2 or K3 civilization so there's really no point. And maybe this is the difference. Maybe all 1000 are visible to K2 or K3's because it doesn't matter. But equally all 1000 aren't visible to K1's. We are so far away from K2 that I see no reason to speculate on the likelihood of this since we have literally no basis for this other than some fun thought experiments. And all of this is based on how we view ourselves and apply those same traits to beings we have never met and possibly can't even imagine. This is simply so far out of our grasp to intelligently speculate on, I tend to just avoid doing it.

genghisjahn 5y ago
I think it was Michael Crichton who said something like, "An equation whose variables can mean anything, means nothing."
- genghisjahn 5y ago
  Here it is: As a result, the Drake equation can have any value from “billions and billions” to zero. An expression that can mean anything means nothing. Speaking precisely, the Drake equation is literally meaningless, and has nothing to do with science https://stephenschneider.stanford.edu/Publications/PDF_Papers/Crichton2003.pdf https://stephenschneider.stanford.edu/Publications/PDF_Paper...

rthomas6 5y ago

> very little visible light and a lot of IR. That sounds just like a brown dwarf. How would a Dyson swarm look different?

wolfram74 5y ago
TLDR: a bright infrared source is differentiable from a dim infrared source. If (big if) you can be confident about the distance of the object, that'll help tell you the total power output. If you have total power output and the black body spectrum, you can gauge it's size. A brown dwarf is, notably, small. If you took Sol and put a dyson swarm around it, the eventual power output would stay the same, just shifted colder as the light is now the waste product of all the industrial activity we did with it (minus any anti matter or magic matter fabrication we did) as opposed hot plasma collisions.
- lrem 5y ago
  How can you get that kind of confidence? I imagine a slightly more advanced civilisation than ours can send a telescope far enough to use parallax. Are there better options?
  - PeterisP 5y ago
    It's not about measuring "size" by looking at width, but rather by looking at the total power emitted (for which you need essentially just the brightness and distance) which gives you the size (mass) of the star. So the OP's point seems to be that a Sol-mass star with a Dyson sphere may have the spectrum like a brown dwarf, but it would have the total emission quantity many, many times larger than a brown dwarf can have.
    - lrem 5y ago
      > for which you need essentially just the brightness and distance Parallax, which I mentioned, can be used for measuring the distance. I'm asking if there are better alternatives for getting the distance. For objects that are sufficiently far or slow moving, we can use Earth's natural movement to get some 2 AU of parallax base. Simply wait half a year before pointing the telescope at the object again. But, for things that move fast enough and are close enough to get some arc offset, we'll get wrong results. Which maybe isn't a problem, because we can detect such movement outright? I literally have no intuition how the math here works out. Hence asking.

jstanley 5y ago

> The only realistic way to get rid of heat in space is to radiate it away and the wavelength of that is a function of temperature. Then why would it definitely be IR? Couldn't a different form of intelligence thrive at a completely different temperature, and rely on elements that have phases that are useful to them at different temperatures?

cletus 5y ago
So the wavelength of black body radiation is called Wien's Law [1]. If you look at the electromagnetic spectrum [2], the IR spectrum is 25 μm to 2.5 μm. Compare those two and you'll see pretty much any reasonable range of temperatures has a heavy IR element. Some things to consider: 1. Tungsten has probably the highest melting point at ~3700K. It seems unlikely that complex matter of any kind can realistically survive at such extreme temperatures; 2. Heat above a certain level can itself be used to generate energy in a straightforward fashion. This itself will generate waste heat, most likely at a much lower temperature. As an aside, recycling heat is often raised as an objection to the IR signature issue with Dyson Swarms but that ignores thermodynamics. Let's say heat recycling for a star like the Sun is 90% effective then that's still 10% energy lost and 10% of the Sun's output is still massively significant. If there's perfect recycling, well that ignores entropy. [1]: https://en.wikipedia.org/wiki/Wien%27s_displacement_law https://en.wikipedia.org/wiki/Wien%27s_displacement_law [2]: http://labman.phys.utk.edu/phys222core/modules/m6/The%20EM%20spectrum.html http://labman.phys.utk.edu/phys222core/modules/m6/The%20EM%2...
- jstanley 5y ago
  Good info, thanks!
- raducu 5y ago
  What if that IR is not radiated in the orbital plane of our Galaxy, but up and dow

jandrese 5y ago

How can we be sure that something we have classified as a Red Dwarf star isn't a Dyson Sphere? All of the energy of the star has to be vented eventually, so a Dyson Sphere should glow like an end of life star that has expanded to the diameter of the Sphere. Also, how do you tell the difference between a solar system full of orbitals vs. a young solar system that has not had the orbital lanes cleared by planets?

cletus 5y ago
I don't believe that any Red Dwarf could be mistaken for a full Dyson Swarm. Some people more knowledgeable than me have put a lot of thought into the science of this. You can probably find a more satisfying answer. As for the second part, that's easy. There are two key differences: 1. Young solar systems are around young stars and young stars are... young. We can typically age stars, particularly those close by; and 2. A protoplanetary disk is, well, a disk. A full Dyson Swarm is a sphere. To be clear, it's not a rigid sphere, it's just a collection of orbitals that end up occluding the star they orbit in the same way as small water droplets form a cloud or fog. Alsos I suspect that a protoplanetary disk, even if we're directly on its plane, won't be as dense as a Dyson Swarm.
PeterisP 5y ago
I don't know if we can tell it for any particular star, but we can reason about large numbers of stars. We have a decent model of how stars must age, given their mass and composition; we have a decent model of how that composition must have evolved as the universe ages, so if there were many Dyson spheres around then I think that should be observable as there being "far too much" red dwarfs compared to how many we should observe.

rsynnott 5y ago

So I think where this idea runs into problems is assuming that people actually want or need a Dyson swarm. The sun puts out 3.846×10^26W. Let's assume a Dyson swarm manages 10% capture efficiency, and a future population of 100 billion. That would result in every person having access to 384TW, or about 25 times Earth's total power consumption. Clearly, that's far too much power for any reasonable use-case, so at that point you're talking about either a far higher population (quadrillions) or far smaller collection area. Earth's population seems to be destined to cap out at about 9bn, and the trend away from population growth is most pronounced in highly developed energy-hungry countries. So _we're_ probably never going to need a Dyson swarm, anyway...

cletus 5y ago
First, you'd be surprised how many people we can support. Like we could likely support more than a trillion people on Earth. The population of a full Dyson Swarm around our Sun likely caps out in the quadrillions, possibly quintillions. Second, it's entirely valid to ask the question of whether we'd ever reach such populations. This is of course unknown. As a solution to the Fermi Paradox, the idea of reaching a steady state (or even shrinking to a fragment) seems unsatisfying as a 100% outcome. Once again, it only takes 1 to keep growing and become detectable. A lot of things are likely to change in the next millenium, for example: 1. I expect we will live much, much longer than we do now; 2. Automation will increase to the point where labour is highly unlikely to be the limiting factor in any kind of industrial output. That leaves resources and energy as the limiting factors. Well, resources are just a proxy for energy. There are several rocky bodies in the Solar System that could, given enough energy, provide unimaginable amounts of raw materials; 3. Despite the wealth of developed nations, we are still living in an era of relative resource scarcity. Individuals in developed nations are certainly generally more prosperous than those in developing nations but it's expensive to raise children in developed nations the way most parents want to raise them: paying for education, housing, etc. I'm not comfortable making the prediction than the modern trend of having relatively few children per individual in the developed world will continue into an era of longer lives, far more abundance and being freed from the need to work their entire lives to set up those children. Lastly, there are some very obvious applications for huge amounts of energy, for example: 1. Extracting resources; 2. Vast amounts of computing power. What would you do with this? We haven't been good at predicting this other than to say that more bandwidth and more computing power has thus far always found applications that people want. One obvious one is I suspect we'll have VR worlds that people will basically live in on a scale we can't possibly yet imagine; 4. Interstellar travel; and, of course 5. Cryptocurrency mining. :)

jdkd8 5y ago

Or every species consumes its planets resources on phones and cars, imploding the environment before the necessary engineering feats to get them to the stars come along. My money is on it being too infeasible engineering wise due to resource exhaustion just building the infrastructure to get there. The carbon feedback loop creating disposable junk is destabilizing stable human climate. I lean towards the idea we’ll have to move away from industrialism at the scale we apply it today. Perhaps synthetic drugs can grow neuron structure that mimics the experience. Or helps acquire muscle memory from skills based work. Trip balls on the couch for 20 minutes and live life believing I just got from Mars Base 1 and have Zappa opening for me wouldn’t be so bad.

peakaboo 5y ago

I think it sounds daft to think speed of light is a hard speed limit, and there is absolutely a way to "cheat". Because aliens are here, and they certainly didn't travel at the speed of light to get here. That doesnt work at all. It's way too slow. My bet is they are extracting energy from space itself, what we call vacuum and we think there is nothing there. And I also think the speed of light only applies to things in our physical universe. Frequently these alien ships blink in and out of our reality. There is much we don't understand as humans.

krapp 5y ago

>This is what gives me confidence that the Milky Way isn't teeming with spacefaring life. Bear in mind that we humans are a spacefaring species. It seems entirely feasible to me that there could be a multitude of intelligent but "quiet" species limited as we are to probes and at best inter-system rockets, even that 100% of spacefaring civilizations thus far remain so, simply because getting to the "Let's Dyson swarm our sun and become Vorlons" stage is far, far more difficult than it appears on paper.

raducu 5y ago

> This requires no new physics and no exotic materials. It could be that Dyson Swarms are possible, but we have 0 examples of space industries so far. It could be an economical impossibility, it could be that the means to easily convert matter into energy is discoverable before the means to economically produce a Dyson Swarm, thus a Dyson Swarm is not necessary to orbit that close to a Star. It could be that the means to capture dark matter is right around the corner, so there's no need to estinguish stars to preserve them. It could be that the means to capture dark energy is also around the corner and there's no need to bother with altering the universe in any way, in fact, it would be a shame to do so. It could be that once a species is advanced enough to transcend its own biology and once it becomes kind of immortal, it no longer reproduces. I'm just pointing out counter arguments, I'm on the opinion that we are completely alone in our Milky Way and most likely the entire Universe. As in there is no bacteria outside our Solar System, anywhere, but there is no way to know yet.