Thanks for the video! I think the above was not denying the need for some explanation, just that the explanation may not be "dark matter" as currently thought of.

I believe so, but in a very modest way.

This "phenomenon", & associated observations may remain little more than conjecture for some time. I just love the quest more than anything!

'Course, all that undiscovered (non-exotic) matter might be there but simply unseen by us - in the form of numerous stars completely enclosed within Dyson spheres by an alien race

@Jnei I think Isaac Arthur discusses that in one of his Fermi Paradox videos on youtube.

@Jnei They'd not only have to build the spheres (a non-trivial task), they'd have to create the extra matter to build them with.

@Coffeo They'd only have to create the matter if they weren't able to harvest it, perhaps using materials that had previously been part of planets surrounding the star. As you say, though, no trivial matter.

@Jnei Again, Issac Arthur has a youtube video, "Starlifting." We cannot create matter, but there is plenty in the Solar system. The Sun, one day, will grow large enough to consume Mercury, Venus, and Earth, so why not use them, except Earth. Anyway, heat would escape from the Dyson (Swarm) a sphere would be very difficult. That heat can be seen across vast distances with an infra red telescope, like James Webb space telescope.

@EdEarl "We cannot create matter, but there is plenty in the Solar system" - exactly. "...heat would escape from the Dyson (Swarm) a sphere would be very difficult" - both would be phenomenally difficult; impossible with our current technology. However, for the fantastically advanced alien race in this hypothetical situation, perhaps using self-replicating machines that mine the inner planets to create more machines that eventually form the sphere or swarm, it might be possible.

@Jnei I think we could start on the swam very soon, using a large iron based asteroid for raw materials. Robot technology needs to be improved, or the BFR (SpaceX rocket that will be able to put 100 people anywhere in the Solar system.) Hiding the exhaust heat would be impossible.

Good discussion on this, guys! This is always what I hope for when I post these!

@EdEarl Agreed on the swarm - that sort of thing, obviously on a far more limited scale at first, probably isn't too far off in my estimation.

You're right in that hiding the exhaust heat from something like the BFR would be difficult; however, it wouldn't necessarily be the case that our alien race would need such a rocket to create their Dyson sphere - it'd be far more simple (and, if they still have money, a hell of a lot cheaper) for them to build the first robot, give it the material it needs to self-replicate and build a few back-up copies of itself, then send them off on their way to the iron-rich asteroid to get on with the real business of building trillions more copies (it's going to need to be either a very big asteroid or they'll need to use several - the sphere, even if technology allows it to be very thin, is obviously going use up a lot of material). Then, the robots travel to the star and take up their positions, joining together to create the sphere. Since they're already in space they don't need to produce as much power as the BFR because they don't need to escape the alien's planet's atmosphere; each robot's heat signature is therefore low and only a percentage of them would be travelling to the star at any one time while others remain longer at the asteroid (you can't have them all hanging around because the asteroid would be swamped before too long), making it more difficult for them to be detected from a distance.

That's assuming that such a Dyson sphere is being constructed at the time anyone searching for evidence that such a thing exists is even there to look, of course - perhaps the reason we can't see any being built is that those aliens have been advanced for a very long time (and might even now be extinct) and they built their spheres millions of years ago.

@Jnei A Dyson swarm or sphere will emit waste heat that can be seen across the Universe. There is no point in trying to hide the heat of rockets. For any observer aliens, the Sun floods their telescopes with heat and light that makes most things invisible from such distances. In a few years the Thirty Meter Telescope will see first light, and it will be able to see some exoplanets. To see something as small as the BFR would require a much larger telescope, maybe 300 meters IDK how big.

@EdEarl If a Dyson sphere, ring or swarm collects energy from one star, it would not "emit waste heat that can be seen across the Universe" - any energy it emits would be a percentage of that released by the star, reducing its "signature" and making it harder to detect.

A sphere could theoretically harness very near to a star's entire energy output, thus making the amount of waste heat miniscule (after all, if you're going to all the effort of building one - even if it's just a matter of building a couple of robots and waiting for them to do the rest, you obviously require a vast amount of energy and you're going to want it to be as efficient as possible).

"There is no point in trying to hide the heat of rockets" - indeed; I can't think of any reason our aliens would want to do so.

@Jnei I'm sorry, but you are mistaken. It is not possible to use up energy; though, black holes turn it into mass (E-mc2), and there are some other ways to make mass from energy. But, none we can use to consume the Sun's energy. Thus, all of that energy will be emitted into the Universe. Even black holes emit energy Hawking radiation, and eventually evaporate. High energy light, ultraviolet and visible light, turn into infra red light (low energy withing the Dyson sphere, and 100% is then radiated into space. There will be more photons of infrared than visible and ultraviolet, so the energy radiated equals the energy absorbed. I'll not post again about this, because I don't want a flame war.

@EdEarl The Dyson sphere, ring, swarm or net isn't intended to somehow "destroy" energy (which is indeed not possible), but to gather it so that whoever constructed it can put it to use - rather like a solar panel gathers solar energy to power a calculator, but on a much larger scale. Therefore, a sphere completely enclosing a star would gathers that energy which is then transported to wherever it's needed, rather like electricity from a solar "farm" being transferred into the grid so that it can be used in homes and workplaces.

Some of the star's energy will, of course, escape, unless the aliens can make it 100% efficient. However, the amount of the star's energy directly reaching objects outside the Dyson structure will be reduced to at least some extent (more for a sphere because it completely encloses the star) because some of it is being "drawn off".

PS: you won't get any flame wars from me. I've never been involved in one, and this is a discussion rather than an argument.

@Jnei OK no flames Energy collected in a solar panel is used elsewhere, for example to run a motor or provide light. In every case, that energy turns into heat and is radiated away from where it is used into space. It cannot be avoided. Technology cannot be developed to do what you say. You are telling me something physicists agree is impossible. Now I'm quitting because it is pointless to repeat myself. You can have the last word.

@EdEarl Yes, of course that energy will ultimately be radiated into space, just as all energy will be; I didn't at any point say that the energy collected by a Dyson structure would be destroyed or would otherwise somehow vanish, merely that it would be collected by such a structure which, by converting that energy into another form so that it can be used elsewhere, would affect the amount of energy detected to be coming from the star. The technology to do such a thing in theory already exists, but not the technology to do it on Dyson structure scale.

@Jnei Yes but if the matter was there already, how would Dyson spheres help to explain dark matter?

@Coffeo That's not exactly what I originally posted. What I was (not very seriously) suggesting was that the missing mass in the universe might not be dark matter we haven't observed yet but stars hidden from view within Dyson spheres.

@Jnei Ah. Gosh.

@Coffeo Like I say, not seriously. Intended only as an amusing aside.

@Jnei Understood. Dyson spheres are interesting to think about, though, quite aside from whether or not they account for dark matter. The land area! The material strength needed to support the polar caps! Do you read SF? Do you know of any hard SF that uses the idea? (I know about Larry Niven's Ringworld series but that is a bit different.)

@Coffeo Indeed; they're a fascinating thought experiment. I do read SF, especially favouring hard SF (and especially Stephen Baxter), but off the top of my head I can't think of an example that uses Dyson structures. I seem to recall a habitat created from numerous nested spheres in one of Iain M. Banks' stories, but IIRC that wasn't a Dyson sphere.

@Jnei Perhaps Matrioshka Brains

@EdEarl Now you mention it, it may have been a matrioshka brain that'd been decommissioned and coverted into a habitat - if I could remember the name of the story (and even if it was in fact Banks) I'd look it up and find out!

That's science, it's all about the questions & when we do learn something we also usually come up with even more questions!

@phxbillcee yes. The complete opposite of the religious mindset. I suppose that's why it's such a struggle for some people to convert. Never any concrete,final "answers".

@Blindbird See my post 'Philosophical Failures of Christian Apologetics, Part 5: Cognitive Closure', it does a good job on this point.

@phxbillcee off I go

@phxbillcee , you didn't say me, but I'm kibitzing too!

@njoy_life_2 That's why its posted!