• Question: As a physicist, how much of your work can you actually see? How much is theoretical, and how much do you need equiptment to view?

    Asked by nancyc to Ben, Jony, Katharine, Mark, Peter on 19 Nov 2011.
    • Photo: Ben Still

      Ben Still answered on 17 Nov 2011:

      We see the particles but not directly.

      Particles have to be seen using different techniques which rely on the small amounts of energy they deposit when they pass through things. We either measure the energy directly, turn it into light and measure the brightness of the light or turn it into electrical signal which we then measure with sensitive electronics. At the end of the day, modern particle physics really just saves a lot of number from electronics and we then have to use specially written software to piece together what happened in our detector.

      Back in the day, before I was born 😉 , particle physicists used to use things like cloud and bubble chambers. Here the energy left behind by particles formed tracks that you could actually see. No electronics readout in these experiments – they literally took a photo of these tracks, before they disappeared, and then used the photos to figure out what was going on. In fact CERN used to have an army of people employed to look over all of these photos, recognise different particles and calculate their energy.

      Nice pictures of bubble chambers http://www.google.co.uk/search?q=bubble+chamber&hl=en&client=safari&rls=en&prmd=imvns&tbm=isch&tbo=u&source=univ&sa=X&ei=vt7ETomzGIK78gPo_rCHCw&ved=0CEIQsAQ&biw=1218&bih=664&sei=wN7ETrCKE8-j8gOXr6XuDQ

    • Photo: Mark Basham

      Mark Basham answered on 17 Nov 2011:

      Hi nancyc,

      At diamond there are various types of experiments some of which have obvious results and others which don’t.

      One method we use is x-ray imaging just like when you go to hospital to get an x-ray but much much brighter, and we can not only see through skin and muscle, but through steel! Now the results of this we get are easy to visualise, cause even when we zoom right in, its just like using a normal camera or microscope to take a picture.

      However one of the other experiments we do is called x-ray Diffraction, and this uses the x-ray light to see where atoms are actually positioned in the material. Now we don’t get a picture of the atoms with this, we get something called a diffraction pattern which looks a bit like this

      Now we can use that pattern(and a few more from different angles) to work out what the atomic structure should look like, and it ends up looking something like this :

      Now you may ask, how do i know it looks like this? And that’s a good question, so we make different experiments which also look at it, and we make sure they are all consistent. Although once a method has been used enough it becomes accepted that the results it produces are good.

      Hope this answers the question.

    • Photo: Peter Williams

      Peter Williams answered on 19 Nov 2011:

      Personally, about half and half. I spend some of my time doing computer modelling, and some of it doing experiments on the accelerators.
      On the accelerators we need equipment to view pretty much everything – in fact we have two whole departments. One work on photon detectors, and the other on electron beam diagnostics.

Comments

  • Photo: nancyc

    nancyc commented on :

    Thanks guys, those pictures are all really cool! When I was little, I always thought a lot of physics was more theoretical, writting out lots of long calculations and thinking about forces and the such, but actually a lot of it is much cooler than that!