Re: Could magnets be used for interstellar propulsion?

From	ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups	sci.physics
Subject	Re: Could magnets be used for interstellar propulsion?
Date	2026-02-02 19:27 +0000
Organization	Stefan Ram
Message-ID	<f-20260202201858@ram.dialup.fu-berlin.de> (permalink)
References	(3 earlier) <fields-20260201175451@ram.dialup.fu-berlin.de> <10loqja$7i98$1@dont-email.me> <10lp9rc$oge5$1@gwaiyur.mb-net.net> <b4g1oklaeg166ko5mbffmooo0tit6llmkt@4ax.com> <gradient-20260202171825@ram.dialup.fu-berlin.de>

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ram@zedat.fu-berlin.de (Stefan Ram) wrote or quoted:
>In rectangular coordinates, the gradient of a vector field 
>f =( f_1, f_2, f_3 ) is defined by:

  That should read, "f^1, f^2, f^3".

>"nabla" f 
>= g^jk ("partial"f^i/"partial"x^j) e_i "tensor product" e_k,

>So, when these derivatices ("partial"f^i/"partial"x^j) are

  "derivatives"

  "g_jk" are the components of the inverse metric tensor and the 
  "e_i" are the coordinate basis vectors. The Wikipedia page also
  has a definition that does not use a basis.

>large, the gradient is large, meaning the field changes a lot,
>which is need for a significant force on a magnetic dipole.

  "needed"

>𝙛=(𝑓¹,𝑓²,𝑓³)
>∇𝙛=gⁱᵏ(∂fⁱ/∂xʲ) eᵢ⊗eₖ

𝙛=(𝑓¹,𝑓²,𝑓³)

∇𝙛=𝑔ⁱᵏ(∂𝑓ⁱ/∂𝑥ʲ) eᵢ⊗eₖ

Thread

Could magnets be used for interstellar propulsion? Jan Panteltje <alien@comet.invalid> - 2026-02-01 11:57 +0000
  Re: Could magnets be used for interstellar propulsion? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-02-01 12:57 +0000
    Re: Could magnets be used for interstellar propulsion? Jan Panteltje <alien@comet.invalid> - 2026-02-01 16:44 +0000
      Re: Could magnets be used for interstellar propulsion? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-02-01 16:55 +0000
        Re: Could magnets be used for interstellar propulsion? Ian <gay@sfu.ca> - 2026-02-01 16:19 -0800
          Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-02 05:35 +0100
          Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-02 05:40 +0100
            Re: Could magnets be used for interstellar propulsion? John Hasler <john@sugarbit.com> - 2026-02-02 08:02 -0600
              Re: Could magnets be used for interstellar propulsion? Jan Panteltje <alien@comet.invalid> - 2026-02-02 14:44 +0000
              Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-03 04:54 +0100
            Re: Could magnets be used for interstellar propulsion? john larkin <jl@glen--canyon.com> - 2026-02-02 07:20 -0800
              Re: Could magnets be used for interstellar propulsion? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-02-02 16:30 +0000
                Re: Could magnets be used for interstellar propulsion? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-02-02 19:27 +0000
              Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-02 22:55 +0100
            Re: Could magnets be used for interstellar propulsion? Ian <gay@sfu.ca> - 2026-02-02 14:30 -0800
              Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-03 02:03 +0100
    Re: Could magnets be used for interstellar propulsion? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-02-09 14:19 +0000
  Re: Could magnets be used for interstellar propulsion? Bill Sloman <bill.sloman@ieee.org> - 2026-02-02 00:41 +1100
    Re: Could magnets be used for interstellar propulsion? "Edward Rawde" <invalid@invalid.invalid> - 2026-02-01 09:58 -0500
    Re: Could magnets be used for interstellar propulsion? Jeremiah Jones <jj@j.j> - 2026-02-02 08:50 -0800
      Re: Could magnets be used for interstellar propulsion? john larkin <jl@glen--canyon.com> - 2026-02-02 09:28 -0800
      Re: Could magnets be used for interstellar propulsion? John Hasler <john@sugarbit.com> - 2026-02-02 11:49 -0600
        Re: Could magnets be used for interstellar propulsion? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-02-02 14:23 -0500
          Re: Could magnets be used for interstellar propulsion? john larkin <jl@glen--canyon.com> - 2026-02-02 12:39 -0800
            Re: Could magnets be used for interstellar propulsion? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-02-02 15:53 -0500
      Re: Could magnets be used for interstellar propulsion? John Hasler <john@sugarbit.com> - 2026-02-02 11:43 -0600
      Re: Could magnets be used for interstellar propulsion? ehsjr <ehsjr@verizon.net> - 2026-02-02 16:49 -0500
        Re: Could magnets be used for interstellar propulsion? Jeremiah Jones <jj@j.j> - 2026-02-02 20:42 -0800
          Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-04 20:11 +0100
            Re: Could magnets be used for interstellar propulsion? Jeremiah Jones <jj@j.j> - 2026-02-05 16:24 -0800
              Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-06 02:09 +0100
                Re: Could magnets be used for interstellar propulsion? Jeremiah Jones <jj@j.j> - 2026-02-06 00:24 -0800
                Re: Could magnets be used for interstellar propulsion? Bill Sloman <bill.sloman@ieee.org> - 2026-02-06 20:18 +1100
              Re: Could magnets be used for interstellar propulsion? Bill Sloman <bill.sloman@ieee.org> - 2026-02-06 18:07 +1100
                Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-07 01:54 +0100
                Re: Could magnets be used for interstellar propulsion? Jeremiah Jones <jj@j.j> - 2026-02-07 19:48 -0800
                Re: Could magnets be used for interstellar propulsion? athel.cb@gmail.com <user12588@newsgrouper.org.invalid> - 2026-02-08 11:42 +0000
          Re: Could magnets be used for interstellar propulsion? john larkin <jl@glen--canyon.com> - 2026-02-05 16:48 -0800
        Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-04 16:36 +0100
          Re: Could magnets be used for interstellar propulsion? john larkin <jl@glen--canyon.com> - 2026-02-04 08:49 -0800
          Re: Could magnets be used for interstellar propulsion? John Hasler <john@sugarbit.com> - 2026-02-04 10:58 -0600
            Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-04 19:44 +0100
          Re: Could magnets be used for interstellar propulsion? john larkin <jl@glen--canyon.com> - 2026-02-04 18:21 -0800
      Re: Could magnets be used for interstellar propulsion? Bill Sloman <bill.sloman@ieee.org> - 2026-02-03 15:54 +1100
        Re: Could magnets be used for interstellar propulsion? Jeremiah Jones <jj@j.j> - 2026-02-03 20:35 -0800
          Re: Could magnets be used for interstellar propulsion? Bill Sloman <bill.sloman@ieee.org> - 2026-02-04 16:59 +1100
          Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-04 16:58 +0100
          Re: Could magnets be used for interstellar propulsion? ram@zedat.fu-berlin.de (Stefan Ram) - 2026-02-05 14:35 +0000
      Re: Could magnets be used for interstellar propulsion? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2026-02-04 16:23 +0100
  Re: Could magnets be used for interstellar propulsion? Colin <colin@example.invalid> - 2026-02-01 18:31 +0000
    Re: Could magnets be used for interstellar propulsion? Jan Panteltje <alien@comet.invalid> - 2026-02-02 05:54 +0000

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