<p>If something is expanding, it needs something to be inside of. Thus the universe and the entire spactime continuum is inside of another spacelike X-dimensional area, which must be in another, and another, etc. Space as we define it is finite. Existance is infinite.</p>
<p>^ No, that is not correct. The universe is infinite in size (It would take far too long to show you the theoretical equations, especially since I don't know your physics background). There is no other "medium" in which the universe is expanding in, this is a common misconception because people don't understand how something can expand without something to expand into. Well, in the case of the universe, it is expanding in...the universe!</p>
<p>This should sound strange (it is!) but the reason for this is because of the properties of infinity. You cannot think of it as just some very large number, it doesn't work that way. Like I talked about above, there are different kinds of infinity, some are larger than others. 1/2 of infinity is infinity, one-billionth of infinity is...infinity! So the best way to imagine how the universe can be expanding but still be infinite is with a well-known analogy (to astrophysicists, at least):</p>
<p>Let's say you go to a hotel to spend the night. You walk in, and it's just a single floor complex with all the rooms in one hallway. You walk into the hallway, and scan up and down the hall and notice that there are an infinite number of rooms, i.e. there are infinite number of doors on both sides of you, extending down the hallway. Unfortunately, the manager of the hotel tells you that there are no vacancies: all infinite number of hotel rooms are occupied with an infinite number of residents. So what do you do? Simple: you walk up to one of the rooms, knock, and tell the resident of your situation. The solution is that all the residents of the rooms just move over one room to the right (...or left, it doesn't matter). This makes the central room vacant, and you can spend the night! If another person comes, everyone just moves to the right again, opening up another room! There are infinite number of rooms, so even if there are infinite residents, you can always make room. This is starkly different if there are, say 20 rooms and 20 residents: there is an obvious limit.</p>
<p>The point is, the infinite universe can expand within itself because of the nature of infinity, there is no end, no barrier that "regular" numbers are limited to. It is literally the expansion of spacetime itself that is always increasing the size of the universe. There is no "X-dimension" it expands into, that's not allowed in quantum physics. </p>
<p>And I have no idea what you mean by "Existence is infinite", that's a pretty vague and senseless statement. </p>
<p>I hope this helps!</p>
<p>Smallz, I like your analogies; they really do help for the non-physicists!</p>
<p>^haha, thanks.</p>
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^ No, that is not correct. The universe is infinite in size
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No, that is not correct/incorrect. It is unproven as of now.</p>
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Let's say you go to a hotel to spend the night. You walk in, and it's just a single floor complex with all the rooms in one hallway. You walk into the hallway, and scan up and down the hall and notice that there are an infinite number of rooms, i.e. there are infinite number of doors on both sides of you, extending down the hallway. Unfortunately, the manager of the hotel tells you that there are no vacancies: all infinite number of hotel rooms are occupied with an infinite number of residents. So what do you do? Simple: you walk up to one of the rooms, knock, and tell the resident of your situation. The solution is that all the residents of the rooms just move over one room to the right (...or left, it doesn't matter). This makes the central room vacant, and you can spend the night! If another person comes, everyone just moves to the right again, opening up another room! There are infinite number of rooms, so even if there are infinite residents, you can always make room. This is starkly different if there are, say 20 rooms and 20 residents: there is an obvious limit.
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<p>Infinite = Infinite. For every room in this hallway, there is a resident. So there are no vacant rooms because the endless number of them are filled endlessy by endless people.</p>
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The point is, the infinite universe can expand within itself because of the nature of infinity, there is no end, no barrier that "regular" numbers are limited to. It is literally the expansion of spacetime itself that is always increasing the size of the universe. There is no "X-dimension" it expands into, that's not allowed in quantum physics.
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<p>Alot of things aren't allowed in Quantum Physics that are allowed in Theoretical Physics generally. String theory is just that, a theory. There could be more than 12 dimensions, so I used the variable X to describe what it is; an unknown.</p>
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And I have no idea what you mean by "Existence is infinite", that's a pretty vague and senseless statement.
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By Existance I mean basic being. A state of being. Everything is. Just Is. Being is infinite. I'm sorry I couldn't find a better way to phrase it I'm having a hard time putting it into words.</p>
<p>….sigh. Let’s go over this again. First, based on your previous posts I know you’re not yet in college, you say you’re the class of 2013, so I assume that makes you a senior in high school. With all due respect, your background in math and physics is quite limited, even if you’re taking AP Calc BC, AP Physics BC, etc etc. Maybe this is a good time to bring up courses I’ve taken in my collegiate career: First physics courses: Newtonian Physics, Thermodynamics, Electromagnetism/Optics, Quantum Mechanics 1, Quantum mechanics 2 (there are no additional QM courses), Astrophysics 1, Astrophysics 2: Cosmology, Astrophysics 3: Planetary astro, with at least 3 more in the semesters to come. Math: Calc 1, Calc 2, Calc 3, Calc 4, Cosmological Statistics, again with several more later. The point I’m trying to make is that when you get to college, that is when you’ll learn about some of the things I’m talking about, if you’ll be a physics major. </p>
<p>You said that the infinite/finite universe is “unproven”, first you have a misunderstanding of the word “proof”. In science, we don’t “prove” anything, we never call things “Laws” or “absolutes”, mainly because that disrupts scientific integrity. Science is a constantly evolving and ever-changing thing and labeling something a “law” would imply that we know everything about it, which we can never be sure of. In the past people threw around the word “law” more freely, that’s why you hear the “Law of Gravity” and such, but nowadays scientists only refer to things as theory: the theory of gravity, the theory of Quantum mechanics, even though our calculations and observations have backed up the vast majority of the ideas presented. </p>
<p>I am not going to lay out the equations showing you why we believe the universe is infinite not just because I now know you don’t have the mathematical/physics background to be able to understand it, but because it is long, tedious, and not easy to do in text-based forums.</p>
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Infinite = Infinite
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<p>That is 100% wrong. You equating all infinities equal to each other is absolutely incorrect. I don’t know if you have always assumed this, if a math teacher told you this, or whatever, but it is not correct. You must not have read my wardrobe analogy, I suggest reading over that. My analogy with the hotels is quite valid, but you need to understand the ‘qualities’ of infinity.</p>
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Alot of things aren't allowed in Quantum Physics that are allowed in Theoretical Physics generally
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<p>Now hang on a minute, that’s not valid. Maybe you don’t understand what theoretical physics is, but it’s the mathematics of our universe that we use to denote laws (as opposed to observations). If something isn’t allowed in Quantum Physics , then it can’t, by definition, be allowed in theoretical physics, especially since the majority of quantum physics is based off mathematical theory! </p>
<p>You bring up string theory’s possible 12 dimensions, but that is definitely not the same as some outer-dimension the universe is expanding “into”. Those 12 dimensions are within spacetime: If you picture a metal cable, from far away it appears to just have the single, length-wise dimension, but up close you notice it has grooves and curves all around it, hence additional dimensions. It’s not like if you look at the cable close up you’re going to find additional dimensions BEYOND the cable. String theory talks about the dimensions WITHIN the fabric of spacetime, not something beyond it.</p>
<p>Now, I don’t mean to come in and just throw all of your ideas out, it’s great that you’re thinking about the universe, but there are many things you haven’t learned yet and you will if you pursue physics as a major in college.</p>
<p>"If you picture a metal cable, from far away it appears to just have the single, length-wise dimension, but up close you notice it has grooves and curves all around it," </p>
<p>...haha what's up Briane Greene?!</p>
<p>and isn't it superstring theory, or M- theory that calls for ELEVEN space-time dimensions?..not 12...</p>
<p>other than that I agree with everything you said in your response to entropy.</p>
<p>^ haha, you're absolutely right, when he talked about the additional dimensions the first thing i thought of was greene's analogy, i guess I should have referenced it! And yea, I think it is 11, not twelve dimensions. I am certainly no expert on string theory, but I don't like it for a couple of reasons I won't get into.</p>
<p>i just read over this post and man…thats CRAZY stuff! </p>
<p>but i have a question: with all the mass in the universe shouldn’t its expansion be slowing down bc of gravity? smallz? anyone?</p>
<p>So without even talking about Dark Energy, it was discovered that there simply wasn’t enough mass in existence in the universe to have an appreciable effect on the expanding universe. Even the ‘discovery’ of dark matter isn’t enough to cause the universe to contract at the expansion velocity of spacetime.</p>
<p>Since Dark Energy was discovered, which is a negative-pressure (imagine squeezing a balloon: normall when you squeeze it pressure increases. With Dark energy the more you squeeze the balloon, the more the pressure decreases!). This is causing the universe to accelerate faster and faster. So no, the lack of matter and the existence of Dark Energy means the universe will expand forever (unless the forces change…)</p>
<p>Gosh, my head hurts just from reading this stuff! This is what I love about Neuroscience - it’s the study of the nervous system. No black holes, no dark energy, none of this gobbledygook…just the nice brain, spinal cord, and little ol’ neurons floating around…</p>
<p>Also, Smallz3141, are you going to grad school? You seem really into this AstroPhysics stuff.</p>
<p>I always include “lol” when I have questions about the complexities of existence.</p>
<p>haha, yeah I plan on going to graduate school.</p>
<p>ok but i have 1 more question. what caused the big bang? how can u just get the entire universe from nothing? didn’t there have to be something to create it, or something there b4?</p>
<p>There is a cyclical view of the Universe. Basically, there is enough matter for the Universe to expand for a while (phase we are in), eventually contract, and then explode again.</p>
<p>It still begs the question: Where did the matter come from in the first place.</p>
<p>One could postulate parallel universe where in our universe, we had a positive energy flux that created everything, with an offsetting negative energy flux in a parallel universe (conservation of energy).</p>
<p>It still begs the question: where did the void come from that permitted an energy flux.</p>
<p>From my limited understanding of this topic, the Universe is expanding at an accelerating rate. So, technically speaking, at an infinitely small moment in time, the Universe does indeed have a “boundary.”</p>
<p>This thread (especially Smallz’s answers) is inspiring me to become an astrophysicist!
lol</p>
<p>You guys bring up some interesting points. </p>
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<p>Boy, if I knew the answer to that I’d have the Nobel Prize. We can study the Big Bang with theoretical and observational evidence for a large chunk of it, up to about 10^-43 seconds after the big bang (.00000000000000000000000000000000000000000001 sec). That is the barrier because General Relativity breaks down at the super high temperatures and pressure we know existed at and before that time. Our theories break down, and that is because there is a lack of unity between general relativity (governing the very large) and quantum mechanics (governing the very small). </p>
<p>What we need is a unified theory, a Quantum Gravity, that explains what happens at this time. Then we could further theorize how the big bang started in the first place. </p>
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<p>That is one theory, that our current universe is one of infinite stages of expansion, then compression of past universes. Maybe the universe before ours crunched back into a singularity (kinda like a black hole), then blew up again creating our universe. The problem with that theory is that it seems to violate the 2nd law of thermodynamics: entropy always increases. If universes kept expanding and contracting, the entropy would be enormous, and while that entropy is high in ours, it’s not as high as would be necessary for this cyclic idea.</p>
<p>However, Black Holes can consume entropy, so one thought is that the black holes eat all of it. That means that either they would have to re-spew the entropy as the black holes “big banged” again, or there would need to be a ton of black holes in our universe, which we don’t see. Also with Dark Energy and the overall lack of matter (regular and Dark), it doesn’t seem likely that our universe will ever contract. Not to say this cyclic universe theory is disproven, but it doesn’t look good right now. </p>
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<p>No, that isn’t the case. The problem is people are thinking of the universe kinda like a table top: ‘‘Even if it expanding, there is an end to the table where you could ‘fall off’.’’ The universe isn’t a table (shocking!). It’s better to think of it like a sphere (like Earth), and this sphere is expanding at an accelerating rate. But you can never fall off the sphere (just like you can’t fall off of earth), there is no boundary.</p>
<p>I hope that helped.</p>
<p>There is “boundary” and there is “boundary”. There is no physical “edge” where you can’t go past, but I think there is an “edge” where, past that, nothing has yet occupied.</p>
<p>Then again, that is my non-astrophysicist view. I haven’t quite got the concept of the big bang not originating from a “point” like water flows from a faucet. Supposedly, the universe is more like the surface of a balloon in terms of expansion. We exist on the surface of the balloon (so what is in the middle?). So what implications that has on “boundary”, I have no idea. When Smallz3141 says “you can never fall off the sphere”, that is true if you are limited to living on the surface of the sphere. But, if you somehow manage to get off the surface, you can fall off.</p>
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<p>But see you’re still under the impression that there is the Universe, and there is some ‘other’ thing in which the universe is expanding into, and that’s not the case. And whether there is a finite or infinite universe, there is nothing that it’s expanding into.</p>
<p>To say there is something “outside” the universe means that outside the universe needs to somehow exist. But we say that all that there is of space and time, “everything that is everything” is inside of our universe (that’s what “universe” means). So therefore if you go outside of the universe there ceases to be dimensions, there ceases to be any time, and that nothingness can’t be labeled as something. You can’t really even say there is “nothing”,because that implies there are spatial and time dimensions where there is no mass/energy. You reach this point where philosophy breaks down.</p>
<p>People have notion that if it’s finite the universe has to be expanding into something, some X-dimension. However that goes against what we talked about above. Instead it’s better to think of it like this: consider it as everything that’s everything is expanding.</p>
<p>And of course my sphere analogy is just that…an analogy. To ask what is inside the sphere is nonsensical, like asking what’s south of the south pole. There is no additional dimension you could jump off into. The universe has no boundary.</p>