What does it mean when they say the universe is expanding?

When scientists talk about the expanding universe, it means that it has been growing ever since it started with the Big Bang. 

Galaxy NGC 1512 in Visible Light External. Photo taken by the Hubble Space Telescope External

Our own outer galaxies are moving away from us, and those farther away are moving faster. This means that wherever you are in the galaxy, all the other galaxies are moving away from you.

However, galaxies do not move into space, they rotate in space because space is also rotating. In other words, the universe has no center; Everything is falling away from everything. If you override a grid space with a Milky Way for every million light years or so, this grid expands over time, so that the Milky Way expands every two million light years, and so on.The universe contains everything that exists, from the smallest atom to the largest galaxy; Since the Big Bang was about 13.7 billion years ago, it has been expanding and its range could be infinite. The part of the universe where we have knowledge is called the observable universe, it is time for light from the area around the earth to reach us.

A well-known analogy for describing the universe is that the imagines the universe as raisin bread flour. As the bread grows and spreads, the raisins move away from each other, but they are still stuck in the dough. In the case of the universe, there may be raisins that we can no longer see because they went so fast that their light did not reach the earth. Fortunately, gravity is in control of things locally and keeps our raisins together.

Edwin Hubble, with the 48-inch telescope on Palomar Mountain. NASA’s “The Hubble Story”. (Credit: Carnegie Institution of Washington

Who Figured This Out?

The American astronomer Edwin Hubble made observations in 1925 and was the first to prove that the universe was expanding. They proved that there is a direct relationship between the motion of galaxies far from the Earth and their distance. This is now known as Hubble's law. The Hubble Space Telescope is named after him, and the single number of extraterrestrial galaxies that describe the rate of cosmic expansion is related to their distant velocities, called the Hubble Constant.

A Storm of Turbulent Gases in the Omega/Swan Nebula (M17) External. Photo taken by the Hubble Space Telescope External

So, is the Universe Infinite?

The beginning of the universe and the Big Bang theory is easy to explain, it talks about how it ends. The universe is likely to cease forever, or be expelled from existence rather than in the Big Bang scenario, but in the future it will be so far away, it could be infinite. Until some time ago, cosmologists (scientists who studied the universe) believed that the rate of expansion of the universe was slow due to the effect of gravity. However, current research suggests that the universe may expand for eternity. But research continues and new studies of supernovae in distant galaxies and the so-called dark energy could modify the fate of the universe.

Kepler’s Supernova Remnant In Visible, X-Ray and Infrared Light External. Photo taken by the Hubble Space Telescope External