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Sally Shaw | University College London | UK

View Blog | Read Bio

Physics Laboratory: Back to Basics

Dark matter –  it’s essential to our universe, it’s mysterious and it brings to mind cool things like space, stars, and galaxies. I have been fascinated by it since I was a child, and I feel very lucky to be a part for the search for it. But that’s not actually what I’m going to be talking about today.

I am a graduate student just starting my second year in the High Energy Physics group at UCL, London. Ironically, as a dark matter physicist working in the LUX (Large Underground Xenon detector) and LZ (LUX-ZEPLIN) collaborations, I’m actually dealing with very low energy physics.
When people ask what I do, I find myself saying different things, to differing responses:

  1. “I’m doing a PhD in physics” – reaction: person slowly backs away
  2. “I’m doing a PhD in particle physics” – reaction: some interest, mention of the LHC, person mildly impressed
  3. “I’m doing a PhD in astro-particle physics” – reaction: mild confusion but still interested, probably still mention the Large Hadron Collider
  4. “I’m looking for dark matter!” – reaction: awe, excitement, lots of questions

This obviously isn’t true in all cases, but has been the general pattern assumed. Admittedly, I enjoy that people are impressed, but sometimes I struggle to find a way to explain to people not in physics what I actually do day to day. Often I just say, “it’s a lot of computer programming; I analyse data from a detector to help towards finding a dark matter signal”, but that still induces a panicked look in a lot of people.

Nevertheless, I actually came across a group of people who didn’t ask anything about what I actually do last week, and I found myself going right back to basics in terms of the physics I think about daily. Term has just started, and that means one thing: undergraduates. The frequent noise they make as they stampede past my office going the wrong way to labs makes me wonder if the main reason for sending them away for so long is to give the researchers the chance to do their work in peace.

Nonetheless, somehow I found myself in the undergraduate lab on Friday. I had to ask myself why on earth I had chosen to demonstrate – I am, almost by definition, terrible in a lab. I am clumsy and awkward, and even the most simple equipment feels unwieldy in my hands. During my own undergrad, my overall practical mark always brought my average mark down for the year. My masters project was, thank god, entirely computational. But thanks to a moment of madness (and the prospect of earning a little cash, as London living on a PhD stipend is hard), I have signed up to be a lab demonstrator for the new first year physicists.

Things started off awkwardly as I was told to brief them on the experiment and realised I had not a great deal to say.  I got more into the swing of things as time went by, but I still felt like I’d been thrown in the deep end. I told the students I was a second year PhD student; one of them got the wrong end of the stick and asked if I knew a student who was a second year undergrad here. I told him I was postgraduate and he looked quite embarrassed, whilst I couldn’t help but laugh at the thought of the chaos that would ensue if a second year demonstrated the first year labs.

oscilloscope

The oscilloscope: the nemesis of physics undergrads in labs everywhere

None of them asked what my PhD was in. They weren’t interested – somehow I had become a faceless authority who told them what to do and had no other purpose. I am not surprised – they are brand new to university, and more importantly, they were pretty distracted by the new experience of the laboratory. That’s not to say they particularly enjoyed it, they seemed to have very little enthusiasm for the experiment. It was a very simple task: measuring the speed of sound in air using a frequency generator, an oscillator and a ruler. For someone now accustomed to dealing with data from a high tech dark matter detector, it was bizarre! I do find the more advanced physics I learn, the worse I become at the basics, and I had to go aside for a moment with a pen and paper to reconcile the theory in my head – it was embarrassing, to say the least!

Their frustration at the task was evident – there were frequent complaints over the length of time they were writing for, over the experimental ‘aims’ and ‘objectives’, of the fact they needed to introduce their diagrams before drawing them, etc. Eyes were rolling at me. I was going to have to really try to drill it in that this was indeed an important exercise. The panic I could sense from them was a horrible reminder of how I used to feel in my own labs. It’s hard to understand at that point that this isn’t just some form of torture, you are actually learning some very valuable and transferrable skills about how to conduct a real experiment. Some examples:

  1. Learn to write EVERYTHING down, you might end up in court over something and some tiny detail might save you.
  2. Get your errors right. You cannot claim a discovery without an uncertainty, that’s just physics. Its difficult to grasp, but you can never fully prove a hypothesis, only provide solid evidence towards it.
  3. Understand the health and safety risks – they seem pointless and stupid when the only real risk seems to be tripping over your bags, but speaking as someone who has worked down a mine with pressurised gases, high voltages and radioactive sources, they are extremely important and may be the difference between life and death.

In the end, I think my group did well. They got the right number for the speed of sound and their lab books weren’t a complete disaster. A few actually thanked me on their way out. 

It was a bit of a relief to get back to my laptop where I actually feel like I know what I am doing, but the experience was a stark reminder of where I was 5 years ago and how much I have learned. Choosing physics for university means you will have to struggle to understand things, work hard and exhaust yourself, but in all honestly it was completely worth it, at least for me. Measuring the speed of sound in air is just the beginning. One day, some of those students might be measuring the quarks inside a proton, or a distant black hole, or the quantum mechanical properties of a semiconductor. 

I’m back in the labs this afternoon, and I am actually quite looking forward to seeing how they cope this week, when we study that essential pillar of physics, conservation of momentum. I just hope they don’t start throwing steel ball-bearings at each other. Wish me luck.

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