This concept would be dependant on having the technology to actually travel at velocities which we can now, only impart to particles Ie: .99c The plan would be to have 3 ships somewhere in space with negligable gravitational effect. 2 of the ships set out in opposite directions along an arbitrary vector. When they have achieved maximum possible velocity they transmit an agreed frequency back to the base ship. This ship checks they relative doppler shift of the 2 signals and adjusts its velocity along the same vector to reach a point where the shift in both signals is equal. Would we not be able to say that along that vector the ship was at rest in an absolute sense??? Not relative to the velocity of any object in the cosmos but in relation to the only absolute , the speed of light. By repeating this procedure in 2 more orthogonal vectors we could achieve a state of rest relative to all directions. I realize there is a degree of indefiniteness in the assumption that both ships would achieve the same velocity as well as the problem of determining exactly how close to c they arrive at , but the first question could be addressed by having the ships switch places for a second , error-correcting run along each vector. As for the problem of determining the actual final velocity , that in a way, may not be that critical. Whatever it might be, it can in a sense be considered absolute. Not that any numeral value could be assigned but because it would be independant of any relative referent and would be dependant only on its inherent conditions ; inertial mass, energy, propulsion system etc. and their relation to the physics of space itself. On this basis there would seem to be some justification for assuming the final attainable velocity in any direction would be equal to that attainable in any other direction in an absolute sense. This just occured to me so I thought I would toss it out there and see what ensues.