Earth's Constant Hum Explained

MattSparkes writes "It has been known for some time that there is a constant hum that emanates from the Earth, which can be heard near 10 millihertz on a seismometer. The problem was that nobody knew what caused it. It has now been shown that it is caused by waves on the bottom of the sea, and more specifically 'by the combination of two waves of the same frequency travelling in opposite directions.'"

Why?

[khristian]

I think these people "researching" it have too free time in their hands...

(...)This creates a standing wave that "goes thump, thump, thump on(...)

Sound more like a kid that's happy for having found out how something works. Well, if that keeps 'em happy, they should go for it ^^

Did ancient greeks know about this?

[torrija]

I think this is a concept related to Pythagoras' Musica Universalis http://en.wikipedia.org/wiki/Musica_universalis [wikipedia.org]. An inaudible sound on all celestial bodies.

Energy

[Anonymous Coward]

is it a harnessable energy source?

I'm guessing it may be to week/dispersed. But would be nice to know if it could be focussed suficiently.

But wait!

[camperdave]

...the waves are making the sound.

Wait a minute. How do we know that it's the waves that are causing the hum, and not the other way around? Perhaps the planet is still ringing from meteor impacts, and the hum is just the resonant frequency. The deep ocean waves may be just a side effect.

I have an idea

[LaughingCoder]

Maybe we could build a clock that used this hum as some sort of synchronization. Then every clock on the planet could be synchronized, since this signal is presumably detectable everywhere.

OK, I didn't say it was a *good* idea :-)

Re:constant hum

[Anonymous Coward]

60 Hz 50, 100 and 120 Hzare noise due to power lines

Things like EKG's and EEG's are very sensitive and contain filters to remove these frequencies

To receive this signal we must filter out other unwanted signals , This is done in seismometers, Taking the concept further we simply center the seismometers filter on 10e-3 Hz and we now have a graphical , output of this wave

Re:Alternate explanation

[twistedsymphony]

They didn't say what causes the waves !

What did cause the waves?, How do we know that the waves weren't caused by the hum?

Not quite right

[unixfan]

All objects have a mean frequency which in this example is causing the frequency that they are observing in the water. The frequency in the water comes from the planet's own resonance, or a harmony thereof.

Tesla noticed this and build a little tool which hit on the harmonic frequency and kept accelerating the oscillation with a device he built until there were "earthquakes" observed all around, and he had to cut short a trip to run home and turn it off. Indeed in manufacturing speakers you try to get this frequency down below audioble range as you don't want the speaker to resonate and alter the sound it's supposed to generate.

It's a very common mistake made by many when they observe a symptom (not realizing there is a real why behind it.)

this is what I found

[mapkinase]

Article reporting the milliHz hum in 1998 [sciencemag.org]
IDA (International Deployment of Accelerometers) [ucsd.edu] used to detect the hum.
Article in Nature (1979) [nature.com] assesses if IDA can be used to detect very low frequency seismic data. Looking at the figure 1 of amplitude(?) ("MD counts" at Rarotonga station not shown on the current IDA map [ucsd.edu]) I can see the aftershocks in 2 hour intervals after the Indonesia earthquake, but the subj frequencies could be detected only by obtaining the spectrum (Fig.2) at mHz range which frankly looks like white noise - irregular beats.

Most interesting figure is Fig.3 which shows the 0.43-0.52mHz of the _processed_ spectrum measured at six different stations around the world at Hour 25 and on. The Alaska station (CMO) has much clearer spectrum compared to the closest (?) RAR station.

All of it must have meant something for a seismologist which I am not.

possible energy source?

[jhfry]

If our whole planet were vibrating at a constant frequency... it seems to be that there is a lot of energy in that hum... any way to harness this?

Re:10 millihertz

[UbuntuDupe]

That kind of made me wonder how it's a "hum". I mean, ... isn't there some minimum threshold a cyclical process has to meet to be classified as a sound? Does the earth's one-revolution-per-year around the sun count as a "hum"? Does "me coming to work and returning home each day" count as a hum?

Re:Throbbing

[mysticgoat]

It's more like "bang the drum softly". Once every ten seconds.

So are there any biological processes that are using this omnipresent beat for a clock frequency? Do any of the intracellular membranes we are familiar with quiver in resonance with the Earth beat? Would it be possible to predict the shape of such a biological structure?

I'm guessing that life has found a way to take advantage of this constant beat to organize sequences of activity. If that it so, there would be health consequences for astronauts: the ISS might need to have a thumper installed on the hull. There are probably also health consequences for anyone working in an environment where the Earth beat is drowned by industrial noise.

On mars the atmosphere shakes once every year

[goombah99]

on mars the viking landers made a suprising discovery. Once every year the temperature and pressure conditions cause the entire atmosphere to shake globally. The seasonal cylce is not symmetric so it only happens once a year and it happens very close to the same day every year. This might seem weird but the martian atmosphere is about 100th as dense as ours so the sound waves can get pretty huge. I happen to known this because I helped discover it (using fortran 4!)