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  1. From Newton to Einstein: the origins of general relativity › from-newton-to-einstein-the
    • The Beauty of Invariance
    • Problems with Electromagnetism
    • Principle of Relativity
    • What About Gravity?
    • The Road to General Relativity

    In the 17th century, Isaac Newton developed a set of equationsthat described the physical properties of the world around us. These equations were very successful, from a description of the flight of a cannonball, to the motion of the planets. They also had a very appealing property: all observers, regardless of whether they are moving or not – i.e. regardless of which “inertial frame” they are in – are equivalent when it comes to their description of the world around them. So two individuals moving in different directions would see events unfold in the same way. Even though formally these individuals would see things in a different way one might say that things move from left to right, whereas the other might say they move from right to left – still the fundamental description of the unfolding events would remain the same, and the laws of physics derived by these individuals would have literally the same form. But in the 19th century, people started noticing that not everything pl...

    The 19th century was a time of extensive study of the phenomena of electricity, magnetism and light. In 1865 James Clerk Maxwell published a set of equations that combined all these phenomena into a single phenomenon of “electromagnetism”. Soon after Maxwell’s discovery, people realised that there is something strange when it comes to his equations. Their form changes when we move from one inertial frame to another. So an individual who is not moving can observe distinctively different physical phenomena than a person who is moving. All the beauty of invariance and irrelevance of observers that we had got used to in Newtonian physics was gone. It now looked like some frames were preferable to others when it came to describing events in nature. Then, at the turn of the 20th century, a new mathematical transformation was discovered that could preserve the structure of Maxwell’s equations when moving from one frame to another. Although many people contributed to this discovery, we now...

    This got Einstein wondering whether the transformation that preserved the structure of Maxwell’s equations was merely a mathematical trick or whether there was something fundamental about it. He wondered whether time and space were absolute, or whether the principle of invariance of the laws of physics should be paramount. In 1905, Einstein decided that it is the invariance of the laws of physics that should have the highest status, and postulated the principle of relativity: that all inertial frames are equivalent, the observer’s motion (with constant velocity) is irrelevant, and that all laws of physics should have the same form in all inertial frames. When combined with electromagnetism, this principle would require that the transformation from one inertial frame to another must have a structure of the Lorentz transformation, meaning that time and space are no longer absolute and change their properties when changing from one inertial frame to another.

    In 1907 Einstein realised that his theory was not complete. The principle of relativity was only applicable to observers moving with a constant velocity. It also did not fit with the Newtonian description of gravity. Einstein, being a patent officer, did not have access to laboratory equipment. To compensate, he had to engage himself in thought experiments. He considered various scenarios in his head and worked through them step by step. These thought experiments showed to him that gravity is not different from acceleration. So standing stationary on the Earth feels just the same as standing in a rocket ship accelerating at a constant 1G. It also showed that the accelerated observer would observe that fundamental geometrical properties change. For example, that the number π (a mathematical constant) could no longer be defined as a ratio of a circle’s circumference to its diameter. So it was not just time and space that lost their absolute meaning, but Einstein realised that also geo...

    All this reasoning convinced Einstein that the geometry of the spacetime and the physical processes that take place in the spacetime, are related to each other and that one can affect the other. It also led to a striking conclusion: what we perceive as gravity is just a consequence of the motion through the spacetime. The larger the curvature of the spacetime the stronger gravity is. It took Einstein eight years to find the relation between the geometry of spacetime and physics. The equations that he presented in 1915 not only led to a completely different interpretation of events around us but also provided an explanation for some baffling or yet to be discovered phenomena: from the anomalous orbit of the planet Mercury, through the bending of light by the Sun’s gravity, to predicting the existence of black holes and expanding universe. It was a bumpy road from Newtownian physics to special and then general relativity. But each step, driven by Einstein’s insight, drove inexorably t...

  2. Einstein showed Newton was wrong about gravity. Now ... › mach › science

    Aug 03, 2019 · Scientists use Sagittarius A*, the supermassive black hole at the center of our Milky Way galaxy, to test Albert Einstein's theory of general relativity.

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  4. Newtonian gravity vs. general relativity: exactly how wrong ... › questions › 52165

    There is no sense in which Newton was proved wrong by Einstein. What relativity did is expand the range of physical conditions over which the theory applied. Special relativity extended the range to include high speeds, and general relativity extended it again to include high gravitational fields.

  5. General relativity is broader and includes special relativity, which was published first. Concepts Related to Newton’s Law of Universal Gravitation Sir Isaac Newton was the first scientist to precisely define the gravitational force, and to show that it could explain both falling bodies and astronomical motions.

  6. Planetary Motion: The History of an Idea That Launched the ... › features › OrbitsHistory

    The ideas outlined in Newton’s laws of motion and universal gravitation stood unchallenged for nearly 220 years until Albert Einstein presented his theory of special relativity in 1905. Newton’s theory depended on the assumption that mass, time, and distance are constant regardless of where you measure them. The theory of relativity treats time, space, and mass as fluid things, defined by an observer’s frame of reference.

    • Holli Riebeek
    • 2009
  7. General relativity - Wikipedia › wiki › General_relativity

    The expansion involves a series of terms; the first terms represent Newtonian gravity, whereas the later terms represent ever smaller corrections to Newton's theory due to general relativity. An extension of this expansion is the parametrized post-Newtonian (PPN) formalism, which allows quantitative comparisons between the predictions of general relativity and alternative theories.

  8. This Is Why Scientists Will Never Exactly Solve General ... › sites › startswithabang

    Dec 04, 2019 · In Newton's theory of gravity, ... we can't practically achieve even that step in a Universe governed by General Relativity. Here's why. ... If we were to replace Earth with a denser version, up ...

    • Ethan Siegel
  9. What is the difference between Newton’s law of motion and ... › What-is-the-difference-between

    Often, the origin of physical terms is very whimsical. So, in particular, the "general theory of relativity" is directly related to the problem of gravity rather than the laws of motion itself, and it is comparable to Newtons Law of Universal Gra...

  10. Criticism of the theory of relativity - Wikipedia › wiki › Criticism_of_the_theory_of

    However, Soldner's derivation has nothing to do with Einstein's, since it was fully based on Newton's theory, and only gave half of the value as predicted by general relativity. Paul Gerber (1898) published a formula for the perihelion advance of Mercury, which was formally identical to an approximate solution given by Einstein.

  11. This One Puzzle Brought Physicists From Special To General ... › sites › startswithabang

    Oct 03, 2019 · Newtonian mechanics broke down at high speeds, as Special Relativity caused lengths to contract and time to dilate near the speed of light. Gravitation was the last Newtonian pillar left, and...

    • Ethan Siegel
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