What does the theory of relativity say?

Question

What does the theory of relativity say?

Answer 1

Simple way to think , it says nothing is absolute in nature, everything is measured with respect to something , Its very deep , special relativity & general relativity are the core components in understanding universe so can't describe much . get richard feynman's Volume 1 lecture series on physics which will be a good starting point

Answer 2

The moral of the story, Einstein's general and special theory of relativity explains the ,  nothing in this universe is absolute but the velocity of light in space, moreover E=mc2 equation mean 'mas' and 'energy' both are diff. name of only one thing, mas and energy can convert in each other,  and also that,      

the universe is like a fabric ,

however this theory can answer most of questions of universe.

Answer 3

The Special Theory of Relativity was published in 1905 and deals with (frames of reference) objects separating with constant high velocities (close to the speed of light). In this first theory, Einstein stated that the speed of light was the absolute limit for all velocities and furthermore all observers, what ever their motion, must measure the speed of light to be exactly the same. Finally, only mass-less objects may attain the speed of light. However, massive objects contract in their direction of motion, their clocks slow down relative to observer's clocks and they gain mass and thus inertia as they accelerate towards the speed of light.

Einstein's theory of General Relativity (1915) is a cause and effect theory. The theory describes the fabric of space-time as a medium that may be distorted by the presence of mass and energy. From his earlier relativity theory, Einstein had related mass and energy in the famous equation: -

E = mc²

From this concept, he described the curvature or distortion of space-time as due to the total sum of mass-energy present within the region of distorted space. It is the curvature of space-time we call gravity. Thus, our planet follows the 'straightest' path or path of least action whilst it orbits the mutually curved space around the Sun. An object falling to earth, under the pull of gravity, is following the curvature of space in the region around the surface of the Earth. Einstein described the relationship between space-time curvature and the mass-energy causing it, in the tensor field equation: -

G = 8πT

Where 'G' is the Einstein tensor representing the 'gravity' or curvature of space-time and 'T' is the total energy tensor representing the mass-energy creating the gravitational curvature of the space-time.

The theory, accurately predicts many features of the solar system, such as the peculiar motion of Mercury’s perihelion, and may be used to account for the gravitational physics of black holes and neutron stars. The extreme high pressure physics at the core of a star may be described using this theory. General relativity also predicted the Big Bang origin of the universe, although Einstein refused to accept the conclusion. He later claimed that this erroneous conclusion was his biggest blunder. Overall, after ninety-three years, General Relativity is still the best theory of gravity that we have!

Answer 4

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Not only in quantum mechanics, but in most parts of physics, time is a variable, not an "experienced quality". Physics requires abstracting away from one's experience.

This is particularly true in general relativity, in which this time variable is a part of the space-time of which the subject concerns the "geometry". Along this line, even earlier in the game of relativity, someone once said, "The world does not BECOME, but IS."

However, in addition to this general abstraction of physics from immediate experience, general relativity entails highly sophisticated calculations with results that are only observable either by highly precise measurements, or else have their effects at only very extreme situations, such as in the neighborhood of a black hole, or at the time of creation of the universe. It is far far removed from immediate experience.

Furthermore, I would say that there is no "proof" of general relativity, it is just the theory that people think is most plausible, because of elegance and consistency, with regards to issues of gravity. So how could you possibly come to this conclusion on the basis of immediate experience, without complex and sophisticated mathematical considerations?

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Special relativity is quite adequate when dealing with an object moving at constant speed and direction in relation to the observer. However, in practice motion is never constant. There are always forces which cause variations in the speed and direction of moving objects. Since subatomic particles move at immense speeds over short distances, they do not have time to accelerate much, and special relativity can be applied. Nevertheless, in the motion of planets and stars, special relativity proved insufficient. Here we are dealing with large accelerations caused by huge gravitational fields. It is once again a case of quantity and quality. At the subatomic level, gravitation is insignificant in comparison with other forces, and can be ignored. In the everyday world, on the contrary, all other forces except gravity can be ignored.

Einstein attempted to apply relativity to motion in general, not just to constant motion. Thus we arrive at the general theory of relativity, which deals with gravity. It marks a break, not only with the classical physics of Newton, with its absolute mechanical universe, but with the equally absolute classical geometry of Euclid. Einstein showed that Euclidean geometry only applied to "empty space," an ideally-conceived abstraction. In reality, space is not "empty." Space is inseparable from matter. Einstein maintained that space itself is conditioned by the presence of material bodies. In his general theory, this idea is conveyed by the seemingly paradoxical assertion that, near heavy bodies, "space is curved."

The real, i.e., material, universe is not at all like the world of Euclidean geometry, with the perfect circles, absolutely straight lines, and so on. The real world is full of irregularities. It is not straight, but precisely "warped." On the other hand, space is not something which exists separate and apart from matter. The curvature of space is just another way of expressing the curvature of matter which "fills" space. For example, it has been proved that light rays bend under the influence of the gravitational fields of bodies in space.

The general theory of relativity is essentially of a geometrical character, but this geometry is completely different to the classical Euclidean kind. In Euclidean geometry, for instance, parallel lines never meet or diverge, and the angles of a triangle always add up to 180�. Einstein’s space-time (actually first developed by the Russian-German mathematician, Hermann Minkowski, one of Einstein’s teachers, in 1907) represents a synthesis of three dimensional space (height, breadth and length) with time. This four-dimensional geometry deals with curved surfaces ("curved space-time"). Here the angles of a triangle may not add up to 180�, and parallel lines can cross or diverge.

In Euclidean geometry, as Engels points out, we meet a whole series of abstractions which do not at all correspond to the real world: a dimensionless point which becomes a straight line, which, in turn, becomes a perfectly flat surface, and so on and so forth. Among all these abstractions we have the emptiest abstraction of all, that of "empty space." Space, in spite of what Kant believed, cannot exist without something to fill it, and that something is precisely matter (and energy, which is the same thing). The geometry of space is determined by the matter which it contains. That is the real meaning of "curved space." It is merely a way of expressing the real properties of matter. The issue is only confused by inappropriate metaphors contained in popularisations of Einstein: "Think of space as a rubber sheet," or "Think of space as glass," and so on. In reality, the idea that must be kept in mind at all times is the indissoluble unity of time, space, matter and motion. The moment this unity is forgotten, we instantly slide into idealist mystification.

If we conceive space as a Thing-in-Itself, empty space, as in Euclid, clearly it cannot be curved. It is "nothing." However, as Hegel put it, there is nothing in the universe which does not contain both being and not-being. Space and matter are not two diametrically opposed, mutually exclusive phenomena. Space contains matter, and matter contains space. They are completely inseparable. The dialectical unity of matter and space is precisely what the universe is. In a most profound way, the general theory of relativity conveys this dialectical idea of the unity of space and matter. In the same way in mathematics zero itself is not "nothing," but expresses a real quantity, and plays a determining role.

Einstein presents gravitation as a property of space rather than a "force" acting upon bodies. According to this view space itself curves as a result of the presence of matter. This is a rather singular way of expressing the unity of space and matter, and one that is open to serious misinterpretations. Space itself, of course, cannot curve if it is understood as "empty space." The point is that it is impossible to conceive of space without matter. It is an inseparable unity. What we are considering is a definite relationship of space to matter. The Greek atomists long ago pointed out that atoms existed in the "void." The two things cannot exist without each other. Matter without space is the same as space without matter. A totally empty void is just nothing. But so is matter without any boundaries. Space and matter, then, are opposites which presuppose each other, define each other, limit each other, and cannot exist without each other.

The general theory served to explain at least one phenomenon which could not be explained by Newton’s classical theory. As the planet Mercury approaches its closest point to the sun, its revolutions display a peculiar irregularity, which had been previously attributed to the perturbations caused by the gravity of other planets. However, even when these were taken into account, it did not explain the phenomenon. The deviation of Mercury’s orbit around the sun ("perihelion") was very small, but enough to upset the astronomers’ calculations. Einstein’s general theory predicted that the perihelion of any revolving body should have a motion beyond that prescribed by Newton’s law. This was shown to be correct for Mercury, and later also for Venus.

He also predicted that a gravitational field would bend light-rays. Thus, he claimed, a light ray passing close to the surface of the sun would be bent out of a straight line by 1.75 seconds of arc. In 1919 an astronomic observation of an eclipse of the sun showed this to be correct. Einstein’s brilliant theory was demonstrated in practice. It was able to explain the apparent shift in the position of stars near the sun by the bending of their rays, and also the irregular motion of the planet Mercury, which could not be accounted for by Newton’s theories.

Newton worked out the laws governing the movement of objects, according to which the strength of gravitational pull depends upon mass. He also maintained that any force exerted upon an object produces acceleration in inverse proportion to the mass of the object. Resistance to acceleration is called inertia. All masses are measured either through gravitational effects or inertial effects. Direct observation has shown that inertial mass and gravitational mass are, in fact, identical to within one part in one trillion. Einstein began his theory of general relativity by assuming that inertial mass and gravitational mass are exactly equal, because they are essentially the same thing.

The apparently motionless stars are moving at colossal speeds. Einstein’s cosmic equations of 1917 implied that the universe itself was not fixed for all time, but could be expanding. The galaxies are moving away from us at speeds of about 700 miles a second. The stars and galaxies are constantly changing, coming into being and passing away. The whole universe is a vast arena where the drama of birth and death of stars and galaxies is played out across eternity. These are truly revolutionary events! Exploding galaxies, supernovas, catastrophic collisions between stars, black holes with a density billions of times greater than our sun greedily devouring entire clusters of stars. These things put in the shade the imaginings of the poets.

Answer 5

"When you sit with a nice girl for two hours, it seems like two minutes. When you sit on a hot stove for two minutes, it seems like two hours that's relativity." -- Albert Einstein

Answer 6

when a man sitting with a girl an hour seems to be like a minute, but when sit under a hot stove a minute seems to be an hour this what einstein explained relativity in a ridiculous manner.