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10 Scary Yet Beautiful Facts About Space & Us

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10 We are so small

Before we can truly grasp the gravity of the threats as well as the beauty that surrounds our planet. We must first realize just how small our planet is the circumference of Earth at the equator is about 24,876 miles and from the North Pole to the South Pole it is about 24,860 miles. Within our solar system we are the fourth largest planet, after us we are dwarfed by Neptune Saturn Jupiter and our own star which is 93 million miles, away from us the Sun, the Sun is a pretty big star but it’s nowhere near the sizes of other stars. That we know about to name just a few larger stars for perspective, there is edit ”Carinae” a star that is over five million times larger than our Sun ”Betelgeuse” 300 times larger than ”etic RNA” if it were our Sun. It would reach as far out as Jupiter and then there’s ”uy scut” the largest star that, we know of you ice cooties mass is unknown but before you ice Kuti comes ”V Y Canis Majoris” a star that is 5 billion times the size of our Sun. We are a part of the Milky Way galaxy there are trillions of stars in our galaxy, and nearly all of them are circled by at least one planet within our Milky Way galaxy. we are not the only solar system so far astronomers have found more than 500 solar systems, and are discovering new ones every year. Scientists estimate that there may be tens of billions of solar systems in our galaxy alone traveling out 150,000 light-years, you can see just how small even stars like uy scuti is within our galaxy it takes our Sun 200 million years, to complete an orbit of the Milky Way and 2.5 million light years. away is the Andromeda galaxy estimated to collide with our own galaxy in a few billion years, and using the Hubble Deep Field or hdf. we can see a very small series of space and observations by the Hubble Space Telescope. itself it shows hundreds of galaxies 5 billion light years, out is the cosmic web where billions and billions of galaxies are estimated to reside and finally 200 million light years, out is the cosmic microwave background radiation, afterglow is what we believe that started us the only thing to be left of the Big Bang. That is our universe what is beyond this other universes, immeasurable heavens. We have discovered less than 0.1% and have found, no other life. Are we all alone in this life? or are we in fact not alone? either thought is terrifying for now all we know is that all in Justices political and religious, existence theories or truths all loves sorrows hopes and dreams, extinct species like the dinosaurs and species yet to come all pasts, presents and futures, thoughts and actions only exist on our small and insignificant planet alone this sort of scale you truly start to think about what truly matters to you what doesn’t matter anymore and what never did what do you think.

9 rogue planets

They are the loners of the universe lost forever in space. Without a star to orbit, when planets form they react with each other gravitationally, and it’s entirely possible that. when our own solar system formed planets, were actually kicked out into interstellar space. There could be as many as 200 billion rogue planets in our galaxy. that’s as many rogue planets as there are stars in the sky, and one of them could be heading our way right now. as you can see in the picture, a collision with another planet sounds unlikely could this really happen as a matter of fact. It already has four and a half million years ago. a young planet about the size of Mars, collided with earth over 25,000 miles per hour 12 times. The speed of a bullet the impact destroyed, the smaller planet Earth survived but barely, afterwards the entire surface of Earth, was liquefied nothing but rock lava and fire, was left everywhere a true vision of absolute hell, The earth at that time had only an atmosphere of molten rock debris that was blasted out 20,000 miles per hour began to orbit the earth gravity began to bring the debris together and the result was our moon.

 8 space debris

sooner or later human civilization must confront the very real asteroid and comet collision hazard that exists within space where we will become extinct on June 14 2002 it was just another busy work day with all the close calls and near misses the people all over the world have come to accept as the normal level of risk in everyday life but on that day behind the Sun what no one saw coming and what no telescope could see behind the blinding light was an asteroid big enough to destroy an entire city from behind the Sun asteroid 2002 MN came hurtling towards Earth but it missed less than 1/3 of the distance to earth that the moon is nobody saw it pass either until three days later when it emerged from Earth’s shadow into the night sky going away though it is rare it is very possible the craters on our Moon are evidence of asteroids comets and general debris hazards that do exist for us today billions of rocky fragments building blocks of a planet that never quite came together when the solar system was formed are out there everywhere ranging in sizes from rocks to pebbles to boulders and some the size of Mount Everest the reason as to why we haven’t had any truly devastating catastrophes with asteroids within the past few million years is mostly because of Jupiter occasionally Jupiter’s enormous gravity draws an asteroid off course causing it to crash into another asteroid and be destroyed or to veer away into new orbits it was no secret that a giant rock smashing into earth was what wiped out the dinosaurs and that particular rock was estimated to only be six miles wide.

7 the sounds of space

it’s a common misconception that there is no sound in space although space is a virtual vacuum this does not mean that sound does not exist there sound does exist as electromagnetic vibrations through specially designed instruments such as the NASA Voyager engine one ic1 and Hawkeye space probes we have used plasma wave antennas to record vibrations all within the ranges of human hearing now I’m going to show you the sounds of our Sun as well as all of the planets within our solar system and I really would like some input on what you guys think especially about Venus and Saturn take a listen.

6 the super void

in 2004 astronomers discovered an empty section of space within the southern area of the Galactic Hemisphere where our Milky Way solar system and the Andromeda solar system reside and that empty space is missing around 10,000 galaxies nicknamed the cold spot this area is 1.8 billion light-years across and it is the largest known structure ever discovered in the universe but scientists are baffled about what it is and why it’s so barren it sits in a region of space which is much colder than other parts of the universe and although it is not a vacuum it seems to have around 20 percent less matter than other regions although the Big Bang Theory allows for areas that are cooler and hotter the size of the void does not fit with predicted models simply put it is too big to exist in this constellation you can see super clusters of galaxies the dark blue symbolizes areas that are more empty than others and much colder the super void resides in the bottom right the latest study of the cold spot suggests that it may be draining energy from light traveling through which is why the area around it is so cold in late 2007 it was argued by many scientists that this super void could be due to a cosmic texture a remnant of a phase transition which is known to be transitions between solid liquid and gaseous states of matter the thing is though they believe it’s a remnant of phase transitions that took place not anytime recently but from the very earliest stages of the universe.

5 multiverse

when the ancients looked into the night sky they believed that the heavens revolved around the earth and mankind but over the centuries this view has changed drastically we eventually learned about our solar system’s existence and our Milky Way galaxy later we discovered that our universe was filled with other such galaxies but it could be that we’re committing the same error as our ancestors by thinking that our contains everything that there is the word multiverse refers to the general idea that our universe might not be unique at all and there may be other universes out there that defy all of our laws of nature what is known as the anthropic principle is the idea that our universe is fine-tuned to allow humans to live a small fiddle with the strength of gravity for example and life as we know it would not exist a coincidence that does not sit easily with scientists the concept of a multiverse neatly addresses this problem with the infinite number of universes that could exist we are simply living in the one that we are only able to meaning that other universes depending on their laws of nature’s and physics could have very different biological life-forms or maybe even paranormal entities and then there’s this theory which is quite hard to put into words so I will just keep it short there are many universes and everything is the same inside each one meaning you exist on every single earth however each outcome of your entire life is different whether you fail school or become top of your class the jobs you receive the people you love or lose and any decision you’ve ever made or chose not to make would have a different outcome throughout your life but unfortunately we are only one human with only one outcome on this planet alone meaning we could never actually prove this multiverse theory to be true because no matter what we are stuck with the outcome that we’re going to have on this version of the universe and the chances of one of those outcomes successfully proving this theory unfortunately are very remote.

4 Supernova

a supernova is a massive explosion generated by a dying star a star in our galaxy goes supernova once every 100 years the explosion hurls matter into space and can shine as brightly as an entire galaxy for short periods stars are giant nuclear reactors producing energy by fusing hydrogen into helium eventually however stars run out of hydrogen to fuse when this occurs the star begins to fuse helium into heavy your metals such as iron the Stars core shrinks while its outer layers expand creating a red giant that consumes surrounding planets but what happens when the Sun runs out of helium fusion simply ends in small stars like our Sun the star becomes a white dwarf and  slowly fades away but when a large star depleted sealian reserve the core collapses within seconds causing temperatures in excess of 1 billion degrees Fahrenheit the outer layers of the stars collapse as well only to explode outward in a massive explosion known as a supernova what’s left of the star’s core becomes a dense neutron star and forms a black hole an area of such densely packed matter that not even light escapes its gravitational pull after a supernova material expelled in the explosion may form nebulae which are massive interstellar clouds of gas and dust over millions of years gravity pulls nebula material together into a dense hot core called a protostar protostars eventually become newborn stars and the newborn stars gravitational effects surrounding the nebula material over time may form asteroids comets and even new planets it is truly the circle of solar life.

3  the dark flow

the eternal dance of light in the night sky has fascinated humankind for thousands of years given birth to God’s myths and finally to science but now there are hints of strange movements in the heavens if they can be verified they will be the first hard evidence that there is an edge to the universe Sasha Kosh Lenski is a NASA astronomer he claims to have detected a pattern of movements in the heavens so bizarre that it could revolutionize our theory on the universe just as the Big Bang once did Sasha wanted to check more precisely how fast and in what direction galaxies are moving to see if there might be any subtle deviations he used in effect that can only be seen when clusters of galaxies are colliding the gases around them get heated to millions of degrees when light from the Cosmic Microwave Background passes through a hot gas it gets subtly altered how much it changes depends on exactly how fast the gas and the galaxies it surrounds are moving sascha continually and methodically check this data for over a year and his data showed something unbelievable all the galaxy clusters no matter where they were in the sky were all veering off to one side of the universe it was as if they were being pulled towards a mysterious attractor beyond the visible edge of the universe he called it dark flow what do you think it is and where is it pulling us to.

2 Supermassive black holes

in nearly every large galaxy astronomers have found evidence of black holes millions even billions of times the mass of the Sun as I spoke about supernovas in number four black holes formed from what is left of a star’s core after it has gone supernova the collapsed core of a dead star implodes and its weight is enough to squash all the atoms right down to their nuclei the result an ultra dense ember called a neutron star the density of a neutron star would be like taking a mountain and crushing it down with so much pressure into the size of a marble neutrons can withstand incredible pressures but if enough matter falls on to them beyond a critical threshold they can be crushed down to nothing when that happens a black hole is born a black hole is gravity taken to the extreme its mass is literally packed into a point and enshrouded within a dark sphere called the event horizon that sphere is the point of no return any gas stars planets or even light that falls in disappears forever Albert Einstein said that gravity is not just
the attractive force of planets or stars like the Sun it is a warping of space and time what scientists call space time with the presence of massive objects with the mass of a star squashed down to a deep point a black hole is basically a deep puncture in space-time if a future Explorer prospecting for data tempted fate by traveling too close to a small black hole they would be ripped to shreds immediately however a supermassive black hole has more spread out gravity the ride would be much smoother what you’d find if you made it inside is the most extreme destination in all of the universe.

1 further speculations and philosophies

so what do we know honestly not much and won’t not for a long time at least a time that expands so much farther after yours and my own lifetime the real question is is can we figure out everything there is to know before Earth is destroyed by some random miraculous terrifyingly beautiful act of this thing that we call the universe after watching this video look up into the night sky and allow yourself to see more than you did before do not feel small insignificant unimportant or pointless instead thank your eyes your brain and your body your own silent companion throughout your life for allowing you consciousness at such an extraordinary time period where you and your fellow man can study these mysteries of existences that are so far away and whatever you believe in don’t allow this video or others to ever discourage that belief whether it be gods science alone aliens the paranormal or nothing instead combine the knowledge we do know of with your own beliefs and theories to see what depths of your own mind you can then explore we too as human beings are made up of the same stuff of galaxies maybe we’re not supposed to know maybe the true meaning of life while you have it is to simply give it some meaning.
thank you so so much for watching everyone I hope this video made you think a little learn new things and have some new questions if any of that happened to you please take a couple seconds to give this video a like as it really will get it out there for others to see it too which would really help me out a lot I had such a wonderful time making this video and it actually helped me let go of a lot of struggles that I’ve been dealing with in my own life and I hope that it can do the same with you follow me on Twitter and Instagram to keep up to date with the latest videos coming out on this channel and if you know what I should count down next post it in the comment section and I will definitely make it happen have a good day or night thanks guys.

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Space

THE DATA CAN BEST BE EXPLAINED AS X-RAYS FROM SOURCES OUTSIDE THE SOLAR SYSTEM

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X-rays are a form of high-energy, electromagnetic radiation released by extremely hot objects. In the early 20th century, astronomers realized that space should be flooded with X-rays from the sun. Moreover, the sun’s X-ray spectrum would reveal a lot about the processes at work within the star. However, X-ray astronomy was not possible until the advent of rockets and satellites. Despite their energy, X-rays are easily absorbed, which is why they are so good at imaging the body. Water vapor in Earth’s atmosphere effectively blocks X-rays from reaching the surface—a good thing for life,
because high-energy X-rays can cause damage and mutations when they impact on soft, living cells.

The first glimpse of the sun’s X-rays came in the late 1940s, during a US Naval Research Laboratory (NRL) program to study Earth’s upper atmosphere. A team led by US rocket scientist Herbert Friedman fired German V-2 rockets into space equipped with X-ray detectors—essentially modified Geiger counters. These experiments provided the first incontrovertible evidence of X-rays from the sun. By 1960, researchers were using Aerobee sounding rockets to detect X-rays, and the first X-ray photos of the sun were taken from an Aerobee Hi. Two years later, the first cosmic X-ray source was detected.

“Nothing is going to happen unless you work with your life’s blood.” Riccardo Giacconi

Extrasolar X-rays

Riccardo Giacconi, an Italian astrophysicist then working for American Science and Engineering (AS&E), had successfully petitioned NASA to fund his team’s X-ray experiment. The team’s first rocket misfired in 1960, but by 1961 it had a new, improved experiment ready for launch. This instrument was one hundred times more sensitive than any flown to date. Using a large field of view, the team hoped to observe other X-ray sources in the sky. Success followed a year later: the rocket aimed its camera first at the moon and then away from it. What the camera saw came as a complete surprise to the team. The instrument detected the X-ray “background”—a diffuse signal coming from all directions—and a strong peak of radiation in the direction of the galactic center.

Stars like the sun emit about a million times more photons at visible light frequencies than they do as X-rays. The source of the X-ray signals, by contrast, radiated a thousand times more X-rays than light. Although a small, barely visible point in the sky, the source was pumping out one thousand times more X-rays than the sun. Furthermore, certain physical processes were taking place within the source and these had never been seen in the laboratory. After weeks of analysis, the team concluded that this must be a new class of stellar object.

Search for the source

There was no candidate in the solar system to account for the intense radiation. The most likely source was named Scorpius X-1 (Sco X-1 for short) after the constellation within which it was located. Herb Friedman at the NRL confirmed the result using a detector with a larger area and better resolution than the AS&E instrument. Sco X-1 is now known to be a double star system and is the brightest, most persistent X-ray source in the skies.

Further launches revealed a sky dotted with X-ray sources, both galactic and extra-galactic. In a short space of time, the team had detected a disparate set of celestial oddities emitting X-rays. These included supernova remnants, binary stars, and black holes. Today, more than 100,000 X-ray sources are known.

The Chandra X-ray Observatory was launched by NASA in 1999. It was initially planned to operate for five years, but was still in use in 2016.

Toward Chandra

By the mid-1960s, instruments were becoming ever more sensitive. Detectors were able to record X-rays one thousand times weaker than Sco X-1 just five years after Giacconi’s discovery. Initially proposed by Giacconi in 1963, Uhuru, the first satellite dedicated solely to X-ray astronomy, was launched in 1970. It spent three years mapping X-rays. This all-sky survey located 300 sources, including a bizarre object in the center of the Andromeda galaxy, and it earmarked Cyg X-1 as a potential black hole. Uhuru also found that the gaps in galaxy clusters are strong sources of X-rays. These apparently empty regions are in fact filled by a low-density gas at millions of degrees Kelvin. Although thinly spread, this “intercluster medium” contains more mass than that of all of the cluster’s galaxies combined.

In 1977, NASA launched its High Energy Astronomy Observatory (HEAO) program. HEAO-2, renamed the Einstein Observatory, was equipped with highly sensitive detectors and revolutionized X-ray astronomy. With its fused quartz mirrors, the telescope was a million times more sensitive than that of Giacconi’s 1961 discovery rocket. Einstein observed X-rays emanating from stars and galaxies, and even from planetary aurorae on Jupiter.

Eager to probe the X-ray background further, Giacconi once again proposed an advanced telescope. In 1999, this became the Chandra X-Ray Observatory, the third of the orbiting Great Observatories. Chandra is the most powerful X-ray telescope ever built, tens of billions of times more sensitive than the early detectors. Its phenomenal performance outstripped all expectations and its mission lifetime was tripled from five to 15 years. As of 2016, however, its mission is ongoing. Chandra’s outstanding technical firsts include detecting sound waves coming from a supermassive black hole. The X-ray data, when combined with optical observations from the Hubble Space Telescope and infrared data from the Spitzer Space Telescope, have provided stunning images of the cosmos.

Active regions of the sun are revealed by combining observations from many telescopes. Highenergy X-rays are shown in blue; low-energy X-rays green.

Realm of the X-rays

X-ray astronomy observes the highest-energy objects in space: colliding galaxies, black holes, neutron stars, and supernovae. The energy source behind this activity is gravity. As matter falls toward a massive concentration of material, particles collide and accumulate. They give up their energy by emitting photons, which at these speeds have X-ray wavelengths (0.01–10 nanometers, or billionths of a meter)—equivalent to temperatures of tens of million of degrees. The same mechanism, is at work in a wide range of dramatic phenomena: active stars more massive than the sun, for example, produce strong solar winds and significant amounts of X-rays. “X-ray binary star” systems, in which mass transfers from one star to its partner, also produce intense radiation.

“The universe is popping all over the place.” Riccardo Giacconi

Seeing black holes

When stars explode at the end of their lives, the blast waves from the supernova compress the interstellar medium, causing the gas to release Xrays. Left within what remains of the supernova, the massive star continues life as a neutron star or a black hole. Turbulence generated by material being torn apart as it is sucked into a black hole will also produce X-rays. The radiation being pumped out causes the outer layers of the supernova remnant to fluoresce in a range of colors.

Certain galaxies have centers that outshine all the billions of stars in the galaxy itself, with emissions that are bright at all wavelengths. The center of such an “active galactic nucleus” is assumed to contain a supermassive black hole. Material falling toward the centers of galaxy clusters—the largest structures in the universe—also shines in X-rays, and is not visible in other light frequencies. Chandra has now taken two “deep field” images of the Xray background—23- and 11-day exposures of the northern and southern hemispheres of the sky. X-ray instruments of the future may help scientists see how black holes are distributed.

Observations in the X-ray spectrum reveal hidden structures. The larger blobs in this patch of sky from an ESA X-ray survey are galaxy clusters; smaller dots are black holes.

RICCARDO GIACCONI

Born in Genoa, Italy, in 1931, Riccardo Giacconi lived in Milan with his mother, a mathematics and physics high school teacher. She instilled a love of geometry in the young Riccardo. Giacconi’s first degree was from the University of Milan. With a Fulbright Scholarship, he moved to Indiana University in the US, and then to Princeton, to study astrophysics.

In 1959, Giacconi joined American Science and Engineering, a small firm in Cambridge, Massachusetts. AS&E built rocket-borne monitoring equipment for measuring electrons and artificial gamma-ray bursts from nuclear weapons. Giacconi was tasked with developing instruments for X-ray astronomy. He was at the heart of most of the breakthroughs in X-ray astronomy, and in 2002, he was awarded a share of the Nobel Prize in Physics for his contributions to astrophysics. In 2016, he was still working in his mid-80s, as principal investigator for the Chandra Deep Field-South project.

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Space

A DAY WITHOUT YESTERDAY

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The idea that the universe originated from a tiny object in the form of an egg appears in The Rigveda, a collection of Hindu hymns from the 12th century BCE. However, there were few scientific clues to the universe’s true origins until Albert Einstein provided a new way of conceiving time and space with his general theory of relativity in 1915. Einstein’s insight led many to revisit the idea that the universe started small, among them the Belgian priest Georges Lemaître, whose 1931 proposal would carry echoes of The Rigveda.

In the 17th century, Johannes Kepler, observing that the night sky is dark, argued that the universe cannot be infinite in both time and space, as otherwise the stars shining from every direction would make the whole sky bright. His argument was restated in 1823 by German astronomer Wilhelm Olbers and became known as Olbers’ paradox. Despite this problem, Isaac Newton stated that the universe was static (not getting any bigger or smaller) and infinite in time and space, with its matter distributed more or less uniformly over a large scale. At the end of the 19th century, this was still the prevailing view, and one that Einstein himself initially held.

Olbers’ paradox is the argument that, if the universe is infinite, not expanding, has always existed, and everywhere contains roughly the same density of stars, then any sight line from Earth must end at the surface of a star. The night sky should be uniformly bright, but this contradicts the observed darkness of the night.

An unchanging universe?

Einstein’s general theory of relativity explains how gravity works at the largest scales. He realized that it could be used to test whether the Newtonian model of the universe could exist long-term without becoming unstable, and to explore which other types of universe might be feasible. The exact relationship between mass, space, and time was explained in a series of 10 complex equations. These were called Einstein’s field equations. Einstein found an initial solution to his equations that suggested the universe is contracting. Since he could not believe this, he introduced a “fix”—an expansion-inducing factor called the cosmological constant—to balance the inward pull of gravity. This allowed for a static universe.

In 1922, Russian mathematician Alexander Friedmann attempted to find solutions to Einstein’s field equations. Starting with the assumption that the universe is homogenous (made of more or less the same material everywhere) and spread out evenly in every direction, he found several solutions. These allowed for models in which the universe could be expanding, contracting, or static. Friedmann was probably the first person to use the expression “expanding universe.” Einstein first called his work “suspicious,” but six months later acknowledged that his results were correct. However, this was Friedmann’s final contribution as he died two years later. In 1924, Edwin Hubble showed that many nebulae were galaxies outside the Milky Way. The universe had suddenly become a lot bigger.

The expanding universe

Later in the 1920s, Lemaître entered the debate about the large-scale organization of the universe. He had worked at institutions in the United States, becoming aware of Vesto Slipher’s work on receding galaxies and Hubble’s measurements of galaxy distances. A competent mathematician, he had also studied Einstein’s field equations and found a possible solution to the equations that allowed for an expanding universe. Putting these various threads together, in 1927, Lemaître published a paper that proposed that the whole universe is expanding and carrying galaxies away from each other and from Earth. He also predicted that galaxies that are more distant from us would be found to be receding at a faster rate than closer ones.

Lemaître’s paper was published in an obscure Belgian journal, and as a result, his hypothesis failed to attract much attention at the time. He did, however, communicate his findings to Einstein, telling him of the solution he had found to the field equations allowing for a universe that expands. Einstein introduced Lemaître to Friedmann’s work, but remained ambivalent about Lemaître’s idea. Famously, Einstein is said to have said: “Your calculations are correct, but your grasp of physics is abominable.” However, the British astronomer Arthur Eddington later published a long commentary on Lemaître’s 1927 paper, describing it as a “brilliant solution.”

In 1929, Hubble released findings showing that there was indeed a relationship between the remoteness of a galaxy and how fast it was receding, confirming for many astronomers that the universe was expanding, and that Lemaître’s paper had been correct. For many years the credit for the discovery of the expansion of the universe was given to Hubble, but today most agree it should be shared with Lemaître and possibly also with Alexander Friedmann.

The primeval atom

Lemaître reasoned that, if the universe is expanding and the clock is run backward, then far back in time, all the matter in the universe must have been much closer. In 1931, he suggested that the universe was initially a single, extremely dense particle containing all its matter and energy—a “primeval atom” as he called it, about 30 times the size of the sun. This disintegrated in an explosion, giving rise to space and time on “a day without yesterday.” Lemaître described the beginning of the universe as a burst of fireworks, comparing galaxies to the burning embers spreading out from the center of the blast.

The proposal initially met with scepticism. Einstein found it suspect but was not altogether dismissive. In January 1933, however, Lemaître and Einstein traveled together to California for a series of seminars. By this time, Einstein (who had removed the cosmological constant from his general theory of relativity because it was no longer needed) was in full agreement with Lemaître’s theory, calling it “the most beautiful and satisfactory explanation of creation to which I have ever listened.”

Lemaître’s model also provided a solution to the long-standing problem of Olbers’ paradox. In his model, the universe has a finite age, and because the speed of light is also finite, that means that only a finite number of stars can be observed within the given volume of space visible from Earth. The density of stars within this volume is low enough that any line of sight from Earth is unlikely to reach a star.

“The radius of space began at zero, and the first stages of the expansion consisted of a rapid expansion determined by the mass of the initial atom.” Georges Lemaître

Refining the idea

Compressed into a tiny point, the universe would be extremely hot. During the 1940s, Russian-American physicist George Gamow and colleagues worked out details of what might have happened during the exceedingly hot first few moments of a Lemaître-style universe. The work showed that a hot early universe, evolving into what is observed today, was theoretically feasible. In a 1949 radio interview, the British astronomer Fred Hoyle coined the term “Big Bang” for the model of the universe Lemaître and Gamow had been developing. Lemaître’s hypothesis now had a name.

Lemaître’s idea about the original size of the universe is now considered incorrect. Today, cosmologists believe it started from an infinitesimally small point of infinite density called a singularity.

“A parallel exists between the Big Bang and the Christian notion of creation from nothing.” George Smoot

Lemaître’s model of a universe expanding from an initial extremely dense concentration of mass and energy is today called the Big Bang model of the universe. Although Lemaître described the initial stages of the process as an “explosion,” the prevailing view today is that expansion is a fundamental quality of space itself and this carries galaxies away from each other, rather than being projected by the initial explosion into a preexisting void.

GEORGES LEMAÎTRE

Georges Lemaître was born in 1894 in Charleroi, Belgium. Following distinguished service in World War I, in 1920 he was awarded a doctoral degree in engineering. He subsequently entered a seminary, where, in his leisure time, he studied mathematics and science.

After his ordination in 1923, Lemaître studied mathematics and solar physics at Cambridge University, studying under Arthur Eddington. In 1927, he was appointed professor of astrophysics at the University of Leuven, Belgium, and published his first major paper on the expanding universe. In 1931, Lemaître put forward his theory of the primeval atom in a report in the journal Nature, and his fame soon spread. He died in 1966, shortly after learning of the discovery of cosmic microwave background radiation, which provided evidence for the Big Bang.

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Planets

GRAVITY EXPLAINS THE MOTIONS OF THE PLANETS

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Gravity is the name given to the force of attraction between any two masses. It is the force that attracts all objects to Earth, giving them weight. It draws objects downward, toward the center of Earth. If the object were on the moon, a much smaller mass than Earth, the force would be six times less and its weight would be one sixth of its weight on Earth. English physicist, astronomer, and mathematician Isaac Newton was the first person to realize that gravity is a universal force, acting on all objects, and that it explains the movement of planets.

“To myself I am only a child playing on the beach, while vast oceans of truth lie undiscovered before me.” Isaac Newton

Describing orbits

The shapes of the orbits of the planets were already well-known in Newton’s time, based on the three laws of planetary motion introduced by Johannes Kepler. Kepler’s first law stated that these orbits were ellipses, with the sun at one focus of each ellipse. The second law described the way that planets moved along their orbits more quickly when they were close to the sun than when they were farther away. The third law described the relation between the time taken to complete one orbit and the distance from the sun: the time taken for one orbit, squared, was equal to the cube of the average distance between the planet and the sun. For instance, Earth goes around the sun in one year, while Jupiter is 5.2 times farther away from the sun than Earth. 5.2 cubed equals 140, and the square root of 140 gives the correct figure for one Jupiter year: 11.86 Earth years.

However, although Kepler had correctly discovered the shapes and speeds of planetary orbits, he did not know why the planets moved as they did. In his 1609 book Astronomia Nova, he suggested that Mars was being carried around its orbit by an angel in a chariot. A year later, he had changed his mind, suggesting that the planets were magnets and were being driven around by magnetic “arms” extending from the spinning sun.

Newton’s insight

Before Newton, several scientists, including Englishman Robert Hooke and Italian Giovanni Alfonso Borelli, suggested that there was a force of attraction between the sun and the individual planets. They also stated that the force decreased with distance. On December 9, 1679, Hooke wrote to Newton saying that he thought the force might decrease as the inverse square of distance.

However, Hooke did not publish the idea and did not possess the mathematical skills to fully demonstrate his proposition. By contrast, Newton was able to prove rigorously that an inverse square law of attractive force would result in an elliptical planetary orbit.

Newton used mathematics to demonstrate that, if the force of attraction (F) between the sun and the planets varied precisely as an inverse square of the distance (r) between them, this fully explained the planetary orbits and why they follow Kepler’s three laws. This is written mathematically as F ∝ 1/r2. It means that doubling the distance between the objects reduces the strength of the attractive force to a quarter of the original force.

The Great Comet appeared in 1680, then again in 1681. John Flamsteed proposed that it was the same comet. Newton disagreed, but changed his mind after examining Flamsteed’s data.

The Great Comet

Newton was a shy, reclusive man, and reluctant to publish his breakthrough. Two things forced his hand. The first was the Great Comet of 1680, and the second was the astronomer Edmond Halley.

The Great Comet of 1680 was the brightest comet of the 17th century—so bright that for a short time it was visible in the daytime. Two comets were seen: one that was approaching the sun in November and December 1680; and another that was moving away from the sun between late December 1680 and March 1681. As with all comets at the time, its orbit was a mystery, and the two sightings were at first not widely recognized as the same object. Astronomer John Flamsteed suggested that the two sightings might be of the same comet, which had come from the outer edge of the solar system, swung around the sun (where it was too close to the sun to be seen), and moved out again.

Halley was fascinated by the mysterious form of cometary orbits, and traveled to Cambridge to discuss the problem with his friend Newton. Using his law that related force to acceleration and his insistence that the strength of the force varied as the inverse square of distance, Newton calculated the parameters of the comet’s orbit as it passed through the inner solar system. This breakthrough intrigued Halley so much that he went on to calculate the orbits of 24 other comets, and to prove that one comet (Halley’s comet) returned to the sun around every 76 years. Perhaps more importantly, Halley was so impressed by Newton’s work that he strongly encouraged him to publish his findings. This resulted in the book Philosophiae Naturalis Principia Mathematica, published in Latin on July 5, 1687, in which Newton describes his laws of motion, his gravitational theory, the proof of Kepler’s three laws, and the method he used to calculate a comet’s orbit.

In his book, Newton stressed that his law was universal—gravity affects everything in the universe, regardless of distance. It explained how an apple fell on his head in the orchard of Woolsthorpe where his mother lived, the tides in the seas, the moon orbiting Earth, Jupiter orbiting the sun, and even the elliptical orbit of a comet. The physical law that made the apple fall in his yard was exactly the same as the one that shaped the solar system, and would later be discovered at work between stars and distant galaxies. Evidence was all around that Newton’s law of gravitation worked. It not only explained where planets had been, but also made it possible to predict where they would go in the future.

Constant of proportionality

Newton’s law of gravitation states that the size of the gravitational force is proportional to the masses of the two bodies (m1 and m2) multiplied together and divided by the square of the distance, r, between them. It always draws masses together and acts along a straight line between them. If the object in question is spherically symmetrical, like Earth, then its gravitational pull can be treated as if it were coming from a point at its center. One final value is needed to calculate the force—the constant of proportionality, a number that gives the strength of the force: the gravitational constant (G).

Newton’s law of universal gravitation shows how the force produced depends on the mass of the two objects and the square of the distance between them.

Measuring G

Gravity is a weak force, and this means that the gravitational constant is rather difficult to measure accurately. The first laboratory test of Newton’s theory was made by the English aristocrat scientist Henry Cavendish in 1798, 71 years after Newton’s death. He copied an experimental system proposed by the geophysicist John Michell and successfully measured the gravitational force between two lead balls, of diameters 2 and 12 in (5.1 and 30 cm). Many have tried to refine and repeat the experiment since. This has led to a slow improvement in the accuracy of G. Some scientists suggested that G changed with time. However, recent analysis of type 1a supernovae has shown that, over the last nine billion years, G has changed by less than one part in 10 billion, if at all. The light from distant supernovae was emitted nine billion years ago, allowing scientists to study the laws of physics as they were in the distant past.

“Nature and Nature’s laws lay hid in night: God said, “Let Newton be!” and all was light.” Alexander Pope

Henry Cavendish measured the gravitational constant using a torsion balance. Two large balls (M) were fixed in place, while two smaller balls (m) were attached at either end of a wooden arm suspended from a wire. The gravitational attraction (F) of the small balls to the large ones caused the balance to rotate slightly, twisting the wire. The rotation stopped when the gravitational force equaled the torque (twisting force) of the wire. Knowing the torque for a given angle made it possible to measure the gravitational force

Seeking meaning

Like many of the scientists of his time, Newton was deeply pious and sought a religious meaning behind his observations and laws. The solar system was not regarded as a random collection of planets, and the sizes of the specific orbits were thought to have some specific meaning. For example, Kepler had sought meaning with his notion of “the music of the spheres.” Building on ideas first put forward by Pythagoras and Ptolemy, Kepler suggested that each planet was responsible for an inaudible musical note that had a frequency proportional to the velocity of the planet along its orbit. The slower a planet moved, the lower the note that it emitted. The difference between the notes produced by adjacent planets turned out to be well-known musical intervals such as major thirds.

There is some scientific merit behind Kepler’s idea. The solar system is about 4.6 billion years old. During its lifetime, the planets and their satellites have exerted gravitational influences on each other and have fallen into resonant intervals, similar to the way musical notes resonate. Looking at three of the moons of Jupiter, for every once that Ganymede orbits the planet, Europa goes around twice and Io four times. Over time, they have been gravitationally locked into this resonance.

The three-body problem

The solar system as a whole has fallen into similar resonant proportions to Jupiter’s moons. On average, each planet has an orbit that is about 73 percent larger than the planet immediately closer to the sun. Here, however, there appears a difficult mathematical problem, and one that Newton had grappled with. The movement of a low-mass body under the gravitational influence of a large-mass body can be understood, and predicted. But when three bodies are involved, the mathematical problem becomes exceedingly difficult.An example of a three-body system is the moon-Earth-sun. Newton thought about this system but the mathematical difficulties were insurmountable, and human knowledge of where the moon will be in the distant future is still very limited. Variations in the orbit of Halley’s comet are another indicator of the influence of the gravitational fields of the planets operating in addition to the gravitation of the sun. Recent orbits have taken 76.0, 76.1, 76.3, 76.9, 77.4, 76.1, 76.5, 77.1, 77.8, and 79.1 years respectively due to the combined gravitational influence of the sun, Jupiter, Saturn, and other planets on the comet.

“I have not been able to discover the cause of these properties of gravity from phenomena, and I frame no hypotheses.” Isaac Newton

Distant supernovae are seen today as they were billions of years ago. Analysis of their structure shows that the law of gravity operated with the same value of G then as today.

Shaping the planets

While Newton searched for religious meaning in his scientific work, he could find none behind his theory of gravity. He did not discover the hand of God setting the planets in motion, but he had found a formula that shaped the universe.

The action of gravity is key to understanding why the universe looks as it does. For instance, gravity is responsible for the spherical shapes of the planets. If a body has sufficient mass, the gravitational force that it exerts exceeds the strength of the material of the body and it is pulled into a spherical shape. Astronomical rocky bodies, such as the asteroids between the orbits of Mars and Jupiter, are irregular in shape if they have a diameter of less than about 240 miles (380 km) (the Hughes-Cole limit).

Gravitation is also responsible for the size of the deviations from a sphere that can occur on a planet. There are no mountains on Earth higher than the 5.5 miles (8.8 km) of Mount Everest because the gravitational weight of a taller mountain would exceed the strength of the underlying mantle rock, and sink. On planets with lower mass, the weight of objects is less, and so mountains can be bigger. The highest mountain on Mars, for instance, Olympus Mons, is nearly three times as high as Everest. The mass of Mars is about one-tenth that of Earth, and its diameter is about half Earth’s. Putting these numbers into Newton’s formula for gravitation, this gives a weight on the surface of Mars of just over one-third that on Earth, which explains the size of Olympus Mons.

Gravity thus also shapes life on Earth by limiting the size of animals. The largest land animals ever were dinosaurs weighing up to 40 tons. The largest animals of all, whales, are found in the oceans, where the water supports their weight. Gravity is also responsible for the tides, which are produced because water bulges toward the sun and moon on the side of Earth nearer to them, and also bulges away from them on the other side where their gravitational pull is weaker. When the sun and moon are aligned, there is a high spring tide; when they are at right angles, there is a low neap tide.

“The motions of the comets are exceedingly regular, and they observe the same laws as the motions of the planets.” Isaac Newton

In his great work Principia, Newton plotted the parabolic path of the Great Comet by taking accurate observations and correcting them to allow for the motion of Earth.

Escape velocity

Gravity profoundly affects human mobility. The height a person can jump is determined by the gravitational field at ground level. Newton realized that the strength of gravity would affect the ease of travel beyond the atmosphere. To break free from Earth’s gravitational pull, it is necessary to travel at 25,020 mph (40,270 km/h). It is much easier to get away from less massive bodies
such as the moon and Mars. Turning the problem around, this escape velocity is also the minimum velocity that an incoming asteroid or comet can have when it hits Earth’s surface, and this affects the size of the resulting crater. Today, gravity is held to be most accurately described by the general theory of relativity proposed by Albert Einstein in 1915. This does not describe gravity as a force, but instead as a consequence of the curvature of the continuum of spacetime due to the uneven distribution of mass inside it. This said, Newton’s concept of a gravitational force is an excellent approximation in the vast majority of cases. General relativity only needs to be invoked in cases requiring extreme precision or where the gravitational field is very strong, such as close to the sun or in the vicinity of a massive black hole. Massive bodies that are accelerating can produce waves in spacetime, and these propagate out at the speed of light. The first detection of one of these gravitational waves was announced in February 2016.

Newton illustrated escape velocity with a thought experiment of a cannon firing horizontally from a high mountain. At velocities less than orbital velocity at that altitude, the cannonball will fall to earth (A and B). At exactly orbital velocity, it will enter a circular orbit (C). At greater than orbital velocity but less than escape velocity, it will enter an elliptical orbit (D). Only at escape velocity will it fly off into space (E).

ISAAC NEWTON

Isaac Newton was born on a farm in Woolsthorpe, Lincolnshire, on December 25, 1642. After school in Grantham, he attended Trinity College Cambridge, where he became a Fellow and taught physics and astronomy. His book Principia set out the principle of gravity and celestial mechanics. Newton invented the reflecting telescope; wrote theses on optics, the prism, and the spectrum of white light; was one of the founders of calculus; and studied the cooling of bodies. He also explained why Earth was oblate (a squashed sphere) in shape and why the equinox moved, and formalized the physics of the speed of sound. He spent much time on biblical chronology and alchemy. Newton was at various times President of the Royal Society, Warden and Master of the Royal Mint, and member of parliament for Cambridge University. He died in 1727.

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