James Benford (president of Microwave Sciences, Lafayette CA) has just published a note in the Journal of the British Interplanetary Society that has relevance to our ongoing discussion of the Wow! Signal. My recent article was in the context of new work at Arecibo, where Abel Mendez and the Arecibo Wow! research effort have refined several parameters of the signal, detected in 1977 at Ohio State’s Big Ear Observatory. Let me slip in a quick look at Benford’s note before we move on from the Wow! Signal.

Benford has suggested both here and in other venues that the Wow! event can be explained as the result of an interstellar power beam intercepting our planet by sheer chance. Imagine if you will the kind of interstellar probe we’ve often discussed in these pages, one driven by a power beam to relativistic velocities. Just as our own high-powered radars scan the sky to detect nearby asteroids, a beam like this might sweep across a given planet and never recur in its sky.

But it’s quite interesting that in terms of the signal’s duration, bandwidth, frequency and power density, an interstellar power beam would be visible from another star system if this were to occur. All the observed features of such a beam are found in the Wow! Signal, which does not prove its nature, but suggests an explanation that corresponds with what data we have.

An interesting sidenote to this is, as Benford has discussed in these pages before, that if the Wow! Signal were an attempt to communicate, it should at some point repeat. Whereas a power beam from a source doing some kind of dedicated work in its system would never recur. We have had a number of attempts to find the Wow! Signal through the years but none have been successful.

Image: The Ohio State University Radio Observatory in Delaware, Ohio, known as the Big Ear. Credit: By Иван Роква – Own work, CC BY-SA 4.0, via Wikimedia Commons.

The note in JBIS comes out of one of the Breakthrough Discuss meetings, where Michael Garrett (Jodrell Bank) asked Benford why, if a power beam explanation were the answer to the Wow!, a technical civilization would limit their beam to a narrow band of less than 10 kHz. It turns out there is an advantage in this, and that as Benford explains, narrow bandwidth is a requirement for high power-beaming systems in the first place.

Here I need to quote the text:

High power systems involving multiple sources are usually built using amplifiers, not oscillators, for several technical reasons. For example, the Breakthrough Starshot system concept has multiple laser amplifiers driven by a master oscillator, a so-called master oscillator-power amplifier (MOPA) configuration. Amplifiers are themselves characterized by the product of amplifier gain (power out divided by power in) and bandwidth, which is fixed for a given type of device, their ‘gain-bandwidth product.’ This product is due to phase and frequency desynchronization between the beam and electromagnetic field outside the frequency bandwidth.

Now we come to the crux. Power beaming to power up, say, an interstellar sail demands high power delivered to the target. To produce high power, each of the amplifiers involved must have small bandwidth, with the number of amplifiers used being determined by the power required. Benford puts it this way: “…you get narrow bandwidth by using very high-gain amplifiers to essentially ‘eat up’ the gain-bandwidth product.’

Thus we have a bandwidth limit for amplifiers, one that would apply both to beacons and power beams, which by their nature would be built to project high power levels. Small bandwidth is the physics-dictated result. None of this proves the nature of the Wow! Signal, but it offers an explanation that resonates with the fact that the four Wow! parameters are consistent with power beaming.