How the Universe Works - The Dark Matter Enigma - Space Discovery Documentary
Explore the biggest question of all. 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. #universedocumentary #spacedocumentary #Universe
The First Moment Of Time | The Universe - Space Documentary HD
When was the first light in the universe?
The speed of light gives us an amazing tool for studying the universe. Because light only travels a mere 300,000 kilometers per second, when we see distant objects, we're looking back in time.
You're not seeing the sun as it is today, you're seeing an 8 minute old sun. You're seeing 642 year-old Betelgeuse. 2.5 million year-old Andromeda. In fact, you can keep doing this, looking further out, and deeper into time. Since the universe is expanding today, it was closer in the past.
Run the universe clock backwards, right to the beginning, and you get to a place that was hotter and denser than it is today. So dense that the entire universe shortly after the Big Bang was just a soup of protons, neutrons and electrons, with nothing holding them together.
In fact, once it expanded and cooled down a bit, the entire universe was merely as hot and as dense as the core of a star like our sun. It was cool enough for ionized atoms of hydrogen to form.
Because the universe has the conditions of the core of a star, it had the temperature and pressure to actually fuse hydrogen into helium and other heavier elements. Based on the ratio of those elements we see in the universe today: 74% hydrogen, 25% helium and 1% miscellaneous, we know how long the universe was in this whole universe is a star condition.
The fusion process generates photons of gamma radiation. In the core of our sun, these photons bounce from atom to atom, eventually making their way out of the core, through the sun's radiative zone, and eventually out into space. This process can take tens of thousands of years. But in the early universe, there was nowhere for these primordial photons of gamma radiation to go. Everywhere was more hot, dense universe.
The universe was continuing to expand, and finally, just a few hundred thousand years after the Big Bang, the universe was finally cool enough for these atoms of hydrogen and helium to attract free electrons, turning them into neutral atoms.
This was the moment of first light in the universe, between 240,000 and 300,000 years after the Big Bang, known as the Era of Recombination. The first time that photons could rest for a second, attached as electrons to atoms. It was at this point that the universe went from being totally opaque, to transparent.
And this is the earliest possible light that astronomers can see. Go ahead, say it with me: the cosmic microwave background radiation. Because the universe has been expanding over the 13.8 billion years from then until now, the those earliest photons were stretched out, or red-shifted, from ultraviolet and visible light into the microwave end of the spectrum.
If you could see the universe with microwave eyes, you'd see that first blast of radiation in all directions. The universe celebrating its existence.
After that first blast of light, everything was dark, there were no stars or galaxies, just enormous amounts of these primordial elements. At the beginning of these dark ages, the temperature of the entire universe was about 4000 kelvin. Compare that with the 2.7 kelvin we see today. By the end of the dark ages, 150 million years later, the temperature was a more reasonable 60 kelvin.
For the next 850 million years or so, these elements came together into monster stars of pure hydrogen and helium. Without heavier elements, they were free to form stars with dozens or even hundreds of times the mass of our own sun. These are the Population III stars, or the first stars, and we don't have telescopes powerful enough to see them yet. Astronomers indirectly estimate that those first stars formed about 560 million years after the Big Bang.
Then, those first stars exploded as supernovae, more massive stars formed and they detonated as well. It's seriously difficult to imagine what that time must have looked like, with stars going off like fireworks. But we know it was so common and so violent that it lit up the whole universe in an era called reionization. Most of the universe was hot plasma.
The early universe was hot and awful, and there weren't a lot of the heavier elements that life as we know it depends on. Just think about it. You can't get oxygen without fusion in a star, even multiple generations. Our own solar system is the result of several generations of supernovae that exploded, seeding our region with heavier and heavier elements.
As I mentioned earlier in the article, the universe cooled from 4000 kelvin down to 60 kelvin. About 10 million years after the Big Bang, the temperature of the universe was 100 C, the boiling point of water. And then 7 million years later, it was down to 0 C, the freezing point of water.
This has led astronomers to theorize that for about 7 million years, liquid water was present across the universe… everywhere. And wherever we find liquid water on Earth, we find life.
What is Dark Matter and Dark Energy?
What is dark energy? What is dark matter? Well, if we knew exactly we would have a nobel prize – we know that they exist though. So what do we know about those strange things?
Check out THE NOVA PROJECT to learn more about dark energy:
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