Is 'negative time' a reality? This experiment suggests so
A groundbreaking study by researchers from the University of Toronto, has revealed a phenomenon where photons were seen exiting a material before they entered it. This observation, marking the first evidence of negative time, was made during an experiment involving atomic excitation. The team has been investigating this light-matter interaction for seven years.
Understanding the concept of negative time delay
Josiah Sinclair, a postdoctoral research fellow at MIT who previously collaborated with the study authors, explained the concept of negative time delay to Scientific American. He stated, "If you built a 'quantum' clock to measure how much time atoms are spending in the excited state, the clock hand would, under certain circumstances, move backward rather than forward." This explanation provides insight into how photons could seemingly exit a material before entering it.
The experiment and its surprising findings
The researchers conducted an experiment to investigate this time delay, also known as group delay, in photons. They directed photons into ultra-cold rubidium atoms and observed atomic excitation. Surprisingly, they found that some photons traversed the atoms faster than the atomic excitation process could finish. This led to a negative transit time, creating the illusion that photons had left the material before actually entering it.
The complexity of the experiment and its implications
The experiment was complex, with the apparatus for photon interaction with ultra-cold rubidium atoms taking three years to develop. The researchers suggest that their findings "imply that negative values taken by times such as the group delay have more physical significance than has generally been appreciated." However, they clarified that these results do not contradict our understanding of time and photons within Einstein's special theory of relativity.
