I've always thought it made more sense that microbial life with took billions of years to develop, and originated someplace other than earth. The reason we don't see hyper-advanced civilizations is because intelligent life is only just starting to pop up alongside us, right now, and perhaps we're one of the earlier manifestations.
Personally I think life originated on earth. We shouldn't look at contemporary prokaryotes to determine how complex prokaryotes were at the start of life. They had billions of years to develop as well and if the more complex ones are fitter than the less complex ones, they will win. E.g. you think rotting plants is a normal thing but there was a time when plants wouldn't and just form giant heaps, forming the coal reservoirs of today.
Anyways, let's assume life originated at some other planet and it has started life at half of the galaxy at the time it reached earth (so we weren't lucky to be "close" to the origin).
Earth is 4500 million years old, and life is assumed to have existed here since 4400 million years. So intelligent life took 4400 million years to "develop" here on earth. Light speed allows you to colonize the milky way comfortably within a million years. What if it takes 100 million years less on some other planet? Or it took just 10 million years less?
Either earth is very close to the real origin (or has been at the start of life), or the filter is in the past, or some other explanation.
This theory is actually proposed by Nick Lane et al - it says that microbial life is probably ubiqutuous and that complex life is not and was a happy accident on Earth, which means its very improbable on other planets. The prereqs for it happened only once on Earth, when one microbe swallowed another and the smaller one became mitochondria enabling complex cell structure and shape. Given that microbial life exist in extreme environments on Earth and that its prereq is just a hot molecular soup, its probable it exists everywhere. On the other hand, the 'happy incident' didn't repeat on Earth to create another complex cell form - all higher life uses the same cell structure.
That's what the great filter theory means when they talk about it being behind us -- we don't see life in other places because developing to where we are now is almost impossible.
I don't buy it though -- we're in an average planet on an average star, nothing about our environment seems to be particularly rare.
I think the statement that we are on an average planet deserves more scrutiny. We have yet to observe another planet like ours.
There are a number of Earth's attributes that we don't understand and have poor extra-solar data on. Particularly, the following:
Technically active plates after 4.5 Byrs.
Effective magnetic core after 4.5 Byrs.
Large amounts of surface water, presumably from our late heavy bombardment.
Small enough to leave with a chemical rocket while meeting the above.
I tend to agree with both your points, but was addressing the specific claim that Earth-like conditions are average, or at least not particularly rare.
We simply don’t have data to support that claim, and the parameters required to make earth habitable for life (as we know it) are vastly more numerous than most people acknowledge.
Lets start with Oscam Razor then: its wast universe. Even on Earth, there are untouched places. All other theories compared to this one, which is easy to understand and also already known to be in effect on this planet, are as close to the truth as theory that great filter are evil pink elephants in the center of the galaxy.
> I've always thought it made more sense that microbial life with took billions of years to develop, and originated someplace other than earth. The reason we don't see hyper-advanced civilizations is because intelligent life is only just starting to pop up alongside us, right now, and perhaps we're one of the earlier manifestations.
This explanation does not work, because of the timescales.
Five thousand years ago, we built the Pyramids. Fifty years ago, we landed on the Moon.
In contrast, it took four billion years to go from single-celled life, to the pyramids.
The odds of us being first by happenstance are astonishingly small. It's much more likely that either we are unique, or that civilizations don't leave much of a trace outside of their solar systems, regardless of whether or not they die out in the blink of a cosmic eye.
It's not my domain, but there are apparently some markers of genetic complexity that give some weight to this theory: https://arxiv.org/ftp/arxiv/papers/1304/1304.3381.pdf