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What is the simplest way to explain general and/or special relativity?

  1. Nov 21, 2013 #1
    Recently (or a few weeks ago), I've started to take interest in the idea of relativity but after watching many videos and reading a couple of websites, I still don't think that I really understand it. I'm probably not suppose to understand it (or at least not yet) considering that I'm still very young and need a lot of time and dedication (and also be good with numbers) to understand it at least partially. I already know a few things about it such as that Lorentz ether theory (I think) had something to do with it in 1895 (which perhaps Einstein later build more upon it which I think I saw it on a video once, but I'm probably wrong), and I also think that it has another connection with Galilean invariance (which I know almost nothing about), I know that the only way for Einstein to prove this theory was to wait many years for a solar eclipse (which took him many tries too), I know that it proposes that space bends around mass (or gravity I suppose) and that it connects space and time (neither would make sense without the other before the big bang), and I also know that special relativity only applies to objects moving at a constant speed (nothing in the universe moves at a constant speed which is why Einstein had to come up with GR), and lastly, I know that time moves slower the closer you get to the speed of light and moves backwards when you go beyond the speed of light (which is impossible and I don't understand why that would happen too). I'm not sure if any of these assumptions are correct (perhaps you can correct me) but the main reason I created this thread was to hopefully read a simple explanation of both theories (to a certain degree at least), I realize this might be hard to answer accurately without getting complicated or technical, but consider it a challenge :tongue:
    And also, try not to use "big" words please :)
     
  2. jcsd
  3. Nov 21, 2013 #2
    I don't want to give a douchy reply here, but wouldn't it be better to take a good book on relativity and actually read it? You'll learn what it is about that way. If we give an explanation here, then you won't know what it's about at all, you'll just know some fancy words.
     
  4. Nov 21, 2013 #3
    This video explains it pretty well imo:
     
    Last edited by a moderator: Sep 25, 2014
  5. Nov 21, 2013 #4

    WannabeNewton

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    Also, what does age have to do with any of this?
     
  6. Nov 21, 2013 #5
    Well, I'm assuming that I'm inexperienced in this field of science since I'm young and have NOT yet acquired enough experience to know more about the subject, and perhaps when I'm older, I will have acquired more time to invest into studying this subject...
     
  7. Nov 21, 2013 #6

    ghwellsjr

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    You do have some misunderstandings.

    First, Einstein's theory of Special Relativity (SR) is simple, he said so himself in his 1905 paper but his theory of General Relativity (GR) is not simple and you cannot really understand it without learning some very complicated math which is why I have never bothered to master it. But I can help you with SR.

    Second, the difference between SR and GR is that SR cannot handle gravity which of course means that we use examples or scenarios where the effects of gravity are small or where we can pretend that it doesn't exist.

    I would say that the easiest way to understand SR is to construct an Inertial Reference Frame (IRF) and limit yourself to objects that move along a single line, towards or away from each other or remain at constant distances. Then learn how to apply a simplified version of the Lorentz Transformation (LT) process where the speed of light, c, is defined to be 1. Then draw a spacetime diagram of whatever scenario you want to consider, keeping in mind that the clocks moving in the IRF will be Time Dilated by the factor gamma. Show the progress of these clocks with dots spaced farther apart than the Coordinate Time of the IRF. Next, use the LT to transform the scenario into a new IRF moving at some constant speed with relation to the original one and draw a new diagram.

    I have made many such diagrams. Do a search on "diagram" with my name and you'll get lots of help. And if you want to propose a new scenario, I'll draw the diagrams for you.
     
  8. Nov 21, 2013 #7
    Well, like I mentioned before, I did read a couple of articles about it and watched many videos about it, but I had many questions and since I can not directly interact with said article or video, I must post my questions somewhere where I can directly ask questions and get their answers quickly, much like this thread, don't you think?
     
    Last edited: Nov 21, 2013
  9. Nov 21, 2013 #8
    I understand. And asking questions is a very good thing. But you're asking us to explain a very complicated theory in just a couple of lines and without using advanced math. Such a thing is impossible to do, and any explanation we do give will be wrong.

    I don't really agree with the age thing. I don't think age should stop you from understanding relativity. Sure, it might take a long time before you really grasp it. But don't limit yourself to youtube videos and forum posts at this stage. Get some actual physics/math books and start working through them. That's the only way to truly grasp the beautiful theory of relativity.

    Do you know some classical mechanics? Calculus? Linear algebra?
     
  10. Nov 21, 2013 #9
    Just a couple of things.
    Relativity is not just about objects with constant speed (inertial motion) but covers acceleration too as long as the acceleration is not due to gravity. GR extends SR to include the effects of gravity. It is worth knowing at an early stage that the instantaneous time dilation in SR is always due to the instantaneous velocity and never directly due to non-gravitational acceleration.

    The rate of time of an object that is moving relative to you is slower relative to your own time, but you never notice time slowing down for yourself. If you use the time dilation equation of SR and insert a value for a velocity that is greater than the speed of light, the result is an imaginary number, not a negative number. That is academic anyway, because no object travelling at less than speed of light relative to you can be accelerated to a speed greater than the speed of light, because that would require infinite energy to achieve.
     
    Last edited: Nov 21, 2013
  11. Nov 21, 2013 #10

    Nugatory

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    You have to have special relativity down cold before you can go anywhere near general relativity.

    The best way to learn special relativity is to start with a first-year college level mechanics textbook that has a chapter or so on SR, something along the lines of "An Introduction to Mechanics" by Kleppner and Kolenkow. (There's nothing magic abut that one, just so happens that I learned from it so I know it works).
     
    Last edited: Nov 21, 2013
  12. Nov 21, 2013 #11

    WannabeNewton

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    Well "young" is a very ambiguous qualifier. I wouldn't consider myself too young to learn GR but I also wouldn't consider myself old enough to do my own taxes. To a reasonable extent, age shouldn't be a factor in when and how you learn a subject.
     
  13. Nov 21, 2013 #12

    Nugatory

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    There's no such thing as "too young". It's more a matter of when you start learning, as it takes some amount of time to pick up the necessary mathematical background.

    If we were to start the clock ticking when you first encounter elementary algebra, another year or so will give you enough math to understand SR (calculus is nice, but only required if you're going to move forward from there). General relativity, on the other hand, needs easily another five years or so more of math.
     
  14. Nov 21, 2013 #13

    pervect

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    I would say that you can understand SR much earlier than GR, and it' a prerequisite, so start on SR first. The simplest approach to SR can be understood with nothing more than high school algebra. I would recomend the k-calculus approach, used by Bondi in "Relativity and Common Sense", and a similar more recent book by Mermin whose name I forget (I haven't read it either it's name should be on the forums).

    In spite of the name , k-calculus doens't actually involve calculus.

    If you want to move onto GR at some point, I would reccomend a 4-vector approach to SR (such as Taylor & Wheler, Spacetime Physics). I'm not sure it's much "harder" than the k-calculus approach, but it's more abstract.

    I'd generally say the k-calculus approach is late high school, the 4-vector approach is early college, so there's not really a huge difference between them.
     
  15. Nov 21, 2013 #14
    The worst thing you can do is convince yourself that you can't do something. It's perfectly possible for you to master the math necessary for GR regardless of your age so long as you have the necessary materials and determination to succeed.

    EDIT: I realize how incredibly lame this sounds, but it's true.
     
  16. Nov 21, 2013 #15
    That was actually pretty helpful, thanks for sharing :)
    I think this was the answer I was looking for, a simple explanation of time dilation, bending of space (although little of it was mentioned in the video), how spacetime reacts when reaching the speed of light, etc.
     
    Last edited by a moderator: Sep 25, 2014
  17. Nov 21, 2013 #16
    Well... if I master the math behind GR, then I'll become the next Einstein, wouldn't I? (and we all know what's the likelihood of that happening) Because, he is only the man that truly understands this theory
    And also, why do we still call it a 'theory'? hasn't it been proven and accepted already for many decades?
     
  18. Nov 21, 2013 #17
    The only way to fail for sure is to never even try. Don't deify Einstein. At the end of the day he was human like everyone else and you can definitely understand GR if you put in the effort.
     
  19. Nov 21, 2013 #18
    Yes but lets be realistic here, also, many people say that Einstein's brain was in some ways much more superior to an average brain of people his age when they studied his brain. There are only a few people that have ever lived that ever truly advanced science & math (obviously such as Einstein, Newton, Archimedes, etc.), so the probability of me reaching the same level is well... very low, so low that me and many others consider it a waste of time and resources to attempt to reach such a level, I know it sounds somewhat depressing but that's how life works, but this is way off topic. Anyways, I think I have the gist of it without getting too technical into the subject
     
  20. Nov 22, 2013 #19

    pervect

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    There are lots of good GR texts out there, some at an undergraduate level. Do do yourself a favor and learn SR first, before attempting GR.

    A lot of mystique still clings to Einstein, and to GR, but the subject is not only becoming widely understood, a certain level of understanding of GR is becoming widely necessary, due to recent advances in precision timekeeping.

    Thinking you need a special super-brain like Einstein's is alleged to have been (whether that's true or not is outside my field) to have some understanding of GR is simply not true.
     
  21. Nov 22, 2013 #20

    Bandersnatch

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    You might have needed to be a genius to invent GR, but you don't need to be one to learn it. Thousands, if not millions, of students do it every year.

    And it's called a theory precisely because it is so solid. The usage of the term in colloquial speech differs diametrically from the meaning it has in academia. If you hear something being called a theory in scientific context, it means it has been tested and showed to produce accurate predictions.
    The confusion with the meaning of the word often creeps into popular media, usually re. the theory of evolution('it's only a theory!'). Somehow it never happens to the theory of gravity.
     
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