By the 1920s, Thomas Edison’s legacy was secured. The American inventor had forever changed the world by introducing the phonograph, the motion picture camera, and the first practical incandescent light bulb. If he had decided to retire that year, his reputation as one of the greatest geniuses of the past two centuries would still be strong today. But he had plans for a new invention, and it was his most ambitious yet—a “spirit phone” that could be used to contact the dead.

Instead of merely fame, fortune, or scientific advancement, one of Edison’s biggest motivations for the new machine was the chance to best a rival one last time. That rival's name? Nikola Tesla.

Tesla and Edison: Old Adversaries

The friction between Edison and Tesla made for one of history’s greatest rivalries. Their relationship went back to 1882, when Edison was a successful scientist and businessman and Tesla a promising young engineer working for the Continental Edison Company in Paris. Tesla eventually moved to the business’s American location on a good recommendation from his supervisor, but Edison wasn't as confident in the new transfer, calling his ideas “splendid” but “utterly impractical.”

As the two men advanced in their careers, the differences between them became more apparent. While Thomas Edison was a tireless experimenter, Tesla preferred figuring out his inventions on paper before picking up any tools. Tesla was a slave to cleanliness, and Edison, in Tesla's words: "lived in utter disregard of the most elementary rules of hygiene."

The conflict came to a head with the “War of Currents.” Tesla’s versatile alternating current (AC) eventually won out over Edison’s safer but limited direct current (DC), marking Tesla’s biggest victory over his former employer.

Though they would likely never admit it, the two men shared several similarities. Both were eccentric, egotistical, and obsessive workers. They also both dabbled in using technology to talk to ghosts.

When Tesla “Positively Terrified” Himself

Around the turn of the 20th century, when electricity was first being used to light rooms at the flip of a switch and make images move onscreen, the idea of using technology to contact spirits didn't seem that absurd. Tesla considered this possibility while experimenting with a crystal radio powered by electromagnetic waves in 1901. The signals he picked up one night were so unnerving that his scientific mind couldn't help but think of ghosts. He wrote in his diary, "My first observations positively terrified me, as there was present in them something mysterious, not to say supernatural, and I was alone in my laboratory at night."

In 1918, he wrote of similar sounds he heard after tinkering with another radio, but he was careful not to automatically attribute them to otherworldly sources. "The sounds I am listening to every night at first appear to be human voices conversing back and forth in a language I cannot understand,” he wrote. “I find it difficult to imagine that I am actually hearing real voices from people not of this planet. There must be a more simple explanation that has so far eluded me.”

There was a simple explanation: The type of radio he used is capable of picking up very low frequency radio signals from unseen sources like electrical storms, atmospheric disturbances, and household electronics. Translated to audio, the signals can sound like the uncanny chatter of disembodied voices.

Edison's Scientific Séance

When Edison learned that Tesla thought his inventions might be used to get in touch with another plane, he wanted in on the action. Though a notable agnostic and critic of the séance-holding mediums that were popular at the time, he became intrigued by the idea of forces existing beyond our world. In 1920, he told The American Magazine, “I have been at work for some time building an apparatus to see if it is possible for personalities which have left this Earth to communicate with us.” Others later referred to this device as his "spirit phone."

Like all of his experiments, this one was rooted in science. Edison pulled from the work of Albert Einstein, particularly his theories of quantum entanglement and special relativity. Edison’s thinking went like this: If it’s possible to convert mass to energy, then maybe the spirits of living people become coherent units of energy when their bodies stop working. And if entangled particles can affect each other across great distances, as the quantum entanglement theory states, then maybe there’s a way for those energy bundles to interact with our physical world.

According to the authors of Edison vs. Tesla: The Battle Over Their Last Invention, Edison put a prototype of his spirit phone invention to the test in 1920. He invited both mediums and scientists to come over and observe a mysterious experiment. They saw a projector-like machine, set out on a workbench, that emitted a thin beam of light onto a photoelectric cell. The illuminated cell was meant to detect the presence of forces and objects moving through the beam—even those invisible to the naked eye. If a being from another world were to attend the gathering and pass through the light, a meter hooked up to the photoelectric cell would let them know, Edison explained.

If his guests showed up that day expecting scientific evidence of ghosts, they were disappointed. Hours passed and the needle on the meter remained still—even the mediums in attendance had to admit there was nothing supernatural going on. But the inventor wasn’t discouraged. Though some skeptics have called Edison's dabbling in the supernatural a hoax, an entry recovered from his personal diary suggests his pursuits were genuine. He continued working on his so-called “spirit phone” throughout the 1920s.

Poor Connection

Edison died in 1931 without producing any evidence of spirits more convincing than the sounds picked up by Tesla’s radio decades earlier. But the quest to transmit a message from the other side using technology wasn’t quite over. In his earthly state, Edison had made plans to continue his work after death. He made a pact with his engineer William Walter Dinwiddie that whoever died first would try to make contact with the other. Dinwiddie passed away in 1920, about a decade before Edison, and as far as we know, that marked the end of any correspondence between the two men.

Though Dinwiddie wasn't around to receive a ghostly message from Edison when he died, others took up his mantle. A group of researchers claimed the inventor reached out to them during a séance in 1941. Edison's spirit allegedly shared the plans for building the spirit phone he had spent the last decade of his life working on. The group followed the entity’s instructions, but when assembled, the machine was no more effective at communing with the dead than the ones Edison had built while he was alive. An essay in the anthology Spirited Things recounting the attempt notes, “Alas, the contraption did not seem to successfully transmit any life units.”