Thursday, 21 June 2012

112 Mercer St

I'm in Brooklyn, on my way back to Sydney after a meeting in Princeton. I'll mention the meeting a little more below, but when in Princeton, all those with an interest in physics should make a little pilgrimage to a small while house just off to the side of campus. It's address is 112 Mercer St.
 The house is interesting as it is where Einstein lived from 1936 until his death in 1955. Einstein's office was not on the main university campus (which is a rather beautiful and surreal place) but at the Institute for Advanced Studies which is just a little further down Mercer St.

Einstein's house is a pretty little wood house on a street of pretty wood houses, and doesn't stand out too much. Interestingly, Einstein did not want the house turned into a museum, and so it is still a private residence, with the current householder being Eric Maskin who, while not being a physicist, holds a Nobel Prize (in Economics).

Just to reinforce that this is not museum, and not to have hordes of physics fans swarming over the garden, there are a few signs on the gates which stress that it is a private residence. This doesn't stop us physics types cruising up and down the street and taking photos :)

Princeton has a lot of alumi, many of them very famous, but the town clearly is proud of its association with one of the greatest physicists who has ever lived. I snapped the below picture in Princeton town.
 Funnily, many thought the red brick building was Einstein's house, even thought the picture has him sitting on a wooden white porch. But you have got to love those slippers!

The conference was not about Einstein, but there was a relation in a quite round-about way. The meeting was to mark the 100 anniversary of the birth of this man,
His name is Martin Schwarzschild, and he died in 1997. Outside of astronomy, his father, Karl, is probably more famous, providing the first analytic solutions to the Eisntein field equations for a spherical mass (and hence predicting black holes).

Inside astronomy, however, Martin had a huge impact on a number of fields, and his ideas and methods are very much in use today. Much of the meeting was about his work on dynamics and our nearest cosmic companion, the Andromeda Galaxy, but, as it is time for breakfast, I'll write about that when I get back to Sydney.

Friday, 15 June 2012

"Statistical thinking will one day be as necessary...

... for efficient citizenship as the ability to read and write.” H. G. Wells

A very quick post today, as things are busy (more about that in a little while), but seeing the above quote at Steinn Sigurðsson "Dynamics of Cats" blog reminded me about something about physics education (and science in general).

I've mentioned before about my thoughts on physics education. Traditionally, this is split into two separate bits, the analytic mathematically bits in lectures, and laboratory work. People who do more of one than the other label themselves are theoreticians or experimenters. They are portrayed as living in different worlds.

The problem is that this completely misrepresents science. Science is the interface between these two, it is an extremely vital component, and we do an extremely poor job of highlighting how important this is.

Just what do mean? Well, let's take a simple example. Suppose someone calculated the scattering of Sun light as it comes through the atmosphere and proclaims "According to my calculations, the sky is blue", and an experimenter looks outside and says "Yes, it is blue", has science been done? Has the scattering theory been proved to be a good description of what does on in the sky? IMHO, the answer is a resounding no.

You might be scratching your head at this point. But ask yourself the question, what does it mean to say something is "blue"? Well, here's some blue.


In fact, there are two blues here, and Oxford blue (the darker colour) and a Cambridge blue (lighter).

So, when your person predicts that the sky is blue, you actually what know know *what* blue they are predicting, and hence, in reality, you are asking "what spectrum of light do you predict?"

They might say "Well, it should look like this" (I know it doesn't actually).
We have a prediction! Now all you need is to take your spectrometer and point at at the sky, and get some data, and viola,
Now you might think "Well, they look similar, can we go now?" and the answer is no.

Why? Because we have reached the crux of the matter. Just how do we compare our theoretical predictions to the data we collect. How do we test the hypothesis? How do we compare one theoretical idea to another?

The answers to these questions are not a mystery, but, at least here, students don't get to see them until their fourth year of undergrad. After three years of learning theory and doing experiments are they given the clues to actually do the comparison, to do real, raw science.

But I have to run, and will write about that at another time.

Saturday, 9 June 2012

The Physics of "Rendezvous with Rama"

While I read science fiction, I don't read a lot of it. I prefer history books (and while the 6th June was focused on the transit of Venus, it is famous for another big historical event). I'm not a fan of "magic" science fiction, where the equivalent of a magic wand is waved, with some pseudo-scientific gobbledygook, to fix a problem.

So, I am going to talk about a book that doesn't, namely Rendezvous with Rama by Arthur C. Clarke.
I'll start with two confessions. Firstly, I don't really like a lot of Clarke's work. And second, I didn't actually read the book; I had it read to me.

To explain the latter statement, way-back-when I worked for the Anglo-Australian Observatory. Like virtually all support astronomers (those who show astronomers observing with the telescope the ropes) I lived in Sydney, but one week in five I had to travel to the telescope, a 5-6 hour drive. So I used audio books to maintain my sanity. And one of them was Rendezvous with Rama. And it stuck because it made me question the physics of what was going on.

I'll cut to the chase. Clarke was correct on his treatment of physics. But let's consider the thing that really got me thinking. Namely, jumping off a cliff.

OK. Let's start at the beginning. The book is about the exploration to a vast space craft that has entered the solar system. The ship is a cylinder, and as the action picks up, it is clear that the interior of the cylinder is intended as a place to live, with the rotation of the cylinder providing an "artificial gravity".
At one point in the story, an explorer finds themself at the top of a cliff, and decides to step off. What happens?

Remember, there is no "real" gravity here, you are just in a rotating space ship. So, perhaps you step off and just float there? Now that would be weird.

To answer the question of what happens, we need to look at the situation from an outside observer.

Let's start by assuming that the cylinder is rotating with an angular speed (radians per second) of ω and that the cliff top is a radius, r1, from the axis of rotation, and the base of the cliff is r2. Remembering our classical mechanics, our instantaneous velocity when we are on the top of the cliff is v = ω r1 and it points in the tangential direction. Something like the picture below.


Now, to the outside observer, once the person steps off the cliff, there is no force acting on them (when they are on the cliff, there is the reaction force provided by the ground which keeps the person going around in a circle). With no force acting, the outside observer sees the person continue to move in the tangential direction until they hit the outer wall of the ship. Bang.

So, when they step off the cliff, they "fall", i.e. the explorer moves from the top of the cliff to the bottom. But let's ask the question what someone rotating with the cylinder, say standing directly at the bottom of the cliff, sees when the person steps off the cliff.

I won't put the geometry here, but it's all simple. The falling person covers the green line distance and uniform speed, so we can calculate the time it takes, and in that time the outer wall rotates a certain distance. I'm going to be lazy and explain everything with pictures, care of matlab.


So, this is relative to someone standing at the bottom of the cliff. In this case, I made the ship have a radius of 2km, and the cliff be 100m high, and the acceleration experienced at the base of the cliff is 1g (at the top it is 5% smaller, so essentially unnoticable).

The blue dots are what you would expect on Earth, the person accelerates as they fall, but gravity acts in a straight line and so the spot they hit the base of the cliff is directly below where they jump off.

The red is what you get on the rotating space ship. The observer at the base of the cliff sees the person accelerate downwards, just as they would on Earth. But unlike the Earth, the faller also moves off to the side! And lands 20m away from where they jumped off. How cool is that?

Remember though, as seen by the external observer, the faller has no force acting on them during the fall. So the faller does not feel any push or pull once they step off, they are just in free-fall. But to the observer at the base of the cliff, who is rotating with the ship, they see the faller accelerate not only downwards, but side-ways as well. It looks like gravity, but not as we know it.

And if that doesn't get you thinking about the very nature of gravity, it should!

Sunday, 3 June 2012

There's more to being an astronomer than doing astronomy

Back in Sydney after a couple of nights in the lovely Port Stephens, in the town of Shoal Bay at the ASA Early Career Research Workshop. Here's the grey sky as seen from my hotel room (it may be grey, but it's a lovely place).
I should point out, with 17 years under my belt since my PhD, and being a professor at a large university, I am not an Early Career Researcher, and so I was there as a grown-up, providing advice and live stories.

I spoke on the topic of networking, something that sounds horribly business-world-like, but is an important aspect of establishing a career. There were a lot of postdocs there, many recently out of their PhD, but a few in their third postdoc, all with the question of "How do we get that career in astronomy?"

The discussions were frank and honest - the room was told that it is a 100% certainty that they all will not have a job in astronomy in the future - and I think the postdocs appreciated this honesty. I'll come back to this at the end.

The whole thing was broadcast on some new-fangled thing called twitter, which was apparently "trending" (I think I know what that means), but it was clear that the broader community is interested in early career advice.

So, here's one of the panel discussions
(pinched from Bryan Gaensler's twitter thing). Those that know Australian astronomy will recognise the people here, all senior "grown-ups" in the community.

There was too much material presented to summarize here, but interested people should check out the twitter feed (and there will be notes coming up sometime in the future). But there are a couple of things I would like to mention.

Firstly, the fact that senior astronomers can find time to attend such workshops shows that they care about the issues facing early career researchers. A lot of my career was effectively flying blind, not really knowing a lot of the key things I now know. We knew that the chance of obtaining a faculty position was slim, but I didn't really know what I needed to do to get one. The fact that I am where I am feels like a lot of being in the right place at the right time, and plenty of luck.

The second thing, which is sometimes forgotten when you read a paper or see a press release, is that the authors are people, and people with lives, partners, children, pets, parents and a mortgage, as well as observatory or university duties to perform. Well, they might not have all of these, but they will have non-astronomical things to deal with. We should not forget this, and we grown ups should be prepared to provide mentoring and advice to help with career choices. We should remember that there is more to being an astronomer than doing astronomy.

I'll finish on a more personal note. In the image above you can see that we were discussing the two-body problem. For those not in the know, what it boils down to is how do a couple survive the constant moving which is part of the astronomy career, jumping from country to country, especially when both have careers of their own, and when children appear on the scene.

While I am not a great fan of public speaking, and can often fake confidence, I felt myself welling up a little when talking about my own experiences. Now I am in the lucky position that we have the two-body problem solved (my wife is a successful career academic also), but in thinking through my own personal circumstances, I remembered how bloody stressful it was getting to where we are today, and this came through when I attempted to talk about it.

So, to the Early Career Researchers out there, it isn't easy, for anyone. But persevere, astronomy is a pretty good life, and a privilege to have.