3 ms·

I’m not a science person but I think I understand the crux of what you’re saying here - have a question though: are those particles finite? And those are light

• tappaseater 21d ago
  The commenter is referring to the Cosmic Microwave Background (CMB). Whilst most of the universe is a dark void, if you tune a radio to a certain frequency, there's a faint, static buzz in the microwave part of the spectrum. It is heard no matter which direction you point the dish. This is a left-over from the Big Bang and started out as light but due to the expansion of space, the wavelength has increased, and that's why it's now received in the microwave part of the spectrum. There are lots of great explainers on the CMB and the history of its discovery is entertaining too. One of the easier concepts in cosmology, and one of the most important.
  • ShinyLeftPad 21d ago
    You don't get microwave radio frequency by increasing wavelength of light, it's the other way around.
    • _Microft 21d ago
      Microwaves do have much larger wavelengths than visible light. https://en.wikipedia.org/wiki/Electromagnetic_spectrum https://en.wikipedia.org/wiki/Electromagnetic_spectrum
      • ShinyLeftPad 21d ago
        Ah my bad, frequency vs length.
  • thenthenthen 21d ago
    Like a doppler shift?
    • andrewflnr 21d ago
      Exactly a Doppler shift.
• dotancohen 21d ago
  Light is not a particle, nor is it a wave. However, under some circumstances it does behave like a particle - we even have a name for that (photon). However for purposes of this type of discussion - how it travels long distances - we need to look at the wave properties of light. The particle properties are more interaction-based. Light moves at the speed of causality - C - so it does not experience time. Therefore light never changes. However, for distant extra-galactic objects, the space that the light is traveling through is expanding! Thus the wave property of light is stretched out as well. So what was once visible light is now so stretched out (in our reference frame) that our eyes can't detect it (that's why the night sky is black). So yes, the light is finite. It itself experiences no change. The number of particles heading in our direction only changes when they encounter some types of mass, such as interstellar or intergalactic gad clouds. If you want to know why light is not a particle (and also not a wave) check out the dual-slit experiments. Fascinating stuff.
  • ButlerianJihad 21d ago
    > Light moves at the speed of casualty - C C is coulombs And casualty is a dead person
    • dotancohen 21d ago
      Typo corrected, thank you!
      • raattgift 20d ago
        Additionally, > light never changes is wrong. A photon has a momentum, which can increase or decrease as it travels through free space. Using general relativity, it's straightforward to define an affine time on a null geodesic (even if one cannot define a proper time on one), and a momentum that is a function of the affine time at each point. The Lyman-alpha forest is a straightforward "laboratory" for this approach, which can calculate the Lyα absorption lines seen when a bright distant quasar or luminous Lyα emitter has atomic hydrogen clouds between the distant source and us (the absorption lines indicate photons with a very narrow range of momenta participated in hydrogen atoms' electrons transitioning from ground to the first excited state, with the later relaxation photons radiating in random directions). The pattern of such dark spectral lines tells us how redshifted the background light and earlier absorption lines are at each gas cloud along the way. https://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html https://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html https://en.wikipedia.org/wiki/Lyman-alpha_emitter https://en.wikipedia.org/wiki/Lyman-alpha_emitter And over much-shorter-than-cosmological distances, https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment