Re: Setting constants like hbar to unity
From: J. J. Lodder (nospam_at_de-ster.demon.nl)
Date: 08/24/04
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Date: Tue, 24 Aug 2004 09:55:04 +0000 (UTC)
greywolf42 <mingstb@marssim-ss.com> wrote:
> "J. J. Lodder" <nospam@de-ster.demon.nl> wrote in message
> news:1gipqxl.blgmfm72alnwN@de-ster.xs4all.nl...
> >
> > Frank Hellmann <Certhas@gmail.com> wrote:
> >
> {snip}
>
> > all distances are measured with a clock, ultimately.
> > When you start asking how those marks on your metre rod
> > came to be where they are you end up at a clock
> > in a standards laboratory.
>
> Only if you used a clock to make the marks. They didn't use clocks in the
> old days.
But they didn't achieve 10^{-14} reproducibility either.
There is no stopping progress :-)
> The redefinition of distance into a time multiplied by light speed was a
> very recent change. And it is not necessary, merely a new convention.
It is absolutely necessary, and not merely a new convention,
from a metrologists point of view.
The reason for it is not a desire theoretical neatness,
but an entirely practical one.
The metre based on the second can be reproduced more accurately
than any directly defined length standard.
(by several orders of magnitude)
-If- somebody were to invent a new length standard,
reproducible to much better than 10^{-14}
the second would be abolished as an independent unit.
> > > Which is why, while in theoretical sciences it may make no conceptual
> > > sense to treat them with different units it certainly makes a lot of
> > > conceptual sense in experimental sciences where you have to treat them
> > > very differently.
> > > Therefore they are here to stay, therefore the confussion and the need
> > > to translate them when going from a theoretically convenient system to
> > > an experimentally convenient system.
> >
> > The nanosecond would be a very practical unit of length
> > for everyday use. It equals about a foot.
>
> Only at lightspeed. And lightspeed varies in the real world ... depending
> upon the local environment.
Of course not.
A nanosecond is 0.299792458 m, exactly, and by definition.
> Of course
????? part of your sentence missing.
> > The nano would be a very practical unit of speed.
> > It equals about 1 km/h
>
> 'Nano' is a prefix of a unit (10^-9). It is not a unit itself. A unit of
> speed would be nanosecond per second (or per nanosecond). Which -- to me --
> indicates that the attempt shows how confusing the whole effort would be.
No doubt some convenient name for '10^{-9}' could be invented.
Lacking an official definition I'll use 'nano', if you don't mind.
BTW, your objection is neither new nor original.
Opposition to the metric system back in 1800 already focussed
on those queer and outlandisch or even 'barbaric' prefixes,
like (then) 'hecto'.
> > The only reason for not changing is backwards compatibility:
> > There is just too much that has been archived in metres,
>
> The whole point of the metric system was to make useful, descriptive set of
> units of rational relationships. There are already metric units for time
> (tics are the equivalent of the second).
>
> > and the conversion factor 299 792 458 m/s is just too nasty.
>
> Far better than slugs, furlongs and feet.
>
> > But: were we still using Parisian toises, and Imperial inches,
> > different of course from US inches, etc. etc.,
> > and only now changing over to new universal 'scientific' units
> > there can be little doubt that there would not be
> > an independent unit of length in the new system.
>
> The history of the metric system is fascinating. Only the yanks retain
> inches. There is no 'US inch.' It's an English inch. But I have heard
> that the Brits went metric.
There was a US inch. And it was different from the imperial inch.
Both were defined independently to 6+ decimal places.
However, 'very recently' it was decided to abolish all independent
definitions of the non-metric units, and to redefine both the US inch
and the imperial inch to be 25.4 mm (exactly).
So, the new inch is not equal to the old 'English' inch.
And indeed, the Brits -officially- went metric,
so perhaps in another hundred years ...
Best,
Jan
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