Sunday, 29 March 2015

Musings on academic careers - Part 1

As promised, I'm going to put down some thoughts on academic careers. In doing this, I should put my cards on the table and point out that while I am a full-time professor of astrophysics of the University of Sydney, I didn't really plan my career or following the musings given below. The musings come from take a hard look at the modern state of play in modern academia.

I am going to be as honest as possible, and surely some of my colleagues will disagree with my musings. Some people have a romantic view of many things, including science, and will trot out the line that science is somewhat distinct from people. That might be the case, but the act of doing science is clearly done my people, and that means all of the issues that govern human interactions come into play. It is important to remember this.

Now, there may be some lessons below for how to become a permanent academic, but there is no magic formula. But realising some of these lessons on what is at play may help.

Some of you may have heard me harp on about some of these issues before, but hopefully there is some new stuff as well. OK. Let's begin.

Career Management
It must be remembered that careers rarely just happen. Careers must be managed. I know some people hate to realise this, as science is supposed to be above all this career stuff - surely "good people" will be identified and rewarded!

Many students and postdocs seem to bumble along and only think of "what's next?" when they are up against the wire. I have spoken with students about the process of applying for postdocs, the long lead time needed, the requirement of at least three referees, all aspects of job hunting, and then, just moments from the submission of their PhD, they suddenly start looking for jobs. I weep a little when they frantically ask me "Who should I have as my third referee?"

Even if you are a brand-new PhD student, you need to think about career management. I don't mean planning, such as saying I will have a corner office in Harvard in 5 years (although there is nothing wrong with having aspirational goals!), but management. So, what do I mean?

Well, if you are interested in following a career in academia, then learn about the various stages and options involved and how you get from one to the other. This (and careers beyond academia) should be mandatory for new students, and reminded at all stages of your career that you need to keep thinking about it. What kind of things should you be doing at the various stages of your career? What experience would your next employer like you to have? It is very important to try and spot holes in your CV and fill them in; this is very important! If you know you have a weakness, don't ignore it, fix it.

Again, there is no magic formula to guarantee that you will be successful in moving from one stage to another, but you should be able to work out the kind of CV you need. If you are having difficulties in identifying these things, talk with people (get a mentor!).

And, for one final point, the person responsible for managing your career is you. Not your supervisor, not your parents, and not the non-existent gods of science. You are.

Being Strategic
This is part of your career management.

In the romantic vision of science, an academic is left to toddle along and be guided by their inquisitive nature to find out what is going on in the Universe. But academia does not work that way (no matter how much you want to rage against it). If you want an academic career, then it is essential to realise that you will be compared to your peers at some point. At some point, someone is is going to have a stack of CVs in front of them and will be going through them and will have to choose a subset who met the requirements for a position, and then rank those subset to find the best candidate. As part of your career management you need to understand what people are looking for! (I speak from experience of helping people prepare for jobs who know little about the actual job, the people offering it, what is needed etc etc).

I know people get very cross with this, but there are key indicators people look at, things like the number of papers, citation rates, grant income, student supervision, teaching experience. Again, at all points you need to ask "is there a hole in my CV?" and if there is, fill it! Do not ignore it.

But, you might be saying, how can I be strategic in all of this? I just get on with my work! You need to think about what you do. If you have a long running project, are there smaller projects you can do when waiting to spin out some short, punchy papers? Can I lead something that I will become world known in? Is there an idea I can spin to a student to make progress on? You should be thinking of "results" and results becoming talks at conferences and papers in journals.

If you are embarking on a new project, a project that is going to require substantial investment of time, you should ensure something will come from it, even if it is a negative or null result. You should never spend a substantial period of time, such as six months, and not have anything to show for it!

Are there collaborations you could forge and contribute to? Many people have done very well by being part of large collaborations, resulting in many papers, although, be aware that when seeing survey papers on a CV now as "well, what did this person contribute to the project?".

The flip-side is also important. Beware of spending to much time on activities that do not add to you CV! I have seen some, especially students, spending a lot of time on committees and jobs that really don't benefit them. Now, don't get me wrong. Committee work and supporting meetings etc is important, but think about where you are spending your time and ask yourself if your CV is suffering because of it.

How many hours should I work?
Your CV does not record the number of hours you work! It records your research output and successes. If you are publishing ten papers a year on four hour days, then wonderful, but if you are two years into a postdoc, working 80 hours per week and have not published anything, you might want to think about how you are using your time. 

But I am a firm believer of working smarter, not harder, and thinking and planning ideas and projects. Honestly, I have a couple of papers which (in a time before children) were born from ideas that crystalised over a weekend and submitted soon after. I am not super-smart, but do like to read widely, to go to as many talks as I can, to learn new things, and apply ideas to new problems.

One thing I have seen over and over again is people at various stages of their careers becoming narrower and narrower in their focus, and it depresses me when I go to talks in my own department and see students not attending. This narrowness, IMHO, does not help in establishing an academic career. This, of course, is not guaranteed, but when I look at CVs, I like to see breadth. 

So, number of hours is not really an important issue, your output is. Work hours do become important when you are a permanent academic because all the different things, especially admin and teaching you have to do, but as an early career researcher, it should not be the defining thing. Your output is. 

Is academia really for me?
I actually think this is a big one,  and is one which worries me as I don't think people at many stages of their career actually think about. Being a student is different to being an postdoctoral researcher, is different to being an academic, and it seems to be that people embarking on PhDs, with many a romantic notion about winning a Nobel prize somewhere along the way, don't really know what an "academic" is and what they do, just that it is some sort of goal.

In fact, this is such a big one, I think this might be a good place to stop and think about later musings.

Saturday, 21 March 2015

Moving Charges and Magnetic Fields

Still struggling with grant writing season, so another post which has resulted in my random musings about the Universe (which actually happens quite a lot).

In second semester, I am teaching electricity and magnetism to our First Year Advanced Class. I really enjoy teaching this class as the kids are on the ball and can ask some deep and meaningful questions.

But the course is not ideal. Why? Because we teach from a textbook and the problem is that virtually all modern text books are almost the same. Science is trotted out in an almost historical progression. But it does not have to be taught that way.

In fact, it would be great if we could start with Hamiltonian and Lagrangian approaches, and derive physics from a top down approach. We're told that it's mathematically too challenging, but it really isn't. In fact, I would start with a book like The Theoretical Minimum, not some multicoloured compendium of physics.

We have to work with what we have!

One of the key concepts that we have to get across is that electricity and magnetism are not really two separate things, but are actually two sides of the same coin. And, in the world of classical physics, it was the outstanding work of James Clerk Maxwell who provided the mathematical framework that broad them together. Maxwell gave us his famous equations that underpin electro-magnetism.
Again, being the advanced class, we can go beyond this and look at the work that came after Maxwell, and that was the work by Albert Einstein, especially Special Theory of Relativity.

The wonderful thing about special relativity is that the mix of electric and magnetic fields depends upon the motion of an observer. One person sees a particular configuration of electric and magnetic fields, and another observer, moving relative to the first, will see a different mix of electric and magnetic fields.

This is nice to say, but what does it actually mean? Can we do anything with it to help understand electricity and magnetism a little more? I think so.

In this course (and EM courses in general) we spend a lot of time calculating the electric field of a static charge distribution. For this, we use the rather marvellous Gauss's law, that relates the electric field distribution to the underlying charges.
I've written about this wonderful law before, and should how you can use symmetries (i.e. nice simple shapes like spheres, boxes and cylinders) to calculate the electric field.

Then we come to the sources of magnetic field. And things, well, get messy. There are some rules we can use, but it's, well, as I said, messy.

We know that magnetic fields are due to moving charges, but what's the magnetic field of a lonely little charge moving on its own? Looks something like this
Where does this come from? And how do you calculate it? Is there an easier way?

And the answer is yes! The kids have done a touch of special relativity at high school and (without really knowing it in detail) have seen the Lorentz transformations. Now, introductory lessons on special relativity often harp on about swimming back and forth across rivers, or something like that, and have a merry dance before getting to the point. And the transforms are presented as a way to map coordinators from one observer to another, but they are much more powerful than that.

You can use them to transform vectors from one observers viewpoint to another. Including electric and magnetic fields. And these are simple algebra.

where we also have the famous Lorentz factor. So, what does this set of equations tell us? Well, if we have an observer who sees a particular electric field (Ex,Ey,Ez), and magnetic field (Bx,By,Bz), then an observer moving with a velocity v (in the x-direction) with see the electric and magnetic fields with the primed components.

Now, we know that the electric field of an isolated charge at rest is. We can use Gauss's law and it tells us that the field is spherically symmetrical and looks like this
The field drops off in strength with the square of the distance. What would be the electric and magnetic fields if this charge was trundling past us at a velocity v? Easy, we just use the Lorentz transforms to tell us. We know exactly what the electric field looks like of the charge at rest, and we know that, at rest, there is no magnetic field.

Being as lazy as I am, I didn't want to calculate anything by hand, so I chucked it into MATLAB, a mathematical environment that many students have access too. I'm not going to be an apologist for MATLAB's default graphics style (which I think sucks - but there are, with a bit of work, solutions).



Anyway, here's a charge at rest. The blue arrows are the electric field. No magnetic field, remember!
So, top left is a view along the x-axis, then y, then z, then a 3-D view. Cool!

Now, what does this charge look like if it is moving relative to me? Throw it into the Lorentz transforms, and voila!


MAGNETIC FIELDS!!! The charge is moving along the x-axis with respect to me, and when we look along x we can see that the magnetic fields wrap around the direction of motion (remember your right hand grip rule kids!).

That was for a velocity of 10% the speed of light. Let's what it up to 99.999%
The electric field gets distorted also!

Students also use Gauss's law to calculate the electric field of an infinitely long line of charge. Now the strength of the field drops off as the inverse of the distance from the line of charge.


Now, let's consider an observer moving at a velocity relative to the line of charge.
Excellent! Similar to what we saw before, and what we would expect. The magnetic field curls around the moving line of charge (which, of course, is simply an electric current).

Didn't we know that, you say? Yes, but I think this is more powerful, not only to reveal the relativistic relationship between the electric and magnetic fields, but also once you have written the few lines of algebraic code in MATLAB (or python or whatever the kids are using these days) you can ask about more complicated situations. You can play with physics (which, IMHO, is how you really understand it).

So, to round off, what's the magnetic field of a perpendicular infinite line of charge moving with respect to you. I am sure you could, with a bit of work, calculate it with usual mathematical approaches, but let's just take a look.

Here's at rest
A bit like further up, but now pointing along a different axis.

Before we add velocity, you physicists and budding physicists make a prediction! Here goes! A tenth the velocity of light and we get
I dunno if we were expecting that! Remember, top left is looking along the x-axis, along the direction of motion. So we have created some magnetic structure. Just not the simple structure we normally see!

And now at 99.99% we get
And, of course, I could play with lots of other geometries, like what happens if you move a ring of charge etc. But let's not get too excited, and come back to that another day.

Saturday, 28 February 2015

Shooting relativistic fish in a rational barrel

I need to take a breather from grant writing, which is consuming almost every waking hour in between all of the other things that I still need to do. So see this post as a cathartic exercise.

What makes a scientist? Is it the qualification? What you do day-to-day? The association and societies to which you belong? I think a unique definition may be impossible as there is a continuum of properties of scientists. This makes it a little tricky for the lay-person to identify "real science" from "fringe science" (but, in all honesty, the distinction between these two is often not particularly clear cut).

One thing that science (and many other fields) do is have meetings, conferences and workshops to discuss their latest results. Some people seem to spend their lives flitting between exotic locations essentially presenting the same talk to almost the same audience, but all scientists probably attend a conference or two per year.

In one of my own fields, namely cosmology, there are lots of conferences per year. But accompanying these there are another set of conferences going on, also on cosmology and often including discussions of gravity, particle physics, and the power of electricity in the Universe. At these meetings, the words "rational" and "logical" are bandied about, and it is clear that the people attending think that the great mass of astronomer and physicists have gotten it all wrong, are deluded, are colluding to keep the truth from the public for some bizarre agenda - some sort of worship of Einstein and "mathemagics" (I snorted with laughter when I heard this).

If I am being paid to lie to the public, I would like to point out that my cheque has not arrived and unless it does shortly I will go to the papers with a "tell all"!!

These are not a new phenomenon, but were often in shadows. But now, of course, with the internet, any one can see these conference in action with lots of youtube clips and lectures.

Is there any use for such videos? I think so, as, for the student of physics, they present an excellent place to tests one knowledge by identifying just where the presenters are straying off the path.

A brief search of youtube will turn up talks that point out that black holes cannot exist because
is the starting point for the derivation of the Schwarzschild solution.

Now, if you are not really familiar with the mathematics of relativity, this might look quite convincing. The key point is this equation

Roughly speaking, this says that space-time geometry (left-hand side) is related to the matter and energy density (right-hand side, and you calculate the Schwarzschild geometry for a black hole by setting the right-hand side equal to zero.

Now, with the right-hand side equal to zero that means there is no energy and mass, and the conclusion in the video says that there is no source, no thing to produce the bending of space-time and hence the effects of gravity. So, have the physicists been pulling the wool over everyones eyes for almost 100 years?

Now, a university level student may not have done relativity yet, but it should be simple to see the flaw in this argument. And, to do this, we can use the wonderful world of classical mechanics.

In classical physics, where gravity is a force and we deal with potentials, we have a similar equation to the relativistic equation above. It's known as Poisson's equation
The left-hand side is related to derivatives of the gravitational potential, whereas the right-hand side is some constants (including Newton's gravitational constant (G)) and the density given by the rho.

I think everyone is happy with this equation. Now, one thing you calculate early on in gravitational physics is that the gravitational potential outside of a massive spherical object is given by
Note that we are talking about the potential is outside of the spherical body (the simple V and Phi are meant to be the same thing). So, if we plug this potential into Poisson's equation, does it give us a mass distribution which is spherical?

Now, Poisson's equation can look a little intimidating, but let's recast the potential in Cartesian coordinates. Then it looks like this

Ugh! Does that make it any easier? Yes, let's just simply plug it into Wolfram Alpha to do the hard work. So, the derivatives have an x-part, y-part and z-part - here's the x-part.
Again, is you are a mathphobe, this is not much better, but let's add the y- and z-parts.

After all that, the result is zero! Zilch! Nothing! This must mean that Poisson's equation for this potential is
So, the density is equal to zero. Where's the mass that produces the gravitational field? This is the same as the apparent problem with relativity. What Poisson's equation tells us that the derivatives o the potential AT A POINT is related to the density AT THAT POINT! 

Now, remember these are derivatives, and so the potential can have a whole bunch of shapes at that point, as long as the derivatives still hold. One of these, of course, is there being no mass there and so no gravitational potential at all, but any vacuum, with no mass, will above Poisson = 0 equation, including the potential outside of any body (the one used in this example relied on a spherical source).

So, the relativistic version is that the properties of the space-time curvature AT A POINT is related to the mass and energy AT A POINT. A flat space-time is produced when there is no mass and energy, and so has G=0, but so does any point in a vacuum, but that does not mean that the space-time at that point is not curved (and so no gravity).

Anyway, I got that off my chest, and my Discovery Project submitted, but now it's time to get on with a LIEF application! 

Sunday, 25 January 2015

The Constant Nature of the Speed of light in a vacuum

Wow! It has been a while, but I do have an excuse! I have been finishing up a book on the fine-tuning of the Universe and hopefully it will be published (and will become a really big best seller?? :) in 2015. But time to rebirth the blog, and what a better way to start that a gripe.

There's been some chatter on the interweb about a recent story about the speed of light in a vacuum being slowed down. Here's oneHere's another. Some of these squeak loudly about how the speed of light may not be "a constant", implying that something has gone horribly wrong with the Universe. Unfortunately, some of my physicsy colleagues were equally shocked but the result.

Why would one be shocked? Well, the speed of light being constant to all observers is central of Einstein's Special Theory of Relativity. Surely if these results are right, and Einstein is wrong, then science is a mess, etc etc etc.

Except there is nothing mysterious about this result. Nothing strange. In fact it was completely expected. The question boils down to what you mean by speed.
Now, you might be thinking that speed is simply related to the time it takes for a thing to travel from here to there. But we're dealing with light here, which, in classical physics is represented by oscillations in an electromagnetic field, while in our quantum picture it's oscillations in the wave function; the difference is not important.

When you first encounter electromagnetic radiation (i.e. light) you are often given a simple example of a single wave propagating in a vacuum. Every student of physics will have seen this picture at some point;
The electric (and magnetic) fields oscillate as a sin wave and the speed at which bumps in the wave move forward is the speed of light. This was one of the great successes of James Clark Maxwell, one of the greatest physicists who ever lived. In his work, he fully unified electricity and magnetism and showed that electromagnetic radiation, light, was the natural consequence. 

Without going into too many specific details, this is known as the phase velocity. For light in a vacuum, the phase velocity is equal to c.

One of the coolest things I ever learnt was Fourier series, or the notion that you can construct arbitrary wave shapes by adding together sins and cos waves. This still freaks me out a bit to this day, but instead of an electromagnetic wave being a simple sin or cos you can add waves to create a wave packet, basically a lump of light.

But when you add waves together, the result lump doesn't travel at the same speed as the waves that comprise the packet. The lump moves with what's known as the group velocity. Now, the group velocity and the phase velocity are, in general, different. In fact, they can be very different as it is possible to construct a packet that does not move at all, while all the waves making up the packet are moving at c!

So, this result was achieved by manipulating the waves to produce a packet whose group velocity was measurably smaller than a simple wave. That's it! Now, this is not meant to diminish the work of the experimenters, as this is not easy to set up and measure, but it means nothing for the speed of light, relativity etc etc. And the researchers know that!

And as I mentioned, understanding the difference between phase and group velocity has been known for a long time, with Hamilton (of Hamiltonian fame) in 1839, and Rayleigh in 1877. These initial studies were in waves in general, mainly sound waves, not necessarily light, but the mathematics are basically the same. 

Before I go, once of the best course I took as an undergraduate was called vibrations and waves. At the time, I didn't really see the importance of of what I was learning, but the mathematics was cool. I still love thinking about it. Over the years, I've come to realise that waves are everywhere, all throughout physics, science, and, well everything. Want to model a flag, make a ball and spring model. Want to make a model of matter, ball and spring. And watch the vibrations!

Don't believe me? Watch this - waves are everywhere.





Thursday, 6 November 2014

Scientists Have Figured Out What Colour The Universe Is

What's old is new again?

Over at Business Insider Australia we are told (with some lovely language) that Scientists have figured out what colour the Universe is. You've got to love a new and interesting astronomy story, but alas, the result is rather, well, beige (I refuse to say latte).
But that's not the point of this post. Now, I am not a young man any more, and my memory is not what it was, but I know I had heard this story before, somewhere in the past.

The story doesn't name any scientists or cite an original article, and so I turned to google. Hmmm - virtually the same story appeared in the UK Telegraph in 2009! Unsurprisingly, the Daily Mail carry very similar stories.

So this "news" is at least 5 years old! But now we have some names! Karl Glazebrook and Ivan Baldry!

A little more detective work leads to New Scientist article entitled The Universe is not turquoise – it's beige. This story from 2002!!!!!!!! corrects and earlier story in which the colour of the Universe was found to be turquoise! So, we're now looking at a story from 12 years ago!

Deep in the depths of my brain I remembered the entire saga (cards on table, I used to work at the AAO with Karl and Ivan) about how they averaged the colours of galaxies, initially finding the average colour to be bluish and then finding with the correct colour interpretation its actually whitish. In fact, Karl has a nice write up on the who thing here.

BUT why has this story resurfaced? There is no new data, no new analysis, nothing. In fact, seven seconds of thought and clicks takes you to a wikipedia page that points out the original press release with the incorrect colour was in 2001, 13 years ago.

So, is there really no new science news interesting enough to be published this week? Do we have to dig up stories from the past? What do we expect to see next? "Scientists discover the universe is expanding"? "Scientist link the orbit of the moon to the falling of an apple"? or even "Proto-scientists discover this water stuff does not burn"? Come one media, you can do better than this!

Sunday, 26 October 2014

The Redshift Drift

Things are crazily busy, with me finishing teaching this week. Some of you may know, that I am writing a book, which is progressing, but more slowly than I hoped. Up to just over 60,000 words, with a goal of about 80 to 90 thousand, so more than half way through.

I know that I have to catch up with papers, and I have another article in The Conversation brewing, but I thought I would write about something interesting. The problem is that my limited brain has been occupied by so many other things that my clear thinking time has been reduced to snippets here and there.

But one thing that has been on my mind is tests of cosmology. Nothing I post here will be new, but you might not know about it. But here goes.

So, the universe is expanding. But how do we know? I've written a little about this previously, but we know that almost 100 years ago, Edwin Hubble discovered his "law", that galaxies are moving away from us, and the further away they are, the faster they are moving. There's a nice article here describing the importance of this, and we end up with a picture that looks something like this
Distance is actually the hard thing to measure, and there are several books that detail astronomers on-off love affair with measuring distances. But how about velocities?

These are measured using the redshift. It's such a simple measurement. In our laboratory, we might see emission from an element, such as hydrogen, at one wavelength, but when we observe it in a distant galaxy, we see it at another, longer, wavelength. The light has been redshifted due to the expansion of the universe (although exactly what this means can be the source for considerable confuddlement).

Here's an illustration of this;
Relating the redshift to a Doppler shift we can turn it into a velocity. As we know, the Hubble law is  what we expect if we use Einstein's theory of relativity to describe the universe. Excellent stuff all around!

One thing we do know is that the expansion rate of the universe is not uniform in time. It was very fast at the Big Bang, slowed down for much of cosmic history, before accelerating due to the presence of dark energy.

So, there we have an interesting question. Due to the expansion of the universe, will the redshift I measure for a galaxy today be the same when I measure it again tomorrow.

This question was asked before I was born and then again several times afterwards. For those that love mathematics, and who doesn't, you get a change of redshift with time that looks like this

(taken from this great paper) where z is the redshift, Ho is Hubble's constant today, while H(z) is Hubble's constant at the time the light was emitted from the galaxy your observing. 

The cool thing is that last term depends upon the energy content of the universe, just how much mass there is, how much radiation, how much dark energy, and all the other cool things that we would like to know, like if dark energy is evolving and and changing, or interacting with matter and radiation. It would be a cool cosmological probe.

Ah, there is a problem! We know that Hubble's constant is about Ho = 72 km/s/Mpc, which seems like a nice sort of number. But if you look closely, you can see that it actually had units of 1/time. So, expressing it in years, this number is about 0.0000000001 per year. This is a small number. Bottom.

But this does not mean that astronomers pack up their bags and head home. No, you look for solutions and see if you can come up with technologies to allow you to measure this tiny shift. I could write an entire post on this, but people are developing laser combs to give extremely accurate measurement of the wavelength in spectra, and actually measure the changing expansion of the Universe in real time!

Why am I writing about this? Because these direct tests of cosmology have always fascinated me, and every so often I start doodling with the cosmological equations to see if I can come up with another one. Often this ends up with a page of squiggles and goes no where, but some times I have what I thing is a new insight.


And this gives me a chance to spruik an older paper of mine, with then PhD student, Madhura Killedar. I still love this stuff!


The evolution of the expansion rate of the Universe results in a drift in the redshift of distant sources over time. A measurement of this drift would provide us with a direct probe of expansion history. The Lyman alpha forest has been recognized as the best candidate for this experiment, but the signal would be weak and it will take next generation large telescopes coupled with ultra-stable high resolution spectrographs to reach the cm/s resolution required. One source of noise that has not yet been assessed is the transverse motion of Lyman alpha absorbers, which varies the gravitational potential in the line of sight and subsequently shifts the positions of background absorption lines. We examine the relationship between the pure cosmic signal and the observed redshift drift in the presence of moving Lyman alpha clouds, particularly the collapsed structures associated with Lyman limit systems (LLSs) and damped Lyman alpha systems (DLAs). Surprisingly, the peculiar velocities and peculiar accelerations both enter the expression, although the acceleration term stands alone as an absolute error, whilst the velocity term appears as a fractional noise component. An estimate of the magnitude of the noise reassures us that the motion of the Lyman alpha absorbers will not pose a threat to the detection of the signal.

Catching the Conversation

Wow!!! Where has time gone! I must apologise for the sluggishness of posts on this blog. I promise you that it is not dead, I have been consumed with a number of other things and not all of it fun. I will get back to interesting posts as soon as possible.

So, here's a couple of articles I've written in the meantime, appearing in The Conversation

One on some of my own research: Dark matter and the Milky Way: more little than large



And the other on proof (or lack of it) in science: Where’s the proof in science? There is none



There's more to come :)