May 13

4 Card Puzzle

Here's an interesting puzzle that tells us a little bit about the way we think.

Did you get it right? Let me know in the comments.

May 13

Pillow illusion

I discovered an illusion when I opened my eyes this morning. I happened to be looking in the direction of 2 stacked pillows and the dark region where the two pillows met appeared to expand for about a second. I noticed it worked better when I was looking at a bright part of one of the pillows instead of the dark region itself.

I've recreated the effect below. To make it work, close your eyes for 10 seconds. When you open them, immediately look at the grey dot. The dark region in the middle should appear to expand for about a second:


Pillow illusion


I'm not sure if this has been done before or even if it works for anyone but me! Let me know if it works for you.

My theory is that when you first open your eyes, your pupils are dilated, so a lot of light is coming in. As a result, the dark patch looks less dark. In the fractions of a second after you open your eyes, your pupils contract. Less light gets in, so the dark patch gets darker. Because there is a gradient from the middle outwards, that darkening could also be interpreted by your brain as the dark patch expanding.

It might be that other things are happening besides your pupils contracting. Your brain does all sorts of adjustments to the information coming from your eyes.

Film camera operators talk about white balancing before taking a shot. It's where they make adjustments to their camera so that things that are supposed to look white actually do end up looking white. Your brain does some pretty intense white balancing too and it leads to a phenomena known as colour constancy. There's also brightness constancy going on in your brain. And if this brightness constancy takes any sort of time to kick in, that could also be an explanation for the effect in this illusion.



Feb 13

Self siphoning beads

Here's a quick video I made of my self siphoning beads:

The chain is the stuff from vertical blinds. The thing you pull on to open and close them. Searching for metal 4.5mm bead chain on ebay gets you the right sort of thing. That also bring up the linkages you'll need to buy to make the chain really long.

The reason it self siphons is that the chain pulling down outside the beaker is longer (and heavier) than the chain pulling down on the inside of the beaker.

The reason the chain loops up higher than the rim of the beaker is a bit of a mystery. I think it's to do with the fact that the beads are changing direction and it can't do that instantaneously as that would represent infinite acceleration. So a big loop is formed. I don't know, something like that.

UPDATE 28/06/13

This video was posted on Reddit where it got loads of upvotes and it's been seen by hundreds of thousands of people. Thanks Reddit! It was seen by Earth Unplugged who invited me to film it in slow motion. Here's that video:

Reddit is great for discussions, here's the original thread. And it was discussed at length in the sub reddit Ask Science. And here is a brilliant analysis from user Silpion with videos and images.

Feb 13

The sound from a vibrating rod

I made a video to show you the cool way a rod of aluminium vibrates when you hit it:

Feb 13

Why is purple weird? A video for the Royal Institution

I was giving my Illusions talk at the Royal Institution and had a few minutes at the end to film this video about purple.

May 11

Turning a webcam into an infrared camera

Turning a webcam into an infrared cameraThe sensors in digital cameras pick up more than just visible light. They pick up a lot of infrared too, that's light below red that we're not able to detect with our eyes.

This can make pictures look funny, so manufacturers add a filter to block the infrared and give you a more natural image. Actually the filters don't do a perfect job and if you fire a TV remote control at your camera phone you should see it light up on the screen.

All this means you can have a bit of fun with your old web cam. You can remove the infrared filter then add a visible light filter so your webcam only sees infrared!

Continue reading →

Apr 11

My bacon was an optical illusion this morning

Which rasher is longer?

Nov 10

Audio Illusion – do you hear the missing fundamental?

Listen to these two sounds:

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

Is the second sound higher or lower than the first sound? (let us know in the comments). Play it again if you're not sure.

Ask a few other people to do the same. You'll find that some people hear the second note as higher and some hear it as lower!

(mini update: so far 5 commenters hear the second note as lower and 8 hear it as higher)

That's because it's an audio illusion. And just like an optical illusion an audio illusion can tell us something about the way we perceive the world around us. Continue reading →

Oct 10

How to make a fire tornado

All you need to make a fire tornado is: Continue reading →

Sep 10

Our Brains Didn’t Evolve – the problem with headlines

Our Brains Didn’t Evolve – the problem with headlines

I read a very interesting article about the development of the human brain in the Observer recently. But there was one very big problem with it - the headline. Continue reading →