| The laws list: E |
The laws list E
Eddington limit to event horizon.
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E.
- Eddington limit (Sir A. Eddington)
-
- The theoretical limit at which the photon
pressure would exceed the gravitational attraction of a light-emitting body.
That is, a body emitting radiation at greater than the Eddington limit would
break up from its own photon pressure.
-
- Edwards-Casimir
quantum vacuum drive
-
- A hypothetical drive
exploiting the peculiarities of quantum mechanics by restricting allowed
wavelengths of virtual photons on one side of the drive (the bow of the
ship); the pressure generated from the unrestricted virtual photons toward
the aft generates a net force and propels the drive.
-
- Ehrenfest paradox (Ehernfest, 1909)
-
- The special relativistic "paradox" involving
a rapidly rotating disc. Since any radial segment of the disc is
perpendicular to the direction of motion, there should be no length
contraction of the radius; however, since the circumference of the disc is
parallel to the direction of motion, it should contract.
-
- Einstein field equation
-
- The cornerstone of Einstein's general
theory of relativity, relating the gravitational tensor G to the
stress-energy tensor T by the simple equation
G = 8 pi T.
- Einstein-Podolsky-Rosen
effect; EPR effect
-
- Consider the following quantum
mechanical thought-experiment: Take a particle which is at rest and has spin
zero. It spontaneously decays into two fermions (spin 1/2 particles), which
stream away in opposite directions at high speed. Due to the law of
conservation of spin, we know that one is a spin +1/2 and the other is spin
-1/2. Which one is which? According to quantum mechanics, neither takes on a
definite state until it is observed (the wavefunction is collapsed).
The EPR effect demonstrates that
if one of the particles is detected, and its spin is then measured, then the
other particle -- no matter where it is in the Universe -- instantaneously
is forced to choose as well and take on the role of the other particle. This
illustrates that certain kinds of quantum information travel
instantaneously; not everything is limited by the
speed of light.
However, it can be easily demonstrated that this effect does not make
faster-than-light communication or travel possible.
-
- Eotvos law of capillarity
(Baron L. von Eotvos; c. 1870)
-
- The surface tension gamma of
a liquid is related to its temperature T, the liquid's critical
temperature, T*, and its density rho by
gamma ~= 2.12 (T* -
T)/rho3/2.
- equivalence principle
-
- The basic postulate of A. Einstein's
general theory of relativity, which posits that an acceleration is
fundamentally indistinguishable from a gravitational field. In other words,
if you are in an elevator which is utterly sealed and protected from the
outside, so that you cannot "peek outside," then if you feel a force
(weight), it is fundamentally impossible for you to say whether the elevator
is present in a gravitational field, or whether the elevator has rockets
attached to it and is accelerating "upward."
Although that in practical situations --
say, sitting in a closed room -- it would be possible to determine whether
the acceleration felt was due to uniform thrust or due to gravitation (say,
by measuring the gradient of the field; if nonzero, it would indicate a
gravitational field rather than thrust); however, such differences could be
made arbitrarily small. The idea behind the equivalence principle is that it
acts around the vicinity of a point, rather than over macroscopic distances.
It would be impossible to say whether or not a given (arbitrary)
acceleration field was caused by thrust or gravitation by the use of physics
alone.
The equivalence principle predicts
interesting general relativistic effects because not only are the two
indistinguishable to human observers, but also to the Universe as well --
any effect that takes place when an observer is accelerating should also
take place in a gravitational field, and vice versa.
-
- ergosphere
-
- The region around a rotating black hole, between
the
event
horizon and the
static
limit, where rotational energy can be extracted from the black hole.
-
- event horizon
-
- The radius that a spherical mass must be
compressed to in order to transform it into a black hole, or the radius at
which time and space switch responsibilities. Once inside the event horizon,
it is fundamentally impossible to escape to the outside. Furthermore,
nothing can prevent a particle from hitting the
singularity in a very short amount of proper time once it has entered
the horizon. In this sense, the event horizon is a "point of no return."
The radius of the event horizon, r, for generalized black holes
(in
geometrized units) is
r = m + (m2 - q2 -
s/m2)1/2,
where m is the mass of the hole, q is its electric charge, and
s is its angular momentum.
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