Cosmology and our View of the World
Origin of the Universe – Laws, Testability, and Observability
Lead: Greg Hilston
Summary by Nicholas Marcellino
Origin of the Universe
What’s a beginning?
When entering this discussion, an important point of information is that space itself, or our universe, is expanding. Now, if time is moving forward, and the universe is expanding, would not the universe contract if we ran time backward? If we ran time on reverse mode long enough, what would happen? We can actually go far back enough that the General Theory of Relativity breaks down, the math no longer makes sense (we would have to divide by zero) and we need to treat the problem differently. The evolution of our universe can be traced back before primitive stars, quasars and impenetrable plasma, but there is no theory accepted that describes the beginning or what came before it.
What about before? Is that really the beginning? Can there even be a beginning? Am I justified using this word so much in this summary? Questions of what happens before the Big Bang, what most of us know as that event that turned our point into a universe, can wrack one’s mind. Physicists Stephen Hawking and James Hartle attempted in the 1980s to construct a theory that claimed the dimension of time would become space-like under the extreme close to the singularity, causing the singularity to smear out, leaving a definite time of creation undefined. The takeaway here is that while we can now explain how the universe evolved, we cannot yet explain how it began.
During discussion, this is often a time when the idea of “God of the Gaps” comes up. This is the assignment of the work of “God” to a problem that has not been solved, or perhaps cannot be solved. While not practical information to have, it does provide a narrative where there is not yet an answer. Various religions were discussed that provide some background on the parts of the universe that science has not caught up to. Some of them specify a Beginning for our universe (though the Creating Figure is eternal in both directions on the time axis); specifically the monotheist religions of Judaism, Christianity, and Islam. Qualitatively, it can be easy to see a resemblance between a creation event like the Big Bang and the creation of the universe by an entity, perhaps using a large bang as part of the creation process.
The Big Bang model above ran into a few problems after its conception: horizon, flatness, and magnetic monopoles. The horizon problem speaks of the observation that when we look into the cosmos and measure the cosmic background radiation, leftover from the Big Bang and at the furthest reaches of our sight, we find that it is nearly a homogenous 2.7 Kelvin, equal to within 1 part per 100,000. This is close enough that we can say here that the CMB reads 2.7 K at all points on the background. This is an issue because there are parts of our universe that cannot have at any time, between the very beginnings of the universe and now, come into causal contact with one another; they are not close enough to have ever been able to exchange information because they are not in each other’s light cone.
The flatness problem refers to the density of the universe. There is a critical value for our universe’s density (10-29 g/cm3), and if the universe has a density that is higher than this, it is a closed universe that will eventually collapse back on itself. A lower than critical density will lead to an open universe that will expand forever. The universe has a lower than critical density, but it is very narrowly close to the critical density in the sense that if we follow time backwards mathematically, the universe’s density gets closer and closer to the critical value, within one part in 1060 just after the Big Bang. If it were ever the critical value, it would have stayed that way, but it wasn’t, just breathtakingly close.
Our third problem we mention is the existence of magnetic monopoles, which our models predict should have been created in the Big Bang, but have never before been observed by humans.
The concept of inflation was introduced to explain these occurrences. It claims that in the very early universe, just after the big bang, the universe (or space) underwent a period of accelerated expansion, possibly increasing the dimensions of the universe by a factor of at least 1033 in only 10-33 seconds. This still does not explain what started the Big Bang, but it has gone a long way in tying up some of the Big Bang’s loose ends.
Before the Beginning
Inflation has moved itself to the front of the picture when we look back in time. The events that occurred during the inflationary period make it difficult to look further back in time, and the uncertainty that inherently comes when examining very short periods of time makes it seemingly impossible to probe any further. This is spelled out in the famous Heisenberg Uncertainty Principle. Long story short, quantum mechanics tells that we cannot measure quantities of time shorter than the Planck time, on the order of 5*10-44 seconds. Speculations within the fields of cosmology and quantum physics have arisen claiming the possibility that inflation could be occurring all the time, outside our own universe, outside of causal contact. This would mean that our own creation event could be one of so many that perhaps ‘creation event’ is no longer the right term to use when describing it: perhaps one in a multiverse?
Just the right fit
There are some properties of our universe that make it seem just perfect for our survival, even our existence in the first place. The relative strengths of the four forces: electromagnetism, gravity, weak nuclear force, and the strong nuclear force, are just right for the formation of fundamental particles. These particles, under the watch of the nuclear forces, form hydrogen and helium that, because the force of gravity is just right, are able to form heavier elements in the bellies of stars and upon their deaths. Life as we know it is impossible without many of these heavier elements. The four forces of nature are in what seems to be a perfect dance, and if just one of them were to misstep just a hair, the chain reaction would change our universe’s conditions so drastically that we would not exist.
This next one is just so cool to me, I have to break character a little to tell it. Planetary orbits around stars, which are essential for life as we know it, which requires a consistent narrow range of conditions to come about, cannot exist unless there are three spatial dimensions. Matter would be behaving quite differently. Another note, electromagnetism only works in a three-dimensional space that has one dimension of time. These are requirements for ‘life as we know it’. Observers may arise elsewhere under conditions I cannot explain, or perhaps understand, but for us, this is what we need.
The Anthropic Principle
The Anthropic Principle shows up in two of our sessions, at the end of this one and as a primary point of conversation two discussions from now. Anthropic reasoning attempts to express the links between the kinds of observers we are and the kind of physical conditions we observe; we can only exist in a universe that holds the conditions for our existence to be possible. We should not necessarily be surprised that we exist and can observe; for that to have happened, it must first be possible! If our universe were inert, we would not be here to reflect upon it.
Above we talked about certain conditions being so perfect, that our universe seems special. We have also talked about the possibility of a multiverse scenario as an explanation of the greater workings before beginnings. A multiverse does give us a way to declare that our place is not particularly special, with all sorts of different universes with different conditions popping up in unseen regions of ‘elsewhere’, ours just being perfect for us (or good enough).