Given the vastness of space, it has to be highly improbable that we’re alone. Still, if there are other intelligent civilizations out there, we have to detect them or their transmissions some day, right? That question been one of the biggest conundrums of astrophysics for years, and unfortunately we might never know the answer. Still, given the age of the known universe, the Earth and subsequently humankind are pretty young, cosmologically speaking. If there are (or were) any technologically advanced alien civilizations out there, we should be able to detect the various signals emitted by their technology – even if those aliens have been dead for ages. In fact, a new study claims that our galaxy could be filled with “ghost” signals from long-gone alien civilizations. Long-gone is better than never-was though, right?

The claim about ghost signals comes fom a team of astronomers and mathematicians from the SETI Institute and the University of California, Santa Cruz who have recently published a new calculation of the Drake equation. The authors include Frank Drake, author of the original Drake equation which is aimed at calculating the likelihood of discovering an alien civilization in our own galaxy. In a nutshell, the equation factors in the average rate of star formation per year observed in the Milky Way, the numbers of stars which host presumably habitable planets, and several hypothetical or currently unknowable variables like the fraction of habitable planets that actually go on to develop intelligent life. Since many of the variables aren’t able to be precisely calculated due to the limits of our knowledge and technology, the Drake equation is unsolvable.

This new iteration of the equation seeks instead to calculate the probability that signals from any hypothetical alien civilizations might pass through our galaxy in a timeframe in which they can be discovered by humans. The new Drake equation factors in the speed of light, radio waves, and other electromagnetic radiation and assumes advanced civilizations only last for 100,000 years or less. With those new variables factored in, the odds are, well…

Still astonishingly low. Terrifyingly low. Think about it: humanity has only been broadcasting (and therefore scanning for) radio transmissions for less than 100 years. Given the speed of radio waves, that means our transmissions are only detectable by the nearest 0.001 percent of the Milky Way. Given the sheer size of the galaxy, not to mention the universe, SETI has its work cut out for it. While the authors note that the likelihood is pretty slim that we will detect a technologically advanced alien race before human civilization comes crashing to a halt, some “ghost” signals from long-dead civilizations likely haunt the galaxy and could possibly even be discoverable right now. How bittersweet would that be, discovering our galactic neighbors only through their cosmic obituary? Sounds like a great premise for a one-shot Star Trek: The Next Generation episode.