Lessons from dark skies
Jul. 18th, 2025 09:58 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
mount_oregano
Why is the sky dark at night? Why isn’t it bright as day with starlight shining in every single direction? This is an old and surprisingly complex question, and it took modern physics to answer it. Two interrelated reasons account for it.
(Photo: NASA’s Hubble Space Telescope. Galaxy cluster Abell 370 contains several hundred galaxies tied together by the mutual pull of gravity.)
1. The universe is finite in both age and size. It began with the Big Bang about 14 billion years ago. The universe contains a limited number of stars, and since light takes time to travel, we can only see the ones that are less than 14 billion light years away. There just aren’t enough stars to fill the portion of the sky that we can see
2. The universe is expanding fast in all directions, so everything is getting farther away from us. The farther away the receding source of the light is, the more stretched its wavelength is, and eventually the wavelength drops below our eyes’ threshold to see the light. In fact, the sky is not dark. It reverberates with the energy from the early universe, just after the Big Bang as matter coalesced, when the universe was very small, messy, and hard to understand. Special telescopes can detect these microwaves, but we can’t see them with our bare eyes.
Now, suppose we take this as a metaphor for life.
We are finite in time.
1. We were born. At first, we were small and messy.
2. We don’t remember our own birth because the threshold of our memory doesn’t go back that far. That’s good, since it was probably unpleasant.
We are finite in space.
3. We can’t observe everything. Knowledge is expanding in all directions faster than it can get to us. The internet more than proves that.
4. We wouldn’t understand everything anyway. Information can be stretched too thin to be intelligible. Again, the internet more than proves that.
The same science that explains the Big Bang does not yet know if the universe will end with a Big Freeze, Big Rip, Big Crunch, Big Bounce, or something completely different although equally Big.
5. We don’t know our own fate. That may be just as well, since it might not be especially entertaining.
6. Or maybe it will be entertaining. Cosmologist George Smoot, who won a Nobel Prize in Physics for his work to confirm the Big Bang Theory, made a special guest fanboy appearance on the television series Big Bang Theory. Scientists are great wags.
Our days are lit by one star, and the rest serve as little more than decoration in the night sky.
7. Half the time, we’re in the dark.
8. However, the darkness is sublimely decorated, and nothing can thrill our imaginations like staring up at the sky at night.
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