A couple of days ago, I had a fun conversation with a student regarding astrophysics. He seemed very well-informed on the subject, so I begin using some physics “slang” to help move the conversation along. The student picked up on most of the references, but then we began discussing the cosmological principle, which is an assumption upon which the Big Bang model (and many other models of the universe) depends. It essentially states:
Viewed on a large enough scale, the properties of the universe are the same no matter where you are
The student was aware that most observations have never supported the cosmological principle, but he brought up the Cosmic Microwave Background (CMB), which he seemed to think supports it. I countered by mentioning the “Axis of Evil,” and he seemed to think I was joking. I was surprised that he didn’t get the reference, so I explained it to him. He was shocked that he hadn’t heard of it before, so he suggested that I write a blog post about it.
To understand the “Axis of Evil,” you first have to understand the CMB. When astrophysicists were working on the Big Bang model of the universe, which essentially says that the universe “exploded” into being from nothing, they realized that such an “explosion” would leave behind a signature: microwaves that appear from everywhere in the universe. The predicted details of these microwaves varied from paper to paper, but regardless of the details, everyone agreed that if the Big Bang happened, there should be a “background” of microwaves found everywhere in the universe. That’s what became known as the CMB.
More than 15 years after the first prediction of the CMB, its existence was confirmed by Dr. Arno Penzias and Dr. Robert Woodrow Wilson, who shared the 1978 Nobel Prize for Physics as a result. Since the real test of a scientific theory is whether or not it can make predictions which are later confirmed by the data, the existence of the CMB helped to solidify the Big Bang Theory as the commonly-accepted scientific model of the universe.
While the existence of the CMB (if the “C” really belongs there) is definitely a confirmation of the Big Bang theory, there are also data that seem to contradict the theory. As mentioned above, for example, the cosmological principle is one of the fundamental assumptions used in the theory, but observations have always argued strongly against that principle. The CMB is no exception.
Why does the CMB argue against the cosmological principle? Remember what the principle says. The universe should look the same everywhere, at least when we get to a large enough scale. Well, look at the image at the top of this post, which (ignoring the white curve and circle for a moment) is one way to represent the CMB in the observable universe (obviously a very large scale!). The red areas are parts of the universe in which the CMB is more energetic (on average), and the blue areas are parts of the universe where the CMB is less energetic (on average). If the cosmological principle were correct, the red and blue should be evenly distributed throughout the observable universe. Even the most untrained eye can see that they are not.
In fact, there are at least two aspects of the image that seem to falsify the cosmological principle. First, the circled part of the image is huge, and it represents a part of the universe whose microwaves are ridiculously low in energy. It is generally referred to as the “CMB cold spot.” Worse yet, there is a universal trend in the microwave energy. The parts of the universe that are below the white curve in the image above have, on average, more energetic microwaves, while the parts of the universe above the curve have less energetic microwaves. That curve is called the “Axis of Evil,” and the cosmological principle says that shouldn’t exist.
Now, of course, astrophysicists who are committed to the Big Bang model (or just the cosmological principle) aren’t willing to give up their precious preconceptions just because of some annoying data, so there are several attempts to “explain around” the CMB. Some think it is simply an anomaly related to the statistical analysis that is necessary to produce the image in the first place. Some think that the cold spot is a remnant of where another universe collided with ours. However, the fact remains that if the image above is an accurate representation of cosmic microwaves, the cosmological principle is simply wrong.
There is one other big problem with the “Axis of Evil,” and it makes me doubt that the “C” should be in CMB. It turns out that the axis seems to be aligned with the very plane in which the planets of our solar system orbit the sun. There is absolutely no reason I can fathom that would explain why a universal phenomenon is linked to our solar system. However, I can image several reasons why something that is related to our solar system is linked to it. In other words, the Cosmic Background Radiation may not be cosmic.
Think about it. We are embedded in our solar system. When we see microwaves coming from all parts of the visible universe, they might just be coming from all parts of our solar system, or all parts of our galaxy. The very fact that the Axis of Evil is aligned with our orbit around the sun argues that it is related to our solar system, not the universe as a whole. Of course, if the CMB is not really cosmic, then it has no value as evidence for the Big Bang. Even if the CMB is cosmic, it clearly argues against the cosmological principle.