Scientists conduct “delayed choice” experiment in space

Credit: India Price/Editor-in-Chief Credit: India Price/Editor-in-Chief

A photon, or a quantum of light, has been known to have both wave-like and particle like properties. It can behave like a speeding bullet-like particle or like a rippling wave, depending on the way it is studied, but not both at the same time. This uncertainty, in some sense, is the essence of quantum physics.

Between 1978 and 1984, James Archibald Wheeler — a pioneer in theoretical physics, proposed a series of experiments to figure out whether photons “understand” their surrounding, and “chooses” to change its behavior depending on the system it is in.

While Wheeler’s proposed experiments have been performed several times, and by many different scientists on Earth, this is the first time these experiments have been performed in outer space.

Francesco Vedovato and Paolo Villoresi of the University of Padua, and their team have attempted to perform one of Wheeler’s proposed experiments using a 1.5-meter telescope at the Matera Laser Ranging Observatory. Firing green laser pulses at the Beacon-C and Starlette satellites was part of the experiment.

The experiment involved passing a laser beam through a beam splitter which would split it into two, differently polarize them (one horizontal and one vertical) and then send the two beams of lights into space. One of the beams was on a longer path, which made it lag behind. These two beams were then reflected off a satellite, subjected to a possible swap of their polarizations based on a random signal from a computer, and then passed through the beam splitter again. If their polarizations were swapped, the gap between the two beams would widen, making them both behave like particles. If it wasn’t reversed, then the two waves would combine, making the light behave as waves.

The random signal, that controls the polarization in the second half of the experiment (after the reflection off the satellite), is the “delayed choice” part of the experiment. This “delayed choice” refers to the fact the light that is being bounced off the satellite has no way of “knowing” whether it should be a particle or a wave, and therefore shouldn’t be able to “choose” to behave in a certain way.

This simply confirms the fact that most behavior of objects in the universe is undetermined until forces act on them, to force them to behave in a certain way.

Jean-François Roch, a physicist at the École Normale Supérieure in Paris, who conducted a more stringent version of Wheeler’s experiments in 2007 said in an article in Science, “This area where you mix quantum mechanics and relativity is still relatively unexplored, … and this is the sort of experiment that raised the possibility of probing the link” between the two.

The team’s findings were published in Science Advances on Oct. 25.