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  2. Zeno's paradoxes - Wikipedia

    en.wikipedia.org/wiki/Zeno's_paradoxes

    He gives an example of an arrow in flight. He states that at any one (durationless) instant of time, the arrow is neither moving to where it is, nor to where it is not. [18] It cannot move to where it is not, because no time elapses for it to move there; it cannot move to where it is, because it is already there.

  3. Length contraction - Wikipedia

    en.wikipedia.org/wiki/Length_contraction

    It's clear that distance AB is equal to length of the moving object. [7] Using this method, the definition of simultaneity is crucial for measuring the length of moving objects. Another method is to use a clock indicating its proper time T 0 {\displaystyle T_{0}} , which is traveling from one endpoint of the rod to the other in time T ...

  4. Comoving and proper distances - Wikipedia

    en.wikipedia.org/wiki/Comoving_and_proper_distances

    e. In standard cosmology, comoving distance and proper distance (or physical distance) are two closely related distance measures used by cosmologists to define distances between objects. Comoving distance factors out the expansion of the universe, giving a distance that does not change in time due to the expansion of space (though this may ...

  5. Special relativity - Wikipedia

    en.wikipedia.org/wiki/Special_relativity

    e. In physics, the special theory of relativity, or special relativity for short, is a scientific theory of the relationship between space and time. In Albert Einstein 's 1905 paper, On the Electrodynamics of Moving Bodies, the theory is presented as being based on just two postulates: p 1 [ 1 ][ 2 ] The laws of physics are invariant (identical ...

  6. Twin paradox - Wikipedia

    en.wikipedia.org/wiki/Twin_paradox

    In their rest frame the distance between the Earth and the star system is α d = 0.6 × 4 = 2.4 light years (length contraction), for both the outward and return journeys. Each half of the journey takes α d / v = 2.4 / 0.8 = 3 years, and the round trip takes twice as long (6 years). Their calculations show that they will arrive home having ...

  7. Hubble's law - Wikipedia

    en.wikipedia.org/wiki/Hubble's_law

    Hubble's law, also known as the Hubble–Lemaître law, [ 1 ] is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away. For this purpose, the recessional velocity of a galaxy is typically determined by ...

  8. Gravitational time dilation - Wikipedia

    en.wikipedia.org/wiki/Gravitational_time_dilation

    Gravitational time dilation is a form of time dilation, an actual difference of elapsed time between two events, as measured by observers situated at varying distances from a gravitating mass. The lower the gravitational potential (the closer the clock is to the source of gravitation), the slower time passes, speeding up as the gravitational ...

  9. Newton's law of universal gravitation - Wikipedia

    en.wikipedia.org/wiki/Newton's_law_of_universal...

    where F is the gravitational force acting between two objects, m 1 and m 2 are the masses of the objects, r is the distance between the centers of their masses, and G is the gravitational constant. The first test of Newton's law of gravitation between masses in the laboratory was the Cavendish experiment conducted by the British scientist Henry ...