The ‘Dyson Sphere’ mystery deepens: Star keeps dimming
wired.co.uk
wired.co.uk
In this series he details several hypotheses and ranks them.
http://sites.psu.edu/astrowright/2016/09/03/what-could-be-go...
Initial guide here:
> Importantly, researchers have concluded that a thin accretion disk around a rotating black hole is the most efficient power source in the universe , a process up to ~50 times more efficient than nuclear fusion occurring in stars (e.g. Thorne 1974; Narayan and Quataert 2005). If any civilization is to climb the Kardashev scale, it would certainly at some point want to master that energetic source. We call such an endeavor black hole star lifting
Instead of a Dyson sphere, you're using a black hole (and apparent mastery of gravity) to leech energy directly from the sun.
Similarly, the heat would still escape from them. Could that explain the CMB?
(I expect that I'm way off the mark, but if nothing else it could make for an interesting premise for some sci-fi.)
No - MACHOs have been pretty well ruled out by now. "Several groups have searched for MACHOs by searching for the microlensing amplification of light. These groups have ruled out dark matter being explained by MACHOs with mass in the range 1×10−8 solar masses (0.3 lunar masses) to 100 solar masses" (https://en.wikipedia.org/wiki/Massive_compact_halo_object)
> Similarly, the heat would still escape from them. Could that explain the CMB?
The CMB comes from everywhere at once, uniformly, all the dark spaces in between stars is glowing. Dyson spheres radiating heat would just look like a bunch of dots glowing in the infrared. I don't see how any number of Dyson spheres radiating heat could produce a continuous, uniform field.
Thanks for the awesome response.
All the energy the star produces has to escape into space somehow. The way it does this is by heating up the sphere until it radiates out into space at the same rate at which the star irradiates the sphere. The bigger the sphere, the cooler it is, because it has more surface area to radiate away heat.
So if your sphere is too small, it may end up glowing at red heat, which might make it difficult to live on.
Calculating the temperature is straightforward:
If you can imagine some alien species building a mega structure in such a short time, you should be able to imagine that they have a way to transfer and store that amount of energy.
The laws of thermodynamics, as we know it, prevents 100% efficiency in doing that, but if they have a directional heat dissipation device, and their generator is highly efficient, we will hardly have any chance to detect that.
I can imagine they could have some version of our power plant, only orders of magnitude more advanced. Instead of moving electrons, they could be generating and moving matter anti-matter stuffs.
If we wanted to be 'found' by aliens, we should do this to our sun.
If there are other advanced societies out there I seriously doubt war is their main motivator in space exploration, the same way Voyager and Curiosity are unarmed. Sure, that makes for fun sci-fi stories, but real life is governed by fairly simplistic game theory rules, at least from a high-level perspective. The motivators we have been given through evolution will be the motivators they have as well. Unless we're dismissing evolution as only a local phenomenon, we should expect similar beings to ourselves. I think the 'hostile alien' scenario shouldn't be our default. Sadly, that approach sells ad impressions and schlocky futurist books and influences a lot of people to believe things that are pretty questionable.
If we discovered a primitive species in the European seas we'd be tripping over ourselves to preserve them and study them and to make sure they never, ever get hurt by us (or a stray asteroid or anything we could prevent). We wouldn't be conquering them with robot subs for their pretty coral jewellery or sub-surface oil or whatever. We have enough pretty things and energy here on Earth and in unihabited places if need be. Life is rare enough that we don't need to attack other life for resources, assuming we ever find any.
Arguably, if your species is mind-mindbogglingly stupid enough to declare war constantly and against the basic rules of game-theory then I doubt your society will survive the nuclear weapons stage anyway and won't ever be in the stars. The nice thing about the Drake equation is that it suggests that Klingon-esque societies don't make it to the space-faring stage, which is nice.
They are products of evolution and, in theory, we'll be very alike in many ways.
But then, maybe a species able to colonize a galaxy can only appear as consequence of those rare exceptions. We, as a not completely selfish species are evidence for that.
Humanity still very much depends on various resources today: fossil fuels, uranium, metals, fish stocks, etc. So wars over resources still very much exist. The sense of "duty to civilize the inferior races" is also alive and maybe even stronger than ever, though expressed with less offensive words.
I would expect a civilization sufficiently advanced to build a Dyson sphere to have reached some sort of sustainability with regard to resources. But what about ideology? What if they deem us barbarians that need to be civilized?
[1] I'm French, hence the "we".
[2] In Jules Ferry speech before the French Chamber of Deputies: http://sourcebooks.fordham.edu/halsall/mod/1884ferry.asp
Once you are post-scarcity, this kind of propaganda will be much less effective. It'll be more obvious its bullshit.
Probably not. There's around a billion stars in the Milky Way galaxy alone, and even more in nearby Andromeda. If some civilization has the technology to travel to our system (which is likely tens of light-years away if not much farther), then it'll also have the tech to go to many, many, many other systems other than ours, which also have habitable-zone planets, and are probably more conveniently-located.
The only real exception is if there's a race that's not all that advanced, and is located very, very close to us, such as in the Alpha Centauri system, 4ly away, so that we're just close enough to make travel here feasible for them, but other habitable-zone planets are significantly farther so that it makes more sense for them to attack us rather than just find someplace else.
But as we're already figuring out now, a mere 4ly is already a really, really long distance with our technology. Our longest-range probes have only gone a small fraction of that distance, and they've just about left the system. It'll be tens of thousands of years for them to go that distance at their current speed. So traveling that distance is already rather unimaginable for us without something like a generation ship or cryo-storage ("suspended animation"), and when you have that, why bother fighting a war if you can just continue on?
Finally, if you have the technology to build a generation ship that can work reliably for 10,000+ years supporting life, you probably have the technology to mine asteroids, build habitats on the Moon and Mars, build large habitats with artificial gravity (by spinning) in Lagrangian points, etc. In short, you already have the technology to make habitats perfectly suited for your species, and there's a whole solar system full of building materials at your disposal. If you have that, why would you want to travel such a long distance just so you can steal a planet from some other race, when it's very unlikely that planet will even be suitable for your biology without significant terraforming?
In a nutshell, the problem with this kind of thinking, and a lot of sci-fi in general, is that it assumes that interstellar space travel is much cheaper and easier than artificial habitat construction, when in fact the reverse is true. This is not to say that artificial habitat construction is that easy either; we still haven't perfected that for really long-term applications. But interstellar travel is really, really hard.
Now, of course, it is possible that we've completely overlooked some fundamental physics and it's actually not that hard to travel light-years very quickly; this would change the equation entirely. There's a Neal Stephenson short story about this, where some warlike and somewhat primitive aliens attack Earth, and are easily defeated by our far-superior weaponry (they basically had 19th-century cannon technology). So the humans get their technology and figure out that faster-than-light travel is actually really easy, we had just overlooked something simple all this time; at the end, the aliens are crying about what they've done, because then the humans set out to become galactic conquerors.
Is that maybe The Road Not Taken by Harry Turtledove?
I don't think there's ever going to be a point when a race has "enough" and doesn't want to explore or build any more. Our ambition should grow with our capabilities. Once you can control a star, why not work on a galaxy?
Every outpost of the empire will essentially have unlimited manufacturing capability and it will take decades to project force, decades the outpost can spend making sure the amount of matter they have devoted to war exceeds the tiny amount of war matter the central empire threw out into space.
The big idea of the book is that Einstein isn't wrong about C being the speed limit. Therefore, to be a starfaring race requires the ability to make commitments and hold to them over extremely long timespans. The connection to game theory is that, as in the Prisoner's Dilemma, the only way you can really make predictably right decisions in cooperation with other entities is if your decision-making formulas are spelled out mathematically in advance; so all can predict how you will act. The first book begins with mankind discovering the galaxy's "rules" on a kind of signpost at a nearby star.
Read the books!
My point is that the very concept of an interstellar resource war, and thus the concept of interstellar control, is incoherent given our present physics. You can take over a system that isn't technologically enabled, but that's it, the resources available to a technologically enabled system are greater than the resources that can be sent into the system.
So it's certainly feasible for an advanced race to build a star empire; the question is why they'd want to do it. If we're talking about humans you might say ambition or imagination. If Vulcans, maybe they'd think it logical to pre-emptively become stronger than any potential aggressors.
You could slam a bunch of mass into a system at extreme speeds, but then they just have to hop into life boats until the storm ends (if they have the capacity to ponder traveling the stars, they have the capacity to spend a decade on a space station).
For aliens. Just like we make traps for birds, so we can tag and study them.
https://en.wikipedia.org/wiki/The_Killing_Star
Warning: the "Plot Threads" section has spoilers.
That's a "current thinking" issue. Prior to industrialization, humanity (statistically per capita) didn't care about preservation. In search or resources you get marginalized conservation thinking. Never-ever is a fantasy, because over a long enough period of time every priority can and will change.
To anyone not getting the reference, read Pandora's Star by Peter Hamilton[1]. It's a lovely read.
Start with Cordelia's Honor https://www.amazon.com/-/dp/0671578286
Edit: various books from the series won 4 Hugo awards, 2 Nebula awards, and were nominated a dozen of times.
Also, be extra careful as the first book ends in a cliffhanger (literally), so be prepared to read the two huge books in one go (not that you'd be able to stop anyways)
The problem then is getting that energy out. I'd use lasers from my panels to my planet. That means my solar panel collective in orbit around the star will have to always point to my planet for maximum efficiency so I don't have useless panels since there's no way i'm building a battery at star energy scale on each panel.
The dimming you see would then be based on the orbit time of my planet around the star, since the panel half halo will always be pointing at my planet. Essentially geostationary around the star.
If it's outside, you might get complaints about the shutting off of the day/night cycle.
If it's inside, you get all the sun's light reflected off the inside of the sphere. Kinda blinding.
But by the time you're building a Dyson Sphere, the vast majority of the people are probably already living in space habitats. There's not much use for stellar-scale energy if everybody still fits on a single planet.
Don't click on that if you have stuff to do today.
Even a few billion miles is still inside the solar system. Pluto is about 4 billion miles away.
It's difficult for something to stay between the Earth and a star and be nearby. The Earth moves around the Sun - this provides a baseline to measure stellar parallax, https://en.wikipedia.org/wiki/Stellar_parallax - and anything close to the Sun is also affected by it gravity. That "close" includes regions well beyond Pluto.
"Occultations" are when one object blocks another. For example, detailed observations of when Pluto went by a star gave us clues that Pluto has a very thin atmosphere. Asteroids also cause occultations, see https://en.wikipedia.org/wiki/Occultation#Occultations_by_as... . They can be used to figure out the size of an object. That page shows an depiction of a occultation by Makemake, which is 50 AU out (further out than Pluto). Its shadow is on the Earth for only a few minutes, and it's over 1400km across.
In the lab under ideal conditions with ideal light sources, it's pretty common for there to be >2.5% error in these types of measurements. For those used to dB unit, this is a ~0.1dB change. In optics, it's very easy to introduce error at this level.
I have a hard time thinking that any intelligent life we were to encounter would be on "our scale", in either direction. They would likely be vastly superior or vastly inferior. Think "they are ants, we are human" or worse "we are ants, they are human".
(I still think that Dyson spheres are an idiotic thing to build. If you're worried about getting energy for your civilization, and you can do stellar-scale engineering, there are better things to do with a star's mass than let it waste its fuel in a big, uncontrolled trash fire, collecting it with solar cells or whatever).
Smaller stars burn fuel more efficiently. Our sun is good for about 4-6 billion years; a much smaller star will last several trillion years.
Both are equally likely :-)