A Philosopher Asked Physicists: ‘What is a Black Hole?’

By Korey Haynes | February 18, 2019 11:30 am
two holes in star-filled space

Physicists know what black holes are, but disagree on how to describe them. (Credit: SXS)

Ask a dozen physicists what a black hole is, and you may get a dozen different answers – at least if those physicists are from different sub-fields. But new philosophy research suggests that may be okay, and may even lead to more interesting findings for black holes in the future.

Such is the conclusion of Erik Curiel, who asked many different physicists across a range of research fields how they defined a black hole. Curiel works at the Munich Center for Mathematical Philosophy at Ludwig-Maximilians-Universitaet in Germany. Having studied both philosophy as well as theoretical physics, Curiel is well-suited to investigate, on its most basic level: What is a black hole?

Agree to Disagree

In his paper, published Jan. 8, in Nature Astronomy, Curiel notes that, “different communities in physics simply talk past each other,” when it comes to the definition of a black hole. They use definitions that apply to the questions within their field, but these definitions may not square with how other physicists see things.

For instance, Curiel finds that astrophysicists tend to use concrete terms to describe what a black hole is and how it acts. Astrophysicist Ramesh Narayan told Curiel, “A black hole is a compact body of mass greater than four solar masses…”

But scientists who study classical physics are more likely to venture into brain-bending explanations of what happens to time inside a black hole, with terms like “the boundary of the causal past of future null infinity,” wording laid down by Stephen Hawking as black holes were first being introduced. Theoretical physicist Gerard ’t Hooft invoked a mathematical definition by telling Curiel, “A black hole is the solution of Einstein’s field equations for gravity without matter…”

In essence, Curiel found that scientists within the same field generally agree on what defines a black hole. But these definitions vary drastically from field to field. Many scientists also admitted that giving a simple explanation of a black hole is still exceedingly difficult, even though they’ve been studying these objects for decades.

Yet to Curiel, this disparity in definitions lets physicists investigate black holes from many different angles, leading to richer and more diverse discoveries. And while scientists may not use the same words to describe black holes, neither do they conflict with each other.

And not all scientists chose technical definitions of any kind. Astrophysicist Avi Loeb summed it up for Curiel in terms anyone could understand, regardless of their physics background: “A black hole is the ultimate prison: once you check in, you can never get out.”

CATEGORIZED UNDER: Space & Physics, top posts
MORE ABOUT: black hole, physics
  • http://www.mazepath.com/uncleal/EquivPrinFail.pdf Uncle Al

    A black hole is the ultimate prison: once you check in, you can never get out.Do you see what you don’t see? Post-merger binding energy mass deficit is about 5% – piddles. There is no post-merger jitter as the “singularities” orbit and/or merge

    … bottom
    … Binary black hole merger is two empty bubbles popping into one.

    A black hole is a [2D(+ epsilon)] membrane, an event horizon with no 3D interior – a bubble. There is no “interior ” singularity. Net binding energy is not a cosmic event. It is a little kiss as combined membranes go spherical again.

    Trapped Information evaporates out as Hawking radiation, revealing no naked singularity at the end. The cosmic disaster is that there s no reason to quantize gravitation.

    • Ryan Snaca AniloHectycle

      That’s untrue. Black holes emit mass in cyclic nature.

  • Glenn

    Very interesting but so what. I guess it may help some college professors get tenure. As a result of various explanations of black holes no ones quality of life will be effected. This my be considered as high tech selfstimulatory behavior.

    • Alan Evans

      Oh you cynic

      • Glenn

        What about pragmatic?

        • ECarpenter

          It’s not pragmatic, it’s anti-intellectual and anti-knowledge.

          • Glenn

            Knowledge for knowledge sake. The theory of everything with a few exceptions. But this ivory tower quest for knowledge will not help put food in a starving child’s stomach. But if that is your life’s quest, it’s your right.

  • Eric Johnson

    This is actually a very interesting subject and can be extended into many areas of the hard sciences. Different disciplines regularly use different definitions and terminology to discuss the same subjects. As a spectroscopist, I am right in the intersection between chemistry and physics and have to adjust my terminology to fit the crowd I am working with at the time.

  • Deplorablewinner

    There is a good reason why the center of galaxies is the home of
    “black holes “. Black Holes are, in all probability, just a point in the center of galaxies in which electromagnetic forces are focused. electromagnetism is 10 to the 39th power stronger than gravity. With that in mind, gravity’s influence is practically zero. It would make more sense to eliminate the “black hole” hypothesis, and opt for the real invisible force that rules everything from the smallest atom to the largest structures in the universe, and that ain’t gravity.

  • Kurt Stocklmeir

    spring constant of time and space is not linear – time and space are elastic – time and space get mad if you try to compress or expand time and space to an extreme – a black hole can not be made – if gravity is strong tidal forces are big – this makes wave length of particles increase – using quantum mechanics particle slows down when wave length increases – this stops particles from moving to star – these stars are a lot like a black hole – the star is a little like a super fluid – these stars wander around their orbits are to an extreme not normal Kurt Stocklmeir

  • Dr. Strangelove

    I like t’Hooft’s answer:
    “A black hole is the solution of Einstein’s field equations for gravity without matter…”

    This means that Einstein’s general relativity is wrong or it doesn’t work in black holes. Reductio ad absurdum. Black holes have a lot of matter with mass. Therefore, any definition or description of black hole derived from Einstein’s field equations must be wrong.

    • ECarpenter

      Well, that depends on how loosely you define “matter”.

    • Glenn

      Or Einstein’s constant to maintain a constant and not expanding universe. We all make errors sometimes.

  • Replier

    If a tree falls in the forest, I hope it falls on a philosophy professor.


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