Time and Relativity

Time and Relativity
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Special Relativity
Episode 4 of Redefining Reality
Until 1905, physical reality consisted of absolute space, absolute time, and the luminiferous aether. Learn how Einstein's special theory of relativity overthrew this deeply ingrained view and heralded an entirely new conception of reality. Examine how cultural figures such as Kurt Vonnegut drew on this legacy.
General Relativity
Episode 5 of Redefining Reality
Relativity was incomplete until Einstein formulated a general theory of relativity that incorporated gravity. See how this breakthrough demolished the age-old idea of gravity as a force, replacing it with the concept of warped spacetime, leading to strange predictions such as black holes.
Special Relativity
Discover the startling consequences of Einstein's principle of relativity: that the laws of physics are the same for all observers in uniform motion. One result is that the speed of light is the same for all observers, no matter what their relative motion: an idea that overturns the concept of…
General Relativity
Special relativity is limited to reference frames in uniform motion. Following Einstein, make the leap to a more general theory that encompasses accelerated frames of reference and necessarily includes gravity. According to Einstein's general theory of relativity, gravity is not a force but the geometrical structure of spacetime.
What Is Time?
Approach time from a philosophical perspective. "Presentism" holds that the past and future are not real; only the present moment is real. However, the laws of physics appear to support "eternalism"--the view that all of the moments in the history of the universe are equally real.
Keeping Time
How do we measure the passage of time? Discover that practical concerns have driven the search for more and more accurate clocks. In the 18th century, the problem of determining longitude was solved with a timepiece of unprecedented accuracy. Today's GPS navigation units rely on clocks accurate to a billionth…
Time in Quantum Mechanics
Quantum mechanics is the most precise theory ever invented, yet it leads to startling interpretations of the nature of reality. Probe a quantum state called the collapse of the wave function that may underlie the arrow of time. Are the indications that it shows irreversibility real or only illusory?
Part of the Series: How We Got to Now
The world today is obsessed by time. Johnson boards a submarine to discover what a lack of natural light means for a sailor's working day and visits Heathrow, the world's busiest airport, to try to get timings right at air traffic control. The story of getting a grip on time…
Mysteries of Modern Physics: Time Series
Time seems to be woven into the very fabric of the universe. But why? In 24 riveting half-hour episodes, Mysteries of Modern Physics: Time shows how a feature of the world that we all experience connects us to the instant of the formation of the universe--and possibly to a multiverse…
Why Time Is a Mystery
Begin your study of the physics of time with these questions: What is a clock? What does it mean to say that "time passes"? What is the "arrow of time"? Then look at the concept of entropy and how it holds the key to the one-way direction of time in…
Time’s Arrow
Embark on the quest that will occupy the rest of the course: Why is there an arrow of time? Explore how memory and aging orient us in time. Then look at irreversible processes, such as an egg breaking or ice melting. These capture the essence of the one-way direction of…
Time Reversal in Particle Physics
Explore advances in physics since Newton's time that reveal exceptions to the rule that interactions between moving particles are fully reversible. Could irreversible reactions between elementary particles explain the arrow of time? Weigh the evidence for and against this view.