If anything can sum up just how little we truly know about the Universe, it’s black holes.
We can’t see them because not even light can escape their gravitational pull, we have no idea what they’re made of, and where does everything inside go once a black hole dies?
Physicists can’t even agree on whether black holes are massive, three-dimensional behemoths, or just two-dimensional surfaces that are projected in 3D just like a hologram.
(Phys.org)—For more than 100 years, scientists have debated the question: when light travels through a medium such as oil or water, does it pull or push on the medium? While most experiments have found that light exerts a pulling pressure, in a new paper physicists have, for the first time, found evidence that light exerts a pushing pressure.
The scientists suggest that this apparent contradiction is not a fundamental one, but can be explained by the interplay between the light and the fluid medium: if the light can put the fluid in motion, it exerts a pushing force; if not, it exerts a pulling force.
The researchers, Li Zhang, Weilong She, and Nan Peng at Sun Yat-Sen University in Guangzhou, China, and Ulf Leonhardt at the Weizmann Institute of Science in Rehovot, Israel, have published a paper on the first evidence for the pushing pressure of light in a recent issue of the New Journal of Physics.
New fundamental research by UT Dallas physicists may accelerate the drive toward more advanced electronics and more powerful computers.
The scientists are investigating materials called topological insulators, whose surface electrical properties are essentially the opposite of the properties inside.
“These materials are made of the same thing throughout, from the interior to the exterior,” said Dr. Fan Zhang, assistant professor of physics at UT Dallas. “But, the interior does not conduct electrons — it’s an insulator — while the electrons on the surface are free to move around. The surface is therefore a conductor, like a metal, but it is in fact more robust than a metal.”
Interesting…
First, we take ‘Time’, as we know it’s one of those things that we take for granted—time moves forward and never backward. But did you ever stop to wonder why it moves in one direction, as opposed to the other?
The question continues to stump physicists. After all, there are certain physical processes that are actually time-reversible—they look the same no matter which way you run them.
For example, gravity operates the same way regardless of Time’s Arrow; a planet will orbit a star in exactly the same way, just with the direction of that orbit reversed. But there is one aspect of the universe that is dependent on the direction of Time’s Arrow: the Second Law of Thermodynamics. This states that the disorder of a closed system (such as our universe) must increase, never decrease.
It’s commonly called “entropy,” and it’s why broken eggs don’t suddenly reassemble themselves, or why dead things don’t suddenly come back to life. Disorganization and chaos are downhill, order and complexity are uphill; complex systems like stars and planets and human beings may emerge locally, but they require an inordinate amount of energy to create, which only increases the overall entropy of the system.
This is why the Second Law of Thermodynamics is universally reckoned as the mechanism that imparts directionality to time—although, understanding the how of a thing is not the same as understanding the why of it.
Now, we see the connection of Dark Energy,
In the question to understand the origins of Time’s Arrow, two Armenian physicists, A. E. Allahverdyan and V. G. Gurzadyan, decided to search for a link between so-called “dark energy” and the Second Law of Thermodynamics. Dark energy is a mysterious quantity that is proposed as an explanation for why the universe is continuing to expand, rather than decelerating and collapsing, as our current understanding of gravity dictates it should.
Kathryn Zurek realized a decade ago that we may be searching in the wrong places for clues to one of the universe’s greatest unsolved mysteries: dark matter. Despite making up an estimated 85 percent of the total mass of the universe, we haven’t yet figured out what it’s made of.
Now, Zurek, a theoretical physicist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), says thanks to extraordinary improvements in experimental sensitivity, “We increasingly know where not to look.” In 2006, during grad school, Zurek began to explore the concept of a new “Hidden Valley” model for physics that could hold all of the answers to dark matter.
“I noticed that from a model-builder’s point of view that dark matter was extraordinarily undeveloped,” she said. It seemed as though scientists were figuratively hunting in the dark for answers. “People were focused on models of just two classes of dark matter candidates, rather than a much broader array of possibilities.”
In the last few years, hundreds of contained “nano” satellites known as CubeSats have been launched in low Earth orbit for many purposes, including for collecting targeted scientific data. Federal agencies such as NASA and the National Science Foundation are exploring the potential of these highly affordable satellites in advancing research goals.
A new report from the National Academies of Sciences, Engineering, and Medicine concludes that CubeSats have demonstrated usefulness for scientific data gathering and can also augment – but not replace — the capabilities of large satellite missions and ground-based facilities. The report identifies examples of high-priority science goals that could be pursued through the use of CubeSats in areas such as solar and space physics, planetary science, and Earth science.
In order to continue building the capabilities of CubeSats for research, federal support is crucial, the report says, which identifies several steps NASA and NSF should take to ensure that CubeSats reach their full potential.
For years, physicists have attempted to explain dark energy — a mysterious influence that pushes space apart faster than gravity can pull the things in it together. But physics isn’t always about figuring out what things are. A lot of it is figuring out what things cause.
And in a recent paper, a group of physicists asked this very question about dark energy, and found that in some cases, it might cause time to go forward.
When you throw a ball into the air, it starts with some initial speed-up, but then it slows as Earth’s gravity pulls it down. If you throw it fast enough (about 11 km per second, for those who want to try), it’ll never slow down enough to turn around and start falling back towards you, but it’ll still move more slowly as it moves away from you, because of Earth’s gravity.
Improving energy efficiencies — nice.
The remarkable properties researchers at the Australian National University (ARC Centre of Excellence CUDOS) and the University of California Berkeley have discovered in a new nano-metamaterial could lead to highly efficient thermophotovoltaic cells. The new artificial material glows in an unusual way when headed.
As shown in the image, the metamaterial comprises 20 stacked alternating layers of 30-nm-thick gold and 45-nm-thick magnesium fluoride dielectric, perforated with 260 × 530 nm holes that are arranged into a 750 × 750 nm square lattice.
Thermophotovoltaics typically use a heated object as a source of radiation that is then converted to electricity by a photovoltaic cell. The caveat is that heated object emits light in all directions and over a broad spectral region, which reduces the efficiency of the light-to-electricity conversion. However, “The demonstrated metamaterial emits thermal radiation predominantly in particular directions and [within] a particular spectral region, which could make the conversion more efficient,” says Dr Sergey Kruk at the Nonlinear Physics Centre in the ANU Research School of Physics and Engineering.
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