Lunacy in the infra-red.

Many amateur (and some so-called professional) ghost hunters make extensive use of electronic equipment. In particular, they do like to have a good supply of infra-red cameras and thermometers.

They are astounded at the 'orbs' (dust) these things pick up, the temperature variations when waving the thermometers around, and when the TV turns itself on they scream 'Proof'.

I scream, too. In despair.

Things reflect infra-red differently to visible light. Plants, for example, reflect infra-red as if they were mirrors. Dark clothes can appear light. Dust shows up exceptionally well. That’s reflection, not emission. Now, why would an insubstantial creature like a ghost reflect infra-red?

The amount of infra-red emitted by an object is related to its temperature. This is something that should be carved in stone and nailed to every ghost-hunter's head. Since ghosts produce cold areas, why on Earth would anyone expect to see them with an infra-red camera? They aren't producing any. If anything, they’ll absorb heat and infra-red light so they won’t be reflecting it either.

Infra-red light passes unhindered through air. Air does not emit infra-red light. Therefore, an infra-red thermometer cannot possibly measure air temperature. It measures the temperature of whatever you point it at, not of the air in between. It is not possible to detect a cold spot with an infra-red thermometer. What you get is an average of the temperatures in its cone of measurement, and the area it measures gets bigger the further you are from an object. Waving it around in the middle of a room will give you wild fluctuations. Read the instructions! Then carve them in stone and nail them to the ghost-hunter’s head too.

I've saved the best for last.

I've seen many of these ghost-hunter programs take place in darkened rooms, with infra-red floodlights so the cameras can see what's happening. Many of the crew carry camcorders with infra-red lights, and there's usually a halfwit waving a thermometer at the walls. In several programs, televisions have turned themselves on and off, even when the 'expert' has the remote control safely tucked away in his pocket.

Wow, how could that happen? Could it be supernatural? Or maybe super-idiocy?

Consider what appears above: infrared reflects differently to normal light, and the room is full of infrared lights. Some of the lights are mobile, hand-held. Some are static, but the people who reflect it are mobile. So is the dust, but that's a separate issue.

TV remote controls work on - yes, you've guessed it - infra-red.

I can aim my TV remote control at the wall behind me. The wall reflects the control's output and the TV changes channels. If you have lots of sources of infra-red in a darkened room, and either the sources or the things reflecting the light move around, chances are that sooner or later your TV will receive the right pulse of infra-red and turn itself on. Or off. You can take the batteries out of the remote, you can hide it in another room, you can smash it with a brick, or with the stones nailed to your head. It doesn’t matter. You won’t need it.

Not when you’ve filled the room with infra-red emitters, and idiots to wield them.