the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics. This puts the time reversal symmetry of (almost) all known low-level fundamental physical processes at odds with any attempt to infer from them the second law of thermodynamics which describes the behaviour of macroscopic systems.

Stated simply, the Novikov consistency principle asserts that if an event exists that would give rise to a paradox, or to any “change” to the past whatsoever, then the probability of that event is zero. In short, it says that it is impossible to create time paradoxes.

For example, a computer with the mass of the entire Earth operating at the Bremermann’s limit could perform approximately 1075 mathematical computations per second. If we assume that a cryptographic key can be tested with only one operation, then a typical 128 bit key could be cracked in under 10−36 seconds. However, a 256 bit key (which is already in use in some systems) would take about two minutes to crack. Using a 512 bit key would increase the cracking time to approaching 1072 years, without increasing the time for encryption by more than a constant factor (depending on the encryption algorithms used).

we built a bicycle with extra counter-rotating wheels (canceling the wheel spin angular momentum) and with its front-wheel ground-contact forward of the steer axis (making the trailing distance negative). When laterally disturbed from rolling straight, this bicycle automatically recovers to upright travel.

the plate trick, also known as Feynman’s plate trick, Dirac’s belt trick, Dirac’s string trick, Balinese cup trick, spinor spanner, Bredon high-five, or quaternionic handshake, is any of several particular physical demonstrations of the mathematical theorem that SU(2) double-covers SO(3). The usual demonstration, as indicated by the name, is to hold a plate on one’s flat palm, then perform two subsequent rotations of the arm holding the plate, which results in the original position. In the cup variant, supposedly inspired by a Balinese candle dance, an open cup of water or wine is held in ones hand and rotated 720 degrees, or any multiple thereof, without spilling the liquid or loosening ones grip on the cup.

the feature of nature that says experimental results are independent of the orientation or the boost velocity of the laboratory through space

Quark, for example, was formerly a nonce word in English, appearing only in James Joyce’s Finnegans Wake. Murray Gell-Mann then adopted it to name a new class of subatomic particle.

physicists predicted that electrons in a one-dimensional chain of atoms could be split into three quasiparticles: a %u2018holon%u2019 carrying the electron%u2019s charge, a %u2018spinon%u2019 carrying its spin (an intrinsic quantum property related to magnetism) and an %u2018orbiton%u2019 carrying its orbital location

since Cat’s Cradle, scientists have discovered some real-world example of crystals that seed the environment, converting other forms (polymorphs) of the crystal into their own.

rigid suit filled with water to allow pilots to withstand up to 10Gs.

A person immersed in liquid of the same density as tissue has acceleration forces distributed around the body, rather than applied at a single point such as a seat or harness straps.

double refraction, is the decomposition of a ray of light into two rays when it passes through anisotropic materials, such as crystals of calcite or boron nitride.

slightly wedge shaped bricks/stones used to build an arch

the basic condition for the safety of masonry is that the thrust line is kept within the middle third of a wall or column

building out masonry step-wise from each side until the stones meet in the middle (precursor to an arch)

that’s why it softens

a line passing down the wall of a building from the top to bottom which defines the position at which vertical thrust can be thought to act on each joint

distortion in material over time

when people are exposed to prolonged, strong vibrations (such as from using chainsaws), their arteries can elongate

shearing load / area

a measure of the tendency for one part of a solid to slide past the neighboring part

angle through which material is distorted as a result of shear stress (in radians)

stiffness of a material in shear (shear stress / shear strain). equivalent of Young’s modulus.

different in different directions (aka aelotropic)

same in all directions (from greek)

area under stress/strain curve (¹⁄₂ * s * e for Hookean materials)

Proportional increase in length due to stress (e = increase/original = I/L)

Force / Area that the force acts over (s = load/area = P/A)

defined as the stress required to break it

roughly stiffness, E = s/e

specified by Inglis: s(1 + 2*sqrt(L/r))

number of times material strength is higher than expected working load

so they could assess the tensions of the ropes by ear

L-sub-G: Point at which cracking system goes from consuming energy to releasing. ¹⁄₂ * 2 * WE / (strain energy)^2

form of fracture where material deforms plastically before breaking in tension

or “fracture energy”: “toughness”, quantity of energy required to break a given cross-section of material

the amount of strain energy that may be stored in a structure without causing permanent damage.

made from springy wood and only four spokes. worked like a bow to absorb shock.

it expands and spreads the shearing forces across a larger area.

the point at which a load must be applied so as to cause no twisting

if a wing isn’t rigid enough, an aileron can cause the wing to twist to such an extent that the opposite effect is achieved

the outside wood is tensioned to 4,000 psi while the inner wood is compressed

two rigid outer layers with a porous lightweight interior sandwiched between them

shell structure in which the load is carried in more or less continuous panels (think exoskeleton)

Researchers were puzzled when they discovered that the same familiar interference patterns were observed with large-scale molecules, and not exclusively with subatomic particles.