Dark matter isn't a case of "fact vs. theory", but "fact vs. fact". We have multiple methods of determining the mass of galaxies and galaxy clusters. One method - counting all the light-emitting stuff - gives a certain number, and all other methods (rotation curves, gas kinematics, gravitational lensing, large-scale structure analysis, and more) give a much higher number. Two possible conclusions: 1) Our understanding of gravity is wrong, or 2) There is a new component of the universe that does not interact with light. Option 1) fails a lot of tests: if you try to make solutions for gravity for certain systems, it doesn't work for others. Option 2) has a solution called "dark matter", a new weakly-interacting massive particle that explains almost all the observations (it's not 100% perfect, but it does much better than the changing-gravity option).

At the same time that all this was happening in cosmology, our particle physics friends were developing extensions to the Standard Model. In many theories they predicted new kinds of particle: ones that just happened to have a lot of the right kind of properties that the cosmologists needed for dark matter. Voila.

Dark matter is the simplest, most parsimonious, most elegant known solution that fits the observational data.

Source: I'm an astrophysicist and I do a podcast, and one of my first episodes was on exactly this.

Yes, we do have motion relative to the CMB, and this causes one side of the CMB sky to appear hotter than the other. Here's an APOD describing it. So everything discussed in the article already happens to us, here on Earth, but in a much less significant way.

Yes, this is how we work :)

I've heard it joked that this is the difference between astronomers and physicists. Astronomers put the observer at the 0-point of the coordinate system, hence larger redshifts are further away. On the other hand, physicists put the 0-point at the "beginning" of the universe: the initial conditions, and mark time after that.

The universe is full of voids - large regions of space empty of matter. Ever since the detection of the Cold Spot, it's been speculated that a "supervoid" could be responsible, but it was thought that a void that large would not fit current understandings of structure formation - essentially trading a too-cold spot in the CMB for a too-big hole in the matter distribution.

But this work, which was made public a year ago and just now got through the referee process, showed that there *is* a supervoid in the direction of the Cold Spot. They found it by looking at the distribution of galaxies in that direction. It turns out that it is a big void, but not very empty; more like a wide shallow dish than a small deep bowl. This can both explain the Cold Spot and be compatible with our understanding of how structure forms.

From a blog by a colleague of mine on the subject: "Questions that p-values can answer" != "Interesting questions about the world'.

Contrary to the summary, this is one of the expected properties of Dark Matter. The leading candidate that answers the dark matter observation problem (which is already well-described by buchner.johannes above) is a new kind of particle, known as a WIMP, for Weakly Interacting Massive Particle. "Weakly" doesn't just mean "not strongly", it means "through the weak force". It's postulated that this new kind of particle, predicted by various extensions to the Standard Model of particle physics, interacts with itself through the weak nuclear force.

What we don't know very well is how efficiently this interaction takes place. Ways to measure this (and hence detect WIMP dark matter) include:

1) Direct detection: Wait for a stray WIMP to hit a block of stuff and detect a flash/vibration/decay product/whatever. Many experiments. Status: ongoing.

2) Production: Make some WIMPs in a particle collider. Status: check with LHC in a few months.

3) Indirect: The weak nuclear interaction produces some by-products, like neutrinos and gamma rays. Thus if you look at a spot where there ought to be lots of dark matter (like the center of the galaxy), you might see some extra gamma rays. The Fermi-LAT satellite is doing exactly this. Status: ongoing.

4) Behavior: The interaction will "slow down" the movement of WIMPs by introducing a little bit of drag. This would be a much much weaker version of what happens to normal matter when clouds of gas run into each other. Using gravitational lensing we can probe the mass distribution and look for such drag effects. That's what this article is addressing.

Whoever is the first to confirm the existence of dark matter (whether WIMP or otherwise) is pretty much guaranteed a Nobel, so the race is on.

If we still don't find anything in ~10 years, then we probably need to go back to the whiteboard and figure out something else.

Shameless self-plug: I'm going to discuss this more in an upcoming episode of my podcast.

*If* this result holds up, it doesn't sink dark energy - it will only be a small correction to the measured value using this particular probe. We have multiple, independent measurements of the existence of dark energy, from the early-universe Cosmic Microwave Background, to the late-universe feature in the galaxy distribution called the Baryon Acoustic Oscillation. In fact, for quite a few years supernova haven't been the principle method of measuring dark energy, because we've suspected issues such as this.

*If* this result hold up, and corrected measurements of dark energy from supernovae are in tension is all other measurements, then that will be interesting and require further study. However, despite having the confirmation of the existence of dark energy for several years, we haven't measured its exact properties very well yet. These corrections will probably shift things around inside known error bars.

For all the aether-claimers: we don't know what dark energy is. We've observed an acceleration to the expansion of the universe and called it "dark energy". This is a name given to an observed phenomena. The Nobel Prize was awarded to the original supernovae groups because it has been *repeatedly, independently* verified, using completely different sets of cosmological probes. This is like observing and measuring the observational reality of gravity without having a theory to explain it, but that doesn't mean that gravity doesn't exist.

As a scientist, I can breathe a sigh of relief: I can finally go back to not double-chorking my results!

It would be great if this *wasn't* the Higgs, because then we would have some clue how to move past the Standard Model. It sucks when nature agrees with your predictions.