Re: Howlers

Tim S <Tim@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Jonathan L Cunningham wrote:


Conversely, you could do dimensional analysis treating mass and time as
the same (it would be a pretty daft thing to do, but you could). If you
did that, you couldn't distinguish momentum from length, but anything
you *can* distinguish (e.g. momentum and energy would still have
different dimensions) must certainly be different.

People do this all the time in GR. You set c and G to 1, and mass,
length and time all come out in the same units. Just as in QFT, you set
c and hbar to 1 and measure distance in reciprocal electron volts, etc.

Yebbut ... they don't think mass and time are the *same* -- they are
just normalising the units. Like a radius of curvature (of a curve at a
point) is not the same thing as the distance along the curve (at that
point) but it makes sense to measure them both in the same units, rather
than in furlongs and angstroms, even if it is a very short, very
straight, line. (I can imagine a curve 3 angstroms long with a radius
of curvature of 2.1 furlongs. Short and straight, it is.) And that's
much like our conventional measurements of mass, length and time.

Jonathan

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