(ORDO NEWS) — We often refer to our expanding universe with one simple word: space. But where does space begin, and more importantly, what is it?
Space is an almost perfect vacuum, practically devoid of matter and with extremely low pressure. Sound waves do not propagate in space because the space is too rarefied and the collisions of molecules due to which sound is transmitted are extremely rare.
Dense clouds of gas and dust, with stars and planets inside, are interspersed in space with areas completely devoid of matter.
From our earthly point of view, outer space most often begins at about 100 kilometers above sea level on the so-called Karman line.
It is an imaginary boundary at a height where there is no air to breathe or light to scatter. Passing this height, the blue color begins to give way to black, because there are not enough oxygen molecules to color the sky blue.
No one knows exactly how big the cosmos is. This is difficult to determine with existing instruments. From the light seen in our telescopes, we have mapped galaxies stretching almost to the Big Bang, which is believed to have started our universe about 13.8 billion years ago.
This means that we can “see” space at a distance of almost 13.8 billion light years. But the universe continues to expand, which makes “measuring space” even more difficult.
In addition, astronomers are not entirely sure that our universe is the only one that exists. This means that space can be much larger than we think.
In addition to the debris particles that inhabit “empty” regions of space, research has shown that these regions are also home to various forms of radiation. In our own star system, the solar wind—charged particles emanating from the Sun—spreads throughout the solar system and sometimes causes auroras near Earth’s poles.
Cosmic rays generated by supernovae and other astrophysical objects also fly through our neighborhood and can be detected by instruments.
In fact, the universe is filled with the so-called cosmic microwave background (CMB), which is essentially the residual radiation from the Big Bang.
The CMB is the oldest radiation our instruments can detect. In addition, outer space is inhabited by a mysterious dark matter – a substance whose existence astronomers know from many indirect signs, but its composition is still not exactly known.
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