Halloween Science

halloween science

For this week’s blog post, we’ve turned out the lights! Although I’m sure Halloween was never really a thing when I was a youngster, nowadays it seems to take up a whole purple-lit aisle in the supermarket, so we’ll go with it. In today’s post I’ll be exploring three spooky ideas, one used in haunted houses, one to create ghosts in the theatre, and one to do with zombie apocalypses. Plus we’ll be suggesting some Halloween science you can try for yourself.



First up – we look at the science behind ghosts. Wait, what, science?! Well, there have been some explanations put forward for why certain places feel haunted, and why people are more likely to witness paranormal sightings in such areas.

The underground vaults at Edinburgh Castle are a good place to start. In these long rooms, sound echoes from one end to another. This causes the vaults to act as a resonance tunnel, and this makes the volume of the sound and the energy in the wave increasingly loud.edinburgh castle

Photo: Kim Traynor CC-BY-SA

This creates a very low frequency soundwave, infrasound. In fact, your ears can still sense it even though you don’t consciously hear it. It is this which causes confusion in the brain and creates the feeling of dread and panic.

But infrasound also affects other body parts.One reported instance of this was by an engineering designer at Coventry University (he was inspired to do this job by one of our engineering shows, rumour has it). This person, Vic Tandy, also noticed the aforementioned depressing and ‘cold chill’ feeling that comes with infrasound, as well as a shortness of breath and even ghostly visions; the feeling that somebody was watching him out of the corner of their eye.

It transpires that the infrasound frequency, at around 18.9Hz, affects us much more than we may think. We’ve looked into extreme sounds before for our show research, but even this is new to us. NASA also noted this frequency has an affect on the eyeball, which causes it it vibrate and effectively ‘smear’ the incoming signals sent to the brain. The result is usually seen as bright orbs in the corner of the eye, or as shimmering. Our eyes are more sensitive to movement than they are to colour, so the latter is more likely.

To test this phenomenon, Tandy set up metal sheets in clamp stands, which vibrated of their own accord. This led him to realise that there was some ultra low vibration occurring, and once the source was tracked down (to ventilation fans), they were able to lighten the mood a little in their research lab. We’ve actually worked with Vic Tandy when designing our Sound at the Extremes show; he told us about his experiences first hand and gave us some fantastic angles on talking about sub-human sound!

You can see Wendy presenting Science vs Ghosts at Ignite Cardiff on the clip below:


Try it yourself…

Although using a very low frequency speaker could re-create this body bending effect, we don’t recommend it! However, resonance can be used in various other experiments. One of the our science made simple favourites is the straw oboe, also known as the musical straw.

It’s incredibly straightforward to make; simply get the non-bendy part of a drinking straw and cut two V shapes into one end. Then blow through the straw with your lips pursed, and this will create a vibrating feeling and some noise.musical_strawImages: science made simple © all rights reserved

In our sound shows we take this once step further and use really long straws so people can really see the effect of resonance. Here is a photo of Zoe and myself performing this at a European physics conference in Germany.


Photo: science made simple © all rights reserved

Here we are cutting away the end of the straw and making it shorter, which makes the pitch go higher and higher. It’s a very simple demonstration to show resonance. And just look how much fun we’re having.

So, how long does a straw need to be to make an infrasound vibration of around 18Hz? Well, the frequency of a wave is directly proportional to its wavelength, and in this case the wavelength is determined by the length of the straw. So, text books out:

halloween blackboard

To achieve the bitter and deadly panic of resonance from a straw oboe, we’d need one which is 9 meters long. That’s a lot of straw and a lot of blowing! If you do try give this a go, let us know how you get on.

Now you see me, now you don’t

Another spooky effect, used on purpose rather than accidentally discovered, is that of the illusion of making something appear and disappear. Now, there are many ways we can do this, with mirrors, lighting and trapdoors to name but a few, but I wish to explore a particular effect which caught my imagination from a few theatre visits.

In the theatre version of The Woman in Black, parts of the set are hidden from the audiences view by an opaque screen. As the play progresses, these areas are revealed not by removing the screen, but by making it go translucent, by changing the angle of lighting. I was fascinated by this remarkably simple yet unexpected phenomena, and had to look into it.

This screen is actually made from a finely woven but lightweight fabric, referred to in the industry as a scrim. It doesn’t absorb any light, however is very reflective and becomes opaque when light is shone onto it, and see-through if light is shone from behind it, allowing the effect of a set appearing and disappearing according which lights you turn on.

Try it yourself

If you want to create an image that magically appears you can use a scrim. But if you don’t have theatre supplies readily at your disposal, you can make an even better effect using polarising filters and sellotape. The polarising filters work by only letting light waves through if they are aligned in a certain direction. The sellotape causes refraction of the light, creating various colours (wavelengths) at various angles. Combine these at different angles, for example by taping an outline of sellotape onto paper, and you can have a magical rainbow coloured appearing and disappearing image.

Don’t know what we mean? Well, we could explain this in more detail, however it’s easier for you to see it for yourself. This effect, as well as others using polarising filters, is fully explained in one of our shows, Beyond the Rainbow, which focuses specifically on the electromagnetic spectrum and what happens beyond visible light. Be very intrigued!


Zombies Attack!

If you really want a great Halloween costume, avoid the broomsticks and hats and head for face paints and torn clothes.  Zombies are definitely the winners when it comes to fright-night. Zombie films are pretty terrifying too, with streets filled with the undead and only a tiny band of the un-infected left to fight it out.  But just how quickly would a zombie attack really spread? To find out you don’t need to consult a master of the occult, a mathematician will do.  It turns out that if you know a few things about a disease like how contagious it is i.e. how likely it is to pass from person to person; how many people are infected to start with and how long it takes to recover, you can get a pretty good idea of how it will spread.

Why not try it for yourself (modelling a disease, not becoming a zombie):


Plus there are a whole lot of zombie-maths resources here too:



And with that we end our spooky science blog post. Which leaves me only the not-so-scientific but equally fun art of pumpkin carving. Here’s my best attempt. Happy Halloween!

pumpkinPhoto: science made simple CC-BY-NC


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Posted in Activity, Exploring Science, Physics