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"In Search of Time's Origin"




Page and Wooters decided to apply the controversial concept that the universe as a whole could be treated as a giant quantum object—subject to the same physical laws as electrons, protons, and other tiny particles of the subatomic world. They imagined splicing the contents of the cosmos into two pieces. Because quantum laws prevailed, the pieces would be entangled. Scientists have found that two entangled particles measured in the lab can have equal but opposite values. If one is spinning clockwise, for instance, the other will be spinning counter-clockwise so that, when summed together, the properties cancel each other out. Page and Wooters argued that in similar fashion, each section of their divided cosmos could independently evolve, but because they were entangled, the changes in one would be counter-balanced by the changes in the other. To someone inside one of the sections, time would appear to pass. But to the outside observer, the overall universe would appear static.

While Page and Wooters had offered a theoretical sketch, based on quantum entanglement, for how the cosmos might appear to be stationary to someone peering in from the outside, there seemed to be no way to confirm or rule out their idea. But, in 2013, Genovese and his colleagues performed an experiment to test whether—at least in the lab—it is possible to create a model of the universe in miniature, with just two particles of light, or photons, generated from a laser. The aim of the experiment was to prove that it is possible to create a situation in which a quantum system, when viewed from outside, appeared unchanging, but when observed from within appeared to evolve.

To do the experiment, Genovese set out to monitor the photons’ polarizations—the directions in which they vibrated. If a polarized particle could be made to rotate at a constant rate, then its position at any moment could be used to mark out intervals in time, just like a second-hand on a clock. The team entangled the two photons together, in such a way that their polarizations took on opposing traits. For instance, if the polarization of one was measured to move up and down, the other would vibrate from side-to-side.

In order to set their photons’ “second-hands” in motion, the team passed both particles through quartz plates, causing their polarizations to rotate. The amount of rotation was related to the actual time spent within the plates, giving physicists a means of measuring the passage of time. They carried out their experiment repeatedly and in each run they stopped at a different moment and measured the polarization of one of the photons. “By measuring the first clock photon, we became entangled with it,” says Genovese. “That means we became part of that universe and can register the evolution of the second photon against our clock photon.” Vested with this ability, the team confirmed that one photon appeared to change when measured against its partner, in the same way that Wooters and Page believed one part of the universe could be seen to evolve if measured against another portion of the cosmos.

However, Genovese still had to confirm the second part of the hypothesis: that when the entire entangled system was monitored as a whole, from the outside, it would appear static. In this part of the experiment, the team took the point of view of a “super observer” standing outside the universe. This external watcher could never look at the individual state of either photon because by doing so he would become entangled with them, becoming an internal observer. Instead, the observer could only measure the joint state of the pair of photons. The team ran the test many times, stopping at different points. They looked at the two photons as a combined whole and measured their joint polarization. Each time, they ascertained that the two entangled photons were polarized in equal but opposite ways. No matter how much time passed, the two photons were always poised in exactly the same “embrace.” The mini-universe appeared to be static from the outside and completely unchanged. It turns out the so-called “problem of time,” discovered by Wheeler and DeWitt, can be resolved if time is an artifact of quantum entanglement.



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