Wednesday, March 16, 2005

No Cosmological Constant After All?

The article Primordial Inflation Explains Why the Universe is Accelerating Today by Rocky Kolb of Fermilab, together with Sabino Matarrese, Alessio Notari and Antonio Riotto has inspired an interesting discussion in Not-Even-Wrong. There's also a Fermilab press release about it today. The pleasant surprise was that the usual crackpot abusing was absent and the discussion was exceptionally civilized and interesting. There was a nice comment about experimental problems related to the detection of acceleration of Universe. I had a temptation to comment but know that my comment would be probably doomed to be off-topic so that I represent my comment here and try to get through a short comment with a link. The cosmological constant was assigned to what was called a super-Hubble perturbation of gravitational field extending over cosmological horizon. The first objection was that the situation outside Hubble patch cannot affect the dynamics inside it. Furthermore, super-Hubble fluctuations are equivalent with anisotropic cosmology: data are however consistent with isotropic acceleration. The latter objection sounds to me rather serious. The idea about interaction with super-Hubble perturbations has some resemblance to TGD explanation based on the notion of many-sheeted space-time. In many-sheeted cosmology the cosmological space-time sheets larger than Hubble radius take the role of super-Hubble fluctuations and can affect the dynamics also in shorter length scales. In TGD framework the explanation of acceleration is based on a new delicate effect related to the manner how the photons from a remote object arrive at the detector. The second difference is that inflationary scenario is replaced with quantum criticality implying flatness of 3-space. Metric is fixed apart from a parameter fixing the duration of the critical period. In many-sheeted cosmology each cosmological space-time sheet is characterized by its own cosmological constant decreasing with the size L of space-time sheet as 1/L^2. The spectrum of L is discrete and comes in powers of sqrt(2) by p-adic length scale hypothesis. Since the photons from a distant object arrive along space-time sheet having size at least of order of distance d to the object, the prediction for the observed cosmological constant is indeed acceptable and decreases with distance and thus with temporal distance. Since gravitational energy density decreases when the size of the space-time sheet increases, Hubble constant increases and the increase of acceleration with the size of space-time sheet gives rise to an apparent acceleration with respect to cosmic time. Jerks in the acceleration are predicted when the size of space-time sheet carrying the photons increases by power of sqrt(2). The paradoxes emerge when a collection of sub-cosmologies corresponding to different Hubble and cosmological constants is lumped to a single cosmology. This is of course unavoidable as long as one sticks to the standard view about space-time. As in elementary particle physics also now the fact that there is an entire hierarchy of scales resolves the almost paradoxes of single-sheeted physics relying on the existence of single scale characterized by Planck length. Of course, also now all length scales are expressible in terms of CP_2 size using p-adic length scale hypothesis. Dark energy and matter have very natural identifications in TGD framework. The magnetic energy of magnetic flux tubes is responsible for the dark energy. Ordinary matter at magnetic flux tubes could be responsible for dark matter. The flow of matter between space-time sheets changes dark matter to visible matter and vice versa and this process has various applications in TGD. For instance, solar corona and recently observed too low chemical abundances at solar surface have nice explanation in terms of dark matter at flux tubes of solar magnetic field. Matti Pitkänen


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