gravity (3)

Ripples, Waves, and Genesis...

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Numerical simulation of the neutron stars merging to form a black hole, with their accretion disks interacting to produce electromagnetic waves. Credit: L. Rezolla (AEI) & M. Koppitz (AEI & Zuse-Institut Berlin)

Topics: Black Holes, Cosmology, General Relativity, Gravity, Research

Scientists have advanced in discovering how to use ripples in space-time known as gravitational waves to peer back to the beginning of everything we know. The researchers say they can better understand the state of the cosmos shortly after the Big Bang by learning how these ripples in the fabric of the universe flow through planets and the gas between the galaxies.

"We can't see the early universe directly, but maybe we can see it indirectly if we look at how gravitational waves from that time have affected matter and radiation that we can observe today," said Deepen Garg, lead author of a paper reporting the results in the Journal of Cosmology and Astroparticle Physics. Garg is a graduate student in the Princeton Program in Plasma Physics, which is based at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL).

Garg and his advisor Ilya Dodin, who is affiliated with both Princeton University and PPPL, adapted this technique from their research into fusion energy, the process powering the sun and stars that scientists are developing to create electricity on Earth without emitting greenhouse gases or producing long-lived radioactive waste. Fusion scientists calculate how electromagnetic waves move through plasma, the soup of electrons and atomic nuclei that fuels fusion facilities known as tokamaks and stellarators.

Ripples in the fabric of the universe may reveal the start of time, Raphael Rosen, Princeton Plasma Physics Laboratory, Phys.org.

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Aharonov-Bohm Effect

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A quantum probe for gravity: Physicists have detected a tiny phase shift in atomic wave packets due to gravity-induced relativistic time dilation – an example of the Aharonov-Bohm effect in action. (Courtesy: Shutterstock/Evgenia Fux)

Topics: General Relativity, Gravity, Modern Physics, Quantum Mechanics

The idea that particles can feel the influence of potentials even without being exposed to a force field may seem counterintuitive, but it has long been accepted in physics thanks to experimental demonstrations involving electromagnetic interactions. Now physicists in the US have shown that this so-called Aharonov-Bohm effect also holds true for a much weaker force: gravity. The physicists based their conclusion on the behavior of freefalling atomic wave packets, and they say the result suggests a new way of measuring Newton’s gravitational constant with far greater precision than was previously possible.

Yakir Aharonov and David Bohm proposed the effect that now bears their name in 1959, arguing that while classical potentials have no physical reality apart from the fields they represent, the same is not true in the quantum world. To make their case, the pair proposed a thought experiment in which an electron beam in a superposition of two wave packets is exposed to a time-varying electrical potential (but no field) when passing through a pair of metal tubes. They argued that the potential would introduce a phase difference between the wave packets and therefore lead to a measurable physical effect – a set of interference fringes – when the wave packets are recombined.

Seeking a gravitational counterpart

In the latest research, Mark Kasevich and colleagues at Stanford University show that the same effect also holds true for gravity. The platform for their experiment is an atom interferometer, which uses a series of laser pulses to split, guide and recombine atomic wave packets. The interference from these wave packets then reveals any change in the relative phase experienced along the two arms.

Physicists detect an Aharonov-Bohm effect for gravity, Edwin Cartlidge, Physics World

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Geodes...

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(Just_Super/iStock)

 

Topics: Black Holes, Cosmology, Dark Energy, Einstein, General Relativity, Gravity


A fifty-year-old hypothesis predicting the existence of bodies dubbed Generic Objects of Dark Energy (GEODEs) is getting a second look in light of a proposed correction to assumptions we use to model the way our Universe expands.

If this new version of a classic cosmological model is correct, some black holes could hide cores of pure dark energy, pushing our Universe apart at the seams.

University of Hawaii astrophysicist Kevin Croker and mathematician Joel Weiner teamed up to challenge the broadly accepted notion that when it comes to the Universe's growing waistline, its contents are largely irrelevant.

"For 80 years, we've generally operated under the assumption that the Universe, in broad strokes, was not affected by the particular details of any small region," said Croker.

"It is now clear that general relativity can observably connect collapsed stars – regions the size of Honolulu – to the behavior of the Universe as a whole, over a thousand billion billion times larger."

Not only could this alternative interpretation of fundamental physics change how we understand the Universe's expansion, but we might need to also consider how that growth might affect compact objects like the cores of collapsing stars.

 

Black Holes May Hide Cores of Pure Dark Energy That Keep The Universe Expanding
Mike McCrae, Science Alert

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