23.4 Strange Consequences

Quantum physics and theory related to wave-particle duality has produced amazing technologies, like the electron microscope while helping to explain the nature and behaviour of electromagnetic radiation.  That being said, the precise answer to the age-old question, "what is light?" still remains.  Perhaps the lack of a clear answer means that it is not a real question.  The science simply reveals a duality-a reality that is accepted, rejected, or modified with new discoveries and insight.

Young's double-slit experiment is a case in point.  The classic two-slit interference pattern (studied in Module 1: Lesson 6) can be formed in very strange ways.  For example, if only one photon of light is directed at two slits, it will go through one or the other opening forming a dot on the screen.  Then another photon passes through one of the openings, again forming another dot on the screen.  Over time an interference pattern forms, even when only one photon at a time is allowed to pass through.  You can see this in Figure 14.29 on page 738 in your textbook.  The photons interfere constructively and destructively, even though they do not pass through the slits at the same time.  The notion that, somehow, each photon is aware of the photons that came before it, is strange indeed!

From its birth in the early 1900s, quantum theory continues to evolve. Today, quantum theory is used in the development of all electronics-cell phones, flat-screen TVs, mp3 players, computers, GPS navigation, car engine monitoring computers, etc.  Even though many people do not know or understand quantum theory, the theory is a cornerstone of our modern life and affects much of what we do daily.  Quantum theory will continue to help shape the technology of tomorrow.