It's astonishing that a theory now approaching its centennial could still be so useful in an age of such rapid scientific development. And yet quantum mechanics shows no signs of waning in its ability to explain and exploit the cosmos. Some physicists make the compelling argument that as the 19th century was known for the development of machines and the 20th century for its information technologies, the 21st century will be characterized by quantum technologies. Scientists are already using quantum principles to make virtually everything electronic vastly smaller, cheaper, smarter and more efficient. But that's only part of the quantum story.
History is a graveyard of visions that fizzled.
Those are lofty claims for a theory so few understand. What makes quantum mechanics so difficult is that the atoms and subatomic particles it describes do not behave in any way similar to the large objects they ultimately form. Unlike the larger classical world where objects from petunias to planets have definite identities, matter at the quantum level takes on multiple realities simultaneously. Light will behave like a wave if it's measured as a wave, or as a stream of individual particles if it's measured that way. It flips back and forth with perfect ease depending on how it's measured.