The distinction between the big bang model and a black hole
India Daily Technology Team
Jun. 13, 2006

The standard big bang models are the Friedmann-Robertson-Walker (FRW) solutions of the gravitational field equations of general relativity. These can describe open or closed universes. All these FRW universes have a singularity at the origin of time which represents the big bang. Black holes also have singularities. Furthermore, in the case of a closed universe no light can escape which is just the common definition of a black hole. So what is the difference?

The first clear difference is that the big bang singularity of the FRW models lies in the past of all events in the universe, whereas the singularity of a black hole lies in the future. The big bang is therefore more like a white hole which is the time reversal of a black hole. According to classical general relativity white holes should not exist since they cannot be created for the same (time-reversed) reasons that black holes cannot be destroyed. This might not apply if they always existed.

But the standard FRW big bang models are also different from a white hole. A white hole has an event horizon which is the reverse of a black hole event horizon. Nothing can pass into this horizon just as nothing can escape from a black hole horizon. Roughly speaking, this is the definition of a white hole. Notice that it would have been easy to show that the FRW model is different from a standard black or white hole solution such as the static Schwarzschild solutions or rotation Kerr solutions, but it is more difficult to demonstrate the difference from a more general black or white hole. The real difference is that the FRW models do not have the same type of event horizon as a white or black hole. Outside a white hole event horizon there are world lines which can be traced back into the past indefinitely without ever meeting the white hole singularity whereas in a FRW cosmology all worldline originate at the singularity.

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India Daily Technology Team
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