10 ms·

Put me firmly in the camp that believes the speed of light is a hard limit on the universe and I'll use Isaac Arthur dismissal of FTL travel as to why. He cont

by cletus 8y ago

Put me firmly in the camp that believes the speed of light is a hard limit on the universe and I'll use Isaac Arthur dismissal of FTL travel as to why. He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. Now this isn't to say there isn't one that's say, 600 million light years away that built their first Dyson sphere 500 million years ago although, in practice, this doesn't really change the probabilities that much. If there's FTL then that billion light year practical limit really goes out the window as you can effectively get anywhere in the universe, making the volume of absence be many, many times the size of the observable universe. I'm not sure why the author is talking about gravity ripping you apart in a black hole. It Is Known [tm] that larger black holes have pretty gentle event horizons. I'm not sure why it matters that a black hole would be spinning. You can pretty much assume every significant mass in the universe is spinning to some degree (a state of zero spin being highly unlikely over even small amounts of time). The author talks about the inner event horizon and I guess that's the point. But all of that is highly theoretical. Nothing is known about the inner workings of a black hole. It's all highly theoretical and beyond the ability of general relativity to describe. No other theory has been able to adequately explain or describe gravity let alone extreme gravity so your view on what's within the event horizon probably depends on which unproven theory (eg string theory) you subscribe to. So this is speculation based on speculation.

felipemnoa 8y ago
>>Put me firmly in the camp that believes the speed of light is a hard limit on the universe and I'll use Isaac Arthur dismissal of FTL travel as to why. I would modify your sentence to say that the speed of light is a hard limit through space. Space on the other hand does not seem to have that limitation [1] [1] https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive
- ThrowawayR2 8y ago
  The Alcubierre drive is a fantasy. It's the equivalent of saying "I can start a business selling unicorn rides if I have a unicorn." The unicorn in this case being "negative mass", there being no way to synthesize such a thing nor even a plausible path by which it might be possible.
  - ben_w 8y ago
    And before anyone mentions Casimir cavities, I did a blog post in the style of a paper about that: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
    - magicalhippo 8y ago
      AFAIK the Casimir force is due to the van der Waals force between the plates, so doesn't that spoil the negative energy party from the get-go? https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/hep-th/0503158 https://arxiv.org/abs/hep-th/0503158
      - sp332 8y ago
        I'm not an expert, but this paper makes a convincing argument that that's not a problem. https://arxiv.org/abs/1702.03291 https://arxiv.org/abs/1702.03291
        magicalhippo 8y ago
        Ah, thanks, hadn't seen that follow-up paper.
  - snowwrestler 8y ago
    We know for a fact that it is possible for space to expand because we have observed that space is expanding. Who knows why or how, or if it should be called “negative mass” or “dark energy,” but observing a phenomenon has always been the starting point for exploiting it. Radiation started out as a small unexplained observation too and look what we’ve done with that. I’m not claiming that the warp drive is around the corner, I’m just saying: we do not yet know enough to rule it out.
    - MrLeap 8y ago
      This is an interesting perspective! The frontier around dark energy / space accelerating in its expansion etc is interesting to me. A bit unrelated, my pet theory is that a dwindling of some quantity creates the things we're measuring as acceleration. My naive intuition is that celestial bodies aren't flying away from each other accelerated by some unseen energy so much as getting smaller. If two things shrink in place, the distance between them grows. Maybe there's some obvious reason why that couldn't be the case, i'd be interested to know!
- cletus 8y ago
  Isaac Arthur did and episode on this topic specifically [1]. It's one of his early ones. There are a whole lot of "ifs" here, just one of which is negative mass. [1]: https://www.youtube.com/watch?v=yCCsmxGjEV0 https://www.youtube.com/watch?v=yCCsmxGjEV0
negamax 8y ago
The space can be bent. I am firmly in the camp that everything is possible. Reason we aren’t in contact with other intelligent life forms is that we are too primitive. But things change a lot with every next leap
- PopePompus 8y ago
  Not everything is possible. There are things which are provably impossible. It is, for example, impossible to find an algebraic solution for general polynomials of degree five or higher. The things we know to be impossible tend to be mathematical, or a "real world" system exactly modeled by math, simply because math tends to be the way we conclusively prove something.
  - negamax 8y ago
    Mathematical/Geometrical fact: Parallel lines can never intersect. But will they not intersect if I bend the space? When you say on algebraic solution exists, that doesn’t mean no solution exists?
llbowers 8y ago
>He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. How do we know an advanced technology would absolutely use Dyson spheres? I'm not asking to challenge but in serious inquiry. Off the top of my head it just seems a highly advanced civilization might be able to come up with something completely different to meet their energy needs.
- ben_w 8y ago
  It would have to violate the laws of thermodynamics to not be visible. I’m not saying “no” (my brother has wondered if dark energy could be waste output of such civilisations, for example), but we have zero reason to treat the idea as anything more than the softest of science fiction.
  - lainga 8y ago
    The GP didn't ask how you would make a Dyson sphere that was invisible, but why it was certain the Dyson sphere would be built at all.
    - ben_w 8y ago
      Ok, but the effect of the energy output of any civilisation is basically the same, and for the same reasons. It doesn’t matter if it’s a star or TARDIS whose inside is eternally expanding and you’re grabbing energy from its internal dark energy field, if you use that energy, you get hot, and that heat is visible. Unless you can violate the laws of thermodynamics.
      - bane 8y ago
        Maybe collect the heat and release it as a laser towards very sparsely populated parts of the sky? Perhaps that helps stabilize the sphere in the orbit of its star?
        8y ago
imglorp 8y ago
I'm in a more conservative camp than speed limits: the practicality one. Even if we ignore the ponies and rainbows of wormhole travel, if you want to travel to a plain black hole to use the magic teleporter, the nearest two are V616 Mon at 11 solar masses and 3000 LY away, and Cyg X1 at 15 SM and 6000 LY. If you buy into the article's assertion that you won't get burned or spaghettified on your way to becoming a nucleon paste, and you want a heavier BH, the nearest is Sag A* at 4.1e6 SM and 25000 LY away. Anyway, to travel between the teleporter and Earth, we're talking most of the resources of a planet to accelerate a mass to substantial fractions of c. Then you've got thousands of years of collisions, radiation, and maybe (assumption?) cultural and biological challenges of living in space for aeons, plus needing another planet's worth of resources to slow down at the destination. All this makes it hard enough even to get a dozen LY to our nearest start system. My opinion is we're in something of a Well World universe, where everyone is pretty well travel-isolated from their neighbors.
- arbuge 8y ago
  > the nearest two are V616 Mon at 11 solar masses and 3000 LY away, and Cyg X1 at 15 SM and 6000 LY. The nearest known ones, that is. They were detected due to their gravitational effect on binary companions we could more easily detect. By that token, it is quite possible there are nearer ones - it's just that detecting them directly if they don't have a binary companion is tough.
  - empath75 8y ago
    Could be one on a collision course with us right now.
- jvanderbot 8y ago
  The author didn't mention using black holes to get around. Hyperspace might be just moving into wherever the events in the movie Event Horizon took place.
  - krapp 8y ago
    Isn't Event Horizon basically just a horror movie, except the haunted house is a spaceship? If you're going to pick a fictional hyperspace "framework," there are many to choose from, all of which are equally nonsensical.
yellowapple 8y ago
I feel like whether or not there are Dyson spheres is distinct from whether or not there are sapient civilizations beyond Earth. Unless the argument is that we don't count as sapient because we don't have Dyson spheres yet? Hell, we're assuming that Dyson spheres are even possible with such a conjecture. I'm not convinced they are (not without materials that border if not cross outright into magic). It's also not certain if they're necessary to build to sustain any size of spacefaring civilization (artificial nuclear fusion would kinda defeat the point).
- cletus 8y ago
  Dyson spheres at some point were conflated to a structure that is a rigid shell around a star, something for which no known material would be able to support. The original idea of a Dyson sphere is now more often called a Dyson swarm to avoid this confusion. A Dyson swarm (the original Dyson sphere) is a cloud of independently orbiting habitats/bodies/structures.
  - yellowapple 8y ago
    That seems like it'd be even less efficient. A "swarm" like that would be inherently reliant on maintaining orbits around the target star. In order to capture even a significant fraction of a star's energy you'll need a lot of stations orbiting that star, and they'll need to overlap (i.e shadow out stations further behind them / get shadowed out by stations further in front of them). Even if a civilization's capable of building that many stations to surround a star in a deliberate sort of Kessler syndrome, it ain't clear that a civilization would ever need to do so.
Cookingboy 8y ago
>He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. I guess the human civilization doesn't count as "sentient" because we don't have a Dyson sphere yet... Also how "unmissable" is a dyson sphere? Do we have the means to survey every single star within one billion light year radius? Hell, we know neutron stars are real, same for blackholes, but does that mean we observed every single one of them and didn't miss a single one?
- sandworm101 8y ago
  Dyson spoke of "swarms", not spheres. The sphere came earlier in scifi. The dyson swarm was a network of solar collectors orbiting a star, a far more practicable structure than the hollow sphere concept. We are babystepping towards this. We have probes out there blocking, harvesting, a tiny fraction of our star's energy already.
jancsika 8y ago
> He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. If a civilization has the intelligence and foresight to build a Dyson sphere, how much more intelligence and foresight does it need to hide one?
- cletus 8y ago
  See [1] and [2] where the idea of hiding a Dyson sphere is covered in depth. It essentially means breaking the laws of thermodynamics, specifically entropy. Hit and object with light from a star and it heats up. It radiates away that heat in a predictable way. [1] https://www.youtube.com/watch?v=QfuK8la0y6s https://www.youtube.com/watch?v=QfuK8la0y6s [2] https://www.youtube.com/watch?v=HlmKejRSVd8 https://www.youtube.com/watch?v=HlmKejRSVd8
  - Sargos 8y ago
    > It radiates away that heat in a predictable way. Unless that heat energy itself is also caught and used.
    - dodobirdlord 8y ago
      That is exactly what is meant by "It essentially means breaking the laws of thermodynamics".
  - ChrisFoster 8y ago
    Waste heat must be radiated away, though thermodynamics would be quite content if that radiation is anisotropic. For example, consider a perfectly insulating black box with small hole. Observers on the opposite side from the hole will not observe any radiation from the interior of the box. I don't think there's any physical limit on collimating the outgoing radiation to hide from everyone outside a narrow beam. It's "just an engineering problem".
    - deleted 8y ago
      [deleted]
cptaj 8y ago
The implications that any advanced civilization would have Dyson Spheres, that these are in any way detectable and overall that the civilization would be unwilling or incapable of hiding themselves; are entirely based on speculation as well.
rsynnott 8y ago
The assumption that anyone who can build a Dyson sphere would want to has always seemed a bit off to me. Energy use in highly developed countries is stagnating or even falling, and the rate of population growth looks set to decline. What do the hypothetical Dyson sphere builders actually want with all the energy?
- cletus 8y ago
  This is really the beauty of the Fermi Paradox because the issue isn't "would everyone do this?". If there are starfaring civilizations (or just civilizations with the necessary technology) within detectable range, it just takes one to go this route. Since we've been unable to detect the telltale signatures of such a megastructure, it either means that none of the civilizations within range have gone this route or there are none. Given what we know about the benefits of a Dyson swarm and how relatively low-tech it is, the idea that no one has gone that route becomes increasingly unlikely with the more civilizations there are.
  - colordrops 8y ago
    How can you be so sure that a Dyson swarm is a sensible route at all given more advanced technology? We can't even figure out the sensible route for tech 5 years out.
  - rsynnott 8y ago
    > Given what we know about the benefits of a Dyson swarm I think there's a real question of whether anyone would actually want one. The sun's total power output per person on earth is 5.5e+16W. That's 3000 times total human energy usage, _per person_. Even if you assume a system population in the trillions, that's still a pointlessly large amount of energy per capita (and again, current population trends don't support that, and we may reasonably assume that most Dyson sphere builders will figure out birth control). Most possible hypothetical uses for them seem to be things like converting all the mass in a solar system into a computer or similar, but again there's a real question of whether there's any market for that. I'm also not convinced we could necessarily detect one. A super-high-tech magic one would capture most of the available energy, leaving a largely invisible thing with mass, which sounds quite a lot like a neutron star. And if you had a lower-tech one that leaked most of the energy, well, that might look distinctive, but if you're throwing most of the energy away you probably don't need a complete Dyson sphere. And in any case, organised searches for Dyson spheres are pretty new, and are small efforts. We might have the data to support them right now, it's just that no-one's noticed yet...
rishav_sharan 8y ago
I really feel that no civilization would build dyson spheres. Why would anyone want to signal others, here i am?
- cletus 8y ago
  A topic also covered in depth: - Secret Aliens [1] - Hidden Aliens [2] Basically you can't hide from a K2 civilization in your same galaxy so there's really no point in trying. [1] https://www.youtube.com/watch?v=IpF25knrGtg&t=1657s https://www.youtube.com/watch?v=IpF25knrGtg&t=1657s [2] https://www.youtube.com/watch?v=tEBn8bc0k-I https://www.youtube.com/watch?v=tEBn8bc0k-I
  - krageon 8y ago
    This reads vastly like "You can't protect from a determined nation-state actor, so why would you protect yourself at all". To me it seems obviously there is a point, namely that you will hide yourself from every non-K2 civilization.
    - chc 8y ago
      I think the assumption is that the difficulty of long-range space travel is such that only the "nation-state actors" in this analogy are likely to attack you in the first place. Just by existing in a universe with the laws of physics ours has, you're effectively secure against attack from low-tech civilizations.
raverbashing 8y ago
I'm more skeptical of the need for Dyson spheres than practicality of ftl travel
PopePompus 8y ago
> I'm not sure why the author is talking about gravity ripping you apart in a black hole. It Is Known [tm] that larger black holes have pretty gentle event horizons. But the article isn't about what happens at the event horizon. It's about what happens at the singularity, well inside of the event horizon for astrophysical black holes.
8bitsrule 8y ago
isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. It is entirely possible that advanced sentient civilizations have realized that there is such a thing as 'enough technology', learned enough to permanently liberate themselves from basic needs, and found other kinds of fulfillment and amusement.
- jeletonskelly 8y ago
  I think it's likely even. Look at the digital worlds we are creating in games. I find it far more likely we build a simulation more enticing than reality and find ways to leave the confines of our current reality behind. Not too different from what happens with the AI in the movie "Her".
mr_toad 8y ago
> I'm not sure why it matters that a black hole would be spinning. Because of frame dragging. https://en.wikipedia.org/wiki/Frame-dragging https://en.wikipedia.org/wiki/Frame-dragging
Illniyar 8y ago
> He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. Or that making a dyson sphere is harder than FTL, or it isn't economically viable to build one. There's no reason to assume a Dyson sphere would be a logical step after achieving FTL
pmiller2 8y ago
The rotation matters because the singularity of a rotating black hole is ring-shaped, not a point: https://en.wikipedia.org/wiki/Ring_singularity https://en.wikipedia.org/wiki/Ring_singularity
xorfish 8y ago
How is it possible to detect a dyson sphere? How easy are they to miss?
Tepix 8y ago
Perhaps these Dyson-sphere-building civilizations only live around red dwarves (because that's where they originated). Red dwarves are dim and hard to detect, especially when they are far away. A red dwarf with a dyson sphere around it would be even harder to detect.
jeletonskelly 8y ago
Does gravity propagate at the speed of light? Like, if I were to plop down a planet somewhere in the solar system, would the gravitational effects be immediate or would it take effect at the speed of light? Because if it's immediate, then we should be able to transmit information through gravity waves if we could build a device to detect subtle enough changes.
- Tenoke 8y ago
  Yes, gravity operates at c. There is nothing that we know of (or have a theory of) that can even in principle travel faster than c.
- minkzilla 8y ago
  It might interest you that a couple of years ago was the first observation of gravitational waves. Here is a BBC article https://www.bbc.com/news/science-environment-35524440 https://www.bbc.com/news/science-environment-35524440
nikofeyn 8y ago
> I'll use Isaac Arthur dismissal of FTL travel as to why what credentials does he have? > Put me firmly in the camp that believes the speed of light is a hard limit on the universe the speed of light isn't a limit in the sense that nothing can be greater than it. it is a crossover point that can't be crossed over for things above or below it to the other side. > I'm not sure why it matters that a black hole would be spinning. black holes that spin are much different than non-spinning holes and have more complicated dynamics. if they are spinning, they are dragging space-time along with them. see this paper that shows some actual visuals of what a spinning black hole might look like and what it does to the light around it. https://arxiv.org/abs/1502.03808 https://arxiv.org/abs/1502.03808

by cletus 8y ago

felipemnoa 8y ago

>>Put me firmly in the camp that believes the speed of light is a hard limit on the universe and I'll use Isaac Arthur dismissal of FTL travel as to why. I would modify your sentence to say that the speed of light is a hard limit through space. Space on the other hand does not seem to have that limitation [1] [1] https://en.wikipedia.org/wiki/Alcubierre_drive https://en.wikipedia.org/wiki/Alcubierre_drive

ThrowawayR2 8y ago
The Alcubierre drive is a fantasy. It's the equivalent of saying "I can start a business selling unicorn rides if I have a unicorn." The unicorn in this case being "negative mass", there being no way to synthesize such a thing nor even a plausible path by which it might be possible.
- ben_w 8y ago
  And before anyone mentions Casimir cavities, I did a blog post in the style of a paper about that: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
  - magicalhippo 8y ago
    AFAIK the Casimir force is due to the van der Waals force between the plates, so doesn't that spoil the negative energy party from the get-go? https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/1605.04143 https://arxiv.org/abs/hep-th/0503158 https://arxiv.org/abs/hep-th/0503158
    - sp332 8y ago
      I'm not an expert, but this paper makes a convincing argument that that's not a problem. https://arxiv.org/abs/1702.03291 https://arxiv.org/abs/1702.03291
      - magicalhippo 8y ago
        Ah, thanks, hadn't seen that follow-up paper.
- snowwrestler 8y ago
  We know for a fact that it is possible for space to expand because we have observed that space is expanding. Who knows why or how, or if it should be called “negative mass” or “dark energy,” but observing a phenomenon has always been the starting point for exploiting it. Radiation started out as a small unexplained observation too and look what we’ve done with that. I’m not claiming that the warp drive is around the corner, I’m just saying: we do not yet know enough to rule it out.
  - MrLeap 8y ago
    This is an interesting perspective! The frontier around dark energy / space accelerating in its expansion etc is interesting to me. A bit unrelated, my pet theory is that a dwindling of some quantity creates the things we're measuring as acceleration. My naive intuition is that celestial bodies aren't flying away from each other accelerated by some unseen energy so much as getting smaller. If two things shrink in place, the distance between them grows. Maybe there's some obvious reason why that couldn't be the case, i'd be interested to know!
cletus 8y ago
Isaac Arthur did and episode on this topic specifically [1]. It's one of his early ones. There are a whole lot of "ifs" here, just one of which is negative mass. [1]: https://www.youtube.com/watch?v=yCCsmxGjEV0 https://www.youtube.com/watch?v=yCCsmxGjEV0

negamax 8y ago

The space can be bent. I am firmly in the camp that everything is possible. Reason we aren’t in contact with other intelligent life forms is that we are too primitive. But things change a lot with every next leap

PopePompus 8y ago
Not everything is possible. There are things which are provably impossible. It is, for example, impossible to find an algebraic solution for general polynomials of degree five or higher. The things we know to be impossible tend to be mathematical, or a "real world" system exactly modeled by math, simply because math tends to be the way we conclusively prove something.
- negamax 8y ago
  Mathematical/Geometrical fact: Parallel lines can never intersect. But will they not intersect if I bend the space? When you say on algebraic solution exists, that doesn’t mean no solution exists?

llbowers 8y ago

>He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. How do we know an advanced technology would absolutely use Dyson spheres? I'm not asking to challenge but in serious inquiry. Off the top of my head it just seems a highly advanced civilization might be able to come up with something completely different to meet their energy needs.

ben_w 8y ago
It would have to violate the laws of thermodynamics to not be visible. I’m not saying “no” (my brother has wondered if dark energy could be waste output of such civilisations, for example), but we have zero reason to treat the idea as anything more than the softest of science fiction.
- lainga 8y ago
  The GP didn't ask how you would make a Dyson sphere that was invisible, but why it was certain the Dyson sphere would be built at all.
  - ben_w 8y ago
    Ok, but the effect of the energy output of any civilisation is basically the same, and for the same reasons. It doesn’t matter if it’s a star or TARDIS whose inside is eternally expanding and you’re grabbing energy from its internal dark energy field, if you use that energy, you get hot, and that heat is visible. Unless you can violate the laws of thermodynamics.
    - bane 8y ago
      Maybe collect the heat and release it as a laser towards very sparsely populated parts of the sky? Perhaps that helps stabilize the sphere in the orbit of its star?
      - 8y ago

imglorp 8y ago

I'm in a more conservative camp than speed limits: the practicality one. Even if we ignore the ponies and rainbows of wormhole travel, if you want to travel to a plain black hole to use the magic teleporter, the nearest two are V616 Mon at 11 solar masses and 3000 LY away, and Cyg X1 at 15 SM and 6000 LY. If you buy into the article's assertion that you won't get burned or spaghettified on your way to becoming a nucleon paste, and you want a heavier BH, the nearest is Sag A* at 4.1e6 SM and 25000 LY away. Anyway, to travel between the teleporter and Earth, we're talking most of the resources of a planet to accelerate a mass to substantial fractions of c. Then you've got thousands of years of collisions, radiation, and maybe (assumption?) cultural and biological challenges of living in space for aeons, plus needing another planet's worth of resources to slow down at the destination. All this makes it hard enough even to get a dozen LY to our nearest start system. My opinion is we're in something of a Well World universe, where everyone is pretty well travel-isolated from their neighbors.

arbuge 8y ago
> the nearest two are V616 Mon at 11 solar masses and 3000 LY away, and Cyg X1 at 15 SM and 6000 LY. The nearest known ones, that is. They were detected due to their gravitational effect on binary companions we could more easily detect. By that token, it is quite possible there are nearer ones - it's just that detecting them directly if they don't have a binary companion is tough.
- empath75 8y ago
  Could be one on a collision course with us right now.
jvanderbot 8y ago
The author didn't mention using black holes to get around. Hyperspace might be just moving into wherever the events in the movie Event Horizon took place.
- krapp 8y ago
  Isn't Event Horizon basically just a horror movie, except the haunted house is a spaceship? If you're going to pick a fictional hyperspace "framework," there are many to choose from, all of which are equally nonsensical.

yellowapple 8y ago

I feel like whether or not there are Dyson spheres is distinct from whether or not there are sapient civilizations beyond Earth. Unless the argument is that we don't count as sapient because we don't have Dyson spheres yet? Hell, we're assuming that Dyson spheres are even possible with such a conjecture. I'm not convinced they are (not without materials that border if not cross outright into magic). It's also not certain if they're necessary to build to sustain any size of spacefaring civilization (artificial nuclear fusion would kinda defeat the point).

cletus 8y ago
Dyson spheres at some point were conflated to a structure that is a rigid shell around a star, something for which no known material would be able to support. The original idea of a Dyson sphere is now more often called a Dyson swarm to avoid this confusion. A Dyson swarm (the original Dyson sphere) is a cloud of independently orbiting habitats/bodies/structures.
- yellowapple 8y ago
  That seems like it'd be even less efficient. A "swarm" like that would be inherently reliant on maintaining orbits around the target star. In order to capture even a significant fraction of a star's energy you'll need a lot of stations orbiting that star, and they'll need to overlap (i.e shadow out stations further behind them / get shadowed out by stations further in front of them). Even if a civilization's capable of building that many stations to surround a star in a deliberate sort of Kessler syndrome, it ain't clear that a civilization would ever need to do so.

Cookingboy 8y ago

>He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. I guess the human civilization doesn't count as "sentient" because we don't have a Dyson sphere yet... Also how "unmissable" is a dyson sphere? Do we have the means to survey every single star within one billion light year radius? Hell, we know neutron stars are real, same for blackholes, but does that mean we observed every single one of them and didn't miss a single one?

sandworm101 8y ago
Dyson spoke of "swarms", not spheres. The sphere came earlier in scifi. The dyson swarm was a network of solar collectors orbiting a star, a far more practicable structure than the hollow sphere concept. We are babystepping towards this. We have probes out there blocking, harvesting, a tiny fraction of our star's energy already.

jancsika 8y ago

> He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. If a civilization has the intelligence and foresight to build a Dyson sphere, how much more intelligence and foresight does it need to hide one?

cletus 8y ago
See [1] and [2] where the idea of hiding a Dyson sphere is covered in depth. It essentially means breaking the laws of thermodynamics, specifically entropy. Hit and object with light from a star and it heats up. It radiates away that heat in a predictable way. [1] https://www.youtube.com/watch?v=QfuK8la0y6s https://www.youtube.com/watch?v=QfuK8la0y6s [2] https://www.youtube.com/watch?v=HlmKejRSVd8 https://www.youtube.com/watch?v=HlmKejRSVd8
- Sargos 8y ago
  > It radiates away that heat in a predictable way. Unless that heat energy itself is also caught and used.
  - dodobirdlord 8y ago
    That is exactly what is meant by "It essentially means breaking the laws of thermodynamics".
- ChrisFoster 8y ago
  Waste heat must be radiated away, though thermodynamics would be quite content if that radiation is anisotropic. For example, consider a perfectly insulating black box with small hole. Observers on the opposite side from the hole will not observe any radiation from the interior of the box. I don't think there's any physical limit on collimating the outgoing radiation to hide from everyone outside a narrow beam. It's "just an engineering problem".
  - deleted 8y ago
    [deleted]

cptaj 8y ago

The implications that any advanced civilization would have Dyson Spheres, that these are in any way detectable and overall that the civilization would be unwilling or incapable of hiding themselves; are entirely based on speculation as well.

rsynnott 8y ago

The assumption that anyone who can build a Dyson sphere would want to has always seemed a bit off to me. Energy use in highly developed countries is stagnating or even falling, and the rate of population growth looks set to decline. What do the hypothetical Dyson sphere builders actually want with all the energy?

cletus 8y ago
This is really the beauty of the Fermi Paradox because the issue isn't "would everyone do this?". If there are starfaring civilizations (or just civilizations with the necessary technology) within detectable range, it just takes one to go this route. Since we've been unable to detect the telltale signatures of such a megastructure, it either means that none of the civilizations within range have gone this route or there are none. Given what we know about the benefits of a Dyson swarm and how relatively low-tech it is, the idea that no one has gone that route becomes increasingly unlikely with the more civilizations there are.
- colordrops 8y ago
  How can you be so sure that a Dyson swarm is a sensible route at all given more advanced technology? We can't even figure out the sensible route for tech 5 years out.
- rsynnott 8y ago
  > Given what we know about the benefits of a Dyson swarm I think there's a real question of whether anyone would actually want one. The sun's total power output per person on earth is 5.5e+16W. That's 3000 times total human energy usage, _per person_. Even if you assume a system population in the trillions, that's still a pointlessly large amount of energy per capita (and again, current population trends don't support that, and we may reasonably assume that most Dyson sphere builders will figure out birth control). Most possible hypothetical uses for them seem to be things like converting all the mass in a solar system into a computer or similar, but again there's a real question of whether there's any market for that. I'm also not convinced we could necessarily detect one. A super-high-tech magic one would capture most of the available energy, leaving a largely invisible thing with mass, which sounds quite a lot like a neutron star. And if you had a lower-tech one that leaked most of the energy, well, that might look distinctive, but if you're throwing most of the energy away you probably don't need a complete Dyson sphere. And in any case, organised searches for Dyson spheres are pretty new, and are small efforts. We might have the data to support them right now, it's just that no-one's noticed yet...

rishav_sharan 8y ago

I really feel that no civilization would build dyson spheres. Why would anyone want to signal others, here i am?

cletus 8y ago
A topic also covered in depth: - Secret Aliens [1] - Hidden Aliens [2] Basically you can't hide from a K2 civilization in your same galaxy so there's really no point in trying. [1] https://www.youtube.com/watch?v=IpF25knrGtg&t=1657s https://www.youtube.com/watch?v=IpF25knrGtg&t=1657s [2] https://www.youtube.com/watch?v=tEBn8bc0k-I https://www.youtube.com/watch?v=tEBn8bc0k-I
- krageon 8y ago
  This reads vastly like "You can't protect from a determined nation-state actor, so why would you protect yourself at all". To me it seems obviously there is a point, namely that you will hide yourself from every non-K2 civilization.
  - chc 8y ago
    I think the assumption is that the difficulty of long-range space travel is such that only the "nation-state actors" in this analogy are likely to attack you in the first place. Just by existing in a universe with the laws of physics ours has, you're effectively secure against attack from low-tech civilizations.

raverbashing 8y ago

I'm more skeptical of the need for Dyson spheres than practicality of ftl travel

PopePompus 8y ago

> I'm not sure why the author is talking about gravity ripping you apart in a black hole. It Is Known [tm] that larger black holes have pretty gentle event horizons. But the article isn't about what happens at the event horizon. It's about what happens at the singularity, well inside of the event horizon for astrophysical black holes.

8bitsrule 8y ago

isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. It is entirely possible that advanced sentient civilizations have realized that there is such a thing as 'enough technology', learned enough to permanently liberate themselves from basic needs, and found other kinds of fulfillment and amusement.

jeletonskelly 8y ago
I think it's likely even. Look at the digital worlds we are creating in games. I find it far more likely we build a simulation more enticing than reality and find ways to leave the confines of our current reality behind. Not too different from what happens with the AI in the movie "Her".

mr_toad 8y ago

> I'm not sure why it matters that a black hole would be spinning. Because of frame dragging. https://en.wikipedia.org/wiki/Frame-dragging https://en.wikipedia.org/wiki/Frame-dragging

Illniyar 8y ago

> He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. Or that making a dyson sphere is harder than FTL, or it isn't economically viable to build one. There's no reason to assume a Dyson sphere would be a logical step after achieving FTL

pmiller2 8y ago

The rotation matters because the singularity of a rotating black hole is ring-shaped, not a point: https://en.wikipedia.org/wiki/Ring_singularity https://en.wikipedia.org/wiki/Ring_singularity

xorfish 8y ago

How is it possible to detect a dyson sphere? How easy are they to miss?

Tepix 8y ago

Perhaps these Dyson-sphere-building civilizations only live around red dwarves (because that's where they originated). Red dwarves are dim and hard to detect, especially when they are far away. A red dwarf with a dyson sphere around it would be even harder to detect.

jeletonskelly 8y ago

Does gravity propagate at the speed of light? Like, if I were to plop down a planet somewhere in the solar system, would the gravitational effects be immediate or would it take effect at the speed of light? Because if it's immediate, then we should be able to transmit information through gravity waves if we could build a device to detect subtle enough changes.

Tenoke 8y ago
Yes, gravity operates at c. There is nothing that we know of (or have a theory of) that can even in principle travel faster than c.
minkzilla 8y ago
It might interest you that a couple of years ago was the first observation of gravitational waves. Here is a BBC article https://www.bbc.com/news/science-environment-35524440 https://www.bbc.com/news/science-environment-35524440

nikofeyn 8y ago

> I'll use Isaac Arthur dismissal of FTL travel as to why what credentials does he have? > Put me firmly in the camp that believes the speed of light is a hard limit on the universe the speed of light isn't a limit in the sense that nothing can be greater than it. it is a crossover point that can't be crossed over for things above or below it to the other side. > I'm not sure why it matters that a black hole would be spinning. black holes that spin are much different than non-spinning holes and have more complicated dynamics. if they are spinning, they are dragging space-time along with them. see this paper that shows some actual visuals of what a spinning black hole might look like and what it does to the light around it. https://arxiv.org/abs/1502.03808 https://arxiv.org/abs/1502.03808