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How to explain Einstein's Special theory of Relativity.

  1. Oct 28, 2012 #1
    Can someone help me with understanding and explaining the Special theory of relativity.

    I know the basics (time dilation, the speed of light, ect), just what's left is Lorentz transformation and I'll understand the theory.

    And also help with explaining the theory to a friend.

    And help is appreciated.
  2. jcsd
  3. Oct 28, 2012 #2
    I am no expert and I am sure some here may be able to explain clearer...

    The Lorentz transform is used to relate co-ordinates of one frame of reference K to another frame of reference that is moving with uniform motion relative to K. It was conceived by Einstein to explain the proven fact that velocity of light is constant to all frames regardless of thier motion or the motion of the source of light.

    Previously the principle of relativity could not account for this. The lorentz transform basically does away with the concept of absoloute time and absoloute space. Space and time will change in just the right way to allow any observer in any reference frame to measure the speed of light to be c.
    Last edited: Oct 28, 2012
  4. Oct 28, 2012 #3


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    Staff: Mentor

    You can help us by asking specific questions.
  5. Oct 28, 2012 #4
    I asked two questions, being; can someone help me understand the theory, and how would I explain this theory to another person.

  6. Oct 28, 2012 #5

    Doc Al

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    Staff: Mentor

    Not really. Those are pretty broad questions! Usually answered in book form. Try to ask more narrowly focused questions.

    You did ask about the Lorentz Transformation, which is specific enough to get a handle on. Here's a place to start: Lorentz Transformation
  7. Oct 28, 2012 #6
    I dont mind getting a long answer, I'd prefer it.
  8. Oct 28, 2012 #7


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    Gold Member

    You might like to read ZapperZ's blog entry https://www.physicsforums.com/blog.php?b=3588 [Broken] for some advice on how to better phrase your question.
    Last edited by a moderator: May 6, 2017
  9. Oct 29, 2012 #8
    Last edited by a moderator: May 6, 2017
  10. Oct 29, 2012 #9


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    Staff: Mentor

    Because it is rude to ask people to write you a book when you could just go find one yourself! It also shows a lack of effort which will make it hard for you to learn.
  11. Oct 29, 2012 #10


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    Staff: Mentor

    The Lorentz transformation is used to derive time dilation, length contraction, and the like; so if "what's left" is the Lorentz transformations, then in fact you haven't even started yet.

    But because you're asking where to get started.... You might try this thread https://www.physicsforums.com/showthread.php?t=628574&highlight=self-study and my post #6 in it.
  12. Oct 29, 2012 #11
    Lochlan, I've been disappointed in some of the responses to your inquiry. It's quite reasonable for someone who has a passion for probing the mysteries of relativity to seek help on a forum like this, even for someone who may not have too much of a background in math or physics.

    It is not easy for us forum members with experience in the subject to provide an explanation of the basic ideas in a way that is easy to grasp. Trying to describe the Lorentz transformations is one way. Another would be to try to tell the story with pictures. We never know to begin with which approach is the more fruitful for a given individual.

    I will try to describe special relativity using pictures, but it will take a while. After putting something together I'll get back to you here if I think the approach has a chance of working for you. But of course, Nugatory has pointed you to some good posts.

    [Edit] Looks like you won't need my help. Check out the links just provided in this more recent thread:

    Last edited: Oct 29, 2012
  13. Oct 29, 2012 #12
    Hi Lochian,

    You may be surprised by some of the answers; let me try to explain why you didn't get a simple three-sentence answer.

    For explanations of how to calculate, you received links to explanations, including one with nice illustrations and animations.
    Apart of that, regretfully, different people understand the theory differently. Of course, everyone who knows SR, agrees on what it predicts; and making correct predictions is what it was meant to do. But even not everyone who knows how to calculate it, also has the feeling to really understand it. Even Feynman had problems to understand a prediction about an accelerating rocket that he correctly calculated!
  14. Oct 30, 2012 #13
    What makes you people so unhappy?
    I'm just asking for someone to explain to me the aspects of the theory (i.e Maxwell's, time dilation, length contraction).
  15. Oct 30, 2012 #14
    I dunno about the other people, but I am happy! :smile:
    And you received the explanations that you asked for (they are in the links, with nice illustrations* and animations by Fowler), but you do not sound happy. :confused:

    * the illustrations start here: http://galileoandeinstein.physics.virginia.edu/lectures/srelwhat.html
  16. Oct 30, 2012 #15
    No I just don't understand how other people cannot understand what I meant when I wrote it, but thank you.
  17. Oct 30, 2012 #16
    You're welcome!
    Perhaps what you really want is some more explanations about deriving the Lorentz transformations; if so, just ask; we can give you links to past discussions with detailed explanations. :smile:

    PS for example: https://www.physicsforums.com/showthread.php?t=478252
    Last edited: Oct 30, 2012
  18. Oct 30, 2012 #17
    hi lochlan
    i don't know much about the math involved in deriving lorentz transformation from SR or deriving length contraction and time dilation but if it help the following paragraphs are my basic understanding of the topic under discussion
    Before SR the entire laws of Physics were Govern by Gallelian Transformation, which is nothing but our basic intuitive knowledge that space and time are absolute. Or in a more simplified manner it is like this, you measured the length of your study table to be say 2.5m and someone say an astronaut travelling at around thousand km/h measures it, it will still be 2.5m. In fact any one in the Universe measures it, it will be 2.5m. This is so evident in our day to day lives that physicist before SR had taken it to be for granted.Even Newtons laws are base on this.
    But when Maxwell started his electrodynamic experiment, he found an anomaly in the Gallelian transformation itself. Physicist of his time had this view that it was Maxwell's electromagnetic theory at fault rather than Gallelian transformation , in which they have a firm believe. They tried to disprove Maxwell's theory only to find Gallelian transformation as the Culprit. Since the entire Laws of physics untill their time were build upon Gallelian transformation, the physicist were plunge into a dark abyss with this BIG QUESTION; ARE ALL LAWS OF PHYSICS INVALID.
    The answer to this question was given by a young fellow name "Einstein" who proposed that there was nothing wrong with the laws of physics(1st postulate), the only thing that was wrong was our perception of absolute space and time (Gallelian transformation) and it must be changed to Lorentz transformation( as a side note lorentz had already introduced a transformation according to which there won't be any anomaly in the electrodynamic experiment but couldn't prove) which Einstein proved using his second postulate.
    So this time, according to SR the length of your table that you measured and that measured by some astronaut moving thousands of km/h w.r.t the table will be different i.e THE MEASUREMENT OF SPACE, TIME ARE RELATIVE. The only thing that is constant is the speed of light which is the basis for such relative measurement of space and time.:smile:
  19. Oct 30, 2012 #18


    Staff: Mentor

    Explaning that in general is well beyond the scope of a forum post; as others have said, it requires a book, or something of similar length. That's why you have not been getting much of a response.

    For the basics of SR, I recommend Taylor & Wheeler's Spacetime Physics. The first few chapters are available online:


    This should give you a start. It should also help you to formulate more specific questions that are more suitable for answering in a forum like this.

    Another thing you could try is to come up with a specific, simple scenario that illustrates the things you are interested in knowing about. It's a lot easier for us here to respond to specific scenarios than general questions like those you've asked; the latter are too open-ended.

    [Edit:] One other good resource online is the Usenet Physics FAQ:


    Some of the pages there on relativity questions may also help you to formulate more specific scenarios that you can ask about.
  20. Oct 30, 2012 #19
    Well, maybe I'll give the picture approach a try here. I'm afraid it will get lengthy and annoy some folks with the amount of space taken up by sketches. Maybe we can break it up into a sequence of posts.

    Here's part 1. For this approach it is critical that you initially try to wrap your head around the concept of a 4-dimensional universe. In some sense all observers move at the speed of light straight into the 4th dimension. So, I start with this picture of a piece of the 4-dimensional world showing a rendition by Paul Davies:
    To further think through the 4 dimension concept, consider sketch A below. We start with a 3-dimensional beam, then see if we can focus on just one surface of the beam at a time. You can build a picture of a 3-D beam by starting with any one of the surfaces and then extrude it into the direction perpendicular to the starting surface. In sketch B we similarly build a 4-dimensional beam by starting with a 3-D beam and then extruding it into the 4th dimension. The only trouble is that we can't show all 4 dimensions in a sketch, so we just show X1 and X2 and indicate an extrusion along the 4th dimension, X4.
    (...continued in part 2)
  21. Oct 30, 2012 #20
    Part 2. I will try taking a giant step here. We can insert more background and detail if needed. We have constructed a 4-dimensional beam. Now we describe a situation with two observers (two physicists studying special relativity effects) one guy at rest in the black inertial frame of reference below and another guy moving at relativistic speed along black's X1 axis. Blue is actually at rest in the blue inertial frame. The blue guy carries along the 3-dimensional beam as he moves along the black X1. But, actually, since all objects are 4-dimensional (including the bodies of the observers), there is actually no motion at all in the 4-dimensional world--only the consciousnesses move at the speed of light along the 4th dimension world lines.

    Here is the whole point of insisting you wrap your head around the concept of a 4-dimensional universe: When the black guy gets the impression that the 3-D beam is moving along his X1 axis at relativistic speed, it's just because the beam is really a 4-dimensional object and that object is slanted relative to black's vertical X4 axis.

    Now, the big clincher for understanding special relativity is catching on to a very strange and mysterious thing that nature does for an observer whose X4 axis is slanted, i.e., the blue X4 axis in our example: Nature somehow rotates the blue X1 axis such that a 45-degree line always bisects the angle between the blue X4 and X1 axis--no matter what the angle of blue X4 is. And of course that same 45-degree line bisects the black X4 - X1 angle as well. And guess what--that 45-degree line is the world line of a photon. The 4-dimensional photon particle is always oriented as a straight line bisecting X4 - X1 angles for all inertial frames of reference. More on that later.



    (end Part 2)
    Last edited: Oct 30, 2012
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