To be fair, Saltire, you can actually use Special Relativity to show the Twins’ Paradox as well. My favorite way to do it requires a ruler, a careful scale length, and the ability to mark straight lines. You are right in saying that the only difference between the two frames of reference is in the acceleration that the rocketship experiences as it turns around to head back home, but acceleration can be modeled just fine with Special Relativity. General Relativity is really more about trying to talk about what accelerating reference frames really are equivalent to as opposed to what constant velocity reference frames are equivalent to. As I wrote the previous sentence, it dawned on me to nitpick my own comment: the Galilean or Newtonian Equivalence Principles are what describes constant velocity reference frames while it is acceleration and gravitational reference frames that are described by Einstein’s Equivalence Principle. Minor, but meaningful! It’s always great when you catch your own errors.
[pedagogical mode]
For those of you with extra time on your hands, try to figure out what the equivalent version of the twins paradox is for a universe that has topology such that if you head off in a straight line you end up back where you started. I found it to be a rather surprising result. For the more lazy among you, a good Google search will give you the answers you seek!
[/pedagogical mode]
MadSam, actually all the atoms heavier than lithium were produced in the cores of stars that went supernova. In fact, it wasn’t until that the quarks decoupled that nuclear particles were formed, and primal nuclearsynthesis as a result of the Big Bang (which was indeed on the order of 12 billion years ago) gave us hydrogen and helium mostly (with some comparably trace deuterium and lithium). It is safe to say that much of the hydrogen in all those sugar and water molecules in your body was created during that first nuclearsynthetic period. The rest of you is considerably younger, as stars had to form and go Kablooie.
Some of your electrons may be fairly old too, though you can make them much more easily than hydrogen, so some of them might be “younger”.
When it gets right down to it, all the energy in the universe is as old as the universe, it’s just a matter of how its packaged.
You’ve asked the question. It’s been answered by several posters. Are you stupid or stubborn that you don’t accept the answer?
Do you believe that Einstenien relativity is true (If you don’t, why are you talking about time dilation)? If you do, then you have no case. Atoms are atoms. The fact that they constitute a spaceship or a biological entity makes not a damn bit of difference, they respond the same way to relativistic phenomona. How many different ways would you like us to answer your question? Go get a book on relativity on report back to us after you’ve read it and understand the basics of what it’s saying.
The key to the Twin Paradox is that there are three frames of reference, not two. You’ve got Earth Frame, Outbound Astronaut Frame, and Returning Astronaut Frame. You can set any one frame to be at rest, but you can’t set two to be at rest at once. So, for instance, if you use Outgoing Astronaut as your rest frame, then astronaut stays at rest for a while, while Earth goes off at a constant speed. Then, astronaut switches to the Returning frame, which is going really fast, and catches up to the Earth. In this frame, it’s the really fast returning frame compared to the fast Earth frame which makes the difference, but you still get the same answer.
