24. Expansion of the Universe - Hubble’s law. What is cosmic microwave background radiation? (3p.) Flashcards
Hubbles Law
Hubble announced that almost all galaxies appeared to be moving away from us. In fact, he found that the universe was expanding - with all of the galaxies moving away from each other. This phenomenon was observed as a redshift of a galaxy’s spectrum. This redshift appeared to be larger for faint, presumably further, galaxies. Hence, the farther a galaxy, the faster it is receding from Earth.
The velocity of a galaxy could be expressed mathematically as 𝑣 = 𝐻𝑑 where v is the galaxy’s radial outward velocity, d is the galaxy’s distance from Earth, and H is the constant of proportionality called the Hubble constant.
What is cosmic microwave background radiation?
The cosmic microwave background (CMB) is thought to be leftover radiation from the Big Bang, or the time when the universe began. As the theory goes, when the universe was born it underwent a rapid inflation and expansion. The CMB represents the heat left over from the Big Bang.
When this cosmic background light was released billions of years ago, it was as hot and bright as the surface of a star. The expansion of the universe, however, has stretched space by a factor of a thousand since then. The wavelength of the light has stretched with it into the microwave part of the electromagnetic spectrum, and the CMB has cooled to its present-day temperature, something the glorified thermometers known as radio telescopes register at about 2.73K degrees above absolute zero.
