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

The fourth dimension

  1. Dec 31, 2006 #1

    disregardthat

    User Avatar
    Science Advisor

    http://sprott.physics.wisc.edu/pickover/fourth.html

    I just read this, and it makes no sense. In my opinion of the fourth dimension all that is written here is garbage. What do you get out of this?

    It is an introduction to a book.
     
  2. jcsd
  3. Dec 31, 2006 #2

    mathman

    User Avatar
    Science Advisor
    Gold Member

    It is an attempt to describe a perfectly plausable mathematical construct (four dimensional Euclidean space) in layman terms. Although it is somewhat hokey, there is nothing particularly wrong with it.

    Warning, it has nothing to do with general relatively or string theory.
     
  4. Dec 31, 2006 #3

    disregardthat

    User Avatar
    Science Advisor

    Well, could you explain what he means of a four dimensional animal? A fourdimensional animal could NOT excist in our world. It must merely be a way of explaining how another dimension is.
     
  5. Dec 31, 2006 #4
    Don't take 4 dimensional animals seriously... it's just a way to enable laymen to understand higher dimensions by the use of analogy. Imagine a 2 dimensional flatland and you stick your your hands through flatland (assuming this is possible...) then the flatlanders will see 5 disconnected blob of fingers, more precisely, the cross sections of your fingers as they pass through the plane. And as time passes, they will observe that the 5 blobs converge to form a bigger blob (now your palm is passing through the plane) etc. So as analogy, if there are 4 dimensional animals come into our world, we would expect the same phenomena, but of course I doubt 4 dimensional animals, if they exist, will have any anatomy that we are familiar with :tongue:
     
  6. Jan 1, 2007 #5

    disregardthat

    User Avatar
    Science Advisor

    Yeah, I get that. Well, I admit it was an ok way to make us understand the fourth dimension mathematical, but in our world we observe it as 'time'. So if there are 4d animals time must stand still for them, if you get me? Since if a 4d animal is capable of moving through the fourth dimension, it means that it can move through time.

    That leads me to a question I have asked in another thread, unanswered: How come that the fourth dimension works as time, AND works as bending of the three dimensional space due to mass? I would understand if it worked as only bending of mass, but it is like we are moving along this 'line' that is added to the three dimensional coordinate system.

    As you described in the 2d blob finger example, the flatlanders didn't observe, and therefore in their world the rest of the animal did not exist. So, how come that the three dimensional objects in the three dimensional coordinate system that we observe, exist at all 'times' as time pass by in the fourth dimension?
     
  7. Jan 1, 2007 #6
    Erm. No. By 4th dimension in my previous post, I meant the 4th spatial dimension, not the temporal one.
     
  8. Jan 1, 2007 #7

    mathman

    User Avatar
    Science Advisor
    Gold Member

    The point I was trying to make in my previous remark is that the fourth (mathematical) dimension of Euclidean geometry is NOT the same as the time dimension of general relativity.
     
  9. Jan 1, 2007 #8

    DaveC426913

    User Avatar
    Gold Member

    That is all very standard stuff in standard 4D talk. There are whole books devoted to the analogy between a 2D-vs.-3D and a 3D-vs.-4D world.

    Read anything about "Flatland":

    http://www.geom.uiuc.edu/docs/forum/polytope/
    http://www.pbs.org/wgbh/nova/elegant/dimensions.html
    http://www.rmcybernetics.com/science/physics/dimensions_2_dimensional_space.htm
    http://www.rmcybernetics.com/science/physics/dimensions_4_dimensional_space.htm
     
  10. Jan 2, 2007 #9

    disregardthat

    User Avatar
    Science Advisor

    I wasn't questioning YOU, I was questioning the fourth dimension as it is in our world:uhh:
     
  11. Jan 2, 2007 #10
    You DID reply to my answer. And since you have further query, all I did is to further clarify that the forth dimension can be spatial or temporal depends on which one do you mean. :rolleyes:

    If there is a forth spatial dimension in our world, we won't notice it just like flatlanders can't see into the third dimension. That has nothing to do with the convention of time as the forth dimension in relativity.
     
  12. Jan 2, 2007 #11

    disregardthat

    User Avatar
    Science Advisor

    Well, I was thinking of the most acceptet theory, general relativity...

    And my questions was based on it's interpretion of the fourth dimension. Not of the silly 4d animals this guy talks about.

    Anyway, how can time both be spatial bending AND time?
     
  13. Jan 2, 2007 #12

    DaveC426913

    User Avatar
    Gold Member

    Because Einstein's legacy to humanity is the knowledge that there is no such thing as '3D space' and ' 1D time', there is only '4D spacetime'.
     
  14. Jan 2, 2007 #13

    disregardthat

    User Avatar
    Science Advisor

    Well, is there any explanation for it?
     
  15. Jan 2, 2007 #14
    I suppose when people talking about 4D animals (I agree it's crazy:rofl: ) or flatlanders, note that they also permit the animals/flatlanders to move around, have a rather decent life (If you read 'Flatland' you know what I mean), i.e. there is dynamics. Therefore a flatland is not just a 2D space, it is 2+1 spacetime, i.e. 2 spatial dimension and 1 temporal dimension. A silly 4D creature would therefore live in a 4+1 spacetime, 5 dimensions if you will in that sense. It is quite standard for people who talk about higher dimensions in the pure mathematical sense not to mention the time dimension (since they weren't talking about GR).
     
  16. Jan 2, 2007 #15
  17. Apr 11, 2008 #16
    seeing across dimensions

    I agree with this statement. First, our 3D world is electromagnetic {EM} in nature and EM does not exist in other dimensions. What little discussion I have seen implies that only gravity exists in other dimensions {up to and including the 11 dimensions of M Theory}. Gravity appears to be the active area in which to find evidence of other dimensions.

    All discussions [I have seen] of what a 2 D person would observe of a third dimension is based on analogy. I would like to see a mathematical derivation. Has anyone seen such a derivation?
     
  18. Apr 15, 2008 #17
    my lecture said how hard it is to understand the concept of 4th dimension. He compared 4th dimension to the time and he said there are 3 tense in the time, namely, past, present and future. So by this he says time kinda 3 Dimensional object. If there is a 4th tense..then that could be the 4th dimension of an object !
     
  19. Oct 20, 2008 #18

    think the truth is that there is no such thing as time, only space. Time is an illusion created by our limited perception. the RATE of time is determined by how fast our mind proccesses information ( like for example with phsycodelics people feel like time is slowing down, because thier mind starts proccessing info faster). Time is the 4 dimensional crossections of our 3 dimensional selfs. if you where to see your entire body in the 4th dimension, it would be like seeing your birth, death, and everything in between in a single instance infinitely. But really time is acually space. Its hard to explain but lets say you picked up a pencil and if you moved it, the pencil would leave a trail of itself behind it . The pencil in the fourth dimension (time as we call it) would acually take up more space than in the 3rd dimension because not only would it have: length, width, and height, but it would also have "moved" from one spot to another" which by looking at it from a 4D perspective would take up space from point (A) which was a desk lets say to point (B) which is the other side of the room. So the only way to imagine the pencil taking up 4D space is to imagine the pencil taking up the 3d space in point (A), point (B) and all movements/locations between point (A) and (B). So the pencil would look like a "snake like" entity in the 4th dimension ( or at least thats the only way we can imagine it)

    > "|" < - pencil

    DESK------------------>>>OTHER SIDE OF ROOM
    Point A |||||||||||||||||||||| Point B
    [1 sec.] [2 sec.] [3 sec.] [4 sec.] [5 sec.]
    ------------------------------------------------->>>

    unfortunatly i cant show a better illistration but if this line was really a 3d pencil then u could measure its 3 dimensions, and also measure its size in the fourth dimension as "movement". Our bodies and everything else in the universe has more than 3 dimensions. and we only see "frames" if you will, of the fourth dimension which we call the "present" Memories are only info. that we collected as we move through the 4th dimension which we call the "past". Keep in mind that time is only created by our limited perception and the only way we could see the 4th dimension as a whole, is if our minds could hold an infinit amount of information at once, or at least enough info. to see your birth, life, and death as one instance.
     
  20. Oct 22, 2008 #19
    Hi thanks for your posts
     
  21. Oct 22, 2008 #20
    no problem, just trying to help, it seems like every one that tries to explain the fourth dimension fails pretty bad at it :/ not sure if my explanation is top notch either, but what can you do. After all it is something that is beyond our full understanding.
     
    Last edited: Oct 22, 2008
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: The fourth dimension
  1. A new DIMENSION? (Replies: 22)

  2. Extra dimensions (Replies: 3)

  3. The Fourth Dimension (Replies: 1)

  4. Dimensions of universe (Replies: 8)

  5. Origin of dimensions (Replies: 2)

Loading...