Smash!

Let's talk about collisions. Pretty much all physics experiments can be broken down into two categories: scattering (for example, particle accelerators) and interference (for example, Young's double slit experiment).

Example of a scattering experiment. I have been trying to convince the guys in the lab next door (who are actually working on an interference experiment) that they need to buff up and dress like this in the lab. Incidentally, the laser safety glasses that he is wearing are correct for the wavelength of light being emitted in the tube, if I compare them to a similar model from Thorlabs.

In certain regimes, the line between the two kinds of experiments gets kind of hazy. You see, there is this thing called wave-particle duality. Sometimes, matter acts like a particle (like little balls smashing into each other), and other times the same matter can act like a wave (like ripples in water overlapping with other ripples, making an interference pattern). This is true even for some large molecules. It is most definitely true for cold atoms, like the ones I am working on.

In our lab, we are doing scattering experiments. We take two clouds of very cold atoms (less than a microkelvin!) and smash them against each other. However, they are so cold that they no longer behave like particles, as your everyday gas would. They instead act like waves and interfere with each other! The way they behave when they collide is nothing like what would happen to a particle. It looks like this:

These are two clouds of atoms trapped in some laser beams. They are about 400 nK and there are half a million atoms in each cloud. We accelerate one cloud towards the other and then release them from their trap so they can expand after the collision. The expanding halo is made up of scattered atoms.

These atoms are moving at pedestrian speeds. If we increase the collision energy a little bit more, the pattern of scattered atoms will look a bit different and develops lobes in funny places. It's one of the things next on the agenda, so watch this space!

I will add a final note about particle accelerator experiments. To do interesting physics and make a name for yourself, it's all about going for extremes. For example, the LHC was made to do higher energy collisions than any other existing accelerator. The other, often forgotten, end of the spectrum is the super slow collision regime. That's where we're at! We're doing the slowest, lowest possible energy collisions! That's pretty extreme.

2011 in Review

It has been 5 months since my last post. That's quite a long time! I have some good reasons for this. In fact, the one new year's resolution I have this year is to write more regularly!

At the end of every year (or start of the next one), I like to review the year and see how things have come along. This time, in particular, perhaps you can see why I haven't really had time for posting much. Also, this year I had two major (only) activities: physics and Taekwon-Do.


2011 In Review

Overall, the year can be summed up in one word: intense.

Let's break it down. 2011 was welcomed at a beach in Napier, after having driven for 12 hours around the East Cape of New Zealand. The next few days were spent traveling around the South Island with one of my close friends and my newly acquired husband. It was a nice trip, but made me realise that I don't really like road trip vacations. Sure, you see a lot, but it's tiring, and I would much rather go somewhere new and spend a few days getting to know the place instead of always being on the move.

Some time in 2010, I decided that 2011 would be the year that I go for my 2nd degree (dan) black belt in Taekwon-Do. Black belt gradings are pretty tough and require a lot of preparation and 100% commitment. I was mentally prepared to start training at the beginning of 2011, and a grading was scheduled for April. I began training 5 or 6 days a week and was generally enjoying myself with it. In March, the ITF Taekwon-Do World Championships were held in Wellington, and at the last minute I got flights to go watch. I'm glad I went, because I found it quite inspirational in regard to my own training.

During these few months, my new supervisor and I were trying to improve our experimental setup and figure out why we couldn't make Bose-Einstein condensates (BECs). We pulled things apart, put them back together, replaced electronics, optimised parameters, etc, but no luck. Even though we were making improvements, BEC still eluded us. It was good to go to training at the end of the day because I could physically vent all my mental frustration and not bring it home with me!

As I'm sure everyone knows, on February 22nd, an earthquake hit Christchurch. We felt it here in Dunedin, which is around 4.5 hours drive away. It was an aftershock of a quake in September, but that earthquake only caused some damage. This time, people died. Friends' homes were destroyed. The whole central city was closed down due to damage and unstable buildings. You hear about disasters around the world all the time and see the damage on TV. Somehow I always felt disconnected from them. This time, it was in my own back yard and my own friends that were affected. It was heartwarming to see all the volunteer initiatives to help Christchurch residents, and it definitely restored some of my faith in humanity! Unfortunately, they are still being shaken by earthquakes and jerked around by politics and insurance companies. I really hope they get a break soon!

Around the end of March, our grading got postponed until July due to lack of numbers. I felt a little bummed, but was glad to have more time to train. I should add at this stage that not only do I practice Taekwon-Do, but I am the instructor of my university Taekwon-Do club, so my own personal training (usually at other clubs) is in addition to the two classes a week that I teach during the semester (though I have some very nice assistants!). By coincidence, around this time, a person I knew who is higher ranked than me who had quit Taekwon-Do a year before suddenly had plenty of time that needed occupying due to a change of personal circumstances. So I asked him to train me, initially just for fitness, and slowly (but unintentionally!) got him back into Taekwon-Do and he eventually joined my club and we became friends.

In May, we had our regional tournament. In the past, I was never a strong competitor, but the training payed off and I got a couple of medals! Our club also got 2nd place overall. My TKD returnee made a very good coach and helped all of us improve our sparring. Unfortunately, around this time, the July grading was canceled due to lack of numbers, so I had to wait until December to grade in the North Island (where there are many more people doing TKD, so the gradings are a lot more regular). A setback, but in the meantime, we would concentrate on the national tournament in August.

Back to the lab: we were dredging the bottom of the barrel. I pored over PhD theses and all kinds of stuff looking for problems other people had that prevented them from getting BEC. The game is to cool a cloud of atoms to almost absolute zero and still have enough atoms in your sample to do interesting experiments. We could get our atoms to less than a microkelvin, but then something would heat them up again, preventing us from reaching the density and temperature needed to form a condensate. In July, on an unusually cold weekend, we finally cracked it. This was an immense relief. The end of my PhD was finally in sight!

From that point on, things moved quickly. We moved into testing out our ultracold atom collider (I will do a post on this later). Just imagine a montage of happy physicists running experiments, collecting data, plotting graphs, writing papers, etc. Fun times! And for me, the evenings were filled with punching, kicking, breaking boards, running, sparring, etc. Personal social life: nil.

For once, our club had a decent contingent going to nationals. We trained together on Sunday mornings, doing 1.5 hours of some sort of sadistic running exercise devised by our coach (the returnee), followed by 1.5 hours of sparring training. The tournament went well. We didn't do spectacularly in terms of placings, but everyone did well. I was certainly very proud of everyone and myself!

Things in the lab plodded along for the rest of the year. We had a setback or two, but nothing dramatic. We submitted a paper on the collider recently. My first paper!

By November, I was starting to feel tired. Training 6 days a week and spending the rest of the time in the lab was getting exhausting! I felt ready, and just wanted to get the grading over with! I should note, at this point, that the first time I went for my black belt, I didn't pass. There were a number of reasons for it, but mainly I was just not that well prepared. 6 months later, I re-tested and I did pass, but the whole thing left me feeling like I just wasn't very good at Taekwon-Do. I became an instructor straight after getting my black belt, not because this was a personal aspiration, but out of necessity, because the previous instructor had finished his studies at university and was moving overseas, and I was the next most qualified person. At the time, I felt like I just barely made it to black belt and that I wasn't cut out for much more.

This year taught me that I am cut out for more. I passed my 2nd dan grading, and I got an A. I certainly didn't do it on my own. Everyone has people helping them for gradings, and I am very thankful for the people who helped me (other more senior instructors and also my personal coach). I now have more aspirations for competing and look forward to this year's tournaments and training some of my students for their black belt grading.

In the lab, perseverance has paid off. Every year, I wish for success in the lab. In 2011, it actually happened and that makes me very happy! The next few months will see the final push to finishing my PhD, which I look forward to very much!

2011 was an intense year. It was a year of sadness and stress for many of my friends. It was also a year of happy events for friends as well (five couples I am friends with got married, one of them expecting their first child any day now). It was a year of frustration in some areas, and ultimately a year of overcoming obstacles and learning that I can be better at whatever I want to be as long as I put in the effort.

This was a triumph

I have been eerily quiet lately (on here anyway), and with good reason. After a very long time of toiling away in the lab, we finally managed to make something that has been eluding us for some time: a Bose-Einstein condensate!

A Bose-Einstein condensate (BEC) is a state of matter that occurs at extremely low temperatures. Other notable states of matter that you may be familiar with in your day to day life are gases, liquids, and solids. Usually the thing that determines what state something is in is temperature, with a fairly strict cutoff between states. The boiling point of water (100 degrees) is a good example. Pressure affects where those cutoffs are, so if you are high up on a mountain, the pressure is lower, and your water will boil at less than 100 degrees.

Not to any kind of scale and blatant disregard for using consistent units.

BECs are cold. Real cold. Ultracold (official term), in fact! They are so damn cold, you can't get anything colder. There is a hard limit in temperature called absolute zero. Nothing can be at absolute zero. It's impossible! However, you can get very very close, and at a billionth of a degree above absolute zero, BEC is a good example. Atoms in a BEC are all as cold as you can get. They are cold because they have very little energy, and they all have the same energy. They act in unison and behave more like waves than particles.

BECs don't occur naturally in the universe (that we know of) because space is much warmer, thanks to the cosmic microwave background. Instead, we have to play all kinds of tricks to get our atoms cold. An experimental setup like this is required for it:

This is around half of the setup.

I suppose you can see why it might take a long time...

Laser Cooling

One of the key techniques used in ultracold atoms experiments is laser cooling. Normally people think of lasers being used to heat things up since they are intense beams of light, so how would you cool something with one? I will answer this question, to spare you tossing and turning all night, unable to sleep because of the inner turmoil of not knowing how lasers can possibly used for cooling.

I'll start with atoms. Atoms in a gas at room temperature move very fast and therefore have a lot of energy, since energy is proportional to velocity squared. Light is made up of photons, which carry momentum that is proportional to the frequency (or colour) of the light. When an atom and a photon collide, they exchange energy. If you get the laser frequency right, then when the photon and atom bounce off each other after the collision, the photon will come out more energetic, and the atom less energetic. The atom is now slower, and therefore has less energy, and is therefore cooler (high temperature = high energy).

There are a few applets at Physics 2000 that let you play around with a few parameters and help you see how laser light can be used to slow atoms down. Check out the rest of the site too! I found it great for learning about Bose-Einstein condensation for the first time, a long time ago...

So far, this is a very simple picture. In real life, things are more complicated. The atoms and photons don't literally bounce off each other. Instead, the atom absorbs the photon and then spits it out again! One might naively think that atoms could be fully slowed to a stop by doing this, but alas, it is not so. There are a couple of limits related to the fact that the atom is always absorbing and emitting photons. However, when physicists hear about limits, they consider them to be a challenge. If that atom won't get any colder, can we trick it into getting colder? The answer is yes.

Have you heard of the legend of Sisyphus? He was a king in ancient Greece who angered the gods, and as punishment, he had to push a huge boulder up a hill, but when he got to the top, the boulder rolled back down and he had to start again. For eternity.

It turns out that by playing some tricks with polarisation, one can replicate this experience for an atom. The atom will always see an uphill potential and will climb the hill. When it gets to the top, it gets transfered into another state and suddenly finds itself at the bottom of a new hill. It looks something like this:

Nicked from here.

This is actually called Sisyphus cooling. You can't stop an atom completely like this (or really at all), but you can make it damn cold! I should note that this is exactly how I feel on Sunday mornings when I voluntarily run up and down a hill for "fun". Try it! You'll love it!

Crackpots

I don't know how prevalent they are in other fields, but physics seems to attract more than its fair share of crackpots. Either that, or I only notice because I'm doing physics. They are mostly harmless, but occasionally they write books and contaminate the minds of the unsuspecting public. (By the way, if you are a physicist or have somewhat of a physics background, check out the free chapter of that book. It's like a sort of physics slapstick comedy.)

I've had various experiences with crackpots over the years. On more than one occasion, ragged, disheveled looking people have wandered into the physics department desperate to talk to someone about their amazing theory that will surely solve some longstanding physics problem or solve the world's energy needs. In all cases, they have little to no physics background and a poor grasp of maths, and they are also very easy to spot from a distance.

I actually (hopefully) managed to discourage one such person. This guy said he had a background in surveying and complained about how current technology for imaging underground was not very good. It's based on blasting sound waves into the ground and then observing their reflections (they do something like this in Jurassic Park). He thought that a far superior method would be to use cosmic rays and that he just needed some help to get his idea off the ground.

Another sort of crackpot exists as well. This is your average person on the street who is not satisfied with (and nearly 100% of the time doesn't understand) a particular theory and comes up with their own. Of course, what they have is just an idea, not a theory as such. I really wouldn't care about this very much at all, but for some reason these people gravitate towards me in social situations. Here is an example of one such situation that took place at a party. I was sitting on the couch minding my own business, when a guy sat down next to me and started making conversation:

Guy: Hi, I'm Bob. How do you know [Party Host]?
Me: Hi. We are students in the same department.
Guy: Oh! So you do physics too!
Me: Yeah.
Guy: Okay, so I have this theory about the universe... I think it's way better than [Standard Accepted Explanation]. Gee, I really like physics, but I never understood maths.

I actually can't remember what his theory was, though I can assure you that it was 100% crackpot. I was in panic mode at that stage, trying to figure out how to politely extract myself from the conversation. Luckily, he got distracted by someone else and went away. Phew. Unfortunately, the next guy who sat next to me proceeded to do exactly the same thing upon hearing that I do physics. I made some excuse, got up and went home. Enough was enough.

I'm told that a similar phenomenon exists in psychology, where people have a driving need to tell psychologists their "theories" about human behaviour. I'm curious about other fields, even non-science fields. Does anyone else have any experiences or funny stories about crackpots?

Lab Tours

Every so often, we give labs tours to high school students. Usually they have an interest in science or are part of a special program. I think walking into a lab like mine can be a little overwhelming for a lot of them. Explaining the physics of what I do is also a little tricky because it's not a topic at all covered in high school, but I do my best to draw analogies with ideas they are familiar with. Some students definitely get more than others. If they are totally quiet, I get the feeling that they didn't understand anything. I consider it to be a good sign if they ask questions!

A few weeks ago, a group of such students came to the lab for a tour. They were part of a group of minority students gifted in science - the kind of kids who will hopefully study science at university. I talked to them a little bit about what it's like to do a PhD (something they didn't know much about), and how it's a lot more practical than studying, doing assignments and taking exams. I also mentioned teamwork. Experimental physics is usually not an isolated venture; it's very common to work in groups of 3 or 4 people on the same project. In my explanation, I happened to say that me and a few other people built up the experimental setup, which involved a wide range of skills.

One girl cut me off.

Girl: You mean you built this yourself??!!
Me: Well, me and some other people. I didn't do it all myself by any means.
Girl: Wow!
Me: ...
Girl: Can you make a TV??
Me: That's more of an electronics engineering thing. Maybe I could assemble a TV, but I wouldn't know how to design all the electronics to make it work.
Girl: Can you make a boom box???

Impress teenagers with your physics skillz. Make a boom box.

Photography Contest!

The local museum runs a wildlife photography contest every year. There are three categories: plant, animal, and human impact on the environment. Last year was the first time I entered, and I won a highly commended prize for this photo:

"Abandoned"

Getting that photo was mainly luck. We were walking on the beach and happened to come across the car. It was late afternoon and the lighting was just right.

The contest rules stipulate that the photo must be taken no earlier than January 2010, and in that time, I have not come up with anything nearly as cool as the car. Out of everything, this is what I came up with and submitted last week:

"Spider on the wall"

"Reclamation"

"Stranded"

"Simplicity"

Click on the captions to get to the high resolution version.

I'll find out how it went in the next couple of weeks!

References

Information spreads quickly on the internet, particularly through social networks like facebook and twitter. Someone learns an interesting factoid, finds a meaningful quote, sees an inflammatory news item, funny video, etc. and immediately shares it with their friends. Very often these tidbits are copied and pasted from friends' status updates or blogs without much thought. I've certainly been guilty of this myself.

It's only natural that misinformation travels through these channels, and it's actually nice to see that only a small portion of shared items (at least from my social group) are blatant conspiracy garbage.

So how can you tell if what you're reading is cow turd, anyway? Read the references! Most of these articles/blog posts/websites have links to the evidence they say backs up their claims. The recent DCA hysteria, documented and debunked nicely in Arstechnica, is a great example of this. It took me about 5 minutes to click on a couple of links from the original page to figure out that this was written by someone who 1) does not understand the process medical treatments need to go through from initial lab tests to treating people, 2) has not done high school level cell biology, and 3) does not have good reading comprehension.

The lesson here is that when you come across something that sounds like a conspiracy or is too good to be true, follow a few links from the source. It doesn't take long to figure out if it's legitimate or crazy talk. Read the references, people!

Antimatter!

I love experimental particle physics papers. They have so many authors! The STAR experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory recently created some anti-helium-4 nuclei. 18 of them, in fact. The effort took no less than 395 authors (+/- 10 or so).

They made the anti-helium nuclei by colliding gold atoms at ridiculously high speeds and detected them in this thing:

They call their detector the Time Projection Chamber. That's the other cool thing about particle accelerator experiments: cool names! I feel inspired to come up with cool names for bits of my experiment, because the current terminology is a bit lackluster. In reality I have "magneto-optical trap" and "science cell", but really something like "atomic decelerator" and "atom interrogation chamber" could make it seem more exciting, or something that makes a cool acronym, like HERCULES or GUNDAM.

Any suggestions? There are lasers and magnetic fields involved, if that helps!

Angels and Demons

Some people get really upset when movies have bad science in them. Despite being a sciencey type myself, I feel the opposite. The more fantastic the concept, the more entertaining I find it. I suppose it's because I take it as a sort of science slapstick comedy rather than the intended movie genre.

Take the movie 2012, for example. Unfortunately it hasn't been ripped to shreds by Insultingly Stupid Movie Physics. Who doesn't want to see a giant tsunami crashing over the Himalayas?

Last night I watched Angels and Demons. It was on TV and I wanted to unwind after a busy day. I'm not a fan of Dan Brown at all. I haven't read his books, but the murder mystery style of the movies is kind of entertaining. For those who haven't seen it, the crux of the movie is that the Illuminati are threatening to destroy the Vatican with some antimatter stolen from CERN.

Now, this antimatter is in a battery powered hand held vial about the size of a water bottle. We are told that the antimatter must be held in a magnetic field or it will just annihilate matter in the container walls. It is true that matter and antimatter annihilate when they come in contact, releasing high energy photons. If you had a milligram, it would be enough for an explosion of the equivalent of 50 tons of TNT. This could potentially be done at CERN with its present capabilities, but it would take 300 billion years to accumulate that much.

There is a nice article at the CERN Courier talking about what it takes to trap antimatter. It takes some very strong magnetic fields, which requires some pretty high currents (since electromagnets are required). So clearly, the hand held antimatter container is highly improbable.

However, this is not what bothered me. What bothers me is that the physicist in the movie says that with their breakthrough in trapping antimatter on a large scale (1 mg), they hope to use it as an energy source to power cities, and not as a weapon. Hold on a second. Their container has a magnetic trap to hold the antimatter. The current for the trap is provided by a battery that lasts up to 24 hours. The magnetic field required to hold antimatter is on the order of several Tesla, generated by superconducting electromagnets. Even if the antimatter is ultracold (like a BEC), you would still need a fairly hefty field. This requires a very high current! Hundreds of amps! Generated by a battery!!

If you have a battery powered device that can trap antimatter, then you probably don't need antimatter as an energy source.