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Location: UFOUpDatesList.Com > 2007 > Aug > Aug 25

Re: 'We Have Broken Speed Of Light'

From: Martin Shough <parcellular.nul>
Date: Fri, 24 Aug 2007 16:44:38 +0100
Archived: Sat, 25 Aug 2007 10:50:45 -0400
Subject: Re: 'We Have Broken Speed Of Light'

>From: Gerald O'Connell <gac.nul>
>To: ufoupdates.nul
>Date: Thu, 23 Aug 2007 12:52:32 +0100
>Subject: Re: 'We Have Broken Speed Of Light'

>>From: Eleanor White <eleanor.nul>
>>To: ufoupdates.nul
>>Date: Mon, 20 Aug 2007 16:35:19 -0400
>>Subject: Re: 'We Have Broken Speed Of Light'

>>>From: Gerald O'Connell <gac.nul>
>>>To: ufoupdates.nul
>>>Date: Mon, 20 Aug 2007 00:55:17 +0100
>>>Subject: Re: 'We Have Broken Speed Of Light'


>My question was intended to draw attention to the fact that
>extraordinary experimental data invariably raises some
>extraordinary questions. The first of these ought to be to go
>back to the assumptions underlying the original theoretical
>status quo, and to ask which of them might need to be suspended
>in order to explain the data.

>In a case like this there is always likely to be controversy
>because the basic assumptions involved are very fundamental
>indeed. Not everybody feels comfortable when baseline
>assumptions about things like 'space', 'movement' or 'speed' are
>called into question. If Physics has taught us anything in the
>last hundred years, then it is to regard our 'common sense'
>ideas about some of these things as potentially treacherous - a
>lesson that some physicists have not entirely taken on board
>(and who can really blame them when the most fundamental ideas
>that we use to categorise empirical data are called into

>Anyway, it would be nice to hear on this from List-members who
>have a sophisticated understanding of frontier physics.

Hi Gerald

It would indeed. In the meantime here is my understanding. As
someone else noted, this is not a new issue and has been
vigorously discussed for more than a decade. The consensus is
that the quantum tunnelling implies no violation of special
relativity. This is because a photon is not a bullet but a
probabilistic wave packet and because there are several
different dispersion velocities associated with photon
propagation, and it depends which one you are measuring.

First, classically speaking there is no constraint in SR that
the phase velocity of a wave has to be subluminal; in fact, the
phase velocity is generally superluminal and tends to infinity.
Also the group velocity of a packet of waves can exceed c. What
may not exceed c is what is called the front velocity. This may
sound strange, but the distinctions start to come into play when
you are tunnelling very long wavelength photons over a small
distance, as is the case with Nimtz (and others, going back
certainly to 1993).

A group velocity greater than c is sometimes claimed to violate
SR because we normally associate the group velocity with the
signal velocity, which is the speed of information carried by
the wave. But this is true only in cases of normal dispersion.
The group velocity can be described as the speed of the envelope
of the wave packet, and you can simulate what happens in cases
of abnormal dispersion (such as negative refractive index) by
combining a couple of simple waveforms (could be water ripples)
so that by the principle of superposition they generate a third,
different waveform which has a new velocity quite different from
either of its parent waves. This velocity can be made
arbitrarily large or even made to propagate in the opposite
direction. It's a bit like looking at the racing wagon wheels in
a western movie and seeing the spokes slow down and rotate
backwards. Some effects like this have been known for decades,
such as the apparently anomalous >c group velocity of light in
some thin metal foils.

In the Nimtz experiments this is the sort of effect that is
thought to happen, but it's complicated because it's a quantum
mechanical tunnelling through a potential barrier rather than a
classical wave propagation. In such a case the question of what
happens if you put a barrier in the way of a photon is already
answered - there is a barrier, and the photon is already
potentially on both sides of it. This again is a perfectly
conventional QM effect that has been known for many decades and
is also a related wave phenomenon that works as well for
electrons or any particle. In this case the wavefunction of an
electron in a box (walls = potential barrier) is found to extend
into regions where for a classical particle the kinetic energy
is negative and it cannot go, i.e. outside the box, but the
quantum particle has a small probability of being there,
proportional to the amplitude of its wave, and sometimes is.

By reference to the questions of wave velocity mentioned above
you can see that the question of "how fast does it go?" might be
complicated, and it is. The wavefunction represents a
probability of measuring some potentiality which, in some sense,
is already there. The question of where the electron/photon is
"really" before we measure it is regarded as a non-question as
it presumes knowledge of a state which is forbidden by the
uncertainty principle. Some aspect of the photon/elecrtron
exists on both sides of the barrier; but the measurable aspect,
the one associated with signalling information - the
"translation of a particle" in the case of the electron -
 happens here and then there, sequentially, and this particle
velocity is alwayts less than c.

Similarly, in the tunnelling-photons case the probability wave
plays the part of the classical wave. Some phase components of
the wave can "travel faster then c" when you arrange things so
that the pulse width of your wave packet is large compared to
the tunnelling interval, because parts of the wave are quantum-
mechanically speaking actually on both sides of the barrier. But
the bit that contains signalling information is not the phase or
the group but the wave _front_, and this front velocity is
approximately equivalent to the group velocity only in this
special case.

As far as I can see, if you extend the barrier to be a spacetime
interval of any practical length then you find that you need
wavelengths proportionately long to see tunnelling, and the
quantity of information tends to zero. Tunnelling photons
between stars for example does have a certain tiny probability
amplitude associated with it, but for any meaningful probability
of seeing it happen you need photon wavelengths of lightyears,
comparable to the thickness of the ptential barrier, which means
because of Planck's e = h-nu relation that they only contain
incredibly small energies.

Anyway the debate has been going on for about 15 years and
that's is the state of play as I understand it. There are lots
of web resources.  There's a very useful partial listing by
Markus Possel updated as of 2001 that contains numerous
references, a few from his page are quoted below.

Martin Shough

Aichmann, H., G. Nimtz and H. Spieker: "Photonische
Tunnelzeiten: sunb-- und superluminales Tunneln" in
Verhandlungen der Deutschen Physikalischen Gesellschaft 7, 1995,
S. 1258.

I'm listing this brief publication (a conference abstract)
despite its being in German as it is the only publication
directly referring to the tunneling of the Mozart symphony that
I know of. The following article has much more content:

Nimtz, G. and W. Heitmann: "Superluminal Photonic Tunneling and
Quantum Electronics" in Progress in Quantum Electronics 21(2)
(1997), S. 81-108.

Contains an expose of Nimtz' interpretation of his and other
tunneling experiments.

Chiao, R.Y. Chiao and A.M. Steinberg: "Tunneling Times and
Superluminality" in Progress in Optics XXXVII (1997), S. 345-

Good summary of the "conventional" view why there is no faster-
than-light information transfer in these tunneling experiments.

Mitchell, M.W. and R.Y. Chiao: "Causality and negative group
delays in a simple bandpass amplifier" in American Journal of
Physics 66(1) (1998), S. 14-19.

Describes a very simple setup with the help of which one can
understand how faster-than-light (or even negative) group and
"signal"-velocities can occur without any violation of causality
and without any faster-than-light information transfer.

Diener, G.: "Superluminal group velocities and information
transfer" in Physics Letters A223 (1996), S. 327-331.

General article about the pulse reshaping which, in the
conventional interpretation, explains the faster-than-light (or
negative) group velocities.

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