bluesam3 t1_jeab7wk wrote

Not an astophysicist, but I can give a lower bound: the lower limit limit on beam divergence angle is (wavelength) / (𝜋 × (initial diameter)). Wikipedia suggests a source diameter of ~60,000 km, and the peak photon energy for the event was 18 TeV, which translates to a wavelength of about 7×10^(-20)m, putting the lower limit on divergence (for a perfect laser) at 7×10^(-20)/(𝜋 × 60000000) = 372 nanoradians, which gives a final radius at that range of 60000km + 2 × sin(372 nanoradians) × (2.4 billion light years), which works out to somewhere in the region of 1,800 light years. This beam was presumably a very long way away from being a perfect laser, and most of the particles will have had lower energies, so that's probably an order of magnitude or several too low. However you slice it, though, that's a pretty wide end target, so it's probably more accurate to say it hit our vague region of the galaxy, rather than that it hit Earth. Certainly it wasn't at risk of hitting the wrong bit of the solar system.


bluesam3 t1_je6cva8 wrote

No, you can have it in datasets of any size. If X causes Y, but also it just happens that in your dataset there's some other factor Z that causes (not Y) and happens to correlate strongly with X (in your dataset). For example, if exposure to some substance causes cancer, but people who are exposed to that substance tend to be exposed to vast quantities of it that kill them immediately (thereby preventing the vast majority of them from living long enough to develop cancer), you'd have a definite causation, but no (or even a reversed) correlation.


bluesam3 t1_jdsjib5 wrote

  1. Because most teenagers and young adults are involved in romantic relationships at some point in that period, and also are interested in reading about them.
  2. Because it's easy to write.
  3. You've written exactly the reason.

bluesam3 t1_jb1v0ev wrote

It's something of a misnomer: it's not the rest frame of the radiation itself, but the rest frame in which the CMB appears the same in all directions: in most rest frames, you'll see it redshifted in one direction, and blueshifted in the other (this is what this looks like for us, for example: the overall hot/cold spots (NB: on this diagram, red is blue-shifted and blue is red-shifted, because humans like red to be hot, even though blue is hotter) are due to our velocity reshifting it, the funky lumps are local effects. If you adjust that to account for shifting the velocity of the observer, you can get it to the point at which that looks almost exactly flat (this famous image scales up the differences by orders of magnitude in comparison to the previous one - actual differences are on the order of one part in 100,000). The reference frame where that image is flattest (modulo a few adjustments for local effects) is the CMB reference frame.


bluesam3 t1_j1b6pb7 wrote

It's very climate-dependent - the colder the outside is, the less efficient air-source heat pumps tend to be (partly due to inherent reasons, and partly due to having to do work to defrost the outside unit) - if you're somewhere with relatively mild winters, COPs above 3.0 are very achievable with domestic units. If you live somewhere with extremely cold winters, it's much less achievable.


bluesam3 t1_ivqbhwg wrote

Interestingly, in England it seems to be high in rural areas in the South, and urban areas in the North, and the opposite in Wales. I wonder why that is?

Also, I'm liking the identification of all of Scotland as Glasgow.