There were some slightly outlandish suggestions that Tunguska could have been created by the evaporation of a larger micro-hole in the atmosphere. Most theories now are that it was a meteorite, with a possible impact crater now found.

I was under the impression that the Tunguska incident was caused by a comet (more ice than actual stone), accounting for no (or a very small) crater and copious amounts of glass spherulites all over the place?

As for Earth feeding a black hole: If Earth was pressed into the size of a ping-pong ball, matter would collapse enough to create an event horizon. The question is if a black hole that small would be able to excert enough gravitational pressure to keep other forces from expanding the matter beyond the black-hole state.

Is that what I get for my garbage recycling,an earth eating black hole! Pfff,I gonna rev my car and toss some cans in the woods while I can.

quote:

I was under the impression that the Tunguska incident was caused by a comet (more ice than actual stone), accounting for no (or a very small) crater and copious amounts of glass spherulites all over the place?

That certainly was the orthodoxy for a long while, but some are saying meteorite again based on the possibility of a lake being a crater. If they probed the lake it might answer the question but probing under a lake in the middle of nowhere will be challenging!

quote:

ping-pong

Boris says it should now be called a wiff-waff ball

In LHC they'll collide protons with energies of 7TeV, so max. possible mass of a micro black hole will be 14MeV. This means such a black hole would evaporate in much much shorter period than Planck time - time needed for light to travel the Planck distance (=~10^-44s - that's so short that if Planck time lasted for one sedond, then our real second would last for 10^27 times age of universe, that's more than a billion times more than there were seconds in our universe up to now)

According to what we believe today this means even it's creation is questionable, since due to quantum fluctuations time space gets so distorted at such scale that you can't really tell future from the past.

This is an odd question but I am quite serious (I find this sort of stuff fascinating although hard to understand!), but if there are black holes going through the Earth (in theory) what would happen if one were to touch a person?

quote:

Originally posted by turnipkiller:
This is an odd question but I am quite serious (I find this sort of stuff fascinating although hard to understand!), but if there are black holes going through the Earth (in theory) what would happen if one were to touch a person?

Depends how big it would be (how large its Schwarzschild radius Rs would be). Firstly, the term "touch" can be misleading. Black hole would simply run through everything, like there is no obstacle. If one with Rs less than a few molecules (1nm) would run through a human body, person would not even feel or detect it, and a black hole would only suck in some atoms/molecules from the body (for comparison, in average human body every second 2000 - 4000 atoms decay through spontaneous nuclear fission). Such black hole would still have a mass of ~10^18kg (!).

With a larger and larger black holes, a contact would soon become fatal, since black hole would tear more "material" from the body.

i think lhc danger is not a balck hole but to turn earth into strangelets

Hello al see this article and ponder its questions and outcomes

arXiv:0808.1415v1 [hep-ph] 10 Aug 2008
On the potential catastrophic risk from
metastable quantum-black holes produced at
particle colliders
R. Plaga a
aFranzstr. 40, D-53111 Bonn, Germany
Abstract
The question of whether the collider production of subnuclear black holes might
constitute a catastrophic risk is explored in a model of Casadio & Harms (2002)
that treats them as quantum mechanical objects. A plausible scenario in which
these black holes accrete ambient matter at the Eddington limit shortly after their
production, thereby emitting Hawking radiation that would be harmful to Earth
and/or CERN and its surroundings, is described.
Such black holes are shown to remain undetectable in astrophysical observations
and thus evade a recent exclusion of risks from subnuclear black holes by Giddings
& Mangano (2008). I further question that their risk analysis is complete for the
reason that it excludes plausible parameter ranges from safety consideration without
giving a sufficient reason. The reasons why Giddings & Mangano drew very different
general conclusions are found to be of a methodological rather than scientific nature.
Some feasible operational measures at colliders that would allow the lowering of
any remaining risk probability are proposed.
1 Introduction
Theories with “extra dimensions”[27], are one of the most popular extensions
of the standard model of particle physics and a central plank of string
theory[13]. If extra dimensions exist the Planck scale could occur at a much
lower energy than usually supposed[2,31]. Subnuclear “micro” black holes
(mBHs) can then be copiously produced at future high-energy particle colliders[10,27],
such as the “Large Hadron Collider” (LHC) at CERN. A production rate
of up to about one BH per second could then occur at the nominal LHC
Email address: rainer.plaga@gmx.de (R. Plaga).
Preprint submitted to Elsevier 10 August 2008
luminosity[10], i.e. the LHC would be a “black-hole factory”[14]. The phenomenology
of this possibility at colliders has received detailed attention, see
e.g. Cavaglia et al.[4].
The possibility that a collider-produced black hole (BH) - or another exotic object
- might catastrophically grow by accretion and thus injure or kill humans
deserves careful attention[36,24,6,32]. A recent scientific comparative study of
global risks[28] has put a risk very similar to the one considered here (from
collider-produced “strangelets”) at the top “response priority” of all current
“untreated risks” (such as, for example, super volcano eruptions and asteroid
impacts). Clearly this potential risk is based on speculative theories. But
these theories were constructed to explore real possibilities. The probability
that they are correct is not negligible.
Recently this risk has been studied in great detail in a seminal paper by
Giddings & Mangano (G & M)[18] 1 . They consider two frameworks for the
description of mBHs. In a standard “first scenario” collider produced mBHs
are treated with a semiclassical thermodynamical description (i.e. assuming
a canonical ensemble). The mBH is described as a heat bath and any back
reaction of the emitted particles on the mBH is neglected. mBHs are then expected
to decay, via the emission of “Hawking radiation”, on extremely small
timescales after their production, thus cannot grow and pose no danger.
In a second scenario G & M assume that mBHs “do not undergo Hawking
decay” in a purely ad hoc manner, in order to “conduct an independent check
of their benign nature”. They rightly point out that this second scenario, while
not being completely unphysical 2 , is not preferred “on very general grounds”.
G & M study the behaviour of mBHs after their production at the LHC in
this scenario and find that for certain possible choices of parameters a collider
produced mBH might accrete Earth on time scales, quote, “that are too
short to provide comfortable constraints”. The existence of mBHs within the
“dangerous” parameter range is then excluded by demonstrating that cosmicray
produced mBHs would accrete white dwarfs with small magnetic fields on
smaller time scales than their age. Similar arguments applied to planets and
ordinary stars are shown to fail to provide general safety limits, because all
neutral cosmic-ray produced mBHs are shown to escape these bodies. Such
arguments remain not completely definite for neutron stars because it remains
unclear if cosmic rays with sufficient energy reach their surface.
It is the aim of the present paper to explore a third scenario, in addition
to the two presented by G & M. Alternatively mBHs may be described by
the “microcanonical ensemble” (i.e. one in which the total energy remains
1 The conclusions of a report[12] by the “lsag group” at CERN on the safety of
microscopic black holes are mainly based on this paper. A very recent preprint of
Koch et al.[25] uses a similar argument than G & M to exclude their safety-critical
case “D4”. My conclusions therefore apply to their work, too.
2 G & M quote Unruh & Sch¨utzhold[35] who constructed a speculative model with
this property.
2
fixed)[20,8,33,19]. It is thought to be more fundamental than the standard
canonical ensemble. The mBH are typically described as extended stringy objects,
like e.g. “p-branes”. They are then a new type of elementary particle
a “quantum black hole”[21,26]. In a sense this framework is more plausible
than both frameworks studied by G & M, because it can avoid a violation of
unitary evolution and energy conservation[9,5], serious problems that are well
known to beset the first scenario used by G & M[30,18]. G & M endorse a
quantum mechanical treatment of mBHs at the end of their section 2.1, but
they do not develop this possibility further in their report.
A treatment of collider produced mBHs within scenario 3 and including extra
dimensions, has been provided by Casadio & Harms (C & H)[7]. In the following
I will exclusively study the behaviour of mBHs in the famous “Randall-
Sundrum 2 (RS 2) model”[31], presented in one of the most frequently quoted
papers in the recent history of high energy physics, within C & H’s framework.
In trying to understand if mBHs could be dangerous I will repeatedly resort
to a use of G & M’s excellent theoretical tools. I try to assume reasonably
mild worst case assumptions, similar to the strategy of G & M3 . However, I
strived to introduce no “ad hoc” or finely tuned assumption, that would deem
highly implausible to specialists in the field.
2 Properties of RS 2 quantum microscopic black holes in the Casadio
& Harms model
Quantum black holes are in principle unstable, i.e. they evaporate because
no conserved quantum number forbids them to do so[18]. However, it is well
known that their Hawking luminosity is strongly suppressed with respect to
semiclassical expectations for black-hole masses below the Planck mass[9] in
4 space-time dimensions. If the additional curved spatial dimension of the RS
2 model exists, C & H predict a Hawking luminosity of the mBH of[7]:
P5 =
MBH~c6
15360G2M3
N
(1)
This formula is expected to be valid for black holes with sizes for which their
metric can be well described by a 5-dimensional Schwarzschild solution. MBH
is the mass of the black hole and MN is the smallest mass for which the usual
4 dimensional expression for the Hawking luminosity:
P4 =
~c6
15360G2M2
BH
(2)
3 G& M wrote: “...at each point where we encountered an uncertainty, we have
replaced it by a conservative “worst case” assumption”.
3
is a good approximation. For given curvature scale “L” (associated with the
warping in the RS 2 model) C & H assume that MN is equal to black hole
mass at which the 5 dimensional Schwarzschild radius reaches is equal L. This
gives:
MN =
3L2c2M3
5
8~2 (3)
Here M5 is the “new” Planck scale (set to 1 TeV in all numerical estimates
below). This normalisation ensures that eq.(1) surely applies. Because usually
MN ≫ M5 the Hawking luminosity P5 of mBHs with a radius < L is strongly
suppressed with respect to the standard 4-dimensional expression P4.
The geometry of mBHs with Schwarzschild radii between L and ≈ 6 × L 4 is
not known, and it remains presently unclear if eq.(2) can be applied in this
“transitional region”. Only for black holes with masses above “MC”, the mass
of a mBH with a Schwarzschild radius of 6L, above which a 4-dimensional description
of the mBH is a good approximation, does this appear to be certain.
MC is given as:
MC ≈
3Lc2
G
(4)
One might equally well normalize the luminosity equally MC setting:
MN = MC (5)
The decision between normalisation in eq.(3) and eq.(5) comes down to the
question of whether the luminosity of a mBH is described by the 5-dimensional
(eq.(1)) or 4-dimensional (eq.(2)) expression in the transitional region between
L and ≈ 6 L. All one can presently say with reasonable certainty is that the
correct normalisation lies at some intermediate value between (and including)
the two extremes.
C & H discuss that with their normalisation metastable mBHs with lifetimes
of many years exist, but only for very large values of L approaching the experimentally
excluded range L>10−4 m[23]. It can be easily shown that with
normalisation eq.(5) mBHs are quasistable for all possible values of L 5 .
Summarising, mBHs may very well be generally “quasistable” (in the sense
of lifetimes exceeding years), without introducing any implausible “ad hoc”
assumptions. These mBHs do emit Hawking radiation, but with a reduced
4 This range was derived from eq.(3.26) of G & M for the scales of L of interest
in this manuscript: 10−9 m < L < 10−4 m. If L was smaller, mBHs in the third
scenario would pose no catastrophic risk.
5 i.e. the range from 1/M5 to 10−4 m
4
luminosity with respect to the standard 4-dimensional Hawking radiation luminosity
by the very large dimensionless factor ( ~
cLM5
)6 (this expression is
valid for the first normalisation (eq.(3))). In scenario 3 and 1 (i.e. the scenarii
without an artificial “switch off” of Hawking radiation) Schwinger radiation
is expected to neutralize mBHs on a very short time scale due to Schwinger
radiation[17,16], i.e. mBHs can be assumed to be neutral. Because G & M
concluded that 5-dimensional sufficiently stable mBHs might accrete matter
at an extremely fast rate (growth rate much below a second, see below section
3) quasistable mBHs are potentially dangerous. In the light of the scenario 3,
without an “a priori safety guarantee”, an astrophysical (or other) exclusion
of the existence of such mBHs is a “critical safety guarantee” rather than an
“additional check of their benign nature” as it was characterised by G & M
for scenario 2.
3 A potential threat from microscopic black holes that Hawkingradiate
at the Eddington limit?
The mBHs in scenario 3 emit Hawking radiation, and according to eq.(1) the
emitted power rises linearly with the their mass. Might this radiation be more
dangerous than the mechanical action of the accretion? Unfortunately this
might be the case for certain parameter choices. For purely illustrative purposes
I set L=10−7 m below. Let us further assume that MN = 1.9 × 105 kg,
a value intermediate between the first and second normalisation (section 2).
According to eq.(1) mBHs would then have a lifetime of about 2 seconds. A
collider-produced mBH that has been captured and slowed down to thermal
velocities, accretes and quickly grows by the “subatomic accretion mechanism”
characterised in section 4.2 of G & M. According to their eq.(4.22) it will take
about 0.15 msec until the so called “electromagnetic radius” reaches atomic
sizes 6 . Thereafter the accretion is well described as Bondi accretion and according
to eq.(4.40) in G& M it will take about 2.2 msec until the mBH’s
Schwarzschild radius reaches L at a mass of 0.54 kg. The further evolution
of the mBH’s shape and size in the “transitional region” between 5 and 4-
dimensional behaviour (see section 2) is not well understood. For simplicity I
will assume that the radius remains constant at L (a radius increase logarithmic
with the mBH’s mass[15] would not change the results appreciably.). For
the exemplary numbers chosen, eq.(4.31) of G & M predicts an increase of the
mBHs mass at a rate of 1.9 × 104 kg/sec. It will take about 20 μsec until its
mass reaches about 1 kg. At this mass the luminosity of the mBH is predicted
by eq.(1) to be 5.1 × 1016 W or an mass equivalent of dm/dt = 0.57 kg/sec
6 A conservative thermal velocity of 1500 m/sec was used to convert the units in
eq.(4.22) to a time.
5
being emitted as UV radiation. It is easy to verify that the five-dimensional
Eddington limit (eq.(B.25) of G & M)
dM/dt =
2.44 × 8mpRBc2
s
c
(6)
has the same magnitude for an efficiency =1. Here mp is the mass of the
proton, RB the Bondi radius (4.1 mm for our parameters), cs the velocity of
sound in the interior of Earth (5200 m/sec) and the Thomson cross section.
Therefore the radiation pressure of this Hawking radiation is intense enough to
limit the amount of accreted matter to the same amount: dm/dt = dM/dt i.e.
the mBHs accretes at the 5-dimensional Eddington limit. All accreted mass is
then reradiated as light and the mBH’s mass remains constant. G & M discussed
the possibility of an radiation limited accretion in detail and excluded
it because in scenario 2 the Hawking radiation is completely switched off.
For the next 3 × 1017 years, a time span vastly exceeding the life time of our
sun as a normal star, the mBH will radiate at the quoted, constant luminosity.
The power of 5.2 × 1016 W is 1300 times larger than the total geothermal
power emitted by Earth[1], and only 3 times less than the total power Earth
receives from the sun. The radiated power exceeds the total seismic power if
the Earth by an estimated factor of many millions[11]. 17000 metric tons of
ambient matter would be converted to radiation each year. While the exact
phenomenology provoked by such a mBH accreting at the Eddington limit
remains to be worked out, eventually catasrophic consequences due to global
heating on an unprecedented scale and global Earth quakes would seem certain.
Disturbingly the effects of such a mBH on a white dwarf or neutron star would
be negligible. Assuming the same mBH parameters as above and the theory
of section 7 in G & M, the luminosity of the mBH accreting at the centre of a
white dwarf is predicted to be 5.9 × 1019 W or a fraction of 1.5 × 10−7 of the
solar luminosity. This is about 104 times smaller than the cooling rate of white
dwarfs in G & M’s sample[18,22] and thus cannot be detected 7 . The accretion
time of a white dwarf would exceed their present age by a large factor of >
1010. Therefore no conclusions about mBHs can be drawn from the observed
existence of such objects. The conditions for a neutron star would be similarly
unspectacular. Completely independent of the doubt raised in section 5, the
argument of G & M fails to exclude the existence of mBHs that are dangerous
because of their intense Hawking radiation.
The numbers given in this section were chosen for an illustrative but not fine
tuned parameter choice. There is a wide range of values for L and MN that
7 G & M find that many mBHs are produced in white dwarfs in the course of time.
However, these mBHs will also tend to merge over time, so that the total number of
black holes in a given white dwarf might remain small. This question needs further
study.
6
lead to dangerous mBHs accreting at the Eddington limit with various luminosities.
In general the example developed above demonstrates that the intuitions that
mBHs accretion must be slow, and that events which are catastrophic for
Earth must also be for compact objects, can be wrong.
4 A catastrophe at CERN?
The luminosity of a mBH accreting at the Eddington limit with the parameters
assumed above corresponds to 12 Mt TNT equivalent/sec[11], or the energy
released in a major thermonuclear explosion per second. If such a mBH would
accrete near the surface of Earth the damage they create would be much larger
than deep in its interior. With the very small accretion timescale (≪ 1 second)
that was found with the parameters in section 3, a mBH created with
very small (thermal or subthermal) velocities in a collider would appear like
a major nuclear explosion in the immediate vicinity of the collider.
5 Does the observed existence of old white dwarfs with a low magnetic
field rule out “dangerous” quasistable black holes?
The doubt raised into the generality of one argument if G & M in this section
applies to all scenarios discussed in the introduction.
In the text following their eq. (E.2) G & M formulate the following assumption:
Mmin > 3 M5 (7)
Thereby G & M introduce the assumption that mBHs in general have a minimal
mass Mmin that exceeds the new Planck scale by at least a factor 3. This
constraint is motivated by the fact that the thermodynamical, semiclassical
treatment of mBHs in their “scenario 1” is expected to be reliable within this
mass range. This is certainly a most reasonable argument for all purposes of
pure research, e.g. when predicting collider signatures etc.. However, it does
not mean that mBHs below Mmin cannot be produced. It rather means that
we are presently unable to reliably predict the behaviour of such mBHs 8 .
This fact raises a fundamental doubt about G & M’s exclusion of “dangerous
8 In a previous paper[17] Giddings wrote: “For masses of order the fundamental
Planck scale [i.e. M5] there is no control over quantum gravity effects which are
likely to invalidate the semiclassical ... picture.”
7
mBHs” by way of observing a certain class of white dwarfs. The exclusion depends
on their careful and detailed demonstration in their section 5 that “dangerous”
mBHs are stopped in white dwarfs after their production in collisions
of cosmic rays. However, this demonstration is based on an assumed validity of
the semiclassical approximation. mBHs deep in the “quantum gravity” regime
(violating eq.(7)) might behave differently and escape white dwarfs, just as
they could escape ordinary stars in the semiclassical approximation.
Concluding, G & M have not demonstrated that white dwarfs stop cosmic-ray
produced mBHs in general. Their exclusion of dangerous mBHs thus remains
not definite.
6 Conclusion
Treating mBHs as quantum objects in one possible consistent way, leads to
the possibility that a mBH produced at a collider is captured by Earth and accretes
at the Eddington limit, thereby emitting Hawking radiation that might
be dangerous to as a whole and/or the inhabitants of CERN and its surroundings.
The astrophysical arguments by G & M do not apply in this scenario,
because the lifetime of white dwarfs with Eddington accreting mBHs turns
out to be extremely long (section 3).
Moreover, for another independent reason, the exclusion of mBHs that threaten
to accrete Earth by G & M cannot be considered definite in general (section
5).
At the present stage of knowledge there is a definite risk from mBHs production
at colliders. This final conclusion differs completely from the one drawn
by G & M. This is not because of any disagreement over the purely scientific
content of their excellent paper. Rather the difference is the sole result
of employing an alternative plausible scenario for the physics of mBHs and
including parameter regions in which mBHs are not expected to be well described
by the semiclassical scenario in the safety analysis.
It is not the aim of the present paper to recommend or discuss consequences
for the future operation of colliders, beyond proposing to introduce (not yet
implemented) safety regulations. I put up for further dicussion three feasable
measures for risk mitigation, at least in the start up phase of LHC:
1. Increase of collision energy by reasonably small factors (say, 2) in one step.
Currently it is planned to perform the first runs at LHC at an energy more
than 5 times higher than previously reached[29]. This might result in the copious
production of completely novel states, which production was exponentially
suppressed at the previous energies. “Proceeding in small steps” mitigates this
risk.
2. No operation in which no or only a very tiny fraction of events are analysed.
Currently it is planned to eventually record and analyse only a fraction of 10−7
8
of all events[34]. This is the equivalent of entering new territory and to be on
the lookout only for the interesting but not the potentially dangerous.
3. Safety considerations influence the trigger and operational procedures. Meta
stable black holes might not yield very spectacular events, but it seems desirable
to ensure that their presence is immediately and reliably detected. An
immediate interruption of operation and detailed offline study of the event
might be a possible risk mitigating measure.
To take such safety measures would not exclude but reduce any remaining
risk. Methodologically similar measures have been taken in other areas of fundamental
research under analogous circumstances, e.g. in biotechnology[3].
7 Acknowledgements
I thank G.t’Hooft, M.Jarnot, M.Leggett and S.Pezzoni for critical comments
on a previous version of the present manuscript. I thank R.Casadio for his
patient and helpful explanations of his theory.
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9
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10

i think they should ask a child

should we recreate the EXPLOSION that started this universe?

Well, that's a point. What's the benefit of all this? I mean, what are the benefits for human kind, apart from confirming or rejecting some bizarre and arcane nuclear Physics theories which no common person gives a cr*p about? Is it worth the risk of destroying ourselves -even if it is so negligible?

I'm with Brillat-Savarin in this:
"The discovery of a new dish confers more happiness on humanity, than the discovery of a new star."

I would hardly call this bizarre and arcane nuclear physics, and it doesn't matter if the common person doesn't care about it, most common people couldn't care less about the processes which give them TV and junk food and tabloid magazines, as long as they keep getting them. The benefit of this is the possibility of discovering the foundations of, basically, everything, and redefining the laws of physics. Some people might be content with the first answer that's given to them, but others feel the need to continue the search for the truer answer.

quote:

Originally posted by HotelBushranger:
The benefit of this is the possibility of discovering the foundations of, basically, everything, and redefining the laws of physics.

And? What's the use of this? I mean, in my lifetime. I don't give a cr*p about the 4th millenium.

Will I be able to teletransport myself next year? Is cancer going to be defeated? Wars are made impossible? Hunger and anger are ending? Will I travel to Alpha Centauri next decade? Immortality is at hand? Will I marry a custom-made AI sweetheart? Hamburgers and hotdogs will be healthy and cholesterol-free from now on? Is SoW development going to be faster?

Right now, this is only a nerd's caprice. Totally OK, but not worth the lives of your neighbors. Playing gods is fun, until you have real god powers. Then, being "destroyers of worlds" becomes no fun at all. Ask Oppenheimer.