Season 17, Episode 13: The Physics of Warp Drives

Hey StarTalkians! Season 17, episode 13 of StarTalk was a live show, in which Neil sat down with Sasheer Zamata and Pete Holmes to talk to particle physicist David Saltzburg and Star Trek science advisor Erin MacDonald.

Science at Warp Speed: StarTalk Live! - StarTalk Radio

(Star Trek from 25:45, Alcubierre from 42:55)

The Star Trek discussion covered some interesting ground, with Erin MacDonald explaining the show’s faster-than-light “warp drive.” During this, they mentioned a paper by Miguel Alcubierre that delved into the real physics of warp drives. 

The Universe’s Speed Limit, Explained

The universe’s “speed limit” (c, the speed of light) would be a thorn in the side of science fiction writers if not for one fact: this is the speed limit within space, not of space itself.

Alcubierre explains this with an example. Imagine two observers on opposite sides of the universe during the initial phase of rapid inflation. Space’s expansion is pushing them apart. If you were watching from “outside,” you’d soon see them moving apart at much faster than the speed of light.

You can visualize this by drawing two dots on opposite sides of an un-inflated balloon, then blowing it up. As the balloon gets bigger, they move apart even faster. The dots don’t really “move”; space does.

Alcubierre’s Warp Metric

Just as expanding space pushes things apart, contracting space brings them together. Alcubierre’s idea is kind of simple: create a region where the space in front is contracting and the space behind is expanding.

His paper goes into the relativistic details. Usually, you’d use the matter-energy distribution to work out how space would look (derive the “metric”) but Alcubierre starts with the space he wants and works backwards.

So he doesn’t prove that you can have a warp drive, but that general relativity allows for metrics that would work like a warp drive.

The Star Trek Connection (and Why We Don’t Have Warp)

In modern Trek, Alcubierre’s paper is a clear inspiration. As Erin MacDonald explains in the podcast, they use matter/anti-matter annihilation to create the warp bubble and “dilithium crystals” to stabilize the field. 

And that touches on the issue with Alcubierre’s proposal. It requires regions of space with negative energy density, and that requires so-called “exotic matter.” Physicists generally believe such regions are impossible, and exotic matter that does this has never been discovered.