Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Am I wrong to think this?

  1. Jul 24, 2011 #1
    statement 1
    I don't know whole mathematics of theory of relativity and general relativity.

    statement 2
    yet I feel comfortable to imagine how these theory works in nature.

    am i wrong to think this? is it wrong to claim to know theory without understanding the
    whole mathematics ?
  2. jcsd
  3. Jul 24, 2011 #2
    what things?
  4. Jul 24, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor

    That isn't what your statement said. You said you feel comfotable which is completely different to claiming to know. It is wrong to claim to know a theory without fully understanding it unless you qualify your level of knowledge. I.e. "Whilst I am not an expert/Whilst I don't have a complete understanding I believe your question can be answered by..."
  5. Jul 24, 2011 #4
    nice change of wording before it's edited out. But, you should have changed these to this.
  6. Jul 24, 2011 #5
    thanks for reply. i was just sharing because if i said , i can imagine how the theory of relativity and general relativity works, without knowing much mathematics, they would say me a budding crackpot. is this kind of feeling a sighn of crackpot.
  7. Jul 24, 2011 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    As long as you understand and explain the limit's of your knowledge you will be fine. Obviously the more you learn the better your future answers will be. Crackpots are different, they hold strong belief about a topic that is counter to their peers and consensus with little/no/flawed evidence. This is typically backed up with ad-hoc arguments where they make up excuse after excuse to maintain their belief e.g

    Crackpot - the apollo missions were fake!
    Astronaut - what about all the engineers who built the rocket?
    Crackpot - they're part of the cover up!
    Astronaut - what about the equipment left on the moon?
    Crackpot - all lies!
    Astronaut - I've been to the moon
    Crackpot - :bugeye: YOU'RE PART OF THE CONSPIRACY!!!
  8. Jul 24, 2011 #7
    The theory of relativity is based on three postulates, none of which is hard to understand, although one is hard to believe. These are:

    1. The laws of physics are the same to all inertial observers (easy to understand and believe.)
    2. The speed of light in a vacuum is the same to all inertial observers (easy to understand, hard to believe.)
    3. The local effects of accelleration are the same as the local effects of gravity. (easy to understand and believe).

    Some of the consequences of these postulates are also hard to believe. For instance, the relativity of time and space, which should be expected given postulate 2. But the bottom line is that you don't need any math at all to understand the theory.
  9. Jul 24, 2011 #8
    So, how does one go from these postulates to 'mass curves spacetime'?
  10. Jul 24, 2011 #9
    Do you want the non-mathematical explaination, or the mathematical one?
  11. Jul 24, 2011 #10
    Actually, since there are only two possible answers to that question, I'll answer both. Since the math explaination goes beyond what the OP is looking for, I won't give it. It can be found in any good book on the general theory such as Schutz, Wald, or Carroll, though there are many others. As for the non-mathematical explanation, I take this from Briane Greene's "The Elegant Universe", Although it is known to be a flawed argument, I think it is a good heuristic explanation.

    On a spinning disk, the tangential lines are foreshortened because of the special theory, but the radial lines are not. In other words, the accelleration of the disk causes the circumference to be shorter than 2 pi times the radius. Thus space is not flat. By the third postulate, mass causes the same effect.
    Last edited: Jul 24, 2011
  12. Jul 25, 2011 #11
    Interesting. You develop a theory on a flawed argument.
  13. Jul 25, 2011 #12


    User Avatar
    Gold Member

    The word "know" is a loaded term in this case. Everyone has some intuition and can probably say they "know" classical mechanics because the basics behind the idea are easily understood. However, if I were to ask the lay person to calculate the deflection angle of a comet passing the Sun given some impact parameter, they wouldn't know where to begin. Same can be said for relativity. A lot of people can have an understanding on kinda how everything works, but the details are way beyond them.

    For example, I "know" about musical theory in that I understand kinda how the theory works and feel comfortable about it without every really sitting down and actually DOING any musical theory. The ideas make sense; doing it on the other hand is where all the work and brainpower actually come in.

    This is the problem with analogies is that they're always flawed in some way. The only proper explanation to general relativity is general relativity itself.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook