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closet mathemetician
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If everything is moving at the speed of light in the time direction all the time, Then how does the light from an event in the past ever catch up and reach me?
closet mathemetician said:If everything is moving at the speed of light in the time direction all the time,
closet mathemetician said:If everything is moving at the speed of light in the time direction all the time, Then how does the light from an event in the past ever catch up and reach me?
bcrowell said:This is apparently Brian Greene's idiosyncratic way of talking about spacetime in his popular-level book. I don't know of anybody else who describes it this way. Judging by the number of people who post about it, it seems to cause a huge amount of confusion. Things don't move through spacetime. Things move through space. When a thing moves through space, it has a world-line which is a curve in spacetime.
closet mathemetician said:You are right, that "moving through time" in, say, a two-dimensional spacetime is represented by a static line in the time direction that is not dynamic. I was playing loosely with the language. However, if I have velocity in space, then my worldline in spacetime has a slope between vertical and one (45 degrees), meaning that there must be two components of velocity, one in time and one in space, in other words, (c,v).
Furthermore, my velocity through space, v, can go from zero to c, (if I don't have mass) but my velocity in time is always c.
No, in this interpretation it is the speed through spacetime (norm of the four-velocity) which is always c, not the timelike component of the four-velocity.closet mathemetician said:Furthermore, my velocity through space, v, can go from zero to c, (if I don't have mass) but my velocity in time is always c.
As bcrowell said, this is Brian Greene's confusing way of explaining relativity in some of his books. For the math behind what he means behind "speed through spacetime", see my [post=430613]post #3 on this thread[/post].ghwellsjr said:"Everything" is moving at the speed of light? Where'd you get that idea from? I thought things with mass could not move at the speed of light.
Please explain.
Light travels through space as electromagnetic waves. These waves do not require a medium to travel and can travel through the vacuum of space at a speed of approximately 300,000 kilometers per second.
When we look at a distant object, we are seeing the light that was emitted from that object in the past. This is because light takes time to travel through space, so by the time it reaches our eyes, it has already traveled for a certain amount of time.
The time it takes for light to reach Earth from a distant object depends on the distance between Earth and the object. For example, it takes about 8 minutes for light from the sun to reach Earth, while it takes about 2.5 million years for light from the Andromeda galaxy to reach us.
We can determine the age of an object by measuring the distance between Earth and the object and calculating the time it took for light to travel that distance. This allows us to see objects as they were in the past, providing us with a glimpse into the history of our universe.
Yes, there is a limit to how far we can see into the past. This is due to the expansion of the universe, which causes distant objects to move away from us at a faster rate. As a result, there is a point where the light from these objects becomes too faint for us to detect, limiting our ability to see further into the past.