Cosmology and our View of the World
Life, The Universe and Everything: Cosmology
Lead: Ethan Cline & James Kilpeck
Summary by Jonathan Wurtz
The origin of the universe and the origin of energys
This talk was given by 2 physics majors, and I am also a physics major, so the lecture and these notes may be physics heavy. I will also be adding a bit of my own knowledge as well.
This talk centered on a general overview of the question “where did the universe come from”. Most of the talk centered on physical theories (e.g. the Big Bang and similar) but also briefly mentioned religious theories as well (Hinduism, Christianity, etc.). Generally, the presentation was very physics-heavy; however, the actual physical theories are highly mathematical and solutions to equations can easily be a page long, or require hours or even days of numeric analysis on supercomputers. So, this was much simplified.
We start off with a discussion of the Big Bang, which is a theory of the evolution of the universe. It should be emphasized that it is a theory of evolution of the universe (in this meaning, evolution means the progression in time of a system; for example, “the evolution of the United States Republican party”). It does not explain why the big bang happened in the first place.
The calculations and theories surrounding the Big Bang follow one of Zeno’s Paradoxes (the paradox of dichotomy) in which we can only take smaller and smaller steps back in time, but never reach “the Beginning”. Current theories stretch back to 10-37 seconds after the Big Bang, and without another theory we cannot get to 0 seconds. Current theories based on observations of the Hubble Expansion and the Cosmic Microwave background place the age of the universe at 13.7B years (deVries: “Bible is off by a bit”).
Experiments are needed to determine the characteristics of the Big Bang in order to go constrain physical theories (in other words, figure out what is a physically relevant idea and what isn’t). COBE (COsmic microwave Background Explorer) looks at the Cosmic Microwave Background (CMB) to look at the very early universe, based on very slight differences in temperature. This is one of the big justifications to the Big Bang model; the predicted and actual data vary by a very, very small amount.
With this in hand, we now jump to a (somehow similar) topic: Vacuum, aka, space with nothing in it. But is a vacuum always a vacuum? It turns out that there are always pairs of particles and anti-particles popping in and out of existence at every point in space, by virtue of the Heisenberg Uncertainty Principle (HUP) energy-time relation. Basically, an amount of energy can be “borrowed” for a small amount of time, as long as the timespan ΔT and the “borrowed” energy ΔE is smaller than ΔE* ΔT ≤ h, where h is Planck’s constant.
But what is the HUP? Simply put, there is a fundamental “Graininess” to the universe at a small scale, the same way as if you look close at a computer screen you see pixels. Because of this, there is always some uncertainty as to where things are (“somewhere within a pixel”). In class, this generated a lot of discussion (about 25-30 minutes) as to how it works. From a physics perspective, this is frustrating because it is Purely Mathematical: quantum physics has a model of describing the universe (actually, several), which is based on simple mathematical statements. These mathematical statements obey the principles that physics is required to satisfy: predict phenomena. We use these sets of mathematical objects, because they WORK. But this is getting at the philosophy of physics. I digress.
With these ideas in hand, we went on to discuss different physical theories that attempt to describe and predict the universe.
This is the idea that the universe is “fine tuned” for life to form. For example, if the gravitational constant were lower by 2%, stars like the Sun would not fuse/light themselves, but if it were higher by 2% the universe would be a big black hole. This then brings up the idea of the anthropic principle, or that we see a universe fine-tuned for life… because we live in it! This principle could be satisfied with a “physical” explanation if we use a multiverse theory, or that there are an infinite number of universes (more on that later).
The False Vacuum
This is one of the current theories to describe the generation of the universe. A vacuum, in a physics sense, is the “lowest energy state”—For example, if you have a small ball sitting at the bottom of a curved bowl; it can’t get to any lower height (thus, lower energy). As the theory goes, imagine the entire universe as that ball. Now, that ball is again sitting at the bottom of a bowl, happily sitting there. However, the bowl is on top of a table, so there is theoretically a “lower energy state”, aka the floor. Thus, the ball in the bowl is in the so-called “false vacuum”. Now, it is postulated that the big bang was the universe/ball somehow jumping out of the bowl and falling onto the floor, releasing a massive amount of energy into the ball/universe. This amount of energy then coagulated into what we see today as matter and energy (through Energy = Mass * Speed-of-Light2 since matter and energy are equivalent).
At the big bang, time did not exist (!)… it “unwrapped” itself as the universe evolved in the first few moments (ah, but what is a “moment” when there is no time…?)
This theory is that everything can be described by one gigantic self-interacting quantum mechanical wavefunction. This runs into interesting peculiarities with “boundary conditions”, or how the wavefunction behaves at the boundary to space. Our universe is theorized to be “infinite but unbounded”… but it’s expanding…? What into? (Be careful with geometric interpretations… imagining 5D space always gets hairy!)
This theory suggests that there is an infinite cycle of expansion and contraction of universes—in other words, there will soon be a Big Crunch, followed by another Big Bang. We just live in one of those cycles.
As an example for a cyclic model, higher-dimensional “branes” (basically, shapes that live in higher dimensions, like a 6D cube) that collide can form our universe. This is one of the theories put forth by string theory. I can’t elaborate much more beyond what is available on Wikipedia.
A “Mommy Universe” that is in a perpetual “false vacuum”, which constantly spawns/decays into “Baby universes” (an infinite amount). Thus, as this theory goes, there are an infinite number of universes, each with slightly different universe conditions (speed of light, etc). This can also be attributed to “quantum fluctuations of the false vacuum” (!?!).
Black Holes all the way down
As a variant of a multiverse model, this theory suggests that each black hole in our universe holds an entire universe inside of it. Thus, there is a constant “evolution” (in the Darwinian sense) of which universes spawn black holes, spawning more universes, ad infinitum; the universes, which spawn the most black holes span the most universes, in some sort of evolutionary process. Related to “Turtles All the way down”.
The universe as a computer simulation
This is the theory that suggests this entire universe is some elaborate simulation in some computer somewhere. (Think: if I were to make a computer simulation, I would want a smallest length scale, local causality due to finite speeds of light, etc…). But this raises the question: where does the computer live (In another simulation?!)?
This is a model based on string theory—this is the idea that the state (position, velocity, consciousness, etc.) of the universe at every point is only determined by the boundary conditions of the universe. By this, imagine holding a rubber sheet in your hands. You only hold it on the edge, but you can twist and stretch it so the interior becomes interesting. This is the same idea except the rubber sheet is the entire universe, the boundary conditions are hard to imagine and the hands are…?
“Most say the universe started with some God/supernatural deity”.
The Pope in 1951 (Christianity) said the Big Bang was compatible with doctrine. We did not go over much of Christian/Judaic/Muslim creationism because most people know that (as claimed by the presenters). However, for Hinduism, their ideas are eerily similar to the Big Bang. For example, one creation story is that the universe started “from a single hot point” (!). Another describes the “cosmic egg” which hatches to form the universe. Furthermore, the timescales they have are much longer—311 trillion year cycles of birth to death, based on the 100-year life of God.