Natural Science Forum / Physics / Relativity / August 2006

Please don't flame me just because of this 'idea'. It's true, that I'm
really thinking like this, and I would really like to hear if other
people are thinking the same way.

When talking about space-time, similar units must somehow be choosen
for space or time.

Yes. The unit of "distance" is ct.
The problem is time doesn't run backwards, so spacetime has no
past or future, everything is preordained.
If we say length is a dimension then the whole ruler exists at once
but we can pick a place on the desk to measure it relative to some
other place say he paperweight to the edge, turn the ruler over and
measure from the edge to the paperweight.
If we say time is a length-like dimension then we can measure it
relative to any other time, but can only measure one way round
or we would know the future.
Fortune tellers and charlatans have always made money on that,
Rasputin and Einstein were no different. All you need do is
persuade the gullible that you are competent and they fall for it
every time, but it helps if you don't comb your hair.

I'm thinking like this:

Nah... you are not thinking at all.

You can't see the forest for the trees or the con for the Eiffel
Tower you bought. It's your money, buy the book, pay
the taxes and fund the super-collider they won't let you play
with.
Time is not a vector, it has no additive inverse.

Curved nothing:
 http://selair.selkirk.bc.ca/aerodynamics1/Support_Graphics/Vortices.GIF

Androcles

Please don't flame me just because of this 'idea'. It's true, that I'm
really thinking like this, and I would really like to hear if other
people are thinking the same way.

When talking about space-time, similar units must somehow be choosen
for space or time. I'm thinking like this: The suggestion is that both
space-units or time-units can be used after one's own choice. There are
only two meanings of the units in practice:

* To indicate if we are talking about time (or time-like) or space
(space-like). The right units makes it intuitive to the reader what the
quantity is.

* The scaling of the units. A reasonable range must be choosen. For
example for length we have 'meters' in daily life. But if we would like
to discuss things like atomic physics, then the scale Ångstrøm (1 Å
= 10^-10 m) would probably be better. It's just like this.

The idea is, that both meter and seconds can be used in space-time
after one's own choice. Only the need to inform the reader about the
meaning, and the choice of units on a relevant scale, are needed to
make the choice.

In this model, the speed-of-light is simply c = 1 (without any units).

This is the advantage of these units described. It's basically the same
as in most litterature in relativity, where 'c=1' is assumed, and
similar units for space and time are usually used.

So here: 1 s = 299,792,458 m in 'space-time length'. Choose meter or
second as it would be best: The symbolic meaning and the best
unit-scale.

What's the opinion on this way of thinking?
(IMHO it's working very well...)

PC

Harald replies:

It's indeed very convenient (and common practice) to choose c = 1
light-second / s, and nothing is wrong with that.
Sometimes c = 1 is presented as if it has no unit, typically by people with
a mathematics background. However, length just isn't time, and therefore
it's inherently incorrect to portray c as a unit-less constant.

Harald

Sure. This is quite standard in modern physics. That's where "light
year" came from. Most theoretical physicists use units in which
c=hbar=G=K_boltzman=1, and the basic unit is cm.

Tom Roberts