Could aliens already know Earth exists and ignore us?

Yes—possibly. They could know Earth exists and still ignore us for a few plausible reasons:

• Zoo hypothesis: advanced aliens may be deliberately avoiding contact, treating Earth like a protected reserve.
• Indifference: we may simply not be important enough to merit the effort.
• Dark Forest idea: they may stay quiet because contact could be risky.
• Timing and distance: they might be seeing Earth’s past, not our current civilization, and detecting life is easier than detecting technology.

So the short answer is: yes, that’s a real possibility discussed in science and philosophy, but it remains speculative.