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Relativity has been met with much resistance in the scientific world. To date, a Nobel Prize has never been awarded for relativity. Louis Essen, the man credited with determining the speed of light, wrote many fiery papers against it such as ''The Special Theory of Relativity: A Critical Analysis''.<ref>http://ephysics.fileave.com/physics/Essen/oxford5-essen.pdf</ref> Relativity also gravely conflicts with [[quantum mechanics]], and although theories like [[string theory]] and [[quantum field theory]] have attempted to unify relativity and quantum mechanics, neither has been entirely successful or proven.
Relativity has been met with much resistance in the scientific world. To date, a Nobel Prize has never been awarded for relativity. Louis Essen, the man credited with determining the speed of light, wrote many fiery papers against it such as ''The Special Theory of Relativity: A Critical Analysis''.<ref>http://ephysics.fileave.com/physics/Essen/oxford5-essen.pdf</ref> Relativity also gravely conflicts with [[quantum mechanics]], and although theories like [[string theory]] and [[quantum field theory]] have attempted to unify relativity and quantum mechanics, neither has been entirely successful or proven.
[[Quantum field theory]], a generalization of quantum mechanics, is fully compatible with special relativity but not with general relativity, and still lacks a vital piece: evidence of the [[graviton]].
Unlike [[Newton]]ian physics, in which space and time intervals are each invariant as seen by all observers, in SR the only invariant quantity is a quadratic combination of space and time intervals (x<sup>2</sup> - c<sup>2</sup> t<sup>2</sup>). The (assumed) instantaneous transmission of [[Newton]]ian gravitational effects also contradicts special relativity.
In quantum mechanics, the [[uncertainty principle]] suggests that virtual particles can sometimes travel faster than the speed of light which would violate causality, but "[t]he only known way to resolve this tension involves introducing the idea of antiparticles."<ref>http://nobelprize.org/nobel_prizes/physics/laureates/2004/wilczek-lecture.pdf (p. 102)</ref> Consequently, in 1928 Paul Dirac derived the Dirac equation, one of the first quantum mechanical equations compatible with special relativity, by which Dirac predicted the existence of antimatter. Four years later, antimatter (the positron) was discovered by Carl Anderson, as successfully predicted by relativistic quantum mechanics. [[Quantum field theory]], a generalization of quantum mechanics, is fully compatible with special relativity but not with general relativity, and still lacks a vital piece: evidence of the [[graviton]].
== Special Relativity ==
== Special Relativity ==
[[Image:Light cone.png|right|thumb|Light-cone diagram]]
[[Image:Light cone.png|right|thumb|Light-cone diagram]]
One important consequence of SR's postulates is that an observer in one reference frame will observe a clock in another frame to be "ticking" more slowly than in the observer's own frame. This can be proven mathematically using basic geometry, if the postulates are physically true without exception.
One important consequence of SR's postulates is that an observer in one reference frame will observe a clock in another frame to be "ticking" more slowly than in the observer's own frame. This can be proven mathematically using basic geometry, if the postulates are physically true without exception.
The length of an event <math>t</math>, as seen by a (relative) stationary observer observing an event is given by:
<math> t = \frac{t_{0}} {\sqrt{1 - \frac{v^{2}}{c^{2}}}}</math>
Where
:<math>t_0</math> is the "proper time" or the length of the event in the observed frame of reference.
:<math>v</math> is the relative velocity between the reference frames.
:<math>c</math> is the speed of light (3x10<sup>8</sup> ms<sup>-1</sup>).
Evidence for time dilation was discovered by studying [[muon decay]]. [[Muons]] are [[subatomic]] [[particles]] with a very short [[halflife]] (1.53 microseconds at rest) and a very fast speed (0.994c). By putting muon detectors at the top (D<sub>1</sub>) and bottom (D<sub>2</sub>) of a mountain with a separation of 1900m, scientists could measure accurately the proportion of muons reaching the second detector in comparison to the first. The proportion found was different to the proportion that was calculated without taking into account relativistic effects.
Using the equation for [[exponential decay]], they could use this proportion to calculate the time taken for the muons to decay, relative to the muon. Then, using the time dilation equation they could then work out the dilated time. The dilated time showed a good correlation with the time it took the muons to reach the second sensor, thereby supporting the existence of time dilation.
The time taken for a muon to travel from D<sub>1</sub> to D<sub>2</sub> as measured by a stationary observer is:
<math> t = \frac{s}{v} = \frac{1900}{0.994\times(3\times10^{8})} = 6.37\mu\textrm{s} </math>
The fraction of muons arriving at D<sub>2</sub> in comparison to D<sub>1</sub> was 0.732. (Given by <math> \frac{N}{N_0} = 0.732 </math>)
Since (from the equation for exponential decay) <math> \frac{N}{N_{0}} = e^{-\lambda t_{0}} </math> then
<math> t_{0} = \frac {ln(0.732)}{ln (0.2)} \times 1.53\times 10^{-6} = 0.689\mu\textrm{s}</math>
This gives the time for the proportion of decay to occur for an observer who is stationary, relative to the muon.
Putting this into the time dilation equation gives:
<math> t = \frac{t_{0}}{\sqrt{1 - \frac{v^{2}}{c^{2}}}} = \frac{0.689 \times{10^{-6}}}{\sqrt{1 - \frac{0.994^{2}}{1^{2}}}} = 6.3\times 10^{-6}\textrm{s}</math>
This is in good agreement with the value calculated above, thereby providing evidence to support time dilation.
====Time Dilation and Creation Science====
{{main|Starlight problem#Humphreys.27_model}}
{{main|Starlight problem#Humphreys.27_model}}
===Length contraction===
===Length contraction===
When two inertial reference frames move past each other in a straight line with constant relative velocity, an observer in one reference frame would observe a metre rule in the other frame to be shorter.
When two inertial reference frames move past each other in a straight line with constant relative velocity, an observer in one reference frame would observe a metre rule in the other frame to be shorter.
The length, <math>l</math>, of an object as seen by a (relative) stationary observer is given by:
<math> l = l_{0} \sqrt{1- \frac{v^{2}}{c^{2}}}</math>
Where
:<math>l_0</math> is the "proper length" or the length of the object in the observed frame of reference.
:<math>v</math> is the relative velocity between the reference frames.
:<math>c</math> is the speed of light (3x10<sup>8</sup> ms<sup>-1</sup>).
===Mass increase===
===Mass increase===
Under this view, the mass, <math>m</math>, of an object as detected by a (relative) stationary observer is given by:
Under this view, the mass, <math>m</math>, of an object as detected by a (relative) stationary observer is given by:
:<math> m = \frac{m_{0}} {\sqrt{1 - \frac{v^{2}}{c^{2}}}}</math>
Where
:<math>m_0</math> is the "rest mass" or the mass of the object when it is at rest.
:<math>v</math> is the relative velocity of the object.
:<math>c</math> is the speed of light (3x10<sup>8</sup> ms<sup>-1</sup>).
Since speed is relative, it follows that two observers in different inertial reference frames may disagree on the mass and kinetic energy of a body. Since all inertial reference frames are treated on an equal footing, it follows that mass and energy are interchangeable.
Since speed is relative, it follows that two observers in different inertial reference frames may disagree on the mass and kinetic energy of a body. Since all inertial reference frames are treated on an equal footing, it follows that mass and energy are interchangeable.
There is a logical difficulty, however, to an increase in relativistic mass. Such increase would only exist in the direction of motion, and the rest mass would remain intact with respect to a force applied in a direction orthogonal to velocity. Neither mass nor energy is a vector, and the notion of the mass of an object having different values depending on the direction of an applied force is illogical. In recent years most physicists have shifted away from Einstein's original reliance on relativistic mass and his suggestion that mass increases.
There is a logical difficulty, however, to an increase in relativistic mass. Such increase would only exist in the direction of motion, and the rest mass would remain intact with respect to a force applied in a direction orthogonal to velocity. Neither mass nor energy is a vector, and the notion of the mass of an object having different values depending on the direction of an applied force is illogical. In recent years most physicists have shifted away from Einstein's original reliance on relativistic mass and his suggestion that mass increases. Instead, most physicists today teach that
:<math>F=\frac{d}{d\tau} p</math>
where <math>p</math> is the momentum defined by <math>\gamma m v</math>, <math>\gamma</math> is the standard Lorentz factor, and <math>\tau</math> is the proper time. Force F defined this way is a vector and thus can handle the directional aspect of the relativistic effects better than the concept of relativistic mass can.
The abandonment by physicists of the concept of relativistic mass, however, has the consequence of undermining the traditional claim under relativity that
The abandonment by physicists of the concept of relativistic mass, however, has the consequence of undermining the traditional claim under relativity that
:<math>m - m_0 = \frac{E}{c^2}</math>
also popularly known as
:<math>E = m c^2</math>
:<math>E = m c^2</math>
Now a concept of the 4-momentum <math>p</math> of a particle is taught, such that the square of the magnitude of <math>p</math> satisfies:
<math>||p||^2 = -p_x^2-p_y^2-p_z^2+E^2 = m_0^2c^4</math>
in any inertial reference frame. The magnitude of the 4-momentum, in any inertial frame, equals the rest mass <math>m_0</math> of the particle (in units where <math>c=1</math>).
== Variable Speed of Light ==
== Variable Speed of Light ==