Title: Black hole - never forms, or never evaporates Authors: Yi Sun

Many discussion about the black hole conundrums, such like singularity and information loss, suggested that there must be some essential irreconcilable conflict between quantum theory and classical gravity theory, which cannot be solved with any semiclassical quantised model of gravity, the only feasible way must be some complete unified quantum theory of gravity. In Vachaspati, the arguments indicate the possibility of an alternate outcome of gravitational collapse which avoids the information loss problem. In this paper, also with semiclassical analysis, it shows that so long as the mechanism of black hole evaporation satisfies a quite loose condition that the evaporation lifespan is finite for external observers, regardless of the detailed mechanism and process of evaporation, the conundrums above can be naturally avoided. This condition can be satisfied with Hawking-Unruh mechanism. Thus, the conflict between quantum theory and classical gravity theory may be not as serious as it seemed to be, the effectiveness of semiclassical methods might be underestimated. An exact universal solution with spherical symmetry of Einstein field equation has been derived in this paper. All possible solutions with spherical symmetry of Einstein field equation are its special cases. In addition, some problems of the Penrose diagram of an evaporating black hole first introduced by Hawking in 1975 are clarified.

Title: Measurement of stimulated Hawking emission in an analogue system Authors: Silke Weinfurtner, Edmund W. Tedford, Matthew C. J. Penrice, William G. Unruh, Gregory A. Lawrence (Version v2)

There is a mathematical analogy between the propagation of fields in a general relativistic space-time and long (shallow water) surface waves on moving water. Hawking argued that black holes emit thermal radiation via a quantum spontaneous emission. Similar arguments predict the same effect near wave horizons in fluid flow. By placing a streamlined obstacle into an open channel flow we create a region of high velocity over the obstacle that can include wave horizons. Long waves propagating upstream towards this region are blocked and converted into short (deep water) waves. This is the analogue of the stimulated emission by a white hole (the time inverse of a black hole), and our measurements of the amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system. Given the close relationship between stimulated and spontaneous emission, our findings attest to the generality of the Hawking process.

Title: Corrections to Bekenstein-Hawking entropy --- Quantum or not-so quantum? Authors: S. Shankaranarayanan (IISER-Trivandrum)

Hawking radiation and Bekenstein--Hawking entropy are the two robust predictions of a yet unknown quantum theory of gravity. Any theory which fails to reproduce these predictions is certainly incorrect. While several approaches lead to Bekenstein--Hawking entropy, they all lead to different sub-leading corrections. In this article, we ask a question that is relevant for any approach: Using simple techniques, can we know whether an approach contains quantum or semi-classical degrees of freedom? Using naive dimensional analysis, we show that the semi-classical black-hole entropy has the same dimensional dependence as the gravity action. Among others, this provides a plausible explanation for the connection between Einstein's equations and thermodynamic equation of state, and that the quantum corrections should have a different scaling behaviour.

Hawking radiation glimpsed in artificial black hole

You might expect black holes to be, well, black, but several decades ago Stephen Hawking calculated that they should emit light. Now, for the first time, physicists claim that they have observed this weird glow in the lab. Read more

'Virtual particle pairs' are constantly being created in 'empty' space....and if they happen to be created near the horizon of the black hole, then one of them can fall in... Normally, they are created as a particle-antiparticle pair and they quickly annihilate/cancel each other out; so obviously, if one fell into the BH then it's not possible for the other one to 'cancel out' , in which case the other one manages to escapes as Hawking radiation.

The particle that fell into the BH is still virtual and must restore its 'conservation of energy' by giving itself a negative mass-energy. The black-hole cancels this negative mass-energy and loses some of it's total Mass and shrinks...

Hawking Radiation is a process using mainly virtual photons (which are their own anti-particle, and thus can carry negative mass energy).

An alternative model is that the process can be regarded as 'perspective process'. A electron-positron pair can be created and it does not matter which one fall into the BH, as from our perspective a particle has 'escaped' from the black hole, (and from our perspective the blackhole has transformed the time and spatial dimensions) and thus, lost mass.

The black-hole Mass (solar masses) radiates like a 'blackbody' with a temperature of (6 x 10^-8/Mass) Kelvin, with the total lifetime of a black hole Mass of about: 10^71 Mass^3 seconds

Ed ~ Hawking Radiation is best understood if you know that the process is with virtual photons, (which are their own anti-particle and thus can carry negative mass energy).

Simulated black holes may prove theory By cramming several thousand superconducting quantum interference devices (SQUIDS), which guide light down a track much like a rail guides trains, scientists hope to simulate the effects of a black hole. The research could help prove a 35-year-old theory originally proposed by physicist Stephen Hawking and cement humanity's fundamental understanding of the universe.

Title: Hawking radiation as seen by an infalling observer Authors: Eric Greenwood, Dejan Stojkovic (Version v2)

We investigate an important question of Hawking-like radiation as seen by an infalling observer during gravitational collapse. Using the functional Schrodinger formalism we are able to probe the time dependent regime which is out of the reach of the standard approximations like the Bogolyubov method. We calculate the occupation number of particles whose frequencies are measured in the proper time of an infalling observer in two crucially different space-time foliations: Schwarzschild and Eddington-Finkelstein. We demonstrate that the distribution in Schwarzschild reference frame is not quite thermal, though it becomes thermal once the horizon is crossed. We approximately fit the temperature and find that the local temperature increases as the horizon is approached, and diverges exactly at the horizon. In Eddington-Finkelstein reference frame the temperature at the horizon is finite, since the observer in that frame is not accelerated. These results are in agreement with what is generically expected in the absence of back reaction. We also discuss some subtleties related to the physical interpretation of the infinite local temperature in Schwarzschild reference frame.

Semiconducting SQUID to help detect Hawking radiation A trick of the light has allowed U.S. scientists to mimic the physics of black holes in the laboratory. Reported in the journal Physical Review Letters, the study paves the way for the first test of a number of theories surrounding the concept of black holes, including the existence of Hawking radiation.

Title: A sonic black hole in a density-inverted Bose-Einstein condensate Authors: O. Lahav, A. Itah, A. Blumkin, C. Gordon, J. Steinhauer

We have created the analogue of a black hole in a Bose-Einstein condensate. In this sonic black hole, sound waves, rather than light waves, cannot escape the event horizon. The black hole is realised via a counterintuitive density inversion, in which an attractive potential repels the atoms. This allows for measured flow speeds which cross and exceed the speed of sound by an order of magnitude. The Landau critical velocity is therefore surpassed. The point where the flow speed equals the speed of sound is the event horizon. The effective gravity is determined from the profiles of the velocity and speed of sound.