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by Bob Yirka , Phys.org
https://phys.org/news/2019-10-physicist-quantum-foam-huge-cosmic.html
Steven Carlip, a physicist at the University of California, has come up with a theory to explain why empty space seems to be filled with a huge amount of energy—it may be hidden by effects that are canceling it out at the Planck scale. He has published a paper describing his new theory in the journal Physical Review Letters.
Conventional theory suggests that spacetime should be filled with a huge amount of energy—perhaps as much as 10120 more than seemingly exists. Over the years, many theorists have suggested ideas on why this may be—most have tried the obvious approach, trying to figure out a way to make the energy go away. But none have been successful. In this new effort, Carlip suggests that maybe all that energy really is there, but it does not have any ties to the expansion of the universe because its effects are being canceled out by something at the Planck scale.
The new theory by Carlip is based very heavily on work done by John Wheeler back in the 1950s—he suggested that at the smallest possible scale, space and time turn into something he called “spacetime foam.” He argued that at such a small scale, defining time, length and energy would be subject to the uncertainty principle. Since then, others have taken a serious look at spacetime foam—and some have suggested that if a vacuum were filled with spacetime foam, there would be a lot of energy involved. Others argue that such a scenario would behave like the cosmological constant.
Thus, to explain their ideas, they have sought to find ways to cancel out the energy as a way to make it go away. Carlip suggests instead that in a spacetime foam scenario, energy would exist everywhere in a vacuum—but if you took a much closer look, you would find Planck-sized areas that have an equal likelihood of expanding or contracting. And under such a scenario, the patchwork of tiny areas would appear the same as larger areas in the vacuum—and they would not expand or contract, which means they would have a zero cosmic constant. He notes that under such a scenario, time would have no intrinsic direction.
More information: S. Carlip. Hiding the Cosmological Constant, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.123.131302 . On Arxiv: https://arxiv.org/abs/1809.08277
Journal information: Physical Review Letters , arXiv
OCTOBER 2, 2019
Quantum vacuum: Less than zero energy
by Vienna University of Technology
https://phys.org/news/2019-10-quantum-vacuum-energy.html
Energy is a quantity that must always be positive—at least that’s what our intuition tells us. If every single particle is removed from a certain volume until there is nothing left that could possibly carry energy, then a limit has been reached. Or has it? Is it still possible to extract energy even from empty space?
Quantum physics has shown time and again that it contradicts our intuition, which is also true in this case. Under certain conditions, negative energies are allowed, at least in a certain range of space and time. An international research team at the TU Vienna, the Université libre de Bruxelles (Belgium) and the IIT Kanpur (India) have now investigated the extent to which negative energy is possible. It turns out that no matter which quantum theories are considered, no matter what symmetries are assumed to hold in the universe, there are always certain limits to “borrowing” energy. Locally, the energy can be less than zero, but like money borrowed from a bank, this energy must be “paid back” in the end.
“In the theory of General Relativity, we usually assume that the energy is greater than zero, at all times and everywhere in the universe,” says Prof. Daniel Grumiller from the Institute for Theoretical Physics at the TU Wien (Vienna). This has a very important consequence for gravity: Energy is linked to mass via the formula E=mc². Negative energy would therefore also mean negative mass. Positive masses attract each other, but with a negative mass, gravity could suddenly become a repulsive force.
Quantum theory, however, allows negative energy. “According to quantum physics, it is possible to borrow energy from a vacuum at a certain location, like money from a bank,” says Daniel Grumiller. “For a long time, we did not now about the maximum amount of this kind of energy credit and about possible interest rates that have to be paid. Various assumptions about this “interest” (known in the literature as “Quantum Interest”) have been published, but no comprehensive result has been agreed upon.
The so-called “quantum null energy condition” (QNEC), which was proven in 2017, prescribes certain limits for the “borrowing” of energy by linking relativity theory and quantum physics: An energy smaller than zero is thus permitted, but only in a certain range and only for a certain time. How much energy can be
borrowed from a vacuum before the energetic credit limit has been exhausted depends on a quantum physical quantity, the so-called entanglement entropy.“In a certain sense, entanglement entropy is a measure of how strongly the behavior of a system is governed by quantum physics,” says Daniel Grumiller. “If quantum entanglement plays a crucial role at some point in space, for example close to the edge of a black hole, then a negative energy flow can occur for a certain time, and negative energies become possible in that region.”
Grumiller was now able to generalize these special calculations together with Max Riegler and Pulastya Parekh. Max Riegler completed his dissertation in the research group of Daniel Grumiller at the TU Wien and is now working as a postdoc in Harvard. Pulastya Parekh from the IIT in Kanpur (India) was a guest at the Erwin Schrödinger Institute and at the TU Wien.
“All previous considerations have always referred to quantum theories that follow the symmetries of Special Relativity. But we have now been able to show that this connection between negative energy and quantum entanglement is a much more general phenomenon,” says Grumiller. The energy conditions that clearly prohibit the extraction of infinite amounts of energy from a vacuum are valid for very different quantum theories, regardless of symmetries.
Of course, this has nothing to do with mystical “over unity machines” that allegedly generate energy out of nothing, as they are repeatedly presented in esoteric circles. “The fact that nature allows an energy smaller than zero for a certain period of time at a certain place does not mean that the law of conservation of energy is violated,” stresses Daniel Grumiller. “In order to enable negative energy flows at a certain location, there must be compensating positive energy flows in the immediate vicinity.”
Even if the matter is somewhat more complicated than previously thought, energy cannot be obtained from nothing, even though it can become negative. The new research results now place tight bounds on negative energy, thereby connecting it with quintessential properties of quantum mechanics.
More information: Daniel Grumiller et al. Local Quantum Energy Conditions in Non-Lorentz-Invariant Quantum Field Theories, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.123.121602
Journal information: Physical Review Letters
…conventional theory suggests that spacetime should be filled with a huge amount of energy—perhaps as much as 10120 more than seemingly exists…
…modern physics failed to calculate the actual value of Dark energy. This is considered to be the biggest failure of modern physics. Quantum physics could calculate only a very small value but modern physicists predict it to be around 10 raised to power 120 times…
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