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 Automatic translation  Automatic translation Category: universe
Updated February 26, 2022

Image: For the philosophers of ancient Greece, paradoxes represent an important problem. With the development of mathematics and physics, certain paradoxes that raised a problem produced new knowledge.

  Dark Night Paradox

Image: Stars have a finite age and therefore a lifespan. Their source of light is too ephemeral for them to be able to saturate space with their radiance. Credit: Stellarium image

  Stromatolites formation of cyanobacteria

Image: Cyanobacteria are the oldest life forms capable of building reefs. They have been present for at least 3.5 billion years despite the low luminosity of the young Sun. There are still 750 million years the luminosity of the Sun was 6 % lower (the irradiance was 1280 W/m2 instead of 1360.8 W/m2 today). Image credit Wikimedia Commons

  Maxwell's Demon

Image: the temperature is proportional to the mean square velocity of the molecules.

  Hubble Ultra Deep Field

Image: In this very small area of the southern sky located in the constellation of the Furnace (3.1 x 3.1 minutes of arc), there are approximately 10,000 galaxies.
Credit: NASA, ESA and S. Beckwith (STScI)

  Paradoxes de Zénon

Image: the rapid Achilles will never catch up with the turtle.

  Mpemba effect

Image: Decrease in water temperature with an initial temperature of 35°C (in red) and 25°C (in blue) until freezing. Water at 35°C freezes in 40 min, and water at 25°C freezes in 50 min.


Image: Despite the centrifugal force, the tea leaves move towards the center and not towards the edges of the cup.

  Langevin twins paradox

Image: The twin paradox was presented by Paul Langevin (1872-1946) at the Congress of Bologna in 1911. According to special relativity, objects that do not experience any force go in a straight line at constant speed. Thus, two inertial reference frames (the Earth and the rocket) are always in uniform rectilinear motion with respect to each other. In spacetime, the rocket cannot be in uniform rectilinear motion since it is returning to Earth. It therefore changed its inertial reference frame. To compare the age of the two twins it will be necessary to wait until they are reunited on the same point of space-time in order to see them from the same point of view.


Popularization video of the site Everything is quantum Representation of superposition of quantum states and quantum decoherence.


Popularization video of the site Everything is quantum. Modern interpretation of wave-particle duality. The observation has the effect of destroying the state of the particle.

  The grandfather paradox

Image: Grandfather paradox. In physics, the principle of causality cannot be violated.


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