There's something that has been bugging me for over a year now and I seem to be unable to find the answer. I would appreciate it very much if somebody could help me out. The thing is that I don't understand how it is possible that in second order phase transitions the correlation legth becomes infinite. I don't understand the scale invariance of thermal fluctuations in these critical phenomena. How is this fact consistent with special relativity? After all a local perturbation should never be able to propagate faster than the speed of light, right? There's something that I am not getting right. But the more I think and read about this the less I understand it. Thanks in advance for your help.