The Delayed Choice Quantum Eraser explained simply provides a shocking answer to whether the future affects the past. Could it be possible that that the future can influence the present? An enhanced version of the famous double slit experiment, called the delayed choice quantum eraser implies exactly that mind blowing scenario – that future events can influence past results.
What exactly is a delayed choice quantum eraser, and how can it possibly show that the future is affecting the past? In 1978, a physicist by the name of John Archibald Wheeler proposed a thought experiment, called delayed choice. Wheeler’s idea was to imagine light from a distant quasar being gravitationally lensed by a closer galaxy. Wheeler noted that this light could be observed on earth in two different ways. This is called a delayed choice because the observer’s choice of selecting how to measure the particle is being done billions of years from the time that the particle left the quasar.
But how could this be?…the light began its journey billions of years ago, long before we decided on which experiment to perform. It would seem as if the quasar light “knew” whether it would be seen as a particle or wave billions of years before the experiment was even devised on earth. Does this prove that somehow the particle’s measurement of its current state has influenced its state in the past? The act of measurement gives reality to the quantum particle. So in the delayed-choice experiment, this means the quantum doesn’t become “real” until you measure it. So this experiment does not prove that the present has influenced the past because the light could have been a wave and particle at the same time, and only become real when it was measured.
However, another more recent experiment set up used a more complicated method to determine this idea of the future influencing a past. It introduced something called the quantum eraser to the delayed choice. So it is called the Delayed Choice Quantum Eraser designed by Kim, Kulik, Shih and Scully in 1999.
It is a complicated construction that introduced entangled pairs of photons to Wheeler’s delayed choice experiment.
I am going to show you a much simpler set up that will illustrate this concept in easier-to-understand terms. The results of this experiment are pretty amazing — because Here’s what happens. It tells us that when the which way information is known, that is, when the detector can ascertain which slit the photon came from, it always presents as a particle. But when the detector cannot ascertain which slit the photon came from, that is, when the which way information is erased, then the photon acts like a wave.
