Cosmic Journeys: Explore the biggest question of all... in 1080p. How far do the stars stretch out into space? And what's beyond them? In modern times, we built giant telescopes that have allowed us to cast our gaze deep into the universe. Astronomers have been able to look back to near the time of its birth. They've reconstructed the course of cosmic history in astonishing detail. From intensive computer modeling, and myriad close observations, they've uncovered important clues to its ongoing evolution. Many now conclude that what we can see, the stars and galaxies that stretch out to the limits of our vision, represent only a small fraction of all there is. Does the universe go on forever? Where do we fit within it? And how would the great thinkers have wrapped their brains around the far-out ideas on today's cutting edge? For those who find infinity hard to grasp, even troubling, you're not alone. It's a concept that has long tormented even the best minds. Over two thousand years ago, the Greek mathematician Pythagoras and his followers saw numerical relationships as the key to understanding the world around them. But in their investigation of geometric shapes, they discovered that some important ratios could not be expressed in simple numbers. Take the circumference of a circle to its diameter, called Pi. Computer scientists recently calculated Pi to 5 trillion digits, confirming what the Greeks learned: there are no repeating patterns and no ending in sight. The discovery of the so-called irrational numbers like Pi was so disturbing, legend has it, that one member of the Pythagorian cult, Hippassus, was drowned at sea for divulging their existence. A century later, the philosopher Zeno brought infinity into the open with a series of paradoxes: situations that are true, but strongly counter-intuitive. In this modern update of one of Zeno's paradoxes, say you have arrived at an intersection. But you are only allowed to cross the street in increments of half the distance to the other side. So to cross this finite distance, you must take an infinite number of steps. In math today, it's a given that you can subdivide any length an infinite number of times, or find an infinity of points along a line. What made the idea of infinity so troubling to the Greeks is that it clashed with their goal of using numbers to explain the workings of the real world. To the philosopher Aristotle, a century after Zeno, infinity evoked the formless chaos from which the world was thought to have emerged: a primordial state with no natural laws or limits, devoid of all form and content. But if the universe is finite, what would happen if a warrior traveled to the edge and tossed a spear? Where would it go? It would not fly off on an infinite journey, Aristotle said. Rather, it would join the motion of the stars in a crystalline sphere that encircled the Earth. To preserve the idea of a limited universe, Aristotle would craft an historic distinction. On the one hand, Aristotle pointed to the irrational numbers such as Pi. Each new calculation results in an additional digit, but the final, final number in the string can never be specified. So Aristotle called it "potentially" infinite. Then there's the "actually infinite," like the total number of points or subdivisions along a line. It's literally uncountable. Aristotle reserved the status of "actually infinite" for the so-called "prime mover" that created the world and is beyond our capacity to understand. This became the basis for what's called the Cosmological, or First Cause, argument for the existence of God. Energy comes from a Greek word for activity or working. In physics, it's simply the property or the state of anything in our universe that allows it to do work. Whether it's thermal, kinetic, electro-magnetic, chemical, or gravitational. The 19th century German scientist Hermann von Helmholtz found that all forms of energy are equivalent, that one form can be transformed into any other. The laws of physics say that in a closed system - such as our universe - energy is conserved. It may be converted, concentrated, or dissipated, but it's never lost. Humans today generate about two and a half trillion watts of electrical power. How does that stack up to the power generated by planet Earth? Deep inside our planet, the radioactive decay of elements such as uranium and thorium generates 44 trillion watts of power. As this heat rises to the surface, it drives the movement of Earth's crustal plates, and powers volcanoes. Remarkably, that's just a fraction of the energy released by a large hurricane in the form of rain. At the storm's peak, it can rise to 600 trillion watts. A hurricane draws upon solar heat collected in tropical oceans in the summer. You have to jump another power of ten to reach the estimated total heat flowing through Earth's atmosphere and oceans from the equator to the poles, and another two to get the power received by the Earth from the sun, at 174 quadrillion watts. Believe it or not, there's one human technology that has exceeded this level. The AN602 hydrogen bomb was detonated by the Soviet Union on October 30, 1961. It unleashed some 1400 times the combined power of the Nagasaki and Hiroshima bombs. With a blast yield of up to 57,000 tons of TNT, it generated 5.3 trillion trillion watts, if only for a tiny fraction of a second. That's 5.3 Yottawatts, a term that will come in handy as we now begin to ascend the power scales of the universe. To Nikolai Kardashev, a Level 2 civilization would achieve a constant energy output 80 times higher than the Russian superbomb. That's equivalent to the total luminosity of our sun, a medium-sized star that emits 375 yottawatts. However, in the grand scheme of things, our sun is but a cold spark in a hot universe. Look up into Southern skies and you'll see the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Deep within is the brightest star yet discovered. R136a1 is 10 million times brighter than the sun. Now if that star happened to go supernova, at its peak, it would blast out photons with a luminosity of around 500 billion yottawatts. To advance to a level three civilization, you have to marshal the power of an entire galaxy. The Milky Way, with about two hundred billion stars, has an estimated total luminosity of 3 trillion yottawatts, a three followed by 36 zeros. To boldly go beyond Level 3, a civilization would need to marshal the power of a quasar. A quasar is about a thousand times brighter than our galaxy. Here is where cosmic power production enters a whole new realm, based on the physics of extreme gravity. It was Isaac Newton who first defined gravity as the force that pulls the apple down, and holds the earth in orbit around the sun. Albert Einstein redefined it in his famous General Theory of Relativity. Gravity isn't simply the attraction of objects like stars and planets, he said, but a distortion of space and time, what he called space-time. If space-time is like a fabric, he said, gravity is the warping of this fabric by a massive object like a star. A planet orbits a star when it's caught in this warped space, like a ball spinning around a roulette wheel.

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