* Astronomy

Chalmers scientists create light from vacuum

Scientists at Chalmers University of Technology have succeeded in creating light from vacuum - observing an effect first predicted over 40 years ago. The results is published tomorrow (Wednesday) in the journal Nature. In an innovative experiment, the scientists have managed to capture some of the photons that are constantly appearing and disappearing in the vacuum.
The experiment is based on one of the most counterintuitive, yet, one of the most important principles in quantum mechanics: that vacuum is by no means empty nothingness. In fact, the vacuum is full of various particles that are continuously fluctuating in and out of existence. They appear, exist for a brief moment and then disappear again. Since their existence is so fleeting, they are usually referred to as virtual particles.
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Lasers could make virtual particles real

Next-generation lasers will have the power to create matter by capturing ghostly particles that, according to quantum mechanics, permeate seemingly empty space.
The uncertainty principle of quantum mechanics implies that space can never be truly empty. Instead, random fluctuations give birth to a seething cauldron of particles, such as electrons, and their antimatter counterparts, called positrons.
These so-called "virtual particles" normally annihilate one another too quickly for us to notice them. But physicists predicted in the 1930s that a very strong electric field would transform virtual particles into real ones that we can observe. The field pushes them in opposite directions because they have opposite electric charges, separating them so that they cannot destroy one another.
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Title: Vacuum Energy, the Cosmological Constant and Compact Extra Dimensions: Constraints from Casimir Effect Experiments
Authors: Leandros Perivolaropoulos

We consider a universe with a compact extra dimension and a cosmological constant emerging from a suitable ultraviolet cutoff on the zero point energy of the vacuum. We derive the Casimir force between parallel conducting plates as a function of the following scales: plate separation, radius of the extra dimension and cutoff energy scale. We find that there are critical values of these scales where the Casimir force between the plates changes sign. For the cutoff energy scale required to reproduce the observed value of the cosmological constant, we find that the Casimir force changes sign and becomes repulsive for plate separations less than a critical separation d_0=0.6mm, assuming a zero radius of the extra dimension (no extra dimension). This prediction contradicts Casimir experiments which indicate an attractive force down to plate separations of 100nm. For a non-zero extra dimension radius, the critical separation d_0 gets even larger than 0.6mm and remains inconsistent with Casimir force experiments. We conclude that with or without the presence of a compact extra dimension, vacuum energy with any suitable cutoff can not play the role of the cosmological constant.

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POP. What are the chances that an everyday object - a rock, a chair, you name it - could suddenly appear out of thin air? Not zero, surprisingly. In fact, given enough space and time, it is conceivable that a conscious being could arise, even if only for a microsecond.
OK, such an event would be incredibly unlikely, but not impossible - at least in theory. Physicists have dubbed such hypothetical beings "Boltzmann brains", after the 19th-century Austrian physicist Ludwig Boltzmann, a pioneer in thermodynamics and statistical mechanics. Boltzmann posed the question of whether the universe could have arisen from a thermal fluctuation; his work presaged the idea that a fluctuation could also give rise to a conscious entity that sees the universe. In this regard Boltzmann brains are not necessarily actual brains, but rather are a metaphor for observers of the universe that might appear spontaneously.

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