Earth's "radio bubble" is well over 100 light years across now. If there are aliens out there, they are probably already on their way to ask us in person why Ross, the largest Friend, doesn't simply eat the others.
Radio signals do weaken and dissipate over time and space. Broadcast signals could fade into the cosmic microwave background in a few light years depending on their strength. The sci-fi trope of aliens picking up Earth tv and radio just isn't plausible.
No, we don't. If you're talking about SETI, that's looking at radio signals. If you're talking about killer asteroid early-warning detection, we generally don't have the capacity to reliably detect voyager-sized asteroids even in our own solar system, let alone in interstellar space.
Imagine how far technology has come in 100 years. Then imagine if the alien had just a 1 million year head start to technology. 1 million years is less than 1/1000 of the age of the universe earlier.
We have literally no idea what technology the alien could have.
Maybe there are aliens out there so advanced that they could be reading our screens right now in realtime from across the galaxy using some weird post-quantum silly sauce we can't even comprehend. But it doesn't seem likely given what we do know and observe, at least not to me (based mostly on the Fermi Paradox and thermodynamics) that there is someone 100 light years away teasing I Love Lucy from the CMB. It seems less likely that they would be able to pinpoint our location based on that, and try to annihilate us.
The aliens have the same physics we do. Science isn't magic. Without quite literally having to replace everything we have known or discovered in the past 250 years from entropy to electromagnetic theory to gravity to motion with brand new theories that somehow equally explain all known phenomenon while also allowing lots of outright magic, no, the aliens are not able to collect radio waves from below the noise floor.
> The aliens have the same physics we do. Science isn't magic.
Show a spacecraft to someone from the middle ages and they would think it's magic.
There is physics that has not been discovered. Lots of things are still unexplained.
> no, the aliens are not able to collect radio waves from below the noise floor
Before we had quadrature modulation and quadrature phase shift keying, we thought we had hit the noise floor for wireless bandwidth. After we thought we really hit the ceiling, we had beamforming. There's stuff that hasn't been thought of. We don't know the unknown unknowns.
After the transition to digital TV our broadcasted signals mostly look like noise, though. Maybe an outside observer would assume that our civilization ended sometime in 2010.
Analogue TV would not be much better. How would the aliens know they're supposed to shoot an electron raygun left-to-right 486 times across a screen, then ignore the next 39 lines, then repeat this 29.97 times a second? And that's before you get into interlacing, horizontal blanking intervals, line 21, luma and chroma (encoded by reference to human eyesight), or different standards altogether like PAL or SECAM, etc.
Analogue TV has always felt so much more clever than digital TV to me, at least from a purely technical standpoint. I guess that's because we're mostly digital natives now, so video codecs seem ordinary and programmable electron rayguns do not.
You can still see from far away that our planet's atmosphere has a very unusual chemical composition that's far out of equilibrium.
We are already using spectroscopy to gain insights into the chemical composition of exo-planets, and we have barely begun doing this kind of research. In even just a few decades we'll be massively better at this.
