Trading with the past and the future

If you are on turn 9 and your neighbour is on turn 5, their universe lies in your past. Portals turn that into a market.

• Backwards: Players who are ahead send goods and blueprints to those behind – expensive, because they haven't been researched there yet.
• Forwards: Players who are behind send raw materials ahead. They arrive as a “delivery from the past”.
• Knowledge as a commodity: Whoever is ahead already knows what's coming, like the stock market crash, and can sell prophecies – real or fake.

The key rule against paradoxes: a delivery to the past never changes the turns its sender has already played. Timelines stay sealed until the sync point.