Even if a sufficiently advanced civ out there is using something like quantum entanglement, they mostly likely didn't just jump from smoke signals to quantum entanglement. So we might be catching signals from the say 500 years while they used radio waves.
Look at us as an example though. We've had radio for a little over 200 years and already realize its limitations.
Smoke signals will have been around for a lot longer than radio. Smoke signals will have been around for 99.9% of the timeline and then 0.1% radio before quantum. To an outside observer it would look like radio was just skipped.
If you scale human civilization into a 1 year time frame we invent radio at 3PM on December 31st.
Assuming that we are right that matter can't 'travel' FTL, it's entirely possible that signals can (despite our current inability to understand how) somehow travel FTL. Once discovered, that method might be a thousand or million times FTL.
Such a relatively instant means of communication would become the defacto standard. Antiquated EM methods and equipment would be forgotten. Noone would be listening for it, just as very few today would recognize semaphore flags, smoke signals, or telegraph codes.
Today we'd not be eligible to join that club. And if we choose to remain certain that it doesn't exist, our determined ignorance would keep us locked out. If we conclude that we aren't special, that there -must- be life elsewhere, then the only logical thing to do is to keep our minds open and keep looking for clues.
We can't ever decide that we know enough. A century ago, the Milky Way was the whole universe. A few more observations changed that forever.
Yet most of the old technologies we've invented are still used by hobbyists and collectors. Morse hasn't ceased to exist, neither have steam trains, analogue radio or horses. None have been forgotten. People are still making crystal sets and wave traps. There's a whole niche on YT of people making primitive huts, fires, bows or making it their weekend hobby through re-enactment etc.
Some of the details are lost like maintenance details, advanced fault finding etc, but the core remains.
After a century of radio and electricity it would be rather silly to only search for other signs of life on the new system of FTL communication we just discovered. It still gives no certainty that the candidate alien discovered the same defacto standard for FTL comms or that theirs will be recognisable.
Any rational search should try and encompass both and probably still emphasise the analogue as any advanced civilisation would very likely go through that phase first, just like we are. We'd be likely to catch more possibilities that way.
The claim isn't that matter can't travel FTL. It's that information cannot. Our current understanding of physics makes this rather fundamental and overturning it would involve seriously drastic changes to our understanding of reality.
Being able to send a message at a million times FTL would make it really easy to send messages back in time.
Actually that is exactly what physics says. Anything with whatever mass, as its relative velocity is accelerated, approaches a mass of infinity as its velocity draws nearer to c. Information, on the other hand, has no mass ...
In the 1890s, Lord Kelvin stated that physics was essentially complete. m'Lord was oh, so wrong.
"Faster-than-light communication is, by Einstein's theory of relativity, equivalent to time travel. According to Einstein's theory of special relativity, what we measure as the speed of light in a vacuum (or near vacuum) is actually the fundamental physical constant c. This means that all inertial observers, regardless of their relative velocity, will always measure zero-mass particles such as photons traveling at c in a vacuum."
Just so you know, entanglement can't be used to transmit data. You must still transport the particles which have become entangled. When you observe them later you are only "instantaneously obtaining information" through the process of elimination.
But isn't there a certain probability we missed those radio waves back when we didn't know radio and now the earth is receiving more sophisticated signals humans can't yet analyze?
We could have missed those signals millions of years ago, but we could also start receive a civ's first ever radio broadcast tomorrow (that would be incredibly lucky).
