In the world, we know that ( principles are clear ), but the following technologies have not yet been achieved:

1. Controlled nuclear fusion. Fusion can occur and achieve short-term net energy gain, but stable and economical continuous operation is not possible.
2. Room-temperature superconductivity. Superconductivity has been fully verified, but currently can only be achieved at extremely low temperatures or high pressures; stable superconductivity at room temperature and normal pressure remains unachievable.
3. Efficient long-term energy storage. Battery energy storage technologies (such as lithium batteries) are mature, but cannot simultaneously meet low cost, ultra-long cycle life (such as seasonal storage), and safety.
4. Artificial photosynthesis. The chemical processes of photosynthesis are understood, but it cannot efficiently, stably convert solar energy into fuel like natural plants and scale up for practical use.
5. "Complete read-write" capability of brain-machine interfaces. Projects like Neuralink can perform simple signal reading and stimulation, but cannot precisely and comprehensively read or write complex thoughts and consciousness.
6. Artificial General Intelligence (AGI). Current AI performs well on specific tasks, but systems with human-level general understanding and autonomous reasoning are still not achievable.
7. Commercial space elevator. Theoretically feasible based on material strength (such as carbon nanotubes), but practically impossible to manufacture materials with sufficient strength for large-scale use.
8. Long-term stable controlled antimatter storage. Antimatter can be produced and temporarily stored (as in experiments at CERN), but large-scale, long-term, safe storage and application are not possible.
9. High-precision long-term climate prediction (over decades). Climate models are well understood, but due to the chaotic nature of the system, long-term precise prediction remains unachievable.
10. Fully autonomous, safe Level 5 autonomous driving. Autonomous driving technology is widely applied, but a system that requires no human intervention in all environments still cannot be reliably realized.