Quantum Theory

The nature of matter

Few concepts in Physics generate wonder quite like Quantum Theory. You only need to look at the shelves in the Popular Science section of a bookstore for evidence. Yet (once again) in schools we play down this sense of wonder. I used to think this wasn’t done deliberately but now I’m beginning to learn that there was once a school of thought that believed in doing exactly that, particularly for Science (more on that later).

Anyways, one of the most incredible ideas in Quantum Theory concerns the nature of matter itself – is it a particle or is it a wave?
For light, we can prove that it’s both (ridiculous though that may sound) and indeed students are expected to know the demonstrations which verify both. There is however no suggestion anywhere in either the textbooks (that I have come across) or in the syllabus that there is anything slightly disturbing in this. There was a single question on the exam paper once which asked why was Quantum Theory considered revolutionary, but that was it. No other reference to what is one of the greatest mysteries of science; how can something be both a particle and a wave. Why do I seem to be the only one who feels so frustrated by this?

So in an attempt to pass on some of this sense of wonder for the microscopic world, I put together the following set of demonstrations for my sixth years on the last day of term. It’s about 22 minutes long so is in two parts. Forgive its amateur appearance.

Advertisements

Quantum Theory – why do we ignore the mystery?

Isn’t it crazy that one of the most wonderful concepts in Physics – the dual nature of light – doesn’t get a better deal from the leaving cert physics syllabus?
Students are expected to know how to demonstrate that light is a wave, and also to be able to recall Einstein’s interpretation of the Photoelectric effect (which proved that light is a particle) but then there is nothing else about what is one of the greatest mysteries in Physics – how can light be both particle and wave?
Quantum Theory is one of the most popular concepts in popular science books, yet we leave it out altogether.
Isn’t there a responsibility on us as teachers to make our voices heard? Or is it the case that we don’t really care?
The following is a video taken during the Solvay Institute of 1927 – it helps to give some feel for the characters involved (see the Quantum Physics page of thephysicsteacher.ie for a link to this and other related videos).

This is one of my favourite videos on quantum theory – it emphasises the wonder, and that’s always a cool trick when introducing any new physics concept to students.

Is it a particle or is it a wave?

Sometimes I think I’d gladly be locked up in a dungeon ten fathoms below ground, if in return I could find out one thing: What is light?
Galileo, from the play Life of Galileo, by Bertolt Brecht

 The single greatest source of debate among physicists in the early decades of the last century was to do with the nature of light. Come to think of it, this concept has probably caused more angst than any other to scientists and philosophers right back to the ancient Greeks.
To take just one aspect; we can prove that light is a particle (via the photoelectric effect) and we can prove that light is a wave (via interference, or the famous ‘double slit’ experiment) yet particles and waves are two completely different phenomena. Particles are ‘things’ and are therefore supposed to be localised in space and have mass. And while there are  different varieties of waves, they are not supposed to be ‘in one place’ or have mass.
So what gives?


 

Answer: nobody knows. To this day there are different interpretations, but none that is accepted by all. The YouTube clip below shows some of the world’s greatest physicists coming together for one of a series of conferences to try to make sense of it all back in the 1920’s. Needless to say they did not reach a consensus. There is wonderful book called QUANTUM which describes in great detail the history of this debate at the beginning of the last century. See here  for a previous post on the book itself.

Now in leaving cert physics we need to know the evidence for light being both a particle and a wave. But there is room in the syllabus or any of the textbooks that I have come across to highlight the bizarre nature of this. It lies at the heart of one of the greatest problems scientists have ever faced, and our response is to simply pretend that there is nothing of note here.

It’s simply not good enough.

Some nice Quantum Physics resources

I may have mentioned previously that one simple way of seeing which science concepts appeal to the general population is to look at popular science programs and note what they are concentrating on; chances are there won’t be much of an overlap between this and the school syllabus. Quantum theory is a case in point – the BBC aired a wonderful Horizon documentary a couple of weeks back entitled “How long is a piece of string?” and while I didn’t catch it when it first went out I figured it was just a matter of time before it appeared on YouTube. Broken up into six ten-minute slots there is a lot of potentially useful material there for the physics class if you’re prepared to drift off syllabus.

The Beeb is understandably a little finicky about their programs appearing on YouTube so you might like to download it while you can.

Hat-tip to my colleague Jerome Devitt for reminding me about this – why is it that our colleagues in the humanities seem to be more comfortable discussing the philosophical implications of modern science than we are?
Have the rest of us really tested and tasted too much?

While I’m at it, probably the most popular YouTube clip on the weirdness of the quantum world has got to be the following clip taken from “What the bleep do we know?”.

It really is a wonderful crazy world out there.

Enjoy.

Youtube – is it just me?

I have had access to youtube in my classroom since last September and it is by a country-mile the geatest ICT resource I have in my arsenal.

You could take away the Interactive Whiteboard, the dataloggers and the DVD player, but I would cry if I lost youtube.

The irony is that I bought a VHS-to-DVD converter last year and it has taken me a full year to convert all my library. At the time I had probably 75 programmes, many on the same VHS cassette, and I was excited at copying each program on to a seperate DVD for easy access.

The big advantage of DVD was that I could scroll straight through to whatever part of the program I wanted – no more rewinding and fast-forwarding. I was also considering putting everything from there onto a large external hard-drive, for even easier access. All of this would take an inordinate amount of time, but would at least encourage me to use the resource more, where previously I would use it sparingly because of the hassle.

I think that for many students a video of anything more than ten minutes would lose their attention.
Hence my fascination with youtube.

This resource is available to everyone, there doesn’t seem to be anything too dodgy on it, or at least if there is it isn’t thrown at you; you would have to go looking for it.

All clips are under ten minutes. My favourites are Quantum Physics clips, because this stuff is not on any leaving cert syllabus (except maybe Religion) and the comments themselves are often revealing.

I wish I had this resource when I was growing up. If nothing else it allows me to see there are so many people out there who are as fascinated by science as I am, and unlike text-books and teacher conferences these people are all only too happy to express their wonder. It really is inspiring.

There are also wondeful demonstrations which can I can incorporate into my own lessons, and the videos usually include all those small but vital bits which text-books and demonstration-books often omit.
I feel like crying when I realise this resource is blocked in most schools.

I have spent quite a while loading up my favourite clips onto the online favourite program delicious.

CESI (Coputer Education Society of Ireland) are having their conference next month so my homework over the next week is to put together ten top reasons for unblocking this site.

Or is it just me?

del.icio.us site tagged with my youtube links are here
CESI
 homepage

Ten Great Ideas

Been thinking about my previous posting.

What are the ten great ideas in Science that we don’t emphasise?

The average student remembers bugger-all about science, but if we were told there were ten things that a student had to remember, what would they be?

1. Kinetic Theory – Everything is made up of atoms and vibrate at temperatures above -273 degrees Celsius.

2. Evolution

 3. Global Warming

4. Each atom is 99.9999% empty, and so therefore all objects which appear solid are almost completely empty space.

5. Deep Time: The age of the universe, the age of the Earth, the age of first life, and the age of humans

6. Science does not offer Absolute Proof

7. Fundamental Attribution Theory: Humans are genetically hard-wired to apportion blame for our own mistakes to others while wishing to take the credit for achievements which are outside our control.

8. Quantum Theory

9. What Science doesn’t know

10. Mass Extinctions