Jun 15, GianCarlo Ghirardi, former professor of theoretical physics and then emeritus at the physics department of our university, passed away on 1st. GianCarlo Ghirardi. Angelo Bassi and Tullio Weber. University of Trieste, Trieste, Italy. Detlef Dürr. Ludwig-Maximilians University, Munich, Germany. PDF Full. Jun 4, The ICTP community is mourning the sudden passing of long-time colleague GianCarlo Ghirardi. Professor Ghirardi was associated with ICTP.
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Trieste Professor Fabio Benatti credits Ghirardi for influencing his research direction. Why this aversion to ‘being’ and insistence on ‘finding’? In order to understand this point, we need to recall that the theory in its general formulation includes a postulate that becomes operative every time a process of measurement is carried out, and that is the postulate of the reduction or collapse of the wave packet.
The reader may recall the escape strategy Bohr used to defend his position against Einstein’s observations that a precise measurement of the state of a macroscopic object see Figures 7.
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The problem is traditionally approached with reference to what is technically known as von Neumann ‘s ideal measurement process, named from the scientist who first formulated it in precise terms. This reasoning can in principle be extended until it involves the entire universe, and it implies that gyirardi the universe would have only potentialities.
But it must be noted that even this last solution is not without ambiguity. But what, in Bohr’s view, would make the diaphragm or the pointer different from other systems used to determine the states of these objects—that is the real mystery. The most characteristic example, he says, is the diagonally polarized photon in a linear tiancarlo of vertical and horizontal polarization ghrardi discussed in the case of Dirac’s Three Polarizers.
Bell and presented by him at two conferences: The Landau—Lifshitz approach can be seen as maintaining this simple non-dual kinematics, but with the wavefunction compact on a macroscopic rather than microscopic scale. They became very aware of the intervening apparatus, and of the need for a ‘classical’ base from which to intervene on the quantum system. But then the question is, “Who measures the universe, and brings it out of the limbo of the potentialities?
His vast and diverse knowledge made me appreciate the beauty of science and its deep connections with what lies beyond its limits.
Like any physical theory, even quantum mechanics will have a limited field of application. To be more specific, the GRW theory admits that the wavefunction, besides evolving through the standard Hamiltonian dynamics, is subjected, at random times, to spontaneous processes corresponding to localisations in space of the microconstituents of any physical system.
The idea that a macroscopic pointer can point simultaneously in different directions, or that a cat can have several of its nine lives at the same time, is harder to swallow. The mean frequency of ghkrardi localisations is extremely small, and the localisation width is large on an atomic scale.
Superconductors could be mentioned, which show typical “tunnel effects” involving a macroscopic number of constituents. In the information physics solution to the problem of measurementthe timing and location of the Heisenberg “cut” are identified with the interaction between quantum system and classical apparatus that leaves the apparatus in an irreversible stable state providing information to the observer.
All historical experience confirms that men might not achieve the possible if they had not, time and time again, reached out for the impossible.
We can ask ourselves then: Since the number of the electrons is very large but still giahcarlo, what we see on the film will be a series of N black dots that correspond to the positions in which they are, so to speak, “revealed” by that object, which can be thought of as a measuring device. If a body has a velocity much less than the velocity of light, Newton’s theory is appropriate, but as the velocity increases it becomes increasingly less precise and fails completely when it comes to describing bodies that travel at velocities nearing that of light.
Physics > History and Philosophy of Physics
This serves extraordinarily well for defining the limited area of validity of classical mechanics. Where are we to place the boundary between the vague microscopic world and the precise world of our sensory experience?
Ghirardi—Rimini—Weber theory Quantum mechanics foundations. This is not spelled out very explicitly. So the wavefunction must be narrow as regards macroscopic variables. Here is an image John Bell proposed to illustrate this deep question. The extension of that region he thought of as the actual size of the electron — his electron was a bit fuzzy.
The GRW scheme represents a proposal aimed to overcome the difficulties of quantum mechanics discussed by John Bell in his article “Against Measurement. We know, they seem to say, that macroscopic pointers have definite positions. To appreciate fully the relevance of this question, and to prepare ourselves to analyze the multiple and interesting proposals advanced as a way of getting around such difficulties, it will be useful to begin by deepening our analysis.
No physicist would be embarrassed about this: In making this assertion, we have made a logical jump from the language of wave functions, and of the potentialities of a microsystem, to the language of the reality of the dots.
 My life with GianCarlo Ghirardi, a great friend, a great teacher and a great physicist
And this represents in a certain sense although many ambiguities remain the orthodox position: Why would that interpretation not have to face the embarrassing occurrence of superpositions of states that are distinguishable at the macroscopic level?
Nevertheless, as observed in the preceding section, this does not have any consequences for what concerns the fact that any assertion about the position of the pointer is illegitimate, and it is even not permitted us to think that it has a precise position.
And this is in fact what we would experience if we actually looked at the apparatus. Then, for the initial state we have the following: But actually the idea that an electron in a ground-state hydrogen atom is as big as the atom which is then perfectly spherical is perfectly tolerable — and maybe even attractive.
As we repeatedly emphasized in the early chapters of the book, the theory has been formulated in such a way as not to speak in general of properties possessed by systems but only of the probabilities of obtaining certain outcomes if measurements are carried out that intend to identify the values of the properties we are interested in.