The universe started out smooth, but quantum wiggles imprinted space with small amounts of extra matter. Even as the space expanded, the dense spots stretched out. When inflation stopped, the young cosmos was left with dense spots ranging from small to large, which would go on to become galaxies and cluster of them.
The two-point correlation function is nailed by all theories of inflation. Researchers need to measure subtler, higher-point correlations to distinguish between theories.
Calculating the three-point correlation functions of a theory of inflation involving exotic particles can be difficult, so it's usually proposed and then played forward to find the best way to do it. Researchers tackle theories one by one. There are many things you could look for. Daan Meerburg is a cosmologist at the University of Groningen.
The process has been turned around by Pajer. Inflation is thought to have caused ripples in the fabric of space. The matrix test was used to check the functions that failed unitarity after Pajer and his team started with all possible three-point functions.
In the case of a certain type of wave, the group found that unitary three-point functions are very rare. The researchers said in a preprint that only three pass the test. The result is very remarkable, said Meerburg, who was not involved. The first signs of inflation will be if primordial waves are ever detected.
Positive signs
The probability of all possible events adds up to 1, just as a coin is certain to have two sides. The odds of each event must be positive in order to think about unitarity. There is no chance that a coin will land on the tails.
From this perspective, Shota Komatsu of the European Organization for Nuclear Research in Switzerland, Lorenzo Di Pietro of the University of Trieste in Italy, and Victor Gorbenko, a theoretical physicist, have all looked at unitarity in de Sitter space. They wondered what the sky would look like in a universe that broke the law of positive thinking.
They were inspired by the Escher world, where anti-de Sitter space and de Sitter space can look the same at all scales. The shrimpy fish have the same proportions to the whoppers in the middle as they do in the outer boundary of Escher's Circle Limit III woodcut. There were dense spots large and small. Taronna and Charlotte Sleight, a theoretical physicist at Durham University in the UK, have been working on a mathematical technique for breaking apart boundary theories between the two worlds.
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The tool developed by the group let them break the waves into waves and take the end of inflation in any universe. They found that each wave had a positive coefficient. Negative waves are not good for any theories. The test was described in a preprint. An independent group led by Joo Penedones of the Swiss Federal Institute of Technology Lausanne arrived at the same result.
The positive test is more precise than the optical one, but not ready for real data. Figuring out how to fit our messy, gravitating universe will need to be modified after both positivity groups made simplifications. These steps are concrete and doable, according to Gorbenko.
Cause for hope.
bootstrappers can move on to other classic bootstrapping rules, such as the expectation that causes should come before effects, now that unitarity is closing in. It is not clear how to see the traces of causality in a timeless snapshot.
Taronna said that the most exciting thing that they still don't fully understand is that. We don't know what's not related to de Sitter.
