Cosmologists Prove Negative Mass Can Exist In Our Universe — The Physics arXiv Blog — Medium

Cosmologists Prove Negative Mass Can Exist In Our Universe — The Physics arXiv Blog — Medium: Today, Saoussen Mbarek and Manu Paranjape at the Université de Montréal in Canada say they’ve found a solution to Einstein’s theory of general relativity that allows negative mass without breaking any essential assumptions. Their approach means that negative mass can exist in our universe provided there is a reasonable mechanism for producing it, perhaps in pairs of positive and negative mass particles in the early universe...

The crucial breakthrough by Mbarek and Paranjape is to show that negative mass can produce a reasonable Schwarzschild solution without violating the energy condition. Their approach is to think of negative mass not as a solid object, but as a perfect fluid, an otherwise common approach in relativity...

If Spacetime Were a Superfluid, Would It Unify Physics—or Is the Theory All Wet? - Scientific American

If Spacetime Were a Superfluid, Would It Unify Physics—or Is the Theory All Wet? - Scientific American: If it is true that spacetime is a superfluid and that photons of different energies travel at different speeds or dissipate over time, that means relativity does not hold in all situations. One of the main tenets of relativity, the Lorentz invariance, states that the speed of light is unchanging, regardless of an observer’s frame of reference. “The possibility that spacetime as we know it emerges from something that violates relativity is a fairly radical one,” Jacobson says. It does, however, clear a potential pathway toward rectifying some of the problems that arise when trying to combine relativity and quantum mechanics. “Violating relativity would open up the possibility of eliminating infinite quantities that arise in present theory and which seem to some unlikely to be physically correct.”

New method for propulsion in fluids | MIT News Office

New method for propulsion in fluids | MIT News Office: The effect itself is surprisingly simple, Peacock explains: “By virtue of heating or cooling the surface of an object, you change the density of any fluid next to that surface.” In the valley winds previously considered, the object was either a glacier or a valley wall heated by the sun, and the fluid was the air passing over it; in this case, it’s the solid wedge and its surrounding water.
The changed density of the fluid generates a flow over the surface, Peacock says, adding, “That flow then creates unbalanced forces, with lower pressure on one side, and higher on the other” — an imbalance that propels the object from the higher pressure toward the lower.

Fire ants writhe to make unsinkable rafts - life - 26 November 2013 - New Scientist

Fire ants writhe to make unsinkable rafts - life - 26 November 2013 - New Scientist: A raft of live fire ants, on the other hand, resists and dissipates external forces equally well on all scales. The ants can act as tiny, resistive springs by flexing and extending their legs, and they break and reform connections with their neighbours to create a flow around external forces, like being prodded with sticks. Importantly, rafts of live ants are significantly more elastic than those made of flash-frozen dead ants.

Mobius strip ties liquid crystal in knots to produce tomorrow's materials and photonic devices

Mobius strip ties liquid crystal in knots to produce tomorrow's materials and photonic devices
...they simulated adding a micron sized silica particle – or colloid – to the liquid crystal. This disrupts the orientation of the liquid crystal molecules.

For example, a colloid in the shape of a sphere will cause the liquid crystal molecules to align perpendicular to the surface of the sphere, a bit like a hedgehog's spikes.
Using a theoretical model, the University of Warwick scientists have taken this principle and extended it to colloids which have a knotted shape in the form a Möbius strip...


By adding these specially designed knotted particles they force the liquid crystal to take on the same structure, creating a knot in the liquid crystal...
"Recently it has been demonstrated that knots can be created in a variety of natural settings including electromagnetic fields, laser light, fluid vortices and liquid crystals.

Self-healing solar cells mimic leaves | KurzweilAI

Self-healing solar cells mimic leaves | KurzweilAI: These biomimetic (nature-mimicking) devices are a type of dye-sensitized solar cells (DSSCs). They are composed of a hydrogel (water-based gel) core, electrodes, and inexpensive, light-sensitive organic-dye molecules that capture light and generate electric current...

“Photovoltaic cells rendered ineffective by high intensities of ultraviolet rays were regenerated by pumping fresh dye into the channels while cycling the exhausted dye out of the cell. This process restores the device’s effectiveness in producing electricity over multiple cycles.”

Team demonstrates gels that can be moved, controlled by light

Team demonstrates gels that can be moved, controlled by light: Using computer modeling, the Pitt team demonstrated that the gels "ran away" when exposed to the light, exhibiting direct, sustained motion. The team also factored in heat—combining the light and local variations in temperature to further control the samples' motions...

"Consider, for example, that you could take one sheet of hydrogel and, with the appropriate use of light, fashion it into a lens-shaped object, which could be used in optical applications", added Balazs.
The team also demonstrated that the gels could undergo dynamic reconfiguration, meaning that, with a different combination of lights, the gel could be used for another purpose.

When fluid dynamics mimic quantum mechanics | KurzweilAI

When fluid dynamics mimic quantum mechanics | KurzweilAI: In the experiments reported in PRE, the researchers mounted a shallow tray with a circular depression in it on a vibrating stand. They filled the tray with a silicone oil and began vibrating it at a rate just below that required to produce surface waves.

They then dropped a single droplet of the same oil into the bath. The droplet bounced up and down, producing waves that pushed it along the surface.

The waves generated by the bouncing droplet reflected off the corral walls, confining the droplet within the circle and interfering with each other to create complicated patterns. As the droplet bounced off the waves, its motion appeared to be entirely random, but over time, it proved to favor certain regions of the bath over others...

The statistical description of the droplet’s location is analogous to that of an electron confined to a circular quantum corral and has a similar, wavelike form.

A scientific experiment is able to create a wave that is frozen in time

A scientific experiment is able to create a wave that is frozen in time "A wave is a deformation in the surface of a liquid that moves at a speed that is independent of that liquid," the researchers explain... "In our case, what occurs is actually the opposite: the water moves very rapidly (at several meters per second), but the wave moves at a speed of zero...

In order to recreate this phenomenon, the scientists constructed a small canal in a laboratory at the University. The prototype is relatively simple, they say: it consists of a semi-submerged panel with a square corner that partially obstructs the flow in a tank of water that is approximately the length of a van.

Particles defy gravity, float upstream | Physics | Science News

Particles defy gravity, float upstream | Physics | Science News: Shinbrot set up two tanks side-by-side and elevated one of them, with water flowing down through a channel to bridge the 1-centimeter height gap. Sure enough, within seconds of adding chalk and mate tea to the bottom tank, particles began climbing up the channel to contaminate the upper tank.

Shinbrot’s experiments led him to the conclusion that Altshuler’s team had also reached: The particles overcome gravity and the current thanks to a property of water called surface tension.