Do the extra dimensions really make sense?

  • Thread starter nuiluidwde
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  • #1
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Main Question or Discussion Point

Is it just me, or are dimensions supposed to simply add another coordinate, i.e., I can move 1m in x, y or z direction and be 1m away from where I started, are the dimensions in string theory based on this concept or do I not understand what a dimension is? The most confusing part is how these dimensions are supposedly rolled up and small, why are they now being treated like manipulable entities?

Also, another poster stated that there are conjectures which say that, given enough energy, a string can leap to another dimension, if each dimension simply represents a coordinate that every material entity has, then why would this make any sense at all?

I know I must have a fundamental misunderstanding somewhere, can anyone explain what dimensions are really considered to be, and how any of these ideas are possible? Thank you :confused:
 

Answers and Replies

  • #2
jal
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I’l try to answer.
Lets start with

http://en.wikipedia.org/wiki/Six_degrees_of_freedom

Six degrees of freedom (6DoF) refers to motion of a rigid body in three-dimensional space, namely the ability to move forward/backward, up/down, left/right (translation in three perpendicular axes) combined with rotation about three perpendicular axes (pitch, yaw, roll). As the movement along each of the three axes is independent of each other and independent of the rotation about any of these axes, the motion indeed has six degrees of freedom.

Therefore, you actually exist in 3 dimensions simultaneously. A dimension is a degree of freedom.
Now go look at

http://en.wikipedia.org/wiki/Dimension
In mathematics and physics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify each point within it.[1][2] Thus a line has a dimension of one because only one coordinate is needed to specify a point on it. A surface such as a plane or the surface of a cylinder or sphere has a dimension of two because two coordinates are needed to specify a point on it (for example, to locate a point on the surface of a sphere you need both its latitude and its longitude). The inside of a cube, a cylinder or a sphere is three-dimensional because three co-ordinates are needed to locate a point within these spaces.

High-dimensional spaces occur in mathematics and the sciences for many reasons, frequently as configuration spaces such as in Lagrangian or Hamiltonian mechanics; these are abstract spaces, independent of the physical space we live in.

Here the definition is different.
Classical physics theories describe three physical dimensions: from a particular point in space, the basic directions in which we can move are up/down, left/right, and forward/backward. Movement in any other direction can be expressed in terms of just these three. Moving down is the same as moving up a negative distance. Moving diagonally upward and forward is just as the name of the direction implies; i.e., moving in a linear combination of up and forward. In its simplest form: a line describes one dimension, a plane describes two dimensions, and a cube describes three dimensions.

Now go look at
http://en.wikipedia.org/wiki/Fourth_dimension
In the familiar 3-dimensional space that we live in there are three coordinate axes — usually labeled x, y, and z — with each axis orthogonal (i.e. perpendicular) to the other two. The six cardinal directions in this space can be called up, down, east, west, north, and south. Positions along these axes can be called altitude, longitude, and latitude. Lengths measured along these axes can be called height, width, and depth.
Comparatively, 4-dimensional space has an extra coordinate axis, orthogonal to the other three, which is usually labeled w. To describe the two additional cardinal directions, Charles Howard Hinton coined the terms ana and kata, from the Greek words meaning "up toward" and "down from", respectively. A length measured along the w axis can be called spissitude, as coined by Henry More.
The geometry of 4-dimensional space is much more complex than that of 3-dimensional space, due to the extra degree of freedom.

After readying those links you are now at the question that I asked at
https://www.physicsforums.com/showthread.php?t=460444
Is N=4 ONLY a mathematical construct?


Other inputs are welcomed.
jal
 
  • #3
PhilKravitz
They do not make sense to me. I do not know of any experimental data to support more than 3 spacial dimensions.

Aditional degrees of freedom are fine. No need to call them spacial.
 
  • #4
arivero
Gold Member
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Consider m^2 = E^2 - p ^2.

Now consider 0=E^2 - (p^2+m^2)
 
  • #5
371
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They do not make sense to me. I do not know of any experimental data to support more than 3 spacial dimensions.

Aditional degrees of freedom are fine. No need to call them spacial.
You're absolutely right! I've found the 6 dimensions other than length, breadth, height and time, and NONE of them are spacial. there are only 3 spacial dimensions.
 
  • #6
there is what is called braneworld scenario . I will give you an example . An ant walks on earth but it can't fly . for her , the world is two dimensional not three dimensional . It's all about our limited ability to imagine or sense the presence of extradimensions
 
  • #7
jal
549
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Consider m^2 = E^2 - p ^2.

Now consider 0=E^2 - (p^2+m^2)
Lack of information. I get nothing.
---

I’ve had this link before but I wish to highlight one particular point.

http://physics.aps.org/articles/v3/105
Viewpoint
A “Little Bang” arrives at the LHC
Published December 13, 2010

Highlight:
One of the other important discoveries at RHIC was that particle jets are strongly quenched when they interact with the quark-gluon plasma.
ATLAS has also observed extremely asymmetric events, in which such high-energy jets basically dissipated entirely, without a companion jet.

What do these results tell us about the quark-gluon plasma?
One theory that could explain this surprising result is a strong coupling theory called the AdS/CFT correspondence, a spin-off from string theory that relates the strong-coupling limit of quarks and gluons to a theory of gravity in a higher dimension.

In the AdS/CFT picture, the equilibration of the quark-gluon plasma is connected to the production of a black hole, and jet quenching can be mapped to falling into this black hole (for reviews, see, e.g., Refs. [9, 10]). Predictions based on this theory suggest that the stopping distance of a jet varies as E⊥1/3/T4/3* [6], which means that at the LHC, a jet with E⊥=100*GeV stops at the same distance as a 35*GeV jet at RHIC—similar to what ATLAS observed. Collectively, these results from ALICE and ATLAS are providing new evidence that the quark-gluon plasma produced at the LHC is still strongly coupled. After just three weeks of the LHC run with heavy ions, we are witnessing a very exciting start of this new era.
 

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