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Event Horizons as the Boundary of the Universe

# Space-Time

We have all seen and heard about the analogy of space-time as a fabric. Mass bends the manifold of space-time such that an object with mass passing by another object does not travel in a straight line but starts to "sink" into the bend caused by the mass. Here is a 3D representation of the bending of space-time.

http://cdnimg.visualizeus.com/thumbs/df/49/grid,planet,space,spacetime-df4956ec0ccee7ecf4f84ea9439b57d0_h.jpg?ts=93246

While I think it is very interesting how objects can be affected by this bend, what we will be focusing on is its relativistic properties. Not only does the path of an object change, but the fabric of space-time can be bent to such an extent that an object's spatial and temporal properties are not the same as that of objects in other inertial frames.

# Time Dilation

Imagine that an astronaut flew around the solar system at near light speed and returned to the Earth. If he or she compared the time on the ship with the time on Earth, they would observe that the time on the ship was a little slower than the time on Earth. In other words, an object moving at near light speed will pass through time at a slower rate than other objects. But from the perspective of the moving object, it seems that the objects around it are passing through time at a faster rate as it speeds up.

# Length Contraction

As an object approaches the speed of light, its spatial properties will also be distorted by contracting its length parallel from the point of view of an outside observer. But for the moving object, its own length will seem unchanged and it is the rest of the universe that undergoes length contraction!