Two NASA Pie Charts Tell Us a Great Deal - And Bring Up Many Questions
I used the two pie charts below left in a previous article, Dark Matter. We'll use them again as we explore dark energy.
Wilkinson Microwave Anisotropy Probe (WMAP) data, launched in 2001 to measure minute differences in temperature in the cosmic microwave background (CMB) across the full sky. The analysis of this data was completed in 2012. The percentages represent the relative contributions of various kinds of matter and energy to the overall mass-energy of the universe (remember that mass and energy are ultimately equivalent). The charts look deceptively simple but when you begin to look more closely they are not. First, it is hard not to notice the very large component of dark energy in the universe today, and yet there was almost none or none in the very young universe (380,000 years old). Where did it come from?
Most physicists believe that our universe is a perfectly isolated system in terms of thermodynamics. This means that whatever energy the universe started out with, that is how much energy it contains today. There are some theories about our universe that challenge this assumption - more than one universe may exist and there may be some kind of transfer of energy between our universe and other universes. You will come across versions of this multiverse theory when you examine black holes and theoretical white holes and when you examine theoretical possibilities for what underlies the mysterious force of gravity. Here, we will consider it to be isolated. That means that the pie charts are accurately the same size - each represents the same total amount of mass-energy. For now, I will leave this question of thermodynamics for a moment as we examine the pie charts in more detail. However, as we will see later on, the very notion of conservation of energy in an isolated system will be challenged by dark energy.
The Pie Charts - The Mysterious Evolution of the Universe
If we added a pie chart for the universe the micro-micro-micro second it popped into being it might consist of just one colour representing the undefined "mother" energy most physicists believe existed before the process of symmetry breaking took place (you can investigate this process further in the Gauge Theory article). This "mother energy" idea is defined by the Theory of Everything. In this pie chart there would be no matter, no photons, no neutrinos and possibly no dark matter or dark energy either.
When you first look at these pies, you might assume that most dark matter simply converted to dark energy over time. Their contributions seem somewhat similar. Importantly, the two are not related to each other in any way except that they are both mysterious - no one knows for certain what they are and what mechanisms are behind them - and they both contribute significantly to the current mass-energy of the universe and how it operates.
Notice the mysterious reduction in the light blue "atoms" slice. We will tackle the mystery of where the atomic contribution to the universe went, next, in Dark Energy Part 4.