Quotes About Spacetime

In technical terms, we say that Einstein has understood that "absolute simultaneity" does not exist: there is no collection of events in the universe that exist "now.

It is the curious local structure of the present that produces black holes.

With a great deal of effort, seeking help from friends better versed in mathematics than himself, Einstein learns Riemann's math—and writes an equation where R is proportional to the energy of matter. In words: spacetime curves more where there is matter. That is it.

Space is a spin network whose nodes represent its elementary grains, and whose links describe their proximity relations. Spacetime

This is how time is depicted in Einstein's general theory of relativity. His equations do not have a single "time"; they have innumerable times.

the world is made entirely from quantum fields. These fields do not live *in* spacetime; they live, so to speak, one on top of the other: fields on fields. The space and time that we perceiv in large scale are our blurred and approximage image of one of these quantum fields: the gravitational field (193).

The wind here is a glinting abrasive thing, a perpetual, face-shredding, eyeball-poking tendency in the fabric of spacetime, inhabited by vast platinum-blond arcs of fire that are centered on the low winter sun. Crystalline

hard to make a time machine out of normal material in your garage by only gently curving spacetime

Ain't spacetime a bitch," said Ram. "Noted," said the expendable. "Nineteen times.

But by 1912, Einstein had come to appreciate that math could be a tool for discovering—and not merely describing—nature's laws. Math was nature's playbook. "The central idea of general relativity is that gravity arises from the curvature of spacetime," says physicist James Hartle. "Gravity is geometry.

His head-snapping insight was that gravity could be defined as the curvature of spacetime, and thus it could be represented by a metric tensor.

Einstein's goal as he pursued his general theory of relativity was to find the mathematical equations describing two complementary processes: 1. How a gravitational field acts on matter, telling it how to move. 2. And in turn, how matter generates gravitational fields in spacetime, telling it how to curve. His head-snapping insight was that gravity could be defined as the curvature of spacetime, and thus it could be represented by a metric tensor. For more than three years he

With his special theory of relativity, Einstein had shown that space and time did not have independent existences, but instead formed a fabric of spacetime.

The curving and rippling fabric of spacetime explained gravity, its equivalence to acceleration, and, Einstein asserted, the general relativity of all forms of motion.

The central idea of general relativity is that gravity arises from the curvature of spacetime

The key question for a quantum theory of gravity is then the following: Can we extend to quantum theory the principle that space has no fixed geometry? That is, can we make quantum theory background-independent, at least with regard to the geometry of space? If we can do this, we will automatically merge gravity and quantum theory, because gravity is already understood to be an aspect of dynamical spacetime geometry.

A singularity is a point or region in spacetime at which some physical quantity such as the density of mass or energy, the temperature, or the strength of the gravitational field, becomes infinite. Whenever they happen, they pose serious difficulties for physics because they signal a breakdown in the description of the world in mathematical terms.

So, Einstein's theory of gravity is a theory of causal structure. It tells us that the essence of spacetime is causal structure and that the motion of matter is a consequence of alterations in the network of causal relations. What is left out from the notion of causal structure is any measure of quantity or scale.

In spacetime, all events are baked together: a four-dimensional continuum. Past and future are no more privileged than left and right or up and down.

one of the key features of a black hole: different observers have paradoxically different perceptions of the same events. To

For two events separated in time, a geodesic is the natural path things would take in spacetime to connect one event to the other.

According to quantum mechanics, at the Planck scale length, instead of a gradually undulating geometry, there should be wild fluctuations and loops and handles of spacetime branching off, the sort of topography that the futuristic Ike encountered. General relativity cannot be used in such untamed territory.

Nonetheless, in all cases matter tells spacetime how to curve, and spacetime tells matter how to move.

With general relativity, we know that before gravity can act, spacetime has to deform. This process does not happen instantaneously. It takes time. Gravity waves travel at the speed of light. Gravitational effects can kick in at a given position only after the time it takes for a signal to travel there and distort spacetime.