**Cosmic Triangles Open a Window to the Origin of Time**https://www.quantamagazine.org/the-origin-of-time-bootstrapped-from-fundamental-symmetries-20191029/**Like fossils, astronomical objects are not randomly strewn throughout space. Rather, spatial correlations between the positions of objects such as galaxies tell a detailed story of the ancient past.**... One curious pattern cosmologists have known about for decades is that space is filled with correlated pairs of objects: pairs of hot spots seen in telescopes’ maps of the early universe; pairs of galaxies or of galaxy clusters or superclusters in the universe today; pairs found at all distances apart. You can see these “two-point correlations” by moving a ruler all over a map of the sky. When there’s an object at one end, cosmologists find that this ups the chance that an object also lies at the other end.

The simplest explanation for the correlations traces them to pairs of quantum particles that fluctuated into existence as space exponentially expanded at the start of the Big Bang. Pairs of particles that arose early on subsequently moved the farthest apart, yielding pairs of objects far away from each other in the sky today. Particle pairs that arose later separated less and now form closer-together pairs of objects. Like fossils, the pairwise correlations seen throughout the sky encode the passage of time — in this case, the very beginning of time.

Cosmologists believe that rare quantum fluctuations involving three, four or even more particles should also have occurred during the birth of the universe. These presumably would have yielded more complicated configurations of objects in the sky today: triangular arrangements of galaxies, along with quadrilaterals, pentagons and other shapes.

Theorists have found it challenging even to calculate what the signals would look like — until recently. In the past four years, a small group of researchers has approached the question in a new way. They have found that the form of the correlations follows directly from symmetries and other deep mathematical principles. The most important findings to date were detailed in a paper by Arkani-Hamed and three co-authors that took its final form this summer.

**... Perhaps the most remarkable aspect of the work, Silverstein and others said, is what it implies about the nature of time. There’s no “time” variable anywhere in the new bootstrapped equation.** Yet it predicts cosmological triangles, rectangles and other shapes of all sizes that tell a sensible story of quantum particles arising and evolving at the beginning of time.

*... This suggests that the temporal version of the cosmological origin story may be an illusion. Time can be seen as an “emergent” dimension, a kind of hologram springing from the universe’s spatial correlations, which themselves seem to come from basic symmetries. In short, the approach has the potential to help explain why time began, and why it might end. *

**As Arkani-Hamed put it, “The thing that we’re bootstrapping is time itself.”**----------------------------

**A Jewel at the Heart of Quantum Physics**https://www.quantamagazine.org/physicists-discover-geometry-underlying-particle-physics-20130917/**Physicists have discovered a jewel-shaped geometric object that challenges the notion that space and time are fundamental constituents of nature.**The amplituhedron reconceptualized colliding particles — ostensibly temporal events — in terms of timeless geometry. When it was discovered in 2013, many physicists saw yet another reason to think that time must be emergent — a variable that we perceive and that appears in our coarse-grained description of nature, but which is not written into the ultimate laws of reality.

The new geometric version of quantum field theory could facilitate the search for a theory of quantum gravity that would seamlessly connect the large- and small-scale pictures of the universe. Attempts thus far to incorporate gravity into the laws of physics at the quantum scale have run up against nonsensical infinities and deep paradoxes. The amplituhedron, or a similar geometric object, could help by removing two deeply rooted principles of physics: locality and unitarity.

Locality is the notion that particles can interact only from adjoining positions in space and time. And unitarity holds that the probabilities of all possible outcomes of a quantum mechanical interaction must add up to one. The concepts are the central pillars of quantum field theory in its original form, but in certain situations involving gravity, both break down, suggesting neither is a fundamental aspect of nature.

In keeping with this idea, the new geometric approach to particle interactions removes locality and unitarity from its starting assumptions. The amplituhedron is not built out of space-time and probabilities; these properties merely arise as consequences of the jewel’s geometry. The usual picture of space and time, and particles moving around in them, is a construct.

**... Recently, a strange duality has been found between string theory and quantum field theory, indicating that the former (which includes gravity) is mathematically equivalent to the latter (which does not) when the two theories describe the same event as if it is taking place in different numbers of dimensions. No one knows quite what to make of this discovery. But the new amplituhedron research suggests space-time, and therefore dimensions, may be illusory anyway.**http://arxiv.org/pdf/1312.2007.pdf