Changing the Model to Fit the Data, Part 2

In Part 1 I looked at Danny Faulkner's counterintuitive complaint that scientists are untrustworthy due to their willingness to revise their theories when new evidence warrants it. Faulkner lists six problems for Big Bang cosmology, then asks why scientists continue revising rather than simply abandoning this model. Faulkner's six problems are the horizon problem, the flatness problem, the smoothness problem, the cosmic age problem, the increasing expansion rate, and string theory.

I summarized the first three problems in my first post; I'll try to make it through the rest in this one.

Observations of globular star clusters led to the cosmic age problem: Measurements of the age of some clusters have, at times, resulted in ages greater than other measurements of the age of the entire universe. But new tools have increased our ability to obtain more precise measurements, both of the universe itself and of the objects within it. The WMAP spacecraft gives the universe's age at a very precise 13.772±0.059 billion years. The more recent Planck spacecraft gives it as an even more precise 13.798±0.037 billion years. For a time, this was still a problem, as some globular clusters appeared to be over 15 billion years old. A re-evaluation of the measurements suggested a date less than 13 billion years. But even today, one star—catalogued as HD 140283, informally known as the Methuselah star—has been measured at an age of over 14 billion years.

When anomalies like this occur, one of the obvious solutions is to step back and re-evaluate the data. Perhaps someone made a mistake. Perhaps we've missed something that could change our estimates. Further studies of globular clusters, published more recently than Faulkner's article, suggest these clusters may not be older than 9 billion years.

Perhaps our tools still aren't precise enough. The official age of the Methuselah star is 14.5±0.8 billion, making the lower end of the range around 13.7 billion. This would make the Methuselah star one of the first objects created after the Big Bang, but at least it would have been created after the Big Bang.

Until we have a firm resolution of these problems, we have a number of possible avenues for further research. In addition, we can review the existing data to see whether someone made a mistake somewhere along the line, or overlooked something that would change our expectations of the outcome. Or possibly added something that shouldn't be there.

When Albert Einstein was working out the implications of his theory of general relativity, he saw what appeared to be a problem. If general relativity was correct, the universe would never be in a static state: It would always be in a state of either expansion or contraction. This did not accord with the then-mainstream belief that the universe was static and eternal. Einstein suspected a still-unknown force was acting to counterbalance gravitational pull, and added a term to the equation that resulted in a static universe. He called this factor the cosmological constant.

A little over a decade later Edwin Hubble discovered that the universe really was expanding, and Einstein removed the cosmological constant from his equations, calling the constant the biggest blunder he had ever made. For six decades, physicists treated Einstein's equations as if the value of the cosmological constant was zero.

Then in 1998, two independent studies showed that not only was the universe expanding, but the rate of expansion was increasing. Once again, physicists have found a need to add a cosmological constant to explain a yet-unknown source of energy (dubbed "dark energy") affecting the expansion rate of the universe. While some publications responded to the news by proclaiming Einstein was right all along, the reality is more complex. While Einstein chose a value that would eliminate the expansion, modern cosmologists use a different value to bring the theory in line with the observed expansion rate. But Einstein was conceptually right about the effects of an unknown energy source on the expansion of the universe.

With the new equation comes a startling implication: Dark energy accounts for 68% of the composition of the universe. Our universe is made up mostly of a type of energy that we cannot detect and do not understand. The nature of dark energy is yet another problem to be solved in our growing understanding of the universe.

And finally, the world of physics has been upended by string theory. Quantum physics has been a very successful model of the universe, but it falls short in explaining how gravity works. String theory, the notion that everything in the universe is made up of tiny one-dimensional vibrating objects known as strings, may be the answer to this problem. But string theory has other implications, including some for Big Bang cosmology. Faulkner doesn't go into any detail about how he thinks this is a problem, and to be honest, I don't understand string theory much better than he does. So I'll stop right there.

Now that we've defined the problems, it's time to look at solutions. I'll start on those in my next post.