Simplify the following text for a Grade 10 native English-speaking person.
Original: This led to a theory of unity between subatomic particles and electromagnetic waves called waveâ `` particle duality in which particles and waves were neither one nor the other , but had certain properties of both .
Simplified: This led to a theory about subatomic particles and electromagnetic waves called wave-particle duality . This is where particles and waves were neither one nor the other , but had certain properties of both .