[sliken]

It's not that ET doesn't have a computer, it's that without omniscience they won't know which of those 200,000 pulsars were pointing at one of 100 billion stars way in the past.

Unless they already orbit all 100 billion stars, but even then it's 100,000 years to collect the data.

Basically with 200k pulsars sprinkled among 100B stars sprinkled over 200,000 light years it's very easy to get lost. A list of frequencies gets less useful over time. You saw a pretty big difference in the data between 1969 and 2002. Imagine the differences in 100k years.

Even a single unknown gravitational interaction could throw the probe way off in speed/direction.

[fapjacks]

Well, I should be clear that the difference in data between 1969 and 2002 was due to measurement error in the original surveys, not due to some kind of actual movement. I have already conceded that over hundreds of millions or billions of years, the map becomes a jumble, but for the next few million years (or from a few million years ago), the map is definitely not "hopelessly incorrect" as the guy states. And actually the whole point of choosing 14 pulsars was so that you had plenty of elbow room for errors arising from e.g. one of the pulsars being flung far and wide by a rogue black hole.

With a computer and observations of "a fair percentage" of the 14 original pulsars, it would still be "fairly easy" to determine which pulsars we're talking about, because from the period alone, you can reduce the total number of candidates to a handful. And so from 200,000 pulsars, from the original 14 period measurements (or 11 in the case of my tattoo), you should be able to reduce the total pulsar pool down to perhaps a hundred or so candidates, just from looking at reasonable possible pulsar periods. Then you can permute through all combinations using a computer to determine which of the pulsars all shared the particular recorded period values at the same time. These values are so precise, and so varied in nature, that you could easily take all 200,000 pulsars in the galaxy, and sort out which 14 you were talking about, if you also could guess that the 14 values were all measured at the same time, that the precise moment chosen to record the period value had to coincide with the precise moment chosen for the other 13 pulsars. Only this select group of 14 pulsars will have had these precise period values at one time, even if many other pulsars in the galaxy have had a specific period value at some point in their history, and this is the genius of Carl Sagan's idea, since you then also can encode a specific time in the data (which happened to have been Voyager's launch date on the golden record, and my birthdate in my tattoo). I still concede that along enormous time scales, it would not be possible to do this, but Carl Sagan's original assertion is definitely not unreasonable across the span of a few million years or so, and a reasonably large enough survey of the galaxy.