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Comment by skj | Hacker News Reader

"Both teams took advantage of a phenomenon called the Sunyaev-Zel’dovich effect that occurs when light left over from the big bang passes through hot gas."

That just seems unreal to me.

Edit: To clarify, I'm not accusing it of being made up. I just think it's amazing.

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They can tell that the big bang is the light source because of Hubble's Law[0]. In short, the universe itself (so space itself) expands[1], and it does so fast enough to create a Doppler effect in light, causing redshift[2].

When we look further out into space, we effectively look "back" into time because of the limit of the speed of light. The older the light, the more it has redshifted because the more space has expanded while it was travelling. So this redshift increases very predictably the further we look out into space and back into time.

As a result, when observing space we can say when light is left-over from the big bang, because we can tell the age of the light by how much its spectral lines have redshifted.

[0] https://en.wikipedia.org/wiki/Hubble%27s_law

[1] https://www.youtube.com/watch?v=_llA2q1rlSg

[2] https://en.wikipedia.org/wiki/Redshift

Just as a heads up, if you ever read stuff about the 'Cosmic Microwave Background' or 'Cosmic Background Radiation', that's the 'light left over from the big bang' bit.

Yeah, totally. The other mindblowing thing is that since photons are moving at the speed of light, thus time for them pretty much stands still.

Thus, if a photon was created at the moment of the big bang and happens to "bump" into something else today then from the standpoint of the photon, it only "lived" for an instant.

(based on my level of physics understanding, so please do correct me if I'm wrong, thanks)

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