disclaimer: Although i am (was) a physicist, I am not a string theorist. On Fri, Aug 28, 2009 at 10:06 PM, Oleg Goldshmidt <p...@goldshmidt.org>wrote:
> Shachar Shemesh <shac...@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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