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A theory that describes how matter interacts dynamically with the geometry of space and time. It was first published by Einstein in 1915 and is currently used to study the structure and evolution of the universe, as well as having practical applications like GPS.

0 votes

Does all of spacetime exist?

Just to offer a counterpoint: That the law of physics are the same for all observers is what is meant by "relativity". Now for any given observer, the distinction between past, present and future …
Stéphane Rollandin's user avatar
1 vote
2 answers
605 views

What are world lines as opposed to arbitrary curves in spacetime?

In GR the spacetime manifold is equipped with a metric which makes it a Lorentzian manifold. It is the metric that is doing the separation of space and time (so that we end up with three dimensions of …
Stéphane Rollandin's user avatar
2 votes

A Hidden Principle in Relativity

I do not agree with the premise of the question, that is the structure of a though experiment. Here is how I would put it instead: We present a setup as seen by an observer We use SR or GR to derive …
Stéphane Rollandin's user avatar
2 votes
Accepted

Concept of time in General Relativity

There is no physical meaning associated to an event. An event is a point in the spacetime manifold, where the manifold itself is a mathematical structure allowing to retrieve the effect of gravity as …
Stéphane Rollandin's user avatar
2 votes
Accepted

What are details of this claim of Penrose about gravity and QFT being at odds with each other?

The relevant paper is I believe On the Gravitization of Quantum Mechanics 1: Quantum State Reduction (Penrose, 2014). This is open access. Penrose actually talks about two types of incompatibility be …
Stéphane Rollandin's user avatar
1 vote

The Fabric of Space-time?

The spacetime of general relativity is highly dynamic. Static representations are very misleading. Static representations include the rubber sheet metaphor, which is static because the rubber sheet is …
Stéphane Rollandin's user avatar
1 vote

Does a Photon take longer to reach me when travelling in the "trough" of a gravitational Wave?

In multi-messenger astronomy it has experimentally be observed that gravitational waves and light originating from a far-away source (for example the 2017 neutron stars merger) are detected on Earth w …
Stéphane Rollandin's user avatar
11 votes
1 answer
469 views

Aren't black holes required to exist forever in our frame of reference instead of evaporating?

I know that for an observer far away, nothing ever crosses a black hole horizon (due to time dilation), while in the frame of reference of a falling observer the horizon is nothing special on its way …
Stéphane Rollandin's user avatar
4 votes

If an astronaut had stationed in International Space Station for the duration of mission, 17...

This is anwered in Gravity on the International Space Station - General Relativity perspective, where we learn that time dilation in the ISS with respect to Earth equator is 1.00000000028655. So afte …
Stéphane Rollandin's user avatar
2 votes

The Time Freezing Room - Theoretically possible?

Unfortunately the longest elapsed time along a world line happens on a geodesic, that is when a body is at rest. So you cannot have time "accelerate", you can only "slow it down" relatively to a refer …
Stéphane Rollandin's user avatar
3 votes
Accepted

When we say energy curves spacetime, which is the cause and which is the effect?

The Einstein equations are differential equations: they state a local relationship between stress-energy-momemtum and curvature that, when solved, gives a global solution, a spacetime. At the local …
Stéphane Rollandin's user avatar
3 votes

Why do objects "fall" along spacetime geodesic lines?

First, only a test particle "falls" along a geodesic. A test particle is an idealized object not only at rest, but which also does not itself contribute to the curvature of spacetime (no mass, no ener …
Stéphane Rollandin's user avatar
2 votes

Why is it said that, because gravity can bend light, that this entails a curvature of space-...

General relativity has not been created to explain the bending of light, which was observed years afterwards only. And indeed, the idea of gravity having an effect on light was not absent from Newtoni …
Stéphane Rollandin's user avatar