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Accelerated Expansion of Space question!

  1. Aug 16, 2010 #1
    I am in a heated debate about the laws of physics with someone who's sole answer to all of my statements has been "because god made it that way". Rather than get into that debate, I was wondering if folks could look over my hypothesis about why the universe is accelerating and point out the known issues with it.

    I wrote it in a very simple language to this person who has no understanding of physics. I have no professional background in physics, and I know that my understandings are extremely simplified and probably wrong, but are my basic concepts possible explanations? Thanks for the help.

    The expansion of the universe is supposedly a mystery. People can’t seem to figure out why space continues to expand rather than slowing its expansion and eventually collapsing back into itself. By looking at biology and simple physics, couldn’t it be assumed that the universe is expanding due to vacuum pressure and the desire for order and even distribution? If this concept doesn’t make sense, look at a biological cell.

    Cells ‘regulate’ their water content with the surrounding environment, and ‘seek’ equilibrium. When surrounded by too much water, they absorb this fluid through their walls to reach equilibrium, reaching hypoxia and destroying themselves. This destruction comes because they try to equalize their water content with their environment, swelling them to beyond their physical capabilities to hold. Another similar concept is industrial vacuums. If you have a chamber and attempt to pump all of the matter; gas, particles, etc. out of it, the few remaining bits of matter will expand to evenly fill the empty space. You will not end up with a small section of matter in a large empty space, as you would think would happen from particle gravity. If you had a cup of water in a vacuum chamber, and sucked all of the gas out of the chamber, the water would quickly boil, and turn to water vapor, and the vapor would not remain in the cup. It would rapidly expand in the ‘empty’ space, filling it with spread out particles. These particles would constantly be moving to fill the empty spaces between other particles, so a rapid churning of vapor in the very sparsely populated space would occur.

    The big bang, the expansion of energy from the center of space, which has cooled to become matter, and everything that we know, essentially threw radiation, light, and gases outward in all directions. Since there was nothing outside of the big bang prior to it occurring, we have what physicists would call simply “nothing”. By their definition, since there was no matter, and no discernable boundary, there was simply nothing. When you try to label this nothing in terms of something normal people would understand, I would say it was more of an everlasting vacuum. A huge empty area, but calling it an area means it has borders, which it doesn’t. It goes on forever. We define space by describing what is in it, and where it is, and since it has neither of these, it is safe to call it “nothing”, but it really is something. We just don’t have words to describe it. Any ways….

    We essentially have this ball of some sort of matter, energy, or higgs boson particles in the center of what would become our universe. We then have this huge expanse of nothingness, ever reaching in all directions. Matter likes to hang out together, (see gravity) but even more so likes to fill empty spaces. It likes things to be uniform. We like balance. So this expansion of matter, plasma, light, and other energy begins flying out in all directions. Light leads the way, since it is the fastest moving thing known to us currently, followed by everything else. This matter expands in all directions, filling the “lack of matter” as it goes. As it fills the space, it is working on evenly distributing itself in this new space (space being the area that matter now exists in). Since we have an area where matter exists, ie. Space, and an area beyond it where it is still a perfect vacuum (although some of this area now has light or radiation expanding through it), matter is pulled (sucked, thrown into, or just wants to be in for the universal laws of uniformity) into the emptiness.

    As the expansion of mass, matter and light expand, the radius of filled space continues to grow. The center of our universe is filled with matter, and as you get further out, you run into an “edge” of expanding space. From simple physics we know that this leading edge should have less energy and matter than further into the now filled space, as you took an expanding sphere with the same matter and energy, and stretched it over a larger area. Think of a circle of particles of sand, and stretch this same circle into a larger circle. The sand will have a lower density over the circle, because you have the same amount of matter stretched over a larger area. As this leading edge gets less and less dense, it means that the space between matter on this leading edge is increasing. This means that the vacuum pressure INCREASES as the density of matter in the expansion increases, with less gravity amongst leading edge particles and more an increase in volume to fill with less matter. This would drive matter to accelerate its expansion. It would continue to accelerate as it tries to fill more fringe volume with less matter.

    This explains the acceleration of the expansion of the universe. The only question that I don’t know the answer to is whether this acceleration would counter the collapse pull of gravity from the matter of the universe. From my knowledge though, gravity is a weaker force, and tends to diminish fairly quickly as you get further from other mass, while getting further from mass actually accelerates vacuum pressure influences.
  2. jcsd
  3. Aug 16, 2010 #2
    Hi Westernnate. First of all, there is no center of universe, or point from where big bang started. It happened everywhere. Second, universe has no edge or any boundary. Simply, space does not need space to expand into.
    From your post I would say that you are trying to explain origin of dark energy. There is a reason why it is called dark, and nobody for now can't tell you for sure why universe is accelerating its expansion. Vacuum energy is one of the candidates, but there are others equally viable.
  4. Aug 16, 2010 #3
    Interesting... So what do people mean when they say that the universe is expanding? I know that the big bang wasn't really a ball of matter that exploded, but more was an event that created "space", but wouldnt that have occured in one area which then expanded like a shockwave?

    I understand what you are saying regarding it was more an event that created time, or space, and not necessarily a physical explosion.

    And not to sound stupid, or ask the ever so common question, but what is outside of occupied space? Is space infinite in all directions, and if so, is it filled with matter infinitely, or is it essentially an everlasting empty 3-d plane with matter expanding through it?
  5. Aug 16, 2010 #4
    Distances between gravitationally unbounded objects are getting bigger.

    More occupied space.
  6. Aug 16, 2010 #5
    More occupied space?

    So there is no edge of occupied space? It's just expanding in all directions? Wouldn't there have to be a focal point that objects were moving away from? Or else objects would move away from some things, and towards others.

    I really appreciate the replies. I guess I just would question how we know that there is no "edge" to occupied space. If there weren't, that would mean that the universe was limitless, which is a phrase that tends to make me skeptical, as I don't like to believe in anything being limitless, or beyond comprehension.

    Again, I appreciate the replies, and understand that these are the basics of physics, and probably way below your typical questions.
  7. Aug 16, 2010 #6
    read FlatLand by Abbot. its about a 2 dimenional person coming in contact with a 3 dimenional being. it will help with imagining the 4th dimenion and your issue.
    plus, another way to think about the issue with "center of the universe," where is the center of the surface for the Earth? youre thinking 3 dimenionally about the 4th.
    Last edited by a moderator: Aug 16, 2010
  8. Aug 17, 2010 #7


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    Every observer in the universe is at its temporal edge [the oldest observable point in spacetime from their perspective]. No matter what direction they look, they see a universe that appears equally ancient in all directions. This creates the illusion they are at its spatial 'center' when, in fact, they are indisputably at its temporal 'edge' due to the finite speed of light. Hence, the concepts of 'centers' and 'edges' of spacetime in this universe are meaningless. The catch is, we know our observable universe has a finite age. It's complicated. BTW, the God argument is a copout. God is beyond our comprehension, the rest is science.
    Last edited: Aug 17, 2010
  9. Aug 17, 2010 #8

    No. Look at images bellow. Black circles represent galaxies. Red circles are same galaxies after some time, and with distances increased. Whatever galaxy you choose, it will appear that it is focal point of expansion, and that others are going away from it with speed proportional to their distance. First picture represents expansion as seen from second galaxy in the second row, second picture represents exactly the same expansion as seen from fourth galaxy in fourth row.


    Bedrock principle in cosmology is, well, cosmological principle. It states that universe is isotropic (same in any direction), and homogeneous (uniform in composition or structure). It only applies on large scale (moon is obviously different than earth for example). It basically means that whatever you do you can't find part of universe which is much different from any other part.

    There are few ways how it can hold. You can learn about possible geometries of universe on many resources on web. You can start with 'Ned Wright cosmology tutorial' (just google it).

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  10. Aug 17, 2010 #9
    what is the fourth dimension? how can the universe be homogenous? how do we know that it is? how do we know there isnt an edge to the universe? what is the universe? this is all very interesting but full of unknowns... how do we know what we know is true? very confusing...
  11. Aug 17, 2010 #10
    So what I am getting, simplified again, is that the universe is sort of a sphere of space, and if you travel in one direction you almost double back on the other side. Not a sphere like the earth is a sphere, but essentially that if you were to go one direction faster than the speed of light you wouldn't ever outrun the expansion of space because you would loop back?

    If we use the balloon analogy that is a pretty famous description of how the universe is expanding, you have to ask, what dimension is beyond the edge of the expansion of the sphere of the universe? I know that the easy and typical answer is that there isn't one, and that the space between matter is expanding, but not filling other space as it does so. It is creating new space where no space existed. How do we know that this space doesn't exist? We can't create new volume to fill with pre-existing matter. When one thing expands, it always fills the area of something else.

    This is my confusion with universe expansion. The theory is that it isn't expanding into something else, but how is this possible? Matter is neither created nor destroyed, but at the same time, isn't this true of volume? You can replace empty volume with filled volume, but you can't create new volume to my knowledge.

    And would the theory that the universe is expanding to fill a vacuum of emptyness work to explain why everything is getting further from everything else? I know that this would mean that there were space (volume) outside of the universe, but how do we know that there isn't? I think a lot of the confusion comes from our perception of a lot of the concepts we use. Space typically applies to a filled, measurable volume that has the concept of time applicable to it, but couldn't it also apply to an infinite void that has yet to encounter mass, energy, or radiation? Universe applies to the filled volume of space, but couldnt there be something outside of it? We wouldn't and cannot know it is there because our observations are based on radiation and light, but in a space without either it isn't possible to observe it, other than it's effects on night passing by it.

    Is it impossible that light has not reached these areas of space, and that it literally has nothing at all within it? A perfect vacuum outside of measurable or comprehensible space? And that our universe is expanding to fill this void?

    I apologize, but I can't view your images on my computer. I am looking at this site at work, and as I work for the fed, the images won't show up. I will check them at home, which may help to answer some of the questions I asked above.
  12. Aug 17, 2010 #11
    Time is the fourth dimension in 3+1 terminology.
    The universe appears to be homogeneous and isotropic at large scale (relative to us)
    Experiment, theory, and observation.
    The geometry inherent in the current model of the universe does not allow for an absolute edge, center, or other fixed point.
    It's where we're having this conversation.
    We don't, it is almost certainly incomplete or wrong, but is a very good approximation which holds with experiment, theory, and observation.
    Yes, it can be confusing.
  13. Aug 17, 2010 #12
    thanks for your answer nismar, there is so much that I dont know!
  14. Aug 18, 2010 #13


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    There is plenty we do not know, and perhaps more than we will ever know. The universe is complicated.
  15. Aug 18, 2010 #14
    Our best measurements show that universe is flat, or at least flat in our observable patch (see WMAP site). Prevailing thought is that if universe is flat, then it is infinite in spatial extent. Of course, there is possibility that curvature is so slight that we are not able to detect it.

    Again a lot of confusion is coming from popular description of big bang as explosion. Stuff is not racing outwards to fill void. Big bang cosmology is about evolution from very very hot and dense state. Anyway, if there was no inflatory field, gravity would easily overcome expansion due to pressure (for example any large enough cloud of gas will collapse to a black hole).

    It is not about what notion applies to what. For example, is notion of planet applicable to a spherical body ten times the mass of Sun? Yes it is. You can easily imagine such huge planet, but in reality physical laws are making it impossible to exist. Much the same, you can't encounter vacuum which does not have, at least, some photon density, and few massive particles in it.
  16. Aug 28, 2010 #15
    If the universe were slowing it's expansion wouldn't it fit our current observations?

    Example. We look at a star and check it's velocity, and then we look at a star twice its distance and find that it is moving faster. Of course farther away star would be moving faster if the universe were slowing its expansion because we are looking at the second star twice as far back in time as the first star we are looking at, and so if the universe were slowing its expansion, looking back further in time would show faster moving stars.

    Is there something I'm missing?
  17. Aug 28, 2010 #16
    No. You take the effects of the interval between measurements into account... and your conclusion that recession speeds would increase due to a slowing of the expansion of space simply makes no sense at all. Sorry.
  18. Aug 28, 2010 #17
    I'm not saying that recession speeds are increasing due to slowing of the expansion of space. I'm saying that the farther out you look, the greater the recession speeds will look since you are looking further back in time.

    In other words, the further back in time you look, the faster something will be going. That would be the case if something was slowing down. The further away a star is, the further back in time we would be seeing it, and thus it would seem to have slowed down less than the star closer to us.

    Are we actually measuring each star's velocity, and then a year (or some amount of time) later measuring them again and seeing that the velocity has sped up? Or are we just measuring the velocity of stars, and then comparing that with the velocity of stars farther away?

    Is that what you meant by taking the effects of interval between measurements into account?
  19. Aug 28, 2010 #18
    I'm saying that the length of intervals between measurements, and relativistic effects are taken into account when producing a result. You're missing a key point however, even if the star is moving away, we're not seeing it further back in time, just in space. The light which reaches us at 1 is the "oldest" we're going to see, and the light at t2... tn is progressively younger. The stars and galaxies are moving away from us, but that doesn't reverse the order in which observations are made, or the light arrives. If we saw the younger and younger light, we would see stars moving TOWARDS us, not away.

    I think you've confused looking at a star 5 billion ly away, vs. one that is 7 billion ly distant with the SAME star or galaxy observed at two different times. Do you understand?
  20. Aug 28, 2010 #19
    That would be the case if the stars velocity was towards us. I wasn't suggesting that. I was suggesting that the expansion is slowing, not that a contraction is occurring right now.

    Perhaps. So we are observing one star 5 billion ly away, and every time we look at it, we see it moving faster away from us? Or is it just farther away from us, cause there's a subtle difference between those two things, but bigger implications.
  21. Aug 28, 2010 #20
    I don't know what more to tell you... the difference isn't subtle, and observations are not exactly unclear: expansion is accelerating. I'm not seeing a sound argument from you to contradict this, never mind showing that the opposite is occurring.
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