Doxa: LHC Cern

source: Libération, December 2, 2018

author: Etienne Klein, physicist, director of research for the CEA

(Commissariat à l’énergie atomique et aux énergies alternatives, France),

and doctor in the philosophy of science. Director of research for the Laboratoire des recherches sur les sciences de la matière.

translation: doxa-louise

HOPING TO GO FURTHER, THE PARTICLE ACCELERATOR IS TAKING A BREAK

Research on the Higgs boson: the red lines show two high energy photons;

the yellow, the traces left by the particles produced in the collision.

Photo AP. CERN

By causing a collision between very high energy protons,the huge machine at Cern allows one to pull from the quantum void virtual particles, as, in 2012, the Higgs boson. Yet toattain a finer grasp of reality, one needs to get even closer tothe primordial universe.

OPINION. Quantum mechanics is in many respects the craziest theory

offered up by physics. Quite a ways form ordinary notions of the real, it

presents itself through laws that defy the wildest imaginings. It also clashes

with the ordinary meanings of words by showing that the void is not space

that is empty... It is an inhabited space, impossible to empty absolutely.

It seems to be filled by what we would call matter that is ‘tired’, made up

of particles that are really there but not really existing. They are like ghosts,

agitated, yes, but not possessing enough energy to truly materialize and thus,

because of this, that cannot be directly observed. These particles, called ‘virtual’

buzz vegetatively forming a soft ontology, not unlike Sleeping Beauties.

In order to bring them fully into existence, it is necessary to furnish the energy

missing for their full incarnation ( their ‘mass energy’, in Einsteins parlance,

that is mc^2). The void itself can in this matter play the role of Prince Charming.

In point of fact, it is more like an impatient banker, agreeing to lend energy to

virtual particles but on the very strict condition that they pay off the loan very rapidly.

And ‘very rapidly’, here means ‘in less than 10^-21 seconds’. By the terms of this

drastic contract, virtual particles can emerge from the quantum void by becoming

real, but with the obligation to go back to it almost instantly to pay off their energy

debt... almost to the point of annihilation! In other words, these pay dearly their

foray into radical existence.

Happily, there is another more efficient way to wake up the interlopers

from the quantum void: it is enough to create a collision, above their heads,

between two high energy particles. These will then offer their energy to the

void at no cost and, as a result, certain virtual particles will become real

and escape their hiding-place. They who were napping away find their

energy of before and leave the quantum void with a more or less

high energy level.

This is the game plan at this huge machine which is the Large Hadron Collider:

it explores the quantic void by exciting it. Concretely it is a particle collider

of 27 kilometers in circumference, built by the Cern on both sides of the

French-Swiss border, which permits collisions between protons (notably) with high
energy. One can guess the level of expertise needed for such an accomplishment:

two beams of minute dimendions, covering in an inverse direction and 11 245 times
per second a ring of 27 kilometers in circumference at a speed near that of light, entering

into a collision at perfectly determined spots. Spread out all along the ring, over 1 200

dipolar supraconducting magnets 15 meters in length, kept cold in superfluid helium,

with high magnetic properties, while supraconducting cavities for radiofrequency

give to each the level of energy equivalent to the flight of an insect.

It is thanks to this powerful collider that in 2012 the Higgs boson was called from
the void, then found and identified thanks to two enormous detectors, CMS (Compact Muon Solenoid) and Atlas (A Toroidal LHC Apparatus). This discovery is major in that it
has provoked a reversal in thinking about the notion of mass. In our minds, the notions
of mass and matter appear as inseperable, as if entangled one with the other: we cannot
imagine a material object without a mass, and we have trouble imagining mass that
would not be incarnate in material things, more or less small. Mass thus appears as an
evident and intrinsic property of material objects.

However, what physicists now know, thanks to the discovery of the Higgs boson
which had been foreseen in 1964, is that in place of being a primitive property of
particles that are ‘elementary’, a characteristic that would be carried ‘by itself’, mass
appears to be no more than a secondary property and indirect because caused by the
interaction of the said particles with... the quantum void. The latter encompasses a quantum
field filling all of space, with which these elementary particles, in truth without mass,
interact more or less strongly, which results in a ‘hampering’ of their movement by
conferring inertia, as if they had mass.

This conceptual revolution gave proof to what is called ‘ the Standard Model of
particle physics’. Yet this cannot be the whole story, because this model, wholly quantic

in nature, does not include gravity. This somewhat special interaction is described
elsewhere in any event, alone in a corner, by Einstein’s General Relativity theory, whose
principles and concepts are totally different from those of quantum physics, and even in

contradiction with them. This hardly matters, because the domains of application

are quite distinct: they co-exist peacefully, without any one impinging on the other.

Up until now, no experiment has been asked to explore physical systems whose theoretical explanation needed both at once. But, and this is a crucial point, such a separation could
not have held sway in the primitive universe, when it was of very small size and chock
full of energy: at that time, the spatial dimensions fo the universe were so minuscule and
the energies so colossal that matter and space-time overlapped, mixing so utterly that
one hardly knows what calculations could translate this situation with exactitude.

The LHC will be stopped to do maintenance work and bring improvements. The
performance of the detectors will be upped so that they may be better equiped to identify
deviations from the standard model. This could herald the path to a ‘new physics’. There
will also be work done to prepare the next increase in ‘luminosity’, this parameter important
to physicists because it determines the number of collisions produced per unit of time:
the greater the luminosity, the more one can observe rare phenomena.

Once the monster thus tweaked has been restarted, the data harvested will perhaps allow
one to do a bit of housekeeping on the numerous theoretical starting points trying to describe
the most dense and hot phases of the primordial universe. Perhaps they will also resolve the excrutiating problem called ‘dark matter’, this matter which seems to produce gravitational
effects without emitting light. According to certain models, it could be made up of particles
not yet identified which the LHC could ‘corner’... The down period ont the machine will
last two years. The quantum void, in turn, will then be in for a visit.

* * *
(Helped me!)