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Welcome to our Physics lesson on Cosmic Radiation, this is the sixth lesson of our suite of physics lessons covering the topic of Chronology of the Universe, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
Prior to 1965, no information existed about cosmic radiation. This phenomenon was discovered accidentally, when a group of astronomers were studying the radio waves incident from the sky through an antenna. They detected a continuous disturbance that interfered with regular waves. After several measurements made to this disturbance, it resulted that it belonged to a continuous EM signal of cosmic origin uniformly incident on Earth from all directions. Measurements made for several wavelengths of this radiation produced a similar curve to that of black body radiation at T = 2.73 K.
After further investigations, it resulted that despite this radiation detected from antennas moves freely in interstellar space, it had once been in close thermal contact with matter. Otherwise, a similar curve to black body radiation cannot be explained. Hence, the only possibility is that this radiation must be the cosmic radiation produced at t = 1013 s after the Big Bang as predicted by this model.
The initial temperature of cosmic radiation must have been 3000 K at the moment of its detachment from matter. However, its temperature has dropped with the increase in the volume of the Universe, as the distance between hot bodies increased with time. Now, after approximately 13.7 billion years, the temperature of cosmic radiation has dropped to 2.73 K.
Since the existence of cosmic radiation confirms the veracity of the Big Bang model, it is clear that the Universe must also contain the neutrinos and antineutrinos distributed uniformly throughout Space, as predicted by this model. Their temperature is believed to be T = 2 K, but the experimental of such elementary particles is very difficult as their interaction with matter is very weak, as explained earlier, and it does not leave any trace in laboratory equipment.
What is the wavelength corresponding to the highest point of the cosmic radiation curve?
From the Wien's Law
where b = 2.898 × 10-3 m · K is the Wien's constant, λm is the characteristic wavelength of black body at temperature T (here, T = 2.73 K), after substitutions we obtain for the characteristic wavelength of cosmic radiation
This wavelength belongs to microwaves EM spectrum.
You have reached the end of Physics lesson 22.11.6 Cosmic Radiation. There are 6 lessons in this physics tutorial covering Chronology of the Universe, you can access all the lessons from this tutorial below.
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