Loren Booda
- 3,108
- 4
chiro,
I respect that this is a mathematical forum, so I will try to remain conscious about the topic of this thread. My apologies for the lack of hard equations. Such relations below will often be expressed in "English." I struggle to provide the best descriptions possible. Coding is an area which I am not familiar with. Do you feel that our exchange is productive? I appreciate your contributions.
__________
http://en.wikipedia.org/wiki/Holographic_principle -- Black hole entropy
The holographic principle was inspired by black hole thermodynamics, which implies that the maximal entropy in any region scales with the radius squared, and not cubed as might be expected. In the case of a black hole, the insight was that the informational content of all the objects which have fallen into the hole can be entirely contained in surface fluctuations of the event horizon. The holographic principle resolves the black hole information paradox within the framework of string theory.
. . .
An object with entropy is microscopically random, like a hot gas. A known configuration of classical fields has zero entropy: there is nothing random about electric and magnetic fields, or gravitational waves. Since black holes are exact solutions of Einstein's equations, they were thought not to have any entropy either.
But Jacob Bekenstein noted that this leads to a violation of the second law of thermodynamics. If one throws a hot gas with entropy into a black hole, once it crosses the horizon, the entropy would disappear. The random properties of the gas would no longer be seen once the black hole had absorbed the gas and settled down. The second law can only be salvaged if black holes are in fact random objects, with an enormous entropy whose increase is greater than the entropy carried by the gas.
Bekenstein argued that black holes are maximum entropy objects—that they have more entropy than anything else in the same volume. In a sphere of radius R, the entropy in a relativistic gas increases as the energy increases. The only limit is gravitational; when there is too much energy the gas collapses into a black hole. Bekenstein used this to put an upper bound on the entropy in a region of space, and the bound was proportional to the area of the region. He concluded that the black hole entropy is directly proportional to the area of the event horizon.
Stephen Hawking had shown earlier that the total horizon area of a collection of black holes always increases with time. The horizon is a boundary defined by lightlike geodesics; it is those light rays that are just barely unable to escape. If neighboring geodesics start moving toward each other they eventually collide, at which point their extension is inside the black hole. So the geodesics are always moving apart, and the number of geodesics which generate the boundary, the area of the horizon, always increases. Hawking's result was called the second law of black hole thermodynamics, by analogy with the law of entropy increase, but at first, he did not take the analogy too seriously.
Hawking knew that if the horizon area were an actual entropy, black holes would have to radiate. When heat is added to a thermal system, the change in entropy is the increase in mass-energy divided by temperature:
dS = dM/T
If black holes have a finite entropy, they should also have a finite temperature. In particular, they would come to equilibrium with a thermal gas of photons. This means that black holes would not only absorb photons, but they would also have to emit them in the right amount to maintain detailed balance.
Time independent solutions to field equations don't emit radiation, because a time independent background conserves energy. Based on this principle, Hawking set out to show that black holes do not radiate. But, to his surprise, a careful analysis convinced him that they do, and in just the right way to come to equilibrium with a gas at a finite temperature. Hawking's calculation fixed the constant of proportionality at 1/4; the entropy of a black hole is one quarter its horizon area in Planck units.
The entropy is proportional to the logarithm of the number of microstates, the ways a system can be configured microscopically while leaving the macroscopic description unchanged. Black hole entropy is deeply puzzling — it says that the logarithm of the number of states of a black hole is proportional to the area of the horizon, not the volume in the interior.
__________
[Speculation]: Regarding the "black hole information paradox," a black hole's "singularity" may be a composite of quantum black holes. Information about the "singularity" would manifest at the black hole horizon as the only variables we may know about a black hole: mass, spin, and charge (and derivations thereof). The extreme symmetry of the Schwarzschild black hole transfers coherently (much like an "isotropic laser" or "holograph") such information that is allowed about the singularity.
__________
Remember the Heisenberg uncertainty principle applies for all quanta: a very small mass complements a very large radius: ΔrΔp≥h, or ΔrΔcm≥h. In other words, small measurements relate to large ones through their action, or units of Planck's constant.
r=radius of action, p=momentum of action, c=speed of light in vacuo, m=mass of quantum, h=Planck's constant.
_________
[Speculation]: M* is the characteristic mass of quantum gravity. This Planck mass demarcates exclusively black hole masses above from those of quanta below. Symmetry between these regions implies a duality for the two classes of entities. The Planck (quantum) black hole, with its mass M*, itself shares and interrelates properties of black holes and quanta. Since inverting the mass scale around M* compares black holes and quanta one-to-one, a black hole could be a real quantum "inside-out" - in terms of that scale - and vice versa:
(Mblack hole·Mquantum)1/2=MPlanck, where M is mass.
__________
http://en.wikipedia.org/wiki/Peculiar_velocityIn physical cosmology, the term peculiar velocity (or peculiar motion) refers to the components of a receding galaxy's velocity that cannot be explained by Hubble's law.
According to Hubble, and as verified by many astronomers, a galaxy is receding from us at a speed proportional to its distance. The Hubble distance expansion, approximately r=c/H0, where r is the relative distance a galaxy is from us, c the speed of light and H0 the Hubble constant, about 70 (km/s)/Mpc. (That is, kilometers per second per megaparsec.)
Galaxies are not distributed evenly throughout observable space, but typically found in groups or clusters, ranging in size from fewer than a dozen to several thousands. All these nearby galaxies have a gravitational effect, to the extent that the original galaxy can have a velocity of over 1,000 km/s in an apparently random direction. This ["peculiar"] velocity will therefore add, or subtract, from the radial velocity that one would expect from Hubble's law.
The main consequence is that, in determining the distance of a single galaxy, a possible error must be assumed. This error becomes smaller, relative to the total speed, as the distance increases.
A more accurate estimate can be made by taking the average velocity of a group of galaxies: the peculiar velocities, assumed to be essentially random, will cancel each other, leaving a much more accurate measurement.
Models attempting to explain accelerating expansion include some form of dark energy. The simplest explanation for dark energy is that it is a cosmological constant or vacuum energy.
http://en.wikipedia.org/wiki/Cosmological_constant -- The cosmological constant Λ appears in Einstein's modified field equation in the form of
Rμν -(1/2)Rgμν + Λgμν = 8∏G/c4Tμν
where R and g pertain to the structure of spacetime, T pertains to matter and energy (thought of as affecting that structure), and G and c are conversion factors that arise from using traditional units of measurement. When Λ is zero, this reduces to the original field equation of general relativity. When T is zero, the field equation describes empty space (the vacuum).
The cosmological constant has the same effect as an intrinsic energy density of the vacuum, ρvac (and an associated pressure). In this context it is commonly defined with a proportionality factor of 8∏ Λ = 8∏ρvac, where unit conventions of general relativity are used (otherwise factors of G and c would also appear). It is common to quote values of energy density directly, though still using the name "cosmological constant".
A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa. If the energy density is positive, the associated negative pressure will drive an accelerated expansion of empty space.
__________
Thus the expansion "ladder" is largely determined by peculiar velocity, the Hubble expansion and a parameter like the cosmological constant.
__________
[Speculation]: Entropy of a black hole is proportional to its surface area. Entropy of conventional matter is proportional to its volume. I assume entropy of a concave spherical cosmological horizon, of reciprocal geometry, to be that of an inverted Schwarzschild black hole -- thus differing in their sign of curvature -- that is, with geodesics converging rather than diverging.
Aside: a simple dimensional argument considering conventional entropy (three dimensional) and black hole entropy (two dimensional) yields individual quanta having entropy proportional (one dimensional) to their propagation.
[Question]: A Schwarzschild black hole of radius RB has entropy proportional to its surface area. Consider it within a closed ("Schwarzschild") universe of radius RH>RB. What is their relative entropy? Remember the universe as having radiating curvature relatively negative to that of the inner black hole.
I respect that this is a mathematical forum, so I will try to remain conscious about the topic of this thread. My apologies for the lack of hard equations. Such relations below will often be expressed in "English." I struggle to provide the best descriptions possible. Coding is an area which I am not familiar with. Do you feel that our exchange is productive? I appreciate your contributions.
__________
http://en.wikipedia.org/wiki/Holographic_principle -- Black hole entropy
The holographic principle was inspired by black hole thermodynamics, which implies that the maximal entropy in any region scales with the radius squared, and not cubed as might be expected. In the case of a black hole, the insight was that the informational content of all the objects which have fallen into the hole can be entirely contained in surface fluctuations of the event horizon. The holographic principle resolves the black hole information paradox within the framework of string theory.
. . .
An object with entropy is microscopically random, like a hot gas. A known configuration of classical fields has zero entropy: there is nothing random about electric and magnetic fields, or gravitational waves. Since black holes are exact solutions of Einstein's equations, they were thought not to have any entropy either.
But Jacob Bekenstein noted that this leads to a violation of the second law of thermodynamics. If one throws a hot gas with entropy into a black hole, once it crosses the horizon, the entropy would disappear. The random properties of the gas would no longer be seen once the black hole had absorbed the gas and settled down. The second law can only be salvaged if black holes are in fact random objects, with an enormous entropy whose increase is greater than the entropy carried by the gas.
Bekenstein argued that black holes are maximum entropy objects—that they have more entropy than anything else in the same volume. In a sphere of radius R, the entropy in a relativistic gas increases as the energy increases. The only limit is gravitational; when there is too much energy the gas collapses into a black hole. Bekenstein used this to put an upper bound on the entropy in a region of space, and the bound was proportional to the area of the region. He concluded that the black hole entropy is directly proportional to the area of the event horizon.
Stephen Hawking had shown earlier that the total horizon area of a collection of black holes always increases with time. The horizon is a boundary defined by lightlike geodesics; it is those light rays that are just barely unable to escape. If neighboring geodesics start moving toward each other they eventually collide, at which point their extension is inside the black hole. So the geodesics are always moving apart, and the number of geodesics which generate the boundary, the area of the horizon, always increases. Hawking's result was called the second law of black hole thermodynamics, by analogy with the law of entropy increase, but at first, he did not take the analogy too seriously.
Hawking knew that if the horizon area were an actual entropy, black holes would have to radiate. When heat is added to a thermal system, the change in entropy is the increase in mass-energy divided by temperature:
dS = dM/T
If black holes have a finite entropy, they should also have a finite temperature. In particular, they would come to equilibrium with a thermal gas of photons. This means that black holes would not only absorb photons, but they would also have to emit them in the right amount to maintain detailed balance.
Time independent solutions to field equations don't emit radiation, because a time independent background conserves energy. Based on this principle, Hawking set out to show that black holes do not radiate. But, to his surprise, a careful analysis convinced him that they do, and in just the right way to come to equilibrium with a gas at a finite temperature. Hawking's calculation fixed the constant of proportionality at 1/4; the entropy of a black hole is one quarter its horizon area in Planck units.
The entropy is proportional to the logarithm of the number of microstates, the ways a system can be configured microscopically while leaving the macroscopic description unchanged. Black hole entropy is deeply puzzling — it says that the logarithm of the number of states of a black hole is proportional to the area of the horizon, not the volume in the interior.
__________
[Speculation]: Regarding the "black hole information paradox," a black hole's "singularity" may be a composite of quantum black holes. Information about the "singularity" would manifest at the black hole horizon as the only variables we may know about a black hole: mass, spin, and charge (and derivations thereof). The extreme symmetry of the Schwarzschild black hole transfers coherently (much like an "isotropic laser" or "holograph") such information that is allowed about the singularity.
__________
Remember the Heisenberg uncertainty principle applies for all quanta: a very small mass complements a very large radius: ΔrΔp≥h, or ΔrΔcm≥h. In other words, small measurements relate to large ones through their action, or units of Planck's constant.
r=radius of action, p=momentum of action, c=speed of light in vacuo, m=mass of quantum, h=Planck's constant.
_________
[Speculation]: M* is the characteristic mass of quantum gravity. This Planck mass demarcates exclusively black hole masses above from those of quanta below. Symmetry between these regions implies a duality for the two classes of entities. The Planck (quantum) black hole, with its mass M*, itself shares and interrelates properties of black holes and quanta. Since inverting the mass scale around M* compares black holes and quanta one-to-one, a black hole could be a real quantum "inside-out" - in terms of that scale - and vice versa:
(Mblack hole·Mquantum)1/2=MPlanck, where M is mass.
__________
http://en.wikipedia.org/wiki/Peculiar_velocityIn physical cosmology, the term peculiar velocity (or peculiar motion) refers to the components of a receding galaxy's velocity that cannot be explained by Hubble's law.
According to Hubble, and as verified by many astronomers, a galaxy is receding from us at a speed proportional to its distance. The Hubble distance expansion, approximately r=c/H0, where r is the relative distance a galaxy is from us, c the speed of light and H0 the Hubble constant, about 70 (km/s)/Mpc. (That is, kilometers per second per megaparsec.)
Galaxies are not distributed evenly throughout observable space, but typically found in groups or clusters, ranging in size from fewer than a dozen to several thousands. All these nearby galaxies have a gravitational effect, to the extent that the original galaxy can have a velocity of over 1,000 km/s in an apparently random direction. This ["peculiar"] velocity will therefore add, or subtract, from the radial velocity that one would expect from Hubble's law.
The main consequence is that, in determining the distance of a single galaxy, a possible error must be assumed. This error becomes smaller, relative to the total speed, as the distance increases.
A more accurate estimate can be made by taking the average velocity of a group of galaxies: the peculiar velocities, assumed to be essentially random, will cancel each other, leaving a much more accurate measurement.
Models attempting to explain accelerating expansion include some form of dark energy. The simplest explanation for dark energy is that it is a cosmological constant or vacuum energy.
http://en.wikipedia.org/wiki/Cosmological_constant -- The cosmological constant Λ appears in Einstein's modified field equation in the form of
Rμν -(1/2)Rgμν + Λgμν = 8∏G/c4Tμν
where R and g pertain to the structure of spacetime, T pertains to matter and energy (thought of as affecting that structure), and G and c are conversion factors that arise from using traditional units of measurement. When Λ is zero, this reduces to the original field equation of general relativity. When T is zero, the field equation describes empty space (the vacuum).
The cosmological constant has the same effect as an intrinsic energy density of the vacuum, ρvac (and an associated pressure). In this context it is commonly defined with a proportionality factor of 8∏ Λ = 8∏ρvac, where unit conventions of general relativity are used (otherwise factors of G and c would also appear). It is common to quote values of energy density directly, though still using the name "cosmological constant".
A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa. If the energy density is positive, the associated negative pressure will drive an accelerated expansion of empty space.
__________
Thus the expansion "ladder" is largely determined by peculiar velocity, the Hubble expansion and a parameter like the cosmological constant.
__________
[Speculation]: Entropy of a black hole is proportional to its surface area. Entropy of conventional matter is proportional to its volume. I assume entropy of a concave spherical cosmological horizon, of reciprocal geometry, to be that of an inverted Schwarzschild black hole -- thus differing in their sign of curvature -- that is, with geodesics converging rather than diverging.
Aside: a simple dimensional argument considering conventional entropy (three dimensional) and black hole entropy (two dimensional) yields individual quanta having entropy proportional (one dimensional) to their propagation.
[Question]: A Schwarzschild black hole of radius RB has entropy proportional to its surface area. Consider it within a closed ("Schwarzschild") universe of radius RH>RB. What is their relative entropy? Remember the universe as having radiating curvature relatively negative to that of the inner black hole.