Exposing PseudoAstronomy

December 21, 2008

Creationist Claim: Spiral Galaxies “Wind Up” Too Fast for an Old Universe


In preparation for a few public lectures I’ll be doing in the next 6 months, I wanted to address another one of the three main (that I’ve see) straight-forward young-earth Creationist claims about astronomy that “prove” we live in a young universe: Spiral galaxies “wind themselves up too fast.”

This is actually the #1 claim in Russ Humphrey’s treatise on “Evidence for a Young World” that you can find on sites such as Answers in Genesis or the Institute for Creation Research (e.g., this link).

Note that the #2 reason presented is that comets would disintegrate too quickly (which I’ve addressed here) and the #5 claim (#3 astronomy claim) is that the Earth’s magnetic field is decaying too quickly, which I will address in a future blog post.

About Spiral Galaxies

Spiral galaxies, such as the one above (M101), are generally medium- to large-sized congregations of stars. They have either a bulge in the center or a bar in the center. The bulk of the galaxy is a disk (much wider than it is thick) that contains spiral arms. For more basic information on galaxies, see this link.

The feature in question in creationist circles is these subjectively beautiful spiral arms themselves. The trick is that these arms are not “solid.” It is not the case that stars either always exist within a spiral arm or they always exist outside of an arm. Rather, the arms are constantly picking up stars and losing others. What the arms represent are just density waves.

The common analogy to think of is cars on a highway. You may be driving along with many dozens or hundreds of meters between you and the car in front of you. Then, for no apparent reason, you start to get much closer to the car in front of you. And then, for the next several kilometers, there are only maybe five to ten meters between you and the car ahead of you. Afterwards, traffic seems to thin out again and there’s a large distance between you and the next car.

What you have just experienced is a density wave. You are a star, traveling the road that is an orbit around the galaxy, and every now-and-then you find yourself in a density wave where you have to slow down.

The mechanism that perpetuates the density waves – why they don’t just dissipate – is that as a star approaches a density wave, it will speed up slightly due to the gravity of the stars there. And as a star is about to leave a density wave, it will slow down a little, again because of the higher gravity there. So they won’t just smooth out over time.

How did the spiral arms get there in the first place? The main idea here is that all you need is a disk of stars. Stars closest to the center of the disk will need to rotate around it faster than those near the edge, just like planets in our solar system (Mercury’s velocity around the sun is much faster than Earth’s). This can easily set up the initial differential rotation needed to start them.

In addition to this, stars do not orbit on circular paths, rather on elliptical ones (Kepler’s first law). When farthest from the center, their velocity will be at its slowest (Kepler’s second law). When you have just a few extra stars traveling a little slower in some parts of a differentially rotating disk, then you will get spiral patterns.

The Creationist Claim

To quote from a source other than Russ Humphreys: “Stars closer to the center of a spiral galaxy orbit the galaxy faster than stars farther away. Over many millions of years, the difference in orbital rates should wind the spiral tighter and tighter. We do not see any evidence for this in galaxies of different ages.” (This is from the Creation Wiki website.)

Problems with the Creationist Claim

The problem with this is that it rests upon the unstated major premise that density waves are physical parts of galaxies that contain a set of stars that is unchanging. That way, the differential rotation will cause them to “wind up” into a featureless disk. As I have already explained above, this is simply not the case. Galaxies are not like figure skaters.

Another problem is a timescale here. Russ Humphreys may be correct when he places a maximum age of “a few hundred million years” on his fallacious understanding of the theory of spiral galaxies. However, many others, including the one quoted above, will say “many millions of years,” or even “thousands of years.”

Those time scales are way too short. The sun takes about 250 million years to orbit around the galaxy once (as anyone who watches Monty Python knows). There is no way that – even given their faulty understanding of the model – galaxies would “wind up” within less than 1% the time it takes a star half-way from the center (about where we are) to complete a single orbit. This is actually a fairly good example (like comets) about how creationists often don’t understand the timescales involved with astronomical phenomena.

Creationist Refutes of the “Naturalistic” Refutes

(1) To quote again from the Creation Wiki website, the very first response to the explanation I have given is, “First of all this is a theory not a proven fact.” This is, to put it nicely, a bogus argument. As I have stated many times on this blog, a scientific theory is when a hypothesis has withstood all attempts to falsify it, and all data are explained by it. So even them saying it’s a theory is an admission of that. However, “theory” is often used in a derogatory manner by creationists because the colloquial definition is more along the lines of, “a vague idea.”

(2) The next response is, “Furthermore, it does not come from first principles, but is simply the latest in a series of theories designed to save the long age theoretical system from reality.” Well, yes it does come from first principles. Try running a computer model of spiral galaxies, and you’ll see it work pretty darn well after only plugging in “first principles” like gravity.

The next part of that, “series of theories,” is not as derogatory as they intend. Science progresses. If one theory has explained all the data to-date but then the next piece it can’t explain, then a new theory needs to be developed. This, of course, is in contrast to creationism where evidence that refutes their “theory” is simply tossed out the door.

The final part of that sentence, “series of theories designed to save the long age theoretical system from reality,” is simply an attempt to paint what I’ve presented as an Argument from Final Consequences (logical fallacy) when it simply is not.

(3) The final claims, that observations of M51 have shown that the arms in the center don’t fit with this theory – is a misreading of the technical literature. The reference given (Zaritsky et al. (1993), “Inner spiral structure of the galaxy M51,” Nature, 364) clearly states:

The coherence of the arms over this large radial range challenges current theories of spiral structure. We suggest that a combination of several mechanisms, such as the interaction of M51 with the neighboring galaxy NGC5195, forcing by the central ‘bar’, or distortions from density waves, is required to generate the observed structure.

No where does it “[call] into serious question [the spiral density wave theory] by the
Hubble Space Telescope’s discovery of very detailed spiral structure
in the central hub of the ‘Whirlpool’ galaxy, M51,” to quote Humphreys. Rather, it states that just using a simple model that I laid out that you would get in an introductory astronomy class does not tell the whole story. It tells a lot of it. But you do need other information in order to explain every detail of the observations.

Final Thoughts

I think that with this post, I’ve fairly tidily explained why creationist arguments for a young universe based on spiral galaxies are fallacious, generally falling subject to a gross misunderstanding of the theories involved, the technical literature, and various other, smaller, factors.

I also want readers to remember that I am not trying to undermine religion. Faith in a divine creator is a completely separate issue. It is only when people use that faith as a starting point to make testable, scientific claims that I will explore them and refute them if fallacious enough.



  1. Great…Thank For Share This.

    Comment by Thiwa — November 18, 2009 @ 11:08 pm | Reply

  2. The very fact that you are able to debate this topic is anathema to “faith”, and regardless of who is right, I rejoice in the fact that the debate takes place at all. And that in a nutshell is my own personal bone to pick with those who choose blind literal translation of the bible over the gift of intellect that God has so generously given us. I can’t help but wonder if one of the missing commandments was something like: God gave you a brain to think with, SO USE IT. Oh wait, I forgot that the devil made me say that. *groan*

    Comment by Darvin — November 24, 2009 @ 9:44 am | Reply

  3. […] “Creationist Claim: Spiral Galaxies “Wind Up” Too Fast for an Old Universe.” Exposi… […]

    Pingback by Dark Canopy » Spiral Galaxies Have Atheists All Wound Up — January 27, 2011 @ 2:40 pm | Reply

  4. I guess you can also compare the density waves in spiral galaxies to a bathtub that drains. Although the water in the centre rotates much faster than those farther, you have a fairly constant spiral structure.

    Comment by Andrie — March 3, 2011 @ 8:23 pm | Reply

  5. […] because spiral arms are density waves, and don’t actually wind with the stars? This is consistent with the idea that astronomical time runs, or used to run, at […]

    Pingback by Some More Distant Galaxies « Eye on the ICR — November 30, 2011 @ 1:55 am | Reply

  6. […] non-issue that is galactic spiral arms is also irrelevant to the issue at hand, but it’s chucked in […]

    Pingback by No More Stars? « Eye on the ICR — December 4, 2012 @ 1:38 am | Reply

  7. I just want to share this:


    1. Galaxies wind themselves up too fast.
    Rotational speed of our Milky Way galaxy is so fast, if the galaxy is more than a few hundred million years old, it would be a featureless disc of stars instead of its present spiral shape.

    1. Galaxies don’t rotate that fast.

    The sun takes 250 million years to orbit the galaxy once.

    So 1 billion years, is only 4 orbits.

    It’d take more than 4 orbits to “wind up” a galaxy.

    So even 4 billion years is not enough.


    Galaxies would not be featureless discs after just a “few hundred million years.”

    Comment by LedFox — December 4, 2012 @ 7:58 am | Reply

  8. This argument is interesting, although incorrect because it neglects the universally-observed self-depreciation of wave energy to steady state when different waves overlap. Also, if stars simply run into density waves that are not at steady-state (that is to say uniform across the galaxy), then the density waves should be somewhat randomly distributed, but as we know from observation of spiral galaxies they are not; instead they form long ordered arms in the spiral. For example, barred spiral galaxies only have two arms without intermittent formation of arms in between them, which should be observed if stars are entering and leaving random density waves. This is not explained by random density waves, but is reasonably explained by gravitational interactions between the stars that form the arms, with the atractive forces holding them into bands (arms) and interact with the centrepital forces stars experience while rotating, resulting in the spiral shape we see. The author is correct that the arms are not solid, but negrects the gravitational forces that hold them losely together. Further, energy waves are self-depreciating with time; for example, when you aggitate water in a bathtub it will make waves, but the waves quickly conter each other and dissapate, ultimately coming to a stop (steady-state). Every time a star enters or leaves an energy wave it would slow that energy wave (i.e. reduce the total energy it has), eventually resulting in uniform star velocity for each distance from a star. If a star orbits a galaxy in 250 million years, then it has made ~40 rotations in 10 billion years, far more than would be necessary to achieve a sudo steasy-state (e.g. there would be very few if any non-dissapated energy waves), so energy waves should be negligable by that point. If spiral arms are indeed the result of density waves, then they can only exist because the density waves have not come close to steady state, which would happen in 40 rotations. We can even estimate how much this would be. Assuming 5% wave energy reduction per complete galaxy rotation, this means that after 10 billion years we have 95%^40 = 12.85% remaining variation in wave evergy, but if the galaxy is 15 billion years we have 95%^60 = 4.6% total remaining wave energy variation, which is not enough support the authors claim that arms are the sole result of density waves. With only ~4.6% remaining variation in wave evergy the galaxy would be much closer to a featureless disk than a spiral structure. Thus we see that, although interesting, this argument falls apart when compared to universally-observed wave interaction dynamics and basic mathematical back-of-the-envelope calculations…

    Comment by johnnytable94@gmail.com — January 16, 2015 @ 5:19 pm | Reply

  9. Just imagine what a spiral galaxy would look like if the universe were only six thousand years old. Except to mention Russell Humphreys’s idiotic white-hole theory, nothing further need be said.

    Comment by John M. — February 14, 2016 @ 12:20 am | Reply

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