Look-UP
by Mitchell Tester, College Student
TIME, Part 2
One of the most polarizing questions in astronomy is “How old is the universe?” This question, besides answering the age of the universe, also insinuates that there was a beginning. And like all beginnings, there must also be an end. No one on this Earth knows for certain how the universe was created, nor do they know why.
This month, in part two of “Time,” I thought we could answer the theorized “how” in the case of the creation of the universe. We’ll leave the why to spirituality and religion, as I am in no place to speak as to the why.
The universe is actively growing, in a certain sense, right this moment as you are reading this. We are moving at an incomprehensible speed. This speed is also not constant throughout the universe. Not only that, but it is entirely relative to the observer. The space between us and other superclusters of galaxies is what shows this relativity. Our solar system, the Milky Way galaxy (our home), and the Local Group (the group our galaxy falls in) all are bonded by their gravitational pull toward one another. Between superclusters, though, lies something strange: an unknown force that pushes these superclusters of galaxies away from each other.
For the sake of understanding when I say the speed of expansion is “relative,” let us take a trip to one of the most distant galaxies, named “MoM-z14.” To an observer from this galaxy, if they were to look at us, they would see that we are traveling nearly two-and-a-half times the speed of light, which is, of course, the fastest known thing in the universe. From here on Earth, though, MoM-z14 appears to be moving away from us at the same speed. There is no center of the universe; there are no edges of the universe. Clusters of galaxies are all moving away from each other, which points to the idea that the universe is expanding, and the space between these distant objects fuels this expansion. The universe has been stretching since its inception after the Big Bang, but what is driving it? The energy behind this is called dark energy. Much is unknown about it, but figuring it out may be able to tell us the secrets of the universe—the beginning and the end. Dark energy is what can explain the expansion of our universe now, but what explains how the universe came to be?
THE BEGINNING
Nearly 14 billion years ago, the universe looked very different from how it looks today. It is theorized that it was very small, and all the energy and matter of the universe was packed into the size of an atom. This atom-sized fireball then exploded, in a sense, expanding into what we know as the universe today. This theory is called singularity. This theory of the Big Bang is usually what people think of when they ask the question, “How does something come from nothing?” That is a very valid question. The singularity theory of the Big Bang is not very accepted by cosmologists in today’s world, as it does not even begin to answer the question of how all this energy came to be in the first place.
The 1970s were the birthplace of the cosmic inflation theory of the Big Bang. It helped answer some of the difficult questions, such as how a singularity (small dense area the size of an atom) would create the conditions needed to create galaxies. A lot of these initial conditions that were needed to create the universe were largely assumed in the case of the pre-inflation model of the Big Bang. Particle physics, the study of matter, helped pioneer the theory of cosmic inflation. A particle physicist by the name of Alan Guth discovered that a positive-energy false vacuum could be the exact conditions that would allow space to expand at an unbelievable rate.
What is a “positive-energy false vacuum,” though? For starters, you hear most people refer to space entirely as a vacuum, as in there is nothing in it. In quantum field theory, it suggests that empty space is not truly empty. I will not go into detail, as quantum mechanics is very complicated, but basically it states that particles in a vacuum will constantly pop in and out of existence, which results in the vacuum always having some level of positive energy. That also means that it is not completely stable. The energy in this positive-energy false vacuum eventually creates a repulsive gravitational field from the negative pressure created by the energy; this causes the universe to inflate, expanding unconceivably fast. The false vacuum will eventually decay, which means that it drops into a lower state of energy. In addition to this, it is also theorized that the decay stopped the inflation phase; after this, all the stored positive energy from the massive inflation and expansion turned into copious amounts of hot particles and radiation. You’ll hear this phase called “hot particle soup,” which indicated the start of (and what caused) the Big Bang. What was before inflation is still unknown to us, as the rapid expansion wiped any physical evidence or clues from the earlier time of where our universe exists now, as in before the Big Bang created all the matter in our universe.
Some say that looking into space can allow you to see into the past. We can see light from stars millions of years ago, due to light traveling at a finite speed, and the distance between us and distant stars being so vast. Something interesting happens when we look past the distant galaxies of stars; we see something we cannot see past. It is something to do with the “hot particle soup” we learned about earlier. The furthest we can see in the observable universe is the Cosmic Microwave Background, or CMB for short. Observable in “observable universe” is important, as it states that the CMB does not serve as the edge of the universe, meaning that the universe is finite, but rather the CMB is as far as we can see. It is very likely, way more likely, that the universe goes on beyond the CMB. What that part of the universe looks like, we haven’t the slightest idea.
The CMB was first discovered by Arno Penzias and Robert Wilson, accidentally. While studying radio waves, they noticed a constant low-level hum coming from every direction in the sky. They diagnosed equipment, removed any potential interfering objects, and then quickly discovered that the real signal was from outside our galaxy. It was stemming from all over, in all directions. This background humming was predicted many years earlier by Big Bang scientists. They predicted that leftover heat from something as big as the Big Bang should fill the universe with something; they just didn’t know exactly what. Penzias and Arno gave the scientific world the evidence that was needed. The CMB is the earliest we can see of the beginning of the universe, 380,000 years after the Big Bang. We cannot see any further, as it is completely opaque.
What does this mean for the future of the universe? Does it have an end? Tune in next month for part 3 of “Time.”
Differences in the density of the early universe can be seen in the variations within the Cosmic Microwave Background (CMB). These differences are the seeds that eventually grew into clusters of galaxies. Source: https://www.astronomy.com/science/ask-astro-how-far-away-is-the-cosmic-microwave-background/
