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Fraser
2010-Jan-06, 04:50 PM
Observational data from nine pulsars, including the Crab pulsar, suggest these rapidly spinning neutron stars emit the electromagnetic equivalent of a sonic boom, and a model created to understand this phenomenon shows that the source of the emissions could be traveling faster than light. Researchers say as the polarization currents in these emissions are [...]

More... (http://www.universetoday.com/2010/01/06/faster-than-light-pulsar-phenomena/)

Hungry4info
2010-Jan-06, 05:56 PM
I don't get it. What exactly is moving faster than light here?

Jerry
2010-Jan-06, 07:08 PM
Nothing. Time is a linear concept, and space is at least three dimensional. Think of an approaching storm: Assume you are in the center of the broad front of a ~1000km wide that storm approaching you at ~30km/hr; and you pick a direction to run that is nearly tangent to the storm; no matter how fast you move, you will not be able to out-flank the storm. A person watching you flee from the edge of the storm will see the storm over-take you at lightning speed.

Now imagine an electrical field rolling just like a storm front; and from a tangent prospective, the field strength will increase at superluminal speed. The geometry of a pulsar can produce the same effect, changing the sum of the currents at a given point at a rate that is greater than the speed of light - the Pauli exclusion principle does not apply to field strength...(yes/no?) so when a linear scaler is applied to the emf shock wave, the rate of change can surpass the speed of light.

Hungry4info
2010-Jan-06, 08:13 PM
:shifty:
I didn't understand that. I'm afraid I know very little about magnetism. I did not understand how the storm analogy relates to the pulsar.

Jerry
2010-Jan-07, 02:38 AM
Sorry -

Envision, rather than a storm and a point, two converging storms from almost exactly opposite directions: With the storms both moving 30kmh. As the two storms 'scissor' together, An observer from the broad side of the gap could see the most distant point in the gap move toward them faster than the speed of sound.

Pulsars are generally assumed to be fast rotating bodies rather than planer storms; but it is possible that the field dynamics within a pulsar leads to converging electrodynamic 'fronts' that are reasonable analogs to two colliding storms: Braiding the Maypole.

Notice that it would be impossible for a pulsar to display field changes in all directions that exceed the speed of light - this could only occur in a very narrow window at a time; hence the pulsed signal.

dgavin
2010-Jan-07, 02:26 PM
Actually a better way to explain this would be to think of an oscillating guitar string.

Under normal circumstances it would have a specific tension and would oscillate at one specific frequency. Say the lower E string.

However change the environment a little by holding a finger on the string at the middle point, without fretting the string, and you get a two octave higher E note. In this case there are actually two opposing oscillations traveling through the string, and as they pass each other they sometimes constructively or destructively interfere. Where they constructively interfere they setup additional secondary oscillations, the first harmonic. Likewise these harmonics do the same, leading to a second, third, etc.

So the sound produced by playing the unfretted middle of the string, is a much richer sound then if you fretted the string at the middle point.

Thinks of the various oscillations of the string as Group Wave velocities.

Now, if you take this into an extreme environment like a pulsar, and it's magnetic fields, what is going is the magnetic fields are oscillating. Because of the extreme nature of this environment, the magnetic fields have multiple oscillations, at multiple frequencies.

Where these frequencies constructively interfere and produce the magnetic equivalent of a new harmonic, these harmonics have a frequency that is faster then light. The current itself is not moving FTL, only the 'harmonic' for lack of a better term.

By the time the harmonics do the same a few times, you wind up with group waves 'harmonics' traveling around 6 times the speed of light.

Now the next bit is just my best guess. Once you start hitting group waves of these velocities, when they constructively interfere with each other, sometimes it causes a complete wave function collapse, and the energy is released as a burst of radio waves.

At least thats the way I understand stand what this article is saying. It's probably a lot more complicated though.

Jerry
2010-Jan-07, 07:44 PM
Excellent analogy, Dgavin.

A good piano tuner will actually tune the three strings used to produce an individual note so that there is a consistant beat frequency between each of the tones. The human ear will detect this as a vibrato in an individual string; and the net result is a perceived sound that can be a magnitudes louder than any of the strings can produce in solo, especially when this sound is coupled via a good sounding box bouncing off the lid and aimed at the audience.

Fortunate
2010-Jan-12, 01:19 AM
Here (http://physicsworld.com/cws/article/news/41378) is a discussion from Physics World. If you have to sign up to view the article, the process if free and easy.

Fortunate
2010-Jan-12, 10:58 AM
Oops, the article linked in the previous post seems to be about a different recently-reported superluminal phenomenon involving bursts from pulsars. Sorry for any confusion.

Fortunate
2010-Jan-13, 01:48 AM
Maybe I am way off the mark, but I envision the superluminal aspect as follows. Suppose that a pulsar rotates at 500 revs/sec, which is about 3,000 radians/sec. Consider a circle of radius
100 km concentric with the pulsar in a plane perpendicular to the axis of rotation of the magnetic field. In one second, the effects of the magnetic field will travel around this circle 500 times, or a distance of about 300,000 km. Thus, the effects will travel around the circle at about the speed of light. For larger radii, these effects will travel at speeds faster than c.

This picture is consistent with the statement on page 3 of this paper (http://arxiv.org/PS_cache/arxiv/pdf/0908/0908.1349v1.pdf) that the superluminal effects will occur when r>c/ω.