The … extra spatial dimensions are put on an essentially equal footing with those of ordinary space and time.

The trouble with these monopoles is the lack of any indication of their actual existence.

The impossibility of the causal communication that would be required for thermalization, in the standard model, is referred to as the horizon problem.

One of the mysterious aspects of the mass problem is the absurdly tiny size that the values that the masses of ordinary particles have when measured in absolute units. For example, the mass m(e) of the electron, in absolute units, is about m(e) = 0.000,000,000,000,000,000,000,043….

People often have strong emotional responses to questions of the origin of the universe―and sometimes these are either implicitly or explicitly related to religious preferences. This is not unnatural; for the issue is indeed that of creation of the entire world in which we live.

The Spacetime singularities lying at cores of black holes are among the known (or presumed) objects in the universe about which the most profound mysteries remain―and which our present-day theories are powerless to describe.

The cosmological constant has hovered in the background of cosmological theory ever since Einstein first put it forward, causing worry to some and solace to others.

As a way of appreciating the problem we can imagine the Creator trying to … start the universe off in a way that resembles what we know of it today. … If the Creator were to miss [the exact way needed] by just the tiniest amount … then an uninhabitable universe … would be the result, in which there is no … time directionality ….