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Universal Quantum Terms

  1. Jan 14, 2009 #1
    Ok, I am not the best man at math but would like to understand the principles behind these sciences. However these terms are really messing me up. Please someone out there help.

    1.) Is there a difference between Quantum theory and Quantum Physics

    2.) What is the difference between Quantum Field Theory and Unified Field Theory

    3.) How do Unified Field Theory and String Theory fit together.

    I will love whoever responds to this with great answers. Thanks for your time and help. My mind is jumbled and I would love to get this slipknot lose.
  2. jcsd
  3. Jan 14, 2009 #2


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    Welcome to PF!

    Hi redhedkangaro ! Welcome to PF! :smile:
    Same thing.

    And Quantum Field Theory is a particular mathematical treatment of them.
    There are Quantum Field Theories for different forces, or combinations of forces.

    Unified Field Theory (when it's discovered! :rolleyes:) will be a Quantum Field Theory for all forces, including gravity.
    String Theory is a particular mathematical treatment of Quantum Physics.

    The principal similarity between Unified Field Theory and String Theory is that nobody's got either of them to work yet. :biggrin:
  4. Jan 14, 2009 #3
    Awesome thanks a bunch but as for my 3rd question I mean do these two theories interacti with each other. I mean I am seeing parts from books saying that string theory is a candadite for Unified Field theory, but how does that work if it has do do with strings rather than the field where the particles are created.
  5. Jan 16, 2009 #4

    String theory is a theory to unify the 3 theories describing the 3 forces

    Its not about the field that the particles are created, its about what each and every single particle in existance is made of. The strings are the particles.

    As i understand it, and very basically, with String theory there has been some success calculating the atomic, electromagnetic and gravity forces with the same formula.

    String theory is saying that all the fundamental particles are made from vibrating strings and as such since they are all the same in a way, calculations can be made tying them all together.

    This apparently works by seeing that every fundamental particles is made from a variety of pure energy strings, which are vibating forms of energy that vibrate uniquely through a series of extra dimensions that exist in every point of space.

    It just needs a little something to make it all work perfectly, problem is no one yet knows what that little something is.

    anyway, thats it very basically, hope that helps
    Last edited: Jan 16, 2009
  6. Jan 16, 2009 #5


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    Hi redhedkangaro! Thanks for your PM:
    No, there is no Quantum field …

    Quantum field theory is the mathematical method that represents every particle by a combination of creation and annihilation operators of that particle … that combination is the "field" for that particle.

    In other words, "field" (in this context) is not the name for the background through which particles move (it is not like an electromagnetic field, for example), it is the name for the particles themselves.

    "string" similarly is the name for a particle (in a different mathematical treatment). :smile:
    I'm not sure that people do use the word "really" … string theory is a mathematical theory, and i don't think it's relevant to the mathematics whether particles "really" are this or that.

    And sorry, I have no idea what you mean by "a unified field of intelligence". :redface:
  7. Jan 17, 2009 #6


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    Hi redhedkangaro! Thanks for your PM. :smile:

    (why do you keep pm'ing? :confused: i do get email notifications of any new post in any thread i've contributed to … so it's much easier if you just reply on the thread :wink:)
    No …

    A quantum wave function is the ordinary distribution function of a particle in "classical quantum" theory.

    A quantum field, in quantum field theory, is the combination of creation and annihilation operators of that particle which represents that particle.

    It looks almost exactly like the wave function, except of course that it's made of operators. :smile:
  8. Jan 17, 2009 #7
    Ok Sounds simple. Haha Im really just confused. Ive read some books on quantum field theory and they seem to say different things. In one book ,a physicist said something like this, " blah blah quantum wave function (quantum field) blah blah" implying that it was the same thing. Another physicist said the quantum field is where all forces and particles are created. So my mind is jumbled. Maybe you can help clear things tim. What exactly are the operators of the Quantum Field?
  9. Jan 17, 2009 #8
    I also wanted to know if my understanding of this was right

    Quantum Theory( the same as quantum mechanics and quantum physics) was combined with eisteins special relativity to produce a relativistic quantum theory. And the only successfull one is the quantum field theory. Once it is found out how gravity fits in then quantum field theory will become a uinified fied theory. Am I correct?
  10. Jan 17, 2009 #9


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    A creation operator for, say, an electron is the operator which adds an electron of a particular state (state means all defining things such as spin, momentum, orbtial angular momentum, etc) to whatever is already there.

    So there's a different operator for each state.

    Similarly, an annihilation operator removes one electron of a particular state from what is already there.

    If C and A are creation and annihilation operators, then CA - AC is a number (strictly, a multiple of the identity operator), wchh is how th fields (which are operators) get turned into probability distributions (which are numbers). :wink:

    Since you're interested, try one of the free books on Quantum Field Theory listed and linked at http://freescience.info/Physics.php?id=95 :smile:
    Yes … as Weinberg, for example, points out, special relativity (and particularly the inability of space-like-separated events to affect each other) plus the "cluster decomposition principle" imply a quantum field theory.
    I think so. :smile:
  11. Jan 17, 2009 #10
    Ok, and these probability waves then become actual locations for things?
  12. Jan 17, 2009 #11


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    uhh? how can a probability be a location? :confused:

    probability means what it says
  13. Jan 17, 2009 #12
    Haha sorry. dumb question anyway. Do you know what these particles have to do with space and time. In other words, is this "Quantum Field" within space and time. And thanks for the link to the books
  14. Jan 17, 2009 #13
    Also from my understanding now, the intereactions of particles create these fields, which inturn give rise to other types of particles and forces in nature, or am I still lost?
  15. Jan 18, 2009 #14


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    Just got up … :zzz:

    Good morning! :smile:
    erm … as I said before, there is no Quantum field …

    there is a field for each particle …

    particles exist within space and time (where else could they be? :confused:)
    Particles and forces are fields (in Quantum field theory).

    And fields interact (it's what fields do! :wink:)
  16. Jan 18, 2009 #15
    Tim you are seriously the man.

    Cool and in string theory these particles or strings, are no longer point like objects but strings which exists from 10-26 dimensions of space time.

    So these forces and particles are fields themselves. The thing thats hard for me to grasp is that i cant imagine these particles moving without having some sort of substance to move in. Do these particles move throughout some sort of thing like ether? or....

    Once again tim your the man. Thanks major props. :D
  17. Jan 18, 2009 #16


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    Particles, and their fields, exist within space and time …

    that is what particles move in …

    why does there have to be a "substance"? …

    why are you not happy to imagine empty space with particles moving through it? :confused:
  18. Jan 18, 2009 #17
    haha youre right its just kinda hard for me to imagine. Ive been studying light an this ether like substance so i must still be on that train of thought. So its time and space that these particles move through. ok makes sense.
    What about strings. They vibrate in space and time only if there are different dimmensions of space and time right?

    And I know im still on this idea of a field, sorry :(
    there is no field, but these forces and particles make these fields

    dont strings do the same?
  19. Jan 19, 2009 #18


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    I'm not sure whether that's physics (ie, reality) or mathematics …

    you could try a four-dimensional string theory (3 space and 1 time), but it wouldn't produce all the known particles and forces …

    we need about 10 spacetime dimensions for it to work.
    hmm … see http://en.wikipedia.org/wiki/String_field_theory and http://en.wikipedia.org/wiki/Relationship_between_string_theory_and_quantum_field_theory :smile:
  20. Jan 19, 2009 #19
    Ok haha im sorry, see math is not my thing but i think the principles behind what quantum physics talks about is very interesting.

    Let me see if ive finally understood:

    Quantum Field theory says that fundamental particles and forces interact with each other, but they are actuall field like and these fields interact.

    So these particles and forces are not created from a field, but are the ones responsible for the interactions of the fields

    String theory says that the particles and forces of nautre are not point like but they are strings which according to string field theory create fields which interact.

    Am I correct?

    My next question is where do these particles and forces come from? Are they jjust fundamental in themselves?
    Last edited: Jan 19, 2009
  21. Jan 19, 2009 #20
    Please dont hate me for asking so many questions :(

    The strings in string theory do they vibrate within or throughout space and time?
    This works if there is more than one dimension

    Also is this statement correct:

    String field theory can be understood as a quantum field theory with infinitely many fields which are unified into one master "string field".
    Last edited: Jan 20, 2009
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