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  2. Tachyon - Wikipedia

    en.wikipedia.org/wiki/Tachyon

    This means that if observer A sends a signal to observer B which moves faster than light in A's frame but backwards in time in B's frame, and then B sends a reply which moves faster than light in B's frame but backwards in time in A's frame, it could work out that A receives the reply before sending the original signal, challenging causality in ...

  3. Electromagnetic absorption by water - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_absorption...

    Liquid water and ice emit radiation at a higher rate than water vapour (see graph above). Water at the top of the troposphere, particularly in liquid and solid states, cools as it emits net photons to space. Neighboring gas molecules other than water (e.g. nitrogen) are cooled by passing their heat kinetically to the water.

  4. Brownian motion - Wikipedia

    en.wikipedia.org/wiki/Brownian_motion

    2-dimensional random walk of a silver adatom on an Ag(111) surface [1] Simulation of the Brownian motion of a large particle, analogous to a dust particle, that collides with a large set of smaller particles, analogous to molecules of a gas, which move with different velocities in different random directions.

  5. Slow light - Wikipedia

    en.wikipedia.org/wiki/Slow_light

    Slow light is a dramatic reduction in the group velocity of light, not the phase velocity. Slow light effects are not due to abnormally large refractive indices, as will be explained below. The simplest picture of light given by classical physics is of a wave or disturbance in the electromagnetic field.

  6. Absorption (electromagnetic radiation) - Wikipedia

    en.wikipedia.org/wiki/Absorption_(electromagnetic...

    A white light source—emitting light of multiple wavelengths—is focused on a sample (the pairs of complementary colors are indicated by the yellow dotted lines). Upon striking the sample, photons that match the energy gap of the molecules present (green light in this example) are absorbed, exciting the molecules. Other photons are scattered ...

  7. Cell signaling - Wikipedia

    en.wikipedia.org/wiki/Cell_signaling

    Receptors may bind with some molecules (ligands) or may interact with physical agents like light, mechanical temperature, pressure, etc. Reception occurs when the target cell (any cell with a receptor protein specific to the signal molecule) detects a signal, usually in the form of a small, water-soluble molecule, via binding to a receptor ...

  8. Optical properties of water and ice - Wikipedia

    en.wikipedia.org/wiki/Optical_properties_of...

    Absorption of light in water. The refractive index of water at 20 °C for visible light is 1.33. [1] The refractive index of normal ice is 1.31 (from List of refractive indices). In general, an index of refraction is a complex number with real and imaginary parts, where the latter indicates the strength of absorption loss at a particular ...

  9. Bacterial motility - Wikipedia

    en.wikipedia.org/wiki/Bacterial_motility

    SRI acts as an attractant receptor for orange light and, through a two-photon reaction, a repellent receptor for near-UV light, while SRII is a repellent receptor for blue light. Depending on which receptor is expressed, if a cell swims up or down a steep light gradient, the probability of flagellar switch will be low.