Physics and more physics

Today, we went to the Open Day at the NPL in Teddington.  The NPL is a big building full of physics.  Some chemistry, but mostly physics.  And it's proper physics.  Lots of it.

It's hard to explain just how much fun it is wandering around the NPL.  It reminded me of one of the better BBC science documentaries.  You know the ones.  On BBC2 or BBC4 and presented by a scientist who loves their subject.  It was like one of those, but one that you could walk up to and touch and ask questions about.

So much stuff I could talk about, so I'm just going to present my ten favourite things from the day...

1. A very echo-y room

The reverb chamber is a small-ish room where things echo. A  lot.  there are no parallel surfaces and no right angles.  Standing waves can't easily get set up.  A single noise will reverberate around the room for 30 seconds with the door closed.  Having a conversation in that room involves a lot of whispering and straining to hear above all the noise.

2. A not-very echo-y room

The first of many spiky rooms.  The spikes mean that almost all the sound which hits the walls is reflected against another spike rather than back into the room.  The silence was almost deafening.  The deadest space I've ever been in.

3. A very cool hologram or two

Not just a dodgy green globe.  Full colour holograms so real that you have to get VERY close before you realise they are not real watches and medals.  Full colour holograms are hard to achieve thanks to the different characteristics of the three component holograms you need to create.

4. Counting electrons

The ampère is currently defined in terms of Ampère's law.  These guys are trying to define it in terms of the flow of charge.  They are doing it by letting electrons pass through a space one at a time and counting them.  Roughly speaking.

5. Redefining a kilogram

The kilogram is still defined as the mass of a block of metal just outside Paris.  All of the other SI base units have less prone-to-wear-and-tear definitions.  The leading proposal is to use a rather nifty bit of kit to define the kilogram in terms of Planck's constant and the charge of an electron.  The brilliance here is that the kit to do it is really not that hard.  With A-Level physics and a bit of mathematical jiggery-pokery you could understand what's going on.  But the brilliance comes from setting it up in such a way that so many of the terms cancel meaning that you're not really concerned about the construction mechanics of the kit itself.

The other possible method of defining the kilogram involves creating a single crystal of silicon in the form of a relatively large sphere, measuring the sphere, using the crystal structure to turn that measurement into a number of atoms and then define the kilogram that way.  Also very cool.

6. Applying force

Big machines which hang weights from things to generate known force.  The fun here is that the equipment of so accurate that the weights have to have different mass in order to generate the same force, as the metre-or-two difference in height of the weight is enough for the difference in the force exerted by gravity on the weight to be different enough to be measured.  On the biggest machine, the top weight is 3g more massive than the bottom one, yet it exerts the same downward force.

7. Blowing up balloons

Take a balloon. Inflate it.  Put it into liquid nitrogen.  The air inside turns to liquid and the balloon shrivels up.  Take the balloon out again and lay it on a desk. The air turns back into a gas and the balloon inflates itself.  Such fun!

8. Firing lasers at things

Take a sample.  Fire a laser at it and measure how hot the other side of the sample gets.  Sounds easy.  Not really. Great fun, though.

9. Telling the time

The second most accurate clock in the world.  It's not actually used to tell the time.  It's used to calibrate the clocks which do tell the time.  It's still cool though.  Though it'd be cooler if it had a minute and hour hand going around on it.

10. Science

The best thing about the day, though, is knowing that there are so many people in the world just as nerdy and interested in physics as me!

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