Wonders of the Universe - Brian Cox [59]
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As we accelerate away from Earth we experience a gravitational pull 1.8 times the strength of Earth – so I weigh nearly twice as much as I do back down on the ground.
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I was able to demonstrate this for myself in the Vomit Comet armed with a model of Einstein. When we were weightless, I let a little plastic Albert float beside my head. One way of understanding why we floated next to each other is to simply state that we were both weightless, so we floated, but think about what this looks like from outside the plane. To someone on the ground looking up at us, the plane, myself and plastic Albert are all falling towards the ground under the action of Earth’s gravity, and obviously we are falling at the same rate. If I fell faster than Einstein, he wouldn’t float next to my head. Indeed, if the much more massive plane fell faster than both plastic Albert and myself, we’d both bump into the ceiling! The fact that we all floated around together is a beautiful demonstration of the fact that all objects, no matter what their mass, fall at the same rate in a gravitational field.
This simple fact inspired Albert Einstein to construct his geometric theory of gravitation, called General Relativity, which to this day is the most accurate theoretical description of gravity that we possess. We shall get to Einstein’s beautiful theory later on, and in doing so we’ll arrive at a very simple explanation of why everything falls at the same rate, and why gravity can be removed by the act of falling
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Gravity holds the water in our oceans and hugs the atmosphere close to the planet. It’s the reason why the rain falls and the rivers flow; it powers the ocean currents and drives the world’s weather; it’s why volcanoes erupt and earthquakes tear the land apart. Yet gravity also plays a role on an even grander stage. Across the Universe, from the smallest speck of dust to the most massive star, gravity is the great sculptor that created order out of chaos.
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© NASA/Corbis
THE INVISIBLE STRING
Everything in the Cosmos is subject to the force of gravity. From the manmade satellites that rotate around our planet creating the technological infrastructure of the twenty-first century, to the orbit of our only natural satellite – the Moon – which journeys around Earth every 27.3 days, it is gravity that provides the invisible string to guide them on their path. The journey of every planet, moon, ball of rock and mote of dust in our solar system is guided by gravity; from the 365-day trip our planet takes around the Sun to each of the orbits of the seven planets and 166 known moons in our neighbourhood. Beyond our solar system, gravity continues to conduct the flow of the Universe, with everything affected by the gravitational pull of something else, no matter how tiny or how massive.
Our solar system orbits around the centre of the Milky Way Galaxy, a place dominated by a supermassive black hole, the heart of a swirling system of over 200 billion gravitationally bound stars. And even this vast, rotating structure isn’t where the merry-go-round of the Universe ends, because even the galaxies are steered through the vast Universe by the action of gravity.
The Virgo Supercluster of galaxies is a good example of how gravitational pull exerts itself. This cluster of galaxies has a gravitational pull on the Local Group of galaxies that surround our Milky Way Galaxy.
NASA / SCIENCE PHOTO LIBRARY
The supermassive black hole at the centre of the Milky Way Galaxy, Sagittarius A*, is the heart of a swirling system of over 200 billion stars which are gravitationally bound.
NASA
The elliptical galaxy M87 is located at the centre of the Virgo Cluster. This huge galaxy includes several trillion stars, a supermassive black hole, and a family of 15,000 globular star clusters which may have been graviationally pulled from nearby dwarf galaxies.
Caltech
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Beyond our solar system, gravity continues to conduct the flow of the Universe, with everything affected by the gravitational pull of something