"Rainbows" from the plane

In my many endeavours to get good photographs from the plane, I once noticed some faint rainbow like colours in the sky below. I wasn't imagining it. On careful observation, I noticed it was more pronounced with clouds, with the overall mist providing a background. I took some photos to later analyze on my computer. Here is what I got. The phenomenon was real indeed. The left are the unprocessed images. The right are the same images with colour greatly enhanced (using Irfanview). Your eyes automatically do these things and can spot the slightest of colour.



While it puzzled me, I left it in the background to ask a physicist friend sometime. It was such a small effect that I would need to show the photo to ask the question. I forgot about it until I undertook a flight a year later. This time, the effect was very clear. With the sun behind me, I could see clear colour bands on clouds, near the shadow of the plane (Open in new tab to see better).



It made sense. I was seeing a rainbow. A rainbow is formed when light undergoes total internal reflection off a water droplet. Clouds also have water droplets. Sunlight reflected off water droplets made the rainbow. Here are some explanatory images from wikipedia .



Simple, isn't it? Well, not so. A rainbow is formed at 42 degrees. So, if you drew a line from your location (your eyes) to your shadow (with conventional rainbows, if you don't see the sun, you might have to imagine where your shadow will fall), and another one from your location to the rainbow (anywhere on it), it will make an angle of 40-42 degrees. A second rainbow (if present) forms at an angle of 50-52 degrees. However, the "rainbows" I was seeing formed at an angle 5-10 degrees and they had multiple ones close by.

With wikipedia, I found I was seeing a phenomenon called "optical glory". The name derives from the Brocken, the tallest peak of the Harz mountain range in Germany. Because the peak is above the cloud level, and the area is frequently misty, the condition of a shadow cast onto a cloud layer is relatively favored and often seen with the coloured halo around the observer's head.

Glory cannot be explained by simple ray diagrams. It is said to be due to some form of interference and back-scattering. Mie scattering, the theory which includes all kinds of scattering off particles of a certain size, predicts that 10-20 micron sized droplets (note - rain drops are 100 times larger) would produce such coloured rings. The angle of the glory tells about the size of the droplet. There are also a host of similar optical phenomenon which produce colour in the sky, depending on the kind of cloud and the position of the sun (Optical Phenomenon).

Everything explained. We're good, right? Well, not quite. Having studied optics, I would have liked an explanation which gave me a reasonable picture in mind (like the rainbow ray diagram) as opposed to "crunch the numbers and you'll get it". Mie scattering theory is one of the messiest theories, which offers very little easy insight. So, I will have to give up my privileged insider status, remain a layman and just repeat what I'm told, just as I do for questions on cosmology and String Theory. I hope the theory of optical glory does not change very soon.

Meanwhile, whenever you get a chance, take a look at the sky. And choose a window seat when flying. You never know what you'll see!

10 Things I learnt in the US - part 2

6. Guns

We've seen them in movies. People keep guns at home. But to actually meet a gun owner was still shocking. I'm also not used to people talking casually about playing with assault rifles or hunting. I happened to go to a gun show once (It was side-by-side with the Heritage India festival), and was amazed by the murder weapons all around, all on sale! Thankfully, loaded guns were not allowed inside. In trying to buy a gun, I found out that one needed to apply for a license, which typically takes 3 days (Thank God, some regulations atleast).

Many people feel that they need guns in case the government attacks them. Others go by "Who will protect your family at home against an intruder?". ("Bowling for Columbine" talks all about this). It is quite amazing that many people feel safer with a murder weapon at home.


7. The Respected Professions

In India, the respectable people are those with a high education and/or high position - doctors, professors, IAS officers, company general managers, etc. However, in the US, people respect those who do a service for the community without high pay. Doctors are CEOs are looked at as money making. Lawyers are totally detested. Professors are looked as elitist. Civil administrators are "part of the Government". School teachers, police officers, military personnel and firemen are the respected professions. They are the ones quoted in newspapers to give a true testimony as to what people feel.

8. Insurance (and Credit Card) Scams

I never realized that scamming could be part a successful business model. One of the simplest ways to make money is to make people fight in order to claim money that was rightfully theirs. Many people don't notice the "mistake", while others try to fight, but get too busy and then forget about it. Insurance companies, apart from the highly regulated home, health and car insurance, are pretty much a law upon themselves. There is always fine print, or millions of documents to provide along with hours on the telephone to claim what should have been yours at the start. For those who fight till the end, like grad students with plenty of time, the company does pay up, and despite all the trouble it has caused, can claim to have "done its job" and move on to the next victim. And until the company name is pasted all over the internet with bad reviews, the scam goes on.

9. Minority religion groups

That there were many conservative Christian groups is one thing. Finding non-mainstream groups who have ultra-conservative beliefs is more shocking. From a colleague of mine, who was once a Mormon, I found out that Mormons live in almost a parallel universe, where creationism, belief in their prophet (who lived in the 1800s), communication with God are all truths, where coffee and alcohol do not exist and where all young people must spend 2 years of their lives in missionary service. One would expect the pluralistic nature of American society, along with communication and media, to prevent people from being so orthodox. But that isn't the case. Like Mormons, there are orthodox Jews, who don't operate machinery on Saturday (due to Sabbath), Amish people who still use horses for transportation, and probably several other lesser groups too.

There are also many extreme Hindu groups, whose views on Christianity and Islam would shock the average Indian ("Christianity and Islam, Capitalism and Communism are the 4 axes of evil in the world"). Some youths take a year off from education or work, to devote their time to the Hindu Swayamsevak Sangh, which sounds uncannily similar to Mormons spending time for missionary service. I wouldn't be surprised if similar groups exist for Islam too.

10. Nicknames

This is one of the more everyday things which does not take long to figure out. Prior to coming to the US, I always believed your name, when formally asked was what is written in your documents. However, during my first teaching lab, when I asked a group of students what their names where, I got "Jen... Ed... Al...". I soon realized that one could choose one's first name everywhere - what your colleagues call you, your credit card, name plate - except for very serious things like your driving license or passport. Many names have an associated short form, like William-Bill, Joseph-Joe, Amanda-Mandy. Some parents even choose a name based on its short form (a friend of mine was named Amanda because her Mom liked the name Mandy). Others, who have a foreign name, choose a more American short form (my favourite is Devarajan-Dave). Still others, (I've known many such Chinese) completely abandon any resemblance to the original name (Weihao - Jennifer, Zhechun-Lance). To all those parents who have ambitious plans to name their kids, if your kids don't like their given name, you may find them being called something completely different.

10 Things I learnt in the US - part 1

Back in India, we hear a lot about the US - News, Hollywood movies and stories from people visiting from the US. Nevertheless, that isn't a complete picture. Here are a list of things that I didn't know or fully appreciate before coming here


1. Immigrants

While I always had the picture of "White America", coming to the Washington DC suburbs, I was surprised by the number of immigrants. In fact, where I live, I hardly hear a proper American accent, either at home, work or outside. My earlier post, "People I meet" talks about this.

2. The Conservative Movement

If many people want to close their eyes and not face the truth, they can create anything for that - media (FOX news), talk shows, books (Intelligent Design), experts, scientists (Will Happer - 'More C02 will be better for humanity') and even museums ('Creation Museum' Seeks to Disprove Evolution, Paleontology, Geology)! While I knew that Americans voted Bush with all his Conservative leanings, I had no idea of the extent of support structure for conservative ideals, however blatantly wrong they may be.

In India, being "conservative" has a negative connotation - "his parents are very conservative and will not allow him to stay out late." Being "liberal" has a positive connotation. Those who'd like to say that they are not enthused by modern radical ideas refer to themselves as "traditional". In the US, the "traditional" people refer to themselves as "Conservative" (which I found quite amusing). Among such circles, "liberal" is a bad word. How can being free and open ever be bad? Well, that's the Conservative Movement.

3. Racial Tensions - what really happens

Back in India, we learn about the American Civil War and racial tensions in the US. We also know of America welcoming talent from all around the world and celebrating their African-American sports heroes. Coming here, I was interested in learning the truth. Is America racist?

The short answer is no. Even in the most Conservative circles, being openly racist is looked down upon. People are polite irrespective of who you are. Still, several subtle biases still exist.

However, the question is more complicated than I initially thought. It is not just about White-Black or White-Brown racism. Tensions exist between all the various minority racial groups. In fact, such groups are more open and explicit about it, since they don't have a "racist" tag to avoid (see "Crash", a 2005 movie). My first glimpse was when I heard a black person rant to his friends about how Hispanic immigrants were a problem. "They cause all the trouble. It's not us. They should all be sent back to their country". Also, when I lived in a predominantly black housing complex, I felt the resentment towards outsiders and would occasionally encounter someone who was rude to me when I asked for directions.

4. Non-Profits

While NGOs in India are associated with social service and upliftment of the poor or underprivileged, there are Non-Profits for everything here - the environment, fiscal discipline of the government, for guns, against guns, monitor of Catholic law makers and even pro- and anti-circumcision. There is a Non-Profit for the wildest idea you may have.

Having been around for a long term, Non-Profits follow certain, almost business models. They have their standard lines, "We've been doing great work .... However, to keep up with the increasing need, we need your contribution" or "... are in great danger. If you don't act now, we will lose ...". Their methods include guilt tripping and sending you freebies (name stickers, greeting cards) to make you feel obliged.

5. Car culture

While I had heard that America was largely dependent on cars, I didn't fully appreciate it until I came here. Large parts of the country do not have decent public transport. Even the suburbs of Washington DC have places where no buses run. In many places that do have buses, they run only weekdays. The concept that you cannot go somewhere because you do not have a car was new to me.

In American culture (includes immigrants and all), people are very helpful towards those without a car. For any get together, you can always be sure that someone will give you a ride, from and to your doorstep. People who live out of public transport's reach, will pick and drop you off at the metro at the very least.

Ironically, one of the hardest things to do without a car is to buy one. The good cars get sold before you reach them. Many cars are in far flung places, out of reach. Seeing a car itself is a half day affair using the metro.

After buying a car, everything changed. There are no time restrictions to return. Far flung addresses don't evoke the question, "How will I get there". While I do my duty to help my car-less friends, I hardly spare a thought for bettering public transport to help the unfortunate people out there who don't have cars.

Of Men and Politics

Here is a joke I once heard from a friend

Mr. & Mrs. Sharma celebrate their 50th wedding anniversary. Friends compliment them on how happy their marriage has been. Mrs. Sharma says
"The secret of our happy marriage is that the woman makes the small decisions, while the man makes the big decisions. For example, I decide the vacations we take and the children's school"

Someone says, "What about the car you drive?" - "Small decision"

"Finance and saving?" - "Small decision"

"House you live?" - "Small decision"

"What then are the big decisions?" - "Who should be Prime Minister; Is George Bush right; Should India sign the nuclear deal"

The joke captures the essence of what I'm going to say. As a kid growing up in India, I remember that in parties, men and women would often separate. The men, would talk about politics, while the women talked about the more everyday things like kids, friends or the vegetable market.

As I got older, many men would try to educate me about the facts of life - Congress misrule for 40 years, how India could have done better if Nehru had been more aggressive on Kashmir and how politicians are ruining the country. I guess I have to mention my grandfather's pet theory on how politicians continue to keep people uneducated and make them reproduce rapidly so that they can get more votes. If only India would make education necessary to be eligible to vote, we can get rid of the "rogues" (current set of corrupt politicians).

With time, I learnt that men with strong political views often never thought things through. Going to college and living in a hostel exposed me to a range of political views. And since we often talked about these things to friends and wing-mates, I learnt how to argue my case out, whatever it might be. It didn't take much probing to tell that men and their strong political opinions were heavily biased or flawed and often said things which had very little basis if at all.

Of course, the men themselves were nice people. It was quite time later before I realized that political opinions were disconnected from the rest of their personality. It seemed strange why a genuinely nice person would have such intense hatred for Muslims, people he has no knowledge about. I also noticed that older people had stronger opinions. The younger men, people in their twenties, usually did not say much and politely listened while the others ranted.

I noticed that women would never enter any of these discussions. One particular "mama" ("uncle") was telling me why India should launch a full scale war against Pakistan. At some point, I felt, "This mama is too extreme. I need another opinion to counter it". When the mami passed by, I looked to her and was hoping she would give her opinion. Surely she couldn't be living with a man who wanted to bomb Pakistan and be quiet about it. She politely asked me about how I was doing, my studies and all, and then left me to the mama after that.

Now, the question is, is there a point to an argument? I guess one is duty bound to defend oneself and one's kind, and needs to educate the lesser enlightened. On several occasions, I've had to tell people in Bangalore that North Indians (in the South, UP doesn't sound very different from Punjab, and so I might as well say all North Indians) are nice and hospitable people, even though the worst politicians and goondas come from there. Many of these discussions have a positive effect and people either rethink their views or maybe just don't say it in my presence. It was through such arguments that I learnt many things, such as how people's lives depend on subsidies - while there may be lots of corruption and misuse, one simply can't eliminate them.

Okay. Then when is an argument pointless? When neither party learns anything new. I've spent many hours trying to show holes in flawed logic and explain that Pakistan consists of people for the most part. A complete waste of time. I take that back. I've learnt something new - never to do it again. Women knew this all along. Makes me feel stupid. Anyway, my policy now is to disagree but not argue. This is quite hard to do, particularly when the other person has a fiery speech ready to be delivered. Despite my staunch resolution not to waste time arguing, one my roommates at College Park got me arguing about why Israel doesn't control the world. This brings me to another point. An argument is even more pointless if its outcome will not change anything. Even if learn that Israel is manipulating Egyptian policy, it doesn't change anything. I'm a powerless individual, who is most likely not to campaign to change Israel's foreign policy. Even if went all out to change something, I probably wouldn't make much of a difference. In that light, one might as well let men have their say on how India should treat Pakistan. Save the argument for how easy it is to use the Internet.

Life in the US has been different, with regards to talking politics. Barring that one roommate, most people my age don't argue about politics. Young couples prefer talking about the more everyday things like work, houses, vacations or kids. Americans do not talk to politics to people they do not know well. Rants, if any, in a group of physicists, are highly leftist and much to my liking. A welcome relief! The occasional time I've visited older Indians (those with grown up kids) in the US, I've chosen the ladies' conversation table.

I had almost forgotten about pointless political arguments. However, recently, on an IITK alumni mailing list, I've noticed that a few people have begun to rant about the so called "Secular India" - how Christians are mass converting Hindus and how Hinduism is dying out. When I voiced my dissent, I was pointedly challenged by one particular person, Mr.X. Since he seemed rational, I wrote a lengthy email educating him about certain things about the South he never knew. To my credit, some other people appreciated my email, and with a halo on my head, I felt that I had done some good. Much to my dismay, it looks like Mr.X's political views haven't changed at all and he has conveniently forgotten the things I said. Also, he isn't the only one and there are a couple others like him, some of them terribly illogical. On further scrutiny, I noticed that these people seem to be my age to a few years older to me. That's when it dawned on me. The next generation of crazy theory politic speaking men is born!

I've sworn to myself. When I get old, I will keep my political views to myself. Even if I have the magic formula to make India a great place, I would do better by working for an NGO or giving to charity.

The People I meet

Key -
Blue - ubiquitous
Reddish Brown - roommates
Lilac - University of Maryland
Green - NIST & Research connections
Light Brown - Random encounters

Living in Washington DC has opened me to a wide variety of people, particularly with respect to national origin. I've always been curious as to where people come from, and often have shamelessly asked people I've just met (Ice cream vendor or taxi driver or metro co-passenger), where they come from. Surprisingly, most people are happy to tell me that and many have told me how life is back in their country.

I've also been fascinated by maps. It felt nice to put all the kinds of people I've met into a colourful map.

Some observations

- I've had roommates from every continent in the world.

- I realize that being in Washington DC, being associated with NIST (National Institute of Standards and Technology) and being associated with UMD (University or Marlyand) all contribute to the diversity of the people I meet.

- Americans, Chinese, Indians, South Koreans, Russians and Mexicans (Filipinos and Brits to a lesser extent) seem everywhere.

- Broadly, I tend to meet people from developed countries through NIST (and research connections), people from developing countries through UMD, and people from other countries through random meetings.

- Amongst the most rare and exotic countries, I've met people from Togo (pop. 6.3 million), Nicaragua (pop. 5.8 million), Finland (pop. 5.2 million), Eritrea (pop. 5.5 million), New Zealand (pop. 4.3 million), Lebanon (pop. 4 million), Mongolia (pop. 2.6 million), Botswana (pop. 1.9 million).

- I've met many people from El Salvador (pop 7 million), a small country in Latin America. El Salvador had a brutal civil war (1980-1992), which may explain how there are so many immigrants here. There are so many Salvadoreans in the Wash DC metro area that there are even Salvadorean gangs (MS-13). Most of the Spanish speaking people I encounter are Salvadoreans.

- I've met a lot of Ethiopians. They speak Amhari. Sometimes, asking someone what language they are speaking (to either their family or colleague) is a better way of asking what country they come from.

- Given that I've personally met people from so many countries, I think that there are people from almost every single country here in Washington DC.

- I've met many African-Americans (so called "Blacks" or people of African origin who have lived in the US since colonial times). The African-American community is quite distinct from the rest of America and I would have liked if I could assign them another place on the map. While many people I've met don't distinguish African-Americans from Africans (I'm referring to people who've recently come from Africa), I think there is a world of difference, from appearance to accent to community. Africans come much closer to other immigrants. They have their tiny communities and look upon the US as opportunity and livelihood. African-Americans have a long history here, and form a large community amongst themselves.

- I've not met anyone who referred to him/her self as a Native American or Pacific Islander. However, according to a study in 2004, Puerto Ricans (US territory in the Carribbean) have 17.6% Native American ancestory proportion. Maybe that is the closest one can get to meeting a true American.

Performing

I started performing on the piano about 10 months ago. Of course, I don't play on an professional circuit, get paid, or anything like that. I only play for friends, fellow amateur musicians (www.amsf-perform.org) and people at retirement homes (younger people may know these as "old age homes"). Here are some of the things that a performer experiences.

The Nervous Beginning

For my first performance, I took up a very simple piece, so that I wouldn't have to worry about technical difficulties and could only focus on the performing aspect. Amongst a group of musicians ranging from beginners to amateurs, I was put last on the list to play. While some people played quite nicely, others seemed to struggle ("They should've practiced more" I felt). By the time I was to play, I was pretty much waiting for my turn. When my turn came, I eagerly went to the piano. When I sat to play, I suddenly found all kinds of things going on. My mind was in a swirl, my stomach had this funny feeling and my hands and legs were shaking. I was no way playing anything like what I had practiced. My mind wasn't working at all and I was just trying to get by. Now I understood where the "They should've practiced more" came from.

The event replayed itself in my mind a few times, and I was still wondering what happened. My piano teacher explained, "Expect to get nervous. Once you're nervous, then you can say, 'Okay, now I'm nervous. Here on, I can only try to do my best' and move on." The good part of nervousness is that it usually doesn't last forever. If you hang on for the first minute or so, your heart slows down, your mind gets calm and you get back into some sort of normalcy where you can "play" instead of "getting by".

Nervous also makes one start the piece faster than what one normally does. "This happens," as pianist Brian Ganz once explained in a masterclass "because the human metronome, the heart, is beating faster than normal". Starting faster when you're nervous is the sure recipe for disaster when your mind is in a swirl and your already shaking fingers can't keep up. Sometimes, in my eagerness to show my piano teacher a piece, I've done exactly that, ending up with my mind blank and finding myself in the middle of nowhere. So, now, I usually make a conscious effort to start slower, so that it is at the right tempo.

Expecting to be nervous has also made a lot of difference. I'm more prepared for the feeling instead of the "What is happening to me?" thing. I also try to make sure that I don't have any problem spots near the beginning

The Problem Of Trying Not To Make A Mistake

In my first performance, I was really trying my best to get everything right. It was a simple piece and I wasn't going to make a mistake. However, what ended up happening was that I was focussing on getting the notes right rather than playing the music. I probably lost out on some of the expression in the process. The beauty of music is in what you do right, not what you don't do wrong. In the end, people listening don't care about the mistakes you made. It is the musical content that matters.

In fact, trying to play perfectly has worked against me. It has taken the focus off normal playing and I've made mistakes where I normally wouldn't have. I remember some of the times I've played in front of my teacher. I'm playing a piece I've practiced a lot the past week and I want to show how well I play. A mistake comes in, makes me conscious, then another, and finally I'm forced to stop, take a deep breath and restart.

In recording, this is a dilemma. Mistakes in a recording really stand out because they grate each time I hear them. So, I'm left between simply playing and letting mistakes be, or trying to be more careful overall at the risk of other problems. Sometimes, I simplify some of the difficult spots, so that the chances of a sour note are low. But there seems to be no solution for it.

Trying To Keep Going

In conversation with my piano teacher, he told me an interesting fact. Pianists, even the best, always make mistakes. But, they just keep going as if nothing happened. Reminded me of a performance I attended. The young pianist, Naoko Takao, was performing wonderfully, when I suddenly heard a sour note. I knew the piece very well and so it kind of jarred me. However, she kept going, making me wonder if I heard it right, and then, at some point I moved on too. She finished the piece very well, and I felt that it was a perfect performance except for one note. Being an informal performance, I saw her talking to a friend as she walked out. She mentioned nothing about the note. Now, when I think of it, I realize that she had probably made several (most likely small) mistakes. What I had noticed wasn't anything out of the ordinary.

When practicing, I normally stop at a mistake to try and fix it before moving on. A piece doesn't feel right if a crucial note didn't sound. However, this is exactly the opposite to what one should do when performing. You can't undo or fix something that has happened. You have to keep going.

Often, particularly for difficult parts, I keep a "backup plan", where I know how to cover up, continue and move on, if I happen to make a mistake. Someone who doesn't know the piece wouldn't notice that something was amiss.

When performing, there are so many unexpected things when performing- "Why didn't that note sound?", "Shoot. I missed the B-flat", "That chord was completely wrong", "That key is out of tune". I keep trying to move on. Luckily, there is something called the auto-pilot mode to help.

The Auto-Pilot Mode

As you learn a piece and play it repeatedly, you develop a kind of muscle memory. This is similar to driving a car on a familiar route, when you can do everything perfectly, while your mind is in another world. While practicing a piece, I can be thinking of something else, like what happened in the lab or a conversation with a friend, while my fingers go on in an auto-pilot mode. The piece is usually quite bland and lifeless when played that way. Plus, it isn't 100% reliable. At the end of a phrase, it suddenly leaves me high and dry and I don't know what to play next. That's when I snap out of my mind wandering and try to get a bearing of where I am.

Nonetheless, auto-pilot mode has rescued me from so many lapses of concentration. I've made an unexpected mistake, and my mind is still in a spin about what went wrong. But my fingers do their job and I get the time to tell myself, "Relax. Keep going", and slowly get back into the piece. When auto-pilot mode fails during a performance, that is complete disaster. You have no idea where you are and your fingers don't know what to do next. You just have to stop, and then try to start somewhere. Hasn't happened to me yet.

The Gremlin

There is a phenomenon peculiar to performing, which my piano teacher refers to as the Gremlin. I'm playing fine, when suddenly a little Gremlin comes inside my head and asks, "Do you know what note you're going to play next on the left hand?". That's when, if I try to think of what I'm going to play on my left hand, I suddenly become conscious of it and what would have normally happened doesn't. Also, If I try to look at my left hand, I suddenly upset the hand-eye routine and make a mistake. The best response to the Gremlin, is to ignore it and get on to auto-pilot mode so that you're not conscious about what you're playing, and things happen as they are used to. The Gremlin visits me atleast once or twice during a performance. Thank God for the auto-pilot mode!

The Performance Piano

In one of my performances, the piano I was playing on just wasn't doing what I wanted it to do. I was playing exactly as I would at home, but the base was sounding over the treble. I tried to fix that by putting more sound in my right hand, made mistakes, gave up on that and then finished the piece, relying a lot on auto-pilot mode. All the carefully crafted expression just did not come out on the piano.

Practicing on a piano at home, I sometimes fine tune things so much that it ends up being very piano specific. It has taken a lot of awareness of the characteristics of my piano and gauging the performance piano to suitably adapt to it, as well as practice on a whole bunch of pianos so that my playing doesn't get very piano specific. I don't want any surprises while performing.

The Early Sigh of Relief

Often, after successfully getting through a particularly tough part, I feel "It's easy going from here. I just have to get through ....", when suddenly, having unconciously switched to auto-pilot mode, it fails me and I snap back with a jolt "It's not over yet", and I try to regain my concentration.

The End

Finally, when I play the last note, I tell myself, "You're done. You can't make a mistake from here". That is indeed a true sigh of relief. After releasing the last note, I look to see what the audience response is. Did they like it? Enthusiastic? Or was it just "some music" for them, which they didn't get? Often makes the case of what I choose to perform the next time.

Laser Cooling and the Anti-Murphy's Law

Laser Cooling follows some kind of Anti-Murphy's law. While normally, something you expect to work doesn't work as well. Like, a kilogram of petrol (or gasoline) in your car has 47 MJ of energy, it gives you less than 18 MJ to run your car. With laser cooling, things which were not expected to work have worked, while things which were expected to work have exceeded their limits.

One of the most fascinating stories I've heard from the history of laser cooling is that of sub-doppler cooling. It is one of the few times in science when experiments beat the theoretical limit.

A brief background of laser cooling. The idea came in the 1970s. For a gas of atoms, all the energy is in its motion. If you can slow the atoms down, their temperature will fall significantly. You do that by shining the proper laser light from the proper direction and using the photon momentum to slow the atoms down. Here is an instructive picture. In the quantum picture, light consists of miniscule, finite particles, called photons, which have a certain energy and momentum, like ordinary particles (for the record, photons differ from ordinary particles in that they have no mass and that they travel at the speed of light). Imagine a truck free-rolling (for eg. putting it on neutral gear at some speed) on a road. Now, if you stood in front of it and threw many balls (probably thousands) at it, it would slow down significantly. The atom is like the truck and the balls you throw are the photons.

What if the truck was moving away from you? If you threw balls at it, wouldn't it move faster? That's when the key concept of doppler shift comes in. When an atom is moving towards a laser beam, it sees the light at a higher frequency (referred to as blue-shifted. Blue light has a higher frequency than red light), the same effect as when you hear a train horn coming towards you at a higher pitch. Similarly, when an atom is moving away from a laser beam, it sees the light at a lower frequency (red-shifted), just like the train horn sounding at a lower pitch when the train has passed you and is moving away from you. The youtube video below is very instructive.



One of the key principles of quantum mechanics is discrete quantum energy states, which play a role when you consider tiny systems. If you consider an atom with 2 energy levels (simplest case; they typically have several), the atom can absorb (and later emit) light at a particular frequency which corresponds to the energy difference between the 2 states. It is referred to as a resonance, where atoms scatter light only if it is at the correct frequency. If you shone resonant laser light on an atom, it would see the light only if it was at rest. If you red-detuned (lowered the frequency) of the light, an atom moving towards the light would see it blue-shifted (increase the frequency). That would bring the light into resonance for that atom. The atom would scatter photons and be pushed back. An atom moving away would see the light red-shifted, which would move it further out of resonance. That atom will not be affected by that laser beam.

So, if you put "red-detuned" laser light from all directions, you'll get atoms trapped at the center. If any atom tries to move in any direction, it sees oncoming laser light on resonance, scatters photons and gets pushed back. One keeps a magnetic field gradient to enhance the effect of the laser beams (I'm skipping the details). This is called a Magneto-Optical Trap (MOT).

Below is a video of sodium atoms in a MOT. It is in a glass cell inside vacuum, so that other atoms and molecules, normally present in air do not destroy it. The bright spot you see is ball of trapped sodium atoms scattering the yellow laser light (same colour as sodium lamps) that is used to trap it. There are probably a billion atoms there.



Back to the story. Once the idea of laser cooling had been established, theorists (physicists who work on theory only) made a simple model for atoms and predicted that you could cool Sodium atoms down only to the doppler limit, 240 uK (microKelvin, 0.000240 degrees above absolute zero, much colder than liquid helium), which is the point at which the heating due to laser light prevents the atoms from getting colder. It was simple and straightforward enough and taken as the best you can possibly do.

When people started doing the experiment, they noticed something strange going on, where things were not behaving as expected. On taking a more careful look, they found out that the atoms were actually COLDER than the 240 uK! On playing around with the setup, they found they could cool the atoms down to 40 uK, 6 times colder than the doppler limit! To put this in perspective, the best solar cells have achieved 25% efficiency. Imagine if a scientist working on a solar cell found that she got more electrical energy from the cell than the total energy falling on it. That simply can't happen! So, how was it possible to beat the doppler limit?

It turned out that, in the simple model, the theorists had assumed a 2-level atom, which is quite reasonable considering that other levels don't participate in the cooling. However, it turned out that the other levels did in fact play a role and instead of preventing the atoms from being cooled to the theoretical limit, actually conspired to enable them to cool to a temperature 6 times lower! So, instead of being stopped at the doppler limit, we now have sub-doppler cooling and a sub-doppler limit.

Another story I've heard is from people who cool Erbium. Erbium is a more complicated atom with many more energy levels. The physicists had worked out the optimal parameters from theory and were making a MOT. They got some atoms trapped, and then decided to play around with the laser frequency. Trying out the laser frequency on the blue-detuned side of the resonance, they found that they were able to do better and got a bigger MOT. How is it possible that laser light which would push atoms away can even trap them? It turned out that the magnetic properties of Erbium played a role, and again conspired to make things work.

There are other such stories I've heard in laser cooling, where some kind of Anti-Murhpy's law seems to exist. While I'm sure that many people who work in the field face the usual frustrations and struggles of trying to make things work like they're expected to, it is amazing that there is are so many instances of Anti-Murphy's law where things have worked better than they should have.