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Space Science

Do We Live In a Giant Cosmic Bubble? 344

Khemisty writes "Earth may be trapped in an abnormal bubble of space-time that is particularly void of matter. Scientists say this condition could account for the apparent acceleration of the universe's expansion, for which dark energy currently is the leading explanation. Until now, there has been no good way to choose between dark energy or the void explanation, but a new study outlines a potential test of the bubble scenario. If we were in an unusually sparse area of the universe, then things could look farther away than they really are and there would be no need to rely on dark energy as an explanation for certain astronomical observations. 'If we lived in a very large under-density, then the space-time itself wouldn't be accelerating,' said researcher Timothy Clifton of Oxford University in England. 'It would just be that the observations, if interpreted in the usual way, would look like they were.'"
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Do We Live In a Giant Cosmic Bubble?

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  • by Goaway ( 82658 ) on Wednesday October 01, 2008 @11:28AM (#25219407) Homepage

    No. The gravitational forces required for time dilation to be that strong are many orders of magnitude stronger than what you'll find on the galactic scale.

  • by Iowan41 ( 1139959 ) on Wednesday October 01, 2008 @11:29AM (#25219419)
    At least as far as gas and dust are concerned. The Standard Model explanation is that a 'nearby' star (the pulsar Geminga) went supernova a good long time ago, and blasted a large bubble (300 ly across) of relatively gas and dust free space, called 'the Local Bubble', and our solar system is well within this bubble. The relationship between that and what is being discussed I do not know, for details haven't been provided even on such things as scale. Do a search on 'Local Bubble' and you will find a great deal of information about this.
  • Re:Being special (Score:5, Informative)

    by meringuoid ( 568297 ) on Wednesday October 01, 2008 @11:42AM (#25219699)
    But what I find hard to believe is that we are in the exact center of such a region. So therefore, the universe should appear to have different properties in different directions. Has anybody seen that?

    There's an unexplained anisotropy [] in the cosmic microwave background. Hot and cold spots don't appear to be quite randomly distributed. Nobody's come up with a good explanation, and it might be an instrumentation error or due to some local gravitational anomaly - say, lensing around the next supercluster over - but at the moment it's very unclear.

  • by tepples ( 727027 ) <tepples@gmail.BOHRcom minus physicist> on Wednesday October 01, 2008 @11:44AM (#25219739) Homepage Journal

    Except if such specialties make our sentient life possible (or much more probable).

    That's called the anthropic principle, and Wikipedia's article [] cites criticisms by several philosophers of science who call it a cop-out.

  • Re:You mean like... (Score:5, Informative)

    by Quietust ( 205670 ) on Wednesday October 01, 2008 @11:55AM (#25219923) Homepage
    There would definitely be significant time dilation in close proximity to said black holes, but beyond even a fraction of a light year it would become negligible due to the rate at which gravitational force weakens.
  • Re:You mean like... (Score:3, Informative)

    by caramelcarrot ( 778148 ) on Wednesday October 01, 2008 @12:00PM (#25220005)
    The gravity from a 3 million sun black hole is no different to 3 million suns, and given that a galaxy will contain billions of such suns - no, that's not sufficient.
  • Year of Hell (Score:3, Informative)

    by vecctor ( 935163 ) on Wednesday October 01, 2008 @12:06PM (#25220103)

    This is the two-parter you mean: [] :)

  • Re:Being special (Score:5, Informative)

    by mcgrew ( 92797 ) * on Wednesday October 01, 2008 @12:07PM (#25220121) Homepage Journal

    This is no harder than believing in dark matter and dark energy, and it's before breakfast

    "Time is an illusion, lunchtime doubly so". -The Hitchhiker's Guide to the Galaxy

  • by Anonymous Coward on Wednesday October 01, 2008 @12:11PM (#25220215)

    This is different bubble. The Local Bubble is rather local (tens of parsecs across) and we can easily see gas outside of it. The bubble in the story could be bigger than the visible Universe (gigaparsecs across) and thus can be fundamentally untestable. Plus, null results (that we can't see outside of this gigantic bubble) make it even more unlikely because over- and underdensities are progressively rarer as they get bigger.

  • Re:Being special (Score:3, Informative)

    by khallow ( 566160 ) on Wednesday October 01, 2008 @12:13PM (#25220261)

    I expect that we will eventually find the concept of the "infinite universe" to be a false path, and that we will achieve great breakthroughs when we find a framework that doesn't rely upon its existence.

    Already happened. Our description of the laws of physics is local in nature and doesn't depend on the extent of the universe.

  • Re:Being special (Score:4, Informative)

    by Artifakt ( 700173 ) on Wednesday October 01, 2008 @12:17PM (#25220341)

    We don't necessarily have to be at or near the center of such a bubble, here's the conditions we might require:

    1. We would have to somewhere be in a bubble that is much less dense than the actual average for the universe,
    2. that bubble would have to be pretty uniformly less dense for the 12 Billion light year radius around us. It doesn't have to be exactly uniform, in fact one reason we might be able to detect it is if it isn't. The bubble doesn't have to be spherical, overall, or uniformly dense, overall, and the nature of the edge, where it becomes more like the rest of the universe is, is allowed some variation as well.
        (In fact, from what the original paper says so far, the center of the bubble could still be even less dense than our part, just so those lower density regions were more than the observable length away.)
        (If this hypothesis develops into a full fledged theory, we would probably be able at a minimum to confirm or reject the existence of even lower density regions, predict how thick the edges of the bubble are, and write an equation that describes how the density would go up, as hypothetically measured at different points in the edge.).
    3. The bubble would have to be pretty big, bigger than the time it takes light to cross the entire part of the universe we can see. Since we estimate the universe is about 12 Billion years old, the edges of the bubble must be more than that number of light years away from our POV. But, we don't have to be equally near all edges.
          (We could still possibly see some effects from what is now farther away, because we can observe things such as the cosmic microwave background, that preserve data from the very early times when things were much closer together. We could also see the indirect effects of gravity on things we can see directly in the visible, Gamma or UV ranges).
    4. We would have to be near enough to an edge in at least one direction that we could see the effects of those hypothetical average density regions that lie farther than 12 Billion light years away. That way, we may never be able to see them directly, but we can infer them from the parts we can see, so this becomes testable. So if the bubble is much bigger than 24 billion light years across, we must not be too near the center. The bigger the bubble is, the farther out from the center we would have to be to detect something, but that's still a pretty general requirement that we be somewhere in a pretty big volume, not really something improbable or requiring a particularly privledged viewpoint. Our view would be unusual, but not unique.
    5. Near enough in point 4 depends on how swiftly the edge of the bubble changes to a more average density, and just what the average is, among other factors. Again, actually coming up with some more specific numbers is what will happen if this hypothesis gets developed into a more established theory. The researchers will calculate some combinations of overall size, rate of change at the edges, and density for the larger universe, and see if there are combinations that predict something we can observe to test them, while throwing out combinations that lead to conclusions contrary to what we can observe. Better yet, a lot of our existing observations can be used to swiftly develop this hypothesis - this is much more testable right now than, say, string theory.

  • Re:Occam's Razor? (Score:5, Informative)

    by philspear ( 1142299 ) on Wednesday October 01, 2008 @12:17PM (#25220351)

    I thought it was for deciding between two or more competing theories. I didn't think it could be used to reject all theories. If you have two theories, one makes two assumptions, one makes just one, it's more likely to be the one that just makes one. While both may be wrong, you can't use Occam's razor to throw BOTH of them out.

    Furthermore, you don't use it at all, or if you did, you forgot to tell us the outcome. You actually just say both sound like deus ex machina, are both silly, and we're not right yet. Didn't even mention any underlying assumptions. That's not Occam's razor, or even rational argumentation. You just have a gut instinct that they're both wrong.

  • Re:Occam's Razor? (Score:3, Informative)

    by H0p313ss ( 811249 ) on Wednesday October 01, 2008 @12:30PM (#25220577)

    You make very valid points and I agree with many of them. However, my point here is that there are two theories, one new, one less new, that IMHO make too many assumptions. The simpler solution is that we really don't understand the problem yet and that there is a more elegant solution waiting to be found. This is the unstated third choice. I should have made that more clear... I'm blaming the cold medication.

    Is this a proper application of Occam's Razor? I'm really not sure I'd care. I'm not sure that even Occam would care...

  • Re:Being special (Score:3, Informative)

    by pla ( 258480 ) on Wednesday October 01, 2008 @12:34PM (#25220663) Journal
    So therefore, the universe should appear to have different properties in different directions. Has anybody seen that?

    Yes. The Wilkinson Microwave Anisotropy Probe [] looked for (and found!) exactly that.

    Now, exactly what the WMAP's findings mean... Well, physicists and cosmologists will probably argue about that for the next century. But as a scientifically-literate non-expert, I would say that an anisotropic CMB seems consistent with (though certainly doesn't require) the "bubble" theory mentioned in TFA.
  • Re:Occam's Razor? (Score:3, Informative)

    by Abcd1234 ( 188840 ) on Wednesday October 01, 2008 @12:57PM (#25220991) Homepage

    "Dark Matter and Dark Energy both felt like big hacks to me."

    To you, perhaps. Problem is, at least in the case of Dark Matter, it's real and we've observed [] it [].

  • Re:You mean like... (Score:3, Informative)

    by Lumpy ( 12016 ) on Wednesday October 01, 2008 @01:25PM (#25221417) Homepage

    incorrect. The gravity from a 3 million sun black hole has a deeper center than if you took 3 million suns and stacked them in a sphere just touching each other.

    The gravity well of the two is quite different. one will be huge because the gravity mass is spread out at last a few hundred thousand suns wide in all directions and the other has a gravity mass that is far FAR smaller. This making the sides of the gravity well steeper and causing a very defined terminator line compared to that of the giant ball of suns.

  • Re:You mean like... (Score:4, Informative)

    by caramelcarrot ( 778148 ) on Wednesday October 01, 2008 @01:32PM (#25221509)
    Considering the point was related to the effects of such a black hole on the outskirts on the galaxy, then yes, the oddities of the gravitational field of the black hole are on a massively smaller scale and totally irrelevant. Your point that the field isn't exactly the same is true, but pedantic and irrelevant to the discussion.
  • Re:You mean like... (Score:5, Informative)

    by Goaway ( 82658 ) on Wednesday October 01, 2008 @01:53PM (#25221899) Homepage

    that would slow down time in the area.

    The point is, no, it would not, not to the degree you are thinking of. Look, we do know what a galaxy is! We know there's a lot of mass in there! And it's easy to calculate the time dilation it causes, and it is negligable.

  • Re:Being special (Score:4, Informative)

    by f()rK()_Bomb ( 612162 ) on Wednesday October 01, 2008 @01:54PM (#25221923)
    The observable universe is actually more like 96billion light years across, its a common mis-conception that because its 13.7 billions years old, its 27billion light years wide. This would b true if space was flat, but on cosmological scales, its highly curved.

    The lower bound on the size of the universe, based on the CMBR is 78billion light years, any smaller, and then light would have circumnavigated it since the big bang, and we would see multiple images in the CMBR []
  • Re:Being special (Score:2, Informative)

    by jessemerriman ( 934509 ) <jessemerriman.warpmail@net> on Wednesday October 01, 2008 @07:24PM (#25226483) Homepage
    Sounds a lot like Julian Barbour's The End Of Time [].

Nondeterminism means never having to say you are wrong.