The other alternatives which may be possible (really?)

Frank Tipler has tossed an idea, according to him when a cylinder is spinning with a billion revolutions a minute any object near to it will push itself into a closed time loop but the catch here is the cylinder should be infinitely long and should be dense in mass (as big as 10 times to sun). Another such idea is cosmic string where a narrow tube arranged along the space which could trap the cosmic rays will wrap the time in it and everything inside it would run slow. Practically these things are not possible in near future.