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

Possible reason for dark energy (?)

Tags:
  1. Mar 24, 2013 #1
    I understand that within my frame of reference, matter (at the "outskirts" of the Universe), which is moving at near the speed of light must be approaching infinite mass. And, of course, we now know that the Universe's expansion is accelerating, further intensifying this mass gain. From this, could we say that at some point out there, the mass might be forming a shell of blackhole-like material? And, due to relativistic effects, at this same point, spacetime is curving around on itself. Might this offer an explanation for a few things:
    (1) the blackhole-like material (let me call it the "superlarity shell" to distinguish it from a black-hole's singularity) has such large gravitational mass that it is accelerating more mass toward it, explaining the effect we call dark energy. In other words, dark energy may not be a push from within, but instead may be a pull from the fringe.
    (2) the relativistic spacetime curvature at the "outskirts" reconciles the issue of the Universe being "infinite" (in the sense that there is nothing outside of the Universe and the Universe goes on "forever" in the sense that there is no discernible boundary, with the issue of the Universe being "finite" since it started as a finite entity within an infinitesimal volume and has been expanding at a finite rate ever since the Big Bang.
    (3) as the "superlarity shell" gets more and more gravitationally massive, each segment might begin to pull-in on adjacent segments to begin the process of the "Big Crunch" as was once proposed. And, as was once hypothesized, this Big Crunch could end in a singularity-bounce to create a new Big Bang. This would explain a "forever" Universe that cycles through expansion-contraction phases, which seems more pleasing than the Universe never ending as it expands forever.
     
  2. jcsd
  3. Mar 24, 2013 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    No. The distance to matter is increasing, but this is not matter moving at relativistic speeds. Instead, space in between is expanding.
    In addition, "mass" is "rest mass" and does not depend on velocity at all.
    No.
    Well, it is possible to say it, but it is wrong.
    No to all.
     
  4. Mar 24, 2013 #3
    relativistic mass

    Didn't Hubble discover that the farther away bodies are, the faster they are moving?
     
  5. Mar 24, 2013 #4
    Yes, and so? It is not a velocity in the usual sense, it's a velocity due to the expansion of the universe itself. For some galaxy in these 'outskirts', our galaxy is moving at near speed of light, and nevertheless we are not part of a black hole shell or whatever.
     
  6. Mar 24, 2013 #5

    phinds

    User Avatar
    Gold Member
    2016 Award

    Yes. So what?
     
  7. Mar 24, 2013 #6

    Bandersnatch

    User Avatar
    Science Advisor
    Gold Member

    The three main misconceptions I can see here are:

    1)An uniform shell of matter produces net force on the objects inside of it.
    This is not true. The net force is always zero. This is explained by the shell theorem, a relatively easy mathematical excercise first shown(or first credited to) Newton.
    The wikipedia article has a good treatment of the subject.

    2)Metric expansion of space is subject to the speed constraints imposed by Special Relativity.
    Also not true. SR concerns objects moving >through< space, and has nothing to say about the expansion of space as such.
    One could understand it this way: SR says that nothing can overtake light, which remains true in the expanding universe.
    The cosmology section's FAQ may prove to be informative here.

    3)Personal theories are allowed on PF.
    Again, not true. Forum rules are pretty clear.
     
  8. Mar 24, 2013 #7

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I think to understand Hubble law you must first understand the idea of universe-rest
    or "CMB-rest". It is the basis for how the distances are defined in Hubble law. And also how the present rate of increase of any distance is defined. So you can't state the law without first thinking about what it means to be at rest with respect to the Background of ancient light.

    There is nothing mysterious about this. The ancient matter of the universe, while still evenly spread out throughout space, emitted light. We live in a soup of ancient light which is coming frm alll directions very uniformly and is about 1000 times cooler than when it was emitted. This is the most ancient light we can see.

    It has a remarkably uniform temperature about 3 degrees kelvin in all directions. As long as you re not moving. The solar system is moving in a certain roughly constant direction at a speed of 0.00123c. That is, a bit over ONE TENTH PERCENT OF THE SPEED OF LIGHT.

    And this means that we see, because of Doppler, a hot spot ahead of us that is a bit over one tenth percent warmer than the rest of the Background, and a Doppler cold spot behind us that is one tenth percent cooler.

    So we know we are moving at 0.123% of the speed of light in a certain known direction and that our observations are off by that amount and so we CORRECT observations so that our data is AS IF it were made by a stationary observer. From an observer at CMB-rest. At rest with respect to the soup of ancient light.

    The Hubble law is about a specific moment in universe time, call it NOW and it is about the separation between stationary observers. It says that any large-scale separation is NOW growing at a speed which is proportional to its size NOW. Universe time is the time clocked by stationary observers who, because they are at rest, are able to agree and synchronize their clocks.

    I almost feel like I should apologize for these little technical details but they are necessary when you state Hubble law because it says the expansion speed if we could measure now is proportional to the distance between stationary objects, measured now.The point is that without the technical details none of the things the law talks about would be defined and the law would not MEAN anything. In popular media they do not give people the background so they are not giving public the straight story.

    The expansion speed discounts any random individual motion (with is THROUGH space and does not count). Hubble law expansion is not like ordinary motion where somebody gets somewhere, approaches some destination in some direction from them.
    In expansion NOBODY GETS ANYWHERE, all the observers just find themselves farther apart. Relative positions do not change.
     
    Last edited: Mar 24, 2013
  9. Mar 24, 2013 #8
    Under what conditions might mass's velocity approach the speed of light if this is not the case at the outskirts of Universe?
     
  10. Mar 24, 2013 #9

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    It is important for you to realize that in ordinary professional cosmology the universe has no "outskirts". All space is approximately uniformly filled with matter. It started out more uniform than it is now, but the matter started falling together into little clumps like stars galaxies clusters of galaxies. But it is still pretty uniform on average over large scale.

    There is no center of expansion, there is no boundary, there is no space "outside", there is no "outskirt" or fringe.

    The popular media does a terrible job, it misleads people by showing them pictures of explosions.

    A whole generation of people has been screwed up by bad journalism (many of them perhaps like you bright thoughtful curious) millions of people mentally screwed up by imprinting their minds with the "big bang" image of an explosion outwards from some central point out into empty space. With "outskirts" being the advancing outer edge of the explosion. The normal professional cosmic model is nothing like that. "Big bang" is itself a highly misleading name. It was originally a derogatory epithet given by the author of a rival model which failed. He didn't like the expansion model and had no interest in giving it a name that would actually give the correct impression. Unfortunately his misleading name caught on. Anyway, keep working on it and you can erase your initial misconceptions.

    ==============
    About mass-ful things going near the speed of light? Sure! Whenever there is a supernova explosion it sends out neutrinos at near the speed of light. Neutrino particles do indeed have mass, and tons of them are ejected from the exploding core of the star. The mass of an individual neutrino particle is very small, but there are a lot of them busting out in all directions!
    So tons of mass is being hurled out into space at, I guess, over 95% of the speed of light.
     
    Last edited: Mar 24, 2013
  11. Mar 24, 2013 #10

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    This is why scientists no longer use the term 'relativistic mass', it creates more confusion than understanding. The universe is described by general relativity, not special relativity [which is where the idea of relativistic mass originated]. An SR description of the universe has long been known to be inconsistent with observational evidence. SR is only valid as a local description. Another issue is no object can become a black hole due to velocity. If it is not a black hole at rest, it is not a black hole at any speed.
     
  12. Mar 25, 2013 #11

    E-8

    User Avatar

    "There is no center of expansion, there is no boundary, there is no space "outside", there is no "outskirt" or fringe."



    Sorry marcus, but you are incorrect. The universe absolutely has a center of expansion as well as a boundary. It is located in the fourth dimension. It is akin to an inflating balloon. You could say the balloon does not have a center of expansion from the perspective of the surface of the ballon as all points on it are expanding uniformally (in 2 dimensions). However, obviously, the center is inside the balloon (in the 3rd dimension).

    Ergo, as we exist on the 3 dimensional surface of an expanding 4 dimensional hypersphere... the center of expansion is in fact on the "interior" of the universe. Which is located in the 4th dimension (which we percieve to be time). Although it is simply an additional spatial dimension that our entire 3 dimensional plane is expanding through at the same rate, which is the speed of light.

    In regards to the boundary issue... there most definitely is a boundary to our universe. It too, exists in the 4th dimension. Every point in our 3 dimensional space is on the surface of the expanding hypersphere. The boundary to the universe is literally all around us.

    Glad i could set the record straight on this issue. It seems that many folks are confused about this very fundamental aspect of our universe.

    : )
     
  13. Mar 25, 2013 #12

    Drakkith

    User Avatar

    Staff: Mentor

    You have not set the record straight. There is absolutely no evidence for any boundary or center of the universe, nor any evidence that the universe is the surface of a hypersphere.
     
  14. Mar 25, 2013 #13

    phinds

    User Avatar
    Gold Member
    2016 Award

    E-8 you need to read the forum rules. Personal speculation, especially when (as in your case) it is UTTERLY devoid of evidence, is forbidden on this forum.
     
  15. Mar 25, 2013 #14
    This is why the "balloon" has to be handled with care. The balloon analogy works well in the most basic equations and visualisations, but it fails in precisely this: the modern cosmological model does not admit a 'center in time' but a beginning. The balloon expands into more space, it occupies increasing pre-existing space, and instead the universe does not expand into anything.
    And another thing, the surface of sphere has no boundary.
     
  16. Mar 25, 2013 #15

    cristo

    User Avatar
    Staff Emeritus
    Science Advisor

    This is incorrect. Note that the balloon description is an analogy; that is, it is not an exact description, but rather a neat way to try and understand. The balloon model posits that we live on the surface of the balloon, in a 2D world. We see that universe expanding equally from all points, and no centre of expansion. But this is an analogy: the two dimensional surface is not required to be embedded in a higher dimensional spacetime.

    Marcus summarises in a sentence the best current knowledge of the universe: "There is no center of expansion, there is no boundary, there is no space "outside", there is no "outskirt" or fringe."
     
  17. Mar 26, 2013 #16

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    I prefer to view the universe as an onion, where the layers are defined by shells of time.
     
  18. Mar 26, 2013 #17

    Bobbywhy

    User Avatar
    Gold Member

    Not exactly. There is some historical evidence that Edwin Hubble did NOT claim more distant bodies were moving away faster. He made it clear these were only "apparent" recession velocities. See the following excerpt from Wiki:

    "In 1931 Hubble wrote a letter to the Dutch cosmologist Willem de Sitter expressing his opinion on the theoretical interpretation of the redshift-distance relation:[28]"

    "Mr. Humason and I are both deeply sensible of your gracious appreciation of the papers on velocities and distances of nebulae. We use the term ‘apparent’ velocities to emphasize the empirical features of the correlation. The interpretation, we feel, should be left to you and the very few others who are competent to discuss the matter with authority."

    http://en.wikipedia.org/wiki/Edwin_Hubble

    Bobbywhy
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Possible reason for dark energy (?)
Loading...