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The universe is expanding at an accelerated rate, however, the nature of this expansion why it's expanding and why it's doing so at such an accelerated rate is uncertain. One culprit has been dubbed dark energy, a hypothetical form of energy that could be seen as anti-gravity. While what dark energy is precisely remains unknown, as a cosmological constant astronomers could roughly agree on its effects to measure the expansion rate of the universe, known as the Hubble constant. But not anymore.

Over the last few months, research has been published and news has followed about new measurements for the expansion rate of the universe. This is a Hot Topic in cosmology. Over the last several years, that earlier agreement has disappeared in the face of a gulf between the value depending on which method you use to measure it. The issue, dubbed the Hubble tension, took center stage, with cosmologists and astrophysicists arguing for one method of measurement and its resulting number over the other. But there is no clear winner.

How could it not become a core issue? The standard model of cosmology the universe started with a Big Bang, inflated exponentially, and has been expanding ever since (made up of regular matter, dark matter, and dark energy in a 5:25:70 proportion) is possibly at stake. The most advanced observatories humans have ever put into orbit to measure extraordinary phenomena can't agree on a single value for the expansion rate.

One, the Planck Observatory, looked at the cosmic microwave background (CMB). That’s the first light ever released in the universe. It is considered the light echo of the Big Bang, emitted once the universe was cool enough for neutral atoms to form, the light no longer shackled to them.

Scientists examining the teeth of ancient pandas discovered at a fossil site in southern Germany have identified evidence that rewrites our understanding of their evolutionary history. Unlike modern pandas, these extinct bears were omnivorous.

Existing giant pandas are famous for their laziness and their fastidious diet of bamboo shoots, leaves and stems. In fact, they are the most herbivorous species in the whole Carnivora order (mammals that are specialized in primarily eating meat), despite having the digestive system of a carnivore.

This makes the eating habits of modern pandas quite peculiar, and scientists are still not sure when they developed this specialized niche, especially as their ancestors were significantly less fussy.

An international team from Hamburg, Frankfurt, Madrid, and Valencia recently discovered the fossilized remains of an extinct species of panda, Kretzoiarctos beatrix, at the Hammerschmiede site in Allgäu, Germany.

K. beatrix is the oldest known ancestor of modern giant pandas. They lived around 11 million years ago and were slightly smaller than today’s species. Despite this, the extinct panda was still a chunky animal, capable of weighing over 100 kilograms (220 pounds).

To date, most of their fossils have been found in Spain, suggesting that pandas originated in Europe and migrated to China at some point in the past. But unlike modern pandas, K. beatrix was actually an omnivore, eating both plants and meat.

The researchers compared the fossilized teeth of K. Beatrix with those of other bear species, including polar bears, brown bears, South American spectacled bears, and both modern giant pandas and their extinct ancestors.

They concluded that the bear from Hammerschmiede did not specialize in hard plants, unlike its modern ancestors, but it also didn’t eat meat exclusively, like polar bears. As such, K. beatrix had a diet that was much more like modern brown bears, containing both plant and animal matter.

A plane has captured the first photo of a spacecraft reentering the Earth's atmosphere from a high-speed orbit as it flew over the South Pacific Ocean.

On September 8, the first of the European Space Agency's (ESA's) Cluster satellites named Salsa made its final journey to Earth. Launched in the year 2000, the four satellites that make up the cluster have spent their time in orbit dipping in and out of the planet's magnetic field, investigating how the Sun and the Earth interact.

Cluster is a constellation of four spacecraft flying in formation around Earth, ESA explains. They relay the most detailed information ever about how the solar wind affects our planet in three dimensions.

When the satellites were launched, space junk regulations weren't what they are today, and it was expected that the spacecraft would fall to Earth naturally with little control over where it would ultimately crash. That isn't ideal, however, and so the space agency responsible for it has monitored it as its mission came to its end, making adjustments to its course in order to push it into the atmosphere over the ocean where any debris that survives reentry will not cause harm to unsuspecting humans or animals below.

“Salsa’s reentry was always going to be very low risk, but we wanted to push the boundaries and reduce the threat even further, demonstrating our commitment to ESA’s Zero Debris approach, ESA Director of Operations, Rolf Densing, explained in a statement. “By studying how and when Salsa and the other three Cluster satellites burn up in the atmosphere, we are learning a great deal about reentry science, hopefully allowing us to apply the same approach to other satellites when they come to the end of their lives.”

A team of physicists have created a one-dimensional gas out of light, studying the strange properties of this strange state of matter.

When you cool certain particles to near absolute zero, some pretty interesting things can start to happen. In particular, something called Bose Einstein Condensate (BEC) can form, a state of matter first hypothesized by Albert Einstein based on the work of theoretical physicist Satyendra Nath Bose. When a gas of bosons subatomic force-carrying particles that have integer spin are cooled to temperatures approaching absolute zero, they form a single quantum object, often compared to it acting as a single atom.

The wave function of a BEC corresponds to the ground state of a macroscopic quantum object, one paper on the topic explains. In other words, a collection of atoms in a BEC behaves as a single quantum entity.

In this strange new state of matter, first created in the real world in 1995, you get a macroscopic look at quantum behavior.

It has plenty of weird properties, including zero viscosity. You get some of this stuff in a glass, it will crawl up the side of the glass. They can sustain vortices that can be used to create analog black holes, and explode in a way similar to a supernova, termed a bosenova. It's pretty clear why you'd want to study this stuff.

You can create BEC out of anything that obeys Bose Einstein statistics. This is easier with bosons subatomic particles with integer spin though you can create it too with fermion pairs, known as Cooper pairs, where the half spins add up to an integer, allowing fermions to occupy the same quantum state.

Photons, god bless them, obey Bose Einstein statistics and so can be turned into a BEC without any complicated pairing. In the new study, a team from the University of Bonn and the University of Kaiserslautern-Landau in Germany did just this, though with the added complication of creating the condensate in one and two dimensions.

The ocean wasn’t a fun place to be during the Mesozoic era, which featured a string of periods during which its waters were extremely depleted of oxygen, causing multiple marine mass extinctions. Now, a new study appears to have found the trigger behind this catastrophic chain of events.

What the team was looking for was evidence to support the theory that plate tectonics may have had a role. That’s because the Mesozoic, which spanned between 185 to 85 million years ago, was also the era during which the supercontinent Gondwana broke up. The team found evidence that as it did so, multiple pulses of phosphorus were released from basalt, a type of volcanic rock, on both the seafloor and continents.

On closer inspection, these pulses matched up with the periods of oxygen depletion, known as ocean anoxic events or OAEs – but were the two linked?

To test the theory out, the researchers used a kind of computer model called an Earth system model to simulate the effect that the phosphorus pulses would have on ocean chemistry, and found that it recreated the string of OAEs.

But how did an abundance of phosphorous lead to a lack of oxygen and, consequently, change the direction of marine life development?

After all, phosphorus is one of the essential elements for life – it’s involved in the formation of DNA and cell membranes and is a key component of cells’ main energy source, ATP. However, as the saying goes, there can be too much of a good thing.