Universe FAQ:
You people sure do ask lots of questions, which is a good thing, so I've compiled a list of the most basic questions that are often asked about me. Unfortunately there's an unwritten law of the universe (yeah, thats me) that says that I can't help you guys cheat, so what you're reading is what a bunch of people have figured out over many years. I'd help you out and give you some clues but that would take the fun out of it, now wouldn't it?
1. What are you?
I am the Universe. I have been defined in many ways by many people but simply put I am all things that exist (matter included) and the space in which these things exist. From earth you can only see part of me, which you define as the "Visible" or "observable" universe.
2. How old are you?
According to NASA's WMAP satellite I am 13.7 billion years old (give or take 200 million years.) This is assuming, however, that the models used to create the satellite are correct. Either way, I am DEFINITELY eligible for the senior citizen's discount at Denny's.
3. How big are you?
Following the logic that light travels a finite distance in a year (roughly 26 trillion miles) and the fact that I am roughly 13.7 billion years old one can estimate that I am about 13.7 billion light years in radius. Its possible that space can expand faster than the speed of light, however, so I may actually be much, much larger than what you can observe. After studying cosmic background radiation from the Big Bang it is estimated that I may be over 78 billion light years in radius (translating into a whopping 156 billion light years in diameter), though this is just an estimate based on our current models.
4. How were you born?
This is widely debated, but the generally accepted theory of my origin is known as the "Big Bang Theory". This theory states that I emerged from an incredibly dense and hot state roughly 13.7 billion years ago. This dense and hot state is sometimes thought of as a "primeval atom" which "exploded" and expanded rapidly eventually leading to what I am today. Please don't take the term "exploded" too literally, an explosion as used on a normal basis isn't exactly what it was, being that there was no space for the contents of this atom to explode into, space actually expanded at the moment of the big bang.
Another interpretation of this theory states that the moment before the big bang (t=0) is referred to as Big Bang singularity meaning that everything was condensed into infinitely small proportions. (Much like what is believed to be at the "bottom" of a blackhole). Unfortunately you have no definitive idea of what happened at the moment of the Big Bang or what came before it as all the laws of modern physics break down at this point, but luckily you have many smart people trying to solve this problem as you read this.
5. What do you do all day?
I spend my time expanding rapidly. How do you guys know this? It was discovered that the "redshifting" of distant galaxies could be measured astronomically. Redshifting is a result of the "doppler effect" much like you experience everyday on earth as an ambulance passes you with its siren on. Light from an approaching galaxy would have its wavelengths "squashed", shifting its appearance towards the blue end of the visible spectrum (Blueshifting). Likewise a receding galaxy would have the wavelength of its light "stretched", shifting towards the red end of the visible spectrum, hence the "redshifting". Edwin Hubble (you named the Hubble Space Telescope after him) used this knowledge as well as dedicated observation to deduce that the galaxies were actually moving away from earth from every viewable angle. This can be imagined visually by drawing a bunch of dots on an uninflated balloon and inflating it. As the balloon inflates you can see the dots travel away from each other in all directions. There was only one conclusion to be drawn, that I am expanding. Einstein didn't like the idea of an expanding universe and resisted this idea for many years. Fred Hoyle was another individual who preferred a "Steady-state" universe over a dynamic one. Hoyle, ironically, is also the individual who coined the term "Big Bang", though he did so in jest.
6. What will eventually happen to you?
This is another one of those uncertainties. As stated above, you've already determined that I am expanding so a factor in my ultimate fate depends on the rate at which I am expanding. Cosmologists call this H, or Hubble's constant. Another major factor in my ultimate fate is my density parameter (called Omega by cosmologists.) Finally, Lambda, or the energy that you associate with empty space (otherwise known as Dark Energy) is a factor. Depending on the value of Omega I can be one of a few "shapes". If Omega is less than 1 then I am negatively curved (hyperbolic) like the shape of a horse's saddle. This is otherwise known as an "Open" universe. If Omega is equal to 1 I am flat. If Omega is greater than 1 I am a "Closed" universe, spherical in shape.
If Omega is less than 1 it is believed that there is not enough matter in me to reverse the original Big Bang expansion. This means I'll continue to expand forever, gradually cooling until my temperatures reach absolute zero, chilling all life within me in the ultimate, eternal winter. This is known as the "Big Freeze." If Omega is greater than 1 there is enough matter in me to eventually reverse the expansion. Sooner or later I'll stop expanding and reverse,contracting and compressing until all matter heats up and life is extinguished in a "Big Crunch". An interesting addition to the Big Crunch theory is the possiblity that once I'm done contracting I'll reverse the process and begin expanding again. This is known as the Oscillating Universe (part of this idea is referenced by Kevin Spacey in the last few lines of the movie K-Pax.) If Omega is equal to 1 I'll continue to expand forever (a sort of middle sibling to the Big Freeze and the Big Crunch.)
7. Is it true that most of you is "missing?"
Basically, yes. Building off of what we discussed above, NASA's amazing WMAP satellite has made great leaps in determining the shape of me. Based on current observations it is determined that I am Flat, within a 2% margin of error. After observing the orbital behavior of galaxies and using WMAP data you've been able to determine that of my total content 4% of me are atoms, 23% of me is Cold Dark Matter, and 73% of me is Dark Energy. What does this mean exactly? This means that only 4% of me can actually be observed by you. The remaining 96% has never been observed, in nature or in a labratory. Observational evidence maintains that the remaining 96% has to exist, or some other explanation is needed to make sense of what you're seeing. Keep in mind that this breakdown is the generally accept "Standard Model." There are others who believe that the laws of gravity need to be modified to exclude the need for extra matter and energy. Recently it was believed that dark matter was directly observed during a galactic collision but the veracity of this finding is under dispute. Yet another one of astronomy's great battles for discovery is underway.
8. Do you have an edge?
Nope. Although it seems crazy now, just a few hundred years ago you thought that your planet was flat. If you ventured too far you would eventually fall off of the edge into who-knows-what (if you weren't eaten by a sea monster first.) Eventually (as a result of many brave explorers and a few great thinkers) you learned that the Earth was a sphere. You can't fall off, at best you end up right where you started. The same applies to me, despite the fact that I am now believed to be flat, I don't have an edge. Assuming you had the had the ability to defy special relativity and make a 5 second trip "around" me you'd end up right where you started.
9. Do you have a speed limit?
Actually, yes. According to Albert Einstein and his theory of special relativity nothing can travel faster than the speed of light. The speed of light in a vacuum is 670 million miles per hour. Light constantly moves at this speed, it does not accelerate or decelerate, it does not brake for animals. Special relativity invokes all sorts of mind-boggling conditions. When you're traveling down the highway at 65mph alongside another vehicle it looks as though both of you are standing still. If you were in empty space moving at this speed alongside the other vehicle, with no other references as to your motion, there would be no way to tell if you were really moving (unless you or the other driver accelerated.) This same concept should apply to light, right? Nope. If you could speed alongside a beam of light it would always appear to move away from you at the speed of light. In the words of Brian Fellows "Thats CRAAAZY!!". As crazy sounding as it is, its true, exceeding the speed of light is impossible. The best you can hope for is 99.9 and a few more 9's. Some rules can't be broken.
10. What is outside of you?
At the moment that question is unanswerable. Its a good one, one that has been asked for ages. As of now you don't know what is beyond me, but many people have ideas. Theoretical physicists spend their lives calculating possibilities for the answer to this question. String theory is a theory that says that beyond atoms at an even smaller, more fundamental level there are tiny strings vibrating like the strings on a guitar. Each "note" that a string plays constitutes a fundamental particle which makes up all matter within me. Building off of this M-Theory states that these strings are tied together in one giant membrane. This membrane is me, floating in a higher-dimensional space (more than 3-spatial dimensions) also know as hyperspace. This introduces the concept that we may be one of many, perhaps an infinite number of parallel universes. Like bubbles floating in a vast ocean, with each bubble constituting an entire universe. Or I could be a single slice in a whole "loaf" of parallel universes floating in hyperspace. In these universes there could be an infinite number of "yous" differing only slightly. There could be a universe where dinosaurs are super-intelligent, a universe where the Nazis won WWII, a universe where stars never formed. Some universes may be devoid of all life, others may be teeming with it. The world of theoretical physics opens all kinds of possibilities, but as of now these possibilities are not verified, and only on paper. As you progress and as technology advances you'll be able to verify or debunk many of these theories. The key is to continue to evolve, learn, and wonder, which is what makes you humans, well, humans.