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 Case for the Wow! Signal

I recommend Robert Gray's book The Elusive Wow! if you want detailed background on the Wow! event of August 15th 1977. The book also describes the author's efforts to replicate the signal. To date, no one has reported a reliable second detection of the Wow! Signal, although efforts to find it have not been persistent.

The Wow! Signal was a single 72 second event detected by the Big Ear radio telescope operated by Ohio State University, which was sweeping past the constellation Sagittarius at the time. This telescope was designed to conduct a survey of the radio sky, not to study individual sources in detail. The survey was successful and a number of new radio sources were discovered. After that, some of the science team thought that a SETI search would be a good use of the telescope.

I think the case against the Wow! Signal as an ET beacon is well known.

We are all well aware of the fallacy of the argument from ignorance. Just because the Wow! Signal has not been proven to be from a known source doesn't mean it's from ET. It's possible that the Wow! Signal was some sort of strange problem with the Big Ear's receiver that only occurred once, or that it was an extraordinarily elaborate and strenuous hoax. For these reasons, you would need to see independent confirmation, and we haven't; Robert Gray's single-handed and largely self-funded efforts to do so have been far from comprehensive.

Since the Wow! Signal was discovered after the fact, when Jerry Ehman went through a stack of printouts, it was too late to get another radio telescope to break off what it was doing, swing over and confirm the signal.  The signal was never confirmed, and no similar signal has been found in that region of space.

The are multiple reasons we think that the Wow! Signal may have been an ET beacon.

Searching for Bracewell Probes - part 2

In the first part, we talked about some of the variables that I think could control the observables of a Bracewell Probe.  This is essentially a first, crude move toward mapping our ignorance of these hypothetical machines.  We can't know what Bracewell probes are yet, or even if they exist at all, but perhaps we can constrain or at least make some reasonable assumptions about what they could be.

Is SETI Silly?

No, I don't think it's silly.  It remains entirely possible that simply by carefully studying the photons flying at Planet Earth from all directions, we will find clear evidence of an extraterrestrial civilization.  However, as I have taken pains to point out, we really don't know what we're talking about when we use that phrase, so we're going to have quite a long (and I think, healthy) debate about that the evidence should be, and how best to find it.

The Search for Extraterrestrial Intelligence (SETI) is a loose affiliation of scientific institutions funded by private donations, trying to find a way to search for other technological species in our galaxy.  It's just one galaxy - doesn't sound too ambitious - but where to start?