Do black holes have singularities?
A new paper by Roy Kerr, the physicist behind the Kerr black hole solution in general relativity, argues that black holes in our universe likely do not contain true singularities, but instead reflect limits of our current theories. Commenters explore how this claim fits with the standard view that singularities signal where general relativity breaks down and quantum gravity must take over, and they contrast different mathematical notions of “singularity” (e.g., infinite curvature vs. incomplete geodesics). The thread branches into related issues such as the black hole information paradox, whether anything meaningful can be said about regions beyond the event horizon, and how time, space and tidal forces behave near and inside black holes.
Scope of Singularities in Black Holes
- Many commenters treat singularities as signs of theory breakdown, not physical infinities.
- Several note that classic singularity theorems actually use “geodesic incompleteness” (finite proper time worldlines that just end) as the definition of a singularity, not “infinite curvature.”
- The paper’s claim that certain rotating black hole solutions can be extended without curvature blow‑ups is seen as mathematically interesting, but some argue it doesn’t really overturn those theorems, which never guaranteed diverging curvature.
- Others emphasize that most physicists already expected quantum gravity to remove singularities; the new twist claimed is “no singularities even within pure GR” for particular setups.
GR, Quantum Effects, and Model Limits
- Strong consensus that GR is extremely successful but incomplete, especially at high curvature/short distances where quantum effects must matter.
- Gravity is described as non‑renormalizable in standard quantum field theory, motivating new approaches to quantum gravity.
- Several people stress that point particles and true infinities have a long history of causing divergences; discrete or field‑based descriptions are preferred.
What Happens at and Inside the Event Horizon
- Extensive clarification that infalling observers cross the horizon in finite proper time and notice nothing special locally, while distant observers see them slow and redshift due to spacetime curvature, not literally “freezing” there.
- Disagreement over whether collapsing matter or infalling objects “ever” reach the horizon or singularity from the external frame, especially once evaporation and time dilation are considered.
- Alternative interior pictures are discussed (e.g., horizon without true singularity, inner structures that later evaporate), but several commenters note stability problems and label some models physically implausible or “unclear.”
Information, Hawking Radiation, and Observability
- Black hole information paradox appears repeatedly: many argue that unitarity should force information to be encoded in Hawking radiation; others are skeptical or emphasize its extreme practical unrecoverability.
- Debate over whether Hawking radiation could ever tell us about interior spacetime vs. merely the quantum state of infalling matter.
- A long subthread wrestles with “falsifiability” and what it means to make claims about regions forever causally disconnected from us; some stress “if‑then” conditional reasoning (“if GR holds, then the interior has property X”) as still scientifically useful.
Conceptual and Pedagogical Issues
- Multiple analogies (stretchy fabric, onions, center‑of‑Earth gravity cancelation) are used, often with caveats about their limitations.
- Several comments push back on popular‑science oversimplifications: “frozen at the horizon,” “infinite gravity,” naive use of escape velocity, and confusing coordinate artifacts with physical effects.