Here's something interesting I've read: the mind-boggling concept at the heart of a theory that University at Buffalo physicist Dejan Stojkovic and colleagues proposed in 2010. They suggested that the early universe --which exploded from a single point and was very, very small at first --was one-dimensional (like a straight line) before expanding to include two dimensions (like a plane) and then three (like the world in which we live today). The theory, if valid, would address important problems in particle physics. Now, in a new paper in Physical Review Letters, Stojkovic and Loyola Marymount University physicist Jonas Mureika describe a test that could prove or disprove the "vanishing dimensions" hypothesis. Because it takes time for light and other waves to travel to Earth, telescopes peering out into space can, essentially, look back into time as they probe the universe's outer reaches Gravitational waves can't exist in one-or two-dimensional space. So Stojkovic and Mureika have reasoned that the Laser Interferometer Space Antenna (LISA), a planned international gravitational observatory, should not detect any gravitational waves emanating from the lower-dimensional epochs of the early universe. Stojkovic, an assistant professor of physics, says the theory of evolving dimensions represents a radical shift from the way we think about the cosmos --about how our universe came to be. The core idea is that the dimensionality of space depends on the size of the space we're observing, with smaller spaces associated with fewer dimensions. That means that a fourth dimension will open up --if it hasn't already --as the universe continues to expand The theory also suggests that space has fewer dimensions at very high energies of the kind associated with the early, post-big bang universe. If Stojkovic and his colleagues are right, they will be helping to address fundamental problems with the standard model of particle physics, including the following: •The incompatibility between quantum mechanics and general relativity. Quantum mechanics and general relativity are mathematical frameworks that describe the physics of the universe. Quantum mechanics is good at describing the universe at very small scales, while relativity is good at describing the universe at large scales. Currently, the two theories are considered incompatible; but if the universe, at its smallest levels, had fewer dimensions, mathematical discrepancies between the two frameworks would disappear. •The mystery of the universe's accelerating expansion. Physicists have observed that the expansion of the universe is speeding up, and they don't know why. The addition of new dimensions as the universe grows would explain this acceleration. (Stojkovic says a fourth dimension may have already opened at large, cosmological scales.) • •The need to alter the mass of the Higgs boson. The standard model of particle physics predicts the existence of an as yet undiscovered elementary particle called the Higgs boson. For equations in the standard model to accurately describe the observed physic of the real world, however, researchers must artificially adjust the mass of the Higgs boson for interactions between particles that take place at high energies. If space has fewer dimensions at high energies, the need for this kind of "tuning" disappears. "What we're proposing here is a shift in paradigm," Stojkovic said. "Physicists have struggled with the same problems for 10, 20, 30 years, and straight-forward extensions extensions of the existing ideas are unlikely to solve them." "We have to take into account the possibility that something is systematically wrong wi our ideas," he continued. "We need something radical and new, and this is something radical and new." Because the planned deployment of LISA is still years away, it may be a long time befo Stojkovic and his colleagues are able to test their ideas this way. However, some experimental evidence already points to the possible existence of lower dimensional space Specifically, scientists have observed that the main energy flux of cosmic ray particles with energies exceeding 1 teraelectron volt --the kind of high energy associated with the very early universe --are aligned along a two-dimensional plane. If high energies do correspond with lower-dimensional space, as the "vanishing dimensions" theory proposes, researchers working with the Large Hadron Collider particle accelerator in Europe should see planar scattering at such energies. Stojkovic says the observation of such events would be "a very exciting, independent test of our proposed ideas." Here's the article I've read: http://www.sciencedaily.com/releases/2011/04/110420152059.htm
It's a very interesting idea, even if somehow far-fetched. I'm impressed they already came up with an (alleged) experiment to test their hypothesis: with so much of extremely early-universe astrophysics relying on theoretical work and very little practical experimentation, it's good to see such devotion to falsifiability. The summary on Phys. Rev. Lett. doesn't address how their theory could explain the issue of the acceleration of the cosmological expansion as the article says, I would be quite interested in that. I will try to dig in the original paper if I have time.
It appears that their idea is based on some kind of causal dynamical triangulation approach to quantum gravity as that's where the idea that space at very small lengths becomes (1+1)-dimensional comes from. The problem I have with quite a lot of QG cosmology stuff is that it either leads to highly unrealistic models, or as I found in one case of renormalization group improved gravity coupled to scalar fields, piddlingly small effects although it may result in some small but possibly detectable corrections to slow-roll inflation. They do, however, have an explanation for the seeming absence of primordial gravitational waves, however - dimensional reduction of gravity seems to suppress the production of such waves in the early universe, so there might be something to it. Then again, there's a lot of interesting early universe ideas, and this might not really prove to be anything special.
The proposal would seem to tie in with the ideas of loop quantum gravity and relational quantum gravity where space-time is an emergent phenomenon, for example; http://rqgravity.net/RelationalQuantumGravity There was also a Scientific American article on the causal dynamical triangulation approach a couple of years ago. http://www.scientificamerican.com/article.cfm?id=the-self-organizing-quantum-universe ETA: which is supposedly closely related to theories of fractal space-time and even the work of Garrett Lisi, which I know very little about and understand even less. Wouldn't the emergence of a fourth spatial dimension be somewhat troubling? I seem to recall that there is a theoretical proof that gravity can't really work with anything other than the three we experience.
The idea of fractal spacetime crops up all over the place - it seems that with asymptotically safe gravity this is the case too.
This is so not my field (sic) but I've read (well, more skimmed to be precise) papers that reckon that asymptotic safety implies that spacetime is fractal in general, with a fractal dimension of 2 on sub-Planckian length scales (which I expect would be relevant to the BB and the immediate environs of space-time singularities). Exactly what sort of fractal - Cantor set, Menger sponge, blah, blah - is debatable, but does it even matter? Is there an experimental prediction that can be tested - say from CMB measurements? There also seems to be quite a lot of flaky research that tries to predict particle masses, but it looks more like numerology than science.
Yes, I remember the early days of the universe. We were so excited when it went from 1D to 2D so we could go from a line to a square.
My avatar is a meerkat, but I guess it could pass for a sloth in a bad light. So, what's "Sid the Sloth" called in Italy?
I have no idea, I don't watch the movies on dvds in italian Even the idea of listening to the trek actors saying "plancia" instead of bridge or " velocita' di curvatura" instead of warp makes me sick
That rendering of "warp speed" does seem odd. Isn't there an equivalent term from weaving that they could have used to preserve the metaphor? My dictionary lists "ordito" for "warp" but you know how misleading dictionaries can be.
they don't use that term... plus I always prefer to hear the original language, and if it's one I don't understand, with subtitles