In the late 1970s, legendary physicist John Wheeler proposed a radical question: Exactly when does the universe notice that we're paying attention to a quantum experiment? And does it really matter?

In quantum world, particles like photons can behave like particles (localized points) or waves (spreading out, showing interference patterns). The classic double-slit experiment is a good ...

Does quantum mechanics allow the future to retroactively influence the past or not? Does quantum mechanics allow the future to retroactively influence the past, as in the infamous delayed choice ...