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Name: Jacob
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Question:
How was light created, going off of the Big Bang theory? I realize that several sub-atomic particles collided, but how did light become? Was light one of the particles that collided, or what?



Replies:
Hello Jacob,

Questions about the early universe are always interesting. The short answer is that as long as the universe has had energy, it has had light in one form or another. Many of the most common (especially in our every day circumstances) particle interactions involve particles of light. Light particles (photons) were certainly present in the early universe. This includes not just the narrow range of visible light, but photons of all energies including very, very high energy photons as well as low energy ones.

Light particles (photons) are different from other particles such as protons and electrons in a number of ways. One of those differences is that (within a few given rules) photons can be more easily created and destroyed than electrons, protons, and their ilk. In fact it is entirely possible to make photons through processes that do not make these other particles.

There is an interesting question related to light and the early universe that you might enjoy thinking about. When did the universe become "transparent?" In the early universe, things we very dense and very hot. As things cooled there was a point at which we had protons and neutrons forming nuclei, but those nuclei and the electrons still had too much energy to form atoms like we are used to seeing today (such as hydrogen and helium). There were lots of photons at this point too, but they would scatter around very strongly from all the electrons and nuclei, never really going anywhere in particular, just randomly being scattered and reflected about. In this respect the universe was a very "opaque" place. Once the universe cooled enough for the electrons and nuclei to form atoms this changed. The photons no longer strongly interacted with the more stable atoms and began proceeding through the universe in a more "unhampered" way and the universe became transparent to light. These photons are still traveling today and can be detected as the "cosmic microwave background radiation."

best wishes,

Michael S. Pierce



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