The cosmic microwave background is leftover radiation from the Big Bang. It holds an enormous amount of information, and despite being from the beginning of the universe, it could tell us how the universe is going to evolve in the future.
The South Pole Telescope, which is also part of the Event Horizon Telescope network. [Daniel Luong-Van/National Science Foundation]
One of the informative properties of cosmic microwave background (CMB) radiation is its polarization. In this case, polarization refers to how the component waves of the radiation are oriented relative to the direction the radiation is traveling in. Cosmological models are especially sensitive to the E-mode and B-mode polarizations of the CMB, where the E-mode is the component that is oriented parallel or perpendicular to the direction of travel while the B-mode is oriented at 45 degrees to the travel direction.
The E-mode of the CMB is especially interesting because it provides a measurement of the Hubble constant, a parameter that describes how quickly the universe is expanding. The Hubble constant can be measured in a variety of ways, and every technique ought to yield a similar value. However, this hasn’t turned out to be the case! The discrepancy ...