Time Travel Experimentally Ruled Out

In his book Physics of the Impossible, Dr. Michio Kaku ranked time travel among the most impossible of science fiction staples. And now a team of scientists in Hong Kong has ruled it out altogether.

This is something Albert Einstein rejected long ago. In his theory of general relativity he described the speed of light as a constant, making it impossible to go any faster. He did view space-time as a fabric that can stretch and shrink. And under certain conditions, called special relativity the fabric could theoretically stretch faster than the speed of light.

For the last ten years, physicists have been trying to test that theory by attempting to measure an individual photon, the particle that makes up light.

The Hong Kong team thought if an individual photon could exceed the speed of light then time travel would be possible. They found that a photon travels the same speed as light itself, 186,000 miles per second.

Experimental physicist Shengwang Du, who led the experiment at Hong Kong University of Science and Technology says, “By showing that single photons cannot travel faster than the speed of light, our results bring a closure to the debate on the true speed of information carried by a single photon.”

Scientists began studying individual photons as a way to test Einstein’s theory of general relativity in 1999 after a team thought they discovered superluminal travel in a small group of photons. That means the photons appeared to be traveling faster than the speed of light. It turns out that was just an illusion, called the superluminal effect.

Until now, there was no way to test Einstein’s theory in the lab. In their experiment the Hong Kong team separated and detected the optical precursor of the photon, a wave-like movement in the front of the particle and which is the fastest part of a single-photon wave packet.

At the same time they discovered that time travel can’t be achieved by traveling faster than the speed of light, they also confirmed Einstein’s theory of causality, showing that effect cannot precede its cause. That rules out the possibility of backward time travel, too.