The Hubble expansion of the universe holds only on the scale of the distances between galaxies.
Imagine pennies being taped to the surface of a balloon that is being filled with air.
Galaxies, like the pennies, don't expand, rather it's the space between the pennies that's expanding..
Galaxies rotate around their centers with the sections of the galaxy that are farther out from the galaxy's center rotating more slowly than the material closer to the center.
Galaxies are also moving away from each other due to the expansion of the Universe brought on by the Big Bang..
The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time.
It is an intrinsic expansion; the universe does not expand "into" anything and does not require space to exist "outside" it..
Galaxies rotate around their centers with the sections of the galaxy that are farther out from the galaxy's center rotating more slowly than the material closer to the center.
Galaxies are also moving away from each other due to the expansion of the Universe brought on by the Big Bang..
In 1929, Edwin Hubble provided the first observational evidence for the universe having a finite age.
Using the largest telescope of the time, he discovered that the more distant a galaxy is from us, the faster it appears to be receding into space.
This means that the universe is expanding uniformly in all directions..
In 1929, American astronomer Edwin Hubble measured the expansion and showed that it obeys a very simple law, where the galaxies move away from one another with velocities that grow in proportion to their distances..
The energy from the Big Bang drove the universe's early expansion.
Since then, gravity and dark energy have engaged in a cosmic tug of war.
Gravity pulls galaxies closer together; dark energy pushes them apart.
Whether the universe is expanding or contracting depends on which force dominates, gravity or dark energy..
This means that no matter what galaxy you happen to be in, all the other galaxies are moving away from you.
However, the galaxies are not moving through space, they are moving in space, because space is also moving.
In other words, the universe has no center; everything is moving away from everything else.Nov 19, 2019.
This means that no matter what galaxy you happen to be in, all the other galaxies are moving away from you.
However, the galaxies are not moving through space, they are moving in space, because space is also moving.
In other words, the universe has no center; everything is moving away from everything else..
Cosmic expansion is a key feature of Big Bang cosmology.
It can be modeled mathematically with the Friedmann–Lemaître–Robertson–Walker metric (FLRW), where it corresponds to an increase in the scale of the spatial part of the universe's spacetime metric tensor (which governs the size and geometry of spacetime)..
Instead, they have been carried along by the expansion of the dough.
An important feature of the expansion of the Universe is that the galaxies themselves do not expand, only the space between them does.
In the raisin bread analogy, the dough rises but the raisins stay the same size.
Mathematically, the expansion of the universe is quantified by the scale factor, , which is proportional to the average separation between objects, such as:
There is no reason to believe there is anything "outside" of the expanding universe into which the universe expands.
Even if the overall spatial extent is infinite and thus the universe cannot get any "larger", we still say that space is expanding because, locally, the characteristic distance between objects is increasing.
Cosmology - Expansion, Universe, Big Bang:
