Mass–energy equivalence

Second, Einstein’s E = mc^2 is not an equivalence of energy and matter. It is the equivalence of energy and mass (i.e. the number of kilograms). So a unit volume of the empty space carries some mass equivalent to the energy – it’s a mass of a few protons per cubic meter. But the E = mc^2 equation does not imply, in any sense, that the mass equivalent to the energy has to take the form of localized particles. It may be dispersed, much like the cosmological constant – whose generalized form is also called dark energy. The main reason why the vacuum contains mass is that this mass contributes to the curvature of spacetime – the gravitational field of mass – and be sure that dark energy does. That is why it was introduced.

Dark energy, unlike mass, carries a negative pressure, and it’s the real source of the accelerating expansion it induces. Ordinary matter has attractive gravity.

— answered May 3, 2011 at 4:33

— Lubos Motl

2012.10.09 Tuesday ACHK


地獄篇 6

Nature is evil. So Nature is not the Light.

— Me@2011.11.14

For example, many animals have to kill each other in order to survive.

Many evil aspects of human nature are designed by Nature. In order to be good, we have to transcend Nature. For example, we can create a society in which we can support each other instead of killing each other.

— Me@2012.10.09

2012.10.09 Tuesday (c) All rights reserved by ACHK