In the summer of 1950, the Italian-American physicist Enrico Fermi went to lunch with some fellow physicists and asked the central question of the Fermi Paradox – “Where is everybody?”. He was referring of course to the lack of concrete evidence of the existence of alien life. Given the size of the then-known universe and the multi-billion years available there should be evidence of life.
A decade later with the rise of radioastronomy and the term of SETI (search for extraterrestrial intelligence) Dr Frank Drake developed a formula to estimate the number of intelligent species withing the reach of a radio telescope like Green Bank or Arecibo.
The Drake equation is: 
N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone); and
R∗ = the average rate of star formation in our Galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space.
When I first encountered the issue in the mid-60’s the space program was well underway, progress seemed inevitable and flying cars were just around the corner. I considered that our ‘L’ value would continue forever or at least for the next millennia or so.
That was then, and now I’m not so sure.
Take electric cars for one small example. Electric cars: a better name would be battery cars; contain batteries which store the electric energy needed to power them. In the U.S. currently, most energy comes from coal, natural gas, hydroelectric or nuclear power. The first two (and by far the largest) produce CO2 (otherwise known as plant food) that allegedly produces global warming and is double-plus-ungood. Hydroelectric dams are under attack and are being torn down because they impede spawning of salmon and other sacred species of fish. Finally nuclear power is beyond the pale, opposed by all right-thinking environmentalists. The above is a series of confused, unproven or certifiable dumb conclusions that are all embraced by “environmentalists”.
The presumably “adult” governors of several states have mandated the end of sale of internal combustion engines (ICE) by 2030 or so. The “renewable” resources, hydro, wind and solar, over five years (2014-2019), zoomed from 13.4% to 18.2% of U.S. total power. So, in effect, 80% of electric vehicles are actually powered by coal/natural gas, hydro or nuclear power. The chances of increasing the number either hydroelectric dams or nuclear power plants being approximately zero at the current time, coupled with the outright antagonism of the current administration towards fossil fuels, it looks like the future will tend towards poorer and more restrictive.
We have met the Great Filter and it is us. I now tend to think that Elon Musk is right – we need to become a multi-planet species, or we are doomed.