When physicists study the edge of the visible universe, they are not looking at "nothing" in the sense of complete emptiness. Instead, they are observing the cosmic microwave background radiation (CMB), which is the afterglow of the Big Bang. This radiation permeates the entire universe and can be detected by sensitive instruments.
The CMB provides valuable information about the early universe and its properties. It is essentially a snapshot of the universe when it became transparent, about 380,000 years after the Big Bang. Before that time, the universe was filled with a hot, dense plasma that scattered light, making it opaque. As the universe expanded and cooled, the plasma recombined into neutral atoms, allowing light to travel freely.
Physicists can study the CMB using instruments like the Cosmic Microwave Background telescopes, such as the Planck satellite or the Atacama Cosmology Telescope. These instruments measure the temperature and intensity variations in the CMB across the sky. These variations provide clues about the density fluctuations in the early universe that eventually led to the formation of galaxies and large-scale structures we see today.
By analyzing the statistical properties of the CMB, physicists can test various cosmological models and refine our understanding of the universe's evolution. They can make predictions about what they should observe based on theoretical models, and then compare those predictions with the actual observations of the CMB. This process helps eliminate the null hypothesis that there is "nothing" to see at the edge of the visible universe and provides evidence for the existence of the CMB and the structure of the early universe.
It's important to note that while the CMB provides a wealth of information, it does not allow direct observation of objects beyond a certain point in the visible universe. The observable universe is limited by the finite speed of light and the age of the universe. Nonetheless, studying the CMB and its patterns allows scientists to probe the characteristics of the early universe and gain insights into its nature.