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## Main Question or Discussion Point

As I understand time dilation, at 90% of the speed of light, a space travelling twin would age at a rate 44% of his/her twin on earth; at 99% it would be 14% and at 99.9% it's 4.5%. And these differences would be permanent. Since relativity explains things in terms of spacetime, does this mean that a rocketship travelling at a constant 90% of the speed of light away from and back to earth - except during turnaround when the rocketship would travel at non-uniform speeds - would shrink to 44% of its earth-length?

My take away from the twin paradox as to time dilation is that when the travelling twin returns to earth, he/she will be younger by a number of years calculated using the formulas and that this difference in aging would be observed by both twins even though they are currently sharing the same reference framework-lightspeed on earth. What about foreshortening? Would the spaceship on its return to earth only be 44% of the length it was when it left earth? This seems more strange than the travelling twin being younger on his/her return to earth even though both would be sharing the same reference framework, but given the unity of spacetime the dilation principle, I assume, should apply to both space and time.

Dave1939

My take away from the twin paradox as to time dilation is that when the travelling twin returns to earth, he/she will be younger by a number of years calculated using the formulas and that this difference in aging would be observed by both twins even though they are currently sharing the same reference framework-lightspeed on earth. What about foreshortening? Would the spaceship on its return to earth only be 44% of the length it was when it left earth? This seems more strange than the travelling twin being younger on his/her return to earth even though both would be sharing the same reference framework, but given the unity of spacetime the dilation principle, I assume, should apply to both space and time.

Dave1939