This is a companion discussion topic for the original entry at https://biologos.org/blogs/guest/are-spiral-galaxies-evidence-against-an-old-universe
As always, I will be available for discussion here. Feel free to share your questions, remarks, and impressions of the astronomical part of the movie Is Genesis History.
Excellent article. It really is amazing that the spiral galaxy argument still finds its way onto many top 10 lists of best evidences of a young-earth. As you point out it isn’t evidence of a young earth even if it were a problem for an ancient universe. I was unaware of recent modeling that provides positive evidence that spiral galaxies are predicted by our current understanding so that was especially helpful.
Every time I look at the “top evidences” of a young earth found on various YEC sites and in talks I can’t help but be amazed at how poor even the best evidence of young earth is. I’ve been collecting sources to provide provide responses to these top evidences lists and this article is just what was needed for this particular argument.
What amazes me is how many of them show a complete disregard for the most basic principles of measurement and mathematics. It’s very common to see them presenting uncertainties of just a few percent as evidence of six orders of magnitude of systematic error.
If you applied that kind of thinking to any other area of science, you would kill people.
Thank you for the discussion of spiral arms and the logic used.
As I think about this, problems 1 and 3 seem like variations of confirmation bias. Which is starting to look like a basic feature of our mental landscape.
I grew up reading YEC literature and overcoming this required a deliberate choice to drill down to foundational assumptions and take a look. What made that possible was a fairly broad undergraduate education in math, science, and history. I asked the question, what can I direcely observe in the present world that rules out or confirms the age of the earth at less than 10,000 years? Evidence is not that difficult to find, even for an educated layperson. It doesn’t get you to an ancient universe but it does rule out the time scale of YEC.
But the evidence was extremely difficult to digest. What I found extremely helpful at that point was exposure to Augustine, which showed me it was possible for an orthodox Christian to think differently about Genesis 1. What I really needed to abandon YEC was an escape hatch. Augustine provided that. And there are different authors may resonate better for others. Augustine’s Literal Interpretation of Genesis is frankly hard to read.
It is difficult to overcome confirmation bias when locked in a false choice between YEC and “godless Darwinism.”
Thank you for a great article Casper. It is interesting how even on a cosmic scale, the “God of the gaps” type arguments arise and fall.
Standard counter: “But dark matter hasn’t been seen! It’s just a ‘tweak’ added to make the numbers look right!”
And standard reply: “The presence of such mass was deduced not just from models of spiral galaxies but also from the gravitational lensing of light from sources behind galaxies and clusters. These measurements demonstrated the presence of mass far in excess of the visible parts of clusters. There are additional measurements that confirm the presence of dark matter via other detection modalities.”
Yes, good point, I have anticipated such responses by pointing out in the article that dark matter was introduced for reasons completely independent from galactic spiral arms. Gravitational lensing is one example, and I give two other examples in the footnote. These do not give us the freedom to “tweak” the amount of dark matter. So the observation that dark matter also helps form and stabilize spiral arms in simulations is actually an interesting achievement of the standard model.
Fun fact: AiG now thinks it might be real- https://answersingenesis.org/astronomy/cosmology/case-for-dark-matter/. That article is actually a pretty well written article on why we are convinced of its reality despite it being not visible directly through electromagnetic radiation. He even exhorts Christians to get on board with it, since it is not ‘historical science.’ Nevermind the fact that all the evidence for it is historical science and he goes to great lengths to explain why the historical science is legitimate.
Hahaha. I like the part in the AiG article about ‘historical science’. So very much compartmentalization is required for a scientist to accept such a distinction.
On a ‘tangential’ subject to whirling galaxies, I remember reading about the challenges associated with explaining the rotational momentum of galaxies and how cosmologists weren’t sure what the answer to that was. I don’t recall how many years ago I read the article, and as you can see, I’m not recalling the details. But can anybody shed light on the “conservation of rotational momentum” challenge, and elaborate as to if cosmologists have since settled on plausible explanations?
I guess it is (or was?) known as the “Angular momentum problem”, at least as titled in this 2009 paper.
So, just to help me visualize things a bit better, the “spinning arms” of a spiral galaxy really are not spinning stars that circle the center of the galaxy, but rather stars that are born and burn out in what we see as arms, but are actually gravity waves of some sort, sort of like a bay filled with bio-luminous organisms, stimulated by passing waves? Or is that off base?
I think that paper covers the angular momentum problem for galaxies pretty well.
Anything that collapses has to get rid of rotational energy, because small initial rotations become more intense during collapse and start to counteract the collapse. This holds for proto-galactic clouds (to become galaxies), proto-stellar clouds (to become stars), and proto-planetary clouds (to become planets). There are different solutions for these different scales, but it boils down to radiating away the energy one way or another. It is an interesting exercise to determine “how” exactly energy is radiated away, but it does not cause sleepless nights for astronomers because more realistic models are leading to better solutions all the time. For example, in the paper you linked to, the authors took into account how exploding stars (supernovae) help to diffuse energy and that led to improved results.
Not sure whether that answers your question, but that’s about all I can tell you.
The spiral arms start as density waves in the galactic disc, caused by gravitational effects (watch out: not to be confused with “gravitational waves”, which are ripples in spacetime itself, something totally different!). A local increase in density tends to attract more mass (mostly in the form of gas and dust clouds, but also already formed stars), further increasing the density. That increased density spurs on the formation of new stars, which are very bright and blue of color, which is why spiral arms are generally bright and blue (seen in the picture). However, in simulations these stars don’t usually “die” in the spiral arm where they are born. Instead, they move on and travel ahead of the spiral arms, just as cars manage to leave behind the traffic jam on the highway at some point. Hope that helps to make sense of it.
Change and Time in Genesis
Thanks for the explanation. The more you learn, the more amazing it all becomes.
I’m fascinated by the work you mention on computer simulations. In the early 1970s I was a research assistant at NRAO. Computers in those days were enormous mainframes, and CRTs (some with the capability of showing as many as 16 colors) were only just beginning to be used to interface with them. (The programs I wrote for the staff astronomers were all submitted on punched cards.)
My memory is certainly faded, so don’t bet the ranch on this, but I seem to recall that one or two of the astronomers were messing around with simulations to see how star clusters and galaxies might possibly form as a result of gravitational interaction. I think the number of “stars” (i.e., mathematical points in the program) was limited to just a few hundred, since the machines couldn’t do more than that without blowing up, but the results were pretty interesting to watch.
Thank you for sharing this, Ted. I love to hear stories that bring into perspective the scientific and technological developments of the past decades. It helps me to appreciate how amazing the opportunities are that we have nowadays in science.
This is a tangent, but I am also looking forward to the kinds of stories that might be told another few decades from now. Me and my younger brother differ just six years in age but it already seems like we grew up in different worlds. I still remember how we used the phone cable to get a few minutes of internet, while my brother has grown up with WiFi everywhere.
Thanks Casper. To be honest, I didn’t read the paper I linked to (but just used it to recall the name given to the challenge.) I should probably do that, though many other matters also vie for my attention right now.
Meanwhile I remember being impressed by having read a similar paper years ago that used this very explanation (collapse and then the counter-effect of greater angular velocity) to explain the flat disk shape of galaxies. I.e. galactic matter ejected from such a spinning system would tend to take on planar features. It made so much sense to me at the time, but from what you say about how the spiral arms themselves are explained, I may need to modify my mental model for how this works. Is it still true to say that our sun does have a somwhat stable orbital velocity around the galactic hub?