<p>I was watching this show on gamma ray bursts last night, and they kept saying the rays were coming from 'the edge of the universe'. </p>
<p>So then I thought to myself: if the universe is infinite, wouldn't it be paradoxical to say something came from the 'edge of the universe'? </p>
<p>am I just misinterpreting what they meant by edge of the universe? can any cosmology nerd clarify?</p>
<p>Well the universe isnt proven to be infinite (as it is almost impossible to prove anything to be infinite, the concept of infinity is very mind-boggling), but maybe they are inferring like some place very far away...</p>
<p>Yeah I figured maybe it was just a colloquialism for 'far away'. I know it isn't proven, but I thought there was a general consensus within the physics community that it is? I honestly don't know though. but thanks</p>
<p>the universe is finite my dear friend.</p>
<p>Yeah. There's a consensus, but it's pretty much the opposite of what you said.</p>
<p>You can find out more at your local library or on Wikipedia!</p>
<p>well, it's expanding indefinitely, at an accelerating rate. so, still--how can you say it's at the 'edge'?! after that comment is made the 'edge' is no longer at that point in space-time.</p>
<p>Just think about it. Light rays travel in straight line right? Yes? And if the universe is infinite, then any point in the universe would be the center of the universe right? If that is, then earth will already be radiated, burned, toasted by the light rays radiated from 1000000000000000000 different light sources.</p>
<p>I just spent 10 mins looking the question up and there's definitely NOT a consensus that it's finite or finite. i looked on nasa/pbs/ and like 10 other credible sources...</p>
<p>ESA: Is the Universe finite or infinite?</p>
<p>Joseph Silk: We don't know. The expanding Universe theory says that the Universe could expand forever [that corresponds to a 'flat' Universe]. And that is probably the model of the Universe that we feel closest to now. But it could also be finite, because it could be that the Universe has a very large volume now, but finite, and that that volume will increase, so only in the infinite future will it actually be </p>
<p>..that's an interview with a professor at cambridge...so he actually implies that one of the most accepted ideas is that it IS infinite.</p>
<p>infinite or finite*</p>
<p>We're not sure if the universe is infinite or finite. It all depends on the very geometry of the universe (flat, spherical, hyperbolic). But if we assume that the Big Bang theory is correct, then we can deduce that there is space(?) outside of our universe within which it is expanding, at some acceleration.</p>
<p>Imagine a big circle (or sphere or 3 dimensional hyperbola) that is expanding at a constant velocity or acceleration. That is, in the theory that I subscribe to, what our universe is. So there is an edge to the solar system, it's just moving farther and farther away.</p>
<p>Gotcha! thanks!...Would you say that's the leading theory among physicists/cosmologists etc.</p>
<p>But if we assume that the Big Bang theory is correct, then we can deduce that there is space(?) outside of our universe within which it is expanding,</p>
<p>HAHAH WOW....just try and conceptualize that for a minute. oh my god. lol</p>
<p>I think of it this way. If you are moving towards the supposed "edge of the universe" you are expanding energy, so there is no such thing because as long as energy exists you are pushing it forward. There's no such thing as a barrier.</p>
<p>^ hence I posed the original question lol</p>
<p>I'm an astrophysics major at UC Berkeley so I should be able to clear some things up (I am no means an expert, obviously). So when they said that gamma ray bursts (GRBs) were at the "edge of the universe" it was very much an expression, meaning very far away. Keep in mind that while the experts on the show know what they're talking about, producers usually don't, so they will include quotes that are more vague and confusing then they mean to. </p>
<p>Now, about the universe. We get into a tricky subject because it is not fully understood, but we have some interesting models. There are really two kinds of "universe", the observable universe, and whatever else is there. We are limited in what we can see (and what we'll ever be able to see) because light and all information travels at a maximum speed, c (the speed of light). There simply isn't enough time for information to reach us from the other side of the universe, so we're are limited to a kind of sphere, roughly 42 billion ly in each direction. Beyond that distance light/information hasn't had enough time to travel to us. </p>
<p>Now, if you were to, say, travel 42 billion ly in one particular direction, you would be able to observe parts of the universe that would have remained hidden to us on Earth, 42 billion ly away. So you can kind of think of it like traveling to different parts of a major city. At one area you can only see so much (buildings are in the way), but if you travel to the opposite side of one of those buildings you can now see a different part of the city (instead of physical objects blocking our view of the universe, however, it is merely the time it takes info to travel to us). </p>
<p>The entire universe (not just the observable universe) is believed to be infinite. There is no edge. There are a couple of different shapes the universe might have. one shape is like a sphere. If you think of the Earth, for example, you can't fall off of it, you can walk in one direction and eventually come back to your starting point. THere is nothing beyond the universe, just like there is nothing south of the south pole (asking "what is beyond the universe" is a nonsensical question, just like asking "what is south of the south pole on earth").</p>
<p>Another shape the universe could be is known as a hyperbole, kinda like a saddle-shape. If you traveled in one direction on this shape, again you would come back to the same point (at t=infiniti). Think of the game Ms. Pacman, if you traveled off the screen, you didn't die, but rather re-appeared on the opposite side! The same general principle holds if the universe is in this shape.</p>
<p>Finally the universe could be just...flat. Infinite in all directions, you would never fall back on yourself. This has interesting consequences, which I won't get into now. </p>
<p>Basically, there is no edge. No barrier that you will 'fall off'. The universe, by definition, is all that there is, so how could you fall off of it? I hope this cleared up some of your questions, feel free to ask some more and I'll try to do my best to answer them.</p>
<p>if the speed of light is constant that how come the universe is larger than 26bly across</p>
<p>So the reason why the observable universe is larger than 26 Gly across (I'm assuming you're basing that off 13 billion years old) is because the actual fabric of spacetime expands at the speed of light, and in fact in the early universe (and now as well) the fabric of the cosmos is actually expanding faster than the speed of light. Now, that might seem like a contradiction of relativity, but einstein's law stating that light/information can't travel faster than light doesn't apply to spacetime itself. Therefore the very fabric of the universe can (and does) travel at c, or faster. Based on that (without doing complicated mathematics), and how long space has expanded faster than c, the observable universe is larger than 26 Gly across.</p>
<p>Oh yeah, try and picture if there was nothing, absolutely nothing that ever existed, no God, no universe, no life that ever began, nothing ever began forever, NEVER, can you imagine?</p>
<p>someone light a blunt..then we'll proceed.</p>
<p>So this may be a good time to explain the consequences of if the universe is "flat", meaning it expands for infinite, and never comes back on itself. We will start with an analogy.</p>
<p>Let's say you are someone who really loves to go out to parties, night clubs, dates, etc. Whenever you can you hit the streets to have some fun. Because of this, you have a pretty extensive wardrobe: you have all kinds of shirts, pants, socks, shoes, scarfs, etc etc. The number of different combinations of clothing is absolutely huge, you certainly don't want to be seen in the same attire twice! Let's say with all your different clothing, you can form 1 million different wardrobes. That means, that if you were to go on 1 million + 1 dates, at some point you would have to repeat an outfit, there's just no way of getting around it.</p>
<p>Now, instead of 1 million dates, let's say you hit the town an infinite number of times. Well, you can only form 1 million different clothing forms, so you'll have to repeat how you dressed. In fact, even though it is rare (1 in a million), you will have to repeat that wardrobe an infinite number of times! Why do I bring this up?</p>
<p>Now let's take our universe. You all probably know there are protons, neutrons, and electrons, with subatomic particles like quarks, bosons, fermions, etc etc. These particles can form a huge number of atoms: Nitrogen, Carbon, Platinum, just to name a few. And these atoms can form huge amounts of other things: peptide chains, carbohydrates, diamonds, chairs, paint, etc etc. However, even though there are a huge number of particles, and that they can be arranged in an unbelievably large assortment of different "things", the fact is there is some limit to the number of arrangements they can make (based on nuclear physics, such as Pauli Exclusion principle, and others.) </p>
<p>Because of that, and if we assume the universe is infinite and flat, that means that if you left earth and traveled in one direction through space, you would, eventually, come up on an exact duplicate Milky Way Galaxy (down to the slightest breeze of dust particles), an exact duplicate of Earth (to the specific atomic make-up of the ocean) to your exact same room, where you are reading this exact same message, written by me! You can't get around it! The number of arrangements of particles is gigantic, couldn't even put it in numbers, but it is finite, so in an infinite universe you must have repeating combinations, just like your wardrobe! In fact, if you kept going, you would run into (though unbelievably rare) an infinite number of these replica You's. So not only would there be intelligent life in other places of the universe, that intelligent life is you, over and over again. </p>
<p>In fact, theoretical physicists calculated that the distance you would have to go before you ran into these repeat societies is 10^10^29 meters. That is a 1 with 10^29 zeroes after it! And you thought you felt insignificant before!</p>