Until now, most astronomers agreed that space has no top or bottom; in other words, the universe is expanding in all directions. But physicists Nodland and Ralston have challenged this principle by claiming that the universe expands preferentially in one direction . This is the conclusion they reached after studying the polarization of sound waves in 160 galaxies from different places.
These physicists have measured Faraday rotation, an effect by which intergalactic magnetic fields cause a rotation of the polarization angle in the sound waves that travel through them. Galaxies located in a particular direction in space show much greater polarization than those located in another. The difference is most noticeable in the more distant galaxies.
The theory has been disputed by the astronomical community, who believe that the measurements on which it is based were made in the 1970s and 1980s, when radio telescopes were not as accurate as they are now.
