Meeting of the American Astronomical Society
January 8–12, 2018, I attended the 231st meeting of the American Astronomical Society (AAS) near Washington, DC. From the numbering, you may think that the AAS has been around for more than two centuries. However, the AAS began in 1899 (I went to the centennial meeting in Chicago in 1999). For most of its history, the AAS has met twice a year, hence the high numbering. I hadn’t been to an AAS meeting in a couple of years, but I was very glad that I attended this meeting, because it was very profitable for me.
The meetings of the AAS allow astronomers to gather, and while there, socialize, network, share our research, and learn new things in our field.
What goes on at an AAS meeting, and why do we have them? The AAS is the professional society for astronomers in the United States, though there are AAS members from other North American countries, such as Canada and Mexico, as well as members from around the world. The meetings of the AAS allow astronomers to gather, and while there, socialize, network, share our research, and learn new things in our field. The meetings kick off with an evening reception and heavy refreshments. But many committees and working groups meet informally that day and even the day before. Then there are four full days of programs. There is a closing reception the final day, again with food. Generally, there are four plenary sessions each day. Like any scientific discipline, astronomy has become very specialized, so it is difficult for most of us to keep abreast of what’s going on in these various subdisciplines of astronomy. Many of the plenary sessions are reviews of different topics, so they are excellent opportunities to catch up on things outside of our expertise.
In between the plenary sessions there are many parallel oral presentations. These presentations are limited to five minutes, with five minutes of Q&A. Such a short format can be frustrating. However, presentations on doctoral dissertations are allowed 15 minutes, with five minutes of Q&A. These are grouped according to subdiscipline, so there is unity within each session. This meeting, I mostly went to presentations on cosmology and extrasolar planets. Each day, poster papers are displayed in the exhibit hall, again grouped by subdiscipline. While one might read these posters any time between 9:00 a.m. and 6:30 p.m., there is an hour set aside early and another hour late in the day for people to stand by their posters to be available for questions. Posters are up for only one day, so you have to check back each day for the new posters. My research partners and I usually present our work in this format. Also in the exhibit hall, there are vendors and space mission representatives. Finally, during lunch and in the evenings, there are various workshops, town hall meetings, and receptions.
What is the Value of the Hubble Constant?
The most interesting plenary session of the meeting was “A New Measurement of the Expansion Rate of the Universe, Evidence of New Physics?” given by Adam Riess. In 2011, Riess shared the Nobel Prize in Physics for the discovery that the rate of expansion of the universe is increasing, so he certainly is qualified to address this question. Ninety years ago, Edwin Hubble discovered that there is a linear relationship between the redshifts and distances of galaxies. That is, the farther away a galaxy is, the faster it appears to be moving away. The accompanying figure represents this Hubble relation, or Hubble law, with a line representing the best fit to the data.
The most straightforward interpretation of the Hubble relation is that the universe is expanding. The slope of the line, the Hubble constant, H0, measures how rapidly the universe is expanding. The value of H0 is an important cosmological parameter, so for nearly a century, astronomers have attempted to measure it as accurately as possible. The direct method of assessing H0 is to collect redshifts and distances of many galaxies. While measuring redshifts of galaxies is straightforward, measuring their distances is fraught with problems.
For half a century, the dominant cosmology has been the big bang model, the belief that the universe suddenly appeared 13.8 billion years ago in a very dense, hot, rapidly expanding state. During the intervening expansion, the universe cooled, and stars and galaxies formed to produce the universe that we see today. Cosmologists expect that gravity from matter in the universe slows the rate of expansion. This ought to show up as a slight upward turn at very great distance in the Hubble relation, but measurements of distances of faraway galaxies are the most difficult to make. Two decades ago, two teams of astronomers (one headed by Riess) tackled this problem by using type Ia supernovae in very distant galaxies to determine their distances. Much to their surprise, both teams found that instead of turning upward, the Hubble relation turned down slightly at great distance. So, rather than slowing, the rate of expansion is speeding up.
A century ago, Albert Einstein anticipated the possibility that the rate of expansion of the universe might increase, though most cosmologists long ago dismissed this possibility. What is causing this? No one knows, and it remains one of the biggest questions in astronomy and cosmology today. The best candidate appears to be dark energy, a hypothetical potential energy field in the universe. As the universe expands, this field releases energy into the universe that not only overcomes the tendency of gravity to slow expansion, but increases the expansion rate. The amount of dark energy in the universe is expressed by the density of dark energy, ΩΛ. The current preferred version of the universe, ΛCDM can be characterized by six parameters with H0 and ΩΛ being two of the six parameters.
I have already discussed the direct observational way to determine H0, but cosmologists think there is a better way to do this. Discovered in 1965, the cosmic microwave background (CMB) is considered the best evidence for the big bang. There are very subtle temperature fluctuations in the CMB, first mapped by COBE (COsmic Background Explorer) satellite nearly 30 years ago, and more recently by the Planck spacecraft. Cosmologists interpret these temperature fluctuations in terms of the ΛCDM model to measure the six parameters that describe the universe. And therein lies the rub. In his presentation at the AAS meeting, Riess summarized recent work of him and his collaborators. Their latest measurement produces H0 = 73.24 (± 1.74) km/s/Mpc. Other studies measuring the Hubble constant in this traditional way give similar results. On the other hand, those determining the Hubble constant by modeling the CMB find H0 = 66.9 (± 0.6) km/s/Mpc. He pointed out that this is a difference of 3.4 σ, indicating that the two results cannot simultaneously be right.
Do astronomers and cosmologists choose to believe a direct measurement of a quantity, or do they believe what the model tells them?
This is a very serious problem. Do astronomers and cosmologists choose to believe a direct measurement of a quantity, or do they believe what the model tells them? This could indicate that the model is terribly flawed. That model is the big bang, something we at Answers in Genesis don’t believe anyway, because it contradicts what Scripture says about the origin of the universe. What does this result mean to biblical creationists? It isn’t entirely clear. Creationists are divided as to what the Hubble relation means, with some thinking that it reflects expansion, while others thinking that it is due to some other effect. No thoughts have emerged among creationists as to what the downturn in the Hubble relation at great redshift means. We still await a comprehensive biblical cosmology.
Before moving on, I’d like to mention a shift in thinking that I observed at this AAS meeting. One poster paper discussed the fact that real data indicate more dark matter in the universe than the big bang modeling of the CMB will allow. About 30 years ago, astronomers embraced the reality of dark matter after opposing it for half a century. Soon, cosmologists began to incorporate dark matter into the big bang model. A few physicists have resisted dark matter, opting instead to toy around with radical changes in physics instead. Some creationists have picked up on this. I think their motivation is a desire to undo the big bang model, something that I’ve written about. From Riess’ comments and those of other speakers at the AAS meeting, I detect that astronomers who have believed in both dark matter for more than three decades and dark energy for nearly two decades now are reconsidering new physics. It’s not that they are rejecting dark matter and dark energy in favor of new physics, but that the direct observational data indicating the amount of dark matter and dark energy are at odds with the indirect measurements from the CMB filtered by the big bang model. It is ironic that recent creationists who seem to reject dark matter because of a perceived association with the big bang model now find themselves in agreement with those who promote the big bang.
Odds and Ends
Another plenary session gave an update on our changing understanding of Jupiter. Most of us are used to seeing the wonderful photos of Jupiter from the Voyager probes four decades ago and the more recent Galileo orbiter. Less well known is the current Juno mission orbiting the Jovian system. The primary reason for this may be less emphasis on visual imaging from this mission. In fact, JunoCam, the only visible light camera aboard the spacecraft, was more or less an afterthought. It was added to gain public interest in the mission. Juno has a heavy emphasis on probing Jupiter’s gravitational and magnetic fields. This is leading to a new understanding of the interior of Jupiter. Juno also has an orbit that takes it over Jupiter’s poles. One surprising result is that Jupiter’s poles are blue.
The speaker also discussed the origin of Uranus’ odd tilt, something that I’ve written on. Most theories require that Uranus underwent at least two early, violent collisions to produce its current 98-degree axial tilt. Now the thinking is that resonances in the early solar system may account for part of this. This requires that both Uranus and Neptune originally orbited between Jupiter and Saturn and then migrated to their current orbits beyond the orbit of Saturn. However, this scenario can’t explain tilt more than 90 degrees, so there still must have been an impact from a body about the size of the earth as well. I find it interesting that astronomers must invoke all sorts of complicated scenarios to explain the solar system that we have.
I find it interesting that astronomers must invoke all sorts of complicated scenarios to explain the solar system that we have.
Another plenary session discussed Venus. Though there hasn’t been a mission to Venus for some time, much debate continues. For instance, there are three schools of thought on past and ongoing geological activity on Venus. Planetary scientists are coming around to the idea that Venus’ surface isn’t static but may be changing faster than thought. Furthermore, now the thinking is that Venus may have had an ocean at one time. Of course, all of this is interpreted in terms of billions of years, so it’s not clear if recent creationists would embrace this.
Another interesting plenary session described new things going on in stellar evolution. I was intrigued by some aspects of this, which prompted me to ask a question at the end of that talk. I had never asked a question after a plenary presentation at an AAS meeting. In fact, I had asked only one question during Q&A in any previous AAS meetings, and that was after an oral presentation. This time, I asked a question after two oral presentations, and I peppered several poster presenters (more than my usual) with questions. I must be getting bold in my old age.
At AAS meetings, a group of self-identified Christian astronomers usually gather for lunch or dinner, a tradition we continued. There were about 20 of us at dinner one evening. It is a diverse group. I seriously doubt that many of them are recent creationists, but most of them seem to know that I am, and that doesn’t appear to matter to them. I find their willingness to accept me refreshing, and I’m thankful for their kind, Christian attitude toward me.
Overall, I enjoyed this AAS meeting more than any I’ve ever attended. I found much that is stimulating to my thinking in developing a creation model of astronomy. Perhaps I won’t wait so long to go back to another meeting.