2004/10/13 | 宇宙背景辐射[Cosmic Background Radiation]
类别(Ω〖物理〗) | 评论(0) | 阅读(55) | 发表于 13:15
The redshifted radiation from the Big Bang which is observed to be nearly isotropic.It was first unambiguously detected by Penzias(1979) and Robert Wilson(1979) in the microwave at a brightness temperatureof K.However, evidence for a 3 K background had been seen in the optical and submillimeter by noting excitation of CN rotation states at 3874 Å and 1.32 mm.The temperature require to produce the observed excitation was K. The COBE satellite measured the temperature to be 2.735 K ± 12 K, with variations of ± 30 K.
The temperature of the CBR as time progresses can be computed starting from the equation of free-streaming photons,
(1)

(2)

(3)

(4)

(5)

(6)

(7)

Therefore, if the spectrum starts out as a blackbody spectrum, it will remain a blackbody spectrum, but will have temperature with
(8)

entropy is also conserved. Let a be the Stefan-Boltzmann constant.
(9)

(10)

(11)

If the pressure is small,, so
(12)

(13)

(14)

(15)

(16)

(17)

(18)
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