The first suggestion of the Big Bang was in 1912. Astronomer Vesto Slipher “conducted a series of observations of spiral galaxies (which were believed to be nebulae) and measured their Doppler Redshift. In almost all cases, the spiral galaxies were observed to be moving away from our own,” according this phys.org article. Later in the 1930s, Edwin Hubble used the world’s largest telescope and showed that the distant galaxies all appeared to be receding from us. That means that the farther away they are, the faster they are retracting. The first and most confident evidence we have came from 1964 when scientists at the Bell Labs discovered the cosmic microwave background radiation, confirming there was a Big Bang. This revolutionized cosmology, how we see the universe, and how we view our place within it.
Scientists have come up with several possible explanations for what happened before the Big Bang, if anything at all, and it is entirely possible that there was no previous era. Assuming this is true, it means that matter, energy, space, and time just began abruptly.
What happened after the Big Bang?
What happened immediately after the explosions is called the Planck Era: the earliest known period of time. According to the theories of physics, one second after the Big Bang, the heat of the universe caused atoms to collide with enough force to create a ten billion degree soup of neutrons, protons, electrons, positrons, photons, and neutrinos. Essentially, cosmic inflations created a soup of sub atomic particle plasma. It appears that this is what gave rise to dark matter and likely the phase in which matter gains superiority over anti matter.
Within the first 300 seconds of the existence of the universe, the elements hydrogen, helium, and some lithium form from the protons and neutrons. This process is called nucleosynthesis and is a theory that accurately predicts the abundances of elements and isotopes found in the early samples of the universe, like some of oldest stars. This verification is a strong indication that our model of the universe is accurate. 300,000 years later, when the nearly uniform soup cooled, atoms formed other nuclei. Photons ceased to scatter through space, turning the prior opaque universe into one with visible light. Those same photons, the actual after glow of the Big Bang known as cosmic background radiation, can still be observed today.
The cosmic background radiation and the Big Bang
Space agencies have launched three missions to study this cosmic background radiation, taking baby pictures of the universe only 400,000 years after its birth. The first two probes map the primordial hot and cold spots in cosmic background radiation, measuring temperature differences that are nearly uniformly distributed across the universe. A third mission, with instruments sensitive to temperature variations of a few millions of a degree, made the most accurate maps of the microwave background radiation yet.
The dark ages before stars were born
About one million years after the Big Bang, we enter a period call the Dark Ages, which are known as the final frontier of cosmology. Little is known about this period, except that is was the period before the first stars were born. The Dark Ages are thought to have lasted about 100 million years. However, due to the limit of current observations, the oldest object we can see are at a time when the universe was only several hundred million years old. Two future projects that have already begun construction, are specifically designed to shed some light on this era and hopefully bring the Dark Ages to an end.
Then, ten billion years after the Big Bang, dark energy, a mysterious force starts to accelerate. After that, 13.8 billion years after the Big Bang, we reach our time today.
The end of the universe
The ultimate fate of the universe all hinges on dark energy. If the universe continues to grow at about the same pace, 30 billion years from now, all the galaxies would be pulled from our view and all the evidence of the Big Bang would be completely lost forever. This would result in all the last stars burning out in about 100 trillion years, so we have plenty of time left.
Dark energy could also intensify resulting in a Big Rip scenario. This would happen in approximately 50 billion years from now. Dark energy would effectively tear everything apart, from superclusters to atoms. On the contrary, if dark energy slowed down, then this would give gravity the upper hand and lead to a collapse 30 billion years from now, ultimately resulting in a Big Crunch.