Assume an eternal, static black hole which has an event horizon, a spherical surface at which any object passes a point of no return and is condemned to move toward a mathematical singularity.(adsbygoogle = window.adsbygoogle || []).push({});

One of the predictions of being inside a black hole is that every spatial direction points towards the singularity. If you had a beacon that emitted photons in all directions, they would all head towards the singularity. If they didn't, they would be violating the law of causality, which would prohibit them from travelling backwards towards the event horizon. Essentially, something would have to travel backwards in time to reach and escape the event horizon.

Consider objects with mass that cannot travel at the speed of light/causality. How would they behave inside this strange universe inside a black hole? Perhaps a mass may tend to accelerate towards the singularity, since that is the behaviour of gravity. However, in this universe inside a black hole, every direction points towards the singularity. Every observable bit of matter would tend to accelerate towards it, such that it may give the appearance, from a given observation point, that everything else is accelerating away from that point, as if space itself were expanding as time moved forward.

Another prediction of the space time geometry within the event horizon of an eternal black hole is that time and space switch roles. One hint that it behaves this way is that it would require the apparently impossible task of moving backwards in time to travel back to the event horizon. Another hint is that the singularity cannot be observed, it exists only in the future, any direct observation of it would require photons/matter moving away from singularity towards the event horizon which violates the law of causality and also require moving backwards in time. The direction of time flows from the event horizon towards the singularity, while a dimension of space (if frozen in time) flows towards the infinite future from the infinite past of an eternal black hole, at least as imagined from the universe on the other side of the event horizon. The derivation of this concept may be difficult to comprehend, but it is reflected in a Penrose diagram of space time inside an eternal static black hole.

If time and space have switched roles, then this may imply that the event horizon, where matter and energy enter this black hole universe, appears to be an event rather than a location. It may appear as if everything in this universe came into existence at the time of this event and began accelerating towards the singularity, which happens to be in every possible direction. It may appear as if a big bang happened.

These imagined observations inside a black hole may seem very strange, however it seems as if it is coincidental to what is observed in our own universe.

I am just a layman, and admittedly my understanding of black hole space time geometry may be rudimentary compared to a professional astrophysicist. But I would like to hear about how I may have gone wrong in this interpretation.

References: Hawking, Stephen & Ellis, G. F. R. (1973).The Large Scale Structure of Space-Time. Cambridge: Cambridge University Press. ISBN 0-521-09906-4. Chapter 5.

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# B An Interpretation of the Geometry of Space-Time Inside a BH

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