Is time travel possible?

Scientists show that a single photon in a vacuum cannot move faster than the speed of light.

“Life can only be understood backwards; but it must be lived forwards.” -- Søren Kierkegaard

The notion of traveling back in time to correct regrettable mistakes like misplacing your iPhone has long been the stuff of science fantasy. Sadly, to the chagrin of sci-fans everywhere, physicists in China now have evidence that suggests it will most likely stay that way.

It was only within the last 10 years that researchers have begun to postulate that time travel was even remotely possible when one experiment at Princeton University demonstrated the superluminal or faster-than-light transmission of optical pulses. It was at once both a startling and exciting finding considering that Albert Einstein's well-tested theory of relativity stipulates that the speed of light, which travels at 186,000 miles-per-second, acts as a de facto speed limit for everything in the universe. And since an object approaching such a speed would experience time slowing down to a crawl, exceeding it would conceivably allow the object to go backwards in time.

But the most stupefying part of all this was that, on a fundamental level, the idea itself violated the basic law of causality, wherein time, by nature, is built upon an ongoing chronological sequence events known as "cause and effect." I mean just imagine the sort of chaos that would ensue if someone traveled back to the past to prevent their own conception.

Alas, researchers at the Hong Kong University of Science and Technology had to render all this tantalizing hoopla moot by measuring the ultimate speed of a single photon in a vacuum and showing that it cannot move faster than the speed of light. This was achieved by passing a photon through a group of laser-cooled rubidium atoms.

"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," says lead author Shengwang Du.

The researchers also added that the test results "confirms Einstein's causality; that is, an effect cannot occur before its cause."

And as for the laser pulse experiment, scientists realized that it was merely a visual effect and that the superluminal 'group' velocity of many photons couldn't be used for transmitting any real data.

Coincidentally, the purpose of the study, published in the Journal Physical Review Letters, was not to investigate time travel but to advance the understanding of quantum data transmissions .

(via Press release)

Image: Back to the Future, Universal Pictures

Related on SmartPlanet:

The fastest innovations on SmartPlanet:

This post was originally published on