Dr. Rainer Plaga has added an appendix to his paper On the potential catastrophic risk from metastable quantum-black holes produced at particle colliders that responds to Giddings and Mangano's rebuttal of August 29, 2008, Comments on claimed risk of metastable black holes.

1. It turns out that Giddings and Mangano (G&M) were barking up the wrong tree when they thought they had uncovered a 10²³ mathematical error on Plaga's part:

They “find a negligible power output [from a black hole with the properties described in section 3 of the present manuscript] of the size 0.1 µW, differing by a factor of 10²³ from [my] claim.”

My reply: G & M employ their eq.(1) to calculate the power output of a 5-dimensional microscopic black hole with a radius of 10⁻⁷ m within the canonical thermodynamic description of microscopic black holes. They correctly find it to be 23 orders of magnitude smaller than the power output calculated in section 3 of my paper for a black hole of the same size and conclude that my result is erroneous. They claim that I mistakenly applied their eq.(1) “written in terms of the mass using the four-dimensional relationship between radius and mass”.

However, I never employ their eq.(1) or my eq.(2) i.e. the thermodynamic,
canonical description to calculate the power output of the black hole in my
section 3. Rather, following Casadio & Harms, I exclusively employ my
eq.(1) (eq. (28) in [7]) which is qualitatively different. Following Casadio &
Harms [7] (sentence after their eq.(28)), my eq.(2) was only used to normalize the luminosity eq.(1) at the mass M_N to the classical expression eq.(2). M_N by far exceeds the maximal mass of the black hole discussed in section 3. This objection criticises something I did not do and did not intend to do. Therefore it does not apply to my paper.

2. So Plaga continues to argue that Hawking radiation itself from an Eddington limited medium sized black hole could wreck havoc on Earth:

As already pointed out in the 4th sentence after my eq.(6) all results on Eddington limited accretion of G&M were derived for their scenario with “switched off” Hawking radiation and therefore do not apply for the case “Hawking-radiation limited” accretion at the Eddington limit, considered in my section 3.

3. On the uncertainty of black hole evaporation:

They feel that a “serious dierence between the microcanonical picture and the usual Hawking calculation appears implausible in the large black hole region” I considered (following Casadio & Harms).

I reply: No reason for this evaluation is given by G & M so I need to wait for their promised “further comments” to take a position.

In light of our poor understanding of black-hole evaporation in general (see
quote below) I feel that in any case it will be diffcult to rule out such a serious difference with reasonable certainty.

4. Plaga restores the notorious or in his revised manuscript!

G & M rightly point out that in my quote: “...at each point where we encountered an uncertainty, we have replaced it by a conservative or “worst case” assumption”. The bold “or” was missing. I corrected this oversight in the revised version.

5. G&M criticized Plaga for citing an outdated version of Unruh's latest thoughts on black hole evaporation, saying "[Plaga] cites Unruh and Schutzhold’s work raising questions about Hawking radiation, without providing the more recent citation to Unruh’s work, that was given in [2] and reflects more up-to-date comments by Unruh on the support of his work for Hawking radiation."

So Plaga quotes from Unruh's latest:

“...Black Hole evaporation is one of the most puzzling features of gravity and quantum theory. The derivation by Hawking is nonsense, in that it uses features of the theory in regimes where we know the theory is wrong. Analog models of gravity have given us a clue that despite the shaky derivation, the eect is almost certainly right. Where then are the particles in black hole evaporation really created?...”

From these quotes I conclude: theories with extra dimensions robustly predict the existence of microscopic collider-producible black holes and Hawking radiation. But the detailed decay properties presently remain very uncertain. It then seems important to study alternatives to the standard thermodynamical treatment of Hawking radiation on the safety issue. This is the aim of my paper.

6. And, as I've repeatedly pointed out in this thread, Plaga notes that G&M's rebuttal completely ignored Plaga's point in his section 5:

Finally G & M’s comment did not address section 5 of the present manuscript in which I argue that their exclusion of dangerous mBHs is not completely definite for a general, simple reason, completely independent of the above arguments [[that G&M's] demonstration is based on an assumed validity of the semiclassical approximation. mBHs deep in the “quantum gravity” regime (violating eq.(7)) might have smaller scattering cross section than expected in the semiclassically and escape white dwarfs, just as they could escape ordinary stars. This would void G & M’s exclusion of the existence of potentially “dangerous” black holes.]

I stand to my general conclusion that there is a residual catastrophic risk from metastable microscopic black holes produced at particle colliders.

Bonus link to Plaga's latest article on cosmic rays: Nature 453: 48-49.