Black hole singularty definable In 3D space?

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The discussion centers on whether the singularity at the center of a black hole can be defined in 3D space, with some arguing that it cannot due to the collapse of space-time at that point. It is emphasized that "singularity" is not a physical entity but rather a mathematical construct where conventional laws of physics break down. The notion that our universe might not be fully describable in three dimensions is challenged, suggesting that we simply need to acknowledge the limitations of our current understanding of gravity. Participants highlight the necessity for a more accurate theory of gravity to explore conditions within singularities. Ultimately, the conversation underscores the complexities of defining singularities within the framework of known physics.
nospoon2016
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Since the center of a black hole is defined as a singularity and space-time collapses at that point (assumption) is it possible to define this point in 3D coordinates? In other words, is it possible that our universe can not be described as a 3D space but rather as a space with 2.99... dimensions?
 
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nospoon2016 said:
Since the center of a black hole is defined as a singularity and space-time collapses at that point (assumption) is it possible to define this point in 3D coordinates? In other words, is it possible that our universe can not be described as a 3D space but rather as a space with 2.99... dimensions?
You are making the mistake of thinking that "singularity" is physical. It is not. In the context of physics "singularity" generally mean "the place where the math mode gives non-physical results and thus does not actually tells us what is going on".
 
I wondered about this because the following is stated on https://en.wikipedia.org/wiki/Gravitational_singularity : "The laws of normal spacetime could not exist within a singularity" and therefore this suggest there is no coordinate system defined at that point/region, or if you like no 'normal' coordinate system. If so such region simply cannot be defined in our known 3 dimensions then our universe is not fully definable in 3D.
 
nospoon2016 said:
I wondered about this because the following is stated on https://en.wikipedia.org/wiki/Gravitational_singularity : "The laws of normal spacetime could not exist within a singularity" and therefore this suggest there is no coordinate system defined at that point/region, or if you like no 'normal' coordinate system. If so such region simply cannot be defined in our known 3 dimensions then our universe is not fully definable in 3D.
Well, no. It just means you have to draw a little circle around that point, say, "Here be dragons!" and then never try to infer anything about the universe by using what goes on inside that point. We would need a more accurate theory of gravity to say what does happen inside that region.
 
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nospoon2016 said:
I wondered about this because the following is stated on https://en.wikipedia.org/wiki/Gravitational_singularity : "The laws of normal spacetime could not exist within a singularity" and therefore this suggest ...
no, it does not suggest anything, really, because that would be making the same mistake you are making of taking "singularity" to be physical. As Chalnoth has also now pointed out to you, you cannot legitimately do that.
 
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
Why was the Hubble constant assumed to be decreasing and slowing down (decelerating) the expansion rate of the Universe, while at the same time Dark Energy is presumably accelerating the expansion? And to thicken the plot. recent news from NASA indicates that the Hubble constant is now increasing. Can you clarify this enigma? Also., if the Hubble constant eventually decreases, why is there a lower limit to its value?
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