Starts With A Bang

Why don’t we have artificial gravity in space? (Synopsis)

In outer space, even though all the masses in the Universe gravitate just as normal, there is no 'up' or 'down' as there is on Earth, as the spacecraft and everyone on board accelerates due to gravity at the same rate. Image credit: NASA / ESA / ISS Expedition 37.

“Designing a station with artificial gravity would undoubtedly be a daunting task. Space agencies would have to re-examine many reliable technologies under the light of the new forces these tools would have to endure. Space flight would have to take several steps back before moving forward again.” -Andy Weir

Ever wonder, in those science fiction shows, how space travelers always stay “down” on their starship? Irrespective of acceleration, and despite the fact that the astronauts we have in orbit around Earth are weightless, they’re always depicted as having a floor and a ceiling that are well-defined, and always find themselves on the floor. This is physically impossible given the laws of physics as we know them today, but one small discovery could suddenly render artificial gravity possible.

This launch of the space shuttle Columbia in 1992 shows that acceleration isn’t just instantaneous for a rocket, but occurs over a long period of time spanning many minutes. For a starship, versus a rocket, the acceleration would be many times greater, even if sustained, than a human body could withstand. Image credit: NASA.

We’ve measured the inertial mass of every particle and antiparticle we know of, and everything has positive mass/energy to it. But gravitational mass has only been measured for the particles, never for the antiparticles. There’s currently an experiment underway, the ALPHA experiment at CERN, whose goal is to measure which way antiparticles fall in a gravitational field. If they fall “down,” then they’re not the solution to artificial gravity. But if they fall “up,” this fictional technology could suddenly become real.

The possibility of having artificial gravity is tantalizing, but it is predicated on the existence of negative gravitational mass. Antimatter may be that mass, but we don’t yet know, experimentally. Image credit: Rolf Landua / CERN.

We presently don’t have artificial gravity in space because there’s no such thing as a negative gravitational mass. But if we get an experimental surprise, all of that could change overnight!