[CamperBob2]

The masking is just a natural result of technological development. We can pick up recognizable signals only from civilizations that have worked out electromagnetic theory but have not yet developed information theory.

50-100 years is probably par for that particular course. A very narrow timespan in the grand scheme of things.

[surge]

Even now we've adopted encryption, which appears sufficiently random. How long til all signals are just encrypted by default. Anyone picking up those signals would have a hard time proving they're not noise.

[dotnet00]

Plus our receivers have gotten more sensitive allowing us to reduce transmit power and a lot of systems use much higher frequencies, which are attenuated more strongly in atmosphere. With another 100-200 years of progress it would probably be pretty hard to pick up a radio signal (that isn't intentionally broadcast) at all from the nearest stars.

[bombcar]

Radio signals sent to space unintentionally are waste - so over time you’d expect them to be reduced or eliminated just because you want to use lower power.

[CamperBob2]

Yep, and that's another layer of noise on top of the noise that results from efficient spectrum utilization. Only n00bs transmit carriers or intelligible sidebands.

[lacker]

Even now we've adopted encryption, which appears sufficiently random.

When you pick up an encrypted signal, it's still obvious there's a signal there. Radio telescopes will pick up cell phone signals, for example; that's why there is a radio quiet zone near the Green Bank telescope. You just can't decode the message itself without the encryption keys and algorithm.

[CamperBob2]

As long as it's over the thermal floor within its own bandwidth, yes, it will be obvious that there's still a signal there.

When it comes to interplanetary reception, though, any intelligently-constructed signals will likely be below the noise floor unless deliberately broadcast for our benefit. No coherent carrier or sidebands? No spreading sequence? No chance of detection, whether encrypted or not.

[ithkuil]

Can spread spectrum be easily detected?

[CamperBob2]

Only if it's strong enough to be obvious there's a signal there to begin with. The idea behind SS is to use more bandwidth than necessary, often much more, so that a much-worse SNR can be tolerated.

Many spread-spectrum applications such as GPS use signals that are well below the thermal noise floor by the time they're received. Those signals generally can't be detected without a known sequence to correlate them against.

[lacker]

We can pick up recognizable signals only from civilizations that have worked out electromagnetic theory but have not yet developed information theory.

Really we are more likely to pick up recognizable signals from civilizations that are intentionally trying to contact us. It's possible we could pick up radio leakage, but the signal would be a lot weaker. So there are orders of magnitude more stars that could be intentionally contacting us, vs accidentally leaking a signal. (At least assuming the ratio of the strength of their intentional vs accidental radio emissions is similar to ours.)