It’s a very interesting thought experiment. What if all knowledge of science and all religion suddenly disappeared from our memories?
Note that this is not a question about the impact on human life. Some really shallow theists may argue that without religion people will start killing each other on the streets. Most reasonable people would think we would go in the dark ages without science. We’re not interested in answering these questions.
What we’re concerned about is where human knowledge is heading, e.g., where our knowledge eventually converges.
If all scientific knowledge were to disappear suddenly, we’d eventually figure it out again. We might discover things in different orders, but we’ll eventually figure out the laws and constants of motion, for example. We’ll eventually understand basic chemistry and discover all the periodic elements. We’ll eventually find out that we are not intelligently designed, but evolved. We’ll discover the speed of light, and it’ll be very close to the value we have now. We’ll know the same relatively precise values for the weak force and the electromagnetic force, and we’ll have theories that describe reality accurately. We might have different terms for all of these scientific concepts, but the essential knowledge will be the same. Science is convergent.
If all religious knowledge were to disappear suddenly, we’d probably still develop religion, but it would be in a specifically different form. I actually want to clarify my statement because I actually suspect that a lot of the general arguments for the “new religion(s)” will be the same as religion now: we’ll probably still develop the Watchmaker argument and the First Cause argument. We MIGHT (but I’m not sure) develop the same garbage Ontological, Transcendental, and Cosmological arguments (but with different names). We’ll probably have some concept of guilt or sin, and there probably might be prophets born of virgins. Religions will probably still restrict people’s sexual lives, diets, and daily conduct. But religion as we know it today will be forever lost, replaced by newly developed religions that are specifically different.
Specifically different means that it wouldn’t be called “Christianity” or “Hinduism” or “Islam.” The prophets and miracles would probably take place in different times, with different characters, with different holy books. You might have to pray 3 times a day and not 5. You might have to face Los Angeles rather than Mecca. You might have to be sprinkled with holy pepper rather than water. It might be the Blessed Virgin Martha. There probably would be the “10 commandments” in some new religion (because of the magical number 10), but the commandments would probably not be the same. The rules for getting into the after-life probably won’t be the same (and the supposed after-life might be pretty different too).
Society would probably still be littered with dangerous superstition, but the overwhelming majority of people would still do good works, supposedly inspired by some good commandments in their holy books.
There would be extremists and moderates. There would be science-deniers and religious scientists. There might be the equivalent of witch-hunts, but there would also be powerful religious movements to fight against social injustice.
Religion is a peculiar thing, isn’t it? It’s a very interesting thought experiment indeed, but religion is not a convergent human endeavor. It’s a manifestation of our natures, projected into very deep metaphors that need, at the very least from time to time, to be subject to the forces of skeptical inquiry and secular criticism.