Are Relativistic Weapons Realistic?

Isaac Arthur (Science & Futurism)
Isaac Arthur (Science & Futurism)Jun 9, 2026

Why It Matters

The analysis underscores that while handheld or shipboard relativistic guns are unrealistic due to extreme g-forces, power needs, and atmospheric effects, beam-driven space weapons could enable devastating, hard-to-detect strikes on installations or planets—shifting strategic concerns toward space-based propulsion and defense.

Summary

Relativistic projectiles—bullets or slugs accelerated to a significant fraction of light speed—are theoretically possible but practically infeasible as conventional weapons. Accelerating even a one-kilogram mass to 0.1c inside a short barrel would subject it to trillions of g’s and, when accounting for the required power delivery in microseconds, demand energy rates far beyond humanity’s current output. Such projectiles would disintegrate in atmosphere and become plasma, and their kinetic energies at relativistic speeds equate to nuclear-scale yields. However, slowly-accelerated relativistic kill vehicles in space using laser sails or beam propulsion remain plausible, allowing coordinated high-speed impacts on fixed targets over days to months.

Original Description

Could you build a relativistic bullet? In theory, yes. In practice, the acceleration, power demand, and atmospheric effects are so absurd that your “bullet” becomes exotic gravel long before it becomes a useful weapon.
A one-kilogram slug at 10% light speed carries roughly 108 kilotons of TNT, but firing it from a railgun would require power levels far beyond modern civilization. Relativistic guns probably are not realistic — but relativistic kill missiles might be.
#science #space #physics #scifi #futurism #relativity
🚀 Join this channel to get access to perks: https://www.youtube.com/channel/UCZFipeZtQM5CKUjx6grh54g/join
🌐 Visit our Website: http://www.isaacarthur.net
❤️ Support us on Patreon: https://www.patreon.com/IsaacArthur
⭐ Support us on Subscribestar: https://www.subscribestar.com/isaac-arthur
🐦 Follow on Twitter / X: https://twitter.com/Isaac_A_Arthur
💬 SFIA Discord Server: https://discord.gg/53GAShE

Comments

Want to join the conversation?

Loading comments...