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WMAP image of the Cosmic Microwave Background Radiation
When the Big Bang Theory was first introduced it was met head on by supporters of the Steady State Theory. In the 50′s and 60′s, these two were the most well-supported cosmological models. The Big Bang only gained a clear upper hand after the discovery of the cosmic microwave background radiation or CMBR in the late 60′s.
The CMBR is a detectable electromagnetic radiation found to have approximately similar strengths and coming from all directions. This observation can only be explained in the Big Bang model.
According to the Big Bang, photons that were once confined were able to propagate when the Universe’s temperature was cool enough to allow the formation of atoms. Prior to this stage, the photons swam in a very hot stew of tiny particles that included baryons and electrons.
In this hot stew, the photons constantly interacted with the electrons through Thomson scattering. And because of this constant scattering, the photons could not propagate away and hence the Universe is said to have been opaque.
Remember that in the Big Bang model, you had a very hot and very dense universe that expanded (and continuous to expand), cooling itself in the process. Thus, when the Universe reached temperatures suitable enough, the free electrons combined with nuclides to form atoms. Only then did the scatterings cease and the photons (a.k.a. electromagnetic radiation) were free to propagate. This period is known as the ‘epoch of last scattering’.
At first, this electromagnetic radiation had high energies and short wavelengths. But as the Universe expanded, the radiation red shifted. Red shifting is a term that denotes an increase in wavelength. Eventually, in our time, it reached wavelengths within the microwave band; hence the word ‘microwave’ in CMBR.
Electromagnetic radiation can be detected. In fact, in the case of visible light, it can be ‘seen’. Thus, various kinds of electromagnetic radiation has allowed us to peer into space and observe galaxies, stars, superclusters and many others.
Now, if you recall, there was a time when electromagnetic radiation was not able to propagate. In other words, nothing could be detected now that comes from that period. Theoretical physicists are never daunted with things they cannot detect and are able to explain what may have happened then.
However, as they move even farther back, they are faced with what is known as a singularity, where energy is infinite and volume is zero. In these conditions, the laws of physics simply breaks down and even the hardiest theoretical physicist has to admit that he’s hit a blank wall.
We’ve got a few articles that touch on the origin of the universe here in Universe Today. Here are two of them:
NASA also has some more:
Tired eyes? Let your ears help you learn for a change. Here are some episodes from Astronomy Cast that just might suit your taste:
- The End of the Universe Part 2: The End of Everything
- Questions on the Size, Shape and Centre of the Universe
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