The universal exponent (nu(r)) of the real polymer size (i.e., the excluded volume chain) is derived from constraining the ideal coil model (nu(i) = 1/2) to a Minkowski-type diffusive spacetime. The square end-to-end distance was expanded in wavenumber power series, whence the leading contribution is extracted according to previously proposed Lorentz transforms acting in Brownian media. In the end, it turns out nu(i) similar or equal to nu(r) sin(1), in good agreement with predictions of the phase transition theory for critical phenomena. (c) 2006 Elsevier Inc. All rights reserved.