# Q & A: Can you turn up the gravity in this room?

Q:
Is it possible to have such a room in which the strength of gravity can be adjusted? Till about two time earth’s gravity.
- Wu Fan
A:
Hi Wu,

Nice question. The answer is yes. If you accelerate an elevator upwards at the acceleration of gravity (9.8 m/sec^2), then the strength of "gravity" inside the room will be double earth's gravity. And if you accelerate it at 19.6 m/s^2, you get three times the gravity in that room.

This isn't quite as trivial as it may sound. Einstein, while working on the General Theory of Relativity, hypothesized that acceleration due to gravity is indistinguishable in every way from acceleration due to anything else (as long as the gravitational field does not change over the volume of the elevator -- otherwise you get "tidal" effects). If the elevator is falling freely, then it will be impossible, from inside the elevator, to tell that one is not in space far away from any gravitating planets or stars. It is the cable on the elevator and our feet on the ground accelerating us away from our natural free-falling trajectories which are determined by the geometry of space and time.

A more practical piece of equipment for testing the effects of large accelerations is a centrifuge. NASA uses (or used) them to train astronauts. These are distinguishable from gravity because they turn around in circles, and lots of experiments (notably, with gyroscopes) can detect rotational motion and differentiate between that and uniform acceleration.

Tom J.

(published on 10/22/2007)