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seeing the Big Bang [Q&A]


Rakshit of Vidyodaya Public School asks, if we see far back in time, 13.4 billion years, can we see the Big Bang, and if so, how?

This is a difficult question to answer because the premise is faulty. First, it supposes the existence of a location in space that can be pinpointed as the site of the Big Bang. The Big Bang was not an explosion of matter spreading out into space, it was the rapid stretching of space itself at all points in the Universe. Which means that every location in the Universe was the place where the Big Bang occurred, and we can’t really point our telescopes in a certain direction to see it.

Second, the Universe was opaque to photons for nearly 380 thousand years after the Big Bang. At that point, it became transparent to photons, and those photons have been continuously redshifted since then to now form what is called the Cosmic Microwave Background. The CMB photons form a near perfect blackbody spectrum of temperature 2.73 degrees K (subject only to anisotropies present in the Universe at the epoch of last scattering, when the temperature was ~3000 K), and this has been observed with microwave observatories such as COBE, WMAP, etc. But while this is an observation of the consequences of the Big Bang, it is not an observation of the instant of the formation of the Universe itself.