World Science Scholars

11.1 The Mathematics of Slow Time

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    • There are actually two right-triangles in this lecture: (1) One in which the hypoteuse = D and the opposite = L (but the adjacent is not specified). (2) One in which the hypotenuse = c, the adjacent = c.cos(theta), and the opposite = c.sin(theta). Prof. Greene shifts from the first triangle to the second then back to the first without making these shifts clear. Not only this is confusing, it also involves additional steps of derivation that could have been avoided if there were only one triangle. Other writers show the derivation of gamma from only one triangle using only Pythagoras theorem.

    • Just to note that always what happens is that WE SEE that other clock is faster or slower than ours, but not that the clock is faster or slower, not that the time goes slower or faster, only that we see one clock different form the other. Since there is not fix and unique reference system it can not be affirm that one clock is faster or slower or the time is faster or slower, only that we measure it differently. The light does not take an horizontal speed when the box move, we SEE that trajectory because our relative movement. Since there is not an absolute space we can not affirm that the light have this or that trajectory, only that in relation to us we measure that trajectoy in our reference.
      I know this is implicity in the explanation.

    • If we consider the case where v=c, then cos theta is c/c. This is 1. Then we know that theta must be 0 degrees. It seems that light itself travels parallel to the direction of its motion and thus its own clock never ticks. I may be taking a leap of logic here. It seems to me a particle of light cannot experience time. From light’s own perspective, it seems its source and destination must be the same with no time or distance between (in direction of source to destination from our perspective.). Is it reasonable to imagine time and (a dimension of) space reducing to zero at the speed of light?

      • yes. if v=c, we can say that the light particle isnt moving at all with respective to the moving clock, or its moving parallel to the bottom(or top) of the light clock without rising at all

    • If we consider the case where v=c, then cos theta is c/c. This is 1. Then we know that theta must be 0 degrees. It seems that light itself travels parallel to the direction of its motion and thus its own clock never ticks. I may be taking a leap of logic here. It seems to me a particle of light cannot experience time. From light’s own perspective, it seems its source and destination must be the same with no time or distance between (in direction of source to destination from our perspective.). Is it reasonable to imagine time and (a dimension of) space reducing to zero at the speed of light?

    • @Timothy, yes, that’s my understanding as well.
      At light speed both the rate of passage of time reaches zero (time dilation) and the length of space is also shortened to zero (length contraction). This also means anything with mass (requiring space to hold that mass) can never reach light speed as it cannot fit in zero space.

    • @timothy, yea, precisely, light doesn’t move along the time axis at all as it cannot experience time due to it’s speed, so for, it is instantaneously starting and reaching it’s destination

    • @timothy, yea, precisely, light doesn’t move along the time axis at all as it cannot experience time due to it’s speed, so for light it is instantaneously starting and reaching it’s destination

    • I am curious as the passage of time is determined by cultural notions of time.

      Can some cultures better perceive time?

    • Look in the light clocks, time ticks via the motion of light and since speed of light is constant therefore when the clock is in motion ,the photon has to cover a greater distance by the perspective of an object at rest . So in the perspective of object in rest time ticks at slow rate but in other clocks such as mechanical clocks .time ticks via the motion of different objects not light. and the speed of the objects are not constant.so from the perspective of an object at rest time ticks at the same rate.

    • Look in the light clocks, time ticks via the motion of light and since speed of light is constant therefore when the clock is in motion ,the photon has to cover a greater distance by the perspective of an object at rest . So in the perspective of object in rest time ticks at slow rate but in other clocks such as mechanical clocks .time ticks via the motion of different objects not light. and the speed of the objects are not constant.so from the perspective of an object at rest time ticks at the same rate.

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