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João Magueijo | A Wisdom Archive on João Magueijo | | João Magueijo A selection of articles related to João Magueijo | |
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| ARTICLES RELATED TO João Magueijo | | | |  João Magueijo: Encyclopedia II - Speed of light - Physics
Speed of light - Constant velocity from all reference frames.
It is important to realise that the speed of light is not a "speed limit" in the conventional sense. An observer chasing a beam of light will measure it moving away from him at the same speed as a stationary observer. This leads to some unusual consequences for velocities.
Most individuals are accustomed to the addition rule of velocities: if two cars approach each other from opposite directions, each travelling at a speed of 50 kilometres per h ...
See also:Speed of light, Speed of light - Overview, Speed of light - Communications, Speed of light - Physics, Speed of light - Constant velocity from all reference frames, Speed of light - Interaction with transparent materials, Speed of light - Faster-than-light observations and experiments, Speed of light - Light-slowing experiments, Speed of light - History, Speed of light - Medieval and early modern theories, Speed of light - Measurement of the speed of light, Speed of light - Relativity Read more here: » Speed of light: Encyclopedia II - Speed of light - Physics |
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| | | | João Magueijo: Encyclopedia II - Faster-than-light - Possibility of FTL Faster-Than-Light travel or communication is problematic in a universe that is consistent with Einstein's Theory of Relativity. In a hypothetical universe where Newton's laws of motion and the Galilean transformations are exact, rather than approximate, the following would be true:
Space and time measurements always give the same results in every 'frame of reference'
Velocities add linearly
There is nothing fundamental about the wave velocity of ligh ...
See also:Faster-than-light, Faster-than-light - Terminology, Faster-than-light - Possibility of FTL, Faster-than-light - Option A: Ignore special relativity., Faster-than-light - Option B: Get light to go faster., Faster-than-light - Option C: Give up causality., Faster-than-light - Option D: Give up absolute relativity., Faster-than-light - Tachyons, Faster-than-light - General relativity, Faster-than-light - Apparent FTL, Faster-than-light - Moving spot of light, Faster-than-light - Relative motion, Faster-than-light - Phase velocities above c, Faster-than-light - Group velocities above c, Faster-than-light - Universal expansion, Faster-than-light - Astronomical observations, Faster-than-light - Quantum mechanics Read more here: » Faster-than-light: Encyclopedia II - Faster-than-light - Possibility of FTL |
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| | | | João Magueijo: Encyclopedia II - Speed of light - History Until relatively recent times, the speed of light was largely a matter of conjecture. Empedocles maintained that light was something in motion, and therefore there had to be some time elapsed in travelling. Aristotle said that, on the contrary, "light is due to the presence of something, but it is not a movement". Furthermore, if light had a finite speed, it would have to be very great; Aristotle asserted "the strain upon our power ...
See also:Speed of light, Speed of light - Overview, Speed of light - Communications, Speed of light - Physics, Speed of light - Constant velocity from all reference frames, Speed of light - Interaction with transparent materials, Speed of light - Faster-than-light observations and experiments, Speed of light - Light-slowing experiments, Speed of light - History, Speed of light - Medieval and early modern theories, Speed of light - Measurement of the speed of light, Speed of light - Relativity Read more here: » Speed of light: Encyclopedia II - Speed of light - History |
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| | | | João Magueijo: Encyclopedia II - Faster-than-light - Apparent FTL
Faster-than-light - Moving spot of light.
Processes which do not transmit information may move faster than light. A good example is a beam of light projected onto a distant surface, such as the Moon. The spot which the beam strikes is not a physical object, just a point of light. Moving it (by reorienting the beam) does not carry information between locations on the surface. To put it another way, the beam can be considered as a stream of photons; where each photon strikes the surface is determined only by the or ...
See also:Faster-than-light, Faster-than-light - Terminology, Faster-than-light - Possibility of FTL, Faster-than-light - Option A: Ignore special relativity., Faster-than-light - Option B: Get light to go faster., Faster-than-light - Option C: Give up causality., Faster-than-light - Option D: Give up absolute relativity., Faster-than-light - Tachyons, Faster-than-light - General relativity, Faster-than-light - Apparent FTL, Faster-than-light - Moving spot of light, Faster-than-light - Relative motion, Faster-than-light - Phase velocities above c, Faster-than-light - Group velocities above c, Faster-than-light - Universal expansion, Faster-than-light - Astronomical observations, Faster-than-light - Quantum mechanics Read more here: » Faster-than-light: Encyclopedia II - Faster-than-light - Apparent FTL |
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| | | | João Magueijo: Encyclopedia II - Faster-than-light - Terminology In the context of this article, FTL actually refers to the transmission of information or matter faster than c, a constant equal to the speed of light in a vacuum, roughly 300 million metres per second. This is not quite the same as travelling faster than light, since:
There are some processes which do propagate faster than c, but which can't actually carry information (See the Apparent FTL section in this article).
Light itself will travel at a speed slower than c when not in a vacuum (causing refr ...
See also:Faster-than-light, Faster-than-light - Terminology, Faster-than-light - Possibility of FTL, Faster-than-light - Option A: Ignore special relativity., Faster-than-light - Option B: Get light to go faster., Faster-than-light - Option C: Give up causality., Faster-than-light - Option D: Give up absolute relativity., Faster-than-light - Tachyons, Faster-than-light - General relativity, Faster-than-light - Apparent FTL, Faster-than-light - Moving spot of light, Faster-than-light - Relative motion, Faster-than-light - Phase velocities above c, Faster-than-light - Group velocities above c, Faster-than-light - Universal expansion, Faster-than-light - Astronomical observations, Faster-than-light - Quantum mechanics Read more here: » Faster-than-light: Encyclopedia II - Faster-than-light - Terminology |
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| | | | João Magueijo: Encyclopedia II - Speed of light - Overview According to standard modern physical theory, all electromagnetic radiation, including visible light, propagates (or moves) at a constant speed in a vacuum, commonly known as the speed of light, which is a physical constant denoted as c. This speed c is also the speed of the propagation of gravity in the theory of general relativity.
One consequence of the laws of electromagnetism (such as Maxwell's equations) is that the speed c of electromagnetic radiation does not depend on the velocity of the object emitting t ...
See also:Speed of light, Speed of light - Overview, Speed of light - Communications, Speed of light - Physics, Speed of light - Constant velocity from all reference frames, Speed of light - Interaction with transparent materials, Speed of light - Faster-than-light observations and experiments, Speed of light - Light-slowing experiments, Speed of light - History, Speed of light - Medieval and early modern theories, Speed of light - Measurement of the speed of light, Speed of light - Relativity Read more here: » Speed of light: Encyclopedia II - Speed of light - Overview |
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| | | | João Magueijo: Encyclopedia II - Faster-than-light - Tachyons In special relativity, while it is impossible to accelerate an object to the speed of light, or for a massive object to move at the speed of light, it is not impossible for an object to exist which always moves faster than light. The hypothetical elementary particles that have this property are called tachyons. Their existence has neither been proven nor disproven.
Tachyons are not structurally stable. The equations of relativity do allow faster than light travel, since the equations are symmetric about the velocity 'c', ...
See also:Faster-than-light, Faster-than-light - Terminology, Faster-than-light - Possibility of FTL, Faster-than-light - Option A: Ignore special relativity., Faster-than-light - Option B: Get light to go faster., Faster-than-light - Option C: Give up causality., Faster-than-light - Option D: Give up absolute relativity., Faster-than-light - Tachyons, Faster-than-light - General relativity, Faster-than-light - Apparent FTL, Faster-than-light - Moving spot of light, Faster-than-light - Relative motion, Faster-than-light - Phase velocities above c, Faster-than-light - Group velocities above c, Faster-than-light - Universal expansion, Faster-than-light - Astronomical observations, Faster-than-light - Quantum mechanics Read more here: » Faster-than-light: Encyclopedia II - Faster-than-light - Tachyons |
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| | | | João Magueijo: Encyclopedia II - Faster-than-light - General relativity General relativity was developed after special relativity, to include concepts like gravity. It maintains the principle that no object can accelerate to the speed of light in its own reference frame. However, it permits distortions in spacetime that allow an object to move faster than light from the point of view of a distant observer, even though it always moved slower than light in its own reference frame. One such distortion is the Alcubierre drive, which can be thought of as producing a ripple in spacetime that carries an object along wi ...
See also:Faster-than-light, Faster-than-light - Terminology, Faster-than-light - Possibility of FTL, Faster-than-light - Option A: Ignore special relativity., Faster-than-light - Option B: Get light to go faster., Faster-than-light - Option C: Give up causality., Faster-than-light - Option D: Give up absolute relativity., Faster-than-light - Tachyons, Faster-than-light - General relativity, Faster-than-light - Apparent FTL, Faster-than-light - Moving spot of light, Faster-than-light - Relative motion, Faster-than-light - Phase velocities above c, Faster-than-light - Group velocities above c, Faster-than-light - Universal expansion, Faster-than-light - Astronomical observations, Faster-than-light - Quantum mechanics Read more here: » Faster-than-light: Encyclopedia II - Faster-than-light - General relativity |
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| | | | João Magueijo: Encyclopedia II - Faster-than-light - Terminology In the context of this article, FTL actually refers to the transmission of information or matter faster than c, a constant equal to the speed of light in a vacuum, roughly 300 million metres per second. This is not quite the same as travelling faster than light, since:
There are some processes which do propagate faster than c, but which can't actually carry information (See the Apparent FTL section in this article).
Light itself will travel slower than c when not in a vacuum (causing refraction), and in certain materials other particles can travel faster than it (but still slower than ...
See also:Faster-than-light, Faster-than-light - Terminology, Faster-than-light - Possibility of FTL, Faster-than-light - Option A: Ignore special relativity., Faster-than-light - Option B: Get light to go faster., Faster-than-light - Option C: Give up causality., Faster-than-light - Option D: Give up absolute relativity., Faster-than-light - Tachyons, Faster-than-light - General relativity, Faster-than-light - Apparent FTL, Faster-than-light - Moving spot of light, Faster-than-light - Relative motion, Faster-than-light - Phase velocities above c, Faster-than-light - Group velocities above c, Faster-than-light - Universal expansion, Faster-than-light - Astronomical observations, Faster-than-light - Quantum mechanics Read more here: » Faster-than-light: Encyclopedia II - Faster-than-light - Terminology |
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| | | | João Magueijo: Encyclopedia II - Speed of light - Communications The speed of light is of relevance to communications. For example, given that the equatorial circumference of the Earth is 40,075 km and c, the theoretical shortest amount of time for a piece of information to travel half the globe is 0.067 second.
The actual transit time is longer, in part because the speed of light is slower by about 30% in an optical fibre and straight lines rarely occur in global communications situations, but also because delays are created when the signal passes thro ...
See also:Speed of light, Speed of light - Overview, Speed of light - Communications, Speed of light - Physics, Speed of light - Constant velocity from all reference frames, Speed of light - Interaction with transparent materials, Speed of light - Faster-than-light observations and experiments, Speed of light - Light-slowing experiments, Speed of light - History, Speed of light - Medieval and early modern theories, Speed of light - Measurement of the speed of light, Speed of light - Relativity Read more here: » Speed of light: Encyclopedia II - Speed of light - Communications |
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