Astronomy, Milestones, Notes on everyday life, Physics

Black Hole Breakthrough

Simon recorded this video right after the news was announced on April 10

Caught Simon’s reaction to Wednesday’s breaking news on video: the first-ever image of a black hole published, made by the Event Horizon Telescope project team. Simon explains why, if you stood next to the black hole, you would be able to see the back of your own head.

Simon loved this video by Veritasium about how the image of the black hole was made (he had watched this one day prior to the actual publication of the black hole image).

Yesterday, wee also watched this beautiful TEDx contribution by Katie Bouman (one of the leading figures behind the algorithm that helped stitch the M87 black hole image data together). The video is from three years ago, when the project was just getting started. Katie is such an inspiration: a computer scientist helping astrophysicists!

Scientists report ‘groundbreaking’ black hole findings from the Event Horizon Telescope: link to the actual press conference.

Electricity, Experiments, Physics

Physics Experiments: Using an LED backwards

We have tried using an LED backwards: not get it to shine by letting an electric current pass through it but produce electricity by shining light on an LED (this is how solar panels work). It’s important to use a sensitive LED for this experiment, and as we have observed, it also seems to be important to use light photons of the same frequency as the colour of the LED (red laser didn’t work on a white LED, but it may have to do with the fact that red light is weaker than white light anyway, i.e. has a lower frequency). The picture below shows us measuring the voltage of the current produced by the LED.

shining a light at the diode produces voltage
the same experiment setting but with the light source turned off produces no voltage
red light not strong (energetic) enough to produce voltage, also when shined on a red LED

We’ve have learned this and a a lot more from Steve Mould’s video on How diodes, LEDs and solar panels work: Photovoltaic cells and LEDs are both made of diodes. Diodes are designed to allow electricity to flow in one direction only but the way we make them (out of semiconductors) means that can absorb and emit light.

In the video, Steve shows how the semiconductor atoms share elctrons. Semiconductors are crystal structures of atoms are replaced by the atoms of neighboring elements, for example a structure where some silicon (Si) atoms are replaced by phosphorus (P) or boron (B) atoms, thus providing for free electrons inside the structure (N-type conductor) or for free “holes” unoccupied by electrons (P-type conductor). A diode is basically two semiconductors pushed together. With enough voltage, the electrones are able to jump from the N-type semiconductor across the depletion zone and into the P-type semiconductor, emitting light (photons) as they fill the holes and go from a high energy state into the low energy state.

If you shine a light at a diode, you can kick some electrons from their shells and thus create free electrons and holes that will move (because of the electric field in the depletion zone) and generate voltage.

Experiments, Physics, Together with sis

Physics Experiments: Double Slit

We have wanted to do the Double-Slit experiment for a long time. Finally, last Friday, armed with a suitable box, we ventured outside. To our common disappointment, light just wouldn’t behave as a wave this time, even though we had no detectors to check which slit the photons actually passed through. What we observed inside the box looked like two perfect stripes. No interference.

No interference: light behaving like particles

Simon looking inside the double-slit experiment box to check for the interference
Simon’s sister Neva dragging the box down the stairs

Experiment failure aside, we were in for a pleasant surprise, too: the box suddenly turned into a huge camera obscura! This is a picture of me and the blue sky as seen from inside the box!

An image of me, the buildings and the sky above as it appears inside the camera obscura

When we got home, and tried to look inside the box again in the dimmer light in the living room, we were finally rewarded with this beautiful interference pattern:

The interference pattern that the light coming inside the box through the double slit creates (proving that light is also a wave)

We can only guess why it didn’t work outside. The wrong angle of the light beams (the sun being high in the sky above our heads)? Or maybe the light wat too bright, too many photons got in? The slits being too wide? We’ll be repeating this experiment for sure.

Physics, Simon teaching, Simon's sketch book

More quantum physics: quarks hit by photons and what does a z boson do?

Simon told me about strong force and what happens to a quark inside a nucleon if a high energy photon hits it and pushes it outside the nucleon: a new quark and antiquark are created.

But what if the photon was so strong that it pushed the quark even further? It would create another quark and another antiquark.

Then Simon switched over to drawing Feynman diagrams to show how a w boson emitted by a quark or a changes that quark or lepton (charm to strange, bottom to top, electron to electron neutrino, etc.) “We don’t know what the z boson does” , Simon says. “Maybe it’s there for no reason!”

Discovering Antwerpen, Group, Notes on everyday life, Physics, Together with sis, Trips

Photons Trapped in Flemish Woods

Simon isn’t fond of magic or fantasy. Plus, he is not fond of long walks in the woods. Both “not fond of” are understatements. What was I counting on when I dragged him to the 2 kilometer long light installation in a forest close to Antwerp? I expected that seeing multiple fountains with photons trapped in water would make up for all the magic, scary music and the long walk. And it did!


Experiments, Murderous Maths, Physics, Simon teaching

Physics Experiments: Light and trapped inside the water stream

Another take at our light trapping experiment, this time using a red laser pointer. We punched a hole in the plastic bottle and filled the bottle with water. As the water flows through the hole, the trick is to point directly at the hole through the bottle. This makes the photons enter the water stream and they can no longer leave it, getting reflected inside the stream and traveling along with it, so no longer in a straight line. This is exactly the way fiber optic cable works.

Simon gave me a whole lecture the other day about how fiber optic cable transmits binary data like a morse code, with long light flashes for ones and short flashes for zeros. (“And underwater robots fix them!”) He explained ASCII, the way to encode English letters and special characters in binary, 95 characters in total: “7 bits allowing for 128 combinations, which is even an overkill. To transfer pixels, you need 24 bits. And 2 to the 24 is exactly the same as 256 to the third (total number of possible shades). I worked this out!”

With two bottles:


How do we see colours

Colours continue serving as a gateway to science. Simon has been comparing mixing paints and light waves and came to the conclusion that primary colours in paint (magenta, yellow, cyan) are the secondary colours in mixing light and the other way around – the primary colours in mixing light (RGB – red, green and blue) are secondary when mixing paints. When mixing the maximum intensity of all the three primary colours in paints you get black (no light), when mixing all the three light waves you get white (maximum light). That’s how light and paint are the opposites of each other, Simon told me.

– How do we get violet paint? – I asked.

– We add full intensity magenta, and half intensity yellow and half intensity cyan.

– But why do we see violet? – I asked.

– It’s because all the green light is being absorbed, and all the blue light is being reflected, and 60 percent of red is being reflected! – Simon explained. He can also give similar explanations about other colours.