Quotes from John D. Barrow

Einstein argued that the laws of Nature should appear to be the same for all observers in the Universe, no matter where they were or how they were moving. If they were not then there would exist privileged observers for whom the laws of Nature looked simpler than they did for other observers.

universal laws prescribe how things will behave not, like human laws, how they ought to behave.

This picture of matter curving space and curvaceous space dictating how matter and light will move has several striking features. It brings the non-Euclidean geometries that we talked about in the last chapter out from the library of pure mathematics into the arena of science. The vast collection of geometries describing spaces that are not simply the flat space of Euclid are the ones that Einstein used to capture the possible structures of space distorted by the presence of mass and energy.

Gravity acts on all forms of mass and energy, but energy comes in a host of very different forms that behave in peculiar ways that were not known in Newton's day. Wotst of all, gravity gravitates. Those waves of gravity that spread out, rippling the curvature of space, carry energy too and that energy acts as a source for its own gravity field. Gravity interacts with itself in a way that light does not.

nothing is higher than heaven; nothing is beyond the walls of the world; nothing is lower than hell, or more glorious than virtue."48

There are about one hundred billion galaxies within this visible universe and the average density of material within a galaxy is about one million times greater than that in the visible universe as a whole, and corresponds to about one atom in every cubic centimetre.

Navy: Please divert your course 15 degrees to the North to avoid a collision. Civilian: Recommend you divert your course 15 degrees to South to avoid a collision. Navy: This is the Captain of a US Navy ship. I say again, divert your course. Civilian: No, I say again, divert your course. Navy: This is the aircraft carrier Enterprise. We are a large warship of the US Navy. Divert your course now!! Civilian: This is a lighthouse. Your call." Canadian naval radio conversation38

A 'group' is simply a collection of changes which possess three simple properties: there must be the possibility of no change, there must exist the possibility of undoing or reversing each change to restore its original state, and any two consecutive changes must give a result that could equally well be attained by another single change.

The impact over the following centuries of Copernicus' leap away from the prejudices of anthropocentrism was felt across the whole spectrum of human investigation. We began to appreciate our place in the Universe was by no means central. Indeed, in many respects, it appeared to be almost peripheral.

Thus we see that the quantisation of atomic energies into a ladder of seperate values, rather than allowing them to take on the entire continuum of possible values, lies at the heart of the life-supporting stability and uniformity of the world around us.

Einstein enunciated what he called the Principle of Covariance: that laws of Nature should be expressed in a form that will look the same for all observers, no matter where they are located and no matter how they are moving.

The presence of the particles of matter , and their motion, determine the local topography of the space in which they sit.