Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What fuels accelerating expansion of our universe

  1. Mar 27, 2005 #1
    where does all the extra space come from ??? ie... the stuff that is forcing objects to become further apart at speeds exceeding light particularly in the early universe stage

    was it present at big bang ?... I don't think so cos that is what inflation is, rapidly expanding space

    is it being pumped into our universe ?... by a white hole or bouncing back from a black hole

    does it divide and multiply like a bacteria ?

    please some help or links would be most appreciated
     
  2. jcsd
  3. Mar 28, 2005 #2
    I'm more worried about where all the energy is coming from. If it's correct that we have a positive cosmological constant then the vacuum energy is estimated to be around 6 x 10^-10 J/m^3. This is a very small energy density, but the exponential expansion (which is what our universe is apparently heading for) caused by the associated cosmological constant means that very soon our universe will be doubling in size roughly every 11 billion years - which means the total energy locked up in the vacuum is increasing by a factor of 8 every ~11 billion years?

    MF :smile:
     
  4. Mar 28, 2005 #3

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The answer to pretty much all of your questions is "nobody knows". There are a lot of theories, but unless you're an expert, I wouldn't recommend bothering with them. Ask again when there's more of a consensus.
     
  5. Mar 28, 2005 #4
    Consider the very first instant in the creation of spacetime. The very fact that it came into existence when before spacetime did not exist means that it is in the very nature of space to expand. Then just after the singularity, when there was a small differential region of spacetime, there could be no differences in any properties from one point to the next in that small region simply because it was so small no change in properties could occur. This means that initially every point of spacetime expanded in the same way and at the same rate as every other point in spacetime. The overall effect is an exponential expansion where the rate of growth of the universe is proportional to its size. So the key to why space expands is resolved by why it came into existence to begin with. We cannot know what happened before creation; we can only go back to a singularity, and perhaps that goes back to negative infinity in time.

    I suppose such a process would be a purely mathematical consideration: what mathematical processes give rise to the growth of a manifold (or a space) from a singularity. There are homotopy classes that describe which kinds of manifolds (spaces) can be continuously shrunk down to a singularity, which manifolds can be continuously shrunk down to a closed line, a surface, etc. So no doubt there are some homotopy considerations involved with the possible spaces (manifolds) that can arise from a singularity.

    Since we are talking about possible manifolds (spaces) that can continuously arise from singularity, it seems natural to construct a superposition of these possible manifolds from the same homotopy class. As I recall, Dynamical Triangulation is an attempt to construct our 3D+1D world from a quantum mechanical superposition various dimensional spaces. They found that such a construction expands with time. Where they got "time" I don't know. Maybe that is just the parameter that controls how the homotopy grows from a singularity. Is there a different parameter for each dimension of homotopy? Is there restrictions on these parameters (so that it forms our known time) since each additional point of added space forms a new point out of which new homotopy classes arise which must be consistent with prior existing growth? I don't know. It would be impossible to say which point was created first. So the parameters that control the shinkage of the homotopies would have to somehow form a consistency with the other parameters from other points. Does this spark any ideas from anyone else out there?
     
    Last edited: Mar 28, 2005
  6. Mar 28, 2005 #5
    interesting stuff guys but I'll have to mull it over cos i'm already feeling out of my depth.

    Incidentally MF where does zero point energy fit into your equation ???

    Is empty space devoid of matter/energy or is there no such thing and space comes loaded with energy so it begs your question as well ???

    You know Mike, I can understand no space just compressed matter, but no time ???

    Doesn't that imply that the initial singularity only existed from the time of the BB ???

    It couldn't have been sitting round forever as there was no measurement to quantify how long forever or an instant was...

    does that make sense ???

    I guess i'll have to settle for "nobody knows" as an answer to where does all the space come from since it didn't exist before the BB and there seems to be more of it being constantly inputted into the system at a faster rate now than sometime before.
     
  7. Mar 29, 2005 #6
    Dunno, but you may find interesting reading on the issue of ZPE and the Big Bang at :
    http://www.ldolphin.org/zpe.html

    MF :smile:

    I realised that if I understood too clearly what I was doing, where I was going, then I probably wasn’t working on anything very interesting
     
  8. Mar 29, 2005 #7
    I believe that Universes Expansion is getting its energy from the same source that the moon is getting its energy to go away from Earth ( we will loose moon one day).

    Its called Centrifugal Energy.

    Please dont delete this post its Just a suggestion.
     
  9. Mar 29, 2005 #8
    The moon isn't getting any energy. You see gravitational orbits aren't exactly circular. It's orbits is slightly expanding. You see you can't really ever get a stable orbit, your orbit is either slightly decaying or slightly increasing. No energy is being added, it's just with the initial angular momentum the moon was originally given it takes X amount of time to travel Y distance from the Earth. Add actually the moon is decelerating. You see as it's orbitally distance increases it's angular velocity decreases as well. So the further away from the Earth it gets the slower it will become.

    As for the expansion of the universe, matter in the universe appears to have a net linear acceleration away from the center of the universe. Unlike the moon, matter in the universe is gaining speed.
     
  10. Mar 29, 2005 #9

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Science is not about "belief", it's about theory and experiment. A good scientist doesn't believe something until it has been satisfactorily demonstrated to them.
     
  11. Mar 29, 2005 #10

    Phobos

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As noted above, that's a different mechanism. Here's a recent topic about the moon's orbit...
    https://www.physicsforums.com/showthread.php?t=67691

    I seem to recall a past topic where Janus explained how this would not happen. You may want to try a search for it.
     
  12. Mar 29, 2005 #11
    some people don't like it when others talk about a "centre" of the universe despite all the talk of bubbles, branes and curved space implying a spherical nature conventional wisdom would still have the centre as being everywhere if you rewind time back to the big bang

    me, I like the idea
     
  13. Mar 29, 2005 #12

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    I would be one of those people who discourage the notion of a center or edge to the universe. There would be distinct observational consequences if the universe had a topology that included these entities. No such evidence exists, and the mathematics we use to describe that topology [which seem to work nicely] admit to no such entities.
     
  14. Mar 29, 2005 #13
    Wow, I was just about to say that though the thought of something outside of the universe, a boundary to the universe and what happened before the big bang exist, our maths and sciences may not be able to explain it, so scientists tend to stay away from those realms.

    Very interesting question though.
     
  15. Mar 30, 2005 #14
    It just occurred to me: We believe that near the horizon of a black hole that some virtual pairs do not recombine because one member of the pair will slip behind the horizon, never to be recovered, so that there remains a surviving virtual particle that drifts away from the black hole to give the black hole a radiation. OK. So I suspect that the same thing is happening with the cosmological event horizon. QED tells us that virtual particle pairs are spontaneously formed, they travel apart for a brief time, then come together according to the uncertainty rule. And the path integral formulation says that some portion of these pairs can travel very far away before coming back together; they can even travel faster than light. So...

    I wonder if anyone has studied the possibility that new particles are created in space due to the fact that some members of virtual pair productions are slipping behind the cosmological event horizon, only to leave behind the other member as a permanent particle? Would this process be responsible for particle creation to begin with? During inflation the universe expands exponentially. At first is expands slowly so that there is no event horizon, then as the universe begins to expand quite rapidly, the cosmological event horizon contracts. Then it would be very easy for members of virtual pair production to slip behind the cosmological event horizon, leaving many particles behind.
     
  16. Mar 30, 2005 #15

    selfAdjoint

    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    But unlike a BH event horizon, our cosmological horizon isn't a "thing" in spacetime, it's just an observer dependent appearance. As I believe Roger Bacon said, "Every eye sees a different rainbow". So there's nothing out there to keep the particles from recombining. Or have I missed something?
     
  17. Mar 30, 2005 #16

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    It is, I have to admit, a charming idea, like Santa Claus or the Tooth Fairy.

    In big bang theory (the public's name for conventional cosmology) there is no centre.

    but in popular imagination there is a centre

    no scientific theory, that I know of, supposes a centre, no professional cosmologist talks about a centre, but large numbers of people seem to LIKE the idea

    Me too. It is a delightful idea, which charms people so that they believe in a "centre of the universe" without needing any reasons. So I guess the best analogy is that

    the centre of the universe (as per spicerack) IS A POEM

    we all love poems, so let's all believe in the centre of the universe together because it is a satisfying image that you cant get out of your head or because it is instinctive in us to want this idea, or whatever makes poems memorable

    (the only awkwardness comes when people inject it into the wrong context, like a quantitative discussion about the universe involving numbers, observation, tested theories etc)
     
    Last edited: Mar 30, 2005
  18. Mar 30, 2005 #17

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    I think it is important to recognize that people (scientist and nonscientist alike) have feelings.

    feelings of attachment, like somebody or some thing is the center of your universe, can be TRANSFERED as you grow and go thru various of life's crises.

    (for example people transfer feelings of love and dependency from mother or parent to teacher to shrink to spouse to grownup child etc. not necessarily in that order)

    you find that professional cosmologists, deep down, feel about the CMB the way people who dont know anything about the real universe probably feel about "the centre of the universe"

    if the CMB were suddenly turned off it would be a terrible psychological loss for cosmologists (analogous to what a religious person might feel if they found they could no longer pray or they had lost the sense of the divine presence)

    the CMB is how many people relate, people who (because they have studied in school) have no "center of the universe"
     
  19. Mar 30, 2005 #18

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    I think the reason the CMB has such a profound hold on the astronomer's imagination
    or anyway one of the reasons
    is because it defines stillness

    a cosmologist lives his or her mental life in a world with no center
    in which (except for the CMB) you CANNOT EVEN SAY WHAT IT MEANS TO STAND STILL

    in cosmology (for people who have been to school and studied it) there is no idea of "home base" that you can orient your mind towards

    but the CMB is spread evenly throughout all space and it is not just something you IMAGINE, you can put up an antenna anywhere in the universe and point it in any direction and LISTEN TO IT

    and it gives you a clear practical idea of what it means to be stationary with respect to it. You can say what our present motion is , relative to it. and you can change coordinates so you can map the universe
    FROM THE STANDPOINT OF SOMEONE WHO IS NOT MOVING (relative of course to the CMB because there is no other marker)

    there are other things that people get from the cosmic microwave background signal, but this practical concept of stillness is one of the chief things and most immediately accessible

    Probably another reason the CMB has such a profound hold on astronomers' imaginations is because it is the oldest light----but the stillness thing has a practical everyday importance because one can base coordinates and orient relative to it. non-moving relative to Cmb is the same as non-moving relative to the hubble flow (i.e. relative to the expansion of the universe).
    When you have no center, then an idea of stillness (which is like the center of the velocity world, the zero velocity) can kind of take its place.
     
    Last edited: Mar 30, 2005
  20. Mar 30, 2005 #19

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    I agree! if the cosmological constant really does arise from a vacuum energy then where is it all coming from. Or do we toss out the conservation law? Apparently there is no energy conservation law in General Relativity (except locally or in some special cases). That whole
    energy issue is a mystery.

    And it's a severe mystery because a huge mass of evidence and argument points to there having been a brief moment of inflation, and that has the same non-conservation problem: a "scalarfield" constant energy density and a vast increase in volume, hence a vast creation of energy.

    I agree with your estimate. I suppose maybe the cosmological constant might sometime be attributed to something else besides an energy, and worked into the theory some other way. The mysteries are staring us in the face.

    and, at least for me, there is a big confusion about where did all the energy in the CMB go? there are essentially the same number of photons as there were in year 380,000 but they have been stretched out a thousand fold and have each lost 999/1000 of their original energy. Where did the energy go?
     
  21. Mar 30, 2005 #20

    turbo

    User Avatar
    Gold Member

    The inflation is a problem, but there is another one that bothers me more: Where did the energy needed to stop inflation and transition to a relatively linear expansion come from? Assuming that inflation is needed to rapidly grow the BB Universe, how did every part of the now-spread-out Universe "decide" to stop inflating simultaneously and manage to avoid developing some really severe anisotropies? I have real trouble understanding how that process could occur.
     
    Last edited: Mar 30, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: What fuels accelerating expansion of our universe
Loading...