home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!usenet.ins.cwru.edu!agate!dog.ee.lbl.gov!csa3.lbl.gov!sichase
- From: sichase@csa3.lbl.gov (SCOTT I CHASE)
- Newsgroups: sci.physics
- Subject: Re: Converting the masses
- Date: 21 Jul 92 20:39:44 GMT
- Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
- Lines: 38
- Distribution: na
- Message-ID: <24760@dog.ee.lbl.gov>
- References: <mcirvin.711489157@husc10> <130889@lll-winken.LLNL.GOV> <mcirvin.711673227@husc8> <1992Jul21.141253.17366@jlc.mv.com>
- Reply-To: sichase@csa3.lbl.gov
- NNTP-Posting-Host: 128.3.254.198
- Keywords: four-vectors
- News-Software: VAX/VMS VNEWS 1.3-4
-
- In article <1992Jul21.141253.17366@jlc.mv.com>, john@jlc.mv.com (John Leslie) writes...
- >In article <mcirvin.711673227@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
- >>dk@imager (Dave Knapp) writes:
- >>
- >>In fact, I think that a more important issue than the definition of
- >>mass is the use of four-vectors in introductory classes teaching SR,
- >>which I think should be encouraged, since it brings beauty and
- >>simplicity to something which otherwise looks like an algebraic junkheap
- >>built on a shifting foundation of paradoxes.
- >>
- > Could someone have mercy on those of us whose college physics is
- >twenty or more years in the past? What is "four-vectors"?
-
- A four-vector is a vector with 4 components. Space-time is four-dimensional,
- with each point being represented by a 4-vector in some arbitrary coordinate
- system as (t,x,y,z). All the equations of relativity (and any theory
- such as quantum field theory which you want to express in a relativistically
- invariant way) are constructed in terms of 4-vectors and 4x4 matricies which
- operate on the 4-vectors. Other examples are the energy-momentum 4-vector
- (E,px,py,pz) and the gradiant operator (dt,dx,dy,dz).
-
- Every four-vector transforms the same way under Lorentz boosts. Therefore,
- energy transforms like the time, while momentum transforms like a length.
-
- When you get down to the nitty-gritty, things get a little more complicated,
- so that my last statement is not exactly true. There are two classes of
- 4-vectors: covariant and contravariant, which transform somewhat differently
- under the Lorentz transformations.
-
- Reference: Taylor and Wheeler's _Spacetime Physics_ is the classic.
-
- -Scott
- --------------------
- Scott I. Chase "The question seems to be of such a character
- SICHASE@CSA2.LBL.GOV that if I should come to life after my death
- and some mathematician were to tell me that it
- had been definitely settled, I think I would
- immediately drop dead again." - Vandiver
-