It's been freezing here lately (Global warming? Where's my share?) so I have been browsing the Internet, looking at the latest waves of alleged ghost detectors in use and on sale out there.
I say 'alleged' because there is no such thing as a ghost detector. We don't know what ghosts are made of (and if anyone says 'ectoplasm' I'll say fine, show me the chemical formula). If we have no idea what something is made of, we can't design a detector to find it. Never hand over money for anything labelled 'ghost detector'. There is no such thing - yet.
It is currently held as fact, though it might not be, that ghosts affect electrical and magnetic fields. It's possible, even likely that this is the case, but not proven. We have to start somewhere so let's look at electrical/magnetic fields and see if they change significantly when odd things happen or when manifestations show themselves. Sounds easy? Well, it's not.
The modern world has an unseemly level of background electromagnetism, especially inside any building with any form of electrical wiring. This is not constant: a fridge switching on in one room will send a measurable pulse through the entire electrical system. Lights turned on and off, anything like that, will send pulses all around the wiring. EMF meters will record these as spikes.
Many researchers perform a 'background level check' before starting, but this is usually done in daylight and is therefore worthless. The lights aren't on, the heating might not be on, in fact most electrical items are off during the day. The background level is the level you measure when nothing's happening, but under the same conditions as those prevailing when something is happening. The difference between the measurement you get when there's activity, and the measurement you get when there's not, is what you need to record.
Lately, I hear of 'proton magnetometers' and laser-with-mirror motion sensors and trifield meters and a host of other super-sensitive detectors. Don't buy them. These are highly sensitive measuring devices, sensitive enough to detect pocket change moving. That's below the background level, and anything below the background level is not realistically detectable. Furthermore, if you report measurements that are lower than the level of background noise, no scientist will ever accept it as proof of anything at all. In any subject. Ever. So spending thousands on super-sensitive machinery is a waste of money unless you're engaged in those physical sciences that the machines were designed for. They were not designed for ghosthunting. They are far too sensitive for that.
It's a question of magnitude, and of magnitude of difference.
If a ghost is largely composed of electromagnetic energy, then the presence of a ghost should produce a lot of it in the immediate vicinity. There should be a big difference in the electromagnetic fields noted in the absence or presence of the ghost. Not some trivial, barely detectable movement of the needle. A big difference. If the theory is correct and ghosts are electromagnetic in nature, you don't need high-sensitivity meters to see the difference. In fact, at too sensitive a setting, the needle will go offscale and you won't get a reading.
So a cheap meter is perfectly adequate to test this theory - and remember, it's a theory, it might be wrong. How much money are you willing to risk wasting, if it turns out that the electromagnetic theory was wrong?
I stress that the theory is not proven but there are reasons for supposing that some form of electromagnetic energy is involved. One of these reasons is the scarcity of ghosts and ghostly activity in daylight. During the day, the world is awash with light, and light is electromagnetic energy. It would be a strong-willed ghost indeed who could manifest against this huge background level. I don't think ghosts are afraid of daylight. I think they're overwhelmed by it. Rather like walking into a gale or trying to be heard over a crowd.
At night, in low light, there is far less background energy for the ghost to overcome. Even so, in order to manifest, there must be a significant energy cost and this must be detectable by some means.
It's not going to need something working in nano-scales and costing mega-bucks. When deciding which measuring devices to buy for ghost investigations, always keep one thing in mind.
You will need some serious evidence (ie big numbers) if you're going to convince anyone. So whatever you measure, if it's not showing a big difference, it's not useful.
Paranormal investigation does not require huge investments in fancy equipment you can't really use. Don't listen to anyone who tells you it does, because you'll find they're more interested in the kudos of having fancy gadgets than in the investigation.
Start small and start cheap. Except the camera. That has to be the best you can afford.