## Thursday, October 12, 2006 ... //

The media were debating the question whether the LHC accelerator is going to destroy our Universe or at least our blue planet. The answer depends on whether or not you believe in physics or not. ;-)

If you do believe in theoretical physics of the last 32 years, including Hawking's semiclassical calculations and/or its confirmations by string theory, you will be almost certain that the black holes, even if they were created, will decay instantly.

If you don't believe theoretical physics, especially if you only believe some parts of it - such as the possible occurence of man-made black holes at the LHC - you may be worried. :-) Perhaps, the black holes will be produced and they will swallow the Earth.

The famous
that is lifeguarding humanity and that has several Nobel prize winners on its science advisory board has concerns, however. One of their new goals is to prevent and make plans for surviving when
such as the decay of our vacuum or the creation of growing black holes or strangelets will occur. One of their main plans how to survive such an LHC catastrophe is to colonize the Cosmos. :-)

Well, I think that even if someone believes that theoretical physics can't be trusted - and many people clearly do - there exists a less scientific argument why the accelerator won't lead to such a catastrophe: the Earth is bombed by a lot of very high-energy cosmic rays and the center-of-mass energy of the collisions is comparable to the LHC energies. So far, these collisions haven't destroyed the Earth, so it is reasonable that some additional collisions we create won't be able to do so either.

Well, yes, I am assuming that it is the center-of-mass energy that decides about the products in such a collision. In other words, I believe special relativity. If we are not allowed to use special relativity in such arguments, it will indeed become very difficult to assure anyone that the LHC is safe and that it won't destroy the Earth. ;-)

#### snail feedback (6) :

Dear Lubos:

I believe in theoretical physics and in Hawking's calculation, but I strongly disagree with your argument that because cosmic ray collisions have not destroyed our blue earth yet, we should feel safe with the collisions at the LHC. LHC collisions differ substantially from cosmic ray collisions in a very simple way that I thought that prominent physicists as yourself should have very easily already identified! Here's my logic, and please correct me if I am wrong:

In collider collisions, two particles moving in opposite directions collide. Momenta cancel. Some mini black holes created this way would be moving slowly, slow enough to get captured by earth's gravitational field. A slow mini black hole would drop into the earth, orbiting within the earth and eventually coming to rest at the center of earth, where it would have forever to accrete matter and grow exponentially. On the other hand, a mini black hole made by a collision between a cosmic ray particle and an earth particle would move at the average of the momenta of the particles creating it. Since one of these particles is a cosmic ray with enormous momentum, it would be moving at a reasonable fraction of the speed of light. To slow to less than escape velocity of the earth it would have to accrete thousands of particles. But there is reason to think that a mini black hole would be about as reactive as a neutrino, a particle that can zip right through the earth or the sun with little probability of a single collision. The probability of thousands of accretions in a single pass through the earth is so low that it is unlikely to happen in trillions of trials over billions of years.

I would tremendously appreciate it if you could provide your thoughts on this argument, as I believe that it makes a lot of sense, at least to me who I am "only" an electrical engineer after all. I am one of these people that have already lost a lot of sleep over this issue and any sensible comment especially from highly educated and respected physicists as yourself, would be invaluable.

Thank you very much, and again I aprpeciate your time!

Respectfully,
Takis Kourouniotis

Dear Lubos:

I need to clarify one point: Yes, I believe in Hawking radiation but in my previous comment I am ASSUMING that Hawking is "wrong" and Hawking radiation does not exist. I am just attempting to expose my thoughts in a worst-case scenario.

Thank you again,
Takis

Takis,

Even if the inertia of two particles that produce a LHC born black hole and Hawking was wrong, the Schwarzschild radius would have to be very close to the Planck length. It would have virtually no gravitational effect on surrounding matter. It could easily pass through an atom with without notice.

I don't know what the numbers are but I would think that it would take trillions of years, if not more to even grow to a substantial size.

I am excited at the prospect of laboratory black holes. By energies it takes to make them and measuring the rate of evaporation we will be able to determine the sizes and number of other possible extra dimensions and possibly proving String Theory.

Eric

The Large Hadron Collider [LHC]at CERN might create numerous different particles that heretofore have only been theorized. Numerous peer-reviewed science articles have been published on each of these, and if you google on the term "LHC" and then the particular particle, you will find hundreds of such articles, including:

1) Higgs boson

2) Magnetic Monopole

3) Strangelet

4) Miniature Black Hole [aka nano black hole]

In 1987 I first theorized that colliders might create miniature black holes, and expressed those concerns to a few individuals. However, Hawking's formula showed that such a miniature black hole, with a mass of under 10,000,000 a.m.u., would "evaporate" in about 1 E-23 seconds, and thus would not move from its point of creation to the walls of the vacuum chamber [taking about 1 E-11 seconds travelling at 0.9999c] in time to cannibalize matter and grow larger.

In 1999, I was uncertain whether Hawking radiation would work as he proposed. If not, and if a mini black hole were created, it could potentially be disastrous. I wrote a Letter to the Editor to Scientific American [July, 1999] about that issue, and they had Frank Wilczek, who later received a Nobel Prize for his work on quarks, write a response. In the response, Frank wrote that it was not a credible scenario to believe that minature black holes could be created.

Well, since then, numerous theorists have asserted to the contrary. Google on "LHC Black Hole" for a plethora of articles on how the LHC might create miniature black holes, which those theorists believe will be harmless because of their faith in Hawking's theory of evaporation via quantum tunneling.

The idea that rare ultra-high-energy cosmic rays striking the moon [or other astronomical body] create natural miniature black holes -- and therefore it is safe to do so in the laboratory -- ignores one very fundamental difference.

In nature, if they are created, they are travelling at about 0.9999c relative to the planet that was struck, and would for example zip through the moon in about 0.1 seconds, very neutrino-like because of their ultra-tiny Schwartzschild radius, and high speed. They would likely not interact at all, or if they did, glom on to perhaps a quark or two, barely decreasing their transit momentum.

At the LHC, however, any such novel particle created would be relatively 'at rest', and be captured by Earth's gravitational field, and would repeatedly orbit through Earth, if stable and not prone to decay. If such miniature black holes don't rapidly evaporate and are produced in copious abundance [1/second by some theories], there is a much greater probability that they will interact and grow larger, compared to what occurs in nature.

There are a host of other problems with the "cosmic ray argument" posited by those who believe it is safe to create miniature black holes. This continuous oversight of obvious flaws in reasoning certaily should give one pause to consider what other oversights might be present in the theories they seek to test.

I am not without some experience in science.

In 1975 I discovered the tracks of a novel particle on a balloon-borne cosmic ray detector. "Evidence for Detection of a Moving Magnetic Monopole", Price et al., Physical Review Letters, August 25, 1975, Volume 35, Number 8. A magnetic monopole was first theorized in 1931 by Paul A.M. Dirac, Proceedings of the Royal Society (London), Series A 133, 60 (1931), and again in Physics Review 74, 817 (1948). While some pundits claimed that the tracks represented a doubly-fragmenting normal nucleus, the data was so far removed from that possibility that it would have been only a one-in-one-billion chance, compared to a novel particle of unknown type. The data fit perfectly with a Dirac monopole.

While I would very much love to see whether we can create a magnetic monopole in a collider, ethically I cannot support such because of the risks involved.

Regards,

Walter L. Wagner (Dr.)

Well Motl are you going to respond to these questions or do you not give a damn that you physicists might destroy the world?