Science News June 14 (Patreon)

[This is a transcript with links to references.]

Welcome everyone to this week’s science news! Today we’ll talk about evidence against dark matter that might also be evidence for dark matter, atoms that breathe, noise cancellation with plasma, wireless power transmission in space, just and safe limits for ecosystems, an update from NASA’s mission to the Asteroid Psyche, swarms of microbots, artificial molecules, moon time, and of course, the telephone will ring.

Three groups of astrophysicists have presented analyses from binary star systems. Two of them claim that the results strongly disfavour dark matter and instead favour modified gravity. The third claims the exact opposite.

We have a lot of astrophysical observations that tell us we’re missing something important. Galaxies rotate faster than they should. Galaxies in clusters move too fast. Gravitational lenses are too strong. The microwave background doesn’t look right, the universe overall is too structured. If we just use Einstein’s theory of General Relativity and the matter that we know and like, it doesn’t work correctly.

Physicists have come up with two ideas to resolve this conundrum. One is to say that the universe is filled with a transparent substance that hovers around galaxies in clouds. It’s called dark matter. The other idea is that there’s something wrong with our understanding of gravity. This idea is called modified gravity. For slow moving bodies this modified gravity simplifies to what’s known as Modified Newtonian Dynamics, MOND for short.

MOND was first proposed by Mordehai Milgrom almost exactly 40 years ago, and the recent results were discussed at an anniversary conference in St Andrews last week. They’re analyses of data from wide binary systems. A wide binary system, as the name suggests, is a system of two stars that orbit each other at a large distance, often thousands of times the distance from the earth to the sun.

The thing is now that the way MOND works is that its effects become noticeable at small acceleration which loosely speaking means weak gravitational fields. You don’t notice MOND near massive bodies because the acceleration is too high. This is why MOND can’t be measured in the solar system. It also shouldn’t affect close binaries. But it should affect some of the widest binaries. Dark matter, on the other hand should have a negligible effect on all those binaries because there just isn’t enough of the dark stuff to affect them.

The data come from ESA’s Gaia mission. The first paper appeared in April and says that the data are consistent with unmodified Newtonian gravity for not-so-wide binaries, but the really wide ones seem to prefer modified gravity. This is what you’d expect if MOND was right. The second paper appeared in May and agrees with that. It says that the data provide evidence for the breakdown of standard gravity. The third was a presentation at the workshop and says there’s no evidence for modified gravity in wide binaries,but rather 16 sigma evidence against it.

According to Marcel Pawlowski, who is enjoying the controversy with plenty of popcorn at hand, the discrepancy might be an issue of sample selection. The latter analysis which seems to find evidence against modified gravity uses only binary systems that are so far apart they should *all see the modified gravity effect, so the calibration might have gone wrong.

This isn’t an issue that will be sorted out next week, but we’ll keep you up to date, so keep the popcorn at hand.

Researchers from the University of Washington have measured how atoms breathe. That’s what the press release said in any case. Have you ever heard of atoms breathing? I didn’t even know they had lungs.

Okay, what the heck does it mean that atoms breathe? They don’t of course. The researchers are talking about phonons, that are collective motions of atoms in materials. There are many types of phonons, depending on how they move. One particular type of phonon is a concentric contraction and expansion of the atomic lattice. It’s called the “breathing mode”. Planet earth also has a breathing mode. It slightly contracts and expands every 10 minutes or so.

In this new paper now, the authors report they have created such a breathing mode in an atomic lattice together with a photon, that’s a quantum of light. It was an accidental discovery. They wanted to create a system that would emit a single photon, and for that they used several layers of a tungsten compound.They then poked it with a laser, which shifted around some electrons. When the electrons flipped back into place, out came not only a photon, but also a breathing mode of a phonon.They played around with this some more and found that they could tune the strength of the interaction between the phonon and the photon by applying a voltage. And all on a tiny chip only a few micrometres in size.

The researchers say that this way of linking photons with phonons could come in handy for quantum information technology and they’re probably right. Even the tungsten atoms found this research breath-taking.

Your Airpods might have active noise cancelling, but do they have a plasmacoustic metalayer? Maybe they soon will.

The more people there are on our planet, the harder it becomes to avoid noise. Small surprise that noise reduction is a booming business. At the moment, you can either use materials that absorb or scatter noise, such as earplugs or foam mattresses. Or you can have active noise cancellation that works by creating a signal that destructively interferes with the one you want to get rid of. Problem with both of those approaches is that they don’t work for all frequencies or only for steady signals, or both.

A group of Swedish researchers has now created a prototype for an active noise cancelling device that uses plasma. In a paper that just appeared in Nature Communications, they explain how they used nothing but ionized air and wires to deaden sound.

It works like this. They have a collector electrode in a grid-form and an emitter electrode that’s a set of thin wires with air between them. That’s the metalayer. When the emitter electrode receives power, it ionizes the air nearby and pushes around air molecules. The researchers then use a microphone to pick up sound, calculate the required voltage to cancel it and effectively let the ions stop the air motion.

It works very much like noise cancelling headphones, but it doesn’t have a membrane, it moves the air directly. This works much faster and over a larger range of frequencies.

In their experiment they used a device just about three centimetres thick to absorb sound waves from twenty to 2000 Hertz almost perfectly.

That’s really impressive. But we must remember to think about the potential impact of this new technology on our social lives. If it wasn’t for the noise, maybe we’d never get to speak to our neighbours.

We’re one step closer to beaming down solar power collected in space to Earth, an idea I talked about in detail in this earlier video.

Space-based solar power has recently attracted attention as a source of clean energy. The idea is to build a huge solar collector in space, about 1 to 2 kilometres in diameter and then beam the energy down to earth with microwaves.

The biggest problems with the idea are that it’s expensive, the efficiency is unknown, and the receiver on the ground takes up a huge area which I think is what’ll ultimately kill the idea.

But researchers from Caltech have now made headway on the second point. In January, they launched a prototype of a solar power satellite into space to test power collection and transmission. One of the prototype’s main features is the MAPLE experiment. Another one of those smart acronyms, this one standing for Microwave Array for Power-transfer Low-orbit Experiment.

MAPLE consists of two separate receiver arrays about a foot away from a single transmitter. The researchers have now demonstrated for the first time that they could transfer energy in space, and they have also successfully beamed down a tiny bit of this energy to earth.

Several other tests are planned for this satellite, such as checking that the photovoltaic system works properly in space and that components can be deployed as desired. I for sure am glad they’re beaming the power down from space. Just imagine what a mess it’d be with cables.

An international team of researchers has developed a set of eight system boundaries for our planet. It’s supposed to help us stay within limits that are save and just for us and the environment.

They distinguish between “just” boundaries that minimize harms to humans and “safe” boundaries that maintain Earth’s systems with no consideration for humans.

Here’s a visualization. The purple lines show “safe” boundaries, the blue lines show “just” boundaries, the green lines show “safe and just” boundaries, and the Earth icons show where we are currently in relation to those boundaries.

According to this paper, the safe boundary for climate change is 1 point 5 degrees Celsius above the pre-industrial era, while the just boundary is 1 degree above. So we haven’t breached the safe boundary yet, but we have breached the just boundary.

For the biosphere, “safe and just” boundaries require that 50 to 60 percent of land are natural ecosystems but we’re currently falling short with 45 to 50 percent.

For water, the safe and just boundaries require us to affect just 20 percent of surface water every month in order to protect ecosystems. Currently, we’re only below this threshold in two thirds of the world.

Sounds like a good idea.

--Because if recent history has taught us one thing, it’s that humans will respect safe limits if you just tell them it’s the smart thing to do.

Hello?

Mr. President.

Yes, the infrastructure for electric vehicles requires substantial investment but…

Yes, carbon capture has been proved to work in the laboratory but…

Yes, synthetic fuel can be used to replace fossil fuel but…

When they told you to talk to a scientist, I don’t think they meant…

Thanks for calling in!

NASA’s mission to the asteroid Psyche is back on track. Its launch was originally scheduled for a period between August and October last year but had been delayed due to software issues. Good to know it’s not just me.

The main goal behind the Psyche mission is to learn more about planetary cores and the formation of our own planet. We know very little about Earth’s core despite, well, living on top of it. Scientists think that Psyche might have a similar composition to that of earth’s core.

The project’s delay was caused in part by Covid-related issues, which led to essential parts being late to arrive for assembly. This meant that the software used on those parts wasn’t properly tested, eventually making it impossible for the mission to take off in its original launch window.

In response, NASA revamped the workflow, adding team members and more oversight. A review two weeks ago showed that those changes were effective, and NASA has announced a new launch window, from October 5 through 25 later this year. The spacecraft is expected to reach the asteroid by 2029, and then maybe psychology will become science.

Researchers at the University of Mainz have shown that swarms of simple, microscopic robots can behave in surprisingly organized ways.

The researchers used groups of small robots, a few centimetres in size, that are powered by light. I can’t quite decide whether they look more like mice or like cockroaches. When they’re not being steered, the robots normally walk in straight lines. But the researchers changed the length, stiffness, and shapes of the robots’ legs to make them walk in different patterns, for example in circles. Then they put them in a confined space. As you can see here, the robots will cluster on some parts of the boundary and push there. That’s because this position is difficult for them to get out of.

The scientists then developed a computer model for this behaviour, and found that it should work with larger swarms and smaller robots under quite general circumstances. This is interesting because it could be a simple way to organize tiny robots so that they move around a larger object. They also found some rather weird synchronized motions though I’m not sure what that’d be good for other than looking dazzling.

Those bots aren’t going to deliver pizza to your door, but maybe they can one day deliver drugs to specific areas of the body.

By the way, if you prefer reading over watching videos, we now have a written version of our weekly science news on substack, and some extra material, too. You find us there at science w t g dot substack dot com.

Scientists from Radboud University in the Netherlands have created artificial organic molecules.

How can something both be artificial and organic? Okay, let’s unwrap this. That the molecules are organic doesn’t mean they’re laid by free range chickens, but rather that they contain carbon-carbon or carbon-hydrogen bonds. That they created an artificial version of those means they created structures in another material, about 10 times as large as the actual molecule, but so that the electron clouds behave almost the same.

Why’d you want to do that? Because that way you can better study and observe these molecules. It’s an example of what’s known as a quantum simulation where you take one quantum system that you can control to study another system that you want to better understand. We’ve talked about that a few times in the past. It’s kind of a boom area in physics at the moment.

For this new paper, they used caesium atoms and an indium-tin surface which they observed with a scanning tunnelling microscope and spectroscopy. They started with an artificial version of one of the most basic organic molecules, benzene, and built up larger molecules from that. Though this is only a test run, it’s a versatile method that has the potential to one day aid the development of new compounds.

Last time I saw an artificial molecule it was Styrofoam balls held together by toothpicks, so I find that quite impressive.

You’ve heard of Eastern Standard Time and Central European Time and maybe you’ve even heard that they’ve renamed Greenwich Mean Time to Coordinated Universal Time, probably so that the Brits wouldn’t constantly tell us we’re mispronouncing Greenwich. But have you heard of moon time?

The European Space Agency is considering giving the moon its own time zone to better coordinate future moon missions. Currently, moon missions run based on the time zone of the country launching the spacecraft. This is going to be very confusing once there’s more than one country up there. The options are to either synchronize moon time with the coordinated universal time or to give the moon its own time zone.

Using earth time on the moon sounds simple enough, but little Albert here has some things to say about that. You see, Einstein taught us that the passage of time depends on how much you’re accelerated. Earth’s gravity is stronger than that of the moon, so on the surface of earth you’re more accelerated and time passes slower. The difference is 56 microseconds per day.

The issue is now that the moon is supposed to get its own satellite positioning system. If this system were to use Earth time, it’d constantly have to be corrected to account for the different passage of time, which would make it cumbersome and prone to error. That’s not good if lives might depend on getting the location on the moon exactly right. On the other hand, using two completely different time systems might make communication with Earth more difficult.

Well, I guess they have some time left to sort this out before the first people move to the moon. Personally, I’d be happy if Americans and Europeans could agree on which day to switch to summertime.