# General theory of relativity. History of general relativity 2022-10-13

General theory of relativity
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The general theory of relativity, developed by Albert Einstein in the early 20th century, is a theory of gravitation that describes the gravitational force as a curvature of spacetime caused by mass and energy. This theory is based on the idea that the laws of physics should be the same for all observers, regardless of their relative motion or location in the universe.

One of the key predictions of the general theory of relativity is that time and space are not separate entities, but rather a single entity called spacetime. In this theory, mass and energy cause spacetime to curve, and objects move along the resulting curves. This means that the path of an object is determined not only by its initial velocity, but also by the curvature of spacetime caused by nearby masses and energies.

One of the most famous predictions of the general theory of relativity is the phenomenon of gravitational lensing, in which light is bent as it travels through a region of spacetime that is curved by a massive object. This effect has been observed in many astronomical observations, and has been used to study distant objects such as quasars and black holes.

The general theory of relativity also predicts the phenomenon of time dilation, in which time appears to pass more slowly in regions of strong gravitational fields. This effect has been confirmed through experiments using atomic clocks and has important implications for the study of extreme gravitational environments such as black holes.

In addition to its predictions about the curvature of spacetime and the behavior of objects moving through it, the general theory of relativity also provides a theoretical framework for understanding the evolution of the universe as a whole. The theory suggests that the expansion of the universe is accelerating due to the presence of dark energy, and has been successful in explaining a wide range of observational data about the structure and evolution of the universe.

Overall, the general theory of relativity has had a profound impact on our understanding of the universe and has led to many important scientific discoveries. It remains an active area of research, with ongoing efforts to test and refine the theory in light of new data and observations.

## History of general relativity

Yet Newton's laws assume that gravity is an innate force of an object that can act over a distance. Supermassive black holes are millions to billions times larger, and are detected in galaxies at distances from Mpc to Gpc. The energy-momentum tensor tells us how four-momentum flows through spacetime. Due to its general covariance, Einstein's theory is not sufficient by itself to determine the To understand Einstein's equations as partial differential equations, it is helpful to formulate them in a way that describes the evolution of the universe over time. It is accordingly, not permitted us to say how things would be if the earth did not rotate. The left-hand side contains second derivatives of the gravitational potential, similar to the Einstein field equation, which has second derivatives of the metric.

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## Einstein's theory of general relativity

These constants work out to have the value: This in fact, shows exactly why gravity is such a weak force. What Is Metric Compatibility and Why Is It Important? Journal for the History of Astronomy. Diploma in Psychological Medicine D. Together they are equivalent to the Riemann tensor, in that they describe spacetime curvature and tides completely. Lasers from the two Keck telescopes point in the direction of the center of our galaxy.

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## Einsteinâs general relativity theory is questioned but still stands âfor now,â team reports

To me, the theory of general relativity is one of the most beautiful theories of nature ever invented, but it is often seen as one of those obscure topics that are not easily accessible to most people. To you, it seemed as though you were heading on a straight line all along, but clearly if you went around the sphere, the trajectory was not really straight. Diploma in Ophthalmology D. What makes this even more clear is that mathematically, the curvature of a function is also described by its second derivatives. Albert Einstein published his theory in 1915.

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## General Relativity For Dummies: An Intuitive Introduction

For another application, I suggest reading orbits around black holes, which covers how to use a so-called effective potential to intuitively visualize these black hole orbits. The amount of deflection that he calculated in 1911 was too small 0. Subtle is the lord: the science and life of Albert Einstein. Thus the circular rods will have their length's contracted. In General Relativity these ellipses do not exactly repeat.

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## General Relativity

Now, any vector can be expressed as the sum of its components with the basis vectors you may be familiar with this in typical Cartesian coordinates already. First of all, what is a tensor anyway? Moreover, if everything in spacetime follows its own geodesic, it means that different parts of an object will each have their own geodesic. An object moves through spacetime in a straight line geodesic , but if the spacetime is curved gravity is present , this line will follow the curvature and may change direction like if you were moving on the surface of a sphere, for example. Thus, the laws of physics should be these kinds of equations, in other words, tensor equations. And we also know that light rays are the fastest way of getting information from, say, the star to the Earth. Remember from earlier that the Einstein tensor is a combination of the Ricci tensor and Ricci scalar, which contain a lot of Christoffel symbol terms.

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## What Is The General Theory of Relativity? : ScienceAlert

Entwurf einer verallgemeinerten RelativitĂ€tstheorie und einer Theorie der Gravitation Outline of a Generalized Theory of Relativity and of a Theory of Gravitation , Zeitschrift fĂŒr Mathematik und Physik, 62, 225â261. Retrieved 11 February 2016. Their tracks are known as geodesics in scientific terminology, which are straight plane lines in curved spacetime. We imagine the universe as a Flatland confined to the surface of a balloon. Thus, the upper path in the figure defines a straight line. A gravitational field is described by the acceleration or force an object would experience if it were to be placed in the field. There is just one more question left; by now, you know how curvature is described and how it causes the effects of gravity, but what causes spacetime curvature in the first place? Imagine setting a large object in the center of a trampoline.

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## Einsteinâs General Relativity Theory Was Game

While falling towards the ground, do you see the cork move towards the top of the water, towards the bottom of the bucket, or stay where it is relative to the bucket and the water? The puzzling surprise in 1962 was their discovery of a rich infinite-dimensional group the so-called BMS group as the asymptotic symmetry group, instead of the finite-dimensional PoincarĂ© group, which is a subgroup of the BMS group. Einstein predicted that massive objects in space, like planets or even black holes, would act like cosmic bowling balls and pull down the fabric of spacetime. So, here we see a clear example of gravity as a fictitious force a force caused by a particular reference frame. Translated by Robert W. Now, how does all this relate to physics? Astronomical observations of the cosmological expansion rate allow the total amount of matter in the universe to be estimated, although the nature of that matter remains mysterious in part. In some sense, the energy-momentum tensor is just a relativistic extension of the Cauchy stress tensor.

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## General relativity

If we stand on any given raisin, all the other raisins will be receding away from us; the further away the raisin is the faster it recedes away from us. Schilpp; Paul Arthur 1979. Click on the button below. These will not be necessary to understand the basics, however. Geometry of Newtonian Gravity The theory that a body's motion can be described as a combination of free motion and deviations from this free motion is at the heart of classical mechanics. We already know that gravity is closely related with acceleration, so maybe gravity too has to do with second derivatives of something. If clear photographs and measurable results had been possible, Einstein's 1911 prediction might have been proven wrong.

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## General Theory of Relativity

The key idea here is to note that the metric itself represents the gravitational potential in general relativity. We can compare the gravitational mass of two objects by weighing them, i. Diploma in Psychological Medicine D. This is fundamentally why gravity is NOT a force, but rather a property of spacetime itself, namely the curvature of spacetime. Michelson designed an instrument called the ad hoc hypothesis in which the length of material bodies changes according to their motion through the aether. This is done mathematically by varying it and setting this variation equal to zero.

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## Theory of relativity

Now we consider two bodies with masses M and m that are both moving to the right at the same speed relative to us. We can also compare the inertial mass of same two objects by measuring their effects in collisions with other objects. Publications of the Astronomical Society of the Pacific. The key thing here is that the Riemann tensor has a clear and intuitive geometric meaning in terms of parallel transporting a vector around two different paths and then comparing them. The object would press down into the fabric, causing it to dimple. The puzzling surprise in 1962 was their discovery of a rich infinite-dimensional group the so-called BMS group as the asymptotic symmetry group, instead of the finite-dimensional PoincarĂ© group, which is a subgroup of the BMS group. Now combine these with the notion of spacetime itself being described by a metric tensor.

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