4 ms·
In the early universe, light could not travel freely, because the ambient temperature was hot enough that the universe was filled with plasma. The end of this p
by isaacg 6y ago
In the early universe, light could not travel freely, because the ambient temperature was hot enough that the universe was filled with plasma. The end of this period is called "recombination", and the light from that point in time is called the Cosmic Microwave Background.
That light is the earliest light we can observe, but it is not the earliest event to have had casual effects on us, nor is the earliest event we can observe.
In particular, that light was emitted about 370,000 years after the Big Bang, while events within the first second after the Big Bang have had casual effects on us.
So there is an important difference between "light" and "casual" in physics.
- throwaway_kufu 6y agoNice, my initial impression of your comment still fits squarely within the door I left open for using causal...except when I was thinking phenomena outside the edges physical space where light reaches us you expand it to outside the edges of time where light still reaches us. Unfortunately I’m now just sort of stuck thinking about causality, determinism and free will...not exactly knowing where you are on Earth I guess it’s a possibility you have never been and never will in my light cone, yet my comment was the causality of your reply in some sense. And in maybe an HN 1st you’ve made me reconsider my position, and Recognize I need to more deeply consider causality as having good use outside phenomena from outside light at the edges of space and time and spacetime.
- panda-giddiness 6y agoOf course they've been in your lightcone -- otherwise it would've been impossible for you two to have a back-and-forth exchange!