Sintering

• It suggests that when averaged on large scales, the Cosmos is homogeneous and matter is distributed evenly throughout.
• This allows a mathematical description of space-time that simplifies the application of Einstein’s general theory of relativity to the Universe as a whole.

Einstein’s legacy

• As a 50-year-old textbook reminds us:
  Matter tells space how to curve, and space tells matter how to move.
• Matter tells space how to curve, and space tells matter how to move.
• Read more:
  Dark matter: our review suggests it's time to ditch it in favour of a new theory of gravity

Ideas about matter have evolved, but not geometry

• We can trace the astrophysics of “stuff” from tiny seed ripples in the primordial fireball all the way to complex structures today.
• They look back all the way to when the first atoms formed, and the Universe first became transparent.
• We receive that same light today, but cooled to minus 270℃ and diluted by the expansion of the Universe.

A ‘lumpy’ Universe

• The expansion of the Universe has been halted entirely within the largest matter concentrations known as galaxy clusters.
• But the idea that the Universe is spatially homogeneous endures.
• Billions have been spent trying to directly detect dark matter, but decades of such efforts have yielded no definitive detection of what makes up 80% of all matter and 20% of all the energy in the Universe today.

An anomalous sky

• Superimposed on it are fluctuations, one of which is abnormally large and has the shape of a dipole: a yin-yang diagram covering the whole sky.
• We can interpret this as an effect due to relative motion, provided we define the cosmic microwave background radiation as the rest frame of the Universe.
• These anomalies have long been explained as a result of unaccounted physical processes in modelling microwave emissions from the Milky Way.

Matter within the sky

• They found that matter, too, is unevenly distributed.
• Conventionally, we assume that an all-sky average of the Universe’s present expansion rate gives one well defined value: the Hubble constant.
• Using cosmic microwave background data from individual opposing hemispheres, a standard expansion history implies different Hubble “constants” on each side of the sky today.
• If matter is much more varied and interesting than expected, then maybe the geometry is too.

• Do viruses, bacteria and other small things get crushed like an ant when stepped on?
• – Ryan L., age 12, Chapel Hill, North Carolina
  Do viruses, bacteria and other small things get crushed like an ant when stepped on?
• – Ryan L., age 12, Chapel Hill, North Carolina When you step on some things, like a banana, they squish and flatten to the ground.
• But when you step on other things, like a rock, they maintain their shape and aren’t affected.

Forces and pressures

• What happens after that depends on how much force you’re exerting and the properties of the object.
• And if your weight is 110 pounds (50 kilograms), the force you exert per square inch is roughly 3.9 pounds per square inch.
• For comparison, the pressure of the air, or atmospheric pressure, on your body at sea level is 14.7 pounds per square inch.

Stepping on a microbe

• Scientists have studied the strength of bacterial cell walls for several reasons, including to find out whether high pressure can kill bacteria.
• People in the food industry use high pressure to make food such as milk safe for us to consume.
• While high pressures can kill bacteria in some applications such as food processing, one person standing on them won’t work.

Slipping through the cracks

• But there’s an added complication that makes it even harder to squish bacteria: They’re incredibly small.
• The average bacterium is only about 1 to 5 microns or millionths of a meter (smaller than ten-thousandth of an inch) in size.
• The surface of your skin has fine grooves called sulci cutis that are, on average, tens of microns deep.

Standing on a pin

• One theoretical way would be to change the bottoms of your shoes from flat to very pointy, with the bottom of the point having a diameter as wide as the tip of a pin.
• While walking on these shoes would be impossible, a 110-pound person would exert a pressure of 5.6 million pounds per square inch.
• These needle-like structures are only nanometers in size, a thousand times smaller than most bacteria, and are called nanorods.
• When a bacterium lands on the surface of the cicada wing, it makes special chemicals that help it stick to the surface.

• FREMONT, Calif., June 14, 2023 (GLOBE NEWSWIRE) -- Engineered materials company Uniformity Labs announces the availability of its ultra-low porosity 17-4PH stainless steel powder UniJet™ SS17-4PH Performance for the Desktop Metal Production System™.
• During the qualification on Desktop Metal’s Production System™, the physical and mechanical properties of UniJet™ 17-4PH powder were extensively evaluated, and the results are outstanding.
• UniJet™ 17-4PH powder yielded parts with, on average, three times lower standard deviation in green density than standard binder jetting powder.
• Binder jetting powders processed with Uniformity Labs technology enables unmatched mechanical properties and can further improve the economics of printing.

• In the race to develop fusion energy, each unique approach requires its own specialized techniques to determine net energy gain, an equation balancing energy in and out that’s known by the letter Q.
• View the full release here: https://www.businesswire.com/news/home/20230605005011/en/
  A new paper , published today in the journal Fusion Science and Technology, establishes the company’s method of measuring and calculating Q in Zap’s sheared-flow-stabilized Z-pinch fusion plasmas.
• The publication will be an important part of Zap demonstrating energy gain on the way to building a commercial fusion system.
• Like other fusion devices, Zap Energy plans to fuse hydrogen nuclei within material called plasma that must be superheated to temperatures hotter than the sun.