Cosmic Horizons

Very quick post today, but an article on our warp drive paper has been published in The Conversation . It's called " Warp drives and reality: new hope for a Galactic Empire? " Here's a taster: Fans of science fiction must be disheartened when introduced to Einstein’s Special Theory of Relativity . Dreams of galactic empires , criss-crossed by roguish princesses and beautiful smugglers, go out the window with one simple rule: “thou shalt not travel faster than the speed of light”. Even a rocket ship travelling just under the speed of light (roughly 1 billion km/h) would take more than 100,000 years to get from one side of the Milky Way to the other. That’s slightly longer than the fraction of a second required to traverse galaxies in science fiction staples such as Star Wars.

Event Horizon was a somewhat dodgy sci-fi-horror movie that came out in the late 1990s. As the title suggests, associated with an Event Horizon is "Infinite Space, Infinite Terror". Luckily, the Event Horizon in the film as a black hole Event Horizon, and I'll leave discussing those to another time. Today, we'll try and understand the Cosmological Event Horizons. To explain these, I am shamelessly going to use the (still) excellent cosmological figures produced by Tamara Davis . OK, let's start with this one. To understand what this picture is telling us, we need to remember a few things. Our universe has three spatial dimensions, and any spatial point can be labelled with three numbers. In a Cartesian coordinate system , these are (x,y,z). As we are dealing with relativity, we are dealing with not only space, but space-time, and every point in the universe is labelled by 4 numbers, the three spatial coordinates and the time, t. So, every point is labelled...

Well, this caps of a busy, but successful week, but Pim van Oirschot (PhD student in the Netherlands, was my MSc student here in Australia a couple of years ago) and I just had a paper accepted for publication. It's called  "How does the Hubble Sphere limit our view of the Universe?" and is basically a response to some other papers published over the last years. Let's start with the basics, as in what is the Hubble Sphere? For gory details, I recommend the classic paper by  Ed Harrison , but simply put, the Hubble Sphere is the distance from us which objects are moving (relative to us) at the speed of light. We know the Universe is expanding, and that expansion is measured in terms of the  Hubble Constant , which is about 72 km/s/Mpc. What this means is objects 1Mpc away are moving away from us at 72km/s, those at 10Mpc are moving at 720km/s, 100Mpc at  7200km/s etc etc. So, if you go far enough, objects will be traveling at the speed of light, and then even fur...

I think I am over the yearly battering with Australian Research Council Discovery Grants with the grant now submitted. The release is matched with the acceptance of a paper from left-field, and so, to quote Monte Python, "And now for something completely different ". Last year, Brendan McMonigal was an honours student with me, and we took a look at the Alcubierre warp drive , a method to travel globally faster than the speed of light, while being quite happy with Einstein's General Theory of Relativity. This stuff often freaks people out, because they get special relativity beaten into them first, without realizing what this actually means in terms of general relativity. Whatever other people think, I love General Relativity. What you can do with the universe is actually pretty cool. So, the warp drive, in hand waving terms, travels at arbitrary speed by messing about with space-time. But what Brendan looked at it the question of what happens to all those particl...

I am slowly recovering from the recent round of grant writing. The internal deadline for our Australian Research Council (ARC) Discovery Projects (DPs) was on Monday, and, as ever, it was late nights and early mornings to put together the 115 pages of science case, budgets, budget justifications, publication records, career histories etc etc etc. Now all I have to do is sit back until July (when the referees' reports come in) and then to November (when the results are announced). If I get my grant, I'll write and say how great the systems is. However, if I am the three in four who will not get funded, I'll have a rant. Anyway, even though the days have been lost to grant writing, science has advanced, and we recently had a paper accepted for publication in MNRAS, using the Hubble Space Telescope to look at clusters around our nearest big galactic neighbour, Andromeda. Many objects are globular clusters, just like the ones we orbiting our own Milky Way. With Hubble Spac...

Not everything that can be counted counts, and not everything that counts can be counted. Albert Einstein , (attributed) I don't know how widely it is known outside academic circles, but researchers these days are surveyed and counted continuously, in an effort to show that tax-payers money is being spent on research excellence and research impact. A number of countries have held such exercises, and here we are into the second round of the  Excellence in Research for Australia . Such exercises have real impact, as some at  The University of Sydney just found out; those not producing enough "research outputs" are in the firing-line for redundancies. With the growth of online databases of papers and citations, it's now easy to get an assessment of someones research output, and with things like Google Scholar it's all nicely displayed; here's mine. People's careers get wrapped into a few metric, and the principle one is the h-index . The idea i...

Back in Oz after a week in the US at the University of California at Santa Barbara (UCSB) . I was at a conference called First Galaxies and Faint Dwarfs at the Kavli Institute of Theoretical Physics . The week started with us being told that this was going to be the best conference we would ever attend, and I must agree that it was. Instead of the usual barrage of 15min talks, we had 40mins of review talks, with discussion sessions, and it was great. What was the point of the meeting? Well, that was summarized by the opening slide by Leon Koopmans ; Essentially, the goal was to bring together two communities, those that study the high redshift universe and the first forming galaxies, and those that look at the tiny dwarf galaxies in our local universe. Why? Because understanding galaxy formation and the links between the nearby and faraway will reveal the inner workings of the universe, especially the nature of dark matter. I'm not going to go through the conference in d...