Faster than Light?

[durabone]

I received these today:

Kevin Spiess - Thursday, January 14th, 2010

And you thought you couldn't go faster than light

Astrophysicists working out of the University of Texas at Brownsville
have been studying an interesting pulsar about 10,000 light years
away from us (a pulsar is a highly magnetic, spinning corpse of a
dead star). Over the course of three days of monitoring, radio waves
emitted from the pulsar seem to have been traveling faster than the
speed of light.

You might have heard that faster-than-light travel is impossible.
This is not entirely true -- there are a couple of catches which
allow for F.T.L velocities. One such catch, as originally proposed by
Mr. Einstein, is that something can travel faster than light if it
does not contain information. This physical law has been observed on
Earth in experiments, but with this pulsar (if confirmed), this is
the first time this sort of thing has been observed off of our
planet. What does or does not constitute information in this context
however, is the subject of both rigorous study and debate.

The radio pulse from the pulsar is suspected to have picked up some
of the excess speed by passing through a cloud of neutral hydrogen
atoms, which causes the radio waves to increase their electromagnetic
wavelength (a process called "anomalous dispersion").

(Note: pictured above is some other pulsar, not Pulsar PSR B1937+21
from this research. Pulsar PSR B1937+21 is the second fastest
spinning pulsar yet cataloged, and spins about 642 times around every
second.)

Source: http://tiny.cc/j0bCc

Source: "Apparent Faster-than-light Pulse Propagation in Interstellar
Space..."

The paper looks intriguing:

Apparent Faster-Than-Light Pulse Propagation in Interstellar Space: A
new probe of the Interstellar Medium
F. A. Jenet1, D. Fleckenstein1, A. Ford 1, A. Garcia1,R. Miller1, J.
Rivera1, K. Stovall1


ABSTRACT

Radio pulsars emit regular bursts of radio radiation that propagate through the interstellar medium (ISM), the tenuous gas and plasma between the stars. Previously known dispersive properties of the ISM cause low frequency pulses to be delayed in time with respect to high frequency ones. This effect can be explained by the presence of free electrons in the medium. The ISM also contains neutral hydrogen which has a well known resonance at 1420.4 MHz. Electro-magnetic theory predicts that at such a resonance, the induced dispersive effects will be drastically different from those of the free electrons. Pulses traveling through a cloud of neutral hydrogen should undergo “anomalous dispersion,” which causes the group velocity of the medium to be larger than the speed of light in vacuum. This superluminal group velocity causes pulses containing
frequencies near the resonance to arrive earlier in time with respect to other pulses.

Hence, these pulses appear to travel faster than light. This phenomenon is caused by an interplay between the time scales present in the pulse and the time scales present in the medium. Although counter-intuitive, it does not violate the laws of special relativity. Here, we present Arecibo observations of the radio pulsar PSR B1937 +21 that show clear evidence of anomalous dispersion. Though this effect is known in laboratory physics, this is the first time it has been directly observed in an astrophysical context, and it has the potential to be a useful tool for studying the properties of neutral hydrogen in the Galaxy.

A couple of comments:

1. The super-luminal group velocity thing I have seen before. Where? (Oh, when I get to the office, I'll look to see if I can find the link to a cool prof's Flash animations if anyone's interested in visualizing the diff between phase & group velocity)

2. I study ULF now for years. One of the things that has jumped out at me for a while in studying this interstellar dispersion phenomenon is just how far delayed very low freq. signals can be. (An analogy would be whistler-mode propagation through the ionosphere see Helliwell). This ratio of the delay (dispersion) must form a very important metric for estimating the total number of photons in the universe.

To see the point, visualize a conduit carrying light-frequency photons, and one carrying 1 Hz photons. If the quantity of photons entering the conduit at the far end, near a star or this pulsar is identical, then the rate that they pop out of the other end of the conduit near us is identical. Photons are not destroyed or created during the transmission in this simple idea. Now if the 1 Hz photons are moving at 1/1000 of the speed of the light freq. photons, are there not 1000x as many photons in the 1 Hz pipe? And so do we not need to take into account this hugely larger proportion of lower energy photons when speaking of dark matter and dark energy?

Given the level of pure empiricism surrounding the huge roar I hear practically every day at the very low end of the spectrum, I doubt that it has been adequately addressed, though I am still fishing for evidence otherwise. Anyone know anything about this?