Posts about gravity

Scientific Inquiry Process Finds More Evidence Supporting Einstein’s Theory

As scientists have been able to see farther and deeper into the universe, the laws that govern its expansion have been revealed to be under the influence of an unexplained force.

In a paper on the arXiv, Astrophysical Tests of Modified Gravity: Constraints from Distance Indicators in the Nearby Universe, are a vindication of Einstein’s theory of gravity. Having survived several decades of tests in the solar system, it has passed this new test in galaxies beyond our own as well.

In 1998, astrophysicists made an observation that turned gravity on its ear: the universe’s rate of expansion is speeding up. If gravity acts the same everywhere, stars and galaxies propelled outward by the Big Bang should continuously slow down, like objects thrown from an explosion do here on Earth.

This observation used distant supernovae to show that the expansion of the universe was speeding up rather than slowing down. This indicated that something was missing from physicists’ understanding of how the universe responds to gravity, which is described by Einstein’s theory of general relativity. Two branches of theories have sprung up, each trying to fill its gaps in a different way.

One branch — dark energy — suggests that the vacuum of space has an energy associated with it and that energy causes the observed acceleration. The other falls under the umbrella of “scalar-tensor” gravity theories, which effectively posits a fifth force (beyond gravity, electromagnetism and the strong and weak nuclear forces) that alters gravity on cosmologically large scales.

“These two possibilities are both radical in their own way,” University of Pennsylvania astrophysicist Bhuvnesh Jain said. “One is saying that general relativity is correct, but we have this strange new form of energy. The other is saying we don’t have a new form of energy, but gravity is not described by general relativity everywhere.”

Jain’s research is focused on the latter possibility; he is attempting to characterize the properties of this fifth force that disrupts the predictions general relativity makes outside our own galaxy, on cosmic length scales. Jain’s recent breakthrough came about when he and his colleagues realized they could use the troves of data on a special property of a common type of star as an exquisite test of gravity.

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Is Dark Matter an Illusion?

Open access letter asks – Is dark matter an illusion created by the gravitational polarization of the quantum vaccum? by Dragan Slavkov Hajdukovic, CERN

Assuming that a particle and its antiparticle have the gravitational charge of the opposite sign, the physical vacuum may be considered as a fluid of virtual gravitational dipoles. Following this hypothesis, we present the first indications that dark matter may not exist and that the phenomena for which it was invoked might be explained by the gravitational polarization of the quantum vacuum by the known baryonic matter.

Let us start with a major unresolved problem. The measured galaxy rotation curves remain roughly constant at large radii. Faster than expected orbits, require a larger central force, which, in the framework of our theory of gravity, cannot be explained by the existing baryonic matter. The analogous problem persists also at the scale of clusters of galaxies.

The favoured solution is to assume that our current theory of gravity is correct, but every galaxy resides in a halo of dark matter made of unknown non-baryonic particles (for a brief review on dark matter see for instance: Einasto, 2010). A full list of the proposed dark matter particles would be longer than this letter; let us mention only weekly interacting massive particles and axions. In spite of the significant efforts dark particles have never been detected…

The scientific inquiry process continues to be used to try and explain the evidence we gather. Unsettled areas of science show how difficult the discovery process is. Once we have settled on theories it is so easy to explain why basic truths of evolution, geology, chemistry… result in what the evidence shows. But getting to the scientific consensus is a challenging process.


Dark Matter Is an Illusion, New Antigravity Theory Says

Physicist David Evans called the new study a “very interesting theoretical exercise,” but he said he isn’t ready to abandon dark matter just yet. “The evidence for dark matter is now very compelling,” said Evans, of the University of Birmingham, who leads the U.K. team for the ALICE detector at CERN’s Large Hadron Collider.

For example, in 2006 astronomers unveiled a photo of two colliding galaxies known as the Bullet cluster that purportedly showed the separation of matter from dark matter. A similar effect was observed in the Pandora cluster earlier this summer, said Evans, who was not involved in the study.

Hajdukovic said he is currently expanding his theory to account for these observations. His preliminary calculations, he said, suggest that “what is observed in the Bullet cluster and more recently at the Pandora cluster may be understood in the framework of the gravitational polarization of the quantum vacuum.”

CERN physicist Michael Doser agreed that Hajdukovic’s ideas are “unorthodox” but did not immediately dismiss the new theory…
“In a few years,” Doser said, “we should definitely be in a position to confirm or refute [Hajdukovic’s] hypothesis.”

Related: The Mystery of Empty SpaceWhy do we Need Dark Energy to Explain the Observable Universe?Dark Matter Experiment ResultsLooking for Signs of Dark Matter Over Antarctica

Quantum Information Theory Postulated As Source of Emergent Theory of Gravity

I love the advances we have made using our understanding of science and engineering, like the internet, air conditioning and antibiotics. I also love the discussion of research where we really have only educated guesses about what the scientific inquiry process is telling us about the way things are. This research from the University of York is very interesting.

Escaping gravity’s clutches: the black hole breakout

Professor Braunstein says: “Our results didn’t need the details of a black hole’s curved space geometry. That lends support to recent proposals that space, time and even gravity itself may be emergent properties within a deeper theory. Our work subtly changes those proposals, by identifying quantum information theory as the likely candidate for the source of an emergent theory of gravity.”

Dr Patra adds: “We cannot claim to have proven that escape from a black hole is truly possible, but that is the most straight-forward interpretation of our results. Indeed, our results suggest that quantum information theory will play a key role in a future theory combining quantum mechanics and gravity.”

It is too bad the University of York supports closed science and allows work to be withheld from the public to support outdated publishers business models. Luckily scientists often support open science and publish material openly – I have provided a link for those interested in science instead of the link the University of York gives to a publishers closed system.

Black Hole Evaporation Rates without Spacetime

Verlinde recently suggested that gravity, inertia, and even spacetime may be emergent properties of an underlying thermodynamic theory. This vision was motivated in part by Jacobson’s 1995 surprise result that the Einstein equations of gravity follow from the thermodynamic properties of event horizons. Taking a first tentative step in such a program, we derive the evaporation rate (or radiation spectrum) from black hole event horizons in a spacetime-free manner. Our result relies on a Hilbert space description of black hole evaporation, symmetries therein which follow from the inherent high dimensionality of black holes, global conservation of the no-hair quantities, and the existence of Penrose processes. Our analysis is not wedded to standard general relativity and so should apply to extended gravity theories where we find that the black hole area must be replaced by some other property in any generalized area theorem.

Related: Gravity and the Scientific MethodGravity May Emerge from Quantum InformationDoes Time ExistWebcast of Astronaut Testing Gravity on the Moonsupport open science

Gravity and the Scientific Method

One of the topics I return to repeatedly is the scientific method – theories must to tested. As evidence mounts that new ideas do a good job of explaining theories they become more accepted. But they continue to be tested in new ways as the ideas are extended and ramification are explored. And science progress means that old conventions can be overturned as new evidence is gathered.

Science is not about current beliefs. Science is about seeking knowledge. If the search for knowledge leads to evidence that old ideas were wrong those ideas are overturned. Since people are involved that process isn’t as clean as it sounds above. People get comfortable with beliefs. They build careers on expanding those beliefs. Most are uncomfortable when they are challenged and don’t accept new ideas even when the evidence mounts. But some do accept the new ideas. Some challenge the new ideas by running experiments. And some of those prove the new ideas faulty. Some become convinced of the new ideas as the results of their experiments make the new ideas seem more sensible (instead of getting the results they expected).

Building the body of scientific knowledge is not nearly as clean and simple as most people think. It isn’t a simple process, what is the underlying truth can be debatable. But the beauty of the scientific process is how it helps us overcome our biases and provide evidence to support the theories we support. The scientific method (combined with our human involvement) doesn’t mean new ideas are accepted easily but it does mean new ideas compete on the basis of evidence not just the power of those that hold the beliefs.

Is gravity not actually a force? Forcing theory to meet experiments
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