Our search for technosignatures – clear signs of advanced civilizations beyond Earth – takes many forms.Many are driven by the famous Drake equation, which attempts to estimate how many technological civilizations there are in the Milky Way.However, there's a big fat question mark at the end of that equation in the form of a variable intended to account for the "longevity" of a civilization.And to be clear, that doesn't mean how long the civilization itself survives. It simply means how long it actively creates a signature that is detectable by our current technology.A new paper, available in pre-print on arXiv from Oxford astrophysicist Brian C. Lacki, argues that, since the chances of us overlapping in time with any such civilization are minuscule, we're much more likely to find the ruins of a "dead" civilization.Surprisingly, the best place to do so might be in our own solar system.A fundamental part of this argument is driven by Earth's own history. Up until now, SETI has focused on receiving "passive" signals from beyond the solar system, typically in the form of radio waves.However, even on Earth, our own "window" of sending radio signals into the vastness of space only lasted for around 100 years. We are actively eliminating most wide-broadcast radio signals in an effort to improve our communications infrastructure.