Black hole unitarity

An open question in fundamental physics is the so-called information loss paradox, or black hole unitarity paradox. Classically, the laws of physics are the same run forward or in reverse. That is, if the position and velocity of every particle in the universe were measured, we could (disregarding chaos) work backwards to discover the history of the universe arbitrarily far in the past. In quantum mechanics, this corresponds to a vital property called unitarity which has to do with the conservation of probability.

Black holes, however, violate this rule. Because of the no hair theorem, we can never determine what went into the black hole. Information is apparently destroyed, as there is no way to reconstruct what went into the black hole. This is an important unsolved conceptual problem in quantum gravity.

On 21 July 2004 Stephen Hawking presented a new argument that black holes do eventually emit information about what they swallow, reversing his previous position on information loss. He proposed that quantum perturbations of the event horizon could allow information to escape from a black hole, where it can influence subsequent Hawking radiation. The theory has not yet been reviewed by the scientific community, and if it is accepted it is likely to resolve the black hole information paradox. In the meantime, the announcement has attracted a lot of attention in the media.

Singularities

The fundamental concern is that since the physical behavior of singularities is unknown, if singularities can be seen from the rest of spacetime, causality may break down, and physics may lose its predictive power. The issue cannot be avoided, since according to the Penrose-Hawking singularity theorems, singularities are inevitable in physically reasonable situations. Still, in the absence of naked singularities, the universe is deterministic - it's possible to predict the entire evolution of universe, knowing only its condition at a certain moment of time (more precisely, everywhere on a spacelike 3-dimensional hypersurface, called the Cauchy surface). Failure of CCH leads to the failure of determinism, because it is impossible to predict the behavior of space-time in the causal future of a naked singularity.

The hypothesis was first formulated by Roger Penrose in 1969, and it is not stated in a completely formal way. In a sense it is more of a research program proposal: part of the research is to find a proper formal statement that is physically reasonable and that can be proved to be true or false (and that is sufficiently general to be interesting).

Planck Units

In physics, Planck units are physical units of measurement originally proposed by Max Planck. They form a system of natural units because they are defined exclusively in terms of the following fundamental physical constants — the units are natural because the numerical values of these five universal constants become 1 when expressed in units of this system.

The Planck units are often semi-humorously referred to by physicists as "God's units". They eliminate anthropocentric arbitrariness from the system of units: some physicists believe that an extra-terrestrial intelligence might be expected to use the same system.

Referring to Duff Comment on time-variation of fundamental constants and Duff, Okun, and Veneziano Trialogue on the number of fundamental constants (The operationally indistinguishable world of Mr. Tompkins), if all physical quantities (masses and other properties of particles) were expressed in terms of Planck units, those quantities would be dimensionless numbers (mass divided by the Planck mass, length divided by the Planck length, etc.) and the only quantities that we ultimately measure in physical experiments or in our perception of reality are dimensionless numbers. (When one commonly measures a length with a ruler or tape-measure, that person is actually counting tick marks on a given standard or is measuring the length relative to that given standard, which is a dimensionless value. It is no different for physical experiments, as all physical quantities are measured relative to some other like dimensioned values.)

...These necessarily retain their meaning for all times and for all civilizations, even extraterrestrial and non-human ones, and can therefore be designated as "natural units"...

Planck's time is how long it takes for light to travel Planck's length. The Planck length is the smallest amount of length with significance, as below this length quantum laws reign, meaning all measurements are nonsense. The speed of any object is limited by Einstein's laws of relativity, which state that nothing can travel faster than the speed of light in a vacuum.

Consciousness causes collapse

Consciousness causes collapse is the speculative theory that observation by a conscious observer is responsible for the wavefunction collapse. It is an attempt to solve the Wigner's friend paradox by simply stating that collapse occurs at the first "conscious" observer. Supporters claim this is not a revival of substance dualism, since (in a ramification of this view) consciousness and objects are entangled and cannot be considered as distinct. The consciousness causes collapse theory can be considered as a speculative appendage to almost any interpretation of quantum mechanics and most physicists reject it as unverifiable and introducing unnecessary elements into physics.

The process of "measurement" in quantum mechanics is regarded as consciousness itself. However, it is not explained by this theory which animals, living creatures, or objects have consciousness, that is, the right to collapse the wavefunction. It is also not clear whether measuring devices might also be considered conscious, though generally measuring devices are considered simply a "chain of observations" that only ends at a conscious entity. Some even suggest that some beings have a "higher consciousness" and therefore more capability to collapse the wavefunction, whereas others believe all conscious entities have an equal capability.

It has been claimed that the theory that meshes well with ancient Eastern mysticism and philosophy, including Hinduism and Taoism, which stress "Oneness".

Amit Goswami, a retired theoretical physicist, supported this theory in some of his writings, including The Self-Aware Universe. The Hungarian physicist Eugene Wigner also supported it.