Shields

Many science-fiction universes depict exotic defensive shielding technology protecting their vessels from enemy attacks. The different depictions of defensive shielding have varying levels of realism.

For more information, please see the main articles for how the shields of each universe behave:

• Shields in Star Wars
• Shields in Star Trek

Concept

Even though many defensive shield technologies rely on exotic physics, any analysis of defensive shielding technology should take into account real-life physics as much as possible.

Conservation of Momentum

A shield should obey Conservation of Momentum. If a shield stops an incoming projectile, its momentum must be transferred to the shield system. If the momentum is greater than what the physical shield system (or its bracings) can withstand, then the equipment may suffer physical damage.

Some dispute this citing Wesley Crusher's homemade tractor/repulsor beam, which didn't seem to transfer momentum to the device. Wesley held it casually while lifting a chair with it. Later he left it sitting on a table projecting a force field keeping people out of engineering. It wasn't knocked off when people tapped the force field. This objection ignores the possibility of the device being magnetically or otherwise secured to the table or of it transferring momentum directly to the floor when lifting the chair. In fact, when Wesley later modifies the Enterprise's own tractor beam into a repulsor, it does in fact give the Enterprise a push off. Far from contradicting the theory that their shields transfer momentum to the ship, this incident only confirms it.

Conservation of Energy

Any energy a shield draws or absorbs must go somewhere, typically--but not always--as waste heat. Many sci-fi defensive shields redirect incoming attacks and glow at the impact point when the energy from the attack is radiated away.

Sometimes depictions of shields suggest that simply having the defensive shielding raised will result in the shield system using a lot of power. However, the energy cannot magically disappear and must still go somewhere, so some rationalization may be required when analyzing those depictions in order for its behavior to make any sense.

Defensive Shields in Different Universes

Star Wars Shields

Most starships in Star Wars use deflector shield technology to protect against enemy attacks and navigational hazards. Any incoming attacks that cannot be completely deflected are absorbed and stored in heat sinks. The shields can become overloaded if the system absorbs heat more quickly than it can be radiated away. The shield system must be shut down while the systems cool off, or the projectors will burn out and require replacement.

Some starships can make use of the energy absorbed from incoming attacks, at least to a certain extent.

Please see the main article on Star Wars shielding for more information.

Star Trek Shields

Shields flare when struck by phaser fire.

Most starships in Star Trek use shields to protect against enemy attacks. As the shields take damage, they weaken, and effects from enemy attacks bleed through with greater frequency.

Please see the main article on Star Trek shielding for more information.