Cosmology and our View of the World
The Origins of the Universe
Lead: Jesse Coburn
Summary by Joshua Skersey
The Origin(s) of the Universe - Finetuning
P. Shaver "Cosmic Heritage" Ch. 5, 6
R. Holmes III. "Three Big Bangs", Ch. 2
To help us cover the origins of the universe, we will talk about Einstein’s Theory of General Relativity, Inflation, the possibility of a multiverse, and some anthropic principles. In our discussions, fine-tuning appeared as a reoccurring topic.
So to start things off, it is important to know some things about Einstein’s Theory of General Relativity. One important thing is that energy and mass are equivalent. Predominantly though, General Relativity states how mass influences space and time. Looking into it further we see that General Relativity manages to unify space, time and mass on the large scale extremely accurately. However when you get to the extremely small scale, it starts to break down and becomes unbounded.
From here, we engaged in a discussion on space-time. Some students ran into problems of what it would mean for time to be considered as a spatial dimension since thinking is somewhat limited to three spatial dimensions, with time being a temporal dimension. To help illustrate what it would mean we looked at some examples of a space-time diagram. An Illustration of a space-time diagram is below.
Getting back on track, we concluded that Einstein’s Theory of General Relativity provides us with a basis for using time as a spatial dimension. Now we’ll use General Relativity as a framework to look at our universe. Doing this, we see that the gravitational pull of the density in the universe in comparison with its expansion rate must mean that our universe has a relatively flat geometry. But why is that? We started discussing what it means to have a “flat” geometry and how having this geometry for our universe appears very unstable. This instability, known as Fine-tuning, states that if the universe started at an ever so slightly higher expansion rate (given everything else stayed the same), today it would have been ripped apart already. On the opposite side, if it would have started with an ever so slightly lower expansion rate the universe would have collapsed again already a long time ago. Another issue that we have seen, from temperature maps taken by COBE and WMAP of the known universe, is that the temperature is homogeneous throughout the universe. The homogeneity seemingly violates causality, by a problem described by Prof. Mӧbius as “The Horizon Problem”. The problem states that, if two points in the universe (i.e. Beyond the horizon) have never had any way to communicate, there is no physical reason why they should have the same temperature, yet they do. This ultimately leads us into inflation. From his observations, Hubble was able to deduce that the universe was expanding. We later discovered from future experiments that the universe is expanding at an accelerating rate. If we picture the universe as a balloon, and we are on the surface, then when the balloon rapidly inflates, our immediate area will appear flat. This rapid expansion helped vindicate inflation.
The realization that something is still driving space apart led us into a discussion of “space being energy”. Many people seemed to have issues with how we were defining and using key words, such as saying that space was essentially energy. To illustrate the problem with saying that someone proposed that if space was energy, and energy is equivalent to mass, then transitively, space must be matter. Ultimately the only real consensus was that inflation has expanded our theoretical bounds as much as it has the universe.
So getting back to our discussion of inflation, we are posed with the question: Since our universe is inflating, where are we inflating from? Furthermore, what are we inflating into? These questions lead to the proposition of a multiverse. What we discussed in class was a multiverse where there is an infinite number of universes, where different things could be happening. An interesting theory is the Many Worlds theory, where everything Quantum Mechanics predicts has a universe where it is occurring. Another theory, which is popular today, String Theory, states that within our universe exist many dimensions, even though we are only aware of four. However, all of these theories have an inherent problem: because we have no feasible way to test them, this makes them really nothing more than hypotheses.
From here, if we accept that there are multiple universes, then logically there are universes with different things occurring. While it was argued that although this assertion may be likely, it is also possible for it to be incorrect. For the sake of moving forward then and seeing what the consequences would be, we accepted the assertion. A good question then: what if there are universes with different constants and how would we picture them? We then started to discuss whether or not we can even say that constants could be different in a different universe. An example raised by one student was that to us Pi is by how much we have to multiply the diameter to get a circle’s circumference. What would that be like in a different universe? This was rebutted by Professor deVries, when he pointed out that Pi is a mathematical quantity, not a physical constant. We then started discussing whether we could actually draw any conclusions from these differences using the knowledge of our physical laws as we have derived them. Assuming though that the different universes do have different constants then seeing what happens when we try to vary the constants, we find that everything that comprises our universe seems to be “fine-tuned” to creating life. If this is the case, then why haven’t we found more life?