Wonders of the Universe
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Note: The grand scale of gravity and universe
On Christmas Eve 1968, Apollo 8 passed into the darkness behind the Moon, and Frank Borman, Jim Lovell and William Anders became the first humans in history to lose sight of Earth. When they emerged from the Lunar shadow, they saw a crescent Earth rising against the blackness of space and chose to broadcast a creation story to the people of their home planet. A quarter of a million miles from home, lunar module pilot William Anders began: ‘We are now approaching lunar sunrise and, for all the people back on Earth, the crew of Apollo 8 has a message that we would like to send to you. In the beginning God created the heaven and the Earth. And the Earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. And God said, Let there be light: and there was light. And God saw the light, that it was good: and God divided the light from the darkness.’
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Science is a word that has many meanings; one might say science is the sum total of our knowledge of the Universe, the great library of the known, but the practice of science happens at the border between the known and the unknown. Standing on the shoulders of giants, we peer into the darkness with eyes opened not in fear but in wonder.
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The word ‘galaxy’ comes from the Greek word galaxias, meaning milky circle
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Maxwell’s equations had exactly the same form as the equations that describe how soundwaves move through air or how water waves move through the ocean.
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The first experimental determination that the speed of light was not infinite was made by the seventeenth-century Danish astronomer, Ole Romer. In 1676,
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Cosmic Microwave Background, or CMB, and its discovery in 1964 by Arno Penzias and Robert Wilson was key evidence in proving that the Universe began in a Big Bang
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in an unremarkable piece of space known as the Orion Spur off the Perseus Arm of a galaxy called the Milky Way, a star was born that became known as the Sun.
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We have learnt a lot about Proxima Centauri since it was discovered by Robert Innes at the Cape Observatory, in South Africa, in 1915.
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All the gold dug out of the ground throughout all of human history would just about fill three Olympic-sized swimming pools. It is this almost vanishing scarcity that makes gold so valuable.
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Our story is the story of the Universe. Every piece of every one and every thing you love, of every thing you hate, of every thing you hold precious, was assembled in the first few minutes of the life of the Universe, and transformed in the hearts of stars or created in their fiery deaths. When you die those pieces will be returned to the Universe in the endless cycle of death and rebirth. What a wonderful thing to be a part of that universe – and what a story. What a majestic story!
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Project Mercury, a series of six manned launches which included the historic flights of Alan Shephard, the first American in space, on 5 May 1961, and John Glenn, the first American to orbit Earth.
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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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Not only are you spinning around as Earth rotates once a day on its axis, not only are you orbiting at just over 100,000 kilometres (62,137 miles) per hour around the Sun, not only are you rotating around the centre of our galaxy at 220 kilometres (136 miles) per second, and not only is the entire Milky Way tearing around the centre of gravity of the Local Group at 600 kilometres (372 miles) per second, but we are also part of even an grander gravitationally driven cycle. The Local Group is part of a much larger, gravitationally bound family called the Virgo Supercluster – a collection of at least 100 galaxy clusters. Nobody is sure how long it takes our Local Group to journey around the Virgo Supercluster; vast beyond words, stretching over 110 million light years, it is, even so, only one of millions of superclusters in the observable Universe. It is now thought that even superclusters are part of far larger structures bound together by gravity, known as galaxy filaments or great walls. We are part of the Pisces-Cetus Supercluster Complex. Gravity’s scope is unlimited, its influence
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things will minimise their potential energy if they can find a way of doing so. So, you could answer the question ‘why does a ball roll down a hill?’ by saying that the ball would have lower gravitational potential energy at the bottom of the hill than the top, so it rolls down. You could also, of course, say that there is a force pulling the ball down the hill. Physicists often work with energies rather than forces, and the two languages are interchangeable.
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With a collapsing cloud of dust, the shape that ultimately forms will therefore be the shape that minimises the gravitational potential energy. The shape must be the one that allows everything within the cloud to get as close to the centre of it as it possibly can, because anything that is located further away from the centre will have more gravitational potential energy! So, the shape that ensures that everything is as close to the centre as possible is, naturally, a sphere, which is why stars and planets are spherical
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On 4 July AD 1054, a nearby star exploded. Chinese astronomers recorded the precise date,
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1967, when physicists Freeman Dyson and Andrew Lenard showed that the stability of matter is down to a quantum mechanical effect called the Pauli exclusion principle. There are two types of particles in nature, which are distinguished by a property known as spin. The fundamental matter particles, such as electrons and quarks, and composite particles, such as protons and neutrons, have half-integer spin; these are known collectively as fermions. The fundamental force carrying particles such as photons have integer spin; these are known as bosons. Fermions have the important property that no two of them can occupy the same quantum state. Put more simply, but slightly less accurately, this means you can’t pile lots and lots of them into the same place. This is the reason why atoms are stable and chemistry happens. Electrons occupy distinct shells around the atomic nucleus, and as you add more and more electrons, they go into orbits further and further away from the nucleus. It is only the behaviour of the outermost electrons that determine the chemical properties of an element. Without the exclusion principle, all the electrons would crowd into the lowest possible orbit and there would be no complex chemical reactions and therefore no people.
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If you try to press atoms together you force their electron clouds together until at some point you are asking all the electrons to occupy the same place (it is more correct to say the same quantum state). This is forbidden, and leads to an effective force that prevents you squashing the atoms together any further. This force is called electron degeneracy pressure,
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In 1930, Chandrasekhar showed that electron degeneracy pressure can prevent the collapse of white dwarfs with masses up to 1.38 times the mass of our sun.
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It is believed that the limit above which no known law of physics can intervene to stop gravity is around three times the mass of the Sun. This is known as the Tolman-Oppenheimer-Volkoff limit. For the remnants of stars with masses beyond this limit, gravity will win.
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One of the holy grails of observational astronomy is to find a pulsar orbiting around a black hole. Such a system surely exists somewhere, and to be able to observe the behaviour of one of these massive cosmic clocks in the intensely curved spacetime close to a black hole would surely test Einstein’s Theory of General Relativity to its limit. It may even, if we are lucky, reveal flaws that point us towards a new theory
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Christiaan Huygens invented the first pendulum clock in 1656, and it remained the most accurate way of telling the time until the 1930s.
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Until now, the shortest period we have been able to measure is 12 attoseconds, or 12 quadrillionths of a second. This is how long it takes light to travel past 36 hydrogen atoms lined up together. That’s not far at all
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This phrase was first used by the British physicist Sir Arthur Eddington in the early twentieth century to describe this deceptively simple and yet profound quality of our universe: it always seems to run in a particular direction.
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Boltzmann’s definition of entropy is essentially a mathematical description of the difference between a sandcastle and a sand pile. It says that the entropy of something is the number of ways in which you can rearrange its constituent parts and not notice that you’ve done so. For a sandcastle, the number of ways in which you can arrange the grains and still keep the highly-ordered shape of the castle is quite low, so it therefore has low entropy. For a sand pile, on the other hand, pretty much anything you do to it will still result in there being a pile of sand in the desert, indistinguishable from any other pile of sand. The sand pile therefore has a higher entropy than the sandcastle, simply because there are many more ways of arranging the grains of sand such that they form a pile of sand than arranging them into a castle. Boltzmann wrote this down in a simple equation, which is written on his gravestone: S is the entropy, W is the number of ways in which you can arrange the component bits of something such that it is not changed, and kB is a number known as Boltzmann’s constant.
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things will get more messy or disordered simply because there are more ways of being disordered than ordered. This means that there is a difference between the past and the future: the past was more ordered and the future will be less ordered, because this is the most likely way for things to play out. This is what Eddington meant by his statement that the future is more random than the past, and his description of the arrow of time as the thing that points in the direction of increasing randomness. And this is why entropy always increases.
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in autumn 2010, GRB 090423 was the oldest single object ever seen, although just after filming a galaxy was discovered in the Hubble Space Telescope’s Ultra Deep Field Image (see Chapter 3) that is slightly older than GRB 090423. Even more poetically named UDFy-38135539, this galaxy currently holds the distance and age record with a light travel time of slightly over 13 billion years. Allowing for the expansion of the Universe, the (so-called co-moving) distance of UDFy-38135539 is currently 30 billion light years away from Earth.
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Proxima Centauri is a red dwarf star – the most common type of star in our universe. Red dwarfs are diminutive and cold, with surface temperatures in the region of 4,000K, but they do have one advantage over their more luminous and magnificent stellar brethren: because they’re so small, they burn their nuclear fuel extremely slowly, and consequently they have life spans of trillions of years. This means that stars like Proxima Centauri will be the last living stars in the Universe.
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After trillions of years of stellar life and death, only white dwarfs and black holes will remain in the Universe, and then, in around 100 trillion years’ time, this age of the stars will draw to a close and the cosmos will enter its next phase: The Degenerate Era.
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