The above image comes from an article published March 16 09 in New Scientist Magazine. Marcus Chown's article can be found at this link:
http://www.newscientist.com/article/mg2 ... ?full=true
One of the arguments I've advanced in my book and my blog has some interesting echoes in this new article, which makes the point I've used for my reasoning about dark matter and dark energy many times before: gravity is the only force that exerts itself across the extra dimensions.
The three blue bars you're seeing above represent the universe at 3 different scales, and the proposition from the scientists whose theoretical work is being reported in this story is that gravity might vary depending upon the scale you are viewing the universe. Those scientists are Justin Khoury, now of the University of Pennsylvania in Philadelphia, and his colleagues Niayesh Afshordi and Ghazal Geshnizjani of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario. To quote from the article:
They have listed a series of cosmological observations that cannot readily be explained with a one-size-fits-all gravity (www.arxiv.org/abs/0812.2244). None of these effects on its own, they stress, necessarily indicates anything amiss. But intriguingly, all of them melt away if you make just one assumption, albeit a controversial one: that how gravity works depends on the scale on which you look at it.
The little graph next to each of the blue bars, then, shows how gravity might vary with scale. For more "local" observations of our universe, the standard linear model for gravity holds true. The second graph indicates that at larger scales gravity operates differently, and this would account for the effects of dark matter, which has been shown to be unevenly distributed throughout the universe - it's "lumpy" rather than smooth. The largest scale shown in this picture, on the other hand, shows how gravity drops off in a way that is larger than the normal linear curve, and this is a proposed explanation for the even distribution of dark energy - the universe is flying apart faster than we should expect it to, because at the largest scales gravity is lower than the linear relationship would lead us to expect.
With my project, I've proposed that dark matter and its lumpiness are explained by the fact that there are other universes which are nearby to our own in the nearest extra dimensions, and are a direct result of the fact that gravity is the only force that can exert itself across the extra dimensions. In the same way, these scientists are proposing that extra dimensions are responsible for dark matter, and there is research being done right now that could, in the next few years actually confirm or deny the existence of extra dimensions through direct observation of gravitational anomalies! Here's a bit more from that article:
According to general relativity, light and matter feel gravity in the same way: they both follow the same paths around massive objects dictated by their warping of space-time. But any pure theory of gravity such as Khoury's variable gravity affects only matter. So proving the existence of hidden dimensions could be as simple as observing the bending - "gravitational lensing" - of light from a distant source as it passes by a galaxy cluster on its way to Earth, and so inferring the cluster's mass. If we can then measure the cluster's gravitational pull on a second cluster - for instance, by how fast it is dragging the second cluster towards it - we can acquire a second, independent mass estimate.
If hidden dimensions are modifying gravity, the two estimates will be different by 20 to 30 per cent, says Khoury. Current galaxy cluster measurements are not quite accurate enough to pinpoint an effect of this size, but the current generation of surveys should deliver a definitive answer within the next 10 years.
The explanation of dark energy that Justin Khoury and his colleagues are proposing is related to my own suppositions, but not as directly connected. With my project, I've proposed that the effects of dark energy come from the highest dimensions, which are furthest away from our own location within the omniverse of all possible universes and multiverses. Thinking of our own universe and all of its potential spacetime expressions as a "point" in the seventh dimension gives us a way to think about how the dimensions beyond that would "pull" equally hard on the universe in all directions, creating the eerily omnidirectional pull that science is seeing for dark energy. With their project, they are proposing that dark energy comes from a brane in at least one additional dimension that is infinite in size: another way of saying what I'm proposing? Not directly, but a similar idea.
Here are some of my past blogs where I've talked about dark matter and dark energy and how they can fit within this way of visualizing the dimensions:
Dark Energy, Linelanders, and the LHC
Randomness and the Missing 96%
Dark Matter, Dark Energy, Dark Information
Poll Questions on Dark Matter and the LHC
Poll Question on Dark Matter/Energy and Dimensions
Enjoy the journey!
Rob Bryanton
