Before telescopes, people looked up and saw stars and constellations. Even after the invention of the telescope, they saw many more, but still assumed that they were simply “there”. That perception was blown away when we learned that the universe is expanding, which transformed the way we think about the universe. Stars have always been unreachable and ultimately unknowable. The more astronomers learn about the complexity of the universe, the more their assumptions and models have multiplied, as well as their uncertainty.
The first question that students should ask is, “How certain is that fact?” Every measurement has a tolerance, and every affirmation has a degree of uncertainty. The distance to the sun is 93 million miles, trusting the experts. Observational measurements have been made with great accuracy, but no one has checked it with a tape measure. That’s not a problem for our sun, but the next stars are measured by parallax. Then the stars that are further away rely on various methods of the cosmic distance ladder. It’s called a ladder because the more distant methods rely upon the assumptions and precision of the nearer methods.
The distances to the stars is one of the conclusions that is most certain about the standard model of cosmology, nevertheless, it is not certain. One significant problem is the calibration of standard candles, which is the brightness used to classify stars. For instance, Type 1a supernovae are considered to be have a consistent brightness throughout the universe. They are crucial in measuring the greatest distances and determining the correct cosmological model. What if the assumption were wrong? What if they change when they are further away? It would affect all the models, and we can never be absolutely certain.
Is the universe 13.8 billion years old? Maybe. The Hubble telescope has measured the galaxy GN-z11 spectroscopically at 13.4 billion light years away. It is in the Ursa Major constellation, the Great Bear. Does that mean that the center of the universe is near the Great Bear. Oh, that it were that simple! What they’re telling us now is that the universe has no center and has no edge. So if we measure a galaxy just as old on the opposite side of the sky, does that mean that both places are the center of the universe? Maybe. Does space fold, like in the Disney movie “A Wrinkle in Time?” The best experts don’t have the answers. We can look and look from afar, but our universe may ultimately remain unknowable.