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Today, Einstein's goal of combining the physical laws of the universe in one theory that explains it all is the Holy Grail of modern physics.
running time 6:21

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In order to solve some of the deepest mysteries of the universe, the rules that govern large objects like galaxies must be combined with the rules that govern small objects like subatomic particles.
running time 8:26

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String theory is radically changing our ideas about the nature of space, opening up the possibility that extra dimensions, rips in the fabric of space, and parallel universes actually exist.
running time 10:02

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Although Newton discovered the law of gravity nearly 300 years ago, until Einstein came along, scientists had no idea how gravity actually worked.
running time 6:04

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Many physicists now believe that strings—miniscule vibrating strands of energy thought to make up all matter—hold the key to uniting the world of the large and the world of the small in a single theory.
running time 4:40

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Strings provide a unified framework for viewing the universe, but for a while, confusingly, there were five different versions of string theory.
running time 4:09

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Einstein's success in explaining gravity as warps and curves in the fabric of space and time set him on a quest to unify gravity with electricity and magnetism.
running time 7:11

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In the 1960s, physicists caught a glimpse of what appeared to be strange, string-like objects hidden beneath the abstract symbols of a 200-year-old equation.
running time 4:12

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What physicists thought were five different theories turned out to be five different ways of looking at the same thing. String theory was unified at last.
running time 5:21

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As Einstein struggled to unite the weak force of gravity with the much stronger force of electromagnetism, physics moved on, examining the bizarre way tiny bits of matter interact with one another inside the atom.
running time 4:30

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Meanwhile, mainstream science was embracing particles as points, not strings, and the Standard Model was born, uniting the strong force, the weak force, and electromagnetism.
running time 6:36

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The extra dimension of space required to unify string theory suggests that we may be trapped on just one tiny slice of a higher-dimensional universe.
running time 5:03

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According to quantum mechanics, at the tiny scale of atoms and particles, the world is a game of chance.
running time 8:24

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By the 1970s, a few young physicists worked on taming the unruly equations of string theory and succeeded in describing how gravity works in the subatomic world, a key element missing from the Standard Model.
running time 7:18

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The weakness of gravity compared to the other forces has confounded physicists for decades, but now string theorists believe that gravity may be leaking into parallel universes.
running time 5:58

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For decades, no one could figure out how gravity operates when you get down to the quantum world of atoms and subatomic particles.
running time 4:25

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A revised version of string theory, free of mathematical inconsistencies, seemed capable of describing all the building blocks of nature, and it launched a hot new field of physics.
running time 5:29

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The origin of the universe has always been a mysterious event in which the laws of physics appear to break down. Could it be that the big bang was caused by the collision of two parallel universes?
running time 7:37

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Now string theory—the idea that everything is made of tiny, vibrating strands of energy—holds out the hope of unifying the world of the very large and the world of the very small.
running time 7:58

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Despite our perception that we live in a universe with four dimensions—three spatial and one temporal—string theory demands that our universe has 11 dimensions.
running time 6:57

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The hunt is on for evidence that supports string theory—for example, extra dimensions or supersymmetry.
running time 6:29

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String theorists have a problem: strings, if they exist, are so small that there's little hope of ever seeing one, so how can the theory be tested?
running time 3:35

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By the mid-1980s physicists had developed five different versions of string theory, raising the question of whether it would prove to be a theory of everything or a theory of nothing.
running time 4:59

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Will string theory turn out to be a dead end? Most string theorists believe that such an elegant and mathematically beautiful idea couldn't be completely wrong.
running time 3:53