No Cross Product in higher dimensions?

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Discussion Overview

The discussion centers around the existence of a direct analogue to the binary cross product in higher dimensions, specifically questioning whether a unique vector can be derived from two vectors in dimensions greater than three. Participants explore concepts such as the wedge product and the properties of perpendicularity in various dimensions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants inquire about the intuitive reasoning or proof for the absence of a direct analogue to the cross product in higher dimensions.
  • There is mention of the wedge product as an alternative, with some participants expressing confusion about why it is not considered a regular vector.
  • One participant suggests that it is possible to find a normal vector to a plane in higher dimensions, questioning if this could be seen as an analogue to the cross product.
  • Another participant discusses the uniqueness of perpendicular vectors in three dimensions, noting that in two dimensions there are no such vectors, and in four or more dimensions, there are infinitely many.
  • A reference to the Hodge dual is made, with a suggestion that it relates to special properties in three dimensions.
  • It is noted that the cross product can exist in seven dimensions, but it is not unique in that context.

Areas of Agreement / Disagreement

Participants express differing views on the existence and nature of perpendicular vectors in higher dimensions, indicating that there is no consensus on the topic. The discussion remains unresolved regarding the direct analogue to the cross product.

Contextual Notes

Participants highlight limitations in understanding the definitions of perpendicularity and vector products in dimensions beyond three, which may affect their arguments.

MathewsMD
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Is there an intuitive reason or proof demonstrating that in general dimensions, there is no direct analogue of the binary cross product that yields specifically a vector?

I came across Wedge Product as the only alternative, but am just learning linear algebra and don't quite comprehend yet why this isn't exactly considered a regular vector.

Is it really unknown on how to find a perpendicular vector to any vector in RN?

Any explanation is greatly appreciated!
 
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MathewsMD said:
Is there an intuitive reason or proof demonstrating that in general dimensions, there is no direct analogue of the binary cross product that yields specifically a vector?
Check the definition of the cross product.

Note: it is possible to describe a plane surface in n>3 dimensions, and thus to find two vectors in the surface that are not colinear, and thus find the normal vector to the surface via an operation on the two vectors in the surface. Would this count as an n-D analogue for a cross product?

Well...
https://www.physicsforums.com/showthread.php?t=526403

I came across Wedge Product as the only alternative, but am just learning linear algebra and don't quite comprehend yet why this isn't exactly considered a regular vector.
The wedge product is an operation on two vectors ... to see why the result is not a vector, just apply your new-found knowledge of what a vector is and see.

Is it really unknown on how to find a perpendicular vector to any vector in RN?
Check the definition of "perpendicular". Does a 4D vector describe an object for which something can be "perpendicular" ... how does the concept make sense in more than 3D?
 
Last edited:
MathewsMD said:
Is it really unknown on how to find a perpendicular vector to any vector in RN?

In three dimensions you can pick two vectors A and B and ask for a vector C that is perpendicular to both A and B. This vector C is unique up to a sign. (Except in the special case that A and B are collinear).

This only works in three dimensions. In two or fewer dimensions, there are no vectors perpendicular to both A and B. In four or more dimensions, there are an infinite number of vectors perpendicular to both A and B.
 

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