Wednesday, October 29, 2014

The Long Delay Echoes

The subject here is a scientific mystery that was well documented by European scientists in the 1920s and 1930s, well before any man made objects were launched into outer space, and then was largely forgotten. The phenomenon has since apparently disappeared, although anecdotal reports still pop up from time to time, and a low level of interest persists. We are discussing it here, because although no one knows for sure what caused the Long Delay Echoes, one plausible explanation is Bracewell Probes. The Long Delay Echoes (LDEs) just possibly might be a clue to how to find such a probe.

Some Basic Background You may Wish to Skip

 I'm sure you know that radio waves generally travel at the speed of light, and can be bounced off of various surfaces and also off the Earth's ionosphere if the radio wavelength is long enough. The speed of radio waves can be a bit slower if they are traveling through a medium such as a plasma or water, but generally the speed is not much less than the 300,000 kilometers per second we are used to. That means, if we send a radio signal out, and see it come back to us, then to calculate the distance to the reflector, we divide the time delay in seconds by 2 (since it went out and back), and then multiply by 300,000 kilometers per second to get the distance. Then, if we send out a radio signal and it comes back 2 seconds later, it must have traveled 300,000 km each way, or most of the way to the Moon. Amateur radio operators often enjoy bouncing their signals off the moon, which generally exhibits a very weak echo delayed about 2 and one half seconds. Strong echoes, or echoes delayed longer than 2.5 seconds, are not moon echoes.

Since the 1960s, there are many radio repeaters in Geosynchronous orbit, but the round trip delay is much shorter than the moon -  less than half a second, and you generally won't see a satellite echo at all unless your signal parameters are just right - and probably illegal.

The Long Delay Echoes

In the 1920s, with radio technology beginning to really develop rapidly, there was a great deal of
Van der Pol
interest in how radio waves propagated. Scientists and radio enthusiasts alike were making measurements to try to understand how radio waves were affected by the Earth, the Sun and the upper the atmosphere. At this point, everyone knew that if you sent out a strong radio signal, you would get a faint echo 1/7 th of a second later as it bounced around the planet.

The LDEs were first noted in 1927 by an early amateur radio operator named Jorgen Hals in Norway. He brought this to the attention of professional scientists. In October of 1928, Hals, Stoermer and Van der Pol observed LDEs on the 9.5 MHz frequency ranging from 3 to 30 seconds.  Now, as noted above, 3 seconds is a bit longer than a moon echo could be, and 30 seconds is far longer. Further experiments were carried out, and Hals observed an echo as long as 260 seconds. These signals weren't bouncing off astronomical objects, such as the moon or Mars, and they didn't have the shift in frequency due the Doppler effect you would expect if the were reflections from the Solar Wind (moving at roughly 1/1000 the speed of light).

After the war, some interest in the LDEs returned, and more observations were made. Budden and Yates conducted a long series of experiments at shorter wavelengths, but observed no LDEs.

In 1960, Ronald Bracewell published his famous paper about alien probes in our solar system, speculating that the Long Delay Echoes may have been transmitted by such a probe as a way of announcing its presence.

In the late 1960s and 1970s scientific interest in the echoes peaked, as documented by Volker Grassman in his excellent survey paper. A number of amateurs reported LDEs in the 1960s, with delays up to 10 seconds. Stanford University got involved in the late 1960s. They recorded several LDEs, and by 1971 had seen one as long 31 seconds.

Two things are certain about LDEs: they are not reflections from astronomical bodies, and they are not echoes from man made satellites. Beyond that, the question remains open. We can't just jump to the conclusion we want, that Bracewell's speculation was correct.

Are there natural explanations for the LDEs? Some work has been done on that, and it turns out that under ideal and fairly delicate conditions, some of the echoes observed might be a result of complex plasma physics in the Earth's ionosphere. The ionosphere is actually multiple layers of the Earth's upper atmosphere where some free electrons are found. A phenomenon known as a plasma wave does exist, and it propagates much more slowly than the speed of light. We know that plasma waves are real from both satellite and radar observations, but it takes special conditions for the wave to be stimulated by radio transmissions and then to grow strong enough to result in an echo.

There may be other natural explanations for LDEs, but just not enough work has been done to nail them down. A combination of theoretical modeling and experiments over many years is usually what it takes to nail these things, and not surprisingly, it hasn't been a scientific priority for space physicists. However, as our understanding of the Earth's plasma environment improves, and modeling tools get better, it might get easy enough to be worth a try.

If we could do the above (and it may take some amateur radio work to observe the echoes), what if
Duncan Lunan
we find that the echoes are still there, and natural explanations still fail? Does that mean we're now hunting for Bracewell Probes? People like Duncan Lunan have attempted to understand the LDEs in terms of a message from a Bracewell Probe. Someone has to be brave and try this, but frankly I think it's premature. It's not completely clear to me that we can scientifically study Bracewell Probes, but I think we should try as best we can.

Should we try and look for evidence of these radio-echoing probes at Earth-Moon Lagrange Points L4 and L5? Can we pinpoint a source for the LDEs? Good questions all. I say lets go and try to find out. What do you think?

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