After many years of agonizing over it, I have still failed to come to terms with the twin paradox. Here's a brief review of my understanding and a few questions: A standard story is as follows: Twin A leaves the earth for planet Zolan 10 light years away. Twin B stays on Earth. Let's say that, over a period of a week, twin A accelerates to 0.8c (relative to Earth and Zolan, which are at rest relative to each other) and then remains cruising at that velocity, decelerates for a week upon approaching Zolan, makes a sweep around the planet (waves at everyone), begins to accelerate once more towards Earth for a week, reaches a cruising speed of 0.8c, and then finally decelerates for a week before landing safely on the earth and having lunch with twin B. Now, I'm not worried about the exact figures, but we can all agree that twin A will have aged more slowly than twin B and will be "younger" than twin B. Why is this? The main problem most people seem to have is how do you get around the apparent symmetry of relative motion problem between the two twins. In order to address this, popular consensus among physicists/cosmologists that I've seen is that this apparent symmetry becomes broken once twin A accelerates from the earth and enters a non-inertial frame, and this is what is responsible for the slowing of twin A's aging relative to twin B. I have a few questions about this. 1) "twin A accelerates from the earth and enters a non-inertial frame"--a non-inertial frame relative to what? To the earth/twin B? Some objective measure of spacetime displacement? To the CMB? I guess what I'm asking is that, is there a way to measure the acceleration of an object/frame without some measure of what to say it is accelerating in relationship to? I'm guessing there's a stock answer to this question, but I'm remiss to recall it at this moment. 2) Lorentz transformations (LT): The equation determining the time dilation factor in twin A's slowing of aging is, AFAIK, contained completely with the LT equations. However, I see no term or provision at all for acceleration in the time dilation equation. So how does acceleration play a role quantitatively in this paradox when it seems as if all you need is a simple velocity difference to create the dilation effect? Are there some equations I am not aware of that address this, or some kind of formalism that can be used to quantify these measures? I'll give three examples of scenarios I'm having difficulty seeing how the standard formalism can address: 2a) Say twin A were to accelerate (and decelerate) for 2 weeks instead of one week in both directions from earth to zolan, but compensates for the lost time by cruising at a speed slightly greater that 0.8c so that the two week acceleration round trip flight time was exactly the same as the one week. Would that make any difference in the age difference between twin A and twin B upon twin A's return? 2b) Say twin A took the exact same trip as above (say the one week version), but now twin B also took a similar trip in the opposite direction to planet Xanadu 5 light years away, but accelerated at a different rate than twin A, and reached a different cruising speed that was, say, 0.5c. How would we calculate their age differences in this situation once they both returned to earth? Could we handle it with only the LT and the relativistic velocity addition formulas? If not, then how? 2c) Finally, let's say we have twin A again going on his trip to Zolan (one week acceleration edition), but now we have twin B centrifuging himself in a 2001: Space odyssey style space station, undergoing rapid centripetal (or is it centrifugal?) acceleration. And then twin A and twin B go for lunch on earth when twin A comes back. Does that make a difference in their age? Or should twin B just as well stayed on earth during twin A's trip? I guess the more broader encompassing question is what it is specifically about twin A's undergoing an acceleration or transition into a non-inertial frame that sets his clock running slower than twin B's. It seems to be this act of accelerating that does it, not simply a relative difference in velocity. But this is the was the LT's lead you believe.