Could it be possible that advanced human civilizations have waxed and waned many times since the first true human species existed on the planet?
There is no archaeological evidence that advanced human civilizations have waxed and waned many times during prehistory. However, according to the Silurian Hypothesis, a thought experiment published by astrophysicists Adam Frank and Gavin Schmidt in 2018, if an advanced civilization had existed millions of years ago, it is unlikely that direct archaeological evidence of such a civilization would still exist today.

While the Silurian Hypothesis is unproven, this suggests that it might be possible that advanced civilizations could have existed in the distant past. Still, without evidence, any discussion of prehistoric advanced civilizations is purely conjecture.
Could you tell me more about the Silurian Hypothesis? Could you please go into detail what would have to have happened for this hypothesis to make sense? How far back in time must it have happened? How big and advanced could the civilization have been? If they were more advanced than us, surely there would be space debris.
The Silurian Hypothesis posits that there could have been an advanced civilization that existed on Earth millions or billions of years ago, before modern humans or any advanced form of life that we know of. Their technological capabilities and impact on the environment could have been so great that their traces would still be visible today. However, due to the lack of evidence, the existence of such a civilization is currently purely hypothetical.

For the Silurian Hypothesis to make sense, the following scenarios would have to occur:

1. The hypothetical advanced civilization existed before the evolution of modern humans, most likely during the era of the dinosaurs (~165 million years ago - 66 million years ago).
2. Their technological capabilities would have been far beyond what we can imagine today. For instance, they could have had a highly complex society that allowed for the development of advanced technologies, including space travel.
3. Despite their advanced technology, they would have been unable to leave any trace of their existence for future generations. There could have been several reasons for this, including an extinction-level event, a cataclysmic event, or a conscious decision on their part to leave no trace.

It is important to note, however, that this hypothesis is purely speculative and there is currently no solid evidence to support its existence. Nonetheless, it is an intriguing thought experiment that highlights the possibility of the existence of an advanced civilization that existed long before our current understanding of human history.