File Name: space and time in special relativity .zip
In physics and relativity , time dilation is the difference in the elapsed time as measured by two clocks.
In physics and relativity , time dilation is the difference in the elapsed time as measured by two clocks. It is either due to a relative velocity between them "kinetic" time dilation, from special relativity or to a difference in gravitational potential between their locations gravitational time dilation , from general relativity.
When unspecified, "time dilation" usually refers to the effect due to velocity. After compensating for varying signal delays due to the changing distance between an observer and a moving clock i. Doppler effect , the observer will measure the moving clock as ticking slower than a clock that is at rest in the observer's own reference frame.
In addition, a clock that is close to a massive body and which therefore is at lower gravitational potential will record less elapsed time than a clock situated further from the said massive body and which is at a higher gravitational potential.
These predictions of the theory of relativity have been repeatedly confirmed by experiment, and they are of practical concern, for instance in the operation of satellite navigation systems such as GPS and Galileo. Time dilation by the Lorentz factor was predicted by several authors at the turn of the 20th century.
Special relativity indicates that, for an observer in an inertial frame of reference , a clock that is moving relative to them will be measured to tick slower than a clock that is at rest in their frame of reference. This case is sometimes called special relativistic time dilation.
Theoretically, time dilation would make it possible for passengers in a fast-moving vehicle to advance further into the future in a short period of their own time.
For sufficiently high speeds, the effect is dramatic. For example, one year of travel might correspond to ten years on Earth. Time dilation can be inferred from the observed constancy of the speed of light in all reference frames dictated by the second postulate of special relativity.
This constancy of the speed of light means that, counter to intuition, speeds of material objects and light are not additive. It is not possible to make the speed of light appear greater by moving towards or away from the light source. Consider then, a simple vertical clock consisting of two mirrors A and B , between which a light pulse is bouncing. The separation of the mirrors is L and the clock ticks once each time the light pulse hits either of the mirrors. In the frame in which the clock is at rest diagram on the left , the light pulse traces out a path of length 2 L and the period of the clock is 2 L divided by the speed of light:.
From the frame of reference of a moving observer traveling at the speed v relative to the resting frame of the clock diagram at right , the light pulse is seen as tracing out a longer, angled path.
Keeping the speed of light constant for all inertial observers, requires a lengthening of the period of this clock from the moving observer's perspective. That is to say, in a frame moving relative to the local clock, this clock will appear to be running more slowly. Straightforward application of the Pythagorean theorem leads to the well-known prediction of special relativity:. Elimination of the variables D and L from these three equations results in:. Because all clocks that have a common period in the resting frame should have a common period when observed from the moving frame, all other clocks—mechanical, electronic, optical such as an identical horizontal version of the clock in the example —should exhibit the same velocity-dependent time dilation.
Given a certain frame of reference, and the "stationary" observer described earlier, if a second observer accompanied the "moving" clock, each of the observers would perceive the other's clock as ticking at a slower rate than their own local clock, due to them both perceiving the other to be the one that is in motion relative to their own stationary frame of reference.
Common sense would dictate that, if the passage of time has slowed for a moving object, said object would observe the external world's time to be correspondingly sped up. Counterintuitively, special relativity predicts the opposite. When two observers are in motion relative to each other, each will measure the other's clock slowing down, in concordance with them being in motion relative to the observer's frame of reference.
While this seems self-contradictory, a similar oddity occurs in everyday life. If two persons A and B observe each other from a distance, B will appear small to A, but at the same time A will appear small to B.
Being familiar with the effects of perspective , there is no contradiction or paradox in this situation. The reciprocity of the phenomenon also leads to the so-called twin paradox where the aging of twins, one staying on Earth and the other embarking on a space travel, is compared, and where the reciprocity suggests that both persons should have the same age when they reunite.
On the contrary, at the end of the round-trip, the traveling twin will be younger than their sibling on Earth. The dilemma posed by the paradox, however, can be explained by the fact that the traveling twin must markedly accelerate in at least three phases of the trip beginning, direction change, and end , while the other will only experience negligible acceleration, due to rotation and revolution of Earth.
During the acceleration phases of the space travel, time dilation is not symmetric. All three clocks simultaneously start to tick in S. The proper time between two events is indicated by a clock present at both events.
From that it can be seen, that the proper time between two events indicated by an unaccelerated clock present at both events, compared with the synchronized coordinate time measured in all other inertial frames, is always the minimal time interval between those events. However, the interval between two events can also correspond to the proper time of accelerated clocks present at both events. Under all possible proper times between two events, the proper time of the unaccelerated clock is maximal , which is the solution to the twin paradox.
In addition to the light clock used above, the formula for time dilation can be more generally derived from the temporal part of the Lorentz transformation. Thus the duration of the clock cycle of a moving clock is found to be increased: it is measured to be "running slow". In special relativity, time dilation is most simply described in circumstances where relative velocity is unchanging. Nevertheless, the Lorentz equations allow one to calculate proper time and movement in space for the simple case of a spaceship which is applied with a force per unit mass, relative to some reference object in uniform i.
Let t be the time in an inertial frame subsequently called the rest frame. Let x be a spatial coordinate, and let the direction of the constant acceleration as well as the spaceship's velocity relative to the rest frame be parallel to the x -axis. The clock hypothesis is the assumption that the rate at which a clock is affected by time dilation does not depend on its acceleration but only on its instantaneous velocity.
The clock hypothesis was implicitly but not explicitly included in Einstein's original formulation of special relativity. Since then, it has become a standard assumption and is usually included in the axioms of special relativity, especially in the light of experimental verification up to very high accelerations in particle accelerators.
Gravitational time dilation is experienced by an observer that, at a certain altitude within a gravitational potential well, finds that their local clocks measure less elapsed time than identical clocks situated at higher altitude and which are therefore at higher gravitational potential.
Gravitational time dilation is at play e. While the astronauts' relative velocity slows down their time, the reduced gravitational influence at their location speeds it up, although to a lesser degree. Also, a climber's time is theoretically passing slightly faster at the top of a mountain compared to people at sea level. It has also been calculated that due to time dilation, the core of the Earth is 2.
Contrarily to velocity time dilation, in which both observers measure the other as aging slower a reciprocal effect , gravitational time dilation is not reciprocal.
This means that with gravitational time dilation both observers agree that the clock nearer the center of the gravitational field is slower in rate, and they agree on the ratio of the difference. High-accuracy timekeeping, low-Earth-orbit satellite tracking, and pulsar timing are applications that require the consideration of the combined effects of mass and motion in producing time dilation. Practical examples include the International Atomic Time standard and its relationship with the Barycentric Coordinate Time standard used for interplanetary objects.
Relativistic time dilation effects for the solar system and the Earth can be modeled very precisely by the Schwarzschild solution to the Einstein field equations. The exact relation between the rate of proper time and the rate of coordinate time for a clock with a radial component of velocity is:. The above equation is exact under the assumptions of the Schwarzschild solution.
It reduces to velocity time dilation equation in the presence of motion and absence of gravity, i. It reduces to gravitational time dilation equation in the absence of motion and presence of gravity, i. Velocity and gravitational time dilation have been the subject of science fiction works in a variety of media.
Some examples in film are the movies Interstellar and Planet of the Apes. Tau Zero , a novel by Poul Anderson , is an early example of the concept in science fiction literature.
In the novel, a spacecraft using a Bussard ramjet to accelerate to high enough speeds that the crew will spend 5 years on board, but 33 years will pass on the Earth before they arrive at their destination. The velocity time dilation is explained by Anderson in terms of the tau factor , which decreases closer and closer to zero as the ship approaches the speed of light, hence the title of the novel. From Wikipedia, the free encyclopedia. Introduction History. Fundamental concepts.
Principle of relativity Theory of relativity General covariance Simultaneity Relativity of simultaneity Relative motion Event Frame of reference Inertial frame of reference Mass Inertial mass Rest frame Center-of-momentum frame Curvature Geodesic Geon Equivalence principle Mass in general relativity Mass—energy equivalence Invariant Invariant mass Spacetime symmetries Special relativity Doubly special relativity de Sitter invariant special relativity Scale relativity Speed of light Time derivative Proper time Proper length Length contraction Action at a distance Principle of locality Riemannian geometry Energy condition.
Equations Formalisms. Birkhoff's theorem Geroch's splitting theorem Goldberg—Sachs theorem Lovelock's theorem No-hair theorem Penrose—Hawking singularity theorems Positive energy theorem.
Postulates of special relativity General covariance Simultaneity Relativity of simultaneity Relative motion Event Frame of reference Inertial frame of reference Mass Inertial mass Invariant Rest frame Center-of-momentum frame Speed of light Maxwell's equations Lorentz transformation. Time dilation Gravitational time dilation Relativistic mass Mass—energy equivalence Proper time Proper length Length contraction Action at a distance Principle of locality Relativity of simultaneity Relativistic Doppler effect Thomas precession Relativistic disk Bell's spaceship paradox Ehrenfest paradox.
Proper time Proper mass Lorentz scalar 4-momentum. History Precursors. Galilean relativity Galilean transformation Aether theories. Alternative formulations of special relativity. Measured time difference as explained by relativity theory. Main article: History of special relativity. See also: Tests of special relativity. Main article: Ives—Stilwell experiment. Main article: Experimental testing of time dilation. Minkowski diagram and twin paradox. Clock C in relative motion between two synchronized clocks A and B.
Twin paradox. One twin has to change frames, leading to different proper times in the twin's world lines. Main article: Hyperbolic motion relativity. Main article: Gravitational time dilation. Living Reviews in Relativity. Bibcode : LRR Reading, Massachusetts: Addison—Wesley.
Einstein, — PDF. Philosophical Transactions of the Royal Society. Annalen der Physik. Bibcode : AnP
Formulate conclusions of the theory of special relativity, noting the assumptions that were made in deriving it. According to the theory of special relativity, it is impossible to say in an absolute sense whether two distinct events occur at the same time if those events are separated in space, such as a car crash in London and another in New York. The question of whether the events are simultaneous is relative: in some reference frames the two accidents may happen at the same time, in other frames in a different state of motion relative to the events the crash in London may occur first, and still in other frames, the New York crash may occur first. If we imagine one reference frame assigns precisely the same time to two events that are at different points in space, a reference frame that is moving relative to the first will generally assign different times to the two events. This is illustrated in the ladder paradox, a thought experiment which uses the example of a ladder moving at high speed through a garage. In , Albert Einstein abandoned the classical aether and emphasized the significance of relativity of simultaneity to our understanding of space and time.
Einstein's Space-Time: An Introduction to Special and General Relativity is a textbook addressed to students in physics and other people interested in Relativity and a history of physics. The first chapters are aimed to afford a deep understanding of the relativistic spacetime and its consequences for Dynamics. It is a remarkable resource for intermediate and advanced undergraduates, as it introduces the more difficult mathematics with a minimum of formalism. Lower-division undergraduates through faculty. The style of the book is fresh and the author, paying attention to details, tries also to explain the material in his own words …. The inclusion of the cosmological constant into the discussion seems timely. I consider the historical approach to be a plus for this overall sound text on Relativity.
The principle of relativity. Unity of space and time. Inertial frames. Latticework of clocks. Rocket frame.
The theory of special relativity explains how space and time are linked for objects that are moving at a consistent speed in a straight line. One of its most famous aspects concerns objects moving at the speed of light. Simply put, as an object approaches the speed of light, its mass becomes infinite and it is unable to go any faster than light travels. This cosmic speed limit has been a subject of much discussion in physics, and even in science fiction, as people think about how to travel across vast distances. The theory of special relativity was developed by Albert Einstein in , and it forms part of the basis of modern physics.
When the theory of relativity appeared in the early s, it upended centuries of science and gave physicists a new understanding of space and time. Isaac Newton saw space and time as fixed, but in the new picture provided by special relativity and general relativity they were fluid and malleable. Albert Einstein. He published the first part of his theory — special relativity — in the German physics journal Annalen der Physik in and completed his theory of general relativity only after another decade of difficult work.
Special relativity changed the way we view space and time and showed us that time is relative to an observer.
In physics , spacetime is any mathematical model which fuses the three dimensions of space and the one dimension of time into a single four-dimensional manifold. The fabric of space-time is a conceptual model combining the three dimensions of space with the fourth dimension of time. Spacetime diagrams can be used to visualize relativistic effects, such as why different observers perceive differently where and when events occur. Until the 20th century, it was assumed that the three-dimensional geometry of the universe its spatial expression in terms of coordinates, distances, and directions was independent of one-dimensional time. The famous physicist Albert Einstein helped develop the idea of space-time as part of his theory of relativity. Prior to his pioneering work, scientists had two separate theories to explain physical phenomena: Isaac Newton's laws of physics described the motion of massive objects, while James Clerk Maxwell's electromagnetic models explained the properties of light.
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