[OT] How many dimensions? (WAS: Power over radio)

[Erez D]

disclaimer: Although i am (was) a physicist, I am not a string
theorist.

On Fri, Aug 28, 2009 at 10:06 PM, Oleg Goldshmidt <pub at goldshmidt.org>wrote:

> Shachar Shemesh <shachar at shemesh.biz> writes:
>
> > Dotan Cohen wrote:
> >
> > Oleg, I understood that the universe has 11 or so dimensions, and that
> > 5 or six can even be measured. But the wikipedia article that you
> > link to claims only 3+1. I have googled a bit but found only very
> > technical explanations, or baby facts with no explanations. Can you
> > sum it up for someone who is familiar with relativity, but is not a
> > physicist?  Thanks.
>
see below...


> Ouch! We need a new list - science for Linux geeks or sth like
> that. Mea culpa!
>
count me in


well, according to newton, we have 3+1 dimensions.
according to relativity, we have 4 (i'll explain the difference later).
according to string theories, we have more (depending on the theory) but
which is practically reduced to 4 for any valid experiment due to that all
dimensions other then the 4 we know are not infinite (i.e. does not go from
minus infinite to plus infinite) but are so small, as any particle position
can not be measured according to Heisenberg's uncertainty principle (it
doesn't contradict the principle, it uses it). so anything other than the 4
main dimensions is useless.

now, the difference between 3+1 and 4 dimensions.
lets take for example a particle in position (x,y). we can choose a rotated
coordinates in which the particle be at (x',y'). we can choose a corrdinates
which x' > x and y'<y. so we can "rotate" the x value into the y value and
vice versa. this is true 2D.
however, if we take a particle (event) at (x,t). we can not rotate the
coordinates. we can shift the origin but not rotate the coordinates, so we
can not choose coordinates in which the event occured in a different time as
we rotated a value from t to x.
so this is 1+1 dimensions.
in newtonian physics, we can rotate the xyz coordinate, we can rotate x into
y and y into z. we can not rotate x into t. so it is a 3+1 coordinate
system.
in relativity, we can rotate x into t, and t into y. so this is real 4D.

erez.
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