You need to add one of the gravity entities to your level in order to eliminate the gravity.
Simply drag the GravityBox into your level.
Then setup the dimensions of the box to cover the gameplay area in which you want to have zero gravity.
You can set any gravity value you like (by default without the gravity box a level has -9.81 z gravity, meaning an object drops down at 9.81 meters per second)
Adding particle effects like: Alien_Environment.tunnel_wind.light_tunnel_wind will enhance the feeling that there is gravity in the tunnel.
Hint: use a planet texture as the moon and set the night sky to maximum star intensity, then you can simulate nice space environments.