One of the great mysteries of modern cosmology is how our universe can be so thermally uniform—the vast cosmos is filled with the lingering heat of the Big Bang. Over time, it has cooled to a few degrees above absolute zero, but it can still be seen in the faint glow of microwave radiation, known as the cosmic microwave background. In any direction we look, the temperature of this cosmic background is basically the same, varying by only tiny amounts. But according to the standard “cold dark matter” model of cosmology, there wasn’t enough time for hotter and cooler regions of the early universe to even out. Even today we would expect parts of the cosmic background to be much warmer than others, but that isn’t what we observe.
One solution to this cosmological problem is known as early inflation. If the observable universe was extremely tiny in its earliest moments, it could have reached a uniform temperature very quickly. Afterwards, the theory says, the universe underwent a brief period of rapid expansion, eventually leading to the universe we observe today. We don’t have any direct evidence for early cosmic inflation, but because it would solve several issues in cosmology, it is a widely supported idea.
Recently, a team of astronomers looked at data from the Planck satellite, which gathered the most accurate measurements of the cosmic background thus far. They wanted to compare fluctuations across vast regions of the sky, known as low multipole moments, with the predictions of the standard cosmological model and a model that’s somewhat stranger, a holographic one. What if everything around you, from the distant stars to your very hands, were a hologram? Like Plato’s cave, our world of solid objects and three-dimensional space would simply be a shadow of a two-dimensional reality. On the human scale a holographic universe would be indistinguishable from the reality we expect, but on a cosmic scale there could be subtle differences we might be able to detect.
In the holographic view of cosmology, early inflation is driven by interactions of the quantum field, which would slightly change the appearance of the cosmic microwave background. This is particularly true for low multipole moments, and this difference makes it possible, at least in principle, to prove that the holographic principle is true. In their paper, published last month in Physical Review Letters, the team report the holographic model fitting the Planck satellite data slightly better than the standard model. The results don’t prove the universe is holographic, but they are consistent with a holographic model.
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