It's like a portal to another world.

Yossarian wrote:

I hate to be a pedant here (this may not be true), but wouldn't a dyson net or ring mean that they aren't harnessing the entire power of the sun and therefore not be a type II civilisation?

acemuzzy wrote:

Harness != fully absorb, perhaps?  E.g. we hardness wind energy, but lo there's still wind.

What acemuzzy said. I mean, I wouldn't hold it against any civilisation that could "only" build a dyson ring.

Blue Swirl wrote:

Yossarian wrote:

I hate to be a pedant here (this may not be true), but wouldn't a dyson net or ring mean that they aren't harnessing the entire power of the sun and therefore not be a type II civilisation?

acemuzzy wrote:

Harness != fully absorb, perhaps?  E.g. we hardness wind energy, but lo there's still wind.

What acemuzzy said. I mean, I wouldn't hold it against any civilisation that could "only" build a dyson ring.

I would. Lazy fucks. They can't even be bothered to exist.

Cross-posted to climate thread.

Hubble finds exoplanet orbiting binary star system using relativity.

More evidence for Europa's lovely plumage.

Rosetta ends its two-year mission to study a comet by crashing into it (in scientific manner).

Trident's budget is £40bn. NASA's annual budget is $20bn. Says it all really.

Do like a bit of Tyson.

I do like Tyson's summary of the argument from ignorance, something like: "You see something in the sky, and you say 'I don't know what that is, so it must be aliens'. No, the sentence stops at 'I don't know what that is'."

Talking about little green men, turns out landing on Mars is really difficult. This is something that Elon Musk and SpaceX are going to have to consider very carefully if they want to land people without turning them into purée.

So 10x the galactic mass in the universe = possibly the missing mass everyone thought must be dark matter?

I don't know I thought we were missing 90% of the mass of the universe. Damn universe, stop losing so much weight!

The missing mass is everywhere, both local and Universal. Our own galaxy moves as if there's a halo of dark matter surrounding it (gravitational reasons). The missing mass isn't just more regular mass, it's mass that we currently can't detect because it doesn't radiate in any measurable way.

I haven't read the article but the extra galaxies don't affect anything. The reason dark matter was proposed is because the formation and movement of individual galaxies seems to indicate there's a gravitational invisible mass surrounding them. The alternative which some brave souls have proposed is that the dark matter doesn't exist and General Relatively needs tweaking (good luck with that).

Then there's dark energy which is an altogether different kettle of fish, which has been proposed to exclusively explain the accelerating expansion of spacetime and counter the effects of gravity. This isn't like pockets of dark matter surrounding galaxies and appears to be universally and evenly distributed through spacetime, possibly because it's a property if spacetime itself.

Sorry, that was a rather garbled and done on the phone in the pub thing while I was waiting for a pal to come back with the drinks so I'll clarify a little more because I love this subject, have studied cosmology to fuck, and am now sitting at home with a keyboard. 

Two different observations and two proposed but utterly unexplained solutions that cosmologists like to precede with dark, basically because they're in it.

Dark Matter

In order for all the galaxies to move and form in the way they do it seems to indicate there is an invisible mass surrounding them that nobody can see. You don't require General Relativity for this and Newton's Laws will suffice because although philisophically wrong, they make a good and practical engineering estimate when looking at the way mass moves without bothering with tensor calculations. You can land a man on the Moon using 300 yr old physics. This is the simplest solution to this particular problem - if there's a gravitationally interacting halo surrounding galaxies then this would fit the observations perfectly. The problem being that we can't see it shouldn't deflect from the simplest solution being a decent fit. You then have to explain why we can't see it so it's best to call it dark until you can figure out what the fuck it is or if it exists at all. And that's currently why the idea of dark matter exists, just for the galaxy problem (actually also there's a slight problem with gravitational lensing observations that this would help solve, and trying to model the current large scale structure of the Universe doesn't turn out right unless you add dark matter into the calculations). It has to account for 28% of the galaxy mass for it all to work out ok when doing the sums, so it's about 27% of all matter/energy in the universe when you figure in all the neutrinos and stuff that doesn't contibute much to the overall mass that is concentrated in the galaxies.

Dark Energy

An altogether different problem that has no link (well everything is linked but we needn't worry about that right now) with the movement of galaxies and is independent of dark matter theory. It's there to try and "explain" why the expansion of the Universe is accelerating. Gravitation is only attractive and any Big Bang driven expansion should be decelerating, and although that strangely doesn't mean that expansion won't stop at infinity, it means it should slow down. Recent observations have demonstrably shown that the expansion is accelerating. This is a problem but not one that hadn't been addressed half a century earlier by Einstein when he proposed the Gravitational Constant. 

When Einstein unleashed GR on the world the implications of it were not properly understood, least of all by Einstein. Black holes and an expanding Universe came a bit later when the scientific community had got to grips with it. Einstein was appalled by the idea his own theory laid out - that the Universe had to be expanding or contracting. For reasons we'll attribute to being a human he believed the Universe was static and unchanging, and that did not at all fit with his astonishingly brilliant update on the theory of gravity. 

So he proposed The Cosmological Constant. This was a constant that had some value, any value, that checked any expansion or shrinkage of the Universe without having to modify his new theory of gravity. THE UNIVERSE MUST BE STATIC! 

Anyhow, although he was wrong (hindsight is a wonderful thing) he did at least have the scientific understanding to envisage that such a constant could exist, even though his personal reasons were bollocks. That idea, that there is a cosmological constant associated with spacetime that negates the effects of gravity have now morphed into the idea of dark energy. Now it's not used to explain stasis but has been attributed to the acceleration. Even when he was wrong he was sort of right. 

Now dark energy is an all pervasive thing only exists to explain an accelerating Universe and it's perhaps easy to take Einstein's view that it's a universal property of space and time. It could account for something like 69% of the total energy of the Universe because although it's slight in density, unlike gravity mass that clumps together this is an intrinsic property of all of space, and there's a lot of space compared to mass cluster. 

Add dark energy (68%) and dark matter (27%) and that's where the figure of 95% comes from. I wouldn't take such a percentage as a fact but it certainly amounts to 95% of theory that nobody has a clue about. Not the most scientific percentage I've ever seen.

Edit: My drunken bad. It's not 28% of total galaxy mass, it's 28% of the total energy mass in the Universe. There's also 5% normal stuff.