La Teoría De La Relatividad De Einstein Y Su Explicación - Enterarse
Según la Enciclopedia Británica
Pero ¿la dilatación del tiempo sucede en la vida real o solo en el gráfico? Aunque no lo creas, también sucede en la vida real. Mientras más rápido te muevas, más lento pasará el tiempo para ti en comparación con otras personas. <anchor>Según la Enciclopedia Británica</anchor>, diversos experimentos lo demuestran, aunque la mayoría de ellos con partículas subatómicas a grandes velocidades.
Relativity - Time, Space, Mass | Britannica
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[relativity](https://www.britannica.com/science/relativity)

Table of Contents


- [Introduction](/science/relativity)

- [Cosmology before relativity](/science/relativity#ref252875)



- [The mechanical universe](/science/relativity#ref252876)

- [Light and the ether](/science/relativity#ref252877)

- [Special relativity](/science/relativity/Special-relativity)



- [Einstein’s _Gedankenexperiment_ s](/science/relativity/Special-relativity#ref252879)

- [Starting points and postulates](/science/relativity/Special-relativity#ref252880)

- [Consequences of the postulates](/science/relativity/Special-relativity#ref252881)

  - [Relativistic space and time](/science/relativity/Special-relativity#ref252882)

  - [Relativistic mass](/science/relativity/Relativistic-mass)

    - [Cosmic speed limit](/science/relativity/Relativistic-mass#ref252884)

    - [_E_ = _m_ _c_ 2](/science/relativity/Relativistic-mass#ref252885)

  - [The twin paradox](/science/relativity/Relativistic-mass#ref252886)

  - [Four-dimensional space-time](/science/relativity/Relativistic-mass#ref252887)

- [Experimental evidence for special relativity](/science/relativity/Relativistic-mass#ref252888)

- [General relativity](/science/relativity/General-relativity)



- [Roots of general relativity](/science/relativity/General-relativity#ref252890)

- [Principle of equivalence](/science/relativity/General-relativity#ref252891)

- [Curved space-time and geometric gravitation](/science/relativity/Curved-space-time-and-geometric-gravitation)

- [The mathematics of general relativity](/science/relativity/Curved-space-time-and-geometric-gravitation#ref252893)

  - [Cosmological solutions](/science/relativity/Curved-space-time-and-geometric-gravitation#ref252894)

  - [Black holes](/science/relativity/Curved-space-time-and-geometric-gravitation#ref252895)

  - [Black holes and wormholes](/science/relativity/Curved-space-time-and-geometric-gravitation#ref252898)

- [Experimental evidence for general relativity](/science/relativity/Experimental-evidence-for-general-relativity)

- [Applications of relativistic ideas](/science/relativity/Experimental-evidence-for-general-relativity#ref252900)



- [Elementary particles](/science/relativity/Experimental-evidence-for-general-relativity#ref252901)

- [Particle accelerators](/science/relativity/Experimental-evidence-for-general-relativity#ref252902)

- [Fission and fusion: bombs and stellar processes](/science/relativity/Experimental-evidence-for-general-relativity#ref252903)

- [The global positioning system](/science/relativity/Experimental-evidence-for-general-relativity#ref252904)

- [Cosmology](/science/relativity/Experimental-evidence-for-general-relativity#ref252905)

- [Relativity, quantum theory, and unified theories](/science/relativity/Experimental-evidence-for-general-relativity#ref252906)

- [Intellectual and cultural impact of relativity](/science/relativity/Intellectual-and-cultural-impact-of-relativity)



- [Reactions in general culture](/science/relativity/Intellectual-and-cultural-impact-of-relativity#ref252908)

- [Philosophical considerations](/science/relativity/Philosophical-considerations)

[References & Edit History](https://www.britannica.com/science/relativity/additional-info) [Related Topics](/facts/relativity)

[Images & Videos](https://www.britannica.com/science/relativity/images-videos)

[![Explaining E = mc2](https://cdn.britannica.com/80/222280-138-41E211F6/Your-Daily-Equation-01-E-mc2.jpg?w=400&h=225&c=crop)](/video/222280/Your-Daily-Equation-01-E-mc2)[![curvature and parallel motion](https://cdn.britannica.com/05/222305-138-EEB2D539/Your-Daily-Equation-27-Curvature-and-Parallel-Motion.jpg?w=400&h=225&c=crop)](/video/222305/Your-Daily-Equation-27-Curvature-and-Parallel-Motion)[![Understand Albert Einstein's theory of relativity, about what is absolute and not relative](https://cdn.britannica.com/20/185520-138-4A4E7E08/Description-theory-relativity-Albert-Einstein.jpg?w=400&h=225&c=crop)](/video/185520/Description-theory-relativity-Albert-Einstein)[![invariance of the speed of light](https://cdn.britannica.com/43/92943-004-EC89C42D/velocities-speed-of-light-Invariance-Arrows-train.jpg)](https://cdn.britannica.com/43/92943-050-8DB198B0/velocities-speed-of-light-Invariance-Arrows-train.jpg)[![Newtonian reference frames](https://cdn.britannica.com/61/91961-004-B96CCE57/reference-frames-velocity-Isaac-Newton-Newtonian-equation.jpg)](https://cdn.britannica.com/61/91961-050-9A9D9B1F/reference-frames-velocity-Isaac-Newton-Newtonian-equation.jpg)[![simultaneous events](https://cdn.britannica.com/62/91962-004-5B9D4732/events-differences-observer-positions-another.jpg)](https://cdn.britannica.com/62/91962-050-86B628ED/events-differences-observer-positions-another.jpg)[![length contraction and time dilation](https://cdn.britannica.com/63/91963-004-10EE1D21/Length-contraction-time-dilation-observer-object-speed.jpg)](https://cdn.britannica.com/63/91963-004-10EE1D21/Length-contraction-time-dilation-observer-object-speed.jpg)[![curved space-time](https://cdn.britannica.com/64/91964-004-ADD11BAD/vicinity-mass-distance-distortion-continuum-amount-relativity.jpg)](https://cdn.britannica.com/64/91964-050-4FDB21E8/vicinity-mass-distance-distortion-continuum-amount-relativity.jpg)[![black hole in M87](https://cdn.britannica.com/26/205226-004-E0B95A1E/Black-hole-M87-centre-evidence-supermassive-black.jpg)](https://cdn.britannica.com/26/205226-050-B2621B00/Black-hole-M87-centre-evidence-supermassive-black.jpg)[![experimental evidence for general relativity](https://cdn.britannica.com/65/91965-004-116CAD96/Einstein-general-relativity-evidence-observation-light-prediction-1919.jpg)](https://cdn.britannica.com/65/91965-004-116CAD96/Einstein-general-relativity-evidence-observation-light-prediction-1919.jpg)

For Students


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[relativity summary](/summary/relativity)

Quizzes


[![Italian-born physicist Dr. Enrico Fermi draws a diagram at a blackboard with mathematical equations. circa 1950.](https://cdn.britannica.com/01/115001-131-7278E518/Enrico-Fermi-Italian-problem-physics-1950.jpg?w=200&h=200&c=crop)](/quiz/physics-and-natural-law)

[Physics and Natural Law](/quiz/physics-and-natural-law)

[![Italian physicist Guglielmo Marconi at work in the wireless room of his yacht Electra, c. 1920.](https://cdn.britannica.com/03/221503-131-D7173869/Italian-physicist-Guglielmo-Marconi-at-work-on-his-yacht-Electra.jpg?w=200&h=200&c=crop)](/quiz/all-about-physics-quiz)

[All About Physics Quiz](/quiz/all-about-physics-quiz)

Related Questions


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Contents


[Science](/browse/Science)[Physics](/browse/Physics)[Matter & Energy](/browse/Matter-Energy)

## [Relativistic mass](https://www.britannica.com/science/relativistic-mass)

in [relativity](https://www.britannica.com/science/relativity) in [Special relativity](/science/relativity/Special-relativity)



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Written by


[Sidney Perkowitz\
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Charles Howard Candler Professor of Physics Emeritus, Emory University, Atlanta. Author of _Empire of Light, Universal Foam, Hollywood Science, Slow Light_, and others.](/contributor/Sidney-Perkowitz/4558)

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Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.](/editor/The-Editors-of-Encyclopaedia-Britannica/4419)

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• [Article History](https://www.britannica.com/science/relativity/additional-info#history)


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## Cosmic speed limit

To [derive](https://www.britannica.com/dictionary/derive) further results, Einstein combined his redefinitions of time and [space](https://www.britannica.com/science/space-physics-and-metaphysics) with two powerful physical principles: [conservation of energy](https://www.britannica.com/science/conservation-of-energy) and [conservation of mass](https://www.britannica.com/science/conservation-of-mass), which state that the total amount of each remains constant in a closed system. Einstein’s second postulate ensured that these laws remained valid for all observers in the new theory, and he used them to derive the relativistic meanings of mass and [energy](https://www.britannica.com/science/energy).

One result is that the mass of a body increases with its speed. An observer on a moving body, such as a spacecraft, measures its so-called rest mass _m_ 0, while a fixed observer measures its mass _m_ as ![relativistic mass](https://cdn.britannica.com/77/79677-004-AC5056A0/mass.jpg)which is greater than _m_ 0. In fact, as the spacecraft’s speed approaches that of [light](https://www.britannica.com/science/light), the mass _m_ approaches infinity. However, as the object’s mass increases, so does the energy required to keep accelerating it; thus, it would take [infinite](https://www.merriam-webster.com/dictionary/infinite) energy to accelerate a material body to the [speed of light](https://www.britannica.com/science/speed-of-light). For this reason, no material object can reach the speed of light, which is the speed limit for the [universe](https://www.britannica.com/science/universe). (Light itself can attain this speed because the rest mass of a [photon](https://www.britannica.com/science/photon), the [quantum](https://www.britannica.com/science/quantum) particle of light, is zero.)

## _E_ = _m_ _c_ 2

Einstein’s treatment of mass showed that the increased relativistic mass comes from the energy of [motion](https://www.britannica.com/science/motion-mechanics) of the body—that is, its [kinetic energy](https://www.britannica.com/science/kinetic-energy) _E_—divided by _c_ 2. This is the origin of the famous equation _E_ = _m_ _c_ 2, which expresses the fact that mass and energy are the same physical entity and can be changed into each other.

## The [twin paradox](https://www.britannica.com/science/twin-paradox)

The [counterintuitive](https://www.merriam-webster.com/dictionary/counterintuitive) nature of Einstein’s ideas makes them difficult to absorb and gives rise to situations that seem unfathomable. One well-known case is the twin [paradox](https://www.merriam-webster.com/dictionary/paradox), a seeming [anomaly](https://www.merriam-webster.com/dictionary/anomaly) in how [special relativity](https://www.britannica.com/science/special-relativity) describes time.

[![Italian physicist Guglielmo Marconi at work in the wireless room of his yacht Electra, c. 1920.](https://cdn.britannica.com/03/221503-131-D7173869/Italian-physicist-Guglielmo-Marconi-at-work-on-his-yacht-Electra.jpg)\
\
Britannica Quiz\
\
All About Physics Quiz](/quiz/all-about-physics-quiz)

Suppose that one of two identical twin sisters flies off into space at nearly the speed of light. According to relativity, time runs more slowly on her spacecraft than on [Earth](https://www.britannica.com/place/Earth); therefore, when she returns to Earth, she will be younger than her Earth-bound sister. But in relativity, what one observer sees as happening to a second one, the second one sees as happening to the first one. To the space-going sister, time moves more slowly on Earth than in her spacecraft; when she returns, her Earth-bound sister is the one who is younger. How can the space-going twin be both younger and older than her Earth-bound sister?

The answer is that the paradox is only apparent, for the situation is not appropriately treated by special relativity. To return to Earth, the spacecraft must change direction, which violates the condition of steady straight-line motion central to special relativity. A full [treatment](https://www.britannica.com/dictionary/treatment) requires [general relativity](https://www.britannica.com/science/general-relativity), which shows that there would be an asymmetrical change in time between the two sisters. Thus, the “paradox” does not cast doubt on how special relativity describes time, which has been confirmed by numerous experiments.

## Four-dimensional [space-time](https://www.britannica.com/science/space-time)

Special relativity is less definite than classical [physics](https://www.britannica.com/science/physics-science) in that both the distance _D_ and time interval _T_ between two events depend on the observer. Einstein noted, however, that a particular combination of _D_ and _T_, the quantity _D_ 2 − _c_ 2 _T_ 2, has the same value for all observers.

The term _c_ _T_ in this invariant quantity elevates time to a kind of mathematical parity with space. Noting this, the German mathematical physicist [Hermann Minkowski](https://www.britannica.com/biography/Hermann-Minkowski) showed that the universe resembles a four-dimensional structure with coordinates _x_, _y_, _z_, and _c_ _t_ representing length, width, height, and time, respectively. Hence, the universe can be described as a four-dimensional space-time [continuum](https://www.merriam-webster.com/dictionary/continuum), a central concept in general relativity.

## Experimental evidence for special relativity

Because relativistic changes are small at typical speeds for macroscopic objects, the confirmation of special relativity has relied on either the examination of subatomic bodies at high speeds or the measurement of small changes by sensitive instrumentation. For example, ultra-accurate [clocks](https://www.britannica.com/technology/clock) were placed on a variety of commercial airliners flying at one-millionth the speed of light. After two days of continuous flight, the time shown by the [airborne](https://www.britannica.com/dictionary/airborne) clocks differed by fractions of a microsecond from that shown by a synchronized [clock](https://www.britannica.com/technology/clock) left on Earth, as predicted.

Larger effects are seen with [elementary particles](https://www.britannica.com/science/subatomic-particle) moving at speeds close to that of light. One such experiment involved [muons](https://www.britannica.com/science/muon), elementary particles created by [cosmic rays](https://www.britannica.com/science/cosmic-ray) in Earth’s atmosphere at an altitude of about 9 km (30,000 feet). At 99.8 percent of the speed of light, the muons should reach [sea level](https://www.britannica.com/science/sea-level) in 31 microseconds, but measurements showed that it took only 2 microseconds. The reason is that, relative to the moving muons, the distance of 9 km contracted to 0.58 km (1,900 feet). Similarly, a relativistic mass increase has been confirmed in measurements on fast-moving elementary particles, where the change is large ( _see below_ [Particle accelerators](https://www.britannica.com/science/relativity/Experimental-evidence-for-general-relativity#ref252902)).

Such results leave no doubt that special relativity correctly describes the universe, although the theory is difficult to accept at a [visceral](https://www.merriam-webster.com/dictionary/visceral) level. Some insight comes from Einstein’s comment that in relativity the limiting speed of light plays the role of an infinite speed. At infinite speed, light would [traverse](https://www.merriam-webster.com/dictionary/traverse) any distance in zero time. Similarly, according to the relativistic equations, an observer riding a light [wave](https://www.britannica.com/science/wave-physics) would see lengths contract to zero and clocks stop ticking as the universe approached him at the speed of light. Effectively, relativity replaces an infinite speed limit with the finite value of 3 × 108 metres per second.