But it is just an optical illusion вЂ“ relativity physics remains unsullied. This will give you the impression that the particle crossed 5,000 light years from points A to B in much less than 5,000 years. So when the particle emits another photon at point B, a point near the tip of the jet вЂ“ that second photon will reach your eye in much less than 5,000 years after the first photon, from point A. But meanwhile, the particle of jet material continues moving towards you nearly as fast as that photon. A photon emitted by a particle of jet material at point A near the start of the jet really will take 5,000 years to reach you. If that jet is 5,000 light years long, it should take at least 5,000 years for anything in it to cross that distance of 5,000 light years. If an active galaxy, like M87, is pushing out a jet of superheated plasma moving at close to the speed of light вЂ“ and the jet is roughly aligned with your line of sight from Earth вЂ“ you can be fooled into thinking its contents are moving faster than light.

Right: Gain media can act like a Newton's Cradle, making light seem to jump the gap superluminally. Left: Stretching the waveform of light can make the leading edge of the wave seem to move faster than light. Although light appears to jump the gap superluminally, in fact itвЂ™s a new light pulse emerging at the other end вЂ“ and still just moving at standard light speed. If you want to see a laboratory set-up, try here. You can mimic more dramatic superluminal motion through a gain medium where the leading edge of a light pulse stimulates the emission of a new pulse at the far end of the gain medium вЂ“ as though a light pulse hits one end of a NewtonвЂ™s Cradle and new pulse is projected out from the other end. In any case, since information (or the photon as a complete unit) is not moving faster than light, relativity physics is not violated.

If you are keen on the technical details, you can make phase velocity or group velocity faster than c (the speed of light in a vacuum) вЂ“ but not signal velocity. Indeed, by being stretched out and attenuated, it may become indistinguishable from background noise.ДЄlso this trick requires the light to be moving through a refractive medium, not a vacuum. The whole wave packet is equivalent to one photon вЂ“ and the leading edge of the stretched out wave packet cannot carry any significant information. However, the physical nature of вЂthe leading edge of a wave packetвЂ™ is not clear. If we consider a photon as a wave packet, that wave packet can be stretched linearly so that the leading edge of the wave arrives at its destination faster, since it is pushed ahead of the remainder of the wave вЂ“ meaning that it travels faster than light. You can produce an apparent superluminal motion of light itself by manipulating its wavelength. As long as the emanations from these point sources are not causally connected, this outcome does not violate relativity physics. There are a range of possible scenarios as to why a superluminal Mexican wave of synchrotron radiation might emanate from different point sources around a rapidly rotating neutron star within an intense magnetic field. This illusion is an example of apparent superluminal motion. ItвЂ™s just a trick really вЂ“ there is no causal connection between the bulbs firing вЂ“ but it looks as though a sequence of actions (first 1, then 2, then 3 etc) moved faster than light across the row of bulbs. ItвЂ™s easy enough to make them fire off in sequence вЂ“ first 1, then 2, then 3 etc вЂ“ and you can keep reducing the time delay between each one firing until you have a situation where bulb 2 fires off after bulb 1 in less time than light would need to travel the distance between bulbs 1 and 2. What you do is to arrange a line of light bulbs which are independently triggered.

Now, whether anything like this really happens with light from pulsars remains a point of debate, but one of the modelвЂ™s proponents has demonstrated the effect in a laboratory вЂ“ see this Scientific American blog post. The faster than light pulsar story is essentially about hypothetical light booms вЂ“ which are a bit like a sonic booms, where itвЂ™s not the sonic boom, but the sound source, that exceeds the speed of sound вЂ“ so that individual sound pulses merge to form a single shock wave moving at the speed of sound.

Superluminal ftl extra parts