Gravity arises from distortions of spacetime. It is not a mysterious force that acts at a distance. The presence of mass causes the distortions and the resulting distortions determine how other objects move through spacetime.Time runs slowly in gravitational fields. The stronger the gravity, the more slowly time runs.Black holes can exist in spacetime, and falling into a black hole means leaving the observable universe.The universe has no boundaries and no center, yet it might still have a finite volumeLarge masses that undergo rapid changes in motion or structure emit gravitational waves that travel at the speed of light.
  • What is a black hole? What do we mean by the event horizon of a black hole?
  • List five major ideas that come directly from the general theory of relativity.
  • What are gravitational waves? What evidence supports their existence?
  • What is gravitational time dilation? What determines how much time is slowed in a gravitational field?
If you are floating freely, then your worldline is following the straightest possible path through spacetime. If you feel weight, then you are not on the straightest possible path.
  • What is a black hole? What do we mean by the event horizon of a black hole?
  • What do we mean by the straightest possible path between two points on Earth's surface?
  • Explain how the idea of spacetime geometry means that the universe has no center and no edges.
  • How can you tell whether you are following the straightest possible path through spacetime?
If we shrank the Sun enough, we could eventually curve spacetime so much that it would become a bottomless pit - a hole in the observable universe, which is called the black hole . The boundary that marks the "point of no return" is called the event horizon.
  • What is the current evidence regarding the possibility of travel through hyperspace, wormholes, or warp drive?
  • What are gravitational waves? What evidence supports their existence?
  • What is a black hole? What do we mean by the event horizon of a black hole?
  • What is a spacetime diagram? What is a worldline? What is an event?
If the Universe began in an explosion and is expanding, is it or is it not required to have a center? No. Once the Universe began to expand, it became like an expanding surface. Space itself was expanding. Once objects began to appear in the Universe, we had some "markers", if you will, against which to establish coordinate locations. Try as we might, however, we have never been able to use these galaxies to establish a spatial preference in the Universe. There is no center, and all of space seems to be expanding away from all of the rest of space. No matter where you are.
  • How can you tell whether you are following the straightest possible path through spacetime?
  • Explain how the idea of spacetime geometry means that the universe has no center and no edges.
  • According to general relativity, how is time affected by gravity? According to general relativity, why does Earth orbit the Sun? Describe the use and limitations of the rubber sheet analogy.
  • According to general relativity, what is gravity? With this view, why does the Earth orbit the Sun?
The shortest path between the two points
  • What is a black hole? What do we mean by the event horizon of a black hole?
  • What do we mean by dimension? Describe a point, a line, a plane, a three-dimensional space, and a four-dimensional space. What does hyperspace mean?
  • What is the current evidence regarding the possibility of travel through hyperspace, wormholes, or warp drive?
  • What do we mean by the straightest possible path between two points on Earth's surface?
In flat regions of spacetime, freely moving objects move in straight lines. The mass of the Sun causes spacetime to curve, so freely moving objects (such as planets and comets) follow the straightest possible paths allowed by the curvature of spacetime. Circles that were evenly spaced in flat spacetime become more widely spaced near the central mass. A mass like the Sun causes spacetime to curve, and the curvature of spacetime determines the paths of freely moving masses like the planets.
  • Describe the idea behind the "rubber sheet" analogy to spacetime and the limitations of the analogy. In the analogy, what does mean? Why does the curvature of spacetime near a star depend on both the star's mass and its size?
  • Describe Mercury's peculiar orbit. What is gravitational lensing? According to general relativity, why does it occur?
  • What do we mean by dimension? Describe a point, a line, a plane, a three-dimensional space, and a four-dimensional space. What does hyperspace mean?
  • Explain the meaning of the statement "Space is different for different observers. Time is different for different observers. Spacetime is the same for everyone."
Gravitational time dilation is the slowing of time that occurs in a gravitational field, as predicted by Einstein's general theory of relativity. a . In an accelerating spaceship (but not in one at constant velocity), time must run faster at the front end and more slowly at the back end. b . By the equivalence principle, time must also run more slowly at lower altitudes in a gravitational field.
  • What are gravitational waves? What evidence supports their existence?
  • What is a black hole? What do we mean by the event horizon of a black hole?
  • What is gravitational time dilation? What determines how much time is slowed in a gravitational field?
  • What is the current evidence regarding the possibility of travel through hyperspace, wormholes, or warp drive?
Einstein proved that time runs more slowly and space is more curved on the part of Mercury's orbit that is nearer the sun. Gravitational lensing is the magnification or distortion (into arcs, rings, or multiple images) of an image caused by light bending through a gravitational field, as predicted by Einstein's general theory of relativity.
  • What do we mean by dimension? Describe a point, a line, a plane, a three-dimensional space, and a four-dimensional space. What does hyperspace mean?
  • What is the current evidence regarding the possibility of travel through hyperspace, wormholes, or warp drive?
  • Describe the idea behind the "rubber sheet" analogy to spacetime and the limitations of the analogy. In the analogy, what does mean? Why does the curvature of spacetime near a star depend on both the star's mass and its size?
  • Describe Mercury's peculiar orbit. What is gravitational lensing? According to general relativity, why does it occur?
Gravitational waves are waves, predicted by Einstein's general theory of relativity, that travel at the speed of light and transmit distortions of space through the universe. Although they have not yet been observed directly, we have strong indirect evidence that they exist.
  • What is a spacetime diagram? What is a worldline? What is an event?
  • What are gravitational waves? What evidence supports their existence?
  • What is gravitational time dilation? What determines how much time is slowed in a gravitational field?
  • What is a black hole? What do we mean by the event horizon of a black hole?
Time runs slower in places where gravity is stronger. Earth is following the straightest path possible through spacetime, but this path happens to go around and around the Sun. we use it to represent spacetime. The issue is it is 2D and we have to ignore any effects of friction bc there is no friction in space.
  • According to general relativity, what is gravity? With this view, why does the Earth orbit the Sun?
  • Explain the meaning of the statement "Space is different for different observers. Time is different for different observers. Spacetime is the same for everyone."
  • Explain how the idea of spacetime geometry means that the universe has no center and no edges.
  • According to general relativity, how is time affected by gravity? According to general relativity, why does Earth orbit the Sun? Describe the use and limitations of the rubber sheet analogy.
Gravity is one of the four fundamental forces; it is the force that dominates on large scales. The fact that Earth goes around the Sun tells us that spacetime itself is curved near the Sun. in other words, what we perceive as gravity arises from the curvature of spacetime.
  • Explain how the idea of spacetime geometry means that the universe has no center and no edges.
  • According to general relativity, what is gravity? With this view, why does the Earth orbit the Sun?
  • According to general relativity, how is time affected by gravity? According to general relativity, why does Earth orbit the Sun? Describe the use and limitations of the rubber sheet analogy.
  • What is gravitational time dilation? What determines how much time is slowed in a gravitational field?
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