Albert Einstein holding the visible Universe, to whose current understanding he contributed so significantly.
Image credit: Albert Einstein by Alvaro De Rújula. The visible universe CC-00 via WMAP/NASA. Used with permission.

On the lower one, the left-hand side describes gravity, the right-hand side its “source.” The symbols c and G are the speed of light and Newton’s constant, which determines the magnitude of the gravitational forces μ and ν are “indices” that “run” from 0 to 3 for time and the three dimensions of space. The 8 and π are other rather well-known numbers.

Image credit: Albert Einstein and his blackboards by Alvaro De Rújula. Used with permission.

Image credit: The diverse perceptions of different professionals by Alvaro De Rújula. Used with permission.

The guy in the rocket would be floating in it (if in a region with no significant gravitational forces), or if he and the rocket were in free fall in a gravitational field, as astronauts are in the Space Station (left). If he is in an accelerating rocket (middle) or at rest in a gravitational field (right) he cannot tell unless he cheats (by looking out of a window).
Image credit: Acceleration = Gravity by Alvaro De Rújula. Used with permission.

Typical sizes in meters are shown on the left-most column. Three of the four known fundamental forces are listed (the weak force does not play a role in stabilizing material objects). Nuclear forces binding protons and neutrons in nuclei are a consequence of the more fundamental Quantum Chromodynamic interactions between quarks. Analogously, chemical forces between atoms are a peripheral manifestation of the Quantum Electrodynamic forces between electrons and nuclei.
Image credit: All things made out of “ordinary” matter. by Alvaro De Rújula. Used with permission.

The sizes of “all” things, on a logarithmic scale in centimetres. The Large Hadron Collider has a radius of about 7 km. A caviar egg, a few millimeters. Spain has a geometric (or logarithmic) average size, in the ensemble of all sizeable things.
Image credit: The sizes of “all” things, on a logarithmic scale in centimetres by Alvaro De Rújula. Used with permission.

Large distances, compared to the full sixe of our Galaxy, represented by a 5 Swiss-Franc coin. A quasar is a gigantic black hole, visible from afar given the intense luminosity of the jets it spits out as it swallows the central areas of its “host” galaxy. Virgo is the cluster of galaxies to which we belong. The ratio of the sizes of the Galaxy and the visible Universe equals that of the coin and the LHC.
Image credit: Large distances by Alvaro De Rújula. Used with permission.

Newton’s laws of the equal but oppositely directed forces of action and reaction (top). Newton’s apocryphal apple leading him to discover the relation between force, mass, and acceleration (F=Ma) (center), as well as the expression for a gravitational force between two objects, in terms of their masses and the distance between their centers (bottom).
Image credit: Newton’s laws by Alvaro De Rújula. Used with permission.

Faraday’s failed experiment on what would have been this second law of induction (of electricity by gravity). The (super?) string may have been premonitory. Many of Faraday’s instruments are preserved at the Royal Institution in Mayfair, London.
Image credit: Faraday’s failed experiment by Alvaro De Rújula. Used with permission.

Image credit: A dialog with an incorrect conclusion by Alvaro De Rújula. Used with permission.

Image credit: Ancient views on gravity and the Universe around us by Alvaro De Rújula. Used with permission.