Gravity - Deepstash

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Gravity

Einstein's special theory of relativity applies only to steady, unchanging motion through space-time, not accelerating motion like an object falling toward Earth.

  • It troubled Einstein that his theory didn't include gravity, and his battle to incorporate it made symmetry central to his thinking.
  • Einstein later understood that gravity is the curvature of space-time itself. Falling objects follow the space-time path carved out for them.
  • After general relativity was published, it appeared that energy might not be conserved in strongly curved space-time. But mathematician Emmy Noether proved that the amount of energy (including mass), the amount of electric charge, the amount of momentum, are all associated with a particular symmetry, a change that doesn't change anything.
  • Noether showed that the symmetries of general relativity ensure that energy is always conserved.

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MORE IDEAS ON THIS

Unified space-time

Unified space-time starts to make sense if we think that the speed of light is a relationship between the distance traveled over time.

Because the speed of light can't change, your laser beam won't go any faster. The measurement of distance and time must be changed instead, depending on th...

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Symmetry

The relationship that mattered most to Einstein's ideas was symmetry. Scientists describe symmetry as changes that don't really change anything. More complicated symmetries have led to the discoveries from neutrinos to quarks.

Symmetry is at the root of our descrip...

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Insights of Albert Einstein

Insights of Albert Einstein

Many insights of Albert Einstein are now part of popular imagination: black holes, time warps, and wormholes show up in movies and books.

Less famous, but probably the most revolutionary part of Einstein's phenomena, is a simple idea that shows how pieces fit together and illuminate the ro...

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Matter

After Einstein, the pull of symmetry became more powerful.

  • Paul Dirac, trying to make quantum mechanics compatible with the symmetry requirements of special relativity, found a minus sign in an equation, suggesting the existence of "antimatter."
  • Wolfgang Pauli, trying to acc...

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Some changes don't change anything

The most fundamental aspects of nature stay the same.

For example, Einstein's papers on relativity show that the relationship between energy and mass is invariant, even though energy and mass can take on many different forms.

Even though matter produces ene...

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Gauge symmetry

From the 1950s, invariances took on a life of their own. New symmetries, known as "gauge" invariances, became productive by requiring the existence of everything from W and Z bosons to gluons.

Gauge symmetry dictates what other ingredients you have to introduce. Gauge symmetries d...

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Dualities

Duality is a closely related idea to symmetry. Wave-particle duality has been around since the beginning of quantum mechanics. But newfound dualities have shown interesting relationships. For example, a three-dimensional world without gravity can be mathematically equivalent to a fou...

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Broken Symmetries

Symmetry, as it is understood, seems not to answer the biggest questions in physics. In some cases, symmetries show the underlying laws of nature that do not show up in reality.

For example, when energy congeals into matter (E = mc2), the result is an equal amount of matter and antimat...

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Relationships over things

We often think of things as the heart of reality. But most often the relationship is more important, not the stuff.

We may think "stuff" like space and time are unchangeable aspects of nature. In reality, the relationship between space and time stays the same.

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Not giving up on symmetry

The idea of symmetry proved very powerful. Giving it up would mean giving up on naturalness - the idea that the universe has to be exactly the way it is for a reason.

But inside black holes, the speed of light (which grounded Einstein's work) will not play a vital role in the future....

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Einstein and Light

Albert Einstein did not think about symmetry when he wrote his first relativity papers in 1905. He was considering several seemingly unrelated puzzles and connecting the dots.

  • Einstein realized that the speed of light - a speed that stayed constant - was a measurable manifestation of...

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MORE LIKE THIS

Einstein and the shape of spacetime

Albert Einstein held that space and time together made up the universe's fabric that could stretch and compress. Einstein suggested that the shape of spacetime is what gives rise to the force of gravity. A concentration of mass, like the earth or sun, ben...

Space-Time

Einstein's theory of general relativity says that Time can be bent, stretched and squeezed, and the four-dimensional fabric with a huge mass creates a dimple, or bending of Space-Time, causing gravity.

This effect of time dilation is proven using GPS satellite technology in space, making a...

Absolute time does not exist

Absolute time does not exist

Time moves slower the closer you are to Earth. In his theory of general relativity, Einstein explained that the gravity of a large mass, like Earth, distorts the space and time around it.

In 2010, researchers placed two precise atomic clocks, one 33 centimetres higher than...

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