That was supposed to be 75% chance of failing the test, of course. Not that it matters much.

Correct me if I'm wrong, but from my skim through the article, it seems like he only used a single drive of each type. That makes it hard to demonstrate that the differences he saw were real, and not just random. I.e., it may be that all drives have a 75% chance of surviving the test, and that the Intel one just happened to be the lucky one. A more robust test would be to test N copies of each drive. N = 5 should give pretty good significance if this really is completely deterministic.

That paper talks about the possility that one might observe plumes, as one of several possible explanations for the terrain features seen on Europa. Actually observing such plumes is something else entirely.

How is that clear? On what do you base the claim that the odds are so good that "it's just a matter of confirming it"? I don't think you would find anybody working in that field willing to make that bold claims.

Oops, that was supposed to be "-78 C" and "2.6e-4 atmospheres".

Yes. I think you would end up with the balloon shrinking until all the CO2 has been converted into a small lump of dry ice.

I don't have statistics on this, but resubmitting after peer review is the standard way of doing things in my field (cosmology). That doesn't mean submitting the version that appears in the actual journal, with its formatting etc, but the version that passed the peer review, with all the reviewer's comments addressed.

As supporting evidence, here is the license of one of the most heavily used pieces of software in my field, camb:

Journals would not be in a position to try to fight this - nobody reads the journals, and everybody reads arXiv, so an attempt to prevent this would blow up in their face.

CO2 freezes at 78 C at a partial pressure of 1 atmosphere. That means that if the atmosphere were 100% CO2, and we were at sea level, but still at -93 C, then there would be CO2 snowing out of the atmosphere. However, the partial pressure of CO2 is much lower than 1 atmosphere simply because so little of the atmosphere is CO2. Since only 0.0397% of the air is CO2, and the local pressure (due to the high altitude) is about 0.65 atm, the partial pressure will be 2.6e-5 atmospheres. At that partial pressure the CO2 freezing temperature is less than -140 C (I couldn't find a diagram that went quite far enough down in pressure).

The physical reason for this is that there are two competing processes involved. CO2 molecules bumping into a solid speck of CO2 and getting stuck (freezing), and CO2 molecules shaking loose from a solid (sublimation). But the former process proceeds faster the more CO2 gas there is, i.e. the more often these collisions happen. Hence the dependence on the partial pressure.

The article lists Sweden among the countries where the years of health are going down, but when you look at the graph for individual countries, Sweden has a strong positive trend, and does not go down significantly in any year. Is that an error, or have I missed something?

On a side note, the article is confusing "Europe" with "The European Union". They aren't the same thing, especially when making statements like "Only the UK, Denmark and the Netherlands appear to have escaped". They didn't consider Iceland, Norway, Switzerland or any of the eastern european countries, for example. (Also, France is among those considered, and also doesn't seem to be declining).

Finally, the study is based on interview subjects' own perception of their health, and so might be affected by news reporing on health or other psychologial effects. But it is definitely an interesting result they've found.

Cosmology.

I'm doing a postdoc right now, and while I don't mind the 60 hour weeks, the uncertainty is what gets at me. After a long education one basically becomes a vagabond, drifting from university to university, never knowing where one will be working in 3 years' time. And the last year of each postdoc is spent writing applications for other places. In my home country, there are 1-2 available permanent positions every decade or so in my field, each of which typically has more than 100 applicants from all over the world. Getting one of those is pretty unlikely, to put it mildly. So I'll have to choose between permanently moving far away from friends and family, or leave my field of research. Unless I'm better than all the 100+ other applicants.

The postdoc situation is a symptom of there beeing too little resources invested in science compared to the number of people who want to do science. Instead, society is investing resources in things like moving imagniary money around really fast (yes, high frequency trading and other finance is a big employer of drop-outs from my field - they can emply more people, and pay much higher salaries, despite their detrimental effect on society). Yes, I am a bit bitter.

This blog post by the same author as what I linked to above discusses LUX directly. It seems like theories will have to be pretty contrived to reconciliate the different experiments. So I guess the detections were just systematic errors after all.

Actually, it separated the hot gas in the galaxies from the stars and dark matter in the galaxies. Stars are so small compared to the distances between them that when galaxies collide, the stars just pass right through each other. The same applies to the dark matter (because it doesn't interact electromagnetically (or it would be visible), it does not experience any significant friction force). But the diffuse, hot gas collides and gets left behind in the collision. So you end up with dark matter and stars on each side of the collision point, and a huge amount of hot gas stuck in the middle. That gas is much heavier than the stars, so without dark matter, the gravitational field should be concentrated around the gas. But instead we see it (through gravitational lensing) to be concentrated around the stars (which is where we would expect the dark matter to be as explained above).

The main lines of evidence for dark matter:

* Galactic rotation curves
* Velocity distribution in clusters of galaxies
* Gravitational lensing in general
* The Bullet Cluster in particular
* The pattern of positions of galaxies in the universe
* The pattern of Baryon-acoustic oscillations in the cosmic microwave background and in the galaxy distribution
* The primordial distribution of light elements in the universe

We know of some kinds of dark matter already: There is a huge amount of neutrinos left over from the big bang, and since these interact very weakly with other stuff, they definitely qualify as dark. Other known kinds of dark matter are black holes, and compact, cold objects made out of baryons (normal matter). So dark matter exists.

The problem is that there isn't enough of the normal kinds of dark matter. To match the pattern in the cosmic microwave background and the amount of hydrogen, helium and lithium in the universe, one needs by far most of the dark matter to be non-baryonic (i.e. not normal matter, but something like neutrinos, but heavier). This kind of dark matter is something we have to postulate exists in order to match observations. But when we do assume it exists, the theory matches observations extremely well. As an example, look at the CMB power spectrum as mesured by Planck. The error bars are so small that you mostly can't see them, and the points lie smack on top of the theory curve. But only if dark matter is included.

And it just so happens that the amount of dark matter that makes theory match the points in that graph also makes the element abundances, galaxy distribution, lensing observations and galaxy cluster velocities work too. Such a coincidence is pretty telling, I think.

But yes, people have tried to avoid dark matter by modifying gravity instead (though nowadays, the most common motivation for modifying graivty is to avoid dark energy). MOND is an example of that. MOND is like normal Newtonian gravity as long as the gravitational acceleration is large (like in the solar system), but instead of falling to arbitrarily low values as distances increase, the gravitational acceleration has an effective minimal value that it approaches as you move away. And such a constant value is just what you need to get the flat rotation curves we observe in galaxies. Which is the problem MOND was invented to solve.

MOND is an elegant solution for galaxies, but it loses all its elegance and predictive power when you try to apply it to the other areas where dark matter shows up. And in some cases it is plainly ruled out as an explanation. MOND, like Newtonian gravity, is a central force, which means that the force points towards the mass that generated it. But in the Bullet cluster, the gravitational force points towards areas with little visible matter, away from areas with much visible matter. This is impossible to fit into MOND. So the Bullet cluster basically killed MOND.

Some of MOND lives on in TeVES, which is an attempt at a relativistic version of MOND. Sadly TeVES has none of the simplicity and elegance of MOND, and while it can explain the Bullet cluster, it effectively does to by using dark matter.

So as I said: It is hard to avoid dark matter. In general there are are large numbers of theories of modified gravity, but all of them are more complicated than general relativity + dark matter, and none of them match observations any better than it.

Several different experiments have tried to measure dark matter directly in the lab, and the experimental situation is pretty confusing. This plot shows the confidence intervals and exclusion limits for various experiments (but it does not include LUX yet). The shaded regions are confidence intervals, that basically say "we've seen dark matter, and its properties lie somewhere in this region. But the dotted lines say "we haven't seen it, and if it exists, it can't lie above these lines".

What is strange, then, is that all of the detections are in regions that have been excluded by other experiements. LUX just makes the situation even more strained by pulling those upper bounds even lower. Still, those bounds and intervals depend on assumptions about the properties of dark matter, and it may be possible to reconcile the results.

It will be interesting to see what happens to those tentative detections when they get more data. My bet is that in the end some systematic effect will be found to be responsible for the apparent signal. Or (much less likely) that they were just flukes. But who knows?

Really now. And how did you arrive at it not being "a whole lot"? Let's insert some numbers, shall we? The mass of the sun is about 2e30 kg. Its Schwartzschild radius is, as you say, 2950 km. The acceleration according to Newtonian gravity at that point is 1.5211095e13 m/s^2. 1.5 meters further out (that's a short astronaut, by the way), the acceleration is 1.5195660e13 m/s^2. The difference is 2.057e10 m/s^2. I.e. roughly 2 billion g. Most of us would find it hard to stay together under such tension, but I guess you're made of stronger stuff!

(Of course, Newtonian gravity doesn't work very well for such strong gravitational fields. But it's enough to tell you that you're in a lot of trouble.)