Science & Technology
Breakthroughs, forgotten inventions, and the tech that shouldn't exist yet.
Quantum Entanglement Explained: How Scientists Create and Detect Entangled Photons
Quantum entanglement is a real and experimentally demonstrated phenomenon in which quantum systems can share correlations that cannot be explained by ordinary local hidden-variable theories. Scientists can create entangled photon pairs using carefully controlled optical systems and then send the photons toward separate measurement stations. The experimental story became especially important through the work of John Clauser, Alain Aspect and Anton Zeilinger, whose experiments tested Bell's inequalities and increasingly eliminated possible experimental loopholes. Their combined work was recognized with the 2022 Nobel Prize in Physics. Modern experiments can generate, manipulate and detect individual photons with extraordinary precision. They are not merely demonstrations of a strange quantum effect; the underlying technology is now important for research into quantum computers, quantum communication, quantum networks and quantum cryptography.
Hafele–Keating Experiment (1971): The Real Experiment That Measured Time Dilation
In October 1971, physicists Joseph C. Hafele and Richard E. Keating carried four highly precise cesium-beam atomic clocks aboard commercial passenger aircraft and flew them around the world, first eastward and then westward. When the clocks returned, they were compared with atomic clocks that had remained at the U.S. Naval Observatory in Washington, D.C. The result was remarkable but extremely small: the clocks that traveled eastward had lost about 59 nanoseconds, while those that traveled westward had gained about 273 nanoseconds relative to the reference clocks. These differences were broadly consistent with calculations based on Einstein's special and general theories of relativity. The experiment became an important real-world demonstration that elapsed time depends on motion and gravitational conditions. It did not demonstrate a time machine or allow people to travel into the past. Instead, it showed that two clocks following different paths through Earth's motion and gravitational field can genuinely accumulate slightly different amounts of elapsed time.