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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

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
- taneq 21d ago
  Actually C is for Cookie. :P
  - drfloyd51 21d ago
    Well, that’s good enough for me.
- andrewflnr 21d ago
  As long as we're nitpicking, casualties include injuries as well as deaths.
Towaway69 21d ago
Philosophical speaking, I wonder what the folks will think of our theories of light, time and space in the not too distant future. Much as the flat earth theories or the universe rotates around the earth, I suspect we don’t really get it yet and we’ll have other ideas in 300 years from now. Just reading here about the theories of light, fundamentally we don’t understand what light truly is. Sure we have this theory and that idea, but these seem too complex and fragile to be really it - imho. I mean no disrespect, and everyone can have their theories and opinions. But we shouldn’t forget the arrow of time continues and it’s still a long way to go.
- arcfour 20d ago
  I feel like we have advanced technology to the point that we can't be that far off from the truth, or at least we would look more charitably back on our views now since they're grounded in observations made with the best tools we have available to us as opposed to e.g. the flat earth where you can actually see and experience the curvature of the earth without needing any specialized tooling at all.
  - Towaway69 18d ago
    > experience the curvature of the earth I'm not an historian but the curvature of the world was probably explained away by some other phenomenon because, after all, the world is flat (for those experience curvature in times of flat Earth). So to "experience" the curvature of the Earth, you first have to know the Earth is round. Much as our "bug free" software is only buggy once we find a bug, before that, the bug was a feature ;) Similar the stars were explained away as holes in a black sphere surrounding the Earth: the light points in a night skies didn't lead to a universal acceptance of the Universe. It was telescopes that made us realize that those "holes in the sphere" were actually galaxies. So my understanding would be, that it was Magellan circumnavigating the Earth that made folks actually "experience" the curvature of the Earth. This might be being pedantic but I am trying to point out that "experiences" are related to understanding and perspective. Experiences are different in different contexts: hence my experiences are different to all those around me. My interpretation of "experiences" differ according to understanding. An apple falling on my head might well have more to do with evilness of various gods than gravity before the invention of gravity. But even gravity is just another interpretation/explanation/myth to explain the "experience" falling apple.

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
taneq 21d ago
Actually C is for Cookie. :P
- drfloyd51 21d ago
  Well, that’s good enough for me.
andrewflnr 21d ago
As long as we're nitpicking, casualties include injuries as well as deaths.

Towaway69 21d ago

Philosophical speaking, I wonder what the folks will think of our theories of light, time and space in the not too distant future. Much as the flat earth theories or the universe rotates around the earth, I suspect we don’t really get it yet and we’ll have other ideas in 300 years from now. Just reading here about the theories of light, fundamentally we don’t understand what light truly is. Sure we have this theory and that idea, but these seem too complex and fragile to be really it - imho. I mean no disrespect, and everyone can have their theories and opinions. But we shouldn’t forget the arrow of time continues and it’s still a long way to go.

arcfour 20d ago
I feel like we have advanced technology to the point that we can't be that far off from the truth, or at least we would look more charitably back on our views now since they're grounded in observations made with the best tools we have available to us as opposed to e.g. the flat earth where you can actually see and experience the curvature of the earth without needing any specialized tooling at all.
- Towaway69 18d ago
  > experience the curvature of the earth I'm not an historian but the curvature of the world was probably explained away by some other phenomenon because, after all, the world is flat (for those experience curvature in times of flat Earth). So to "experience" the curvature of the Earth, you first have to know the Earth is round. Much as our "bug free" software is only buggy once we find a bug, before that, the bug was a feature ;) Similar the stars were explained away as holes in a black sphere surrounding the Earth: the light points in a night skies didn't lead to a universal acceptance of the Universe. It was telescopes that made us realize that those "holes in the sphere" were actually galaxies. So my understanding would be, that it was Magellan circumnavigating the Earth that made folks actually "experience" the curvature of the Earth. This might be being pedantic but I am trying to point out that "experiences" are related to understanding and perspective. Experiences are different in different contexts: hence my experiences are different to all those around me. My interpretation of "experiences" differ according to understanding. An apple falling on my head might well have more to do with evilness of various gods than gravity before the invention of gravity. But even gravity is just another interpretation/explanation/myth to explain the "experience" falling apple.