Life as a Physicist

We like to say that science is deterministic. You do x,y, and z, and then a will happen. I 100% agree with this. Except when it comes to noise.

What is noise? This is part of the problem – it comes in so many forms. Noise is like a weed. We call a plant a weed when it doesn’t belong. Got grass in your garden? It is a weed. Got grass in your lawn? Definitely now a weed. Is your cell phone making buzz-buzz-buzz sounds on your computer speakers? Noise! Are you using the cell phone signal to talk? Not noise!

But electronic noise is more insidious than the weed analogy implies. If you have an iPhone you can do the following experiment. Sit down at a computer that has separate speakers – the key is that an exposed wire connects the speakers to the computer. Place the iPhone near the speakers*. Wait for a few minutes. Now you’ll hear the buzz-buzz-buzz. So you know the source – you put the iPhone near the computer and it makes that buzzing sound. Lets say you didn’t know that. You had the iPhone in your pocket, and you walked up to your computer – it would start buzzing. You’d notice that every time you were near you’d get the buzzing. You might conclude you were the source of noise (talk about a loud heartbeat!!). You’d be both right and wrong.

The beauty of science is that if you do a, b, and c, then x will happen. Electronic noise is very much about science – if you do x, y, and z then you’ll get noise. The problem is it is very very difficult to determine what x, y, and z are. Above x might be “walk near your computer”, and y might be “have iPhone in your pocket”. You might get x right away, and then give up on fixing the speaker. A computer is no good if you can’t be near it! If you figured out y you might be able to do something different (like leaving your iPhone across the room, or better shield your speakers).

This is why finding and diagnosing electronic noise is an art.

I was on shift for two nights last week. On Friday night we saw a strange noise pattern in D0’s calorimeter. The pattern of noise is called high noon. And it was in four crates of electronics – typical high noon noise is never seen in more than one crate at a time. Experts were here until 2am trying to figure out what the source was. No clue. Eventually they went home – have to investigate the next morning when everyone was awake. Impact on data seemed to be minimal, and the automatic noise detection algorithms seemed perfectly capable of detecting this type of noise.

There were other problems with the detector that night too. A muon phototube kept looking synchronization with the readout. Each time this happens an automatic system would rap its knuckles and bring it back into line. Finally, after it had lost sync about 20 times, we decided to hit it with a hammer: reset it. And lo… the noise in the calorimeter, which had been mocking us for the last 6 hours disappeared.

Keep in mind – the muon system is meters away from the calorimeter system. They share no common electronics – not even racks of electronics are shared by the two. But the muon system was acting like the cell phone, transmitting electronic noise and the calorimeter was acting like an antenna – the speaker wire – and picking up the noise. D0 has been running since 2001. As far as I know, no one had seen this particular failure mode before.

If anyone tells you science isn’t an art – that there is no room for creativity – they are full of it. There are a lot of unknowns in unsolved problems – and it takes some creativity to guess what those unknowns are. And that is also the point behind reproducibility – to make sure you found x, y, and z that produce effect a.

Long live art!

* BTW, the iPhone isn’t the only one that will do this, it is just the worst offender of any of the smart phones I’ve seen. And easy way to fix it is place the iPhone on some tin foil. I’m not sure if that is because the tin foil becomes an antenna and so the iPhone needs less power to communicate with the tower or because it provides some shielding. But it works. See? Art!

Overbye has a good article in the Science Times today. It discusses all the recent results from satellite experiments that, given proper interpretation, may indicate further direct “particle” evidence for dark matter. That would be huge!

The reason I mention the article, however, is Overbye puts in a bunch relating to the competition between the various theorists who are trying to explain the dark matter signals. For example,

That theory was called “a delightful castle in the sky” by Dr. Gordon Kane, who said he was glad it kept Dr. Arkani-Hamed and his colleagues busy and diverted them from competing with him.

And there are a bunch more comments similar to that. Worth the read for the science as well as some of the story about how science is done. It ends with a great quote by ex-UW postdoc, who is now a professor at NYU, Neil Weiner:

In a year or two, we’ll either not be talking about this idea at all, or it will be all we’re talking about.

I love his optimism. If we actually know something definitive in a year or two that would be great! Sadly, in that time scale I don’t think the LHC will have very much to contribute (perhaps in two??)!

I listened to a fascinating podcast from NPR Science Friday on the way into work today. The segment, titled “When not in control, people imagine order”, describes how people in (stressful) situations out of their control they will come up with reasons for why things are happening around them – even if they aren’t correct. One example used in the broadcast was stamping your feet before going into a meeting. If you do that, the people in the meeting will be more likely to accept and agree with your ideas. Clearly, there can be no external cause-and-effect, but you could see… we all have these little superstitions. How about a base-ball batter. They noted that military personal in battle environments tend to do the same thing. Fun fact: sales of astrology books increased during the great depression (does anyone know how to see sales of astrology books as a function of time on Amazon?).

As you might imagine, recognizing patterns in what is going on around us is part of our survival programming. If we can make order out of what is going on, we can predict it, and thus we can take advantage of it. Leave meat out? Bear comes around. Hey – lets set a trap! Except, it can go too far – stopping your feet can’t possibly have any effect on the people in the meeting; the best it can do is boost your confidence. But if you knew that perhaps you could take a more direct path to boosting your confidence (shot of tequila!?).

What I really liked about this was that this is what my job is supposed to be. I’m supposed to look at data and come up with patterns to describe the data I see. There are lots of effects that might or might not be relevant. All of us in this field think up patterns where they don’t actually exist. Indeed, one is encouraged to come up with patterns no matter how crazy. The key is that the patterns have to be tested. The stomping feet thing might be based on a one-time accident. But here we would have to invent a double-blind study to test that before declaring the correlation was causal.

The program is worth a listen – it is short, about 20 minutes. And you get to hear someone call in and note that this study can’t really be correct because it implies that everyone who thinks the Kennedy assassination was a conspiracy must be making up a pattern that doesn’t exist because they are under stress. And we all know that conspiracy theory is correct.