SETI - An alternate strategy

To date most SETI research has focused on the assumption that an advanced extra- terrestrial society will want to "communicate" with similar beings throughout the universe. But it is my belief that given the vast distances and time that communication via a "communications channel" even if it is one way, such as optical or radio frequency transmissions will be impractical.

Current SETI searches assume that an advanced civilization will use extremely powerful omni-directional transmitters or highly directional and focused signals targeted at our solar system. The challenge with either approach is the fact that successful one-way communication between intelligent species is the dependency on the “L” term in the Drake equation. L represents the length of time for which such civilizations release detectable signals into space. If L is relatively short then possibility of two separate intelligent civilizations being coincident in time to send and receive a signal is very small. So even though there may have been many intelligent civilizations we will probably never be aware of their existence.

Given these constraints I suggest instead that we look for extra-terrestrial intelligence in a similar way we searched for signs of intelligence on earth prior to the modern age. We cannot hope to communicate to prehistoric man, but we know that intelligent beings existed on earth thousands of years ago through archaeological evidence such as cave paintings, pyramids, monuments, etc.

More recently societies have been burying time capsules for future generations to discover and hopefully marvel at our accomplishments and perspectives of the future. Indeed several spacecraft have included time capsules to be hopefully discovered by humans or extra-terrestrial intelligent beings in the far future. Part of the Apollo 11 Lunar Module, still on the moon, includes a plaque showing the arrangement of the Earth's continents in 1969. The LAGEOS satellite (which will re-enter the atmosphere in 8.4 million years) contains a plaque showing the arrangement of the Earth's continents in the past, present, and future. Pioneer 10 and Pioneer 11 both contain plaques that give pictorial information about their time and place of origin. The two Voyager spacecraft each contain a golden record that contains pictures and sounds of Earth, along with symbolic directions for playing the record and data detailing the location of Earth.

The understandable challenge of physical time capsules is the probability of locating and/or discovering these time capsules by future generations or aliens. Given the vast distances of space it is highly improbable that these time capsules will ever be discovered by any kind of intelligent being.

So rather than deploying physical time capsules can we think of a way of deploying electromagnetic time capsules made from self amplifying or self re-generating optical and RF signals that propagate forever and are easily discoverable and locatable? SETI researchers, in the past, have often speculated on self replicating robots that could travel to distant planets and recreate themselves by using local materials, but the complexity of such a device boggles the mind. Self amplifying and regenerating electromagnetic signals on the other hand would conceivably be much easier to deploy and possibly be achievable with current technology.

Self amplification and regenerating signals could use natural physical process such as gravitational lensing, stellar corona pump amplification, orbital angular momentum and other techniques to propagate electromagnetic signals indefinitely. But rather than being a straight line propagation in the direction of the original signal, self amplification and regenerated signals may propagate in all sorts of random directions depending on the physical properties of the amplification and regeneration process itself. As such the signals may be bouncing around the galaxy from one star to another in no particular predetermined direction.

Given that they depend on natural physical processes for amplification and regeneration the originating transmission does not to be that powerful or directional. It is conceivable that low power transmissions are that all is required to launch a self amplifying and regenerating electro-magnetic signal. The signals may also be in a part of the spectrum that is not usually commonly assumed for inter-stellar transmission but rather exist in parts of the spectrum associated with the physical amplification and regeneration process.

There are a host of problems with current inter-stellar electromagnetic signaling such as attenuation, dispersion, group delay, etc etc. Given these limitations how could we hope to deploy a self replicating optical signal that will maintain its integrity over the vast distances and time of space?

One intriguing possible solution is using gravitational lenses to refocus and amplify a inter-stellar electromagnetic signal. In an interesting post ( by Paul Gilster of Centauri Dreams he calculates that a ‘Sun-Alpha Centauri direct radio bridge exploiting both the two gravitational lenses, this minimum transmitted power is incredibly… small! Actually it just equals less than 10-4 watts, i.e. one tenth of a milliwatt is enough to have perfect communication between the Sun and Alpha Cen through two 12-meter FOCAL spacecraft antennas.`

One should also note that a gravitational lens acts like a lens with a gradient refractive index which also collimate and reduce electromagnetic dispersion.

Other possible mechanisms for self replicating signals include RF Orbital Angular Momentum (OAM), quantum entanglement and using stellar corona as pump amplifiers. As an example see the recent post about solar corona masering. I am sure there are other possible candidates. I challenge the reader of this missive to think of other ways of creating self replicating electromagnetic time capsules.

If we can come up with a plausible mechanism for deploying self replicating optical/rf time capsules the next obvious step would be to see if we can detect any such phenomena in our local inter stellar region.

Instead of searching for communications signal from an extra terrestrial intelligent civilization we should perhaps instead look for "archaeological" evidence of their existence with the most likely candidate being a easily discoverable self replicating electromagnetic time capsule.

If you have any suggestions or comments, or think I am completely nuts please feel free to contact me at

Thursday, November 12, 2015

User the solar corona as a laser (maser) pump amplifier

In discussions with Ken Tapping, an astrophysicist at Canada's National Research Council he points out that:

 "There are circumstances under which masering is possible in the solar atmosphere. These do not involve energy changes inside atoms but are do do with electron/magnetic field resonances.

On occasion we see short-lived, very intense, narrow-band and highly-circularly polarized bursts from solar flares. These are widely believed to be due to “electron/cyclotron masering”.

The picture starts off with a solar flare, which produces a population of high-energy, relativistic electrons. Some of these find their way into a bipolar magnetic loop, with both ends rooted in the photosphere. The electrons execute trapped motion, bouncing between the ends of the loop, where the structure tapers and the magnetic field strength increases.

If these particles have initially a wide distribution of pitch angles, those with high pitch angles (with a larger velocity component along the magnetic field lines) will tend to penetrate further down the throat of the loop, where the density of ambient plasma is higher.  There they have a much higher probability of hitting something. They get thermalized and scattered, so that after a few bounces the pitch angle distribution has a deficit of high pitch angle electrons; there are conical holes (loss cones) in the distribution. If the electron distribution is a high-energy beam, the pitch angle distribution of the electrons in the loop will not be initially isotropic. It can have a deficit of low-pitch angle electrons. After a few reflections and a loss cone has developed, the electron pitch angle distribution can become interesting. If the initial pitch angles are high enough, all the electrons will get deep enough in the solar atmosphere for them to be thermalized by collisions. This electron bombardment of that dense plasma makes X-rays we can detect as X-ray bursts. However, if part of the pitch angle distribution lies outside the loss cone we may end up with a narrow distribution of electron pitch angles right up against the loss-cone boundary.

The electrons are spiralling around the field lines at the cyclotron (or gyro frequency). A radio wave emitted at the cyclotron frequency can be amplified as it propagates. I tend to retreat into mathematics because some of this is hard to picture, especially in the relativistic case.  If you look at the equation for the absorption coefficient for radio waves going through a plasma, and plug in the sorts of conditions mentioned here, the absorption coefficient can be negative. That is, the waves are amplified as they pass through the plasma rather than attenuated. This is masering. However, this does not work for the fundamental frequency. Attenuation at the gyrofrequency is huge, due to other resonances, but not for the third or so harmonic. This still gets amplified and because it has a frequency well above the plasma or other frequencies at which the plasma has high attenuation, it radiates off into space and to Earth, where we can detect them.

If one wanted to produce these emissions on demand, one could do this by providing the high-energy electrons. A modulated stream of electrons could be used, since the emission damps very quickly due to energy loss by those electrons. However, this means we are modulating the power supply, which we have to provide. Alternatively, launching sausage or torsional wave modes in the flux tubes making up the loop would modulate the pitch angle, thus modulating the loss-cones. However, the modulation rate would then have to be low, because to the time these waves require to move to and fro in the loop. Sausage waves would be best because they damp rapidly.

It is true that masering provides an efficient amplification process, but in the solar case, the powering and modulation process would be hard to do efficiently. Since the mirroring depends essentially on the tapering of the magnetic loop, the cyclotron frequency varies along the tube, so the resonance conditions for waves at a given frequency will be met in only a small part of it.

There is another process that might be more interesting. It is less efficient but easier to drive from a low-energy source.

Once again we have a loop filled with high-energy electrons produced by a flare. In this case rather than producing synchrotron emission, they generate plasma oscillations. Imagine the electron being a surfer, but in this case he enters the scenario with high energy, which he give to the wave and not vice versa. Plasma waves fill the tube.

Plasma waves are not radio waves. You need some sort of mode conversion process to transform them. Much of the solar radio emission we observe is due to scattering of these waves off thermal ions, which is very low efficiency. However, if we launch whistlers (electron cyclotron waves ) along the field lines, they pass through a zone where they resonate with the plasma waves, converting them to radio waves with high efficiency.  More over, they get past the problem that radio waves with a frequency equal to the plasma frequency cannot propagate. The whistlers act like a mixer, producing radio emissions at the plasma frequency minus the whistler frequency and at the plasma frequency plus the whistler frequency.  The former cannot propagate and that sideband is suppressed, feeding its energy back into the conversion process and the upper sideband. Because this is at a frequency above the plasma frequency, it propagates off into space.

The really strong metre-wavelength bursts observed in solar noise storms might be produced by this process. They are intense, short-lived, narrow band, polarized, and that fits the bill.

An active region could be pumping electrons into such a magnetic loop for days.

Getting close enough to drive the whistler production could be a challenge. A pulsed particle accelerator could do it, or nuclear devices exploded in the right place."