Why are only hydrogen and helium created

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Discussion Overview

The discussion revolves around the question of why only hydrogen and helium were primarily created during the Big Bang, with some participants exploring the conditions that limited the formation of heavier elements. The scope includes theoretical aspects of nucleosynthesis and the processes involved in element formation in the early universe.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that the Big Bang primarily produced hydrogen and helium, questioning whether time constraints or other factors contributed to the absence of heavier elements.
  • Another participant mentions that a small amount of lithium was also created, but highlights that beryllium cannot be formed through fusion of lithium with hydrogen or helium due to instability.
  • It is proposed that the next sustainable fusion reaction after lithium involves the fusion of three helium nuclei to form one carbon nucleus, which occurs in stars under specific conditions of high temperature and density.
  • One participant states that the universe cooled too quickly for nucleosynthesis to continue beyond about 20 minutes after the Big Bang, making the formation of heavier elements a longer and more complex process.

Areas of Agreement / Disagreement

Participants generally agree on the primary elements formed during the Big Bang and the limitations on creating heavier elements, but there are nuances regarding the processes and conditions involved that remain open for further exploration.

Contextual Notes

The discussion does not resolve the complexities of nucleosynthesis or the specific conditions required for the formation of heavier elements, leaving some assumptions and dependencies on definitions unaddressed.

david2
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in the beginning the big bang only created hydrogen and helium.

why is that?

was there just not enough time to create heavier elements or is there another reason?

thx.
 
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A small amount of Lithium as well.
The problem after that is the next element, Beryllium, cannot be made by fusion of Lithium with Hydrogen or Helium.
(If it did happen, that would be an unstable isotope which would quickly decay back to lighter elements)
After Lithium, the next sustainable fusion reaction is fusion of 3x Helium to 1 Carbon.
This occurs in stars, which have a stable high temperature and density in the core, and it is a more lengthy process than H to He,.
Immediately after the big bang conditions were not like that, the Universe was rapidly expanding and temperature falling.
https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
 
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thank you very much for the answer.

I will dive into the info you gave me.

cheers
 
david2 said:
in the beginning the big bang only created hydrogen and helium.

why is that?

was there just not enough time to create heavier elements or is there another reason?

thx.
Yes. The universe became too cool for nucleosynthesis after only about 20 minutes. It takes much longer to fuse heavier elements, as they need long chains of sequential reactions to produce. So elements heavier than helium were only produced in trace quantities.
 
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kimbyd said:
after only about 20 minutes

wow, that is very very short.
 

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