# Was there a singularity before the Big Bang or after it? [duplicate]

I am slightly confused. Some say that the initial state of the universe was a singularity, and some say that before the Big Bang; there was a singularity. Can anybody elucidate?

• It is meaningless to say "before the Big Bang" because space-time came into being at the Big Bang, so there was no time before that. Jan 15 '15 at 14:20
• No one can say whether or not the initial state of the universe was a singularity. The current theories are good backward to a point close to, but short of, where such a singularity might have occurred. (See @jwimberley answer.) What happened earlier than that no one can say. Many authors are a bit too loose with the language on this point. Even Stephen Hawking has expressed things in a way that can be misleading. Jan 15 '15 at 14:52
• Very relevant article that addresses this to some extent: profmattstrassler.com/2014/03/21/… Jan 15 '15 at 15:57

Different authors use different definitions of "Big Bang". One (the latter you refer to) is that the Big Bang only refers to the expansion of the universe from age $\epsilon$ to a while later, where $\epsilon$ is the earliest time for which the Big Bang theory has experimental/observational support (from nucleosynthesis, CMB, etc.). More formally, this usage restricts the "Big Bang" to refer to the period of expansion from a very small scale factor $a_{min}$ up to some larger scale factor - usually at recombination ($a_{max} = 0.001$). The actual "singularity" at $t=0$ is not the only possibility and does not have direct experimental/observational support.
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