You may opt-out by. But what is it expanding into? In that case, there really would be no center of the universe - the only way you can define the center is to mark out the edges and find the point that's equally in between all of them. What is the universe expanding into? The answer is that there is no difference, absolutely none. (Intermediate), What do I need to do to become an astronomer? Share on Pinterest. Embedded in the dough are a bunch of raisins, spread throughout. He also did most of the development for the former version of the site. Instead, it will read one billion light-years the whole time. Finally, we can return to the original question. If we want to understand the actual way that the universe functions, we need to find some way to incorporate Einstein's ideas into our mental picture and imagine space as a more complicated entity which is capable of doing things like "bending" and "stretching". On the other hand, if it was ‘open’, the Universe would keep expanding forever. It is an intrinsic expansion whereby the scale of space itself changes. Now, someone puts the dough in the oven and it begins to expand. But if the universe is expanding, then what is it expanding into? (Beginner), Why is Earth's core molten? (Intermediate), How do we define distance in an expanding universe? (Advanced), Which planet is most similar to Earth? (Beginner), Can artificial gravity be created in space? Not only that, but the farther away something is, the faster it will appear to be moving away from you, just like the relationship that Edwin Hubble (and all the astronomers who came after him) saw and still see today. When scientists talk about the expanding universe, they mean that it has been growing ever since its beginning with the Big Bang. Image credit: NASA / WMAP science team, via http://map.gsfc.nasa.gov/universe/bb_tests_exp.html. The collection of galaxies that make up the universe is moving through space; therefore, the universe is expanding into even more space than it already encompassed. To help us imagine this, a lot of people have come up with analogies for the universe in which space is represented by something more tangible. How? (To the best of my knowledge, this analogy was originally proposed by Martin Gardner in his 1962 book Relativity for the Million.) But according to Einstein's theory of general relativity, space isn't really as simple as our common sense tells us. The distance between adjacent number in your list has "stretched" (it is now 2 instead of 1), but can you really say that the total extent of all your numbers has "expanded"? (Intermediate), How are galaxy distances inferred from their recessional velocities? Every book I have seen has defined the universe as "everything". (Beginner), When was the last time all of the planets were aligned? What is the universe expanding into? (Beginner), What happened to the Arecibo Telescope? For example, you and I aren't expanding, the Earth isn't expanding, the sun isn't expanding, even the entire Milky Way galaxy isn't expanding. It's just expanding. (Intermediate), How many stars are born and die each day? So we don't think there is any way to observe or measure what is beyond, unless it had some effect on us that we currently don't know about. Is there truly a center to this loaf of bread (or to our Universe)? In the old picture, it is easy to say where the center of the universe is - it's the point in space that all the galaxies are moving away from. The universe began in a Big Bang nearly fourteen billion years ago, and has been expanding ever since. So if you are stuck inside the dough, and have no way to see anything except the dough, and if you are so far from the "edge" of the dough that you can't see it and it can't have any effect on you, then what difference do you notice between the point where you're at and the point that is actually at the geometric center of the entire blob of dough? 28 November 2013, by Fraser Cain Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that Now, imagine that you can only live on and see a tiny, tiny region of this balloon: one that's just perhaps a millimeter (or about a thirtieth of an inch) in diameter. (The bread is the invisible fabric of space; the galaxies are the raisins within.) However, if you just want a short answer, I'll say this: if the universe is infinitely big, then the answer is simply that it isn't expanding into anything; instead, what is happening is that every region of the universe, every distance between every pair of galaxies, is being "stretched", but the overall size of the universe was infinitely big to begin with and continues to remain infinitely big as time goes on, so the universe's size doesn't change, and therefore it doesn't expand into anything. This new picture of the universe which I am asking you to imagine is, on a practical level, much different from the old picture in which the galaxies are all moving through space away from some point at the center. But if you didn't include this cosmological constant, others soon realized, you'd wind up with a Universe that wasn't static in time, but where the fabric of space itself was either expanding or contracting with time. (Intermediate), What's going to happen on December 21st 2012? Therefore, the collection of galaxies (which we call the "universe") is expanding, and it is certainly fair to ask what it is expanding into. Copyright © 1997 - If these numbers represent the distances between galaxies in an infinite universe, then it is a good analogy for why the universe does not necessarily expand even though it stretches. But that's part of the wonder and joy of science: until we know, we have to admit that even the most absurd-sounding explanation that can't be ruled out is actually possible. © 2021 Forbes Media LLC. All Rights Reserved, This is a BETA experience. (Intermediate), What was the bright, smoothly moving star that I saw? But it could be doing much, much more. I have won numerous awards for science writing. Well, what if instead of just being really really big, the dough were infinitely big - that is, you could walk forever in a straight line and never reach a place where the dough ends. Where did the Big Bang take place? If you combined these two facts -- that there were distant galaxies that rapidly moved away from us -- you noticed an interesting trend: the farther away a galaxy was from us, the faster it appeared to be moving away! You could be perfectly justified in saying that the distance between the galaxies has not changed as time goes on. Image credit: NASA and ESA, via http://www.spacetelescope.org/images/opo9919k/. (Intermediate), How could galaxies have gotten so far away in only 14 billion years? That’s a complicated question. Since the dough represents the space that we live in, we have no way to see "outside" of the dough to get a sense of the entire shape and figure out where the center is. I kind of get the idea about of distances getting larger. The Universe doesn’t need to be expanding into anything greater than itself; it may simply be expanding, because that’s what space does in general relativity. We give you the same unsatisfying answer, but … Image credit: Robert Kirshner, PNAS, 101, 1, 8-13 (2004), of the distance/velocity relationship of... [+] distant galaxies. Of course, when we think of space in everyday life, we don't think of it as something which is capable of stretching. Thank you for your time. The galaxies simply sit there. The short answer is that this is a nonsense question, the Universe isn't expanding into anything, it's just expanding. The galaxies outside of our own are moving away from us, and the ones that are farthest away are moving the fastest. He explains this … I understand that the red spectra indicates that things are moving away from us but that is drifting not expanding, right? The expanding universe is due to gravity, which means that in regions of high density, the dominant gravitational effects are entirely local. For example: What is the distance between two galaxies? (Beginner), What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? Although the galaxies haven't moved through space at all, they get farther away from each other as time goes on because the space in between them has been stretched. The short answer is that this is a nonsense question, the Universe isn’t expanding into anything, it’s just expanding. It is unclear whether the universe as a whole is really "expanding" - all that we really measure is a stretching of the space between each pair of galaxies. In our new picture, though, the galaxies are just raisins spread throughout the dough - their presence is largely irrelevant to the question of the universe's expansion. One of the most spectacular discoveries of the 20th century was that the Universe itself was expanding. Astrophysicist Jocelyn Bell Burnell answers 10-year-old Owen's question. A rapid motion, where the faster-moving galaxies wind up farther away over time. What Is (And Isn't) Scientific About The Multiverse, The Pillars Of Creation Haven't Been Destroyed, Say New NASA Images. Image credit: NASA, Goddard Space Flight Center, of an illustration of the expanding Universe. All of the galaxies in the universe are moving away from each other, and every region of space is being stretched, but there's no center they're expanding from and no outer edge to expand into anything else. The universe began its cosmic life in a big bang nearly fourteen billion years ago, and has been expanding ever since. (Advanced), Do galaxy mergers have a major impact on star formation rates within the galaxies? (Intermediate), Is the Moon moving away from the Earth? Does it ever curve back in on itself and reconnect? In the standard physics theory, the galaxies are all getting farther apart; that is the expansion of the Universe. And a sphere, as well as any other curved surface, can only be thought of as sitting in a bigger space. Since astronomers know that the Universe is expanding, whats it expanding into? (Beginner), Why is looking out into space the same as looking back in time? The Universe is out there, waiting for you to discover it. If the dough does have a boundary, then it is legitimate to ask what is beyond the boundary that the dough expands "into". However, as time goes on, the space between the galaxies "stretches", sort of like what happens when you take a sheet of rubber and pull at it on both ends. We can determine the past expansion history of our Universe, we can find that the expansion is accelerating rather than any of the other options (and hence, describe the expansion), but as far as what's happening outside of what we can observe, we have more questions than answers. When was this discovered? But the thing is, as Jeremy points out, a balloon is an entity expanding in front of you into another entity, which is air. We often hear that our universe is expanding and the galaxies are moving further away from one another. What does the universe expand into? Dame Jocelyn Bell Burnell: 'We live inside our universe … Indirect Contributions Are Essential To Physics, The Crisis In Theoretical Particle Physics Is Not A Moral Imperative, Why Study Science? Into what “space” is it expanding and what happens to that “space” when the universe contracts/has contracted? We not only don't know, we have no idea how it would ever be possible to know. There are many, many reasons that cause something to stretch or expand. The Same Reason You Would Study Anything Else, The (Mostly) Quantum Physics Of Making Colors, This Simple Thought Experiment Shows Why We Need Quantum Gravity, How The Planck Satellite Forever Changed Our View Of The Universe. (Intermediate), What would happen if an asteroid 10 kilometers across hit the Earth? Einstein's fix for this was to make up an invisible, outward-pushing force that prevented this collapse from occurring, a cosmological constant. But as far as what lies beyond the part of the balloon we can observe, including in dimensions beyond the two that make up the surface of the balloon, we simply don't have the information to say. The dough represents space, and the raisins represent the galaxies. I am a Ph.D. astrophysicist, author, and science communicator, who professes physics and astronomy at various colleges. Just get yourself a giant tape measure and clip it to a faraway galaxy, then come back to our galaxy and hold on tight. What Is The Universe Expanding Into? (Beginner), How far is each planet from Earth? Here's the short answer: That question doesn't make sense. What would it look like, for example? When light is emitted from one galaxy and travels through space to another galaxy, during its trip through space it also will be stretched, causing it to have a longer wavelength and therefore causing its color to appear more towards the red end of the spectrum. We have 3495 guests and no members online. For example, there is the analogy with a sheet of rubber (or sometimes a balloon) that I mentioned above. When you bring the tape measure back in, however, you will notice something unusual; due to the stretching of space, your tape measure will have stretched as well, and if you compare it to an identical tape measure which you had sitting in your pocket the entire time, you will see that all the tick marks on it are twice as far apart as they used to be. I'm afraid these questions always lead to wierd territory but that's because we're dealing with the fundamentals of reality, it would be a surprise if it didn't bake our brains. What is the universe expanding into? So far so good. The universe is everything, so it isn't expanding into anything. When Einstein put forth his general theory of … That said, cosmologists are pushing the limits of mathematical models to speculate on what, if anything, exists beyond our spacetime. As you can see, the concept of "distance" in this new picture of the universe is somewhat more complicated than in the old picture! In the standard physics theory, the galaxies are all getting farther apart; that is the expansion of the universe. (Intermediate), What makes certain lunar eclipses so special? We say the universe is expanding, and by expanding we mean the distance between objects gets larger over time. The Universe can expand without there being anything outside it for it to expand into, says science writer and astrophysicist Adam Becker. The universe cannot expand into nothing (i.e., into the absence of anything)! Treknology: The Science of Star Trek from Tricorders to Warp Drive, Beyond the Galaxy: How humanity looked beyond our Milky Way and discovered the entire Universe. Is it infinite, or simply bigger than we can perceive? That's because on these relatively small scales, the effect of the universe's stretching is completely overwhelmed by other forces (i.e. (Intermediate), What color is each planet? Interested in getting a telescope and want to support Deep Astronomy? The boundary at the edge of the dough represents the "edge" of space. If, on the other hand, the universe has a finite size, then it may be legitimate to claim that there is something "outside of the universe" that the universe is expanding into. While this could have been due to a number of factors, including: only the last option was validated by the full suite of data supporting both the general theory of relativity and the astrophysical distribution and properties of all the galaxies observed. My favorite analogy, though, involves imagining the universe as a gigantic blob of dough. I bet some people were wondering about that!). Physicist: Probably nothing. These aren't wild guesses, but hypotheses that tackle kinks in the scientific theory of the Big Bang. Or was there an initial set of conditions that the fabric of the balloon started off with that determined these expansion properties before anyone ever came along to observe it? The universe cannot expand into nothing (i.e., into the absence of anything)! In the 1910s, Vesto Slipher noticed that the spiral nebulae in the sky were redshifted, consistent with the interpretation that they were moving away from us. We do know that the universe doesn’t need anything to expand into, and we haven’t seen any evidence that there is anything outside of the universe. My two books, Treknology: The Science of Star Trek from Tricorders to Warp Drive, Beyond the Galaxy: How humanity looked beyond our Milky Way and discovered the entire Universe, are available for purchase at Amazon. Images credit: J.R. Eyerman, LIFE Magazine. Atheists claim the universe came into being out of nothing. (Beginner), Astronomy Department at Cornell University. (Intermediate), How do you measure the distance between Earth and the Sun? A more accurate word for what the universe is doing might be "stretching". If you look at any other region of the balloon that you can see, you can tell it's expanding, as the things within it will be moving away from you. Now, for those of you who want a more comprehensive discussion: Let me begin by saying that "expanding" isn't really the best word to describe what is happening to the universe, although that is the word that is often used - a word choice which I think leads to a lot of unnecessary confusion regarding what is already a difficult topic! (Beginner), If I were hypothetically wearing a spacesuit and sitting on one of the Voyager space probes at their current positions in space, how much light would I have? Thinking about infinity is always complicated, but a good analogy can be made with simple math. The raisins move apart from each other, but relative to the dough they don't move at all - the same particles of dough that start off near a particular raisin will always be next to that raisin. (Intermediate), What is the difference between a "star" and a "sun"? (Note that we might have to have an "imaginary" tape measure whose atoms aren't actually being held together by intermolecular forces in order for the scenario described above to actually take place as described. (Intermediate), Why do the planets orbit the sun? To answer these questions, think of an ant walking on the surface of an expanding bubble. This is what leads us to see redshifted light when we look at faraway galaxies, and it is measurements of this redshift that allow us to estimate the distances to these galaxies.). If the universe is expanding what is it expanding into? The definition of the Universe is that it contains everything. What Was It Like When The Universe First Created More Matter Than Antimatter? But how does the universe expand and what is it expanding into? We call that "Metric Expansion of the Universe". The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. The Universe doesn't need to be expanding into anything greater than itself; it may simply be expanding, because that's what space does in general relativity. One of the most spectacular discoveries of the 20th century was that the Universe itself was expanding. Let's go back to the dough analogy - sure, you can imagine that even if the dough is really really big, it has some point within it which is the geometric center. Image credit: ESA/Hubble & NASA and N. Gorin (STScI); Acknowledgement: Judy Schmidt. For instance, if the shape of the Universe was ‘closed’, then at some point the expansion would eventually be triumphed by contraction, causing the Universe to gradually collapse into itself. (Beginner), (Intermediate) >" onclick="window.open(this.href,'win2','status=no,toolbar=no,scrollbars=yes,titlebar=no,menubar=no,resizable=yes,width=640,height=480,directories=no,location=no'); return false;" rel="nofollow">, Is the universe expanding faster than the speed of light? What it is expanding into?  The Curious Team | Web Design © Siliconian | Image Credits | Team Login, What equipment do I need for astrophotography? The complete and honest answer is we don't know, and moreover, we can't know! When Einstein put forth his general theory of relativity, he swiftly recognized that there was a consequence he was unhappy about: a Universe that was filled with matter in all directions would be unstable against gravitational collapse. Please take the time to browse our site and first try to use the resources online to find an answer to your question. If the Universe is doing that and the universe is everything then it's very hard to grapple with our view of the universe in terms of our human brain's ability to model the universe. Imagine you have a list of numbers: 1,2,3,etc., all the way up to infinity. The universe does not expand "into" anything and does not require space to … If we're lucky, perhaps someday we'll devise a way to find out. We're used to this concept in almost all of our experience, as an expanding balloon expands due to the air inside of it increasing, and to the balloon itself pushing out against the molecules on the outside. But there has still been some speculation. Are there four (or more) spatial dimensions, total? In our new picture of the universe, however, with the raisins and the dough, the tape measure will not unwind at all as the universe expands, because the galaxies are not actually moving with respect to each other! (Intermediate), How are light and heavy elements formed? (Beginner), How does the position of Moonrise and Moonset change? Share on Pinterest. Then you multiply every number in this list by 2, so that you now have 2,4,6,etc., all the way up to infinity. Instead, the galaxies are in some sense stationary - they do not move through space the way that a ball moves through the air. In our old picture of the universe, the answer would be simple, although very unsatisfying. Finally, I should point out that not everything in the universe is "stretching" or "expanding" in the way that the spaces between faraway galaxies stretch. Space, to us, just seems like something which is there, and which everything else in the universe exists within. All we do know is that based on our current understanding of theoretical cosmology, the universe does not have a boundary - it is either infinite or it wraps around itself in some way. I am a Ph.D. astrophysicist, author, and science communicator, who professes physics and astronomy at various colleges. Image credit: Wikimedia Commons user Caroldermoid. Related Posts. The long explanation is below. So the total size is the same! In the old picture, this is an easy question to answer theoretically (though not necessarily in practice!). In the last hundred years physics has gotten pretty weird, and defining “universe” has become a little tricky. (Intermediate), Are there telescopes that can see the flag and lunar rover on the Moon? (Intermediate), How is it proved that the Universe is expanding? If you could help me to understand this, it would be appreciated. Ask any astronomer and youll get an unsatisfying answer. It is only when we look across far enough distances in the universe that the effect of the universe's stretching becomes noticeable above the effects of local gravity and other forces which tend to hold things together. Our Universe is like a three dimensional version of the balloon's surface, where galaxies are like raisins baking in a gigantic loaf of bread. The universe began in a Big Bang nearly fourteen billion years ago, and has been expanding ever since. By definition, we exist within space and have no way to leave it! Where is the center of the universe? Therefore, given atheism, the Big Bang would be a non-starter! The universe is not expanding into anything, not even expanding into nothingness. The Universe can expand without there being anything outside it for it to expand into, says science writer and astrophysicist Adam Becker. Because the universe’s size is already infinite, its size can’t increase. In the 1920s, Hubble discovered that these nebulae were in fact galaxies, and determined their distance from us. Besides, it's the space between the galaxies that's expanding mostly. However, because we are, by definition, stuck within the space that makes up our universe and have no way to observe anything outside of it, this ceases to be a question that can be answered scientifically. Therefore, given atheism, the Big Bang would be a non-starter! (That is why, in the analogy of the tape measure I discussed above, the tape measure that you keep in your pocket does not get stretched, while the one that goes between two galaxies does get stretched. How to judge the universe is not expanding as fast or faster than light. Sajan Saini explains the existing theories around the Big Bang and what, if anything, lies beyond our universe. (Beginner), If Mars is only about 35-60 million miles away at close approach, why does it take 6-8 months to get there? The light from these distant galaxies getting "tired" and losing energy as they travel through space. In the new picture, though, this isn't so clear. In other words, the universe has no center; e… In our old picture of the universe, the answer would be simple, although very unsatisfying. However, the galaxies are not moving through space, they are moving in space, because space is also moving. This means that no matter what galaxy you happen to be in, all the other galaxies are moving away from you. Most of us are graduate students at Cornell, and all of us do this voluntarily, in our own time, fitting it in around our other work. If the universe is indeed infinite, then the simple answer to the original question is that the universe doesn't have anything to expand into. The analogy implies that there's a surrounding space, a third dimension, into which the bug universe expands. These are questions that we have no way to give a scientific answer to, so the simple answer is that we don't know! So the answer in that case is that we really don't know what, if anything, the universe is expanding into. Illustration of a planet or star explosion. This page was last updated June 27, 2015. And is there something bigger and grander than what we can ever hope to observe, that it truly is expanding into? From our vantage point, we can only see that the balloon is expanding. An initial explosion, which pushes some galaxies farther away from us by the present. But how does the universe expand and what is it expanding into? Or so it seems. If we assume the universe is infinite, then it’s not really expanding into anything. Ask a grown-up: what is the universe expanding into? It became apparent very quickly -- as early as the 1930s -- that there are no two ways about it: the Universe is, in fact, expanding. Here’s why: Einstein’s equations of general relativity describe space and time as a kind of inter-connected fabric for the universe. The difference between "expanding" and "stretching", for me at least, is that an "expanding universe" conjures up an image where there is a bunch of galaxies floating through space, all of which started at some center point and are now moving away from that point at very fast speeds. The Universe is either expanding into a multiverse, it is infinite so isn't expanding into anything, or it's expanding into itself via some hyperspace curvature. But for our universe, that is a very complicated question to ask! Ask Ethan: How Large Is The Entire, Unobservable Universe? Opinions expressed by Forbes Contributors are their own. Remember, the galaxies aren't actually moving away from each other - they're sitting still! We can measure the raisins within our view -- where "our view" is determined by the speed of light and the amount of time that's passed since the Big Bang -- and we assume that there's more raisins and more bread outside of what we can see, but that's all we can know. I have won numerous awards for science writing since 2008 for my blog, Starts With A Bang, including the award for best science blog by the Institute of Physics. This is a very good question which is not at all easy to give a satisfactory answer to! As the galaxy moves away, it will pull on the tape measure, and you will easily be able to read off the distance as the tape measure unwinds... one billion light-years, one and half billion light-years, two billion light-years, etc. Ask an Astronomer is run by volunteers in the Astronomy Department at Cornell University. This universe, both past and future, has no outside. Finally, we can return to the original question. (Intermediate), What will happen to Earth's tides as the moon moves away from us? Couldn't you, for example, simply take the stretchy fabric of the balloon -- perhaps with two hands, perhaps with four hands (with a friend, or by yourself if you're a mutant) -- and pull it in multiple directions at once? But this definition is not very useful. I am very confused about things my science book says about the expanding universe. We can assume (it would be illogical not to) that there's more balloon out there beyond what we can see; we can track exactly how the balloon is expanding today and how it's been expanding throughout the Universe's history; we can measure the properties of everything observable to us and study how it affect and is affected by the balloon, and so much more. But what's causing the expansion? Observations seem to agree with these predictions in the sense that if the universe does have a boundary, we know that the boundary is so far away from us that we can't currently see it and it doesn't have any effect on us. What we really care about is the dough, and whether or not it has a boundary. Sajan Saini explains the existing theories around the Big Bang and what, if anything, lies beyond our universe. Quote Come on, admit it, youve had this question. Whats outside of the Universe? In fact, we can go a step further and imagine that the center isn't even there at all! That is what I meant when I said that the galaxies aren't really moving through space as the universe expands - here, the raisins aren't moving through the dough, but the distance between the raisins is still getting larger. You started off with numbers that went up to infinity, and you finished with numbers that went up to infinity. (Beginner), Can we find the place where the Big Bang happened?

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