Thursday, 29 September 2011

Still in the Dome

I'm still at Kitt Peak, on the 5th night of a 6 night run at the Mayall 4-m Telescope. Observing sometimes make me think of life in a nuclear shelter, post-apocalypse. No windows, no daylight, being very tired and drinking lots of coffee, which is not good given the nearest toilet is two floors down, down a very nuclear-shelter-like steel stairway. When the mighty dome moves, it's like another nuclear strike. In the control room, it's a little dark, with music thumping, and science being done.
Bed at about 6am with sleep to the early afternoon, followed by an hour or two of absorbing Sun-shine. Today we had a trundle around Kitt Peak to see the other telescopes. Here's a couple of snap-shots:



After a little instrument failure, we're back on the sky, but one thing I think people don't know is that we typically finish the night when it is still dark outside. Why? Well, even when the Sun is well below the horizon, it still lights up the sky and, while imperceptible to the human eye, there is enough light to swamp out detector. So, we normally push things as hard as we can (15 minutes into astronomical twilight) and then call it quits.

Of course, we still have a 4-m telescope and a wide-field camera (with a 36'x36' field of view) to play with, and while we can't do science, we can still get some pretty images. Yesterday, we decided to go after the Crab Nebula, with exposures of no more than a few seconds. We got three bands (B, V & R), which let's you make a false colour image of the Crab, and this is what I got.
The colours aren't perfect because I had to tone down the blue (for the aficionados, I didn't flat field the blue and so adjusted the colours so we wouldn't see the results), but you must admit, it's rather pretty :)


Wednesday, 28 September 2011

Long way to the chemist’s: a rough guide to distances in the universe


My article, Long way to the chemist’s: a rough guide to distances in the universe, was published in The Conversation (in fact, it's lead article :). Following on from my article on stars, I was asked to think about distances in the Universe.

My guiding idea is the marvelous quote by Douglas Adams from The Hitchhiker's Guide to the Galaxy;
"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."
I've spend quite a bit of time thinking about scale in the Universe, and remember animated discussions as a young PhD student with a good colleague on the question of "If the Milky Way was a 1p coin, how far away would the edge of the [Observable] Universe be?", and the distance (of order a couple of km) always struck me as being exceedingly close!

Also, in these articles, while you can convey the relative distances, it's hard to really demonstrate the underlying structure to the Universe. Things aren't thrown about randomly, but stars, of course, live in galaxies, and most galaxies live in groups. As an example, here's the Hickson Group

Remember, those are pretty large galaxies in there, with many hundreds of billions of stars. The Milky Way is no different, sharing this bit of the Universe with Andromeda and more than 70 dwarf galaxies. Here's a schematic of the Local Group

You can see that the Milky Way and Andromeda are the centres of attention, surrounded with a little bunch of dwarf galaxies, with a few more scattered throughout the Local Group.

As we move up in scale, then we get bigger agglomerations of galaxies, into spectacular clusters. This is Abell 1869
The orange blobs are galaxies. Unlike the Milky Way, which is a spiral, these are generally elliptical, and it is thought they get this way through repeated collisions. If they started off as spirals, all of that structure is lost and we are left with a blob of stars.

Of course, this is the future of our Milky Way, as in roughly three billion years it will collide with Andromeda. John Dubinski of Toronto shows us what will happen


These groups and clusters are not randomly scatter through space, but sit together embedded in a cosmic web. One of the great Australian astronomical successes is the 2dF Galaxy Redshift Survey which charter the positions of almost a quarter of a million galaxies using the 2dF spectrograph on the Anglo-Australian Telescope and produced a map of the (relatively nearby) structure of the Universe.

What did they find? Here's on of their maps (and look at the distance scale)
And the cosmic web is revealed. Isn't it wonderful!

But science is more than just making pretty pictures. What do our theories predict? I don't have time to describe the various steps involved, but here's a patch of a simulated universe taken from Shaun Coles' (of Durham University) website
I am always amazed by how good the match is. On large scale, our ideas of the cosmos seem of work fine. Where they start to wobble is on the smallest scale. But more about that in another post.

With regards to my The Conversation article, I spent quite a bit of time ensuring the scales are correct, which can be tricky to do when you juggle metres, with light years and giga-parsecs, but, of course, that's what it's all about.

Not everyone is concerned with accuracy. Case in point, the new background for Mac os X is a lovely picture of a galaxy I will be observing again, namely the Andromeda Galaxy. Here's Mac's picture:
Quite lovely. Until you compare to a "real" picture of Andromeda, such as this
by Rob Glender and we see that Mac have excised one of the lovely dwarfs orbiting Andromeda, namely NGC 205 (also known as M110). Maybe they thought that users might think it's a smudge on the screen, or maybe it just isn't pretty enough, but not everyone seems to be that interested in accuracy.

Sunday, 25 September 2011

Intermission: View from the 4m

After a rushed week, it was time to hop on a plane and head for the US. After passing through LA Airport (not my favorite, especially given the time taken to fingerprint me and the several hundred people who arrived with me, but the passport checking guy was friendly and chatted about astronomy - holding up the hundreds behind me :), I got into Tucson yesterday where it was 37C.

Today was the drive up to Kitt Peak, through very stark desert, with amazing cacti and people seemingly living in the middle of nowhere. Definitely cooler, the view from almost 7000 ft over the desert is very cool. Here's the view from the bottom of the 4m Mayall Telescope, overlooking the rest of Kitt Peak.

The clouds, of course, aren't exactly a good sign, and we've lost a little time this evening to them, but things look like they will be running a soon. I will write a little more about the science later in the week.

Before going back to the clearing skies, a couple of interesting things about the trip so far.

Firstly, it was very interesting switching from the Qantas AirBus 380, with its hundreds of passengers, to the much smaller American Eagle plane, with less than 40 seats, for the LA to Tucson leg.

And secondly, heading out of LA, we flew over the sea, and, as I had a window seat, I gazed at the huge city and the boats on the ocean. We were still climbing and one boat looked a bit weird, sort of long and blue, but with bits sticking out at the back. I wondered a bit more, and as it dawned on me that I was looking at, it broke the surface and there was a gush of water vapour. Now, I'm not say it was a blue whale (but it was blue), but apparently they being seen off the coast of California.
Blue whale or not, it was pretty cool.

Monday, 12 September 2011

Peer Review: The Fallacy of Fine-Tuning

A quick post today, as I am running behind on a couple of things, but I have had a book review published in The Conversation. The book is The Fallacy of Fine-Tuning: Why the Universe Is Not Designed for Us by Victor Stenger, and is on a topic I have thought a lot about over the year, but never published on, namely "why are we here, in this Universe"?

For those of a religious inclination, the answer is apparently obvious, the Universe was fine tuned to be habitable. For those grounded in a more scientific approach to understanding the Universe, the answer is not so clear and straight forward. If we start to play around with the fundamental physical parameters, such as the strength of forces etc, it appears we end up with mainly dead Universes.

Heck, even messing with the content of the universe, in terms of the amount of matter, ends up with universes that collapse too quickly, or expand so fast that stars (and hence people) cannot form.

 I think it is safe to say that most astronomers (and physicists) don't really think about this stuff too deeply, and there aren't a lot of papers out there on the topic. Why? Well, I think in the first case there is the "fringe" feeling to the entire Anthropic Principle, especially some of the comments about it in the book by Barrow and Tipler
while the string theorists think it's all in the bag with the idea of the multiverse
But I am not particularly satisfied by it all, although this book does demonstrate that some of the claims of fine tuning are not as fine-tuned as originally thought. In fact, the author has a little web interface called MonkeyGod which allows you to make your own universe and see if you will get stars and heavy elements (the ingredients of life).

In summary, this is something we should probably give some serious thought to, and this book is not a bad place to start.

Friday, 9 September 2011

Could physics predict a giraffe?

I have a cosmological post brewing, so I thought I would touch on a slightly different topic, namely the question of "could physics predict a giraffe?" The following has the usual "buyer beware" clauses; I am a physicist, an astrophysicist at that, and not a chemist, or a biologist, and definitely no a philosopher of science, although I may end up annoying all of them. To start with, let's look at the subject, to wit, a giraffe.

The reason for the post is because of an article over at The Curious Wavefunction titled Why biology (and chemistry) is not physics. The basic argument is this;

Physics is a fundamental science, and identified the basic workings of the Universe. How do nuclei hold themselves together, how does the Universe expand, why do electrons flow through conductors etc etc. That's physics. Now, physics is "reductionist", in that all complex processes can be broken down into a the application of relatively simple underlying physical laws. An example; the thing that is the source of friction, which stops your car when you apply the breaks, and the force stopping you from falling to the centre of the Earth, both the electromagnetic force, the same force that gets electrons to flow through wires. And, of course, with just gravity and electromagnetism, we can explain the physics of everyday experiences.

However, apparently biology and chemistry are somehow different, and that if you try to reduce biological and chemical processes to the basic bits and pieces (i.e. into physics) you somehow lose something.

The issue with the article that kicked this off is that, even given all the basic rules of the Universe, the laws of quantum mechanics and general relativity, physics would be unable to "predict a giraffe". Why? Because somewhere along the line, there were random events (that mutated the genetic code of proto^n-giraffes) and physics just would not take this into account. The final paragraph of the article hammers home the point:
"This role of contingency and accident is one of the most important reasons why the reduction of chemistry and biology to physics won't work. In addition as I have described before, reductionism cannot account for variety in chemistry. Yet another reason why chemistry and biology are not physics."
The "variety in chemistry", after a little reading, suggests that chemists have broader intuition based on experience, and that is lost when you try and reduce chemistry to basic physics.

Well, I grew up in the country and often worked on farms, and I can tell you what all of this smells like (to me). Before I continue, an intermission.

Right, I'll start with something controversial. There is no such things as physics, chemistry and biology. Well, of course we have departments of Physics, Chemistry and Biology, and people who label themselves as physicists, chemists and biologists, and even journals dedicated to further, ultra-fine refinements of subsets of these areas. But where is the boundary between chemistry and physics, or chemistry and biology?

Take a look at this image

The caption for this image reads "A picture of the simplest ion channel known - antibacterial gramicidin A.  It conducts monovalent cations at near diffusion rates, causing collapse of the membrane potential and killing hapless bacteria.  Here Gramicidin A (helical dimer in red) is embedded in lipid bilayer (only the phosphate head groups in green are shown) and solvated with a KCl solution (K blue, Cl red and water is in the background).  Because of its simplicity, gramicidin offers an ideal channel structure for testing new methods and ideas."

Now, is this biology, chemistry or physics? It has a number of buzz-words from all fields, but it is actually research being done by the Computational Biophysics group at the University of Sydney. Why is this physics? Because it is being done in a department with a big sign saying Physics across the front door, by a person who labels themselves as a physicist as they did a degree in a different large building with Physics written across the door.

You don't have to look far to see that, at the edges, these subjects are blurred, and the labeling of physics, chemistry and biology can seem a little arbitrary. But people like to put things in boxes with rigid walls, even then the walls do not exist.

Back to the matter in hand. As ever, xkcd makes a deep comment on the issue;
Note, mathematics, especially pure mathematics, is not science. But this encapsulates some of the key points (although, as I pointed out, there are not rigid divides between the "fields") and even touches on physics envy.

So, could physics predict a giraffe? I think here it is important to realise that much of science is the science of complex systems, where lots of simple underlying processes interact to produce a more complex outcome. Some people think complex systems are somehow magical, but they aren't really, they produce unexpected results, yes, but the underlying processes are simple. Also, some seem to think that because a system is complex, it is somehow unpredictable. Again, this is not really the case. If we know the initial conditions well enough, we can evolve a system using the simple rules and see what happens (and yes, I do know what chaos is).

One of my fav complex systems, cosmological n-body simulations.
Lot's of little masses, following simple rules, producing complex outcomes. What's the limiting issue? Computational power. More computational power, the more things we can follow, the more detailed outcomes we can determine.

When we break it down, a giraffe really is just a bunch of fundamental (i.e. physical) processes interacting in a complicated way. With enough computational power, we could simulate all the processes going on in a giraffe, and hence an entire giraffe. With enough computational power, we could simulate the evolution of a giraffe, including all of the random possible events that happened along the way, and as well as all the giraffes that exist, we could find all the other animals that could have evolved instead of giraffes.

Now, I'm not saying this is computationally easy. We definitely don't have the computational power today to do this, and we may never really have it (it may take an actually universe to compute such things), but fundamentally it is possible.

I'll say it again, even if you hate reductionism, all processes, at the end of the day, however complex, boil down to physical interactions. You may wave your hands and go on about the variety of chemistry and complexity of biology, but this does nothing but reinforce the imaginary walls between the fields. Sure, you have intuition and ideas guided by your experience, but physics is at the basis of everything. If you don't believe this, then at some point you have to inject magic. And that just isn't science.

OK. On a lighter note, seeing we are talking about giraffes, why do they have such long necks? I'm sure you'll say something about them browsing the leaves high in the trees, but surely giraffes have long necks because their legs are so long, and without it, they would not be able to drink? 

Saturday, 3 September 2011

2D Universe - Calculting the force

You'd think as a teacher of relativity, I would understand time a little better, but I seem to have little clue to where it all goes every week (luckily Sean Carroll over at Cosmic Variance points out that time is a more slippery customer than you may expect).

It's been a little while, so I thought I would catch up on my 2D Universe. Those who have been following closely will have seen that we have derived our equations of motion over the surface of a sphere, and now all we need at the acceleration terms. This is where it starts to get a little sticky.

The first part is the easy point. If you remember, we want a gravitational-like force, and this depends on the distance between the two objects. Now, again, there is more than one way to skin a rabbit (is there?) but I am going to take the computationally simple approach.

Any point on a sphere is denoted by our two coordinates, (θ,φ); remember, it's a 2D surface, so no radius to worry about. But let's pretend it's a unit sphere, so we have r=1, then we can convert these polar coordinates to Cartesian with the usual transformation. Matlab has an inbuilt function for doing this, sph2cart, although one has to be careful with which angle is which (remember, there is some ambiguity in the definition of which angle is θ and which is φ). So, any point on the sphere gets mapped to a Cartesian point, (x,y,z).

Now, we can treat these coordinates as components of a unit vector, and then all we need to do is to take the dot product of two such vectors to give


The angle, ξ, is just the distance between the points on the sphere. Excellent!!

So, in my 2D spherical universe, the strength of gravity varies as ξ-1 (unlike gravity in our 3D universe which goes as the inverse square of distance). However, given we are on a sphere, I have made two components of the force, one on the shortest distance between two point, which is just ξ, and one on the longest, which is 2π - ξ. Why? So, if I have two objects at rest at opposite poles, then there is no net force acting and they just sit there.

Now, as I said, the magnitude of the force is the easy bit. The hard bit is working out which direction the force points in. Hmmmm. This needs a little more thought, but the key thing is that we are asking for the bearing you must set off from point one to travel to point two. Of course, jolly old navigators sorted this one out long ago.

There a lots of approaches, but I want a vector bearing, so I followed this little set of recipes, which work very well. The good thing is that you end up with a vector, W, in a tangent plane, which is, as the name suggests, a plane which is tangent to the surface of the sphere at the point of interest.

The bad part is that, because I was working with Cartesian coordinates, I now have a 3D vector with components in (x,y,z), but what I really need is components in the angular coordinates on the sphere. Here I call on the magic of tensors, especially the rules that let you convert from one coordinate system to another, so my acceleration in angular coordinates is related to that in Cartesian coordinates via

Those in the know will recognise this as the Jacobian. Looks messy, but how do we know this has worked? Well, our vector is in the tangent plane, and so ar should be zero (there should be no vector pointing in the radial direction). And there isn't, so it is all wonderful!

So, that's it. We now have our gravitational attraction in the polar coordinates of the sphere, so that completes the equations of motion. We integrate and we get
Wonderful! (Well I think so). Right, I think this is now done and dusted, and I promised to get back to zombies soon. I'll also put together some notes on the shapes of oceans on non-spherical worlds, but that's for later.