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  2. List of unsolved problems in physics - Wikipedia

    en.wikipedia.org/wiki/List_of_unsolved_problems...

    Problem of time: In quantum mechanics, time is a classical background parameter, and the flow of time is universal and absolute. In general relativity, time is one component of four-dimensional spacetime, and the flow of time changes depending on the curvature of spacetime and the spacetime trajectory of the observer. How can these two concepts ...

  3. List of unsolved problems in astronomy - Wikipedia

    en.wikipedia.org/wiki/List_of_unsolved_problems...

    Why is the distant universe so homogeneous when the Big Bang theory seems to predict larger measurable anisotropies of the night sky than those observed? Cosmological inflation is generally accepted as the solution, but are other possible explanations such as a variable speed of light more appropriate? [31]

  4. Cosmic time - Wikipedia

    en.wikipedia.org/wiki/Cosmic_time

    Cosmic time [5]: 42 [6] is a measure of time by a physical clock with zero peculiar velocity in the absence of matter over-/under-densities (to prevent time dilation due to relativistic effects or confusions caused by expansion of the universe). Unlike other measures of time such as temperature, redshift, particle horizon, or Hubble horizon ...

  5. Olbers's paradox - Wikipedia

    en.wikipedia.org/wiki/Olbers's_Paradox

    Olbers's paradox, also known as the dark night paradox or Olbers and Cheseaux's paradox, is an argument in astrophysics and physical cosmology that says the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe.

  6. Gravitational redshift - Wikipedia

    en.wikipedia.org/wiki/Gravitational_redshift

    Navigational signals from GPS satellites orbiting at 20 000 km altitude are perceived blueshifted by approximately 0.5 ppb or 5 × 10 −10, [10] corresponding to a (negligible) increase of less than 1 Hz in the frequency of a 1.5 GHz GPS radio signal (however, the accompanying gravitational time dilation affecting the atomic clock in the ...

  7. Faster-than-light - Wikipedia

    en.wikipedia.org/wiki/Faster-than-light

    Some processes propagate faster than c, but cannot carry information (see examples in the sections immediately following). In some materials where light travels at speed c/n (where n is the refractive index) other particles can travel faster than c/n (but still slower than c), leading to Cherenkov radiation (see phase velocity below).

  8. Driving at night can get harder starting as early as your ...

    www.aol.com/lifestyle/driving-night-harder...

    According to the market research platform Gitnux, 10% of drivers reported having problems with night vision, while 62% feel less confident driving at night compared to during the day. Those ...

  9. Two-body problem in general relativity - Wikipedia

    en.wikipedia.org/wiki/Two-body_problem_in...

    In (1+1) dimensions, i.e. a space made of one spatial dimension and one time dimension, the metric for two bodies of equal masses can be solved analytically in terms of the Lambert W function. [11] However, the gravitational energy between the two bodies is exchanged via dilatons rather than gravitons which require three-space in which to ...