Kenneth Mellendorf

" To understand things moving close to, or at, the speed of light, Einstein's Theory of Special Relativity is required.  Einstein invented the idea of space-time:  thinking about time as just another dimension.  What makes it hard to imagine is the fact that we can't "see" it.  Someone who lives in a two-dimensional existence, perhaps a spot on a piece of paper, could never move up  from the paper, probably could not even imagine the dimension perpendicular to the paper as even existing.  Erase the dot, and as far as other dots are concerned it has disappeared.  This is how the time dimension is imagined to relate to us.  It is there, but we cannot see it.  We move along the time dimension, but our senses can only experience one point (what
we call "now").

As for traveling through time, relativity is based on perception.  Both spatial length (distance) and time length between events can appear different to different observers, depending on how fast the observers are moving with respect to each other.  So long as speeds are not near the speed of light, everything works the same for everybody.  If an observer sees you as moving close to the speed of light, and you in turn see the observer as moving close to the speed of light, effects of relativity start to matter. The time between events and the distance between events as you see things can appear different from how the other observer sees things.  Passage of time as a very fast particle sees it is different from how you see it. There are particles that, when still, appear to exist for less than one second before decaying into smaller particles.  When these particles move close to the speed of light, they can live long enough to get here from other stars. According to Einstein's theory, the particle sees things as a fast moving solar system moving to it.  The particle sees the distance traveled by the solar system, as well as the time for the journey, to be much smaller than we see it.  For the particle, the time of the journey was half of a second.  For us, it was several years.  Each is correct in its own frame of reference.

As objects, even objects as big as galaxies, travel toward or away from you, they appear to become flattened.  The width stays constant, but distance from front to back appears to shrink. This is not noticed until the object is moving close to the speed of light. As the speed approaches the speed of light, such distances (and corresponding time durations) approach zero.  How a speed of light particle truly experiences time can not be known for sure, but it appears that at the speed of light, everything is in one position and everything happens at one time.  Distance and time cannot be percepted at the speed of light. This in turn supports the theory that no object can be accelerated to the speed of light:  it would require infinite force and infinite energy. Likewise, no speed-of-light object can be slowed down.  It can be delayed for short spurts of time, but not actually made to travel slowly. "