Günter Nimtz
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Günter Nimtz (born 22 September 1936) is a German physicist, working at the 2nd Physics Institute at the University of Cologne in Germany. He has investigated narrow-gap semiconductors and liquid crystals. His claims show that particles may travel
faster than the speed of light Faster-than-light (also FTL, superluminal or supercausal) Superluminal motion, travel and Faster-than-light communication, communication are the conjectural propagation of matter or information faster than the speed of light (). The special theor ...
(''c'') when undergoing quantum tunneling.


Academic career

Günter Nimtz studied Electrical Engineering in Mannheim and Physics at the University of Heidelberg. He graduated from the University of Vienna and became a professor of physics at the University of Cologne in 1983. During 1977 he was a research associate for teaching and researching at McGill University, Montreal/Canada. He achieved emeritus status in 2001. During 2004 he was Visiting Professor at the
University of Shanghai University of Shanghai, also known as Shanghai College and Hujiang University (), was a university established by the American Baptist Missionary Union and the Southern Baptist Convention in Shanghai. It was the predecessor of University of Sh ...
and of the
Beijing University of Posts and Telecommunications The Beijing University of Posts and Telecommunications (BUPT) () is a key national university distinguished by the teaching and research in the field of cable communications, wireless communications, computer, and electronic engineering. BUP ...
. From 2001 to 2008 he was teaching and doing fundamental research at the
University of Koblenz-Landau The University of Koblenz and Landau (German ''Universität Koblenz-Landau'') is a public university located in Koblenz and Landau, Germany, founded in 1990. History and profile The University of Koblenz and Landau is one of the youngest univers ...
.


Industrial research and development

In 1993 Günter Nimtz and Achim Enders invented a novel absorber for electromagnetic anechoic chambers. It is based on a 10 nanometer -thick metal film placed on an incombustible pyramidal carrier (United States Patent: 5,710,564 and other countries). At the E. Merck Company / Darmstadt Nimtz designed an apparatus for the production of ceramic aerosols (patented and applied, 1992).


Experiments related to superluminal quantum tunneling

Nimtz and his coauthors have been investigating superliminal quantum tunneling since 1992. Their experiment involved microwaves either being sent across two space-separated prisms or through frequency-filtered waveguides. In the latter case either an additional undersized waveguide or a reflective grating structure had been used. In 1994 Nimtz and Horst Aichmann carried out a tunneling experiment at the laboratories of
Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
after which Nimtz stated that the frequency modulated (FM) carrier wave transported a signal 4.7 times faster than light due to the effect of quantum tunneling. Recently, this experiment was successfully reproduced by Peter Elsen and Simon Tebeck and represented at "Jugend forscht" the German pupil competition in Physics 2019. They won the first prize of Rheinland-Pfalz and the Heraeus Prize of Germany. Alfons Stahlhofen and Nimtz in a 2006 paper described an experiment which sent a beam of microwaves towards a pair of prisms. The angle provided for total internal reflection and setting up an
evanescent wave In electromagnetics, an evanescent field, or evanescent wave, is an oscillating electric and/or magnetic field that does not propagate as an electromagnetic wave but whose energy is spatially concentrated in the vicinity of the source (oscillati ...
. Because the second prism was close to the first prism, some light leaked across that gap. The transmitted and reflected waves arrived at detectors at the same time, despite the transmitted light having also traversed the distance of the gap. This is the basis for the assertion of faster-than-c transmission of information. Nimtz and coworkers asserted that the measured tunneling time is spent at the barrier front, whereas inside the barrier zero time is spent. This result was observed in several tunneling barriers and in various fields. Zero time tunneling was already calculated by several theoreticists.


Scientific opponents and their interpretations

Chris Lee has stated that there is no new physics involved here, and that the apparent faster-than-c transmission can be explained by carefully considering how the time of arrival is measured (whether the
group velocity The group velocity of a wave is the velocity with which the overall envelope shape of the wave's amplitudes—known as the ''modulation'' or ''envelope'' of the wave—propagates through space. For example, if a stone is thrown into the middl ...
or some other measure). Recent papers by
Herbert Winful Herbert Graves Winful (born 3 December 1952) is a Ghanaian-American engineering professor, whose numerous honours include in 2020 the Quantum Electronics Award. He is the Joseph E. and Anne P. Rowe Professor of Electrical Engineering, Arthur F. ...
point out errors in Nimtz' interpretation. These articles propose that Nimtz has provided a rather trivial experimental confirmation for General Relativity. Winful says that there is nothing specifically quantum-mechanical about Nimtz's experiment, that in fact the results agree with the predictions of classical electromagnetism ( Maxwell's equations), and that in one of his papers on tunneling through undersized waveguides Nimtz himself had written "Therefore microwave tunneling, i.e. the propagation of guided evanescent modes, can be described to an extremely high degree of accuracy by a theory based on Maxwell's equations and on phase time approach." (Elsewhere Nimtz has argued that since evanescent modes have an imaginary wave number, they represent a "mathematical analogy" to
quantum tunnelling Quantum tunnelling, also known as tunneling ( US) is a quantum mechanical phenomenon whereby a wavefunction can propagate through a potential barrier. The transmission through the barrier can be finite and depends exponentially on the barrier h ...
, and that "evanescent modes are not fully describable by the Maxwell equations and quantum mechanics have to be taken into consideration." Since Maxwell's laws respect special relativity, Winful argues that an experiment which is describable using these laws cannot involve a relativistic causality violation (which would be implied by transmitting information faster than light). He also argues that "Nothing was observed to be traveling faster than light. The measured delay is the lifetime of stored energy leaking out of both sides of the barrier. The equality of transmission and reflection delays is what one expects for energy leaking out of both sides of a symmetric barrier." Aephraim M. Steinberg of the University of Toronto has also stated that Nimtz has not demonstrated causality violation (which would be implied by transmitting information faster than light). Steinberg also uses a classical argument. In a ''New Scientist'' article, he uses the analogy of a train traveling from Chicago to New York, but dropping off train cars at each station along the way, so that the center of the train moves forward at each stop; in this way, the speed of the center of the train exceeds the speed of any of the individual cars. Herbert Winful argues that the train analogy is a variant of the "reshaping argument" for superluminal tunneling velocities, but he goes on to say that this argument is not actually supported by experiment or simulations, which actually show that the transmitted pulse has the same length and shape as the incident pulse. Instead, Winful argues that the group delay in tunneling is not actually the transit time for the pulse (whose spatial length must be greater than the barrier length in order for its spectrum to be narrow enough to allow tunneling), but is instead the lifetime of the energy stored in a
standing wave In physics, a standing wave, also known as a stationary wave, is a wave that oscillates in time but whose peak amplitude profile does not move in space. The peak amplitude of the wave oscillations at any point in space is constant with respect ...
which forms inside the barrier. Since the stored energy in the barrier is less than the energy stored in a barrier-free region of the same length due to destructive interference, the group delay for the energy to escape the barrier region is shorter than it would be in free space, which according to Winful is the explanation for apparently superluminal tunneling.This Winful explanation is wrong and it becomes obvious e.g. in a standing wave guide set-up at frequencies below the cut-off frequency. There is no measurable stored energy. For a summary of Herbert Winful's explanation for apparently superluminal tunneling time which does not involve reshaping, see This becomes obvious wrong in a standing wave guide set-up at frequencies below the cut-off frequency. Apart from these strange interpretations further authors have published papers arguing that quantum tunneling does not violate the relativistic notion of causality, and that Nimtz's experiments (which are argued to be purely classical in nature) don't violate it either.A number of papers are listed i
"Faster-than-light speeds in tunneling experiments: an annotated bibliography"
Markus Pössels Webseiten.
Some oppositional theoretical interpretations have been published.


Nimtz' interpretation

Nimtz and others argue that an analysis of signal shape and frequency spectrum has evidenced that a superluminal signal velocity has been measured and that tunneling is the one and only observed violation of special relativity.G. Nimtz and A. A. Stahlhofen, "Universal tunneling time for all fields", Ann. Phys. (Berlin), 17, 374, 2008 However - in contradiction to their opponents - they explicitly point out that this does not lead to a violation of primitive causality: Due to the temporal extent of any kind of signal it is impossible to transport information into the past. After all they claim that tunneling can generally be explained with
virtual photons A virtual particle is a theoretical transient particle that exhibits some of the characteristics of an ordinary particle, while having its existence limited by the uncertainty principle. The concept of virtual particles arises in the perturbat ...
, the strange particles introduced by Richard Feynman and shown for evanescent modes by Ali and by Cargnilia and Mandel.C. Carniglia and L. Mandel, Phys. Rev. D 3, 280, 1971; S. T. Ali, Phys. Rev. B 7, 1668, 1973 In that sense it is common to calculate the imaginary tunneling wave number with the Helmholtz and the Schrödinger equations as Günter Nimtz did in and Herbert Winful did in . However, Nimtz highlights that eventually the final tunneling time was always obtained by the Wigner phase time approach. In and Günter Nimtz outlines that such evanescent modes only exist in the classically forbidden region of energy. As a consequence they cannot be explained by classical physics nor by special relativity postulates: A negative energy of evanescent modes follows from the imaginary wave number, i.e. from the imaginary refractive index according to the Maxwell relation n := \sqrt for electromagnetic and elastic fields. In a publication, Nimtz again explicitly points out that tunneling indeed confronts special relativity and that any other statement must be considered incorrect. All waves have a zero tunneling time.


Related experiments

It was later claimed by the Keller group in Switzerland that particle tunneling does indeed occur in zero real time. Their tests involved tunneling electrons, where the group argued a relativistic prediction for tunneling time should be 500-600 attoseconds (an attosecond is one quintillionth of a second). All that could be measured was 24 attoseconds, which is the limit of the test accuracy. Again, though, other physicists believe that tunneling experiments in which particles appear to spend anomalously short times inside the barrier are in fact fully compatible with relativity, although there is disagreement about whether the explanation involves reshaping of the wave packet or other effects.


Temporal conclusions and future research

Nimtz' interpretation is based on the following theory: The expression 1 \over in the Feynman photon
propagator In quantum mechanics and quantum field theory, the propagator is a function that specifies the probability amplitude for a particle to travel from one place to another in a given period of time, or to travel with a certain energy and momentum. In ...
means that a photon has the highest probability of traveling exactly at the speed of light (hv = pc), but it has nonvanishing probability to violate the laws of special relativity, as a “virtual photon”, over short time and length scales. While it would be impossible to transport information over cosmologically relevant time scales using tunneling (the tunneling probability is simply too small if the classically forbidden region is too large), over short time and length scales, the tunneling photons are allowed to propagate faster than light, in view of their property as virtual particles. The photon propagation probability is nonvanishing even if the photon’s angular frequency omega is not equal to the product of the speed of light ''c'' and the wave momentum ''p''.T. S. Ali, Phys. Rev. D7, 1668 (1973) Nimtz has written in more detail on signals and the described interpretation of the FTL tunneling experiments.H. Aichmann and G. Nimtz, Found. Phys. 44, 678 (2014) Although his experimental results have been well documented since the early 1990s, Günter Nimtz' interpretation of the implications of these results represents a highly debated topic, which numerous researchers consider as incorrect (see above, #Scientific opponents and their interpretations). Some oppositional studies on zero time tunneling have been published.T. Hartman, J. Appl. Phys. 33, 3427, 1962; W. Franz, Phys. Status Solidi, 22, K139, 1967; Collins et al., J. Phys. C20, 6213, 1987; F. Low and P. Mende, Ann. Phys. NY, 210, 380, 1991; G. Nimtz, LNP 702, 506, 2006; Zero time tunneling – revisited, G. Nimtz and H. Aichmann, Z. Naturforsch. 72a, 881 (2017) The common descriptions of FTL-tunneling signals presented in most textbooks and articles are corrected into final conclusions according to Brillouin and other important physicists.


Selected works

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References


External links

* * {{DEFAULTSORT:Nimtz, Gunter 1936 births Living people 20th-century German physicists 21st-century German physicists Academic staff of the University of Cologne