The gravitational field of a rotating black hole is powerful and strange. It is so powerful that it warps space and time back upon itself, and it is so strange that even simple concepts such as motion and rotation are turned on their heads. Understanding how these concepts play out is challenging, but they help astronomers understand how black holes generate such tremendous energy. Take, for example, the concept of frame dragging.
Black holes form when matter collapses to be so dense that spacetime encloses it within an event horizon. This means black holes aren’t physical objects in the way they are used to. They aren’t made of matter, but are rather a gravitational imprint of where matter was. The same is true for the gravitational collapse of rotating matter. When we talk about a rotating black hole, this doesn’t mean the event horizon is spinning like a top, it means that spacetime near the black hole is twisted into a gravitational echo of the once rotating matter. Which is where things get weird.
Suppose you were to drop a ball into a black hole. Not orbiting or rotating, just a simple drop straight down. Rather than falling in a straight line toward the black hole, the path of the ball will shift toward an orbital path as it falls, moving around the black hole ever faster as it gets closer. This effect is known as frame dragging. Part of the “rotation” of the black hole is transferred to the ball, even though the ball is in free fall. The closer the ball is to the black hole, the greater the effect.
This view of the M87 supermassive black hole in polarized light highlights the signature of magnetic fields. (Credit: EHT Collaboration)A recent paper on the arXiv shows how this effect can transfer energy from a black hole’s magnetic field to nearby matter. Black holes are often surrounded by an accretion disk of ionized gas and dust. As the material of the disk orbits the black hole, it can generate a powerful magnetic field, which can superheat the material. While most of the power generated by this magnetic field is caused by the orbital motion, frame dragging can add an extra kick.
Essentially, a black hole’s magnetic field is generated by the bulk motion of the accretion disk. But thanks to frame dragging, the inner portion of the disk moves a bit faster than it should, while the outer portion moves a bit slower. This relative motion between them means that ionized matter moves relative to the magnetic field, creating a kind of dynamo effect. Thanks to frame dragging, the black hole creates more electromagnetic energy than you’d expect. While this effect is small for stellar mass black holes, it is large enough for supermassive black holes that we might see the effect in quasars through gaps in their power spectrum.
Reference: Okamoto, Isao, Toshio Uchida, and Yoogeun Song. “Electromagnetic Energy Extraction in Kerr Black Holes through Frame-Dragging Magnetospheres.” arXiv preprint arXiv:2401.12684 (2024).
The post Another Way to Extract Energy From Black Holes? appeared first on Universe Today.
Rongoā Māori is the “indigenous way of healing”: a combination of herbal and spiritual medicine used by the Māori of New Zealand. As The Encyclopedia of New Zealand notes, there were both supernatural and human illnesses, with the former treated through spiritual means (e.g., prayers, dunking in water, and other treatments described below), and the latter through herbal remedies. Here, for example, are the supernatural maladies and remedies:
Mate atua – supernatural illnessesMate atua were supernatural afflictions, sometimes caused by malevolent spirits when a person had broken a tapu (religious restriction). Dealing with mate atua required a tohunga (priest). His first job was to determine the hara (transgression) committed, and to identify the spirit. The tohunga took a thorough case history of all the patient’s actions before they got ill, sometimes including the patient’s and family’s dreams.
A tohunga’s jobTohunga were experts in various fields, including the arts, agriculture, fishing, warfare and healing. They were also seen as the earthly medium of the gods, and were intensively trained in whare wānanga (houses of higher learning). Tohunga held a position of authority and respect, but also had the huge responsibility of keeping their people healthy.
Finding the cause was the first stage of treatment, followed by exorcism of the spirit that had possessed the patient. The next stage was a whakahoro (purificatory rite) to remove the effects of the tapu. This usually involved dipping the patient in a stream while the tohunga performed a karakia (prayer) or incantation.
MariungaThe Ngāti Porou leader Tuta Nihoniho described the mariunga – a wand of wood such as karamū, māpou or maire, which was touched to the body of an invalid and received their essence. It was then taken to a tohunga, who could tell whether the patient would recover.
Takutaku riteAnother rite, the takutaku, involved touching the patient with a karamū leaf, which was then floated downstream. The malevolent spirit would be carried to sea and then to Te Waha o te Parata (a huge whirlpool, caused by a great monster), and finally to the underworld. Freed of the spirit, the patient was then sprinkled with, or immersed in, water.
The site also lists a number of herbal plants used for “human” illnesses, although, as far as I know, none of them have been tested by the gold standard of modern medicine: controlled, randomized, and double-blind testing. I have no doubt that some of these plants do work, but in the absence of testing we won’t really know which ones, and how efficacious they are.
As Wikipedia notes, these forms refer. .
. . . . to the traditional Māori medicinal practices in New Zealand. Rongoā was one of the Māori cultural practices targeted by the Tohunga Suppression Act 1907, until lifted by the Maori Welfare Act 1962. In the later part of the 20th century there was renewed interest in Rongoā as part of a broader Māori renaissance.
Rongoā can involve spiritual, herbal and physical components. Herbal aspects used plants such as harakeke, kawakawa, rātā, koromiko, kōwhai, kūmarahou, mānuka, tētēaweka and rimu.
The practice of Rongoā is only regulated by the Therapeutics Products Bill in the case of commercial or wholesale production so that “Māori will continue using and making rongoā just as they have for generations.”
The Tohunga Suppression Act outlawed traditional medicine in favor of “Western” medicine, but, as the note above shows, the ban lasted just 55 years, and Rongoā Māori is now again legal, though its practitioners often realize that they need to send patients to modern doctors if a traditional cure doesn’t look propitious.
However, there seems to be a move afoot to make Rongoā Māori coequal to modern medicine, if not in curative properties at least in “deep mutual respect.” But, those two items are not independent, for how can a modern physician respect medicines that haven’t been properly tested, much less have any respect for supernatural cures?
What is bad about the attempt to get “deep respect” for indigenous medicine that hasn’t been properly vetted, is that with medicine, unlike with incorporating other indigenous ways of knowing into teaching (e.g., Māātauranga Māori), human lives and health are at stake, so I do have issues with the article below in the ANZ Journal of Surgery (click to read for free).
This study is really an anecdotal one, and with a very small and geographically limited sample, too. The authors recruited four colorectal “Western” surgeons (WS) from the Christchurch region of New Zealand, all of whom had expressed interest in Rongoā Māori (RM). Likewise, the authors recruited seven Rongoā Māori practitioners, four of whom volunteered to be part of the study. Therefore we have a total of eight subjects, all of whom were asked their views about the medicine practiced by the other group. The interviews took place once, and were 30-60 minutes long. The actual study thus lasted a maximum of eight hours.
The upshot:
Western surgeons’ perspectives on RM
The results are no surprise: the doctors didn’t know much about RM. But they were “open to collaboration”, though it wasn’t clear what kind of collaboration. (I can understand that a Māori patient might want a Māori RM practitioner around, at least for solace and cultural comfort.) And of course the doctors thought that, in general, there needs to be better communication between practitioners of modern and of indigenous medicine. Finally, the surgeons cited “systemic barriers, such as bureaucratic hurdles and the absence of clear referral pathways” as impediments to collaboration or “integration”.
Rongoa practitioners’ perspectifes on modern medicine
The indigenous doctors “often feel overlooked within the healthcare system. And this leads to the article’s theme: that modern medicine must be infused in some way with indigenous medicine: a “genuine collaboration”. For instance we read this:
Rongoā practitioners often feel overlooked within the healthcare system. This highlights the need for initiatives that aim to raise the profile of Rongoā Māori within New Zealand’s healthcare system (Table 1). One practitioner mentioned ‘collaboration is minimal, at this stage like the non-Māori community certainly don’t even know that Rongoā exists or anything about it and so that’s not being referred’.
. . . Formulating a genuinely collaborative approach requires recognition of Rongoā Māori as a an option in the patient care journey. ‘Building relationships is key… maybe starting with shared learning experiences,’ one practitioner suggested, proposing foundational steps towards effective collaboration.
. . . . This perspective challenges the healthcare sector to move beyond tokenistic inclusion, advocating for a genuine integration of Rongoā Māori that honours its potential to contribute to improved health outcomes, particularly for Māori patients.
. . . Understanding Rongoā Māori in its full depth requires acknowledging and valuing its comprehensive approach to health, which integrates the spiritual, mental, and physical dimensions of well-being.
The problem here is that we do not know the potential of RM to contributed to improved health outcomes–not without scientific testing of RM remedies, especially the “spiritual” ones. The article refers repeatedly to “mutual respect” of the two types of medicine, as well as the advantage of RM in being “holistic” (presumably meaning it uses spiritual cures as well as medical ones).
The conclusion, which was inevitable, is that modern medicine should collaborate with RM in curing patients. I quote from the paper (bolding is mine):
As identified in the interviews, it is imperative that a curriculum for healthcare professionals encompasses not only the theoretical concepts but also the practical applications of Rongoā Māori. This requires a willingness to move beyond a cursory acknowledgement of Indigenous practices within the medical education system to embedding it as a vital component of healthcare training. It was proposed that an effective educational initiative could take the form of an immersive wānanga on a marae, where tauira (students) and tākuta (doctors) would have the opportunity to learn directly from Rongoā practitioners in a setting that honours the roots of the mātauranga.28–30 In addition to this, incorporating placement based learning would further enable Western practitioners to observe the holistic model of care first hand. This aligns with the insights from the interviews where it was emphasized that Rongoā Māori is dynamic in its practice and does not follow a prescribed regimen.17 By having the opportunity to experience this personalized approach, healthcare professionals can better appreciate the value of nurturing this collaborative relationship.
. . .Recognizing the immense benefits that a holistic model of healthcare offers, there is an unequivocal need to navigate and dismantle the systemic barriers that Rongoā practitioners are faced with. This necessitates a concerted push to ensuring Indigenous healing practices are formally recognized within healthcare frameworks to facilitate a collaborative coexistence with Western medical practices. Moreover, establishing structural support to facilitate funding and infrastructure is an essential component to enhancing the capacity of the current healthcare system to address a diverse range of health needs and allowing this to thrive. It is paramount that this collaboration is guided by Rangatira and Tohunga in this field to ensure the delivery of health services is culturally congruent and responsive. The move towards an inclusive healthcare system that respects the diversity of cultures aligns with Te Tiriti o Waitangi’s principles, honouring Māori sovereignty and self-determination over their health.
“Te Teriti,” of course, is the 1840 Treaty of Waitangi, which made England the sovereign government of New Zealand, conferred on the Māori British citizenship with all the attending rights, and allowed Māori to keep their lands and possessions. But there is nothing about health in that treaty at all, though of course anybody can “self determine” whether they get care, and whether they get RM care, modern medicine, or both. But the Treaty of Waitangi has assumed an almost sacred position in New Zealand culture, now viewed as mandating that all aspects of Māori culture and “ways of knowing” must be considered coequal in the country. Right now there’s a big battle about how far Māori “ways of knowing” are taught as coequal to science in schools, and the indigenous people seem to be winning that fight. This article is just a salvo in the battle for medicinal hegemony.
But before they win the Battle of Medicine, any RM-based cures, whether they be based on plants or supernaturalism, must be tested—and tested according to the best procedures of modern medicine, usually double-blind, randomized, and controlled trials. Without those trials, you simply can’t be sure that a treatment works. Saying “our tradition shows that it works” is not sufficient, nor is the claim “well, it worked for me!” We all know the power of confirmation bias and of the placebo effect, and the kind of testing described above is designed to eliminate these effects. (As Richard Feynman famously said, “You must not fool yourself, and you are the easiest person to fool.”)
So no: there cannot be deep mutual respect between indigenous medicine and modern (aka “Western”) medicine until indigenous treatments are tested according to the standards of Western medicine. It will not work the other way around.
I am heartened that some RM practitioners recognize when herbs and superstition won’t work, and summarily hand their patients over to modern doctors. But I don’t think RM should be integrated with modern medicine, or treated with great respect. Until it’s proven efficacious, the null hypothesis should be that the untested treatments of RM comprise quackery
The campaigning for President reaches a fever pitch today, and then tomorrow people head for the polls to cast their vote (many of us, including me, have voted by mail already). This is of course an unscientific poll of readers, so let’s call it the Nate Goldenberg poll. There are two of them, and of course votes are anonymous. First, tell us your own choice:
Note: There is a poll embedded within this post, please visit the site to participate in this post's poll.and then tell us who, in your view, will win:
Note: There is a poll embedded within this post, please visit the site to participate in this post's poll.I’ve left the second poll unexpired because we have no idea how long the vote-counting will go on!
Of course you are encouraged to leave comments pertaining to both questions.
My friend Andrew Berry, who teaches and advises biology students at Harvard, has long had the bug that infected me when I was younger: the desire to trek in Nepal, where the mountains are impossibly high. This summer he took a long guided trek into little-visited parts of Nepal (guides are required for these places), producing a great 37-minute video (bottom) accompanied by music and sound. (For further mountain adventures, see Andrew’s one-hour video of his 2023 trek to Dolpo and the fabled Kingdom of Mustang, featured in these pages.) The notes below are his:
Limi Valley Trek, June ’24
Like Jerry, I’ve spent a lot of time over the years in Nepal, most often on a trail, trekking. It’s hard to beat a high altitude encounter with the mightiest mountains on earth. I’m on an academic schedule, which means that I have plenty of opportunity to go travel over the summer, but unfortunately trekking, Nepal, and the summer don’t really go that well together. The most pressing of my university responsibilities cease around the beginning of June. The monsoon typically arrives in Nepal in the middle of that same month, veiling the mountains in banks of cloud, soaking the trekker (and everyone else), and delighting/stimulating/exciting the voracious leeches that inhabit the montane forests. In short, monsoon trekking is pretty dismal.
There are however some regions of Nepal that are less affected by the monsoon than others. Specifically, the further west and north you go, the less the impact. It is, after all, the Bay of Bengal branch of the monsoon that inundates Nepal, so it is coming from the east. Heading north is to take advantage of the rain shadow imposed by the main cordillera of the Himalaya. Some regions of Nepal are north of the range — they’re politically Nepal but geographically, culturally, and linguistically Tibetan. In summer ’23 I went to Dolpa and Mustang, this summer to Simikot, the main town in the NW corner of Nepal. This kind of trekking is a far remove from the kind of ‘teahouse’ trekking that Jerry and I are accustomed to: you walk from village to village and stay in local accommodations, meaning that you can get away with carrying little more than a sleeping bag. To visit the more remote areas, you’re required to have expensive permits and to be accompanied by officially recognized guides. In addition, because these routes take you beyond inhabited areas, it’s necessary to camp and to be self-sufficient in food and other supplies. The result of these joint requirements is a logistically complex undertaking — thank goodness for the excellent outfitter I work with in Kathmandu, Raj Dhamala of Himalayan Trekkers.
I’ve always wanted to go to Simikot. After spending six months in Nepal before going to university, I had a map of the country on the wall of my room for all three years of college. As I stared at it, Simikot came, for me, to symbolize the remote, inaccessible Nepal that had been out of bounds for me the year before (for financial and permitting reasons). It’s taken a few years actually to convert that fixation into an actual visit (42, if you insist on asking!), but I’m happy to report that Simikot didn’t disappoint. The town is clustered around a Twin Otter landing strip, a slice of the horizontal — well, a slice of gentle slope — in a world of plunging verticals. The mighty Karnali river crashes through its gorge far, far below. Plenty of trekker-tourists come through (for many, it’s a jumping off point for a visit to Buddhism’s holy mountain, Kailash, in Tibet), but Simikot remains primarily an administrative and trading center. Google Translate’s influence has not apparently extended to Simikot (or at least it hadn’t when this sign was painted)
Our route started — initially in a Jeep — and finished in Simikot. Two weeks. Its main focus was the Limi Valley, which runs W-E just south of, and parallel to, the Chinese/Tibetan border. An upside of the timing is that this is the time of year that livestock — cattle, sheep, goats, yak — are moved up to high altitude summer pastures, meaning that we frequently encountered people and their animals undertaking the same seasonal migrations that their ancestors (both human and animal) have done for aeons. It truly is a privilege to spend time in such spectacular country, and to meet so many people living lives so far removed from ours. With Raj in Kathmandu, I had discussed the possibility of tacking on a (minor) peak ascent on to the trek, but I ended up wimping out. Just a hike for me: 5000m (16,400′) over passes is plenty high enough for me. I think Ang Dawa, one of three wonderful Sherpa guides with me, was a little disappointed by this lack of serious climbing (he’s summited Everest five times, so he’s entitled to his disappointment)
Here’s a video montage from the trip. I like to take panoramic photos in country like this, and I think a slow pan across images like these is the best way to appreciate the scenery. Also, I can’t resist shooting plenty of video too. So much to see!
Be sure to enlarge the video:
I was away last week, first at CSICON and then at a conference in Dubai. I was invited to give a 9 hour seminar on scientific skepticism for the Dubai Future Foundation. That sounds like a lot of time, but it isn’t. It was a good reminder of the vast body of knowledge that is relevant to skepticism, from neuroscience to psychology and philosophy. Just the study of pseudoscience and conspiracy thinking themselves could have filled the time. It was my first time visiting the Middle East and I always find it fascinating to see the differences and similarities between cultures.
What does all this have to do with alternating vs direct current? Nothing, really, except that I found myself in a conversation about the topic with someone deeply involved in the power industry in the UAE. My class was an eclectic and international group of business people – all very smart and accomplished, but also mostly entirely new to the concept of scientific skepticism and without a formal science background. It was a great opportunity to gauge my American perspective against an international group.
I was struck, among other things, by how similar it was. I could have been talking to a similar crowd in the US. Sure, there was a layer of Arabic and Muslim culture on top, but otherwise the thinking and attitudes felt very familiar. Likely this is a result of the fact that Dubai is a wealthy international city. It is a good reminder that the urban-rural divide may be the most deterministic one in the world, and if you get urban and wealthy enough you tend to align with global culture.
Back to my conversation with the power industry exec – the power mix in the UAE is not very different from the US. They have about 20% nuclear (same as the US), 8% solar, and the rest fossil fuel, mostly natural gas. They have almost no wind and no hydropower. Their strategy to shift to low carbon power is all in on solar. They are rapidly increasing their power demand, and solar is the cheapest new energy. I don’t think their plan for the future is aggressive enough, but they are moving in the right direction.
What I did not encounter was any defensiveness about fossil fuels, denial of global warming, or any conspiracy nonsense. The UAE is the world’s 8th biggest oil producer, so I would not have been surprised if I had. At the end of the day, the science and the tradeoffs are pretty much the same. There are regional differences in terms of how much wind, sunshine, and water there is locally, and that affects the calculus, but everyone is dealing with the same technologies. But I still found it fascinating to be in a conversation with someone half-way around the world, from an entirely different culture, and hit all the same talking points that I have been discussing for years. We even discussed net metering (he was in favor) and Germany’s poor decision to shut down their nuclear industry.
And, of course, the conversation turned to the question of AC vs DC (which he brought up). Most nerds and technology history buffs know that there was a big fight between Edison and Tesla about whether or not the electricity infrastructure in the US should be alternating or direct current. Edison favored direct current, while Tesla favored alternating current. AC won out largely because it is more efficient to transmit over long distances and to alter the voltage with transformers.
The question of AC vs DC is raising its head again, however, because technology has changed. I am not an expert in electrical engineering, and I have had enough conversations with experts to know that this topic is very technical and complex. So I am not going to try to explain the technical details, but just discuss some of the main issues. There are essentially two reasons to rethink the AC vs DC choice. The first is that as technology has improved, the advantage of AC over DC had diminished. The transformer advantage still exists, but transmission efficiency is not as big of an issue as it was. AC and DC are not very different over short and medium distance, but AC still has an increasing advantage over longer distances.
But the second reason has to do with solar power and electric vehicles. An increasing number of homes have both, and even battery backup to boot. And, in the opinion of many experts, with whom I agree, it is a reasonable goal to maximize the number of residential homes that have all three – solar, EVs, and battery backup. All three of these technologies are DC. So in such a home the solar panels convert their DC power to AC, which then gets converted back to DC to charge the EV. You can have either DC-coupled or AC-coupled battery systems – in the former the power remains DC, while in the latter it is converted to AC before being stored in the battery. DC-coupled systems are more efficient (97.5% vs 90%).
In a modern home, therefore, there could be an entirely DC system where the power from the panels to the battery to the EV (which is just another batter) is all DC. The car battery can then also more easily be used as additional storage without conversion. Every time you convert AC to DC and back you get about a 3% energy loss, and having an all DC system would avoid that loss.
In terms of appliances, it’s a mix. Many of the bigger appliances, like refrigerators and dishwashers, use AC. While most of the smaller appliances, like computers, light-bulbs, and microwaves, use DC power. In order to have a 100% DC home, therefore, all that is necessary is to convert a few large appliances to DC, or for them to have their own DC to AC converter. DC also makes sense for a distributed power system, rather than distant centralized power production. Microgrids could be all DC. All of this makes some experts advocate for a future with residential DC power grids and all DC homes. We would likely need a hybrid system where we will have AC for long distance transmission. There is also still the advantage that AC is easier to alter voltage, but that is not a deal-breaker for DC if the home system were all at the same voltage.
The largest barrier, of course, is technology inertia. It is difficult to change over entire industries and change standards. At this point it’s difficult to predict what will happen, and the default will be for no change. I suspect, however, that this conversation will increase as the penetration of solar power, home battery backup, and EVs increases. At some point “going DC” for the home may be a thing, with the advantage of knocking 10% or so off of electricity demand (by eliminating multiple conversions).
It may happen first in developing nations and those who are currently building a lot of new infrastructure, like the UAE, leaving older industrialized nations with their crusty technology.
The post AC vs DC and other Power Questions first appeared on NeuroLogica Blog.
If you’re curious to know what my book is about and why it’s called “Waves in an Impossible Sea”, then watching this video is currently the quickest and most direct way to find out from me personally. It’s a public talk that I gave to a general audience at Harvard, part of the Harvard Bookstore science book series.
My intent in writing the book was to illuminate central aspects of the cosmos — and of how we humans fit into it — that are often glossed over by scientists and science writers, at least in the books and videos I’ve come across. So if you watch the lecture, I think there’s a good chance that you’ll learn something about the world that you didn’t know, perhaps about the empty space that forms the fabric of the universe, or perhaps about what “quantum” in “quantum physics” really means and why it matters so much to you and me.
The video contains 35 minutes of me presenting, plus some Q&A at the end. Feel free to ask questions of your own in the comments below, or on my book-questions page; I’ll do my best to answer them.