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If the universe is expanding, what is it expanding into?

If the universe is expanding, what is it expanding into?
Zoe from Wiltshire (Age 5-14)
Rhiannon Potter from Dorset (Aged 5-14)
Laura Young from Surrey (age 5-14)
Magan Davies from Staffordshire (Age: 5-14)
Hector Yapp from Staffordshire (Age: 5-14)
Allan Phillipson from Derbyshire (Age: 45-54)
Scientists say that the universe is expanding. My question is what is it expanding into?
Neil from Bedfordshire
Age 45-54

I have posed this question on other Science forums (fora?) But nearly always received the reply saying that the question is irrelevant!
Q: If the universe is expanding, what is it expanding into?
Ken Wright from Cambridgeshire (Age 45-54)

We know that basically the universe is made up of space and contains galaxies with solar systems, planets, comets, asteroids, black holes, dust, cosmic rays etc. The universe is said to be expanding – but into what? Where is the end of the Universe and WHAT IS BEYOND IT? It cannot be expanding into nothing, even nothing is something.
Nigel Le Gresley from Essex (Age 55+)

If the Universe is expanding, what is it expanding into (i.e. what lies beyond the Universe)?
Robin Ingledew from Middlesbrough (Age 55+)

If the Universe is ‘expanding’ into what area/space/ material is it expanding and does it matter? Or is it ‘expanding’ or as in times past the world was not ‘expanding’ but the knowledge of it by a few was ‘growing’?
John Ramsbottom from Devon (Age 55+)

Science tells us that the universe is always expanding. Now from my knowledge things only expand if they are either a) growing or b) physically or chemically changing. So my question is this: Why is the universe expanding? What is it expanding into? And does it want to expand; is it conscious and does it want to expand?
Leah J. Warren-Williams from Somerset (Age: 5-14)


22 Responses

  1. It’s not expanding into anything we can see or measure. It’s not really very helpful to try to think about it doing this as a result. It’s very hard to imagine how something could expand if it’s not expanding into anything, but in order to make sense of a question in a scientific way we have to be able to find a way of answering it by looking at what happens in the real world. There’s no way we have at the moment of finding something we can see in the universe that would help us answer this (because of course all of what we can see has to be inside the universe, not outside), and our best theories describing the universe don’t give us a way of asking this question either.

  2. On March 4th, 2008 at 11:45 am Kieren Lythgow said

    I believe the Universe is not exactly expanding ‘into’ anything. Since the big bang the Universe has been expanding and is now a particular size. The very fact it is expanding means it cannot be infinite. I believe the Universe is evolving and there is no space/matter around it.

  3. What is space expanding into?…

    John Wheeler once summed up the key idea in Einstein’s General Theory of Relativity in the following neat phrase:
    “spacetime tells matter how to move, and matter tells spacetime how to curve”. We think of the first half of this metaphor by visualising spacetime like a stretched sheet of rubber onto which we drop a heavy weight, which will cause the rubber sheet to bend and stretch. The second half of the metaphor is a bit harder to visualise: the notion that the “shape” of space itself is determined by its matter and energy content. More specifically, Einstein (and others) found that when the equations of GR were written down in a form suitable to describe the large-scale properties of the Universe as a whole, they appeared to predict that spacetime is not static but expanding, in the sense that the separation between e.g. two distant galaxies increases with time – behaviour consistent with Edwin Hubble’s discovery in the late 1920s that distant galaxies are receding from us with a speed proportional to their distance.

    According to our “common sense” view of the world, it might seem natural, or indeed necessary, for this
    expansion to be “into” something – i.e. for there to exist another space outside the Universe into which the
    expansion takes place. The plain truth is, however, that this is *not* required in GR. It *could* be the case that the expansion of our Universe is embedded within a higher dimensional “superspace”, but it doesn’t have to be. Moreover, the Universe could be infinite and still expanding…

    For more on the history of Hubble’s discovery, what it means, and how we measure the expansion today,
    see some pages I put together for the Association for Science Education:


  4. Comment:

    I think that the universe is expanding into nothing it is making space to expand into and as it is sphere it can do this, also if you try to reach the end you would probably never make it as the universe will always go faster than you but if you do make it to the end and then keep going you will go around and around the sphere and think you havnt reached the end

  5. This question falls into the catagory of “old chestnuts”
    and must be classified in the same way as “what happened before the Big Bang?” These are questions which with our very restricted understanding of the nature of matter and the basic laws of physics, have, as yet, no meaning.
    Until we can understand what makes the observable Universe tick, we cannot begin to understand what may or may not exist outside it or before it existed.
    Cosmologists and physicists have been struggling for years to come up with an “all enbracing” theory that can unify the laws of quantum mechanics and gravity and have so far failed to do so. This is not really surprising since we rely on observations of natural phenomena and we have a very restricted view of the Universe as a whole. What we can actually see of the Universe is confined to matter which radiates in the electromagnetic spectrum. Unfortunately, this comprises only about 4% of the entire matter/energy of the Universe. The latest theories that get close to a “theory of everything” require us to imagine a Universe that exists in 11 dimensions. Most people find it difficult to imagine a Universe in 4 dimensions – three spatial and one time. It may well be the case that our brains have not yet evolved to a state that can begin to process this information, but this dosen’t stop us from trying!
    It would be a pretty boring life if we understood everything and there was nothing else to discover.

  6. I think the above discussion can be summed up as: an expanding universe is an abstract concept (which is really outside our immediate experience) to which we have applied a concrete verb, i.e. to expand. As we are dealing with a metaphor, as explained by Martin Hendry, trying to pursue the metaphor to its logical conclusion is unhelpful. All we end up with is the conclusion that it is a poor metaphor. To state the universe is expanding like a balloon begs the question, what is it expanding into? The balloon expands into air so the universe must be expanding into something, surely. However, the universe only resembles in 3D the expanding properties of the balloon in 2D, not the air inside the balloon nor the air outside of it. So what we are trying to conceive is an expansion in 3D analogous to the 2D expansion of the surface of the balloon. The surface of the balloon does not expand into anything when dealing only in 2D. Does that help?

  7. The post above refers to the balloon model of the Universe, which is unsatisfactory as it is a 2D model of our 3D Universe. It might be helpful instead to think of raisins in a cake. If the cake is the Universe, any raisin will see everything around it moving away from it no matter where in the cake it is as it bakes. The cake doesn’t expand into anything, but we know it’s bigger – it has expanded – after baking. I hope that helps.

  8. This is a very subtle and deep question that’s often asked, but it’s hard to answer because the answer stretches the imagination, and challenges our perceptions about the world.

    Let’s start with one picture that’s not quite right. An expanding balloon expands into the space around it, but that’s not what the Universe does, so it’s a half-truth, or a poor analogy. The analogy is slightly better if you consider the centre of the balloon to be the START of the Universe, and TIME to be measured as distance from the centre. Then instead of the two-dimensional surface of the balloon being your analogy for the Universe at one instant, the whole three-dimensional space becomes the Universe’s past, present and future. Even this isn’t quite perfect, because it hides some differences between time-like and space-like separations in relativity, but it’s better than the original balloon picture.

    So far so good (ish), but I think this still avoids the question: how can space expand, contract, and be curved, if it’s not embedded somehow in some higher-dimensional space? For example, we’ve been imagining a balloon’s surface (two dimensions, and curved) embedded in a three-dimensional flat space. How can our Universe expand, contract and be curved if it’s not inside something? I hope the following will help answer this.

    Imagine a line of army ants on the surface of the balloon. They march (or walk, or whatever it is ants do) in what they believe to be a straight line. But the surface they march on is curved, so the line wraps its way all over the surface, even crossing itself in places. The ants don’t understand this because they are so tiny that they don’t know the surface is curved – like flat-Earthers they think their land is flat.

    These straight-as-possible army-ant lines are called ‘geodesics’. It turns out that you can completely describe all the curviness of space in relativity using these army-ant lines. This means you don’t NEED to embed your surface in a higher-dimensional space, because everything you need to know can be figured out from measurements on that surface.

    So, if the ants are clever enough, they can figure out everything they need to know about the curvature of the balloon they’re crawling all over, by just taking measurements on that surface. And in OUR Universe, we can figure out all we need to know about the curvature of OUR space using measurements within OUR space.

    But if we can figure out everything we need to know using measurements within our own space, we don’t need to refer to any higher-dimensional space at all. Then scientists, being a sceptical bunch, then ask: if we don’t need to refer to this higher-dimensional space, then do we need to suppose that this higher dimensional space exists at all? After all, it doesn’t affect anything that we measure…?

    This is the difficult leap for the mind to make: that a surface can be curved, but not embedded in a higher-dimensional flat space. So our Universe isn’t expanding INTO anything – it’s just expanding.

    This is just one example of how Physics makes enormous demands on a person’s imagination.

    Now, there’s a possible argument against all this that you might try and make. I don’t think it’s a good argument, but it’s worth spelling out. You could argue that flat space is SIMPLER, so the curvy space of our Universe has to be embedded in something, because the simplest space is a flat one. You’d then get into arguments about whether the Universe HAS to be simple. I won’t bother you with this to-ing and fro-ing, because there’s a surprising argument against it: it turns out that ‘simplicity’ is very difficult indeed to define! To give you some idea why, you may be surprised to hear that it’s been proved that EVERY quantity in a curved space has an EXACT analogy in a flat space, and vice versa. It’s a one-to-one match. So which one is the simpler?

    Finally, I have to own up that I’ve skated over something: relativity has a combined concept of space and time, called ‘spacetime’. All the comments above apply to spacetime as well as to space. To find out more about relativity, try ‘The Time And Space Of Uncle Albert’ by Russell Stannard, or ‘Introducing Einstein’ by Joseph Schwartz and Michael McGuinness.

  9. A good way I’ve found to think about this it to consider living on the surface of an expanding sphere. The surface of our planet has a finite surface area yet has no edge. You can walk around the planet and eventially end up back where you started. If our planet were expanding what we would observe would be an increase in the surface area of the sphere, it would take longer to walk around it, but there would still be no edge. This is analogous to the expanding universe but with one fewer dimensions. The universe is a 3d space, but is expanding in to another dimension. There is no edge- if you travelled far enough you would end up back where you started. So, like the expanding sphere, the volume of space is increasing, but there is still no edge, it would just take you longer to travel ‘around’ it.

  10. I read that the universe is actually ‘flat’. I don’t really understand fully but maybe it is only expanding in certain directions. Scientists’ satellite cameras have taken ‘pictures’ of celestial bodies billions of light years away, even hundred bilions, until they have reached the ‘ends’. There, you would find ‘dark matter’ which is something light cannot penetrate through. Perhaps after a couple more billion years it will ‘expand’ and show us more.

  11. Well, I may only be 9 years old, but I personally ask myself ‘How do scientists know the universe is expanding?’ I asked my dad and he said to me ‘They just do. They do experiments to see whats out there.’ So I think that maybe the universe isn’t expanding. If so, how can anyone know? There are very religious people who think God made the world, perhaps they are right, or they are wrog who knows. No one. Some things are better left undiscovered.

  12. Well, the issue with the analogy of walking on the edge of our planet is that you ARE already on the outside…and in that case, the sky or ‘space’ would be what it is expanding into.

    An answer worded similarly puzzling, it is expanding into the same ‘nothing’ that existed before the big bang…and not to get off topic, but then ask yourself what existed before in order for the big bang to even occur.

  13. If, as has been proposed, there is more than one universe, could it be that our universe is expanding into the space left by one which is contracting?

  14. Maybe we should ask, what is space? Where did it come from? How doe’s something come from nothing? If you took off running and I threw you a football. You were able to run and catch it, because you had the space to run in, in the first place. The big bang could never had taken place if it were not for this thing we call space.

  15. In the book ‘The Tao of Physics’ the idea of interpenetration describes how the whole universe is contained inside every particle and yet all the particles together make up the universe.

    Of course particles are sometimes matter and sometimes energy to we have to start by imagining something as difficult as the original question, but to this question we can more confidently pose a real life analogy.

    If our realm of sensual experience where like the frequency range on a radio set we could ‘hear’ all the stations our set let us tune in to. That wouldn’t mean other stations outside that range couldn’t exist, just that we wouldn’t be equipped to receive them. The dial wouldn’t go far enough in each direction.

    Human knowledge is like that radio set, we can understand those things within our range of experience. Those things our species has used for references since we began to learn. We do increase our range over time but currently have no idea by how much it will be necessary in order for us to grasp these concepts.

    In the meantime we have the immense pleasure of trying!


  16. everybody thinks there was a big bang but there was non .the reason univers is expanding is because of external force is pulling it in all directions..universe is only 10 percent of the force pulling it..if you like to know what is pulling it send me an email thank you

  17. i think the universe is not expanding into anything.

  18. The universe is in equilibrium. The red shift is due to the degeration of the photon. ie Slowing down in Hz because its been traveling thru space for billions of years. If i were on a journey that long I’d get tired too! If the universe is expanding then why do scientists need dark matter to make their models work? Wouldnt that add more gravity to the system to hold it together? Yet we see galaxies colliding all around us. Including the Milky Way with Andromeda in time.The universe is itself a blackhole. If you shine a beam of light it would be bent (traveling around the entire universe) by enough stars to come back on itself. So the mass of the universe exceeds the escape velocity of light! Thats why when you look up at night its black.Oh yah a little more proof the universe is the largest scale blackhole we observe? The energy density in the vacuum is infinite. Meaning there is an infinite amount of information contained in every point in space. Electro-magnetism is the radeative side of the event horizon forming matter, the stuff we see.Gravity is a result from the contractive side of the event horizon, the singularity and is at the center of every atom and every cell and planet, star, galaxy ect. There are other universes out there we are just on this side of the event horizon and have no way currently, of observing beyond our universe with scientific equipment. Our bodies on the other hand tell another story if one listens correctly.

  19. Everthing that exists or will ever exist is consciousness without it we go into a state of total non existance !!

  20. When most people think about something expanding, they’re thinking about an expansion of matter within space. A dynamite exploding is an example of an expansion of matter in space; Naturally the matter requires extra space to expand into, because there is no such thing as matter existing independent of space. This type of thing is our only real-world experience of what it means for something to expand. Unfortunately this concept is completely and fundamentally different than what is happening with the universe. The expansion of the universe is NOT the expansion of matter that we’re familiar with, but an expansion of space itself. Relative to the space it resides in, matter is not actually moving at all. Galaxies only appear to be rushing away from us because the space between us keeps getting bigger.

    Asking what space is expanding into is like asking “You claim hexagons have 6 sides. But then what do they smell like?” – Thats a silly question, because geometrical shapes don’t need to smell like anything in order for them to have 6 sides. Similarly, “You claim the universe is expanding. But what is it expanding into?” is irrelevant, because space is NOT like matter – nothing needs to exist “outside” of it in order for it to get bigger.

  21. Beyond our universe there is “something” that can be measured by parameters similar in measure and scale to time and space are present beyond our universe! Assuming that, that something contains exactly same energy or mass or space or time is a mistake. It could be anything we cant measure yet…. maybe that something has different number of dimensions than our universe! may be same 4 or more than that- 5, 6, 7 etc…totally different shape than our universe (assumed spherical) ….

    Also see my comment in

  22. Our universe may simply be expanding in to darkness (dark matter) which could be described as nothing, this then equates to nothing actually being something.
    If you close your eyes you can see this ‘nothing’ If this dark matter or simply darkness is viewed as a number
    starting at number 1 it would go on infinetly outside/bejond our own universe, because we all know and quite readily except that their is no last number in the numerical sence and therfore logic would suggest that dark matter is infinet and there is no end.

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