Ask Ethan: Why doesn’t radiation dominate the Universe?

<p>Today, our Universe is filled with stars and galaxies, and is not only expanding, but the Universe&rsquo;s expansion is accelerating. If we were to break up the Universe into the different types of energy that compose it, we&rsquo;d find that it was dominated by dark energy, which makes up 68% of the Universe&rsquo;s energy density. Next would be dark matter, as it composes some 27% of the Universe&rsquo;s energy density, followed by normal matter (protons, neutrons, and electrons), that makes up about 4.9% of all that&rsquo;s out there. The other 0.1%? That&rsquo;s made of things like neutrinos and photons, where all photons and the fastest-moving neutrinos both behave as forms of radiation.</p> <p><a href="https://medium.com/starts-with-a-bang/ask-ethan-why-doesnt-radiation-dominate-the-universe-41c9a2975875"><strong>Read More</strong></a></p>