Spatial dimensions of our universe

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Discussion Overview

The discussion revolves around the nature and implications of spatial dimensions in our universe, particularly contrasting the arguments presented by Max Tegmark regarding the limitations of spatial dimensions suitable for life with the higher-dimensional frameworks proposed in string theory. The scope includes theoretical considerations and conceptual clarifications regarding the existence and implications of additional dimensions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant references Tegmark's article, questioning whether the argument against spatial dimensions beyond three contradicts string theory's allowance for 10, 11, or 26 dimensions.
  • Another participant clarifies that Tegmark's argument pertains to extended spatial dimensions that are suitable for life, as opposed to compactified dimensions that are theorized to exist at small scales.
  • A participant asserts that since we exist in a universe that supports life, it must have 3+1 dimensions, prompting questions about the implications of additional dimensions on general relativity and gravitation.
  • Further discussion highlights the distinction between small scale and large scale dimensions, noting that compactified dimensions are tightly wrapped and that the reasons for their differing sizes remain unknown.
  • Another participant mentions that quantum gravity and string theory are approaches attempting to address the implications of higher dimensions on physical laws.
  • It is suggested that string theory posits that particles are one-dimensional strings, with their properties influenced by the characteristics of extra dimensions, indicating that ten spatial and one time dimension are necessary to explain observed particle characteristics.

Areas of Agreement / Disagreement

Participants express differing views on the compatibility of Tegmark's arguments with string theory, and there is no consensus on the implications of additional dimensions for general relativity or quantum theory. The discussion remains unresolved regarding the nature and significance of these dimensions.

Contextual Notes

Participants note the lack of understanding regarding why some dimensions are compactified while others are not, and the discussion includes unresolved questions about the effects of additional dimensions on established physical theories.

cryptist
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On the page 17 of this article by Max Tegmark http://arxiv.org/pdf/gr-qc/9704009v2.pdf, in figure 7, it has been argued that why spatial dimensions other than 3, is not possible for our universe. But in string theory, people are talking about 10, 11 or 26 spatial dimensions (even if these dimensions are thought to be in extremely small scale). Are these two contradicting? If no, why?
 
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We are living(!) on a universe that contains life. So our universe has to have 3+1 dimensions then. What is the difference between small scale dimensions and large scale dimensions? For example what would happen to general relativity and gravitation in that case (the universe with more than 3 dimensions)? Again does quantum theory predict these other dimensions?
 
What is the difference between small scale dimensions and large scale dimensions?

size.
The small ones appear to be tightly wrapped...'compactified'.
Nobody knows why some are small and others are large.
For example what would happen to general relativity and gravitation in that case (the universe with more than 3 dimensions)?

quantum gravity and string theory are approaches trying to tackle such questions
Again does quantum theory predict these other dimensions?

String theory suggests that 'particles' are strings...one dimensional extensions of point particles...whose characteristics, like energy,charge, spin are determined by the nature of the extra dimensions. Seems so far ten spatial and one time dimension are needed to account for the particle [string] characteristics we observe.
 

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