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Dimension's i dont get it?

  1. Oct 23, 2003 #1
    Hey there...I know this is prob a realy simple question...but what is a dimension...i really dont get it. Also did we make up time or was it around b4 humans were around?
  2. jcsd
  3. Oct 23, 2003 #2
    For me the best way to describe a dimension is when you look at a swimming pool; full of water. The water in the pool is a dimension and the sides of the pool and the surface of the water could be considered dimensional barriers.

    Another way to look at it is to imagine the inside of your computor monitor as a dimension or for instance one room from another.

    Because time is an abstraction given for movement it is considered as a dimension, the 4th. It has no length/width or depth thus no volume yet it certainly exists as movement measured by us as time.

    movement may have been before us but possibly it was only measured by us.
  4. Oct 23, 2003 #3

    Ok..but if a dimension is just like an area with a barrier is 3D 3 areas with a barrier. It just doent make any sense. its just a word we made up to explain something we dont understand. Do u know where im comin from or am i makin no sence?
  5. Oct 23, 2003 #4
    Sorry I don’t think that’s right. In this analogy the water would represent space.

    Let’s imagine that swimming pool again only this time it has a metre scale running down each side, and one running down the wall indicating depth. There is a swimmer in the pool and we want to describe his position in the pool.

    Assume he is treading water and you have your eyes next to the floor on one side of the pool. You see the scale and our swimmers head. The reading on the scale that lines up with the swimmers head is his position in one dimension.

    Now let’s look at our swimmer from the roof. By reading where the swimmer lines up with the scale on both sides of the pool we can measure his position in 2 dimensions. If we include the swimmer's depth we can then specify their position in 3 dimensions.

    Now add a clock on the wall. If we attach the time from the clock to the swimmer’s co-ordinates then we have measured their position in 4 dimensions - One coordinate for each dimension describing the swimmers position in space and time.
  6. Oct 23, 2003 #5
    The Reason why we have them is just to have a way of describing position. Lets say we have a box with all 12" sides and we want to describe it's shape to you.

    2 Dimensional shape would be just looking at one side. We can see that the box is 12" high and 12" wide, but until the box is angled to us we can only see that it is flat like a piece of paper.

    3 Dimesionally if we turn the box we see the depth appear and we see we have a 12" W by 12" H by 12" deep box.

    We need time to apply the coordinates to a fixed point. For instance if the corner of the box was sitting square to one wall on a spot at, 10' from the walls of a square room at, 0 feet elevation, we could say that the box sits 10' from two of the walls 9' from the other two walls and the top is 12" elevation, but then if someone moves the box the dimensions relative to the walls (Coordinates of the box) have to change. We have to say, "Well it was there a minute ago."
  7. Oct 23, 2003 #6


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    What 3 dimenisons means is that to describe the exact postion of a point you need a minimum of three numbers.
  8. Oct 23, 2003 #7
    Same information as Mr. Big but even simpler:

    The first dimension is length.

    The second dimension is width.

    The third dimension is depth.

    The fourth dimension is time.

    All four dimensions always exist together. We can focus our attention on one or another but everything that exists always has all four.
  9. Oct 23, 2003 #8


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    Imporatnatly time is most defintely NOT the 4th spatial diemsion it has fundamnetally different properties, it is however considered to be the 4th dimension of space-time (in this each point is called an event and it needs 4 co-ordinates to describe it's postion, one being proportional to time)
  10. Oct 23, 2003 #9
    ohhh I see....you are talking about the usual 4 dimensions dimensions being away of measureing space and time....ahhh I see

    I was thinking about dimensions as being a volume ((4dimensions) as a physical entity and not a construct.

    Example might be for instance the legendary atlantis slipping in to a dimension that co-exists with the one we live in or the idea of parallel universes as separate dimensions co-existing.

    my mistake sorry
  11. Oct 24, 2003 #10


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    Not much of a mistake- there are theories that include more than 3 space dimensions.
  12. Oct 24, 2003 #11


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    We have a policy here: if you don't know the accepted, textbook answer for a problem, please don't respond to it. It will only confuse people. We don't tolerate alternative theories here, only in the theory development forums.

    - Warren
  13. Oct 24, 2003 #12
    choot ....if you could be so kind as to refer me to the ...hmmmm textbook you have in mind and tell me what level it tries to teach at....I might get an idea as to what aspect or dimension I should refer to.....
  14. Oct 24, 2003 #13


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    There are a couple of different uses for the term dimension in the world of phyics.
    1. Physical units of measure are refered to as dimensions. When someone speaks of dimensional analysis they mean the process of solving the problem using ONLY the dimensions (units) of the quanities involved. For example, If I know something has moved 25m is 10s, I can start by considering distance (m) divided by time (s) to get a quanity (m/s) now recoginzing that this is the units of velocity I can be sure that dividing 25 by 10 will yield a velocity. This is a very good habit to form when leaning Phyics, doing dimensional analysis can prevent many errors.

    2. The dimension of a system is size of the set of numbers required to compeletly specify the state of a system. To specify the location of a body in space/time requires 4 coordinates. So space-time is called 4 dimensional. Three of the 4 space-time dimensions are required to specify a location in space, the 3 numbers used dependent on your choise of coordinate system, you can use rectanglar, also called Cartesan coordinates, or spherical or cylindracial, or even make up your own system. One thing will remain constant, you will need 3 numbers to completely specify the location of a object in space.

    It is not uncommon to encounter problems which require more then 3 or even 4 dimensions. Linear Alegbra is an entire field of Mathematics that deals with methods of working N dimensional problems. Where N is any integer. So do not think of dimensions as simply dealing with space-time but in a much more general sense where space-time is just something with 4 dimensions. It is not uncommon to solve physics problems in a 6 dimensioal phase space where in additon to position, the momentum of a body is also specified by 3 numbers.
  15. Oct 24, 2003 #14
    I can't add to what integral said other than this:
    In mathematics, values which are not associated with any unit are called 'dimensionless numbers'.
    So 0, log x, 2 are dimensionless numbers
    but log x meters, 2 seconds are dimensions.
    Note that explicit zero-values, for example, the distance between two touching objects, are expressed as dimensionless 0, and not 0 units, so we say, the distance between the two objects is zero and notzero meters or zero inches etc. etc.
    Last edited: Oct 24, 2003
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