Interestingly, this type of decoherence will occur anywhere there is a horizon that only allows information to travel in one direction, creating the potential for paradoxes of causation. The edge of the known universe, called the cosmological horizon, is another example. Or consider the “Rindler horizon,” which forms behind a continually accelerating observer approaching the speed of light so that light rays can no longer reach them. All these “killer horizons” (named after the German mathematician of the late 19th and early 20th centuries). william murder) cause the decoherence of quantum superpositions. “These horizons are really looking at you in exactly the same way,” Satishchandran said.
Exactly what it means for the edge of the known universe to observe everything within the universe is not entirely clear. “We don’t understand the cosmological horizon,” Lupsasca said. “It’s super fascinating, but much more difficult than black holes.”
In any case, by setting up thought experiments like this, where gravity and quantum theory collide, physicists hope to learn about the behavior of a unified theory. “This is likely to give us more clues about quantum gravity,” Wald said. For example, the new effect may help theorists understand how entanglement is related to spacetime.
“These effects have to be part of the final story of quantum gravity,” said Lupsasca. “Now, are they going to be a crucial clue down the road to gaining insight into that theory? It is worth investigating.”
The Participatory Universe
As scientists continue to learn about decoherence in all its forms, Wheeler’s concept of a participatory universe becomes clearer, Danielson said. All the particles in the universe, it seems, are in a subtle superposition until they are observed. The definition emerges through the interactions. “I think that’s what Wheeler had in mind,” Danielson said.
And the finding that black holes and other killing horizons observe everything, all the time, “like it or not,” is “more reminiscent” of the participatory universe than the other types of decoherence, the authors said.
Not everyone is ready to buy into Wheeler’s philosophy on a grand scale. “The idea that the universe is observing itself? That sounds a bit Jedi to me,” said Lupsasca, who nonetheless agrees that “everything watches itself all the time through interactions.”
“Poetically, you could think of it that way,” Carney said. “Personally, I would just say that the presence of the horizon means that the fields that live around it will get caught up in the horizon in a really interesting way.”
When Wheeler first drew the “big U” when Wald was a student in the 1970s, Wald didn’t think much of it. “Wheeler’s idea didn’t seem to me to be solidly supported,” he said.
And now? “A lot of the things he did were enthusiasm and some vague ideas that later turned out to be really accurate,” Wald said, noting that Wheeler anticipated Hawking radiation long before the effect was calculated.
“He saw himself holding the light of a lamp to illuminate possible paths for other people to follow.”
original story reprinted with permission from how much magazine, an editorially independent publication of the simons foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.
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