Complex sentence: Hannes Alfvén's once suggested that plasma may play an important role in the universe, and wrongly asserted that electromagnetic forces are far more important than gravity when acting on interplanetary and interstellar charged particles.
Split into simpler sentences: Hannes Alfvén's once suggested that plasma may play an important role in the universe. He asserted that electromagnetic forces are far more important than gravity when acting on interplanetary and interstellar charged particles.