If we wanted to represent humanity most honestly to aliens, we would just give them a constantly updated full documentation of our cultures and knowledge. But that is not possible.
So in METI we may consider sending “a copy of the internet” as a massive snapshot of what we currently are, or as the Voyager recording did, send a sample of what we are. In both cases it is a snapshot at a particular time: had we sent the message at some other time, the contents would have been different. The selection used is also a powerful shaper, with what is chosen as representative telling a particular story.
That we send a snapshot is not just a necessity, it may be a virtue. The full representation of what humanity is, is not so much a message as a gift with potentially tricky moral implications: imagine if we were given the record of an alien species, clearly sent with the intention that we ought to handle it according to some – to us unknowable – preferences. If we want to do some simple communication, essentially sending a postcard-like “here we are! This is what we think we are!” is the best we can do. A thick and complex message would obscure the actual meaning:
The spacecraft will be encountered and the record played only if there are advanced space-faring civilizations in interstellar space. But the launching of this ‘bottle’ into the cosmic ‘ocean’ says something very hopeful about life on this planet.
– Carl Sagan
It is a time capsule we send because we hope to survive and matter. If it becomes an epitaph of our species it is a decent epitaph. Anybody receiving it is a bonus.
How should we relate to this already made and launched message?
Clearly we want the message to persist, maybe be detected, and ideally understood. We do not want the message to be distorted by random chance (if it can be avoided) or by independent actors.
This is why I am not too keen on sending an addendum. One can change the meaning of a message with a small addition: “Haha, just kidding!” or “We were such tools in the 1970s!”
Note that we have a present desire for a message (possibly the original) to reach the stars, but the launchers in 1977 clearly wanted their message to reach the stars: their preferences were clearly linked to what they selected. I think we have a moral duty to respect past preferences for information. I have expressed it elsewhere as a temporal golden rule: “treat the past as you want the future to treat you”. We would not want our message or amendments changed, so we better be careful about past messages.
However, adding a careful footnote is not necessarily wrong. But it needs to be in the spirit of the past message, adding to it.
So what kind of update would be useful?
We might want to add something that we have learned since the launch that aliens ought to know. For example, an important discovery. But this needs to be something that advanced aliens are unlikely to already know, which is tricky: they likely know about dark matter, that geopolitical orders can suddenly shift, or a proof of the Poincaré conjecture.
They have to be contingent, unique to humanity, and ideally universally significant. Few things are. Maybe that leaves us with adding the notes for some new catchy melody (“Gangnam style” or “Macarena”?) or a really neat mathematical insight (PCP theorem? Oops, it looks like Andrew Wiles’ Fermat proof is too large for the probe).
In the end, maybe just a “Still here, 38 years later” may be the best addition. Contingent, human, gives some data on the survival of intelligence in the universe.