What is Outer space?
The Basics
Outer space is a vacuum. Well, almost. A vacuum, unlike that used to suck up dust bunnies in a messy home, is devoid of matter. Space is almost a perfect vacuum because it is nearly empty. But while there is no air in space, there are gas and dust particles that form what is called the “interstellar medium,” or simply the matter that fills interstellar space. About 99% of the interstellar medium is composed of interstellar gas, which is mostly hydrogen and some helium. The rest is interstellar dust. For clarity’s sake, the “Universe” is basically...well, everything that exists, while “outer space” is the space outside of the atmospheres of planets and stars. Space is simply one part of the Universe.
In addition to being devoid of air, outer space is also devoid of atmospheric pressure, like that which exists on Earth and allows humans to breathe. For a human to breathe properly, the air pressure in her lungs has to be lower than the air pressure outside of her lungs because air moves from high pressure to low-pressure areas. Think about climbing a mountain; the further up one goes, the harder it is to breathe. Air pressure decreases as altitude increases, which makes the process of moving air through the lungs more difficult. In space, therefore, where there is no atmospheric pressure, it is impossible for a human to breathe without a spacesuit.
If, by chance, a human were to drop suddenly into outer space, the air in her lungs would expand due to rapid decompression, which would likely cause her lungs to rupture. Additionally, decompression can lead to ebullism, which causes tissue swelling and bruising, and can even lead to an embolism. When the lungs are exposed to a vacuum, oxygen diffuses out of the bloodstream, leading to hypoxia, or oxygen deprivation. Within fifteen seconds, this unfortunate space-goer would be unconscious. While unconscious, she may be able to survive for about a minute in space, though she would have a better chance of survival if she managed to immediately exhale all of the air in her lungs upon entering space [1].
The Solar System and the Milky Way Galaxy
The Solar System is simply a planetary system like any others that exist in the Universe, all of which consist of planets orbiting a host star. The term “Solar” comes from our Sun, which is named Sol after the Latin word for sun, solis [2]. Our solar system is located in the Milky Way Galaxy. The closest planetary system to ours is Alpha Centauri, at 4.37 lightyears from the Sun. According to NASA, “Most of the hundreds of billions of stars in our galaxy are thought to have planets of their own, and the Milky Way is but one of perhaps 100 billion galaxies in the universe" [3].
What, then, is a galaxy? Simply put, “A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity” [4]. The way that scientists categorize galaxies is by shape. For example, our galaxy is a spiral galaxy. The other two types of galaxies are elliptical and irregular. The closest known galaxy to the Milky Way is the Canis Major Dwarf Galaxy, at 25,000 lightyears (or 236,000,000,000,000,000 kilometers) from the Sun. Even if lightspeed travel were possible, it would still take 25,000 years to reach the Canis Major Dwarf Galaxy.
Milky Way Galaxy
How big is the Universe?
First, we have to distinguish between the observable Universe and the unobservable Universe. The observable Universe is “...a spherical region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time…” [5]. However, the word “observable” here refers to the physical limitations created by the speed of light. The Universe is about 13.8 billion years old, so light could only have traveled a certain distance in that amount of time. Anything that exists further than that distance is completely undetectable. One might think, then, that the observable universe has a radius of 13.8 billion lightyears, but scientists have calculated its radius to be 45.7 billion lightyears. Now, this calculation does not mean that we can actually see anything 45.7 billion lightyears away from us, but “It represents the spherical realm that contains all things that could potentially be known through their light signals” [6]. The observable Universe is full of “known unknowns,” so to speak, while the unobservable Universe contains “unknown unknowns.”
How large, then, is the unobservable Universe? To put it simply, we may never know. Scientists still do not know if the Universe is finite or infinite, but if the radius of the observable Universe is 45.7 billion lightyears, then the Universe might as well be infinite because that is too large a distance to even comprehend, at least for me. What we do know is that the Universe is expanding and that its expansion is accelerating. For a more detailed explanation of the size of the unobservable Universe, read this article by Ethan Siegel.
Observable Universe
Do aliens exist?
Considering how large the Universe is, as well as how many sci-fi movies portray aliens as green creatures with huge black eyes, it is not uncommon to want to know if aliens do, in fact, exist. So far, astronomers estimate that there are 500 solar systems in the Milky Way Galaxy. And one 2016 study estimates that there are two trillion galaxies in the observable Universe. If our Solar System is only one of 500 in the Milky Way, which is only one of two trillion galaxies in the Universe, there can be almost no doubt that life exists elsewhere in the Universe. Now, would extraterrestrials all look like E.T.? Probably not, but they would most likely look different than humans on Earth do because any interstellar lifeform that exists in interstellar space would have different needs than we do, so they would have evolved very differently [7]. In short, aliens exist. And they might be living among us right now...
1. Harvard University, "The Human Body in Space: Distinguishing Fact from Fiction," Science in the New, last modified July 13, 2013, accessed December 6, 2020, http://sitn.hms.harvard.edu/flash/2013/space-human-body/.
2. NASA, "Our Solar System: Overview," NASA Solar System, accessed December 6, 2020, https://solarsystem.nasa.gov/solar-system/our-solar-system/overview/.
3. NASA, "Our Solar System: In Depth," NASA Solar System, accessed December 6, 2020, https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/.
4. NASA, "What Is a Galaxy?," Space Place, accessed December 6, 2020, https://spaceplace.nasa.gov/galaxy/en/.
5. Wikimedia Foundation, "Observable universe," Wikipedia, accessed December 6, 2020, https://en.wikipedia.org/wiki/Observable_universe#:~:text=The%20observable%20universe%20is%20a,Earth%20since%20the%20beginning%20of.
6. Paul Halpern, "How large is the observable universe?," PBS, last modified October 10, 2012, accessed December 6, 2020, https://www.pbs.org/wgbh/nova/article/how-large-is-the-observable-universe/.
7. John Brandon, "What Would Aliens Actually Look Like? We Asked 7 Experts," Popular Mechanics, last modified August 6, 2014, https://www.popularmechanics.com/space/deep-space/g1592/we-asked-7-experts-what-would-aliens-actually-look-like/.