In the earliest days of electrical power, (the late 1800s) the inventor of the
light bulb, Thomas Edison, elected to power his creation with direct current.
Direct current 'DC' is fine for short distances, and when no need for changing voltages
is required DC works fine, but hums not a bit. It was soon discovered that
AC 'Alternating Current' was far superior for transmission over longer distances,
could properly pass through transformers, allowed the use of brushless electric motors,
and is what powers our world today.
The laws of nature seem to be universal across the universe so this same alternating current
discovery will be made by any sentient species bright enough to develop electricity. Their lights will hum!
In the western hemisphere AC alternates, which produces a 'Sine Wave', with a frequency of
60 times per second. In Europe, and other countries, AC alternates at a rate of
50 times each second. This produces copious quantities of hum.
Twice each cycle the voltage in an alternating circuit goes to zero and reverses polarity.
At 60 cycles this produces 120 pulses of light from most lamps each second.
At 50 cycles lights pulse 100 times each second.
Click the animation for more about Sign Waves
The western hemisphere hums at 120Hz. (cycles per second),
and most of Europe hums at 100Hz.
50 and 60 cycles per second were chosen for a verity of technical reasons. Much below 50
cycles and our visual senses perceive flicker, which would make thirty or forty cycle
electric lights troublesome for us to use. As electricity is generated by spinning a
coil of wire around a magnetic field, frequencies much above 100 cycles per second would
require spinning the generators too fast to insure long trouble free operation.
The laws of physics seem to be the same throughout the universe, and so should we
expect animal physiology to be similar to ours. Animals living in a similar
environment to ours would be expected to have a similar visual system, and as they
became technological, would choose similar electrical frequencies, for the same visual
and mechanical reasons.
and why it's
likely to fail
For over a half century SETI has been listening for radio signals from extraterrestrials.
For a verity of technical reasons, the odds of classic SETI ever hearing an
extraterrestrial radio signal are worse than one in several hundred billion.
Scott Bidstrup has written an excellent paper
'Why The SETI Project Is Doomed To Fail'.
Obviously you can't prove a negative, and Mr. Bidstrup's article weighs heavily to the
negative. As much as I'd rather not, I must agree with many of Bidstrup's conclusions.
I believe Hum-SETI avoids many of the pit falls of the previous SETI experiments.
And will shine a light on our neighbors.
(please excuse the pun, for I simply could not help myself. :-)
and why it's
likely to succeed
High power output from ET's outdoor lighting, and its, broad pattern of radiation,
will sweep over us slowly, over many hours, not as the fleeting glance of a directed
radio or laser signal would.
Very narrow signal bandwidth. Alternating current varies by less than a fraction of one
cycle per second (Hz), so is relatively easy to sort from the background noise,
which will be exceedingly high.
Likelihood that a civilization will radiate AC light for more than a hundred years is very
high, where our civilization is now transitioning away from analog radio and TV signals
towards digital, which is far harder to receive. We may someday move
away from alternating current lighting, but AC lights will outlast high power analog
For nearly 70 years we have broadcast our television in what's called 'Analog'.
This analog signal is nearly as easy to decode as placing grandmother's sewing needle on an
old fashioned record to hear the sound recorded in the wiggly, analog groves.
Analog line and frame sync pluses, imbedded in the TV signal made decoding such a signal
very easy. The bad news, at least for the SETI people, is we are transitioning away from
analog broadcasting to digital. It's assumed that ET will follow a similar path, and after
a hundred years or so may switch to digital transmission.
Digital TV is a much more difficult signal to decode. Some have said, "Even detecting an
extraterrestrial digital television signal may be impossible, as the digital signal
looks so much like background noise it may be undetectable". That was until recently.
Scientists and engineers, through their work improving our own digital transmission and
reception, and through the decryption of encrypted digital data, have discovered a multitude
of ways to detect and decode digital signals previously thought impossible.
I have no doubt - should we hear the lighting-hum from a neighboring star system, some country
on this planet earth will construct the required equipment to receive and decode their TV transmissions
in record time, regardless of their mode of modulation or encryption.
Since the 1960s the Search for Extra-Terrestrial Intelligence,
has been limited to listening for radio transmissions from intelligent extra-terrestrial
beings. So far we've heard not a peep from neighboring worlds. This is understandable as
our radio receivers are too insensitive to receive anything but a very high power
transmission intentionally directed at our solar system. A less than likely prospect to
A project called Optical SETI
has been tried, and it too has been fruitless.
Optical SETI, as practiced by Harvard and others, is looking for a high energy LASER beam,
intentionally directed at us by a world of beings intent on advertising their presence to
neighboring worlds like ours. Presuming a race of sentient beings would expend the time and
effort to build and operate a multi-gigawatt laser simply to say 'Hello' seems less than
sensible in my opinion. We should be looking for something they may be unintentionally
sending in a wide swath away from their planet, and that is their artificial lighting.
Earth, for the last hundred years or so, has been radiating manmade light into space.
We now emit nearly 100-terawatts of
artificial light out to the stars. This manmade optical radiation is far brighter
than all of our radio transmissions combined, and unlike earth's myriad of radio transmitters
operating on millions of different frequencies, our artificial light is modulated at
only two very narrow, and easily detectable, frequencies.
Assuming most extraterrestrial sentient beings utilize the same part of the electromagnetic
spectrum for their vision as we, (a near absolute necessity if they're biological),
the supposition that they'll eventually invent electric lighting is a pretty safe bet.
The artificial light, generated by earth, blinks 'Hums' at a low note
from 100 to just under 400 cycles, or pulses, per second, depending on phases and
harmonics. Stars, other than a few pulsars, don't blink or hum at anything near these
frequencies, so detecting this attribute of artificial light over a few hundred light years,
and even through the glare of bright stars is something we can accomplish with today's technology.
Why does our light, and presumably that produced by other intelligent species, blink or hum?
See the sidebar to the left.
I propose a search for extraterrestrial intelligences in the optical band of the
electromagnetic spectrum, utilizing existing terrestrial telescopes, and some simple
off-the-shelf electronics, not to directly detect the light, but to detect the
alternating current attribute of the light radiated from planets inhabited by
sentient beings who are at, or near, our level of technical achievement.
Scientists have recently detected the reflected light from 51-Peg-b, a half Jupiter size planet
orbiting a star about 50 light-years from earth, and soon ESPRESSO at the VLT, and the European E-ELT,
will have the ability to do spectral analysis of the reflected light from earth-size
exoplanets around many other stars.
The reflected starlight from a planet will be orders of magnitude higher in amplitude
than any artificial light that might be generated by the inhabitants of such a planet,
but filtering for the AC modulation of that light will make the artificial light much easier to detect.
Hum-SETI cares little about the spectrum and all about the modulation.
The following is a simple block diagram of my proposal to detect the hum of
extraterrestrial artificial light, which I call Hum-SETI
to differentiate it from other forms of SETI:
The above is an oversimplified diagram, to convey the overall Hum-SETI concept.
the star's light will most likely overshadow that of the artificial light from the planet,
making detection from earth impossible. A technique called
will most likely need to be employed to eliminate the starlight, and enhance any
artificial light radiated from planets surrounding it.
Nulling Interferometry employs two telescopes, such as the Large Binocular Telescope located
in southeastern Arizona. The starlight from one telescope is delayed by 180-degrees and
combined with the non-delayed light from the second telescope. This effectively eliminates
the starlight, while reinforcing the out of phase planetary light that is coming in at a
slight angle to the starlight. This scheme should greatly reduce much of the unwanted
noise, but of course, will limit the viewing time to about a third of that planet's year.
Obviously as the planet's orbit takes it through the back 180-dgrees of its orbit, the
hemisphere facing us will be in daylight and not have their lights on. As the planet
passes in front of its star the hemisphere facing us will be in the dark, so will have
its lights aglow, but its angle to our telescopes will coincide with the star's angle,
thus the planets light will be nulled-out via the nulling interferometry. Only about
twenty or thirty percent of its orbit will the planet be far enough from its star to
not suffer from our nulling interferometry, but still have some of its night-side
exposed to us.
Assuming planets, fit to support sentient beings, will have an orbital period somewhere near
ours, plus double or so, or minus half our year or so, we will need to sample each star of
interest every few weeks, or months, to insure we catch the planet in the proper part
of its orbit, in order to see an appropriate portion of its night-side.
The above are simplified block diagrams, in order to illustrate the Hum-SETI concept.
Some R&D will be required. The actual apparatus may include other components such
as spectral filters, optical gates, and other optical and electronic hardware,
in order to optimize the overall performance of the Hum-SETI system.
Phases & Signal to Noise The Two Big Challenges
Phase shift, across the face of a target planet, will cause some of the light's A.C.
modulation to be at, or near, 180-degrees out of phase, which will negate a percentage
of the modulation effects, but an equal and opposite phase shift will reinforce the A.C.
modulation, making at least some of the radiated light appear to have an even higher
amplitude. Digital signal processors, running the appropriate algorithms,
should easily 'see' the several phases of continent-wide alternating current lighting.
The ratio of signal to noise, in a project of this sort, will be extremely low.
Without the recent advances in digital signal processing the level of extraterrestrial
artificial light entering the Hum-SETI apparatus would be overwhelmed by the
background noise and completely undetectable.
Stars, dust, gasses, other interstellar objects, and earth's atmosphere, produce high
levels of undesirable optical noise increasing the challenge to 'hear' the relatively
weak hum from any possible galactic neighbors. With the advent of modern digital signal
processing, extended sampling times, the extremely low modulation rate of the
expected signal, and the use of nulling interferometry, I believe these challenges
can all be overcome.
With today's highly sophisticated digital signal processing electronics, detecting
the optical 'hum' of a nearby civilization, that was near the same level of development
as earth, in my opinion, will offer a far
better chance of success than do the other forms of SETI.
What the Signal is Likely to Look Like
The incoming signal will be mostly random noise, but if there's a repeating signal,
such as a low frequency sine wave, the Digital Signal Processor will over time accumulate
small amounts of nonrandom noise. As the nonrandom noise accumulates, it will eventually
describe a sine wave, with the frequency, "Hum", of the extraterrestrial's alternating
I'm steadfastly in the
Carl Sagan camp
, as are most other scientists, when it comes to extraterrestrials. The late Carl Sagan
believed the universe was probably teaming with intelligent beings, but they have never
visited earth in the flesh.
Until some yet unknown law of physics allows us to violate, or sidestep, the
speed of light limit,
I'll stay with Carl on this matter. But like Dr. Sagan, I so do want to detect an
intelligent extraterrestrial species.
Just knowing that we are not alone in the universe will have profound implications for us
earthlings. And just maybe we'll learn how an advanced civilization has worked through
their social and other challenges, and apply that information
for the betterment of all mankind.
What do we do after Hum-SETI receives an unambiguous indication of artificial light
emanating from a far-off planet? We watch their television of course!
The Next Step What do we do after we hear the hum?
It's been postulated that should we ever receive an audio only, or text only, transmission
from an extraterrestrial civilization, we'd never be able to translate it to something we
Until the discovery of the
Rosetta Stone in 1799,
and its decipherment over twenty years later, we had no idea what the ancient
Egyptian hieroglyphs were trying to say. There is no Rosetta Stone in an audio or text
Once a sentient species develops electricity it follows that they will soon develop radio,
followed shortly thereafter by the invention of television. Unless the extraterrestrials
are bereft of the sense of hearing, their television, like ours, will include sound.
Moving pictures with a running commentary is an instant Rosetta Stone, and would allow us
to understand these new neighbors in a very short period of time, but receiving their
television signals will be a challenge.
Television signals are far weaker than the light pollution given off by a developed planet,
and are much more complicated and wider in bandwidth than simple low frequency alternating
current. Receiving and decoding ET-TV will require a very large antenna, sensitive receiver,
and much more processing power than that needed to hear the hum of their lights.
One of the few radio telescopes capable of possibly receiving ET-TV is the 300 meter
Arecibo dish in Puerto Rico,
assuming the signal impinges on that hemisphere of earth, and is within Arecibo's tracking range.
A bit like the physical laws dictate the frequency of an extraterrestrial's alternating current lighting,
similarly their analog television signals will most likely be broadcast in a range of about 50MHz to around 500MHz.
This range is below that which nearly all of today's radio telescopes operate. Other than Arecibo, most radio
telescopes operate above 500MHz. Arecibo is capable of operating as low as 50MHz, but may be in the wrong position
on earth, or too low in gain to properly receive ET's relatively weak television signals.
The proposed, but not yet constructed,
Square Kilometer Array (SKA) may have the gain and ability to receive ET-TV,
but like so many other radio telescopes it, as planed will, by necessity, ignore the frequencies below 400MHz.
This is an economic consideration, as lower frequencies require larger dish diameters, and far higher costs to construct,
than do smaller dishes optimized for the reception of higher frequencies.
An array of large dishes, from two to three hundred-meters each, could be easily excavated into the earth of a high and dry area, such
as the Atacama desert in Chile, or even in the ice of the Antarctic continent. The Arecibo dish is 167 feet deep from rim to center.
A similar dish, excavated in flat ground, or ice, would require an excavation less than 90 feet below grade at the center.
The excavated material would be pilled around the rim to a height of little more than 80 feet to create a dish with similar
dimensions to Arecibo. In that 50 to a few hundred MHz, the frequencies we will be interested in, does not require
a reflective surface as uniform as do >1GHz dishes, simple screen material could be used to follow the excavation's contour.
Sharing simple low cost commercial radio towers for receiver support; these dishes could be constructed fast and at a
relatively low cost. Additional dishes would be excavated as needed, until sufficient signal levels were achieved.
Television requires a relatively wide bandwidth, between 3 to 5MHz for 20 to 60 or so frames per second.
Unlike current SETI receivers, which sample very narrow frequencies, the receivers for this venture would be
specifically designed for high gain, low noise, and wide bandwidth.
An analog TV signal is relatively simple to detect and decode. The horizontal and vertical framing pluses define each frame.
By necessity ET's modulation scheme will be something similar to ours but may differ in polarity and other factors.
A first pass analysis of the 50 to 500MHz band will scan for the framing pluses only. Detecting the framing pluses will
locate the exact transmission frequencies. The receivers would then be optimized for those particular frequencies.
The frame content would be analyzed. An algorithm would then be developed to decode and display the video and sound.
Will ET Go Digital?
Like us, in fifty to one hundred years of analog TV transmission an extra terrestrial civilization will likely have the technology,
and the will, to switch to a higher resolution digital TV system. If no analog TV is detected in the lower 50 to 500MHz band
our dishes and receivers would be modified to scan up through a few GHz for ET's digital signals. Digital TV differs greatly
from analog TV but will still have some relatively easily recognizable attributes. Decoding the digital signal to produce
viewable television will be a much larger challenge than the simpler analog signal,
but with enough computing power it is well within our abilities.
We Want Our ET-TV
Assuming we are eventually successful at receiving ET-TV - the several channels of
extraterrestrial television, that we'd most likely tune into, would then be put on the Internet for all to view and learn from.
If you find any errors in the facts or logic of this web page, or simply differ in
philosophy, or opinion, I am interested in your feedback.
If you personally know someone at NASA, at one of the SETI organizations, or a member of
congress, please pass this web site on to them. We need our ET-TV!
Permission granted to use text, and graphics,
on this site, as long as attribution and a link to this site is included.
Translations welcome. If you have a translation of this site please send a link and it
will be listed here.
If you reference Hum-SETI in any blog, forum, web site, or article, an email
would be appreciated. J.R. Whipple
Power & Phases
Electrical power is commercially generated and distributed as three phases,
each phase being 120-degrees from the other. Three is the optimum number of
phases for the most efficient distribution of alternating current, so would
most likely be chosen by any advanced sentient species as they went through their
electricity development cycle.
Separate branches of street and commercial lighting are powered by only one
phase of the three, so in earth's western hemisphere a large area of artificial
illumination will exhibit flicker twice the rate of all three phases, or hum
at 360 cycles per second, and 300 cycles in the countries utilizing 50 cycle A.C.
At the upper practical limit of alternating current, about 100 cycles per second,
is of course a relatively long time period of ten milliseconds. Elevation variations,
as we have across our planet, will cause but a few microseconds of phase shift to
the aggregate radiated light, as will Doppler shift, due to planetary spin and orbital
velocities - So these effects can safely be ignored. Phase shift across an entire
continent, or hemisphere, will cause noticeable phase smearing, but should be easily
corrected in the digital signal processor. (See the center-panel block diagram.)
In that 100 cycles per second is most likely the high end of most extraterrestrial's
alternating current, and 30 cycles would likely be the low end, the sampling period
would be relatively long, insuring the weakest of signal could be differentiated
from the high background noise.
Digital Signal Processing is a relatively new technology which is rapidly evolving.
DSP is the representation of a signal by a sequence of numbers.
The numbers can then be manipulated or changed by a computing process to change or
extract information from the original signal. Often this includes the extraction
of wanted signal from unwanted noise. Bandpass shaping is another possible change
that could be made.
DSP can even originate or create a signal from numbers in sort of a
reverse process. One advantage of this is that there is no requirement for tuning as
the signal is now just a sequence of numbers in the computer. This makes DSP a very
stable and flexible way of dealing with electronic signals, and especially shines at
resolving very weak signals from very strong background noise.
An input signal is first passed through a low pass filter and then digitized with an
analog to digital converter. This is called sampling. Discreet samples are taken of
the input analog signal and represented at that moment by a digital value.
The higher the sampling rate verses the frequency of interest the better we can
reconstruct the original signal, or pull it out of the noise.
Processing of the digital signal from of the A/D converter's output often consists of
addition, multiplication, and delay. Addition and multiplication are very familiar
terms and computers are very efficient at handling those operations. Delay refers to
the ability of the processor to cause phase shifts, or comparisons of different parts
of the signal and causing a change to take place in the output signal such as eliminating
background noise, and other undesirable attributes of the original signal.
The DSP process can and often does involve complicated higher order mathematics such as
Discrete Fourier Transforms (DFT). This is a mathematical technique to determine the
content of a signal mathematically. Other mathematical methods include the Inverse
DFT (IDFT), the Fast Fourier Transform (FFT) and the Z-transform.
All of these mathematical tools are employed to manipulate a digital signal in special
ways to produce the desired result. For example we may want to eliminate any specific
impulse signals that may happen to come along, for example noise, phase shift, signal
smear, and more.
With the proper digital signal processor, and appropriate programming, the weakest of
signal can be pulled up out of the strongest noise.
Some relatively nearby sentient beings may have started their evolution to a technological
society a hundred or a thousand years ahead of us - But if they're a hundred or a thousand
light years away from earth, we may be just in time to hear them humming today.
Maybe most life starts and follows an evolutionary path similar to ours, but some planets
never had an event that killed off their dinosaurs. Are technological beings limited to
mammals, or mammal-like creatures with opposable thumbs? If so, some planets,
much older than earth, my still have only dumb lizards roaming about.
After all, our big lizards had over 150 million years to grow a sentient brain, and
apparently failed to do so, while we, in a scant million years or so, grew brains and thumbs.
Time and space are spread out in front of us, displaying all things past. Have some planets
hummed in the past, but have outgrown the need?
Is it possible that we're alone in the universe?
Sure it's possible, but highly unlikely.