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Science News Feb 22
🕑 Added 2023-02-22 16:00:05 +0000 UTC[This is a transcript with references.]
Welcome everyone to this week’s science news. Today we’ll talk about whether dark energy is made of black holes, four types of solar systems, exoboots, whether banning short-haul flights makes sense, 3D printing with sound, smart contact lenses, how copper makes fuel, a new method to extract carbon dioxide from seawater, and of course the telephone will ring.
A lot of people asked me to comment on a paper that made headlines last week by claiming that black holes are dark energy, so here we go.
All stuff in the universe carries energy. Mass is a type of energy because E equals mc squared and all that. But the universe contains different types of energy. The best current data say that about 4 percent of the energy in the universe is normal stuff like what we are made of. 22 percent is dark matter and the remaining 72 percent is dark energy.
Dark energy and dark matter are two different things with different properties and different effects. Dark matter is the stuff that makes galaxies rotate faster, dark energy is responsible for the expansion of the universe. Black holes, as commonly understood, are neither dark matter nor dark energy, they are formed from the collapse of stars and subsequent mergers or accretion. They are made of and behave like normal matter. The vast bulk of these 4 percent normal matter is gas, either in galaxies or in intergalactic space. Black holes make up at most a few percent of those 4 percent.
This by itself already tells you that the idea that black holes are dark energy is politely speaking difficult to make sense of. I’d require a small fraction of 4 percent to come out being 72 percent, and if you can make that happen then maybe you could make your magic work on my ad revenue thank you.
But let’s look at what they did in the paper. It’s actually two papers. In the one paper they did an extended data analysis of a sample of black holes in galaxies at different distances from us. Roughly speaking, the farther away the galaxy, the younger it is. So, this means their data collects galaxies of different ages and that allows them to infer how fast the black holes in them grow. They find that supermassive black holes grow by about a factor of seven to twenty in 9 billion years which is faster than expected from models of mergers and accretion.
In the other paper they then suggest that really these black holes might be made of dark energy. If that was so, then their mass would grow with the cosmological expansion, so that could explain the observations. And indeed, they find that the observed growth fits with this idea extremely well, a cynic might say suspiciously well, but we don’t want to be cynical, do we.
Be that as it may, just because the mass of an object increases doesn’t mean it’s made of dark energy. The defining property of dark energy is that it has a negative pressure that’s equal in magnitude to the energy density. They don’t explain how black holes would give rise to this negative pressure; they just assume they do.
Let me just say I am not particularly convinced by this, eh, argument, if you can call just assuming your conclusion an argument. For one thing, the theory is sketchy to say the least. And they can of course not actually track the growth of black holes because that takes billions of years. Instead, they look at the typical size of black holes in a certain type of galaxies of different ages. There are a lot of uncertainties in getting from samples of galaxies at different ages to the growth of black holes.
Most importantly, we don’t ever observe all galaxies and we don’t observe all supermassive black holes in those galaxies. So they have to extrapolate from the observed sample to the total population. And the observations have errors, so it’s difficult to infer the black hole masses. They discuss this all in their first paper and conclude that if they account for all those uncertainties they still can’t explain the growth of the black holes though I’d have expected the error bars to be larger.
In any case, they propose a few other tests of the idea that includes precision measurements of the cosmic microwave background at low angular momentum, strong lensing of gamma ray bursts, and a couple of other predictions that are conveniently difficult to check.
The biggest problem with this idea is the claim that there is something in need of explaining in the first place. Einstein’s theory of General Relativity has two free parameters. One is the strength of gravity, also known as Newton’s constant. The other is the cosmological constant. The cosmological constant is a constant of nature and it determines the curvature of empty space. It explains all observations currently attributed to dark energy. It doesn’t have to be “made of” something any more than Newton’s constant has to.
I really think physicists are screwing themselves over by calling this constant dark energy. If they’d called it more appropriately “empty space curvature” no one would think there’s anything mysterious about it.
It seems likely to me that soon enough someone else will come up with a perfectly mundane explanation for the data and you’ll never hear of this idea again. Meanwhile I’d like to propose that really the universe is made of 100 percent dark humour.
Now here’s some real space news, a research team in Switzerland has developed a classification of planetary systems.
When you think of a solar system you probably think of something like this. Small planets near the sun, bigger ones farther out. But it turns out this isn’t necessarily the case. In their new paper, the astrophysicists looked both at observations of 41 planetary systems, as well as a database of computer-generated ones. They then classified these systems by the distribution of sizes of planets and found that they come in four different types.
You can see them in this illustration. Some, like ours, are “ordered.” Small planets near the sun and getting bigger as you move away. Then there’s the “anti-ordered” class. The planets are big near the sun, and they get smaller as they get further away. There’s the “mixed” class with no real pattern at all, and finally the “similar” class in which the planets sit like peas in a pod. Guess which of these is the most common?
Peas in a pod turn out to be most common. These systems make up about 80 percent, in good agreement between observation and simulation.Anti-ordered and mixed are about 8 percent each. And it turns out that solar systems like ours are actually the least common.
So we may not quite be at the centre of the universe, but we can still insist we’re kind of special.
From exoplanets to exoskeletons. A group of researchers in the United States has developed a better way to correct balance with exoboots.
Being bipedal isn’t easy. Humans have a relatively high centre of mass on a pretty small base, which means our muscles are constantly working to prevent us from toppling over. But if your ankle gives way it takes about 130 milliseconds for neurons in the brain to send a message to the ankle to correct posture, and sometimes that isn’t fast enough.
It’s not such a big problem for most of us. But it can be for people who have mobility issues due to injuries or neuropathic diseases, or maybe also workers in difficult environments, such as uneven or shaking ground. So, engineers have started to make exo-boots with motors that stabilize the ankles and prevent falls.
In the new paper that was just published in Science Robotics engineers report that exoboots work better if they act before the brain sends its own signal rather than piling onto a correction that’s already underway. They fitted ten people with ExoBoots and put them on a surface that randomly shifted one way or the other. They found that the posture was most stable when the ExoBoot reacts about 100 milliseconds faster than the human brain. In this case the participants withstood 9 percent more perturbations in their balance than if they corrected the motion entirely on their own.
I like the direction this research is taking, let’s just stop using brains, it’s too much trouble.
A group of researchers from the UK and Spain looked at how many carbon dioxide emissions could plausibly be saved by cutting down on short-haul flights, in a case study of Germany. It’s a timely investigation since France just banned short-haul flights if there’s a rail alternative taking less than 2 and a half hours.
But switching from planes to trains has downsides. Not only does it increase travel times in many cases, a lot of short-haul flights bring people in for overseas trips, so if the train’s delayed, that causes a big problem.
One can reasonably question whether the trouble is worth it. While about 2 percent of global carbon dioxide emissions come from airplanes, only 81 percent of those come from passenger flights. And of the passenger flight emissions only a third come from short-haul flights. If you multiply all these percentages, you get a total of less than half a percent of global carbon dioxide emissions. And of course, replacing the flight with something else won’t make those emissions disappear entirely.
But just how much can one reasonably save? In this study, they looked at Germany because the country has both a lot of short haul flights and train connections that could potentially be used as replacements. Indeed, the German railway has a “rail and fly” program in partnership with several airlines. In case that sounds good, the last time I tried to take a train to the airport the train didn’t go and neither did the next one and I ended up calling a taxi.
For their new paper, the authors analysed data from passenger bookings, airline schedules and train schedules for 87 routes across Germany, and then calculate alternatives to short-haul air travel. They found that between 53 and 272 thousand flights could be avoided. But the easiest flights to avoid are the shortest ones, so correspondingly the carbon dioxide emissions that are prevented are not all that much. Altogether they find that Carbon dioxide emissions would be reduced between 2 point 7 and 22 per cent.
They also warn that this would cause longer travel times which people would find inconvenient. Therefore such bans would only make sense if neighbouring countries have similar regulations. Otherwise people would just replace short-haul flights in one country by short-haul flights to another country where the ban isn’t in place.
I would propose that we shrink the diameter of Earth to 1 kilometre so we can bike everywhere, that’ll fix it, you heard it here first.
A group of researchers at the Max Planck Institute in Germany has figured out how to 3D print objects with sound waves.
You can now seemingly 3D print anything from guns to teeth to houses. But one of the issues is that it’s slow because you have to do it layer by layer. If you’ve ever made croissants yourself, you’ll understand the problem. Scientists have therefore been trying to come up with a faster method, a “one shot fabrication” as it’s been dubbed.
But how do we do that? Spontaneously combusting things into existence would be pretty cool, unfortunately that violates a few laws of nature. The next best idea that researchers have come up with, at least for small objects, is to embed microscopic grains into a fluid, use ultra sound to move them into the right positions, and then use light or chemical reactions to fix the grains in place all at once. The problem for this has been to come up with the right sound field to create arbitrary shapes.
But they’ve now figured out how to do it and you can see here how it works. Pay attention to the centre of the metal circle. The sound waves are trapping these tiny particles that are floating in water and then move them into the right place. It takes a while and the density seems somewhat low, but in the paper they put forward a way to calculate the sound field that at least in principle would work for any possible shape.
They have done that for a couple of different materials. Here you see grains of silica gel. These are biological cells, more specifically mouse myoblasts that could eventually form muscle. A nice thing about this method is that the sound waves are gentle, so they don’t damage the cells. And finally, they used microscopic hydrogel beads.
The researchers say that the method might have other uses, such as stimulating nerves inside the brain.
Hi Elon,
Nah, I like writing papers about quantum mechanics. If I’d wanted to be a billionaire, I’d have been born into a billionaire family, hadn’t I.
I appreciate the thought.
A Korean research team has figured out how to 3D-print contact lenses that can show signals directly on the eyeball.
Smart contact lenses have been on the drawing boards for several years, ever since Google realized people don’t like walking around with bulky glasses that announce they’ve got too much money in their bank account. Google has since developed a contact lens for diabetics that monitors glucose levels and transmits the information to other devices. But the quest for contact lenses that can be used in place of smart glasses for augmented reality has not gone particularly well. One of the pioneers, Mojo Vision, exited the field just last month.
The Korean group now found a particularly inexpensive way to make it work. They used a 3D printer to create a mould for a contact lens and poured in a hydrogel. Then they inserted rings of transparent electrodes made of a type of glass, an electrolyte solution as a battery, and used electrochromic ink to print shapes on the contact lens. The electronic ink can change colours when the right signal comes from a nearby sender. Then they hooked the sender to a GPS receiver, and showed that it was capable of displaying driving directions onto the lenses.
Of course in a car you can project the arrows onto the wind shield, and cars will soon drive themselves anyway. But I’m sure those lenses will come in handy at the next thanksgiving dinner when you need to know whether cousin George is about to turn left or right.
Researchers from Lawrence Berkeley National Laboratory in California have been able to film how copper gets hold of carbon dioxide and converts it into fuel.
One of the most obvious and in my opinion most underexplored ways to mitigate climate change is to replace conventional fossil fuels with synthetic fuels. That’s because the issue with fossil fuel isn’t so much that it releases carbon dioxide in and by itself. It’s that it releases carbon dioxide which has been underground for a long time. But if you create fossil fuels with solar energy by taking carbon dioxide out of the air, then burning those fuels doesn’t increase carbon dioxide levels. The good thing about this solution is that we already have the infrastructure for using this kind of fuel.
But how do you do that? Well, you take carbon dioxide and water and energy, and rearrange the molecules to make, for example, propane, which is a type of fossil fuel. For this you need a catalyst. Scientists have known since the 1970s that copper makes a good catalyst for this reaction but just exactly how it works, they didn’t fully understand.
In the new study they have now been able to take images of the process by using a combination of an electron microscope and x-rays spectroscopy. The discovered that nanoparticles of copper, given the merest hint of energy, change shape into copper nanograins which grab onto the carbon dioxide, and force the carbon atoms to accept another electron which then facilitates the reaction with water.
The researchers hope that better understanding this process will allow them to produce synthetic fuels more efficiently.
A group of researchers from MIT have come up with a new method to extract carbon dioxide from seawater.
Increasing carbon dioxide levels affects the ocean in many ways. First because the water warms up with the atmosphere, which is bad for many species, for example coral reefs. Warmer water can carry less oxygen which is bad for many species, for example coral reefs. And the ocean absorbs part of the carbon dioxide from the atmosphere, which makes the water more acidic. This is bad for many species, for example coral reefs. Coral reefs are basically the perpetual piñata at the carbon dioxide party.
But there’s a positive side to this, which is that carbon dioxide is much more concentrated in sea water than in air, measured by volume. In air, the concentration is roughly a microgram per litre, whereas in seawater it’s about 100 times higher. So if you want to suck carbon dioxide out of the atmosphere, a smart way to do it is to let the ocean absorb it and then filter it out of the ocean.
The currently used method to do this is called “bipolar membrane electrodialysis” and requires special membranes that are quite expensive to produce.
In the new paper, the researchers now propose a new method that works without those membranes. It works with bismuth and silver electrodes that swing the pH value of the water from roughly 8 to 7. This converts the dissolved inorganic carbon back into carbon dioxide which is removed using a low-pressure system. The water is then fed through a second container in which the voltage on the electrodes is reversed which swings the pH value back to slightly alkaline before the water’s discharged back into the ocean.
In their experiments, they were able to remove 87 percent of the dissolved inorganic carbon. They say that the process requires less energy input than other methods, does not produce unwanted by-products, and is comparably inexpensive. They are, however, still trying to work out how to strip the carbon dioxide gas from the water without the need of a low-pressure system because that’s both inconvenient and energy intensive. Another issue is that the electrodes are degraded during the process which quickly reduces their efficiency.
So there are still a few challenges on the way to saving the world, but stay tuned, we’ll be back next week with more amazing news from the world of science.
Comments
Rad Antonov
Thanks for covering the black hole paper. I didn’t understand the mechanism by which the black holes grew to be more massive than expected. They didn’t explain any physics, just threw out a scaling relationship and fit the data to determine k. Is there a GR question here that perhaps deserves closer theoretical scrutiny?
In a 1 km diameter Earth you can walk everywhere, you don't need even a bike!
D Brown
It seems like many of your observations are veiled references to Occam's Razor.
