Author Louisa Gilder ’00 Gives Public Lecture on New Book

Dartmouth alumna Louisa Gilder ’00 gave a public lecture this past Thursday, Nov. 20 on her new book, The Age of Entanglement: When Quantum Physics Was Reborn. The talk touched on many of the topics discussed in her book, including a historical account of the development of quantum physics and the concept of quantum entanglement. The book became available on Nov. 11, from Knopf Publishing Group, and is on sale at the Dartmouth Bookstore.

The talk began with an introduction by Dartmouth professor Miles Blencowe, who advised Gilder in the senior independent study from which the book grew.

Gilder then explained particle-wave duality, the concept that matter may exhibit both particle-like properties and wave-like properties under different circumstances. As an example, she referred to the classic double slit experiment, where a stream of electrons is fired at two slits in a metal plate, with a detector placed a small distance behind the plate. The electrons, which are typically thought of as particle-like, end up being distributed on the detector in a density pattern which is just like an interference pattern, as if the electrons were waves that could interfere.

She then introduced the concept of quantum entanglement, where the properties of two quantum particles separated by a large distance seem to demonstrate a phenomenon that moves faster than the speed of light. For instance, if we have two quantum particles that become entangled after interacting and we carefully move them so that there is a large distance between them, then measurement of the property of one particle instantly has implications for the properties of the other particle, no matter how large the distance.
Such a phenomenon would violate the principles of general relativity.

The rest of the lecture consisted of brief portraits of some of the physicists featured prominently in her book. Among the most important of these was John Bell, the Scottish physicist for which Bell’s Theorem is named.

Quantum theory makes predictions for properties of particles in terms of probabilities, and many have speculated that quantum physics could be incomplete. These speculators have postulated that there may be some “hidden variables” that would be included in a greater theory that would encompass quantum physics and also give us definite knowledge of the properties of particles. Bell’s Theorem uses entangled particles to show that no such greater theory could exist, and subsequent experiments have validated its truth.

In addition to identifying historical physicists important in progressing our understanding of entanglement, she also spoke of physicists that have found innovative applications for entanglement. One of these was Artur Ekert, who came up with an important protocol for quantum cryptography. With his scheme, an encrypted message cannot be intercepted and read without the sender and recipient finding out about the eavesdropping.