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  • The Physics of Time: Time is a complex concept. People typically think of time in terms of units such as seconds, minutes, hours, etc. On Earth, humans historically defined units of time such as day, month and year in terms of astronomy. A day is the amount of time it takes for one rotation of Earth on its axis. A month is the amount of time it takes for the moon to complete one orbit of the Earth. A year is the amount of time it takes for Earth to complete one orbit of the sun. Smaller units of time such as the hour, minute, and second are then just subdivisions of these. But units of time are completely arbitrary. Humans could have defined time units in other ways. Time units are not time. More about time.
  • Climate Change: Weather is the current state of the atmosphere in terms of temperature, rain, humidity, wind, etc. for a specific location. Weather changes from minute to minute, and thus is considered short-term. Climate is essentially the average weather for a significant period of time for a particular region, and thus is considered long-term. Since climate is based on weather and weather changes, climate also changes. More about climate.

  • Quantum Mechanics: Quantum mechanics (QM) is the branch of physics focused on very small things. Atoms are made of electrons, neutrons and protons. Neutrons and protons are made of quarks. Electrons and quarks are believed to be indivisible and so are called elementary particles. Thus, the behavior of elementary particles is described by quantum mechanics. More about quantum mechanics.

  • Interpretations of Quantum Mechanics: Interpretations of quantum mechanics (QM) fall within the realm of the philosophy of physics. They are a conceptual way to relate QM mathematics and concepts with QM observations and the physical meanings of these observations. There are three main types of interpretations: collapse theories, Many Worlds theories, and hidden variables. More about interpretations of quantum mechanics.

  • Dark Matter and Dark Energy: Despite their similar sounding names, dark matter and dark energy are not related. Dark matter is a hypothetical kind of matter that cannot be seen with telescopes. Dark energy is a hypothetical kind of energy that is thought to permeate space. More about dark matter and dark energy.