- 4136 - COSMIC MICROWAVE BACKGROUND - The cosmic microwave background radiation (CMB Radiation) verifies the fact that the universe is expanding. This is one of the most profound discoveries of the 20th century. This means that the universe was much smaller, denser, and hotter in the distant past.
-------------- 4136 - COSMIC MICROWAVE BACKGROUND
- At such high density and temperature, the
universe was in the plasma state, and matter and radiation were in thermal
equilibrium. Nothing could coagulate to form even the atoms or molecules of
matter that we see today.
-
- Then, the universe expanded and both matter
and radiation cooled. Today, the predicted age of the universe is 13.7 billion
years. After the initial 400,000 years, something amazing happened in the
universe.
-
- With a map of CMB, measured by the Wilkinson
Microwave Anisotropy Probe (WMAP), a space-based microwave telescope for
studying the CMB, we learned an enormous amount about the evolution and
composition of the universe.
-
- In 1965, Bell Lab’s Radio astronomers- Arno
Penzias and Robert Wilson were trying to map signals from the milky way. While
calibrating the horn radio antenna (designed to track the satellite echo), they
detected a constant noise. This noise was due to radiation that was strongest
in the microwave region of the radio spectrum. The radiation was unaffected by
the antenna direction and was of cosmic origin. It is now called the “cosmic
microwave background” (CMB) radiation.
-
- The CMB radiation has a temperature of 2.7
Kelvin and its spectrum is a thermal black body curve. Since birth 13.7 billion
years ago, the universe is continuously expanding and cooling.
-
- After 400,000 years from the start of the
universe, it cooled down to a temperature of 3,000 degrees Celsius. At this
point, the simplest atoms formed in the universe and the matter decoupled from
the radiation. The light from this time has been traveling through space ever
since. This is what gives us the cosmic background radiation.
-
- The CMB radiation can be detected all around
us from here on Earth or in space. It is like we can measure the afterglow of
the Big Bang. Instead of seeing the afterglow at 3,000 degrees, today we see it
just at -270 degrees Celsius (3 Kelvin). This is due to the reason that the
universe has stretched, which makes it appear much cooler.
-
- Before the decoupling of matter and
radiation, the universe was extremely dense and hot that it was actually opaque
to all radiation. After the decoupling, it transitioned from an opaque to a
transparent state. The residual radiation of that stage of the universe is what
we call as the CMB radiation now.
-
- In 1992, a satellite named COBE measured
the CMB over the whole sky. COBE has established that CMB is almost completely
uniform, with an almost constant temperature over the whole sky. But then the
question arises that if the universe was so uniform, how were the different
structures such as stars and planets were formed?
-
- Because the CMB radiation is not completely
constant. There were tiny fluctuations, or ripples, in the temperature, at the
level of just one part in 100,000. CMB radiation is evidence of the Big Bang
origin of the universe. Even today, the investigation of the CMB radiation
gives crucial insights to the beginning, expansion, and the various occurring
phenomena in the universe.
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August 31, 2023 COSMIC
MICROWAVE BACKGROUND 4136
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