From MSNBC News:
Israeli physicist Amos Ori envisions a time machine that is created from a doughnut-shaped vacuum enveloped within a sphere of normal matter. Space-time would be bent upon itself inside the vacuum by focusing strong gravitational fields.
Unlike past ideas for time machines, this new concept does not require exotic, theoretical forms of matter. Still, this new idea requires technology far more advanced than anything existing today, and major questions remain as to whether any time machine would ever prove stable enough to enable actual travel back in time.
More here.