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?