Time travel: is it possible?

Is time travel possible? The laws of physics in the microscopic world suggest that it is because the physical processes they define at the subatomic level appear to be either entirely or mostly time symmetric.  In other words the theoretical statements that describe them remain true if the direction of time is reversed.  However, the … Read more

The story of life in four spatial dimensions.

One of the most puzzling questions in modern cosmology is why the density of matter and energy appears to be find tuned to the value that allowed life to evolve. For example the density of mass to energy in the early universe must have been very close to a specific value to explain how stars … Read more