The Big Bang theory, a well-known model of the Universe proposed a century ago by the astronomer Georges Lemaître, is one of the most well-known theories explaining the beginning of the Universe. However, scientists have not yet proved or refuted this theory. How can we say, then, that the Big Bang is a possibility?
Lamaître theorized that the Universe began at a single point, known as a “singularity”. All the matter in the Universe was concentrated within this singularity. This point, known as time 0, or “t=0”, is estimated at 13.6 billion years ago. The singularity would then be followed by rapid inflation. At these early stages of the Universe, protons and electrons (both components of neutral atoms) moved freely around space. At this point, photons, particles that carry light, scattered outward from the electrons (see this page for more information on this phenomenon).
Once fluctuations and anisotropies in the Universe commenced, the free protons and electrons combined to form the first element: Hydrogen. The scattering of photons stopped due to the lack of free electrons available for this to happen. However, the photons that had already been scattered prior would continue to travel around the Universe, as these photons would barely be impacted by the creation of the new Hydrogen atoms. This would happen until the apparition of the first stars, and matter as we know it, would have been formed. All the while, the Universe would continue its expansion.
One of the strongest observational pieces of evidence for the Big Bang is the Cosmic Microwave Background, often abbreviated as CMB. The CMB is radiation, mainly in the microwave wavelengths, that remains from the beginning and can be found anywhere we look in the Universe. It was accidentally discovered by Penzias and Wilson of Bell laboratories in 1964 when performing satellite communication experiments. The CMB is one of the things predicted by the Big Bang theory. When all the electrons and protons could move freely, photons would be emitted, and, as explained before, these would be moving around the Universe now too. The information that these photons carry is an image of the Universe during their time of their emission. Therefore, the photons would form what is known as the “afterglow” of the Big Bang. This is exactly what the CMB represents.
Other observational pieces of evidence include the expansion of the Universe and Hubble’s law. By observing the galaxies around us and their movement, we have determined that galaxies are moving away from us. This means that the Universe is expanding uniformly at each point, and this would be explained by the Big Bang theory.
However, some questions arise, like “What was there before this singularity?”. This question cannot be answered at this moment, and some scientists even think it is futile to think about it. The Big Bang, this singularity, was “t=0”, i.e. time began with the Universe, it came to creation with the Universe. We do not know what there was before this point, and we don’t even know if the concept of “before” can be applied to it, as we don’t know if time existed at this point. As can be seen, the Big Bang model is coherent with a lot of observations but raises many questions while answering others.
Edited by Briana Fannin