Cosmic Horizons

A busy weekend, so here is some weekend thoughts (and associated reading) for you. It's all to do with relativity and are linked with some blog posts. Time does not flow : To paraphrase Shakespeare, All the world is a 4D manifold, and all its players are but worldlines. Basically, General Relativity tells us that the Universe is a 4D canvas and our paths are traced out. It's all there, past, present and future (from any individual's perspective). The Universe does not unfold as we progress into the future. It's all already written out (like a path on a map). Enter the philosophers and discussions on freewill, but taking relativity at face-value, there isn't any. Heck, it doesn't even tell us which direction our experience of time flows in, we set that with a decision on dt/dτ. Energy is not conserved : In general, energy is not conserved in General Relativity. This one usually freaks out the students, but it caused Einstein a whole host of headaches as well.

It's Friday, it's pouring with rain, and time for a grumpy post. The BBC is running a story Has physics become cool again? . While the overall story is good news, that the number of people people doing A-Level physics in the UK is on the way up, it also high-lights what I see as a big problem, basically the media's portrayal of physicists. Words like "nerd" and "geek" to generically describe scientists makes my blood boil, as does their portrayal as socially inadequate, Star Trek obsessed, comic-book reading dweebs. Case in point: Apparently "smart is the new sexy". And our own Beauty and the Geek had this  bunch Not to mention Nerds FC . In fact, each year we get an email circulating around our physics department that Beauty and the Geek are looking for new contestants, but from physics they are only looking for geeks, not beauties. Harmless fun you may say. But is it? We moan about falling numbers in science, and in physics, the n

Again, with teaching, PhD reviewing, public talks etc, things have been very busy, but should calm down a little in the next few weeks. So, again, a brief post this week. An as I am feeling grumpy, I'm going to comment on Is dark matter an illusion created by the gravitational polarization of the quantum vacuum? (original paper here ). We are all aware that we don't know what dark matter is, but there are a couple of things we do know; 1) we know that we need something to explain the way we observe the Universe 2) that something may be something material (like a dark matter particle, or left over black holes) or even a modification to our laws of physics, such as modified Newtonian Dynamics or (cue weird music) leaky dimensions, or other such stuff. Now, I will say this again. We know this. IMHO, most astronomers don't worry too much about this and they go with the simplest assumption, that dark matter is just that, matter which is dark. Most papers report very simpl

Well, after saying that I am not much of a star person, my article on the sizes of stars was just published in The Conversation . It's titled They might be giants: a mind-blowing sense of stellar scale and covers the size of stars from red dwarfs to hypergiants. The mini-cusps appear in the article as well :) For a quick review, I fully recommend this video on YouTube; It makes my head hurt a little every time I watch it.

Magnetars !! I'm not a star person (they are useful kinematic tracers and stellar evolution [being on the Red Giant Branch] allows us to isolate stars in specific systems), but with ARC Postdoctoral Fellow, Sean Farrell, I'm an author on a paper on the detection of candidate magnetar outside the galactic plane. The study uses mainly X-ray observations, plus a lack of an optical source (from the PAndAS survey; my contribution to the paper) to identify one of these weird objects. Basically, these are neutron stars which huge magnetic fields, and this results in some dramatic bursts of energy. Co-author, Bryan Gaensler , and I gave some talks on "Music and the Cosmos" over the last could of years, and he recounts the story of SGR 1806-20 ; and I'm surprised that more people don't really know about it. Basically, this magnetar is 50,000 light-years away, and 50,000 years ago, it had a major energy burst, releasing, in one tenth of a second, the same amount of e

PhD student, Hugh Garsden, postdoc, Nick Bate, and I just had a paper accepted for publication in MNRAS. As you can see by the title, we combine two separate astrophysical techniques to probe the inner regions of quasars, namely gravitational microlesing. I don't have much time this week (too much teaching and paperwork to do), but will expand on these in the near future. In summary, microlensing accounts for the gravitational lensing due to the myriad of compact objects, be they stars, planets or black holes, as they pass through the line of sight. Unlike the relatively boring microlensing within the galactic halo, this microlensing results on beautiful and complex magnification maps; Reverberation mapping happens when a flare from the central engine of a quasar, typically thought to be an accretion disk orbiting a supermassive black hole, propagates through surrounding clouds of high velocity material, the Broad Line Region. I pinched the below picture from Brendon Brewer'