Faster than light, light

[jason rice]

I heard about the experiment on NPR, they had another physicist come on 
after Wang and say that the experiment did not really exhibit the phenomena 
that the NEC team claimed.  According to this gentleman, a tracer of light 
precedes and follows the pulse, and the cesium vapor alters this tracer and 
makes it appear as if the pulse itself is exiting before it has entered the 
chamber.  This guy was pretty dismissive of the whole project and noted that 
this tracer phenomena had been documented by other researchers in the past.
Jason Rice


>From: Chuck Grimes <cgrimes at tsoft.com>
>Reply-To: lbo-talk at lists.panix.com
>To: lbo-talk at lists.panix.com
>Subject: Faster than light, light
>Date: Thu, 20 Jul 2000 22:51:26 -0700 (PDT)
>
>
>
>Gain-assisted superluminal light propagation
>
>L. J. WANG, A. KUZMICH & A. DOGARIU
>
>NEC Research Institute, 4 Independence Way, Princeton, New Jersey
>08540, USA
>
>Correspondence and requests for materials should be addressed to
>L.J.W. (e-mail: Lwan at research.nj.nec.com).
>
>
>Einstein's theory of special relativity and the principle of
>causality(1-4) imply that the speed of any moving object cannot exceed
>that of light in a vacuum (c). Nevertheless, there exist various
>proposals(5-18) for observing faster-than- c propagation of light
>pulses, using anomalous dispersion near an absorption line(4),(6-8),
>nonlinear(9) and linear gain lines(10-18), or tunnelling
>barriers(19). However, in all previous experimental demonstrations,
>the light pulses experienced either very large absorption(7) or severe
>reshaping(9, 19), resulting in controversies over the
>interpretation. Here we use gain-assisted linear anomalous dispersion
>to demonstrate superluminal light propagation in atomic caesium
>gas. The group velocity of a laser pulse in this region exceeds c and
>can even become negative(16, 17), while the shape of the pulse is
>preserved. We measure a group-velocity index of ng = -310(+-5); in
>practice, this means that a light pulse propagating through the atomic
>vapour cell appears at the exit side so much earlier than if it had
>propagated the same distance in a vacuum that the peak of the pulse
>appears to leave the cell before entering it. The observed
>superluminal light pulse propagation is not at odds with causality,
>being a direct consequence of classical interference between its
>different frequency components in an anomalous dispersion region.
>
>see:
>
>http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/
>v406/n6793/full/406277a0_fs.html
>
>-------------------
>
>Comments?
>
>Chuck Grimes

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