New evidence for dark energy

Chandra X-ray observatory has given new evidence of the existence of dark energy. This striking result has been obtained with the observation of Abell 85. This is a galaxy cluster located about 740 million light years from Earth.

darkenergy

I have found another beautiful article on NewYork Times about (see here). Dark energy is currently described by a non-null cosmological constant in the Einstein equations but no explanation is known whatsoever about its origin. Currently, a famous explanation uses the anthropic principle but was criticized by Steven Weinberg (see here). This argument seems to support very strongly the landscape view of string theory but whatever relies on anthropic arguments cannot be said to be really satisfactory for our understanding. So, physicists are looking for something better but nothing is in view. Rather, quantum field theory gives a too large account for this constant. As this is a major breakthrough in our understanding of universe, it is a serious reason to stay tuned waiting for more information.

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4 Responses to New evidence for dark energy

  1. tomate says:

    Do they give evidence of universe accelerated expansion being called Dark Energy, or for something which is intrinsically a quantum-field-theoretic or other quantum-gravity-theoretic phenomenon? I mean, do we know by any such experiment that an explanation has to be searched for in some foundamental theory of matter?

    • mfrasca says:

      This effect can be seen as a force counteracting gravity. Indeed, we now that galaxies recede each other due to the expansion of the universe. This implies that a cluster like this should expand in time. This is seen not happening and could be interpreted as the effect of a counteracting force. A counteracting force impeding expansion can be introduced into Einstein equations with the so called cosmological constant and, indeed, the reason why Einstein introduced such a term into his equations was just to avoid solutions with an expanding universe. The measured value of such a constant is indeed very small and unexplained so far. We have no theory able to recover from fundamental principles its value. Quantum field theory gives a too much high value while some anthropic arguments may settle this but these are very unsatisfactory being not an explanation at all. Of course, string theorists through the problematic landscape could see anthropic ideas quite acceptable. As a physicist I cannot be happy with this.

      Marco

  2. hermann says:

    Dear Marco.
    In a recent paper, an italian physicist working at Bologna University (Appignani), suggest the possibility that the universe is not accelerating, but the light is slowing down. His geometrical approach seems to be, at least, awsome. I think we can’t be sure about universe acceleration until we have elimineted every possible other cause.
    If the Appignani work is correct and some experiment will prove it, we will not need any evidence of dark energy.

    • mfrasca says:

      Dear hermann,

      As you may know there are several different models claiming that, assuming a varying speed of light, all the cosmological problems fade away. These represent an alternative to the inflationary models. The work of Appignani

      http://arxiv.org/abs/gr-qc/0407117

      has the advantage to get rid of dark energy and dark matter and so, in a single hit, you will solve all cosmological problems. If you speak Italian, here is a report about all this matter also citing Appignani’s work

      http://ulisse.sissa.it/chiediAUlisse/domanda/2007/Ucau070908d001

      These ways to see the cosmological problems are far from being accepted while the inflationary paradigm seems to be more widely accepted. Anyhow, Appignani’s theory could get in trouble if any of the WIMP experiments around the World should unveil dark matter particles and either Tevatron and LHC should discover possible candidates for this. I would like to remember here that at Tevatron people observed leptonic jets, a finding yet to be confirmed, but if true it would be a serious confirmation hint favoring dark matter models.

      My personal view is like the point discussed in the following New York Times article

      http://www.nytimes.com/2007/03/11/magazine/11dark.t.html?_r=1&scp=1&sq=smoot%20cosmology&st=cse

      so, it is possible that a very smart model could solve all the matter but presently such a model does not seem to be in view and there is much work to do. Of course, if experimental evidence should emerge we are ready to accept the model that fits our data at best.

      Marco

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