A method for simpler Sci-Fi world-building. Take one element and push it beyond our current milieu. Visualise your city with all the details, smells, people, everything. Hold it there, luxuriate in it.

Now change something and see what happens. Einstein used the Thought Experiment technique to reimagine the rules of our universe. Rules that took decades to prove were explored first in his mind.

Explore:

1. The immediate rippling effects
2. The second-order effects, the return ripples that mingle with the first.
3. How can you use that in your story?
4. How can you reveal the unintended consequences in the end?

For more timeless work, use constants. Things that won’t change and keep those true in your story. E.g. people will be people; they will err, be human, and relearn the same lessons on earth or in the stars.