Construction of the tangent vector space in GR

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Alan Grayson

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Feb 16, 2025, 5:33:29 PM2/16/25
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I got into a fairly heated argument with a Ph'D in physics from Brent's alma mater, the University of Texas at Austin, concerning the construction of the tangent vector space in GR. For this and other reasons we are no longer in communication. He insisted on including particle paths of all velocities passing through a point P on the spacetime manifold, aiming to construct the tangent vector space at P. I objected since this would violate one of the basic postulates of GR, which preclude particles assumed to be exceeding light speed. I was berated for making such a criticism. Initially I thought these faster than light speed particles were needed to form a vector space, in order to satisfy the linear additive property of a vector space under the field of real numbers. But suppose these vectors are constrained to be added relativistically, so no pair when added, can exceed light speed. Will this be sufficient to satisfy the linear additive property of vectors in a vector space, without violating the postulate of GR precluding faster than light speed particles? TY, AG 

Alan Grayson

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Feb 16, 2025, 9:07:10 PM2/16/25
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On Sunday, February 16, 2025 at 3:33:29 PM UTC-7 Alan Grayson wrote:

I got into a fairly heated argument with a Ph'D in physics from Brent's alma mater, the University of Texas at Austin, concerning the construction of the tangent vector space in GR. For this and other reasons we are no longer in communication. He insisted on including particle paths of all velocities passing through a point P on the spacetime manifold, aiming to construct the tangent vector space at P. I objected since this would violate one of the basic postulates of GR, which preclude particles assumed to be exceeding light speed. I was berated for making such a criticism. Initially I thought these faster than light speed particles were needed to form a vector space, in order to satisfy the linear additive property of a vector space under the field of real numbers. But suppose these vectors are constrained to be added relativistically, so no pair when added, can exceed light speed. Will this be sufficient to satisfy the linear additive property of vectors in a vector space, without violating the postulate of GR precluding faster than light speed particles? TY, AG 


Since the LT is linear, I think it will work to restrict the velocities on the tangent space to less than light speed. I'm puzzled why the physics guru from the U of Tx adamently objected to my criticism and implied simple fix for his obvious error. AG 

Brent Meeker

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Feb 16, 2025, 11:14:42 PM2/16/25
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What's his name?  I still know a few people there.

Brent
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Alan Grayson

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Feb 17, 2025, 12:07:58 AM2/17/25
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I'm sure you know him. RW. AG

Alan Grayson

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Feb 17, 2025, 12:17:53 AM2/17/25
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He also got angry when I told him I believed spacetime is positively curved. He said I should calculate the curvature tensor, since it would be zero if spacetime is flat. I responded, asking him why I should do that, since whatever I calculated, assuming I knew how to do it, wouldn't prove anything since the result would depend on my assumptions. He never replied -- a sad ending for me, for what I considered a friendship. AG
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