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I'm really sorry to bother you with my surely stupid questions, but I am 13 years old and today I read some lines about Special Relativity and General Relativity at school and found myself stuck on some thoughts I can't cease to think about... I really hope that you will be so kind to help me, because I'm not clever enough to solve these things out by myself.

(1) I read that every object which has mass curves space-time (though maybe just infinitesimally). (a) Is it right? (b) Does energy (which I think is massless) curve space-time too in the same way? (c) it seems to me that everything which exists alterates space-time in some way... if we can calculate the space-time metric starting from the properties of an object, can we deduce the properties of an object knowing the metric of the region of space-time it occupies? (d) is it legitimate to suppose a complete identity between objects and the regions of space-times they occupy? (e) if I remove all the objects in the universe, does space-time continue to exist? (f) what is exactly a "frame of reference"??

(2) I read about time dilation, lenght contraction and mass increase. I imagine a spaceship, 1 km long say, which is traveling at a speed where relativistic effects are manifest. (a) why does time slow down in the spaceship? (b) the lenght contraction of the spaceship is a "real" phenomenon (the ship is really shorter while traveling than when it was orbiting around Earth) or simply an optical effect seen by an observer outside (of the frame of reference) the ship?

(3) Consider again the starship above and suppose that there are two men, one in the bow of the ship and one in the stern of the ship. They both have a nuclear clock (that's to say a really precise clock) which have been perfectly synchronized (if it is possible). (a) Will they find a difference of time between them (though a small one) after a certain period of time though they are on the same spaceship? (b) is there a formula to calculate this difference of time? ('cause I would like to make some calculations on different scenarios)

(4) I read that relativistic effects become significat only near the speed of light. This means that there are relativistic effects at any speed but they are irrelevant and/or undetectable or that they just don't happen (don't exist) below certain speeds? I was thinking about the most stupid experiment in history: suppose we have a huge platform, 100,000 km long (or more if needed) and 20,000 km wide, with a mass of 1,000 kg. At each of the two ends of the platform we put a clock capable of measuring even the smallest interval of time (Planck time I think). The platform is stationary in space. (a) After a period of time (arbitrarily long), am I going to detect a tiny, infinitesimal difference in the time measured by the two clocks? (b) if so, which is the formula I might use to calculate that difference?

I know I am really stupid and ignorant, and I apologize if I'm wasting your time with these questions which are probably really trivial for you... but, as I told you, I am 13 and since I know nothing about physics I thought to ask here instead of killing my curiosity. I also apologize for my terrible English... I'm from Switzerland :)

Thanks for having had the patience to read my silly questions and thanks in advance to those who will have the kindness to descend to my level and help me understand. Thank you very much!

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# Doubts of a 13 years old boy about simultaneity, time dilation, spacetime behavior

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