What is the difference between a singularity and a black hole

In real life, this does not happen. Instead, the singing causes the goblet to shatter to pieces when the shaking becomes too violent. Every scientific theory has its limitations. Within its realm of validity, a good theory matches experimental results very well.

But go beyond the limitations of a theory, and it starts giving predictions that are inaccurate or even just nonsense. Physicists hope to one day develop a theory of everything that has no limitations and is accurate in all situations. But we do not have that yet. Currently, the best physics theories are quantum field theory and Einstein's general relativity. Quantum field theory very accurately describes the physics from the size of humans down to the smallest particle.

At the same time, quantum field theory fails on the planetary and astronomical scales, and, in fact, says nothing at all about gravity. In contrast, general relativity accurately predicts gravitational effects and other effects on the astronomical scale, but says nothing about atoms, electromagnetism, or anything on the small scale.

Using general relativity to predict an electron's orbit around an atomic nucleus will give you embarrassingly bad results, and using quantum field theory to predict earth's orbit around the sun will likewise give you bad results. But as long as scientists and engineers use the right theory in the right setting, they mostly get the right answers in their research, calculations, and predictions.

The good thing is that general relativity does not overlap much with quantum field theory. For most astronomical-scale and gravitational calculations, you can get away with using just general relativity and ignoring quantum field theory.

In both cases the singularity was a single point where the curvature of space time are infinite. It is believed that at this point the general theory of relativity almost universally accepted as 'the' accurate description of gravity ceases to hold true.

The singularity of a rotating black hole is essentially the same except that it exists in a ring thus the name ring singularity. The consequences of a rotating black hole if they exist - we have no direct proof that any type of black holes exist however, are very different from non-rotating ones. It has infinite density and therefore does not exist within space-time as it is the point of infinite curvature of space-time.

The big bang singularity is where all the mass of the universe used to be concentrated. It had all of the properties of a black hole singularity but from it 'grew' space time and matter was released into this space as the fundamental particles of very high energy. This is the big bang. While spacetime singularities in general are frequently viewed with suspicion, physicists often offer the reassurance that, even if they are real, we expect most of them to be hidden away behind the event horizons of black holes.

Such singularities therefore could not affect us unless we were actually to jump into the black hole. A naked singularity, on the other hand, is one that is not hidden behind an event horizon. Such singularities appear much more threatening because they are uncontained, freely accessible to the rest of spacetime.

The heart of the worry is that singular structure seems to signify so profound a breakdown in the fundamental structure of spacetime that it could wreak havoc on any region of the universe that it were visible to.

Because the structures that break down in singular spacetimes are in general required for the formulation of our known physical laws, and of initial-value problems for individual physical systems in particular, one such fear is that determinism would collapse entirely wherever the singular breakdown were causally visible.

In Earman's , pp. As a result, there could be no reasonable expectation of determinism, nor even just predictability, for any region in causal contact with what it spews out.

One form that such a naked singularity could take is that of a white hole , which is a time-reversed black hole. Imagine taking a film of a black hole forming from the collapse of a massive object, say, a star, with light, dust, rockets, astronauts and old socks falling into it during its subsequent evolution.

Now imagine that film being run backwards. This is the picture of a white hole: one starts with a naked singularity, out of which might appear people, rockets, socks—anything at all—with eventually a star bursting forth. Absolutely nothing in the causal past of such a white hole would determine what would pop out of it, since, as follows from the No Hair Theorems section 3.

This description should feel familiar to the canny reader: it is the same as the way that increase of entropy in ordinary thermodynamics as embodied in the Second Law makes retrodiction impossible; the relationship of black holes to thermodynamics is discussed in section 5. Because the field equations of general relativity do not pick out a preferred direction of time, if the formation of a black hole is allowed by the laws of spacetime and gravity, then those laws also permit white holes.

Roger Penrose , famously suggested that although naked singularities are compatible with general relativity, in physically realistic situations they will never form; that is, any process that results in a singularity will safely ensconce that singularity behind an event horizon. This conjecture, known as the Cosmic Censorship Hypothesis, has met with some success and popularity; however, it also faces several difficulties.

Penrose's original formulation relied on black holes: a suitably generic singularity will always be contained in a black hole and so causally invisible outside the black hole. As the counter-examples to various ways of articulating the hypothesis based on this idea have accumulated over the years, however, it has gradually been abandoned Geroch and Horowitz ; Krolak ; Penrose ; Joshi et al. More recent approaches either begin with an attempt to provide necessary and sufficient conditions for cosmic censorship itself, yielding an indirect characterization of a naked singularity as any phenomenon violating those conditions, or else they begin with an attempt to provide a characterization of a naked singularity without reference to black holes and so conclude with a definite statement of cosmic censorship as the absence of such phenomena Geroch and Horowitz This has been the subject of recent philosophical work, primarily by Manchak b, a, a.

Recall the discussion of maximality and extendibility in section 1. Although Geroch's definition had powerful conceptual appeal, in the event it has proven untenable: Krasnikov showed that, according to it, even Minkowski spacetime fails to be hole-free. Manchak b showed how an emendation of Geroch's definition could fix the problem. He then showed that, under the assumption of global hyperbolicity a strong condition of causal well-behavedness for a spacetime , one gets a nice hierarchy of conditions relating to determinism: geodesic completeness implies effective completeness Manchak's own condition , which implies inextendibility, which implies hole-freeness Manchak a; see section 1.

In related work, Manchak b showed that, in a sense one can make precise, it should be easier to construct a machine that would result in spacetime's having such a hole than one that would result in time-travel. In short, creating the possibility for indeterminism seems easier in the theory than the possibility for causal paradox! Manchak shows that, if a spacetime has no epistemic holes then under mild conditions on the niceness of the causal structure the spacetime has no naked singularities as standardly construed.

The condition differs also in its modal character from other such hole-freeness conditions, for it makes significantly weaker and more conceptually and technically tractable modal claims. Issues of determinism, from an epistemic perspective, are intimately bound up with the possibility of reliable prediction. See the entry Causal Determinism.

The general issue of predictability itself in general relativity, even apart from the specific problems that singular structure may raise, is fascinating, philosophically rich, and very much unsettled.

One can make a prima facie strong argument, for example, that prediction is possible in general relativity only in spacetimes that possess singularities Hogarth ; Manchak ! See Geroch , Glymour , Malament , and Manchak , for discussion of these and many other related issues.

Here again, as with almost all the issues discussed up to this point in this entry regarding singularities and black holes, is an example of a sizable subculture in physics working on matters that have no clearly or even unambiguously defined physical parameters to inform the investigations and no empirical evidence to guide or even just constrain them, the parameters of the debate imposed by and large by the intuitions of a handful of leading researchers.

From sociological, physical, and philosophical vantage points, one may well wonder, then, why so many physicists continue to work on it, and what sort of investigation they are engaged in. Perhaps nowhere else in general relativity, or even in physics, can one observe such a delicate interplay of, on the one hand, technical results, definitions and criteria, and, on the other hand, conceptual puzzles and even incoherence, largely driven by the inchoate intuitions of physicists.

Not everyone views the situation with excitement or even equanimity, however: see Curiel for a somewhat skeptical discussion of the whole endeavor. The challenge of uniting quantum theory and general relativity in a successful theory of quantum gravity has arguably been the greatest challenge facing theoretical physics for the past eighty years. One avenue that has seemed particularly promising is the attempt to apply quantum theory to black holes. This is in part because, as purely gravitational entities, black holes present an apparently simple but physically important case for the study of the quantization of gravity.

Further, because the gravitational force grows without bound as one nears a standard black-hole singularity, one would expect quantum gravitational effects which should come into play at extremely high energies to manifest themselves in the interior of black holes. In the event, studies of quantum mechanical systems in black hole spacetimes have revealed several surprises that threaten to overturn the views of space, time, and matter that general relativity and quantum field theory each on their own suggests or relies on.

Since the ground-breaking work of Wheeler, Penrose, Bekenstein, Hawking and others in the late s and early s, it has become increasingly clear that there are profound connections among general relativity, quantum field theory, and thermodynamics. This area of intersection has become one of the most active and fruitful in all of theoretical physics, bringing together workers from a variety of fields such as cosmology, general relativity, quantum field theory, particle physics, fluid dynamics, condensed matter, and quantum gravity, providing bridges that now closely connect disciplines once seen as largely independent.

In particular, a remarkable parallel between the laws of black holes and the laws of thermodynamics indicates that gravity and thermodynamics may be linked in a fundamental and previously unimagined way.

This linkage strongly suggests, among many things, that our fundamental ideas of entropy and the nature of the Second Law of thermodynamics must be reconsidered, and that the standard form of quantum evolution itself may need to be modified. While these suggestions are speculative, they nevertheless touch on deep issues in the foundations of physics. Indeed, because the central subject matter of all these diverse areas of research lies beyond the reach of current experimentation and observation, they are all speculative in a way unusual even in theoretical physics.

In their investigation, therefore, physical questions of a technically sophisticated nature are inextricable from subtle philosophical considerations spanning ontology, epistemology, and methodology, again in a way unusual even in theoretical physics. Because this is a particularly long and dense section of the article, we begin with an outline of it. Section 5. We conclude in Section 5. Suppose one observes a quiescent black hole at a given moment, ignoring any possible quantum effects.

As discussed above in section 3. These quantities, like those of systems in classical mechanics, stand in definite relation to each other as the black hole dynamically evolves, which is to say, they satisfy a set of equations characterizing their behavior.

A black hole is stationary if, roughly speaking, it does not change over time; more precisely, it is stationary if its event horizon is generated by an asymptotically timelike Killing field. On the face of it, the Zeroth, First and Third Laws are straightforward to understand. It may seem that, because nothing can escape from a black hole once it has entered, black holes can only grow larger or, at least, stay the same size if nothing further falls in.

This assumes, however, that increased mass always yields increased surface area as opposed to some other measure of spatial extent. Surprising as it may sound, it is indeed the case that, although nothing that enters a black hole can escape, it is still possible to extract energy i. It is therefore not obvious that one could not shrink a black hole by extracting enough mass-energy or angular momentum from it.

It also seems to be at least possible that a black hole could shrink by radiating mass-energy away as gravitational radiation, or that the remnant of two colliding black holes could have a smaller surface area than the sum of the original two. It is most surprising, therefore, to learn that the Second Law is a deep, rigorous theorem that follows only from the fundamental mathematics of relativistic spacetimes Hawking , and does not depend in any essential way on the particulars of relativistic dynamics as encapsulated in the Einstein field equation Curiel See the entry Philosophy of Statistical Mechanics.

For those who know classical thermodynamics, the formal analogy between its laws and the laws of black hole as stated should be obvious. For exposition and discussion of the laws of classical thermodynamics, see, e. One formulation of the Zeroth Law of thermodynamics states that a body in thermal equilibrium has constant temperature throughout. The First Law is a statement of the conservation of energy.

It has as a consequence that any change in the total energy of a body is compensated for and measured by changes in its associated physical quantities, such as entropy, temperature, angular momentum and electric charge. The Second Law states that entropy never decreases.

The Third Law, on one formulation, states that it is impossible to reduce the temperature of a system to zero by any physical process. Indeed, relativistically mass just is energy, so at least the First Law seems already to be more than just formal analogy. Also, the fact that the state of a stationary black hole is entirely characterized by only a few parameters, completely independent of the nature and configuration of any micro-structures that may underlie it e.

Recall the discussion of the No Hair Theorems in section 3. Still, although the analogy is extremely suggestive in toto , to take it seriously would require one to assign a non-zero temperature to a black hole, which, at the time Bardeen, Carter and Hawking first formulated and proved the laws in , almost everyone agreed was absurd.

All hot bodies emit thermal radiation like the heat given off from a stove, or the visible light emitted by a burning piece of charcoal ; according to general relativity, however, a black hole ought to be a perfect sink for energy, mass, and radiation, insofar as it absorbs everything including light , and emits nothing including light.

So it seems the only temperature one might be able to assign it would be absolute zero. See section 5. In the early s, nonetheless, Bekenstein , , argued that the Second Law of thermodynamics requires one to assign a finite entropy to a black hole. His worry was that one could collapse any amount of highly entropic matter into a black hole—which, as we have emphasized, is an extremely simple object—leaving no trace of the original disorder associated with the high entropy of the original matter.

This seems to violate the Second Law of thermodynamics, which asserts that the entropy disorder of a closed system—such as the exterior of an event horizon—can never decrease.

Adding mass to a black hole, however, will increase its size, which led Bekenstein to suggest that the area of a black hole is a measure of its entropy. This conjecture received support in when Hawking proved that the surface area of a black hole, like the entropy of a closed system, can never decrease Hawking Still, essentially no one took Bekenstein's proposals seriously at first, because all black holes manifestly have temperature absolute zero, as mentioned above, if it is even meaningful to ascribe temperatures to them in the first place.

Thus it seems that the analogy between black holes and thermodynamical objects, when treated in the purely classical theory of general relativity, is merely a formal one, without real physical significance. His analysis of the behavior of quantum fields in black-hole spacetimes revealed that black holes will emit radiation with a characteristically thermal spectrum: a black hole generates heat at a temperature that is inversely proportional to its mass and directly proportional to its surface gravity.

It glows like a lump of smoldering coal even though light should not be able to escape from it! The temperature of this Hawking radiation is extremely low for stellar- and galactic-scale black holes, but for very, very small black holes the temperatures would be high. Everest—and so be about 10 -7 m across, the size of a virus. This means that a very, very small black hole should rapidly evaporate away, as all of its mass-energy is emitted in high-temperature Hawking radiation. Thus, when quantum effects are taken into account, black holes will not satisfy the Area Theorem, the second of the classical laws of black hole, as their areas shrink while they evaporate.

Hayward et al. These results—now referred to collectively as the Hawking effect—were taken to establish that the parallel between the laws of black hole and the laws of thermodynamics was not a mere formal fluke: it seems they really are getting at the same deep physics. The Hawking effect establishes that the surface gravity of a black hole can, indeed must, be interpreted as a physical temperature.

Connecting the two sets of laws also requires linking the surface area of a black hole with entropy, as Bekenstein had earlier suggested: the entropy of a black hole is proportional to the area of its event horizon, which is itself proportional to the square of its mass.

Furthermore, mass in black hole mechanics is mirrored by energy in thermodynamics, and we know from relativity theory that mass and energy are identical, so the black hole's mass is its thermodynamical energy. The overwhelming consensus in the physics community today, therefore, is that black holes truly are thermodynamical objects, and the laws of black hole mechanics just are the laws of ordinary thermodynamics extended into a new regime, to cover a new type of physical system.

We will return to discuss Hawking radiation in more detail in section 6. Although it is still orthodoxy today in the physics community that there is no consistent theory of thermodynamics for purely classical black holes Unruh and Wald ; Wald , , i. Curiel a, Other Internet Resources has recently argued that this is not so. He argues, to the contrary, that there is a consistent way of treating purely classical black holes as real thermodynamical systems, that they should be assigned a temperature proportional to their surface gravity, and, in fact, that not to do so leads to the same kinds of inconsistencies as occur if one does not do so for black holes emitting Hawking radiation.

In a recent article, Dougherty and Callender challenge the orthodoxy from the opposite direction. They argue that we should be far more skeptical of the idea that the laws of black holes are more than just formal analogy, and that, indeed, there are strong reasons to think that they are not physically the laws of thermodynamics extended into a new domain. Their main argument is that the Zeroth Law of black holes cannot do the work that the standard formulation of the Zeroth Law does in classical thermodynamics.

In classical thermodynamics, the standard formulation of the Zeroth Law is transitivity of equilibrium: two bodies each in equilibrium with a third will be in equilibrium with each other. They point out that this transitivity of equilibrium underlies many of the most important constructions and structures in classical thermodynamics, which mere constancy of temperature surface gravity for a single system in equilibrium does not suffice for.

Curiel , however, recently proposed a strengthened version of the Zeroth Law for black holes, based on a characterization of transitivity of equilibrium among them, in an attempt to address this challenge. This is an area of active dispute. Wallace , provides a more comprehensive exposition and defense of the claim that black holes truly are thermodynamical objects, attacking the problem from several different directions, and offers specific rejoinders to several of the other arguments made by Dougherty and Callender The most initially plausible and promising way to explain what the entropy of a black hole measures, and why a black hole has such a property in the first place, is to point to the Hawking radiation it emits, and in particular the well defined temperature the radiation has.

For exposition and discussion of the standard relations between temperature and entropy in classical thermodynamics, see, e. There are, however, many technical and conceptual reasons why such an explanation is not viable Visser b, , summed up in the slogan that Hawking radiation is a strictly kinematical effect, whereas black hole entropy is a dynamical phenomenon. This fact is discussed in more detail in section 8 below. What, then, is the origin and nature of the entropy we attribute to a black hole?

When describing a cloud of gas, we do not specify values for the position and velocity of every molecule in it; we rather describe it using quantities, such as pressure and temperature, constructed as statistical measures over underlying, more finely grained quantities, such as the momentum and energy of the individual molecules.

On one common construal, then, the entropy of the gas measures the incompleteness, as it were, of the gross description. In the attempt to take seriously the idea that a black hole has a true physical entropy, it is therefore natural to attempt to construct such a statistical origin for it.

The tools of classical general relativity cannot provide such a construction, for it allows no way to describe a black hole as a system whose physical attributes arise as gross statistical measures over underlying, more finely grained quantities. Not even the tools of quantum field theory on curved spacetime can provide it, for they still treat the black hole as an entity defined entirely in terms of the classical geometry of the spacetime Wald In any event, on any view of the nature of entropy, there arises a closely related problem, viz.

See Jacobson et al. Explaining what these microstates are that are counted by the Bekenstein entropy has been a challenge that has been eagerly pursued by quantum gravity researchers.

In , superstring theorists were able to give an account of how M -theory an extension of superstring theory generates the number of string-states underlying a certain class of classical black holes, and this number matched that given by the Bekenstein entropy Strominger and Vafa At the same time, a counting of black-hole states using loop quantum gravity also recovered the Bekenstein entropy Rovelli It is philosophically noteworthy that this is treated as a significant success for these programs i.

Sadly, we have no black holes in terrestrial laboratories, and those we do have good reason to think we indirectly observe are too far away for anything like these effects to be remotely detectable, given their minuscule temperatures. There are no convincing derivations for more general, physically relevant black holes. This is noteworthy because it poses a prima facie problem for traditional accounts of scientific method, and underscores the difficulties faced by fundamental physics today, that in many important areas it cannot make contact with empirical data at all.

How did a theoretically predicted phenomenon, derived by combining seemingly incompatible theories in a novel way so as to extend their reach into regimes that we have no way of testing in the foreseeable future, become the most important touchstone for testing novel ideas in theoretical physics?

Can it play that role? Philosophers have not yet started to grapple seriously with these issues. In a thoughtful survey, Sorkin concisely and insightfully characterizes in ten theses what seems to be a popular view on the nature of black-hole entropy when studied as an essentially quantum phenomenon, which is distilled into the essential parts for our purposes as follows.

The entropy:. These theses concisely capture how radically different black-hole entropy is from ordinary thermodynamical entropy. The first, as is already obvious from the Second Law of black hole mechanics, underscores the fact that black-hole entropy is proportional to the surface area of the system, not to the bulk volume as for ordinary thermodynamical systems.

The second articulates the fact that the underlying entities whose statistics are conjectured to give rise to the entropy are the constituents of perhaps the most fundamental structure in contemporary physics, spacetime itself, not high-level, derivative entities such as atoms, which are not fundamental in our deepest theory of matter, quantum field theory.

The fourth states that the Second Law of black hole thermodynamics, generalized to include contributions from both black holes and ordinary matter as discussed in section 5. This will be discussed further in section 6. This is of a piece with the fact that the Second Law for black holes in the classical regime is a theorem of pure differential geometry section 5. In so far as one takes Bekenstein entropy seriously as a true thermodynamical entropy, then, these differences strongly suggest that the extension of entropy to black holes should modify and enrich our understanding not only of entropy as a physical quantity, but temperature and heat as well, all in ways perhaps similar to what that of the extension of those classical quantities to electromagnetic fields did at the end of the 19th century Curiel a, Other Internet Resources.

This raises immediate questions concerning the traditional philosophical problems of inter-theoretic relations among physical quantities and physical principles as formulated in different theories, and in particular problems of emergence, reduction, the referential stability of physical concepts, and their possible incommensurability across theories.

One could not ask for a more novel case study to perhaps enliven these traditional debates. Dougherty and Callender have challenged orthodoxy here, as well, by arguing that the many ways in which the area of a black hole does not behave like classical entropy strongly suggests that we should be skeptical of treating it as such. What is the electromagnetic spectrum? What is a planet? What is a dwarf planet? Why do the planets orbit the Sun? Donate with Crypto. If you quote this material please be courteous and provide a link.