The Origin of Chemical Elements (Alpher, Bethe and Gamow, 1948)

Ah, the famous alpha-beta-gamma paper.

Our first post-war paper which tried to address the question of “Where did all this stuff come from”?

This paper uses the discovery by Hubble and others that the universe appears to be expanding, and as things expand they cool down. So if we run the history of the universe in reverse, what do we get? What was the preferred model for the origin of the universe when this paper was published? Who is Fred Hoyle?

This paper is not perfect in its assumptions, but from a simple model predicts much of the abundance of the elements that we observe. Spend some time looking at the two equations, and the one graph.

Where does the graph err?

What do the two equations represent?

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10 Responses to “The Origin of Chemical Elements (Alpher, Bethe and Gamow, 1948)”

  1. Kevin Greenwood Says:

    For a paper as groundbreaking as this, I think it’s pretty fantastic for Gamow to add Bethe as an author solely for pun appeal. The concepts put out in this paper were difficult for me to understand until I realized I was thinking on the wrong timescale. As I understand it, Alpher states that it took (according to the second equation) around 20 seconds from time-zero of the big bang for the neutron gas to expand and cool enough for beta decay to occur, and thus beginning the building up process of the elements. The fact that there is a time-zero where temperature was too high for aggregation (strong nuclear force?) to occur sent Fred Hoyle into a fit and caused him to sarcastically mock the “Big Bang” on BBC radio, essentially shooting himself in the foot by naming the theory that would overshadow his steady-state model. Despite that though, it was Hoyle’s work on nucleosynthesis in stars that adequately explains the abundance and formation of heavier elements that are lacking in this paper.
    As shown in curve, the very early universe would have been rich in light elements, helium and hydrogen being most abundant. The log curve more or less stays above 0 up until elements with a mass of 60, and then steadily declines down to elements with atomic mass of 100 and levels out from there. Alpher (citing Hughes) attributes this to the neutron capture cross sections of the newly-formed nuclei. While small nucleui during this time would be incredibly abundant, as larger and larger nuclei formed, wouldn’t their cross-sections, being larger, be much more likely to capture neutrons? Deuterium, being twice as large as a sole proton, is twice as likely to hit a neutron, but wouldn’t something like Iodine, being much, much bigger, be far more likely to capture more neutrons? In a sea of small particles, the big agglomerates, just by being big, should be soaking up neutrons and alpha particles, unless f(t) in the first equation is large. Does that sound right?

  2. Hunter Burgin Says:

    I must say that I really enjoyed this paper for a number of reasons. For one, it was without a doubt one of the most groundbreaking papers from the 20th century, cosmologically speaking in helping us understand how everything around us came “to be”. I also really enjoyed this paper because it was developed to a large extent by a Ph.D grad student as his dissertation, proving that at any time a hard working student can make groundbreaking strides in the world of science.
    As I am sure we are all aware, the topic of Big Bang Nucleosynthesis is very complicated and is made accessible with secondary texts from the Internet and beyond. During my research I came across a couple sources that helped outline the exact series of events that took place during the five chaotic minutes of the universe’s birth. Beginning from nothing, there were high energy quarks that collided with one another until eventually forming protons, neutrons, and electrons and so on until we had what we basically see today in just under five minutes time. My research led me to wonder what, if anything, happened before the Big Bang? I came across several theories for the universe’s termination such as the Big Crunch, Big Squeeze, and Big Rip which led me to wonder if one of these had occurred prior to OUR Big Bang and if the universe is just a cyclical being expanding and imploding on itself continuously without our knowledge due to our, relatively speaking, short time in existence. I wonder if this is a question that we can ever truly solve because in order to find the answer we would have to peer into a time before time existed.

    • profhurst Says:

      Good discussion and lots of broad ranging ideas, although we should focus on the paper itself. As for what comes before the big bang is akin to asking “What’s north of the north pole…”

  3. Porter Marsh Says:

    Though he coined the term, Fred Hoyle actually objected to the idea of a big bang. The idea of the universe existing in equilibrium “seemed attractive, especially when taken in conjunction with aesthetic objections to the creation of the universe in the remote past. For it is against the spirit of scientific enquiry to regard observable effects as arising from “causes unknown to science”, and this in principle is what creation-in-the-past implies.”
    My question is: what about the creation of the universe being in the past is a cause unknown to science? If the universe had no beginning and exists in equilibrium would that not be a cause unknown to science?

  4. Josh Ellsworth Says:

    Given that the authors acknowledge that their model requires that the universe is expanding out from a singularity, it seems counter intuitive that they propose the manufacture of all of the elements in the brief period of time wherein temperatures and density were appropriate for fusion. Obviously it’s easy to criticize given what we know now, but it seems to me that they propose increasingly unlikely collisions occur (over and over again, yielding an ordered pattern of products) given the extreme rates of expansion and cooling that would occur after t=20 seconds. Also, given that alpha particles were well known as stable pieces of nuclear breakdown, as well as products of the CNO cycle, why didn’t the authors think to use them as building blocks, especially given the abundance of elements with nucleons made of of multiples of alpha particles? The assumption that neutron capture cross sections was more important than intrinsic stability may have blinded them to this possibility, even though the huge abundance of Hydrogen and Helium in the universe and in stars screams otherwise.
    I found it interesting that Hoyle was spot on about stellar nucleosynthesis but could not come to terms with the notion of a singularity. His notion of matter being generated essentially as stellar flux (probably not the best analogy) is interesting, though one wonders how he thought that to be more plausible than a big bang.

  5. Adam Settimo Says:

    Alpha, Beta, and Gamma! This paper brings together a lot of views, both supporting and not. One thing is certain. While this paper is only about a page, its just the tip of the iceberg when it comes to the time and endless, exciting and interesting, internet searching it can create. Along those notes, Hoyle is an interesting character. I’m not sure if what I read was true, but the term, “Big Bang,” being accidentally coined by him is ironic, and very entertaining, considering his adamant proclivity to their Steady State Theory.
    I also would like to bring up the whole Hubble/Lemaitre foul up. I found lots of sources saying that his paper came out a couple years before. That he first proposed the expansion of the universe, the big bang theory (hypothesis of the primeval atom), Hubble’s constant,…
    Any thoughts on this?
    My personal question about the article specifically, comes from the top of the second column where it is stated that the building up process was completed while the neutron gas was “rather high.” Is this implying that the creation on heavier elements were also within the first few minutes of the big bang?

  6. Tony J Says:

    This article fascinates me. It was interesting to read up on Hoyle and how he opposed the big bang (amongst other popular theories e.i. life originating in space). I like the graph they provided about relative abundance but I’m not sure where they came up with the calculated curve. Is it just a best fit line? Also I’m having trouble comprehending the first equation. Can anyone help me out there? Oh wait never mind equation one is the calculated curve. Right?

    It’s also very fascinating to think of the universe as having angular momentum. I had not heard this before this paper. Is it still spinning? Probs.

  7. Daniel Begay Says:

    It took a lot to wrap my head around this article. And I still cannot fathom the idea of the how they came up with these question to ask or even to get started on the idea of the origins of the elements. Another interesting point, in their postwar time, after they unlocked this nuclear technology and weren’t busy trying to race to build the best nuclear bomb, they were able to focus on finding out the origins of the elements. It shows that the current events of the time, do play a huge role in the advancement in science.

    My questions:
    The second question shows that they observed the density at t0=20 sec, did they mean to say that when you look at t0=0 sec, the numerical value for density was so high, that it’s not possible to observe it? And based on there equation at t=0, what did the authors of the paper imagine what was happening at that time?

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