The expansion of the universe is a phenomenon, which describes the
inherent property of the universe, where two galaxies that are gravitationally unbound
tend to increase the distance to each other and the rate of expansion is even accelerating.
Far away parts of the observable universe will not be observable in the near
future, because the velocity of expansion is higher than light speed from an
outside perspective.
Detailed Definition:
The expansion of the universe is a phenomenon, which explains an
inherent property of the universe to expand. The fact that the universe seems
to expand, was first doubted because of the gravitational force and the fact
that releases of energy like the big bang should normally lose power and should
slow over time, but the opposite was observed. The elusive culprit was found
quite fast. Dark matter is to be responsible for this phenomenon, but since we
know even less about dark matter than about the expansion of the universe,
details of how and why it expands are still unknown.
This expansion occurs at
every location of the universe and only gravitationally bound galaxies will be
able to observe each other, because unbound galaxies will escape our observable
universe at some point. The expansion can in some way be compared to an elastic
rubber band, where the distances also increase when you stretch it, but not
literally and not on a human scale. It is more that at a scale so far zoomed
out, that the universe looks like a cosmic fluid and at this scale it is apparent
that the density is decreasing over time. There are three viable methods to
measure this expansion. One is based on redshifts, while another on the cosmic
distance ladder. Those measurements gave non-matching results, and so 2018 information
from gravitational waves made it possible to determine the rate of expansion
even more precisely.
Etymology:
Expansion à from Latin expandere à spread out
Universeà from Old French univers à from Latin universum
Sample Sentence(s):
In a thought
experiment of an ascending civilization in a faraway galaxy in the far future,
they would only be able to observe their neighbouring galaxies and will think that this is all there is to the universe and
all this due to an expansion of the universe.
The rate of expansion of the universe is thought
to be accelerating.
