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In 2001, British Electrical Engineer Roger Shawyer first introduced the “impossible drive,” known as the EmDrive. It earned that nickname because Shawyer claimed it could produce thrust without propellant. If true, that would make it a reactionless drive—a machine that appears to shove itself forward without throwing anything backward. That’s a direct problem for the conservation of momentum, which just so happens to be one of the load-bearing rules of physics…..Continue reading…
By Darren Orf
Source: Popular Mechaanics
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Critics:
The nature and mechanism of gravity were explored by a wide range of ancient scholars. In Ancient Greece, Aristotle believed that each of the classical elements had a natural place in the universe which it tends to move toward – earth at the center of the universe (the center of the Earth, which was known to be spherical); then water, air, fire, and aether in concentric shells from inner to outer.
He also thought that the speed of a falling object should increase with its weight, a conclusion that was later shown to be false. While Aristotle’s view was widely accepted throughout Ancient Greece, there were other thinkers such as Plutarch who correctly predicted that the attraction of gravity was not unique to the Earth.
Although he did not understand gravity as a force, the ancient Greek philosopher Archimedes discovered the center of gravity of a triangle.[13] He postulated that if two equal weights did not have the same center of gravity, the center of gravity of the two weights together would be in the middle of the line that joins their centers of gravity.
Two centuries later, the Roman engineer and architect Vitruvius contended in his De architectura that gravity is not dependent on a substance’s weight but rather on its “nature”. In the 6th century CE, the Byzantine Alexandrian scholar John Philoponus proposed the theory of impetus, which modifies Aristotle’s theory that “continuation of motion depends on continued action of a force” by incorporating a causative force that diminishes over time.
In 628 CE, the Indian mathematician and astronomer Brahmagupta proposed the idea that gravity is an attractive force that draws objects to the Earth and used the term gurutvākarṣaṇ to describe it. In the ancient Middle East, gravity was a topic of fierce debate. The Persian intellectual Al-Biruni believed that the force of gravity was not unique to the Earth, and he correctly assumed that other heavenly bodies should exert a gravitational attraction as well.
In contrast, Al-Khazini held the same position as Aristotle that all matter in the Universe is attracted to the center of the Earth. Waves on oceans, lakes, and other bodies of water occur when the gravitational equilibrium at the surface of the water is disturbed by for example wind. Similar effects occur in the atmosphere where equilibrium is disturbed by thermal weather fronts or mountain ranges.
Planets orbit the Sun in an ellipse as a consequence of the law of gravity. Similarly the Moon and artificial satellites orbit the Earth. Conceptually two objects in orbit are both falling off of the curve they would travel in if the force of gravity were not pulling them together. Since the force of gravity is universal, all planets attract each other with the most massive and closest pair have the most mutual affect. This means orbits are more complex than simple ellipses.
General relativity predicts that energy can be transported out of a system through gravitational radiation also known as gravitational waves. The first indirect evidence for gravitational radiation was through measurements of the Hulse–Taylor binary in 1973. This system consists of a pulsar and neutron star in orbit around one another.
Its orbital period has decreased since its initial discovery due to a loss of energy, which is consistent for the amount of energy loss due to gravitational radiation. This research was awarded the Nobel Prize in Physics in 1993. The first direct evidence for gravitational radiation was measured on 14 September 2015 by the LIGO detectors. The gravitational waves emitted during the collision of two black holes 1.3 billion light years from Earth were measured.
This observation confirms the theoretical predictions of Einstein and others that such waves exist. It also opens the way for practical observation and understanding of the nature of gravity and events in the Universe including the Big Bang. Neutron star and black hole formation also create detectable amounts of gravitational radiation. This research was awarded the Nobel Prize in Physics in 2017.
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