Showing posts from November, 2013

Seeing length contraction

It's the 50th anniversary of both the assassination of John F. Kennedy and the first episode of Doctor Who, and yes, I did get up at 6:50 and watched The Day of the Doctor. So, today's post is about Time and Relative Dimensions in Space.

Everyone loves a bit of relativity, even though its consequences can be quite mind-bending. Of course, one of the things that happens is that when things are moving relative to each other you get length contraction, and people disagree on how long something is. Length contraction is responsible for some cool physical effects, including explaining why two parallel currents attract one another.

Check out this excellent video by Derek Muller on Veritasium which explains this.
While the video is mostly correct, there is something which is not quite right. Notice the bit where he drives passed himself in a car, he sees the car squeezed due length contraction. So, the question I want to look at is "What do things look like moving at relativist…

Major Substructure in the M31 Outer Halo: the South-West Cloud

Another week has flown by and I don't know where the time went. But another good week in terms of research with a new paper accepted.
This one is led by postdoctoral researcher, Nick Bate, with newly minted doctor, Anthony Conn, and PhD student, Brendan McMonigal. The focus of the study, substructure in the halo of the Andromeda Galaxy from, you guessed it, the rather fantastic Pan-Andromeda Archaeological Survey (PAndAS). The focus this time is a particularly prominent blob, known as the South-West Cloud (or, more colloquially to us, Japan). Here's a map of the substructure again. OK - I'll admit that the SW-Cloud doesn't look a lot like Japan, but the name stuck.
As you can see, it's a reasonably big chunk of stuff, but we want to know what it is. And that's the focus of the present paper. This is my favourite picture from the paper, presenting the density of stars in and around the SW-Cloud. As you can see, it's a bit of a mess, but the SW-Cloud is clea…

Dynamical Modeling of NGC 6809: Selecting the best model using Bayesian Inference

Science has been in the news over the last week, and it's been quite a successful research week for me. But while science has been in the news, I'm not 100% impressed by the way it has been presented.

Firstly, there was the lack of a dark matter detection by the Lux experiment. The reports around the web on this have been generally OK, but some have indicated that this is somehow a failure. But what is important, and is often not appreciated, is that in science the lack of a detection is as important as a detection. Negative results like this rule out possibilities and so are vital in cutting down the possibilities for what dark matter is. In fact, a lot of dark matter searches basically following the Holmes adage "eliminated the impossible, whatever remains, however improbable, must be the truth". Not seeing something increases our knowledge.

The second made me a little unhappy. The article in question appeared in the Conversation and was titled "Is it possibl…