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

Higher dimensions

  1. Jul 16, 2004 #1


    User Avatar
    Gold Member

    Basically what are they, and how going about our normal activities
    would we notice them?
    Its hard for me to imagine them, how do they interact, is spacetime
    the same looking out from each dimension, could a six dimensional
    object exist?
  2. jcsd
  3. Jul 30, 2004 #2
    I bet they're hard for you to imagine...if you could imagine them you'd be one of the most remarkable humans to ever live. Basically, they are no different than the three "ordinary" spatial dimensions, except they're essentially curled up into a space so tiny, about the size of the Planck length, that you traverse the entire dimension and end up back where you started (they would have to be circular) in almost no time at all so you don't notice them in our macroscopic life. If the regular dimensions are also circular, than the only difference is the fact that the higher dimensions are curled up. One major difference that you would notice if you could look into one of the extra dimensions is that since their so small, and they're circular, you would theoretically be able to see yourself. As much as I dislike referring to certain writings in posts, it seems almost like a shortcut, Brian Greene explains them much better than I could in his book "The Elegant Universe". Their existence was first proposed by Franz Kaluza early in the 20th century. He wrote Einstein, who immediately expressed interest in the idea, only to express skepticism soon after. However, he eventually came around and offered to present Kaluza's paper to the Academy. The fascinating aspect of extra spatial dimensions is that if general relativity is applied to them, just as gravity can be explained as disturbances in the familiar, extended, three dimensions, the other fundamental forces can be explained as disturbances in the extra dimensions. When Kaluza added a fifth dimension to Einstein's equations, it was Maxwell's equations of electromagnetism that emerged! Unfortunately, there were some unresolved problems with extra dimensions, so the idea was put on the shelf. When string theory came around, it was revived again. In case you aren't familiar, string theory (the main focus of "The Elegant Universe") is built around the premise of all fundamental and messenger particles being just vibrating loops of energy. It's an attempt at a theory of everything, trying to unify the four fundamental forces as well as marry the conflicting general theory of relativity with quantum mechanics. One problem it was experiencing was that the incomplete calculations of string theory were producing negative probabilities. By increasing the number of dimensions a string could vibrate in, the negative numbers started to decrease. In fact, by increasing the number of spatial dimensions to nine, the negative numbers dissappeared altogether. Due to the incomplete nature of string theory, a more robust form of it called M-theory suggests that the number may actually be ten spatial dimensions, and one time dimension, for a total of eleven. Of course string theory still has a long way to go, and is still speculation for the most part. However the idea is intriguing, and extra dimensions do provide a very complete picture of reality. To answer your final question, yes a 6-dimensional is possible, actually if M-theory is correct than every object in the universe has ten spatial dimensions, since it's fundamental strings are 10-dimensional. However, since the curled up dimensions are so tiny we don't notice our extended nature. Some work by Einstein suggests that in theory curled up dimensions could be extended...wouldn't that be interesting. Firing up the hyperdrive, captain...
  4. Jul 30, 2004 #3
    People ask:what is string theory?
    I would say this is the answer:
    A description of consciousness -
    The extra dimensions of string theory are new properties of particles that cause our consciousness.In other words colours,sounds,smells and feelings are properties associated with strings.
    Last edited: Jul 30, 2004
  5. Jul 30, 2004 #4
    Not really that remarkable... You just have to get your mind use to it. Just like you learn a second language or recognize mathematical logic in retrospect to the real world, it all becomes second-nature after awhile.

    Dimensions are just physical properties. The only difference between spatial dimensions and dimensions like mass or electric charge is that we easily identify spatial ones in our everyday lives, therefore we like to separate them as if they're somehow special or different in someway.
  6. Jul 31, 2004 #5
    If people asked me, first I'd say I really don't know. If they pressed me I'd say its an attempt at a unified theory. The extra dimensions are basically "rolled up" within the "fabric of space" and the vibrations of strings in these dimensions and the way the strings (and branes) are oriented in these dimensions give rise, hopefully, to many different physical phenomenon.

  7. Aug 2, 2004 #6


    User Avatar
    Gold Member

    Sorry for my tardy reply luck hasn't been with me of late,
    I can see the need for these higher dimensions in some areas of
    research, but im unsure if they are a reality, it seems ST needs
    them to survive, but as this theory evolves is it possible," or even
    probable", that these dimensions can be calculated out, or are
    they the bedrock of the theory?
  8. Feb 11, 2010 #7

    I understand the word 'dimension' to mean 'spatial dimension'. Are you saying that, in the context of string theory, the word 'dimension' is actually just used to mean 'physical property'? Because that doesn't seem to be the case. From the reading I've done, admittedly as a layperson, the extra dimensions proposed in string theory are meant to be spatial dimensions.

    Like Wolram, I find it difficult to imagine more than three spatial dimensions. In fact, I find the idea incomprehensible. How can there be more than three spatial dimensions? WHERE would they exist? I would look for answers in "The Elegant Universe", as suggested by LastOneStanding, except for one thing: it was a talk given by the author (Brian Greene) - http://www.ted.com/talks/brian_greene_on_string_theory.html - that started me looking for a better explanation than he'd given, so I suspect that well may be dry.

    Can anyone offer a cogent explanation of how more than three spatial dimensions could exist? Or even how to go about trying to conceptualize this idea?
  9. Feb 12, 2010 #8
    Hmmm. We perceive and measure 3 spatial dimensions because because light and other energies only apparently travel in ways that are 3 ways linear independent. But we assume the trajectories are linear, don't we?

    If a photon were to travel forward in the duration of time its spin orientation is less than Pi and backward or sideways when its orientation is greater than Pi (at a different speed) then spin orientation would be an additional dimension, wouldn't it?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?