Monday, January 30, 2017

31 jan. 2017 learning physics gravity & relativity.

31 jan. 2017
learning physics
gravity & relativity.
https://www.newscientist.com/round-up/instant-expert-general-relativity/

Instant Expert: General relativity

(Image: XMM-Newton/ESA/NASA)
Welcome to the first in our new monthly "Instant Expert" series.
This month, astrophysicist Pedro Ferreira of the University of Oxford offers a concise, up-to-the minute summary of what a well-informed person should know about general relativity.
Find out more about Instant Expert

ABOUT THE AUTHOR

Pedro Ferreira is professor of astrophysics at the University of Oxford. He works on the origin of large-scale structures in the universe, on the general theory of relativity and on the nature of dark matter and dark energy



1. PAST, PRESENT AND FUTURE

Albert Einstein's general theory of relativity is one of the towering achievements of 20th-century physics.
Published in 1916, it explains that what we perceive as the force of gravity in fact arises from the curvature of space and time.

Einstein proposed that objects such as the sun and the Earth change this geometry.
In the presence of matter and energy it can evolve, stretch and warp, forming ridges, mountains and valleys that cause bodies moving through it to zigzag and curve.
So although Earth appears to be pulled towards the sun by gravity, there is no such force. It is simply the geometry of space-time around the sun telling Earth how to move.

The general theory of relativity has far-reaching consequences.
It not only explains the motion of the planets; it can also describe the history and expansion of the universe, the physics of black holes and the bending of light from distant stars and galaxies.

General relativity at 100: Einstein’s unfinished masterpiece

mg22830420.600-1_800Einstein’s general theory of relativity is an undoubted work of genius.
Yet 100 years on, it still raises many questions – and physicists continue to look for something better.
(Image: Quibe)
Click here to find out more.



EINSTEIN'S INSIGHT

2. HOW GENERAL RELATIVITY SHAPES OUR UNIVERSE

Einstein's general theory of relativity has revealed that the universe is an extreme place. We now know it was hot and dense and has been expanding for the past 13.7 billion years.
It is also populated with incredibly warped regions of space-time called black holes that trap anything falling within their clutches.

3. FRONTIERS OF GENERAL RELATIVITY

General relativity predicts that the universe is full of exotic phenomena. Space-time can tremble like the surface of a pond and it seems to be full of a mysterious form of energy that is pushing it apart. It is also conceivable for space-time to be so warped that it becomes possible to travel backwards in time.

GRAVITATIONAL WAVES





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