SkyShot, Volume 1, Issue 1
Author: Andrew Tran, University of Georgia '23
Overview
Understanding the past and future of our universe is an idea that cosmologists have worked on for several decades, tying into several big-picture, philosophical questions, such as "Why are we here?" or "What is the destiny of humanity in this vast universe?" Using theoretical models, calculations, and observations, physicists have been able to determine the stages and conditions that the universe has experienced from the Big Bang to today. From what astronomers have measured, it has also been possible to predict how the universe will look hundreds of billions of years into the future. After analyzing the densities of baryonic matter and dark energy, it has become known that the universe is expanding at an accelerated rate, and using this information allows for calculated inferences about the behavior of the universe throughout its chronology, going as far back as 13.7 billion years ago.
Figure 1: The Timeline of the Universe (NASA, 2006)
The Moment of Creation
The first stage in the timeline goes back to about 13.7 billion years ago, where it all began with the Big Bang. This moment is often referred to as the ‘Planck epoch’ or the ‘Grand unification epoch’, and marks a period of time that wasn’t even a microsecond long [4]. When the universe was at this stage, all of the four fundamental forces of nature, that being the three in the Standard Model (strong nuclear, weak nuclear, and electromagnetic), and gravity, were bonded together. The universe was extremely high in temperature, at around 1030 degrees Kelvin.
A common misconception with the Big Bang is that it was an explosion that allowed the universe to exist à la Genesis, when really it was more like all of the space expanding violently at once, increasing the distance between all of the structures in the universe that would eventually become galaxies and stars. The Big Bang truly marks the transition that the universe took from being barely a few millimeters across, to the cosmic size that we can see today [2]. It is often denoted as the ‘birth’ of our universe because it’s where the fundamental ideas and laws of physics that we know today, such as general relativity and quantum mechanics, begin to work. This is where four fundamental forces of physics, that being the gravitational, strong nuclear, weak nuclear, and electromagnetic force began to break down, and separate. We have been able to validate and justify the Big Bang Theory, as it provides an explanation for many observations we’ve made, such as the Cosmic Microwave Background (CMB) and Hubble’s Law which indicates the expansion of the universe.
The Infant Universe
Next is the period of time when the universe was only a few hundred thousand years old, just an infant compared to its age today. At this point, the scale of the cosmos had already begun to inflate. The tiny subatomic fluctuations within the fabric of the universe at this stage are speculated to have been the seeds for what would someday become galaxies.
Figure 2: Galaxies like NGC 4414 formed
Thanks to tiny quantum fluctuations. (NASA/Hubble, 1999)
During infancy, the universe began to form several kinds of subatomic particles, which would someday be classified as quarks, leptons, and gauge bosons [6]. From these subatomic particles, a large amount of matter and antimatter were formed, which annihilated one another whenever they interacted. However, the amount of matter just slightly exceeded the amount of antimatter, so that’s why today there’s only mostly matter in the universe today (though, if it was antimatter that was more abundant, we would have just ended up calling that matter anyways).
About 1 second after the Big Bang, protons and neutrons (the essential building blocks of atoms) formed, and at around 2 minutes, collided, creating heavier elements such as deuterium [7]. For about 50,000 years, the universe was too high in temperature for light to be able to travel, so it was just a cloudy, blurry plasma permeating everywhere. Eventually, the universe began to cool down, and began to be dictated by matter instead of radiation, forming the first molecules [8].
Over 300,000 years later, with temperatures much lower now, neutral atoms could be produced. This is the epoch known as “recombination.” Ionized atoms were formed as well, including hydrogen and helium, which are still the most abundant elements in the universe today. As we reach the end of the universe in its infancy, it starts to become transparent, since the ionized atoms have attracted electrons, neutralizing them. The atoms no longer scatter light, so they can now travel freely, illuminating the stage of the cosmos. Atoms that were recently formed release photons that can still be detected today in the cosmic microwave background radiation, which is the furthest we can peer back in time into the cosmos—glimpses of the leftover radiation emitted during this era, at the microwave wavelength.
Figure 3: The Cosmic Microwave Background Radiation (NASA/WMAP, 2010)
The Dark Ages
Unlike the Dark Ages following the fall of the Roman Empire, the Dark Ages refer to a time in the universe, lasting nearly a billion years, when the first stars and galaxies in the universe had yet to shine. The cosmos were making the transition from out of the “soup” of subatomic particles.
What made the universe so “dark” at this time was that the light that could now travel freely was affected by the expansion of the universe, stretching out or red-shifting into wavelengths of light not in the visible spectrum. This darkness would end up lasting hundreds of millions of years. During the Dark Ages, the majority of the matter that occupied the universe included dark matter, and neutral, uncharged amounts of hydrogen and helium [3].
Figure 4: An artistic representation of dark matter (Shutterstock)
Eventually, the most ancient stars and galaxies began to form, due to the accumulation of baryonic (ordinary) matter and dark matter into disk-like structures. This point is commonly referred to as the “Epoch of Reionization” [3]. Galaxy clusters would begin to form, slowly transitioning the universe out of the cosmic dark ages.
The Present Day (Galaxy Era)
After the dark ages, we’re brought to the present day, often referred to as the ‘galaxy era’ of the universe. Some time into this stage, the Milky Way, then our solar system, and then the Earth entered the universe. And then just under 13.7 billion years following the Big Bang, the human race walked the Earth for the first time. If you were to scale down the entire history of the universe from the Big Bang until today into one calendar year, humans would have appeared just before midnight on New Year’s Eve.
Figure 5: The golden age of our universe? (NASA/Hubble, 2003)
There is an estimated maximum of two trillion galaxies in the observable universe. Given our observations of the incoming light from galaxies, we have been able to conclude that the universe is expanding at an accelerating rate. The more matter and mass there is in an object, the more gravitationally attractive it will be, so one would expect that the combined masses of all the galaxies and groups of galaxies in the universe would result in everything collapsing in on one another. Since this isn’t the case, it means there is a mysterious force, which we still don’t know much about, pushing everything apart: dark energy. We have been able to conclude that dark energy makes up 68% of everything in the universe, dark matter makes up 27%, and normal, baryonic matter to be barely 5% [5]. This makes sense since the universe can only accelerate if the density of matter is less than the density of dark energy.
If the universe is expanding at an accelerating rate, that would mean that the galaxies are getting further apart from one another. Eventually, humanity will see fewer and fewer stars in the night sky. Our descendants, several thousands of years into the future, may not get to enjoy astronomy and stargazing as we get to today.
Eventually, the last stars in the universe will dim, maybe explode in a supernova, but then eventually shut off for eternity. This brings us to the last stage in our timeline of the universe. What will be in store for existence as we know it?
The Future and Fate of Our Universe
The last stage of the universe timeline brings us to a point where the stars and galaxies begin to stop forming. The universe continues to expand at an accelerating rate, due to the effects of dark energy. Given current models and data that we have in cosmology, the most likely scenario that the universe will experience is the “Big Freeze,” in which the universe will keep expanding until it reaches a temperature of absolute zero. Some other theories, such as the “Big Rip” and the “Big Crunch” involve the universe going out in a spectacular and flashy way. But the one that seems to be our destiny is cold and silent.
Eventually, once all of the stars have lived out their lives, all that will be left in the universe are black holes, constantly feeding on anything that gets near them, and maybe a few white dwarfs [1]. It has been theorized that by this point protons will decay as well. The beautiful cosmos that we once knew will become a bizarre place mostly occupied by stellar corpses twisting and turning spacetime. During this period, black holes may merge together and release gravitational waves.
Figure 6: The universe will be dominated by these stellar predators. (NASA/JPL, 2013)
However, all things in the universe must come to an end, and this includes black holes. Due to the phenomenon, known as Hawking radiation, black holes over time will evaporate as a result of the quantum effects near the event horizon, the boundary at the edge of the black hole, or “point of no return” where nothing may escape [1]. Once the last black hole dies, the universe will see a glimmer of light one last time, when the last stellar remnant evaporates. Then, everything will go dark. Life will be unable to thrive in this universe anymore. The concept of time will become irrelevant.
Perhaps it won’t be all bad, though. The last survivors, which may include humans, could find a way to escape this universe, and go to an entirely different one. Physicists have for many years postulated the idea of a multiverse, and if it’s true, then life—humanity, could live on to see another day.
References
[1] Adams, Fred C.; Laughlin, Gregory (1997). "A dying universe: the long-term fate and evolution of astrophysical objects". Reviews of Modern Physics. 69 (2): 337–372. arXiv:astro-ph/9701131. Bibcode:1997RvMP...69..337A. doi:10.1103/RevModPhys.69.337. S2CID 12173790.
[2] Bridge, Mark (Director) (30 July 2014). First Second of the Big Bang. How The Universe Works. Silver Spring, MD. Science Channel.
[3] Byrd, D. (2017, July 16). Peering toward the Cosmic Dark Ages. EarthSky. https://earthsky.org/space/cosmic-dark-ages-lyman-alpha-galaxies-lager
[4] Chow, Tai L. (2008). Gravity, Black Holes, and the Very Early Universe: An Introduction to General Relativity and Cosmology. New York: Springer. ISBN 978-0-387-73629-7. LCCN 2007936678. OCLC 798281050.
[5] Dark Energy, Dark Matter. (n.d.). Retrieved November 26, 2020, from https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy
[6] First Light & Reionization - Webb/NASA. (n.d.). Retrieved November 26, 2020, from https://jwst.nasa.gov/content/science/firstLight.html
[7] Kolb, Edward; Turner, Michael, eds. (1988). The Early Universe. Frontiers in Physics. 70. Redwood City, CA: Addison-Wesley. ISBN 978-0-201-11604-5. LCCN 87037440. OCLC 488800074.
[8] Ryden, Barbara Sue (2003). Introduction to Cosmology. San Francisco: Addison-Wesley. ISBN 978-0-8053-8912-8. LCCN 2002013176. OCLC 1087978842.
[9] WMAP Big Bang Theory. (n.d.). Retrieved November 26, 2020, from https://map.gsfc.nasa.gov/universe/bb_theory.html