Over the past five years, I’ve witnessed – and refereed – a few online shouting contests between people who are convinced they know the source of the world Hum. Passion may be a great engine for scientific research, but it is a poor arbiter of it. In my view, four hypotheses have survived the most trivial examinations and the available evidence. Each of these hypotheses has its difficulties. I am examining and testing them in turn.
- VLF radio frequencies between 3 Hz and 30 kHz (and possibly ELF frequencies below 3 kHz) are interacting with living tissue and activating the human auditory system in a way the brain interprets as sound, and sometimes as perceptions of physical vibration (The perception of EM energy as hissing and/or popping sounds has already been established at higher frequencies, such as radar and microwaves). I have a built a unit that aims to completely block VLF radio waves within an enclosed space. I conducted this experiment and I heard the Hum as loud as ever. This is not conclusive, of course, and I need to at least confirm using electronic measuring devices that the box does what I claim it does. Nevertheless, the EM theory is in doubt now. There of course is the related theory that exposure to some types of EM energies causes subsequent perceived audio effects, just as certain types of intense acoustic exposure can lead to perceived audio effects (i.e. tinnitus).
- The world Hum is caused by the (increasingly) grand accumulation of low-frequency sound and infrasound from human activity, including for example mining, marine traffic, air traffic, windmill farms, smelters and blast furnaces, freeway traffic, the electric grid, factories, and so on.
- The world Hum is the result of a terrestrial/geological process. Many geological processes can work very quickly, such as during earthquakes. Some can work over months or years (e.g. volcanoes). I have a person digging into the historical records to find evidence of the Hum in 19th century England. If it can be solidly established that the Hum has occurred in past centuries, then this would be a piece of confirming evidence for this theory.
- The world Hum is an internal body process along the lines of otoacoustic emissions and tinnitus. If the currently accepted timeline of the Hum is correct, then I think this theory is unlikely. If we find historical evidence of the Hum, then this theory becomes a serious contender.