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...