Physicist Proposes Solution to Arrow-of-Time Paradox

The laws of physics, which describe everything from electricity to moving objects to energy conservation, are time-invariant. That is, the laws still hold if time is reversed. However, this time reversal symmetry is in direct contrast with everyday phenomena, where  it’s obvious that time moves forward and not backward .

For example, when milk is spilt, it can’t flow back up into the glass, and when pots are broken, their pieces can’t shatter back together. This irreversibility is formalized through the second law of thermodynamics, which says that entropy always increases or stays the same, but never decreases. This contrast has created a reversibility paradox, also called  Loschmidt’s paradox , which scientists have been trying to understand since Johann Loschmidt began considering the problem in 1876. Scientists have proposed many solutions to the conundrum, from trying to embed irreversibility in physical laws to postulating low-entropy initial states.