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From: gwyn@brl-smoke.UUCP
Newsgroups: net.physics
Subject: Re: The death of bogus physics
Message-ID: <2192@brl-smoke.ARPA>
Date: Sat, 29-Mar-86 01:47:39 EST
Article-I.D.: brl-smok.2192
Posted: Sat Mar 29 01:47:39 1986
Date-Received: Tue, 1-Apr-86 07:17:44 EST
References: <12603@ucbvax.BERKELEY.EDU> <2049@brl-smoke.ARPA> <12699@ucbvax.BERKELEY.EDU>
Reply-To: gwyn@brl.ARPA
Organization: Ballistic Research Lab (BRL)
Lines: 43

In article <12699@ucbvax.BERKELEY.EDU> weemba@brahms.UUCP (Matthew P. Wiener) writes:
>In article <2049@brl-smoke.ARPA> gwyn@brl.ARPA writes:
>>In answer to the fellow who wanted to know what the difference is
>>between space and space-time:  When one diagonalizes the symmetric
>>part of the metric (the only part considered in normal general
>>relativity) using real coordinate mappings, one of the four
>>diagonal elements will have different sign than the other three.
>>In the transformed (local Lorentz) frame, that coordinate will be
>>associated with the direction of time while the other three are
>>spatial.
>
>I don't believe this.  The fellow asked for laymen's terms only.

So?  I would like a layman's explanation of how the universe works
in 25 words or less, but I don't think it's very likely.  The
problem with simpler, inaccurate explanations is that one then has
to work even harder to correct all the misperceptions that the
oversimplified explanation produces.  Since nobody had answered
the question about "the difference between space and spacetime"
(see! already a misperception) satisfactorily, I decided to supply
an accurate answer as an aside to another posting.  I really don't
think this topic could be explained to a layman without many pages
of discussion and examples, in any event; without resorting to
something like my principal axes of the metric tensor explanation,
a layman's explanation would sound something like:  "At any place
in the universe, at any time, there are three directions of space,
which have no preferred alignment, and one direction of time.
Time is that which a clock measures, and space can be measured by
yardsticks."  I don't think that would be particularly
enlightening.  Worse yet, a clever layman is likely to ask
embarrassing questions such as:  "Is there any place in the
universe with only two space directions?  Two space and two time?
etc.?"  Then one would have to explain more accurately anyway.

If you think you can answer the layman's question better,
please do so, and more power to you.


	"We know for certain, for instance, that for some
	reason, for some time in the beginning, there were
	hot lumps."
		-- Firesign Theater, "I Think We're All
					Bozos On This Bus"