Cosmic Horizons

Everyone loves black holes. Immense gravity, a one-way space-time membrane, the possibility of links to other universes. All lovely stuff. A little trawl of the internets reveals an awful lot of web pages discussing black holes, and discussions about spaghettification, firewalls, lost information, and many other things. Actually, a lot of the stuff out there on the web is nonsense, hand-waving, partly informed guesswork. And one of the questions that gets asked is "What would you see looking out into the universe?" Some (incorrectly) say that you would never cross the event horizon, a significant mis-understanding of the coordinates of relativity. Other (incorrectly) conclude from this that you actually see the entire future history of the universe play out in front of your eyes. What we have to remember, of course, is that relativity is a mathematical theory, and instead of hand waving, we can use mathematics to work out what we will see. And that's what I did. ...

So, my plans for my blog through 2017 have not quite gone to plan, but things have been horrendously busy, and it seems like the rest of the year is likely to continue this way. But I did get a chance to do some recreational mathematics, spurred on my a story in the news. It's to do with a problem presented at the  2017 Raytheon MATHCOUNTS® National Competition  and reported in the  New York Times.  Here's the question as presented in the press: Kudos to 13 year old Texan, Luke Robitialle, who got this right. With a little thought, you should be able to realise that the answer is 25. For any particular chick, there are four potential out comes, each with equal probability. Either the chick is pecked from the left pecked from the right pecked from left and right not pecked at all Only one of these options results in the chick being unpecked, and so the expected number of chicks unpecked in a circle of 100 is one quarter of this number, or 25. AB...

I hate starting every blog post with an apology as I have been busy, but I have. But I have. Teaching  Electromagnetism  to our first year class, computational physics using  MatLab , and six smart  talented students  to wrangle, takes up a lot of time. But I continue to try and learn a new thing every day! And so here's a short summary of what I've been doing recently. There's no secret I love maths. I'm not skilled enough to be a mathematician, but I am an avid user. One of the things I love about maths is its shock value. What, I hear you say, shock? Yes, shock. I remember when I discovered that  trigonometric functions  can be written as infinite series, and finding you can calculate these series numerically on a computer by adding the terms together, getting more and more accurate as we add higher terms. And then there is  Fourier Series ! The fact that you can add these trigonometric functions together, appropriately weighted, to ma...

There was a movie, in the old days, Journey to the Far-Side of the Sun  (also known as Doppleganger) which (spoiler alert) posits that there is a mirror version of the Earth hidden on the other side of the Sun, sharing the orbit with our Earth. The idea is that this planet would always be hidden behind the Sun, and so we would not know it there there. This idea comes up a lot, over and over again. In fact, it came up again last week on twitter. But there's a problem. It assumes the Earth is on a circular orbit. I won't go into the details here, but one of the greatest insights in astronomy was the discovery of Kepler's laws of planetary motion , telling us that planets move on elliptical orbits. With this, there was the realisation that planets can't move at uniform speeds, but travel quickly when closer to the Sun, while slowing down as their orbits carry them to larger distance.  There has been a lot of work examining orbits in the Solar System, and you can  s...

I am exhausted after a month of travel, but am now back in a sunny, but cool, Sydney. It's feels especially chilly as part of my trip included Death Valley, where the temperatures were pushing 50 degrees C. I face a couple of weeks of catch-up, especially with regards to some blog posts on my recent papers. Here, I am going to cheat and present two papers at once. Both papers are by soon-to-be-newly-minted Doctor,  Foivos Diakogiannis . I hope you won't mind, as these papers are Part I and II of the same piece of work. The fact that this work is spread over two papers tells you that it's a long and winding saga, but it's cool stuff as it does something that can really advance science - take an idea from one area and use it somewhere else. The question the paper looks at sounds, on the face of it, rather simple. Imagine you you have a ball of stars, something like this, a globular cluster: You can see where the stars are. Imagine that you can also measure the s...

Slightly under the weather as a very nice man removed four of my wisdom teeth yesterday, so a quick post for today. But we've got a new and exciting paper accepted. Cosmology has come a long way, and we now have exquisite data which point us to the make up of the Universe, a curious mix of dark matter, dark energy, and a few baryons like ourselves. But there's a problem. It's a boring Universe. What, you say! Boring. Yes, we have dark matter and dark energy, things that we still really need to discover in terms of their "quantum properties" such as are they this particle or that, this field or that, but we know what their effects on the expansion of the Universe are; dark matter is is gravitationally attractive, just like everyday matter, and dark energy is repulsive, driving the expansion acceleration of the Universe. But as far as we can tell from the data, dark energy appears to be the same as  Einstein's Cosmological Constant.  And the completely b...