Albert Einstein
(Copyright © 2005 Piero Scaruffi | Legal restrictions - Termini d'uso )

Philosophy of Nature

  • Laws of nature must be uniform
  • Laws must be the same in all frames of reference that are "inertial"
  • The speed of light is the same in all directions
  • Lorentz transformations
  • The length of an object and the duration of an event are relative to the observer
  • All quantities must have four dimensions, a time component and a space component (e.g., energy-momentum)
  • Equivalence of mass and energy (E=mc2)
  • Space and time are not absolute
  • "Now" is a meaningless concept
  • The past determines the future
  • Nothing can travel faster than light
  • Time does not flow (no more than space does), it is just a dimension
  • Space and time are different dimensions of the same space-time continuum
  • Each observer has a different perspective on the events in the space-time continuum (e.g., length or duration)
  • Past and future are segments of space-time continuum
  • Each observer's history is constrained by a cone of light within the space-time continuum
  • Each observer's history is a "world line", the spatio-temporal path that the observer is actually traveling through space-time
  • "Proper" time is the spacetime distance between two points on a world line (the time experienced by the observer as she travels along its world line)
  • Relativity for systems accelerated with respect to one another
  • Principle of Equivalence: Forces produced by gravity are in every way equivalent to forces produced by acceleration
  • It is no possible to distinguish between gravitational and accelerational forces by experiment (e.g, an acceleration of 9.8 m/sec2 in outer space is "equivalent" to gravitational force on the Earth)
  • All forces (gravitational or not) are due to acceleration
  • Newton's hypothesis that every object attracts every other object is unnecessary
  • Masses curve spacetime.
  • Spacetime's curvature determines the motion of masses.
  • Einstein's law of gravity: Every object, which is not subject to external forces, moves along a geodesic of spacetime (the shortest route between two points on a warped surface), its "world line"
  • Spacetime "is" the gravitational field
  • When an object appears (in 3D space) to be "at rest" but under the effect of gravitational attraction, it is actually being "accelerated" (attracted) towards the center of the earth along its world-line (in 4D spacetime) which happens to be curved by the spacetime curvature caused by the Earth's mass
  • It is spacetime that is curved, not the geodesic.
  • Gravitation is not a force
  • Physics = Geometry of space-time
  • Gravitation = space-time curvature
  • Relativity theory is ultimately about the nature of gravitation
  • Relativity explains gravitation in terms of curved space-time, i.e. Geometry
  • "Gravitational force" becomes an effect of the geometry of space-time
  • The curvature of space-time is measured by a "curvature tensor" (Riemann's geometry)
  • Each point is described by ten numbers (metric tensor)
  • Euclid's geometry is one of the infinite possible metric tensors (zero curvature)
  • Other geometries describe spaces that are not flat, but have warps
  • What causes the "warps" is energy-mass
  • Clocks slow down in a gravitational field
  • Light is deflected in a gravitational field
  • Cosmological constant to counterbalance the effect of gravity

(Copyright © 2005 Piero Scaruffi | Legal restrictions - Termini d'uso )