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In a universe with blocktime the past, present and future all exist at the same time. But what makes it appear that for example my body is going from one movement to the next? What makes movement possible anyhow? I read that Einstein said that the division af time in a past, present and a future is illusion, and a persistent one, but the fact that two spaceships in motion relative to each other doesn´t prove that past, present and future all exist together. It depends on how the spaceships came into movement. A spaceship traveling towards us has a different line af event happening at the same time, as the same spaceship seen from a place at the other side of it, and makes the situation symmetrical. And that time prevents them to all happening at the same time (it´s impossible to talk about these things without reference to time) needs a mechanism to show how that can be accomplished.

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closed as unclear what you're asking by ACuriousMind, Sebastian Riese, Gert, Daniel Griscom, John Rennie Feb 4 '16 at 8:12

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    $\begingroup$ It's not clear to me what exactly your question is. Are you asking how the apparent arrows of time arise? Typical GR does not explain "why" observers perceive themselves to move in a certain direction along their worldline, it just states they do. (For that matter, Newtonian mechanics also doesn't explain "why" time passes. It's not a question a typical physical theory aims to answer, as it is irrelevant to predict what happens) $\endgroup$ – ACuriousMind Feb 3 '16 at 14:31
  • $\begingroup$ Block universe theory of time instead of Blocktime ? a very pertinent question on this theory $\endgroup$ – user46925 Feb 3 '16 at 16:01
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I have just watched one of Brian Greene's videos which gave this Blocktime impression as well, yet it is misleading. https://www.youtube.com/watch?v=VYZQxMowBsw

Perhaps this may help you. Say we have a very long train that is 600,000 km long. Clocks are located at the opposite ends of the train, and there is also one clock located in the middle of the train. Let's say that all the clocks are in sync.

Due to the length of the train, if a burst of light was released from both ends at the time of 12:00AM, the light from both ends will reach the middle clock when the middle clock says 12:00AM plus 1 second, and it does so since light travels across a distance of 300,000 km in a total time period of 1 second. Thus to an observer located at the middle of the train, both bursts of light occurred simultaneously, thus both shared a time of "NOW".

Imagine that the train is accelerated to 260,000 km/s. To an external observer, who did not choose to accelerate, from his point of view the clock at the rear of the train is ahead of the middle clock by 0.866 of a second, and also that the clock located at the front is lagging behind the clock located at the middle by 0.866 of a second, all as verified via the Lorentz transformation equations.

However, if you do the math, you find that if bursts of light were released from each end of the train when each clock at each end had independently displayed the time of 12:00AM, once again the bursts of light will reach the middle of the train when the clock at the middle displays the time of 12:00AM plus 1 second. Thus, even though the two bursts of light were released 1.732 seconds apart ( 0.866 + 0.866 = 1.732 ), both bursts of light still reach the middle clock at the same time. Thus to an observer located at the middle, it appears as though both bursts of light occurred simultaneously, thus both had shared the time of "NOW".

Thus in this case, the line of "NOW", extends from the middle of the train in the forward direction, to -0.866 sec, and extends from the middle of the train in the reverse direction, to +0.866 sec. Not to forget also that the train is moving at 260,000 km/s in the forward direction. Thus whatever direction you are traveling across space, be it away from Earth, or toward Earth, if looking in the direction of travel, this line of "NOW" has you looking toward the past.

Meanwhile, let it also be noted that to those who chose not to accelerate, the clocks that are located at the ends of the train, are seen as being offset from each other by a total time period of 1.732 seconds, and also, despite there being two different times indicated by these clocks, to those who had chosen not to accelerate, both clocks share what is being the "NOW".

If again onboard the moving train, bursts of light were released from each end of the train when each clock at each end had independently displayed the time of 12:00AM, from the external observers point of view, the burst of light at the rear occured first, and then the burst of light at the front occured 1.732 seconds later on.

Thus even though those onboard the train, who are looking in the same direction as the train is traveling, are oriented in a direction that points them in the "NOW" direction that points to the past, in truth they are looking toward future events that have not yet occurred. These two effects cancel each other out such that neither observers "NOW" has truly extended into the actual future. Thus in either case, the future is left untouched, thus BockTime does not exist.

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  • $\begingroup$ waw ... this rejoins the texts on how the time metrics changes in a BH. Insert something at the top for the readers which could think that you don't understand the question :) $\endgroup$ – user46925 Feb 3 '16 at 16:10

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