My biggest criticism with both the Drake and Seager equations is that they do not account for the TIME FRAME for optimal intelligent life. What do I mean? Our planet is more than 4.5 Billion years old. Our star (the Sun) is more than 4.6 Billion years old. Whereas life has existed on Earth for approximately 3.5-4 Billion years (meaning that life began at a very early stage in the development of the planet), intelligent life is relatively new. <br><br>Think of it this way: <br>- Homo sapiens have existed for roughly 300,000 years (meaning that homo sapiens had not developed for nearly the entire age of this planet). <br>- Humans (from the earliest form) have only existed for 200,000 years.<br>- Civilization (in a modern context) has only existed for 6,000 years.<br>- Written language has only existed for roughly 5,000 years.<br>- The first telescope patent was filed just over 400 years ago. <br>- Industrialization only began roughly 200 years ago.<br>- Radio waves were first identified less than 150 years ago. <br>- The first radio telescope was built 83 years ago.<br>- The first exoplanet was discovered (or determined to exist) less than 30 years ago. <br><br>So, the "window" of intelligent life is vastly smaller than the window for life itself. If all of the variables for these equations (Drake's and Seager's) are met, the window of contact is much, much smaller. Even if Proxima Centauri b, Gliese 667 Cc or any other exoplanet was determined to be habitable, this doesn't mean that life would necessarily exist. After all, Venus and Mars are in our habitable zone and do not currently have any known life (let alone intelligent life). Yet, even if those exoplanets actually had life, the window of time for INTELLIGENT life is so infinitesimally small (using our planet's history as a primer) that the odds of intelligent life existing at the time that we're looking is, well, just as infinitesimally small. <br><br>For example: Let's say that Proxima Centauri b is ideal for life and meets all of the criteria from both the Seager and Drake equations. The chances that they are advanced enough is , well, improbable. Moreover, the idea that an advanced intelligence (living or artificial) on another planet has decided to search for life in our direction, they would have had to do it at the right time. If they tried to contact us just 200 years ago, we were incapable to hear or know it. <br><br>This is particularly more problematic for planets outside of our immediate galactic "neighborhood." The vast distance between our planet and planets far, far away also represents distance of time. Those intelligent beings would have to be looking in our direction at just the right time. The "window of opportunity" to contact us (thus far) is less than 83 years. Realistically, the window is roughly 30 years. <br><br>How would this be accounted for in a probability equation? <br><br>My perspective: It is likely that the search for intelligent would have to be limited to a very particular distance between our planet and an exoplanet given the very small window. I would start at 50 light years of distance (currently potential exoplanets around approximately 133 "close" stars). We could then shift further in space. I believe that there are more than 250,000 stars within 250 light years of our solar system.,(reply>), @Zeb...and, yet, it isn't factored into any probability equation. That's precisely my point.,(reply>), Chris M It is rudimentary. Everyone is aware of the fact intelligent life may exist in a small window or indeed not have evolved yet.,(reply>), ​@Zeb - Uh...okay. I'm not a novice or a purveyor of "rudimentary high school level analysis." So, your subtle attempt at condescension is duly noted with a pair of rolling eyes. <br><br>No one is questioning the intellect of Dr. Drake or Dr. Seagar. No one is even questioning the validity of the probability equations that they've devised. <br><br>Obviously, physicists have thought about these things. However, that still doesn't explain why these intelligent life opportunity windows aren't included in the probability equations. <br><br>I'm an engineer. During college and grad school, I interned and co-oped for NASA at Langley Research Center. I noticed the tendency (due to budget constraints) to consider projects that provided the greater likelihood for success. <br><br><br>While it would be great to send rovers all over the planet Mars in the search for either past/present life or the clues (or, as Lex and Dr. Seager said, "hints") of life. However, budget constraints necessitate the need to prioritize their projects via risk and chances of success. Landing sites are selected accordingly. <br><br>Projects that might be worthwhile yet riskier and/or provide less payoff (such as the Aerial Regional-scale Environmental Survey [ARES] or "Mars Plane") were cancelled. This is because they wouldn't contribute efficiently to the primary mission of searching for past or present life on Mars. <br><br>In this sense, the opportunity window would greatly limit the probability of life that could be contacted (or could contact us). Our window has been very small. However, it is worth studying to find optimal probability for intelligent life.,(reply>), Chris M This is a very rudimentary high school level analysis dude, these people are exceptionally well educated and intelligent. Have a read of Saeger’s papers, she’s more than aware of all of this (as is a 1st year undergrad taking an exoplanets module...)