ASTR 001 Lecture Notes - Lecture 20: Cosmological Principle, Cosmic Microwave Background, Bell Labs
Document Summary
The universe cools as it expands; the stretching of light results in a reduction of temperature (cid:894)thi(cid:374)k wie(cid:374)"s la(cid:449)(cid:895). If the universe is large, cool, and expanding today, it must have been smaller, warmer, and expanding in the past. If universe were: infinite, unchanging, everywhere the same. The universe is isotropic it looks the same in every direction. The universe is homogeneous each volume is about like every other volume. Large (cid:448)olu(cid:373)es of the sk(cid:455) i(cid:374) differe(cid:374)t dire(cid:272)tio(cid:374)s, (cid:1005)(cid:1004)(cid:1004)"s of mp(cid:272) in size, look about the same. The isotropic and homogeneous nature of the universe are often spoken of together as the cosmological principle. Basically, it says that the universe is more or less the same everywhere, and it looks more or less the same from any location. Two consequences: there is no preferred location (i. e. , a center) in the universe; and our own milky way (and sun and) is not in any particularly special place.
