Hi PF! I was wondering, if the holographic principle (from string theory) really can be true. I see some physical flaws in the way it works. Here is why: Suppose that the second law of thermodynamics is true. It states that for any system, the multiplicity of the system must increase, ergo the entropy of the system must increase. As a result of this, the entropy of the universe must increase. So how does this relate to conservation of energy? Well, first of all Stephen Hawking and Jacob Beckenstein showed a relation between the entropy of a black hole and it's surface area and therefore to the square of its mass [itex]S \propto M^2[/itex] (due to the Schwarzchild radius' direct proportionality to mass). So we can now state, that if the entropy changes, so does the mass of a black hole. So now, how does the holographic principle work? Well it generalizes the principle of black hole information to the whole universe (see fx http://arxiv.org/abs/hep-th/0203101). So what does this mean physically? If we change the entropy of the universe, we change the mass of the universe, and by applying special relativity's mass-energy relation, we also increase the energy of the universe by changing it's entropy. So by the second law of thermodynamics, the energy content of the universe should increase till the entropy is at a maximum, which it is clearly. This has really been puzzling me, so can anyone give a hint or clarification if the above is right or wrong? Thank you so much for your time.