Does the expansion of the universe make the Sun bigger? What about the Milky Way? Why or why not?

The Big Bang theory is a scientific explanation of how the universe began. It suggests that the universe started from an incredibly dense and hot state and has been expanding ever since. This concept helps explain why galaxies are moving away from each other. Imagine blowing up a balloon. The dots on the surface move apart as the balloon inflates. The same happens in the universe; space itself is stretching, pushing galaxies away from each other.
The theory is backed up by several key observations:

• The cosmic microwave background radiation—afterglow of the initial explosion.
• The abundance of light elements like hydrogen and helium.
• The redshift of galaxies, which shows they are moving away from us.

Even though the Big Bang theory explains the large-scale structure and behavior of the universe, it doesn't directly affect smaller structures like solar systems or galaxies due to stronger forces at play.

The redshift phenomenon is an essential piece of evidence for the universe's expansion. It refers to the way light from distant galaxies shifts to longer, or 'redder' wavelengths as it travels through expanding space. Think of it like the sound of a siren that gets lower in pitch as an ambulance moves away from you.
There are different types of redshift:

• Cosmological Redshift: Caused by the expansion of the universe.
• Doppler Redshift: Occurs due to the motion of an object moving away from the observer.
• Gravitational Redshift: Happens in the presence of strong gravitational fields.

Cosmological redshift is the one most relevant to universe expansion. As galaxies move away from us, the light they emit gets stretched, shifting toward the red end of the spectrum. This observation is a cornerstone in understanding our expanding universe.

Gravitational forces are the invisible glue holding together stars, planets, and galaxies. They are described by Albert Einstein's theory of general relativity, which explains how massive objects cause space to curve, attracting other objects toward them.
In small systems like our solar system:

• The Sun's gravity keeps the planets in orbit.
• That same gravity affects the moons orbiting planets.

These forces are so strong that they override the expansion of the universe at such scales. Even within galaxies, the collective gravity from stars and dark matter is strong enough to hold the galaxy together. This is why the distance between individual stars or planets within the Milky Way does not increase due to cosmic expansion.
The effects of gravitational forces are prominent at all scales—from keeping us on Earth's surface to forming supermassive black holes at galaxy centers. They ensure that structures like the Sun or the Milky Way remain intact despite the universe's overall expansion.