Item from Foundation by Isaac Asimov
Energy field that blocks fast-moving projectiles but allows slow objects through — standard protection in the Empire era, its physics shaping combat doctrine across the galaxy.
The personal shield changed warfare in the Galactic Empire. Because the field blocks any object moving above a threshold velocity, projectile weapons and energy blasters became useless against shielded targets. This forced combat back to close quarters — slow thrusts with knives and swords could penetrate the field, making blade fighting relevant again in a civilization with nuclear technology. The Foundation's early military advantage over peripheral kingdoms came partly from nuclear technology but also from the fact that the kingdoms had lost shield technology along with everything else. A shielded Foundation agent was effectively invulnerable to the crude weapons available on regressed worlds. In later eras, shield technology became less decisive as the Foundation's neighbors regained technological parity. But the shield's cultural impact persisted — it had shaped martial traditions, architectural design (defensive layouts assumed shielded attackers), and even fashion (clothing designed to accommodate shield generators). Technology shapes culture long after the technology itself becomes obsolete.
When inactive, the generator is a small device worn at the belt or wrist. When activated, a faint shimmering field surrounds the wearer — barely visible in normal light, more apparent as a slight optical distortion when the wearer moves. Impacts against the shield produce bright flashes at the point of contact, the energy dissipation visible as brief flares of light. The field extends a few centimeters from the body, conforming roughly to the wearer's outline.
Also known as: energy shield, Holtzman shield, personal force field