The Milky Way Galaxy (and thus the Sun and the Earth) originated in a locally ov
ID: 118161 • Letter: T
Question
The Milky Way Galaxy (and thus the Sun and the Earth) originated in a locally overdense region that would correspond to a hot spot in the CMB for some alien astronomer far away from us. Let's assume we are exactly in nse region the center of this local overde (a) At the time of CMB decoupling, how far away (in physical dis- tance) from the point that would eventually become the Earth was the edge of our local "hot patch?" (b) Today, how far away is the edge of our local overdense CMB r gion! (c) How far away would the alien astronomer have to be in order to see the CMB photons that were emitted by the atoms that would go on to form the EarthExplanation / Answer
b) CMB (Cosmic Microwave Background Radiation) is an electromagnetic radiation region, left over in the sky in early stage of Big Bang cosmology that is seen in microwaves which can be found to be unusually large and cold. It is approx 70 µK colder than average CMB temperature (approximately 2.7 K). It covers a larg region of the universe, roughly 150 to 300 Mpc or 500 million to one billion light-years across and it is 6 to 10 billion light years away.