Science News May 31 (Patreon)

[This is a transcript with references.]

Welcome everyone to this week’s science news. Today we’ll talk about a new study that sheds doubt on the big bounce model of the universe, quantum repeaters, a quantum simulation of curved space time, a snake-robot, metamaterials in space, underwater mining, how to compute with water, who’s to blame for climate change, and of course, the telephone will ring.

I’ve got several requests to comment on a paper from researchers at the University of Vienna that made rounds last week. It appeared on a few science websites with the somewhat vague claim that the group created a quantum simulator that sheds light on quantum gravity or something like that.

Before I shed light on the paper, please allow me a more general comment. Most of these science websites just repeat press releases. The press releases are written by people who get paid to make their institution look good, and who for the most part don’t understand the content of the paper. They’re usually informed by the authors of the paper, but the authors have an interest in making their institution happy. The result is that almost all science headlines vastly exaggerate the novelty and relevance of the research they report on.

This is why we always look at the papers and it’s why, as you have probably noticed, our science news tends to be a little more, shall we say, grounded, than your average popular science news. Some might say we’re boring; I would say we’re realistic.

Now about the paper that the headlines were about. It doesn’t contain the phrase “quantum gravity”. You don’t even need to read the paper to figure that out, you can just search it.

The paper is the report of an experiment. For this experiment, they trapped two clouds of about 20 thousand Rubidium atoms on a chip with a bunch of electric and magnetic fields. The clouds have the shape of a cigar and are a fraction of a millimetre long. They couple the two clouds together with more electromagnetic fields and then decouple them. This creates a kind of shock wave traveling through the clouds. Then they measure the correlations between the clouds after various time intervals.

The rest is interpretation. The interpretation says that perturbations in the atom clouds behave as if they were perturbation in a curved space-time, if you identify the speed of sound in the gas clouds with the speed of light in space-time. This is because you can use the electric and magnetic fields to make the speed of sound in the gas dependent on the place. So, you can manipulate how the perturbations travel kind of like it would happen in a curved space-time. Then you can call that a “quantum simulation” of a curved space-time.

Here’s what they don’t say in the press release. These atom clouds that they used for the experiment are cigar shaped which means they’re effectively one-dimensional. But there’s no gravity in only one dimension of space. You don’t have to take my word for it, you can look it up in Weinberg’s book on general relativity. So even the link to a curved space-time is somewhat of a stretch.

Now look, I don’t mean to be dismissive. This is a nice experiment and all and I hope they have fun with their Rubidium atoms, but it isn’t going to teach us anything about quantum gravity.

A new paper that was just published in PRL casts doubt on the idea that the universe went through a big bounce, rather than starting with a big bang.

Physicists have many ideas for the beginning of our universe. The simplest one is a Big Bang where the energy density in the universe was incredibly high. The Big Bang did not happen at a particular point but everywhere. If you find that confusing, you’re not the only one, and you’ll be happy to hear that I made a video about this in particular.  

The second most popular idea is that, yes, the universe had this phase of high energy density, but it wasn’t the beginning. Rather, it was itself the end of a previous phase in which the universe contracted. This is called a “Big Bounce”. There are several of these Big Bounce models. The best known one is probably Penrose’s Cosmic Cyclic Cosmology, which you can learn about in my previous video.

However, it isn’t the best-studied one because it’s kind of difficult to figure out how to use Penrose’s model, I speak from my own experience. The most studied bounce model is probably that of Loop Quantum Cosmology . It’s based on the idea of Loop Quantum Gravity, the main competitor of string theory.

This image shows the temperature fluctuations in the cosmic microwave background, CMB for short, that is all around us. This image shows what’s known as the power spectrum, that roughly speaking counts how many temperature patches there are in the microwave background at each size. On the left are the large patches. If you squint your eyes you can see that for the large patches , the measurement results, that are the dots, are somewhat below the red curve, that’s the prediction from the big bang model. if you squint even more you might see that every second one of them seems to be higher.

The discrepancy isn’t huge, but bounce models inspired by Loop Quantum Cosmology have the advantage of reducing this discrepancy. Here you see some examples for how the curves would look for bounce models. Note how they fit better on the left side.

In the new paper they now say that if you have a bounce model which does that, it would also have another property, which is to induce new correlations in the CMB. They’re known as the bi-spectrum or three-point correlations. I know this sounds somewhat intimidating but don’t worry, only thing you need to know is that these correlations don’t seem to be there.

The authors now say you can’t have your cake and eat it too. Either you have a bounce model that explains the large scale CMB properties, but then it screws up the bi-spectrum. Or it agrees with the bi-spectrum, but then it doesn’t help with the large scales.

This doesn’t rule out bounce models. To begin with it’s only a particular type of bounce models that they looked at. It does take away one of their appeals, but there’s still the appeal that you can make them more complicated and continue writing papers about them.

Quantum repeaters have moved closer to application, I repeat, quantum repeaters have moved closer to application.

A new article that was just published by researchers from the University of Innsbruck in Physical Review Letters has taken us a step close to the quantum internet.

The quantum internet is a planned network which can maintain quantum properties during transmission. There’s a lot of money going into this at the moment because physicists have managed to convince governments that it’ll be useful for secure data transfer. The issue with the quantum internet is that the signals are weak, and they get screwed up easily. This means that along the line you have to amplify and repeat them.

A repeater for non-quantum signals, receives an electrical signal as input, and outputs an amplified copy. This allows signal transmission over long distances without losing power. Unfortunately, the very reason that the data on the quantum internet is safe is that you can’t measure it without destroying it. But this also means you can’t read it out and copy it.

The idea of a quantum repeater gets around this problem by using a process called entanglement swapping. It basically works by using a sequence of shorter but robust quantum links with initially no signal on them. Then you take the quantum signal that you want to send, don’t measure it but just swap it onto the shorter links, station by station. That way, you don’t ever need to look at the message to pass it on. It’s like you can retweet Elon without reading what he wrote.

The new paper now reports that the researchers were able to use quantum repeaters to transmit quantum information over the length of two optical fibres, each 25 kilometres, separated by the repeater. This allowed them to send quantum information over 50 kilometres basically without information loss. It’s a new record and moreover, they did it with optical signals at the standard wavelength of telecommunication networks.

So maybe it won’t be long until we have the quantum internet and then you’ll understand why I keep making jokes about it.

Hi Albert,

Yes, I know this was a little dense. But finding an analogy for quantum mechanics is as difficult as, ah, I can’t think of a good analogy.

I can’t think of a metaphor either. Quantum mechanics is just weird, like ancient Egypt, all cryptical symbols and worshipping cats.

Spooky. Yes, like talking to dead people you mean. I get it. Talk soon.

NASA engineers  have built a snake robot designed to explore tricky parts of Earth, our moon and other places in the solar system.

The robot is called EELS. Yes, that’s another smart acronym, it stands forExobiology Extant Life Surveyor. It haslittle churning blades that let it move across sand or snow or ice.

The design allows it to slide into lava tubes, glaciers, and to go under water. The robot’s head has four pairs of stereo cameras fitted with lidar. That way it can create a 3D map of its environment and make decisions about where to go. You can see it being lowered into a glacier in Canada here. . One of its uses could be to look for signs of life in the ocean beneath the icy surface of En’celadus, one of the moons of Saturn, which would require slipping down narrow vents and swimming.

The snake robot is made up of components with 28 little motors like steering wheels. And its skin can sense how much pressure it is exerting on its surroundings which is useful for climbing.

I’m just not sure, based on what I see in the video, where they’re gonna plug it in?

I know you’re all tired of me going on about meta-materials, but I’m sure before you know they’ll be everywhere. Indeed, they’ll soon be in space. The European Space Agency is about to test the use of meta-materials to slim down optical equipment.

Metamaterials are not the next big thing in material science, they’re the current big thing. They have custom-designed nanostructures that give the material desired optical, electrical, or acoustic properties. I talked about this in more detail in an earlier video.

The European Space Agency, a Bulgarian start-up,and the Australian Research Council have banded together to test optical meta-materials for space.  Most importantly they want to know how well the materials will cope with the rough conditions during take-off and how much they will degrade in space.

Besides allowing new ways of directing and manipulating light, meta-materials have another benefit which makes them attractive for space-travel. It’s that they are smaller and lighter than traditional optics components, and it’s easier to shed a few pounds of weight by replacing a piece of glass than convincing astronauts to cut back on the pizza.

By the way we have a newsletter with some additional news items that don’t make it into the video. It goes out once per week and is completely free. You can sign up for it at sabinehossenfelder dot com slash newsletter.

According to new research from scientists at the Helmholtz Centre for Polar and Marine Research, underwater mining is more problematic than we thought.

Underwater mining or deep sea mining has become an increasingly hot topic in recent years, both politically and scientifically. It turns out that in some areas, the ocean floor is covered with “nodules”. They look like rocks but are extremely rich in minerals such as nickel and cobalt, minerals that we need for all those batteries that are supposed to get us to net zero. There’s a lot of money to make there. But scientists have warned about the possible environmental harm of messing around in the deep seas, which are one of the least-researched places on Earth.

In the paper the researchers say that nodules have another problem. It’s that they’re radioactive.  Turns out that the nodules absorb radioactive isotopes of thorium and protactinium from water and sediment. These isotopes themselves are created by the decay of dissolved uranium isotopes in the ocean. This has been going on for a few million years and the resulting level of radioactivity can be substantial. Though they depend on the location, according to the researchers the levels can be up to 1000 times the currently allowed amounts. Whew! Thank goodness it wasn’t 1001 times!

The highest risk probably comes from inhaling the stuff. In case it seems unlikely that someone might accidentally inhale a fist-sized rock, the issue is that the nodules are typically crushed and dried as part of mining operations. There is also the problem that you need to remove the radioactive compounds before using the stuff for something else. Maybe we could just power cars with little nuclear reactors? What could possibly go wrong?

A paper by researchers from Australia proposes that we compute with water. Yes, water.

The behaviour of some physical systems is difficult to compute algorithmically. In such cases you can however still simulate the system by using another system as model that you can control. This is the idea behind wind tunnels, and also that of quantum simulations.

The idea of the new computer is that you identify certain features in the water and learn to initiate them for further computation. These first tests were done using a tank of water as an analog computer. Suitably programmed, this water-computer was able to “remember” past inputs and predict a set of chaotic and random data better than a conventional computer given the same data.

The researchers say that this could become a prototype for a new type of microchip that would use fluid properties as the basis of computation. A particularly promising basis for computation are soliton-like waves, or solitary waves

The chips would also enable cheaper and more reliable forecasting for chaotic data sets like financial markets, natural disasters, and weather which could make them competitors for quantum computing, where progress is currently, erm, treading water.

When faced with a problem as large as climate change, the most important thing to do is of course to find someone to blame for it. Blaming is much more convincing if you have science to back it up. A recent study now provides ammunition forthat.

A group of sociologists has quantified the financial reparations that fossil fuel companies owe society to atone the damage they have caused to the climate and, with that, to all of us. They used a model based on a previous study’s estimate for how much fossil fuel emissions will shave off the global GDP between 2025 and 2075. The number they arrived at is a stunning 70 trillion US dollars.

The authors say the responsibility should be split evenly between fossil fuel producers, the organizations who use fossil fuels, and the politicians who fail to regulate their emissions.

Within the group of fossil fuel producers, companies are further divided into three groups based on the wealth of the nation they’re based in as well as ownership structures. The idea is that companies from richer countries should contribute more to paying reparations than that of poorer countries.

The highest payers would be Saudi Aramco with 42 point 7 billion us dollars, followed by Gazprom with a little more than 20 billion and ExxonMobil, with 18 point 4 billion. Those amounts would have to be paid annually for 25 years in a row.

This is the first quantitative study attempting to hold fossil fuel companies accountable for their actions. The next question might be what to use the money for. Are they going to pay? Well, if we’re going to phase out fossil fuels what are they going to pay with? Until someone’s figured that out, I think I’ll keep on dusting those solar panels.