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Homework Help: Theory of special relativity (conceptual problems)

  1. Dec 3, 2007 #1
    [SOLVED] theory of special relativity (conceptual problems)

    hi all, i've got a few physics questions for you to put some thought into and perhaps to share some expertise with me also...

    i'm currently studying about the special theory of relativity and i've got a few conceptual questions that i need help in clarifying on. i'll post the question and give MY answer (of what i have so far) and please correct if i'm wrong or suggest a more suitable answer. thank you.

    question 1: does the earth really go around the sun? or is it also valid to say that the sun goes around the earth? discuss in view of the first principle of relativity (that there is no best reference frame). explain.

    my answer:yes, the earth orbits around the sun. this is because if we were to be an observer in the distant space looking at the solar system, we would need to have one rocket on (either the right or the left) so that we spin in a circle and thus, would actually witness the earth move around the sun.

    question 2:does time dilation mean that time actually passes more slowly in moving frame of references or that it only seems to pass more slowly?

    my answer:i am not sure of this answer... but i think yes, time really does pass more slowly because the clock loses "ticks" ?? doesn't the twin paradox support this answer?? or am i getting confused?

    question 3:can a particle of nonzero rest mass attain the speed of light?

    my answer:truely i say, i do not have a clue for this one. what does "nonzero rest mass" mean, explicitly? is it somehow related to m = m rest/ (squareroot) 1 - v(squared)/c (squared)???

    question 4:is our intuitive notion that velocities simply add completely wrong?

    my answer:unfortunately i have no idea for this question either... my thought is, however, no, adding velocities is not completely wrong. but i haven't the clue as to why or even how to explain it.

    and yes, those are my 4 questions and answers "so far". any help, insights and/or suggestions would be greatly appreciated! thanks.

  2. jcsd
  3. Dec 3, 2007 #2


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    1. I don't think this can be answered in the context of special relativity since, in the scenario of the earth moving around the sun, the earth frame is not inertial.

    2. Well, what do you know about time dilation? Is it something that is inherently true to one's own clock, or is it a relative phenomenon?

    3. Nonzero simply means not zero; so the questions could be rephrased as "can a particle whose mass is not zero travel at the speed of light?"

    4. Try this website for some info on this question.
  4. Dec 3, 2007 #3
    thank you for that.

    1. that is what i was thinking too, prior to what i wrote above. however, is is really impossible to answer this question in context of the theory of special relativity? are you sure?

    2. i know much about time dilation (and that time in general is all relative, there is no absolute time). i've done some research on the net and quite frankly, i've read people who've written that one's own clock actually does slow down and still others who wrote that it is a relative phenomenon. i am stumped, but i know one thing, the functioning and slowing down of the motion of a clock is not true. but i do not know where to go from here.

    3. well, since you put it that way, yes, can't it? a non zero net force can travel at the speed of light if there was an infinite amount of energy right? clarification needed :)

    4. thanks for the site. i'll read it.
  5. Dec 4, 2007 #4


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    Well, str only says that inertial frames are equivalent. Since the earth frame is not inertial, then this implies that, in the context of str, the earth is rotating around the sun.

    Ok, if you were moving at some proportion of the speed of light, would you notice your own clock slowing (i.e. would your proper time change) or would only observers notice your coordinate time to change?

    But there's no such thing as an infinite amount of energy. No, massive bodies cannot travel at the speed of light. Only particles with zero rest mass can (and always must) travel at the speed of light.
    You're welcome.
  6. Dec 10, 2007 #5
    thanks again, problems solved. i've asked others too and i've finally gotten all the clarification and answers i $needed to answer those 4 questions.

    thread is now closed: problem solved.
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