Blowing young minds with quantum mechanics

This morning I had my next visit to Loreto Kirribilli for mentoring with my four students there. They’re learning about waves at the moment in their science class, and the teacher suggested I talk about something related to light.

I started by asking them if they had any questions and one girl asked about sonic booms. I explained that by drawing diagrams to show how an object moving faster than sound creates a shock wave. Along the way I also mentioned the Doppler effect, since it’s closely related.

Then having started with sound waves I moved on to talk about interference, explaining destructive and constructive interference. I talked about how interference is used in noise-cancelling headphones and how they work. Then I went into an explanation of the double slit interference pattern, framing it first in terms of sound waves, building on the example of the headphones to explain the pattern of loud and soft areas.

All right, now we were ready to talk about lightβ€”also a wave. And if we take a single-wavelength light source like a laser and shine it on double slits, we get the same interference pattern as bright and dark spots of light. And if you change the wavelength, you change the spread of the pattern. So far, so good.

Then I switched tracks and started talking about electrons, which we had discussed at length last time. I explained how you can create a beam of electrons, by ionising something and accelerating them in an electric field. One girl asked if this was related to cathode rays, so we took a bit of a diversion into that and why they were called cathode rays historically. And how old cathode-ray TVs and displays worked.

Then I asked a question: What if we fire this beam of electrons at a double slit?

I could virtually see the wheels turning in the girls’ heads as they pondered why I was asking this question, and what the answer could possibly be. I didn’t keep them in suspense too long. I said you’d see an interference pattern, exactly as if it was a beam of light. This is what’s actually observed if you do the experiment. I explained that electrons are not “particles” in the way we think of macroscopic particles like marbles or grains of sand. They don’t behave in the same way as macroscopic particles. They behave like waves. I tied this back to last time’s discussion of electron orbitals in atoms, and explained that this wave behaviour is what’s behind the strange shapes of the orbitals, as the electrons are essentially interfering with one another.

I also mentioned that if you change the speed of the electrons (by changing the voltage of the electric field in the beam generator), then you change the spread of the interference patternβ€”exactly as if you were changing the “wavelength” of the electrons.

At this point the teacher reappeared. I asked him how much longer we had, and he said about three minutes. I said, “Great. That’s enough time. I’m just about to blow their minds.”

Okay, I said, so we get this interference pattern when we fire a whole bunch of electrons at a double slit. What if we slow it down? What if we fire one electron at a time; say one per day? Today we fire one electron. Where will it land?

Again, it was obvious the gears were turning in their heads. I said, “Well, it might end up here, right in the middle.” And I drew a dot. “Tomorrow, we fire another electron. Where’s that going to land? Maybe not the same place. It might end up here.” And a I drew a dot off to one side. “And the next day?” I kept adding more dots, one at a time, faster and faster, talking through that each electron was being fired once per day, so they couldn’t possibly be interfering with each other, but that over time as the dots accumulate you see exactly the same interference pattern emerging.

A single electron passing through double slits will have a chance of landing in different positions depending on the interference of its wave nature. We have no way of predicting where any individual electron will land, but we know it will have this shape built up over many electrons. Which slit does a single electron “go through”? We don’t really know. It acts like it goes through both at once. Matter at small scales like electrons and atoms doesn’t behave at all like macroscopic objects. It exhibits this mixed wave/particle nature that seems odd to us.

I looked from the whiteboard I was drawing on to the girls and they were all staring at me wide-eyed, absolutely rapt.

And the bell went off, and it was the end of our time together for the day. It was really cool. This was our last lesson for this term. They have a mid-year break, and then in the new term after the break the teacher needs to organise plans for the rest of the year. So it’ll be a few weeks before I see them again. But definitely looking forward to it!

After the lesson I took Scully to Maggio’s bakery for a slice of pizza, and I picked up another one of their award winning apple pies, to take home for dessert tonight. Back home, I packed a bunch of cards for sending to eBay buyers:

Packages

Then I had to drag them all up to the post office for mailing. It was quite a task carrying all of them and handling Scully at the same time, even though I drove most of the way there.

Back at home I did another section of the Lego D&D set. First, photos of stage 16 which I did yesterday. Skeletons!

Lego D&D set, stage 16

Lego D&D set, stage 16

And the roof frame is completed, awaiting the next storey to be placed on top. And today’s stage 17 was just this cool displacer beast:

Lego D&D set, stage 17

Lego D&D set, stage 17

Which fits into the room like this:

Lego D&D set, stage 17

This evening I restarted my critical thinking/ethics classes, with the new topic on “The Countryside”. One notable response I got was to the question “How important is it for children from the city to experience the countryside?” I expected answers like it’s good to see farms where your food comes from, or to see wildlife. But one student said that it was a good idea because there’s no Internet connectivity there and kids can spend time off their devices!

Oh, and one kid was joining from a new country: Lebanon. He’s normally in Dubai, but is travelling, and took the time to still connect to my class. But someone joining from Lebanon brings my country list up to 53.

New content today:

Science mentoring meeting

Today I visited Loreto Kirribilli school to meet with four Year 9 students who the teachers there have selected for mentoring in science. They are advanced students with a strong interest in science. I introduced myself and briefly described my career from university degrees to industrial research, then asked the students what areas of science they were interested in and what they hoped to learn in our mentoring sessions.

They have a diverse range of interests in terms of topic: physics, biology, chemistry, astronomy, computer science. But one thing I found out was they have a common desire to obtain a more rounded and deeper understanding of science than they are taught in classwork. Actually understanding what the science is, rather than just learning ways to solve problems that will be on their exams. They were a little reserved but hopefully will get more enthusiastic as they get used to the mentoring sessions.

We finished up our time (we had 50 minutes) with a discussion of atomic theory, going a bit deeper into quantum physics than they get at a Year 9 level. It ended up a bit rambly, because there are so many interesting digressions I can make along the way! Hopefully the next session (in a fortnight) will be a bit more focused. Th girls have been given some homework to come up with some specific questions they are interested in, either about science topics or careers.

In other news, there was a strange meteorological phenomenon today. Th sky was a weird blue colour and there was a strange ball of light in it. Yes, the rain has finally ended, after beginning on 30 April. It was so nice to be out and about without getting wet.

The dampness left behind a nasty legacy though. I mentioned the mould spots in the house yesterday. Today I went around with some mould killer and treated all the areas I could see. It’s horrible, but hopefully stopped before it gets too serious.

All of this meant I didn’t have a lot of time to write my ethics class for the new week. I dashed it off quickly after dinner. The topic is “Arguments”, as in heated disagreements, not logical arguments. What causes arguments? How can an argument get out of control? How does it feel to be in an argument? What strategies can you use to stay more calm and reasonable in an argument? What’s the difference between healthy debate and harmful argument? And so on.

New content today:

Cinnamon rolls!

My wife and I made cinnamon rolls today! Before rising and baking:

Cinnamon rolls

And after:

Cinnamon rolls

She got me a “bake at home” box with all the dry ingredients and instructions. We aded milk, butter, and an egg and produced 20 rolls. Most of them will be taken to Mother’s Day lunch at her mother’s place tomorrow.

This morning I did a 5k run, managing to time it almost perfectly in between the rain, which has hung around all day. (It’s pouring as I type this.) There was a news article this morning saying that we might potentially break the record of 16 rainy days (β‰₯ 1 mm) in a row for Sydney. It’s been 12 so far, and the forecast is about 50/50 for it lasting at least another four days.

It’s pretty horrible. We have a drying rack in the bathtub, festooned with wet clothes from whenever we go outside, and they take forever to dry because the air is so humid. There are umbrellas constantly drying off, and wet shoes everywhere. I don’t mind 3 or 4 days of rain, but when it gets up near two weeks without respite, it’s pretty miserable.

We gave Scully a bath this afternoon because she’s been getting a bit “wet dog” smelly. We might need to do it again in another few days.

Oh, apparently there have been sightings of the aurorae caused by the current geomagnetic storm as far north as Sydney’s latitude. Just not in Sydney, of course, because we’ve been under a blanket of cloud and rain. Pretty sure we missed the last lunar eclipse or two because of rain too.

And oh yeah… I didn’t post anything yesterday because it was online board games night with my friends. It was… a rainy Friday. I did some online classes, took Scully out briefly, but spent most of the day inside sorting through more Magic: the Gathering cards to get them into sellable lots. For dinner we had pizza at the local pizza place, which is always good. They have a nice cosy “al fresco” area out the back where we can sit with Scully, which is covered and sheltered from the rain.

New content yesterday:

New content today:

Late night Zoom meeting for photography standards

I’m up late tonight because I have a Zoom meeting for ISO Photography Standards, beginning at 11pm. I’m on a special ad-hoc committee to consider the issue of skin tone colours on photographic test charts. We specify various International Standard printed test charts that people can use to test camera colour reproduction. And of course skin tones are of crucial importance because of how sensitive we are to when they don’t look quite right, so many of the charts include patches of colours meant to represent skin tones. But the issue is that many of these were designed decades ago, and the representation is mostly based on European, light skin tones, with few or no darker tones.

So we’ve assembled a group of experts from around the world to consider how we specify these going forward, in a more inclusive way. We need to think about and discuss what range of colours to specify, how they should be reproduced and displayed, and how their reproduction should be quantified and measured. It’s complicated by the fact that our visual system is very finely attuned to skin tones, not just as flat colours that might be printed on a chart, but also by spectral reflectance, lighting and metamerism effects, subsurface scattering, angular effects, and salience effects caused by our brain’s innate ability to recognise the difference between an actual person and a patch of colour.

Some of the group members have been discussing in email the potential need to specify test charts with fully three-dimensional models of human faces with synthetic skin that includes translucent layers, which is a far cry from the traditional methods of testing camera colour reproduction with a printed flat chart with square patches of solid colour. So… I expect this Zoom meeting is going to be concentrating on what exactly the scope of our problem is, and how complicated we should go in addressing the fundamental problem of expanding the range of skin tones in our standards.

In other happenings, I basically spent all day today writing my lesson plans for this week’s new Outschool ethics classes, on the topics of Candy for the younger kids, and Fossil Fuels for the older ones. I also made quiche for dinner, using cauliflower leaves as the vegetable in the filling, which turned out pretty good. I’m pretty stoked to discover that the leaves on cauliflowers are not only edible, but yummy.

New content today:

Ethics of dinosaurs

I spent much of today writing my lesson plans for this week’s topics for my ethics classes: Dinosaurs for the younger kids and the closely related but more general Paleontology for the older kids. I get to overlap many of the questions by doing this, so it should have taken me less time than usual to prepare the lesson plans, but I was a bit lethargic today and ended up frittering away a good chunk of time.

I also need to revise my slides for the class on Colour and Human Vision, because I volunteered to give a guest lecture to the university students next week, during their project period. This isn’t part of the coursework, but the lecturer has liked to have someone do a bonus lecture on tangentially related material to the image processing course. Last year I did one on the Science and Engineering of Photography. I was hoping to revise the slides today, but didn’t get to it. Maybe tomorrow!

I made vegetable soup for dinner, so we can have the leftover converted into minestrone tomorrow. And after my three classes in a row this evening I’ve just made myself some sticky rice with banana and cinnamon for dessert, since the soup wasn’t super filling.

New content today:

Emoji hemispherism

Today I was looking through the various moon emojis showing different phases. Here they are in the emoji sorting order as displayed on MacOS/iOS*:

πŸŒ•πŸŒ–πŸŒ—πŸŒ˜πŸŒ‘πŸŒ’πŸŒ“πŸŒ”

And I noticed the various crescent, gibbous, and quarter moon emojis are all named as if viewed from the northern hemisphere. They’re completely wrong from a southern hemisphere point of view.

πŸŒ— is named “last quarter moon”, but to me that’s a first quarter.

🌘 is named “waning crescent moon” but to me that’s a waxing crescent. And vice versa.

And the ordering is backwards. For me the progression of phases over time as viewed in the sky is as follows:

πŸŒ•πŸŒ”πŸŒ“πŸŒ’πŸŒ‘πŸŒ˜πŸŒ—πŸŒ–

Northern hemisphere assumptions in things are so insidious, and it’s really annoying. Pretty much everything that is ever designed or shown that depends on what hemisphere you’re in is presented as if the northern hemisphere is the default. And so it’s all messed up for people in the south.

( * I also checked the Unicode standard and in that the ordering of the moon phase emoji is given as:

πŸŒ‘πŸŒ’πŸŒ“πŸŒ”πŸŒ•πŸŒ–πŸŒ—πŸŒ˜

So the same order cyclicly, but starting with the new moon. )

On other topics, today I did a 2.5k run, and clocked under 13 minutes again. But I still feel a bit out of form and need to run a few times a week for a bit to get my times back. I did some housework, cleaning the bathroom and shower and stuff. And spent much of the rest of the day writing Darths & Droids comics. I still need to produce 3 more before next Saturday to have enough buffered for my trip to Japan. At this time next week I’ll be at the airport!

New content today:

Reacquaintance with a physics professor

Today I had two ethics classes, including the first older kids on the topic of The End of The World, which was fun. I worked on some comic stuff and took Scully for walks. And I also had to send off a package of my photography greeting cards after getting an order for eight of them from the UK last night.

But the main thing I want to talk about is something I forgot to mention yesterday. Ever since I moved into this neighbourhood I have occasionally seen a man joggingβ€”or more recently walkingβ€”around on various streets. After the first few times I recognised him, but I never stopped to say anything. Recently he’s started walking around with a walking stick, on ageing legs. A couple of weeks ago I passed him walking the other way while I was out walking Scully, and I smiled and nodded, and he smiled and nodded back. I knew who he was, but I had no idea if he would remember me.

Yesterday I was out walking Scully and I saw him ahead on the path through the park, walking the same direction, slowly with his walking stick. We caught up, and I finally took the opportunity to say hello.

“Professor Melrose, hello. I don’t know if you remember me…”

He said, “I do recognise you, but I’m sorry, I’ve forgotten your name.”

He is Professor Don Melrose (Wikipedia, Australian Academy of Science, ResearchGate), who was the head of Theoretical Physics at the University of Sydney when I was doing my undergraduate and Ph.D. studies there. My office was on the floor above his, and I didn’t interact with him directly too often, but we certainly knew each other. I checked his publications and we have only one degree of separation – we share a common co-author.

I reminded him who I was, and that I’d worked with Dick Hunstead. We had a bit of a catch up over the next few minutes as we walked together along the path. I gave him a very brief rundown of my career after leaving the university with my degrees, and learnt that he lives just on the other side of the park to me, in a block of apartments that I’ve walked past hundreds of times. I kind of regret not having spoken to him much earlier, but it was good to finally do so and catch up. I’m sure we’ll exchange a few words next time we see each other.

And a couple of photos: Autumn foliage on London plane trees:

Autumn dapples

And Venus setting over the railway station this evening:

Venus over the station

New content today:

Solar eclipse day

Today there was a total solar eclipse visible from Australia. Totality was seen at the remote Western Australian town of Exmouth (pop. 2800), and virtually nowhere else on land. But the rest of Australia got various amounts of partial eclipse. Here in Sydney we got 19% totality. I was planning to go out with a pinhole and project the image of the sun with the moon partially obscuring it and take some photos.

But…

19% solar eclipse...

I basically couldn’t see the sky all day. It was heavily overcast, and raining for much of the day. It reminded me of another partial eclipse, back in 2012, when we had 70% totality here in Sydney:

70% Totality Eclipse, Sydney

At least it’s consistent.

There was a break in the rain at lunch time and I took Scully for a walk. For dinner tonight I wanted to use some sweet potatoes and an eggplant, and I searched for some recipes for inspiration. I ended up making vege burger patties, which we ate on burger buns with tomato and salad greens (and chilli sauce on mine).

Sweet potato and eggplant burgers

They turned out pretty good!

Another thing I did today was work some more on porting my notes into Obsidian from OneNote. I’m getting close to having all my gaming stuff transferred. I’m really liking Obsidian and its superior organisational features. The fact that I can hyperlink documents is great, and it makes notes naturally form clusters of related concepts. And it has a graph feature where you can see your notes as nodes, with the links:

Graph showing document nodes and hyperlinks

Neat! This is mostly the gaming part of the graph. You can see some of the other topics I keep notes on on the right hand side.

New content today:

Explaining the weather

It rained heavily overnight, but had cleared by morning. It was a warm, sunny day, but there was a chilly breeze coming in off the harbour, which we noticed during a lunch time walk with Scully around the Greenwich peninsula, which involved walking along the water in many places.

At home I upgraded my Mac to MacOS Ventura. I’d been putting this off because I didn’t want to do it on a day where I had Zoom classes, lest something go wrong. Some past upgrades have taken a couple of hours or so, so I set it up to begin before we went for our lunch walk. But it was pretty quick, and done in about 20 minutes with no dramas, and the computer was ready even before we left for the walk.

Much of the day I spent working on my lesson on weather for tomorrow’s science class. I found a really cool diagram showing different cloud types on Wikimedia Commons, which I felt compelled to share here:

Cloud Atlas of cloud types

It’s available there in much higher resolutions, so click through if you want to see it in detail.

In cooktop news: I made roast vegetables for dinner tonight. I prepared the potatoes (regular and sweet) by parboiling them first with a pinch of baking soda, to roughen up the surface so they absorb the oil and bake nice and crispy. After ten minutes, I wondered why the water wasn’t boiling, only to discover that the gas had been one the whole time without being lit.

This is a very rare occurrence – I can probably count on the fingers of one hand how often I’ve done this in over 20 years of living here, but it was annoying and a bit worrying. One problem is that I can’t smell gas leaks. The ethyl mercaptan that they put in the gas specifically so that people can smell leaks happens to be a chemical that some significant fraction of people are genetically incapable of smelling, and I happen to be one of them. Anyway, the kitchen window was wide open, and I turned on the rangehood as soon as I realised what had happened, and no harm done. But, add another reason on the side of converting to induction cooking.

Oh, another thing I completed today was converting my travel diary from our road trip to Orange back in September into HTML format and uploading it to my website. I added a map of the route and the distances driven (recorded from the car odometer), and you can see the result here. I still need to insert photos to illustrate it… which I’ll get to at some point.

New content today:

Science and Engineering of Photography

This evening I gave my lecture on the Science and Engineering of Photography to the students in the image processing course at the University of Technology Sydney. As I think I mentioned before, this is a special bonus lecture for the students, not part of their coursework, to give them something interesting in their project period during the last 4 weeks of the semester. So I used up most of the first hour of tonight’s three hour time slot with that. There weren’t a lot of students present, but some were listening in on Zoom as well, and several came up to me afterwards to say they liked it.

Earlier today I finished off the last three Outschool classes of the week’s topic on Risk. I assembled a couple of new Irregular Webcomic! strips for this week. And with other random daily stuff like eating lunch and taking Scully for a walk, that ate up the day before I headed into town, where I had some satay chicken and rice for dinner at Spice Alley before the lecture.

The other notable thing about today is that we had over 50 mm of rain, with almost all of it between 6:30 and 9:30 in the morning, so it was really pouring down then. The forecast was 1 to 5 mm! In the next week we’re looking at another 50 mm or so, with thunderstorms indicated almost every day. Yep… after setting a record for wettest year ever, we’re now heading into spring thunderstorm season.

New content today: