Dark energy may be composed of photons with negative inertial and gravitational mass Since the photons comprising dark energy would have negative mass, they could not be observed even though they exert a repulsive gravitational force on photons that have positive mass

Photon energy is the energy carried by a single photon The amount of energy is directly proportional to the photon’s electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength The higher the photon’s frequency, the higher its energy

Photons are a ​quantized​ particle This means they exist only in discrete amounts of energy, rather than any amount of energy in between So if a photon is the result of a “falling electron,” a photon must also come in only specific energy amounts, or quanta

Photons build up the electromagnetic wave They are elementary particles, and as such are governed by quantum mechanical equations and rules This oscillating behavior of the fields is similar to transverse waves on a string, though there does not exist a medium that is oscillating, but just the fields

Photons with more energy are ultraviolet radiation, X-rays, and gamma rays (gamma rays have the most energy) Photons with less energy are infrared and radio waves (radio waves have the least energy) Photon: ↑ Light is made of particles called photons, which travel in waves

A photon is a tiny particle that comprises waves of electromagnetic radiation As shown by Maxwell, photons are just electric fields traveling through space Photons have no charge, no resting mass, and travel at the speed of light

Science: Can photons travel ‘faster than light’? LIGHT cannot travel faster than it does in a vacuum The proposed effect, however, is very small indeed: the photons can exceed Einstein’s limit by only one part in 1036

Photons could conceivably decay, but new analysis of the cosmic microwave background shows that a visible wavelength photon is stable for at least 1018 years For a photon to decay, it must have a mass—otherwise there’d be nothing lighter for it to decay into

km/sec

Cheetah Cheetahs

“erous cats”

• Tiger – Panthera tigris The tiger (Panthera tigris) is the largest of all cats
• Lion – Panthera leo
• Jaguar – Panthera onca
• Leopard – Panthera pardus
• Snow Leopard – Panthera uncia
• Mountain Lion – Puma concolor
• Cheetah – Acinonyx jubatus

Egyptian mau