相关论文: Why is the Universe Accelerating?
The principles of General Relativity allow for a non-vanishing cosmological constant, which can possibly be interpreted at least partially in terms of quantum-fluctuations of matter fields. Depending on sign and magnitude it can cause…
The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations. Arguments are commonly presented to the…
A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic…
The discovery ten years ago that the expansion of the Universe is accelerating put in place the last major building block of the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark…
The discovery ten years ago that the expansion of the Universe is accelerating put in place the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark energy. Yet the underlying cause of…
After a short history of the $\Lambda$-term it is explained why the (effective) cosmological constant is expected to obtain contributions from short-distance-physics, corresponding to an energy scale of at least 100 GeV. The actual tiny…
Recent astronomical observations of distant supernovae light-curves suggest that the expansion of the universe has recently begun to accelerate. Acceleration is created by an anti-gravitational repulsive stress, like that produced by a…
Theoretical approaches to explaining the observed acceleration of the universe are reviewed. We briefly discuss the evidence for cosmic acceleration, and the implications for standard General Relativity coupled to conventional sources of…
Two sides of cosmological constant problem are discussed: a mysterious compensation of all contributions to vacuum energy with the accuracy of 100-50 orders of magnitude and a surprising equality of a constant vacuum energy density to the…
The "cosmic triangle" is introduced as a way of representing the past, present, and future status of the universe. Our current location within the cosmic triangle is determined by the answers to three questions: How much matter is in the…
In this colloquium-level account, I describe the cosmological constant problem: why is the energy of empty space at least 60 orders of magnitude smaller than several known contributions to it from the Standard Model of particle physics? I…
The cosmological model best capable of fitting current observational data features two separate epochs during which the Universe is accelerating. During the earliest stages of the Universe, such acceleration is known as cosmological…
Increasing evidence suggests that most of the energy density of the universe consists of a dark energy component with negative pressure, a ``cosmological constant" that causes the cosmic expansion to accelerate. In this paper, we address…
The traditional "explanation" for the observed acceleration of the universe is the existence of a positive cosmological constant. However, this can hardly be a truly convincing explanation, as an expanding universe is not expected to have a…
The accelerating expansion of the Universe points to a small positive value for the cosmological constant or vacuum energy density. We discuss recent ideas that the cosmological constant plus LHC results might hint at critical phenomena…
Observations suggest that nearly seventy per cent of the energy density in the universe is unclustered and exerts negative pressure. Theoretical understanding of this component (`dark energy'), which is driving an accelerated expansion of…
Recent cosmological and astrophysical observations point out that the Universe is in accelerating expansion and filled up with non-luminous matter. In order to explain the observed large scale structures and this accelerating behavior one…
In a recent paper (Phys. Rev. D95, 103504 (2017)) it is argued that, due to the fluctuations around its mean value, vacuum energy gravitates differently from what previously assumed. As a consequence, the universe would accelerate with a…
Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed…
It is a mystery why the density of matter and the density of vacuum energy are nearly equal today when they scale so differently during the expansion of the Universe. We suggest a paradigm that might allow for a non-anthropic solution to…