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Silly doubt on relativity

  1. Nov 12, 2011 #1
    Hello ,

    I have this question in my mind from long time. There are two travelers in two trains and one observer on ground(Stationary). One train is travelling at 99.99% speed of light and another train is travelling at speed of light . My question is that the person who is at light speed train what he is going to see ? How they are all going to see each other?

    (sorry my English is not very good)

    Regards,
    Asutosh
     
  2. jcsd
  3. Nov 12, 2011 #2

    Integral

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    Massive objects cannot travel at c. Your question has no answer.
     
  4. Nov 12, 2011 #3
    Assume that the massive objects are travelling at c.
     
  5. Nov 12, 2011 #4

    Integral

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    Non physical assumptions lead to nonsense results.
     
  6. Nov 12, 2011 #5

    bapowell

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    This assumption simply cannot be made within the framework of special relativity.
     
  7. Nov 12, 2011 #6
    Alright instead of train make it as space shuttle which can travel @ c.
     
  8. Nov 12, 2011 #7

    bapowell

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    Are you serious? Aren't space shuttles massive objects?
     
  9. Nov 12, 2011 #8

    Ryan_m_b

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    Objects with mass cannot travel at c. It is physically impossible, you might as well be asking how many corners a square circle has.
     
    Last edited: Nov 14, 2011
  10. Nov 12, 2011 #9
    because we living in type0 civilization.
     
  11. Nov 12, 2011 #10
    The civilization I live in makes sense, perhaps you live in a different one.
     
  12. Nov 12, 2011 #11

    bapowell

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    I don't know...have you heard Rick Perry speak lately? :tongue2:
     
  13. Nov 12, 2011 #12

    Fredrik

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    The problem with your original question isn't that trains are much slower than space shuttles. The problem is that you asked us to make an assumption that's logically inconsistent with special relativity. The assumptions of SR don't contradict each other, but they imply that massive particles have speeds <c in inertial frames. So when you asked us to assume that a massive object moves at c, you asked us to contradict the theory we were going to use to answer the question.
     
    Last edited: Nov 12, 2011
  14. Nov 12, 2011 #13

    Ryan_m_b

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    Unless you have a type∞ civilisation it's not going to happen :rolleyes: it takes infinite energy or infinite time to accelerate an object with mass to c. Therefore it isn't possible.
     
  15. Nov 14, 2011 #14
    Ok cool denge!
     
  16. Nov 14, 2011 #15
    I have a question myself...

    I've read a lot of threads where people ask questions about "what would happen..." when some mass/observer is "moving at c".

    Why is it that responders pretend to act dumb and pretend that they don't understand the question, saying there is no answer, saying it is a non-physical assumption, does not compute... etc?

    These responders know good and well that the uninitiated are asking a perfectly good question, but making a tiny error in their question's rigor when saying "going at c" rather than saying "approaching c", "almost c", "very close to c", "near c", or "99.99999998% of c"...

    It only takes an additional phrase in the answer to clarify that "at c" is not possible for masses, but "as close to c as you want to get without getting there" is possible for thought experiments. Then the examination of the adjusted question may be considered physically/mathematically.

    Why the snub rudeness to people that don't indicate they know the special insider way to properly phrase high speed mass questions concerning light dynamics?

    If this was being done nicely to lead the questioner to the appropriate way to reform the question with alignment to rigor as in the Socratic method that would be fine, but the way people just drop the obtuse one liners and act like they don't have a clue as to what the question pertains just seems obnoxious.

    When someone makes the "mass going at c" mistake, why not immediately suggest an adjustment to the thought experimental conditions to correct the lack of rigor and proceed, rather than snubbing the questioner with terse "pretended ignorance"?
     
  17. Nov 14, 2011 #16

    Ryan_m_b

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    You are assuming that the OPs of these questions are simply using "at c" by mistake and really want to ask about "near c". In my experience this is not the case, rather such threads are down to a misunderstanding that travelling at c for a massive object is down to what is possible and not because we simply don't know how.
     
  18. Nov 14, 2011 #17

    bapowell

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    Agreed. So, why didn't you do this rather than spending your whole post lecturing the rest of us here for being dumb and insensitive to the OP?
     
  19. Nov 14, 2011 #18
    "...travelling at c for a massive object is down to what is possible..."

    That phrases has no meaning to me.
     
  20. Nov 14, 2011 #19

    Ryan_m_b

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    What I mean is that in my experience the OP is of the understanding that the reason science says "nothing can travel at c" is down to our not being able to figure out how to do it yet. This is a common, but incorrect, understanding hence why I said it was a misunderstanding because most of the time OPs don't realise that it is physically not possible.
     
  21. Nov 14, 2011 #20
    Don't you see that I did do just that? The correction is inherent within the criticism. Perhaps the OP now knows how to ask the question in a way that will attract polite and thoughtful answers? And perhaps those answering now have a nice technique with which to address questions that are flawed by lack of rigor?
     
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