rybak+time+dilation

One of the most enthralling aspects of Relativity is its new understanding of time. The term "time dilation" might evoke images of Salvadore Dali's timepieces hanging on twigs, however, time dilation is all but surrealistic. As stated earlier, if the speed of light is constant, time cannot be constant. In fact, it doesn't make sense to speak of time as being constant or absolute, when we think of it as one dimension of spacetime. Special Relativity states that time is measured according to the relative velocity of the reference frame it is measured in. Despite of the simplicity of this statement, the relativistic connection between time and space are hard to fathom.

There are two twin brothers. On their thirtieth birthday, one of the brothers goes on a space journey in a superfast rocket that travels at 99% of the speed of light. The space traveller stays on his journey for precisely one year, whereupon he returns to Earth on his 31st birthday. On Earth, however, seven years have elapsed, so his twin brother is 37 years old at the time of his arrival. This is due to the fact that time is stretched by factor 7 at approx. 99% of the speed of light, which means that in the space traveller’s reference frame, one year is equivalent to seven years on earth. Yet, time appears to have passed normally to both brothers, i.e. both still need five minutes to shave each morning in their respective reference frame.