# Special theory of relativity paradox (buoyancy) Tags: special-relativity, inertial-frames, density, buoyancy - Score: 20 - Views: 1855 - Answers: 6 - Answered: yes - Asked by: sixtytrees (325 rep) - Asked: 2025-10-10 - Edited: 2025-10-11 - Site: physics ## Question We have a submarine (sub) in a frictionless liquid and the average sub density is equal to the density of a liquid. Sub is fully submerged not touching the bottom. Now the sub moves at near speed of light. In the reference frame of liquid the sub undergoes relativistic contraction, has higher density now and must sink. In the reference frame of a sub the liquid undergoes relativistic contraction, is now more dense. Hence, the sub must resurface. Contradiction. How to resolve it? Idon't think we need GTR, Newtonian gravity should be enough. ## Answers ### Answer by hecate (score: 10 [ACCEPTED]) As @controlgroup's comment pointed out, I believe that in this fluid there is a preferred frame of reference, which could lead to the answer that there is no need to consider SR at all (recall that when Maxwell's equations weren't compatible with Galilean relativity, before Einstein people thought that the EM waves were tr