JProthero

Muon-Catalyzed Fusion [1].

Briefly it's a genuine, and scientifically uncontroversial, form of 'cold' fusion enabled by muons — a more massive relative of the electron that was in the news recently thanks to the potentially interesting results coming out of the Muon g-2 experiment at Fermilab [2].

Like conventional 'hot' plasma fusion, in all experiments to date the energy input needed to sustain the process has exceeded the output, but it may be possible to use it to generate power. Unlike conventional fusion though, it receives relatively little attention, and there is no well-funded international effort to tackle the associated technical challenges. As with conventional fusion the technical challenges seem formidable, but it could be an interesting technology if a way could be found to make it work.

Listeners of Lex Fridman's podcast may recall that it was briefly mentioned in the episode he made last year with his father, Alexander Fridman, who is a plasma physicist [3]. As someone who has been interested in the idea for years and barely hears any mention of it, I was pleasantly surprised it came up.

It was also covered on the MinutePhysics YouTube channel in 2018 [4].

[1] https://en.wikipedia.org/wiki/Muon_catalyzed_fusion

[2] https://www.youtube.com/watch?v=O4Ko7NW2yQo

[3] https://www.youtube.com/watch?v=hNCz-8QIWuI

[4] https://www.youtube.com/watch?v=aDfB3gnxRhc

Bonus fact: Muon-Catalyzed fusion was first demonstrated by the Nobel laureate Luis Alvarez, who, with his geologist son Walter Alvarez, later proposed the 'Alvarez hypothesis' for the extinction of the dinosaurs by asteroid impact.

> What's the material difference, in your opinion, between the threat of the central bank selling back existing government bonds, and the government just creating new bonds of precisely the same type.

In the former case (where the central bank sells back government bonds it has previously purchased from investors as part of a quantitative easing scheme), all else being equal, money is withdrawn from circulation and the total stock of government debt remains the same.

In the latter case (where the central bank does not sell any of the government bonds acquired from investors and the government issues new bonds of equal value instead), the total stock of government debt increases, and assuming the government spends the money raised from selling the new bonds as is usually the case, the amount of money in general circulation remains the same (though investors in government bonds have less of it, to the extent that they are not net recipients of the increased government spending).

This is assuming the simplest model; in practice of course, the details will differ consequentially depending on how these processes operate in different jurisdictions. For example, to the best of my knowledge the central banks I'm most familiar with are required to remit interest payments on government debt back to their national treasuries; and in the European Union, direct central bank monetisation of government debt is supposed to be illegal — things like this complicate the picture in reality.

I can see from your other comments that you are well-informed about these details, so I would defer to you there.

> Wait a second there. There are different attitudes about falsifiability?

Yes.

My understanding is that Karl Popper first proposed falsifiability as a criterion for a scientific theory in part because he found that some supposedly scientific ideas (Freudian psychoanalysis was a particular target of his) failed to make predictions that could be definitively tested: it was a feature of these 'theories' that they could be interpreted in such a way as to accommodate any conceivable observation.

I think you are right that there is a strong consensus among scientists that for a theory to be considered scientific, it must make predictions which can be tested empirically, so that those predictions can be either verified or falsified. The difficulty some scientists have with a strict attitude towards falsifiability though is that many theories that make falsifiable predictions in regimes where the theory can be tested, also make consequential predictions about phenomena that are not readily observable, and might not even be observable in principle.

For instance, observations suggest that the universe is expanding at an accelerating rate; that the pace of expansion increases with distance; and that the expansion is unconstrained by the speed of light. This means that there are vast numbers of galaxies which were once receding from the Earth slowly enough that signals from them (e.g. light that can be imaged by telescopes) could be detected on Earth, but which are now receding from Earth faster than light. Without instruments capable of probing the universe with signals that can exceed the speed of light (something that is currently thought to be impossible), the future of these distant galaxies that have crossed the 'particle horizon' [1] will be forever unknowable to observers on Earth. Predictions about the future evolution, or even existence, of those galaxies are therefore not strictly falsifiable, because it would be impossible to make the necessary observations. Despite this, astronomers have no reason to believe that those galaxies cease to exist, or that the known laws of physics cease to apply to them, once they can no longer be observed by scientific instruments on Earth.

In other words, apparently credible scientific predictions could be made about a large and ever-increasing volume of the universe, but those predictions could never be tested observationally: they would be unfalsifiable. Currently accepted models suggest that, in the distant future, the entire universe except our local group of galaxies will recede into this unobservable domain, and will therefore be inaccessible to any astronomers around at the time.

String theory similarly makes predictions that might never in principle be testable (and thus falsifiable) because doing so is thought to require experiments that would necessarily collapse into black holes were they ever to be attempted.

Proponents of the Many Worlds interpretation of Quantum Mechanics arguably have a similar problem in that it is typically thought to be impossible to interact with the hypothesised other worlds in a way that could confirm or refute their existence. The cosmologist Sean Carroll (who is a proponent of the Many Worlds interpretation) has written a paper on this subject titled 'Beyond Falsifiability' [2], which is discussed on his website [3].

The physicist David Deutsch, who has played an important role in establishing the theoretical basis of quantum computation, has argued that a quantum computer could effectively demonstrate the existence of the other worlds of the Many Worlds interpretation [4], so falsifiability is perhaps less of a problem from that perspective.

[1] https://en.wikipedia.org/wiki/Particle_horizon

[2] https://arxiv.org/abs/1801.05016

[3] https://www.preposterousuniverse.com/blog/2018/01/17/beyond-...

[4] https://thereader.mitpress.mit.edu/the-many-worlds-theory/

The 'Ian Bell' referred to in this comment should be John Bell (John Stewart Bell).

From the article:

> The first of these ideas says that if demand for a product rises and the supply does not then its price is going to increase. Economists would say this is so basic that no one could really argue with it. So let me do so.

First, this assumes that there are no alternative products available. The reality is that there usually are. Few things are so essential now that this is not the case. Secondly, this assumes we will not wait for what we want. We often will, and that smooths demand.

That buyers may choose alternative products, and that purchases may be deferred, both seem to be valid observations to me, but neither amounts to an argument against the proposition that the price of a product will increase if demand for that product rises and its supply does not.

If buyers purchase alternative products, or defer their purchases, then they are not buying the product in question, and demand for that product therefore does not in fact rise.

The author appears to be trying to criticise an orthodox prediction in economics about what will happen under certain conditions not by — as he suggests he is doing — arguing with the logic of the prediction, but instead by asserting that the conditions the prediction applies to do not arise.

Regardless of whether his conclusions about price inflation make sense, he does not actually make the argument that he purports to.

It might also be worth noting that the current practice of quantitative easing incorporates a potential corrective mechanism for inflation that the traditional monetary expansion associated with historical episodes of hyperinflation did not.

When central banks engage in quantitative easing, they purchase financial assets (typically government bonds, corporate debt, stocks etc.) that can in principle be sold back to the market at a later date. When an initial central bank purchase is made, the amount of money in circulation increases, but that increase can be reversed if the asset is sold. If the asset is sold at purchase price, there is no net change in the money supply; if it is sold at a loss there is an increase proportional to the loss, and if it is sold at a profit there is a decrease proportional to the profit.

If money creation is instead used to, for instance, purchase consumable goods and services or pay wages (this is typically what happens when hyperinflation occurs), then the monetary expansion cannot be reversed in the same way — some other mechanism like tax rises would be needed.

The economic behaviour of the recipients of the newly created money is also significant. If consumers are the recipients then, all else being equal, the prices of the goods and services that consumers buy may be expected to rise. If banks and large corporate investors are the recipients of the money then, all else being equal, the prices of the things those organisations buy (principally investments like bonds and stocks) may rise.

My understanding is that the experience with quantitative easing has been that it has caused a kind of price inflation, but primarily the prices affected have been those of the assets purchased by institutional investors (i.e. stock markets have risen, and bond yields and interest rates in general have been suppressed).

The original observation about galaxy rotation curves never meant much to me. I didn't know enough astrophysics to have an intuitive appreciation of the significance of the disagreement between the theory and the measurements, and I felt that the universe was a sufficiently large and mysterious place that some unexpected observations — particularly at the scale of galaxies — were inevitable. It seemed arrogant to me to expect that vast, complex cosmic structures should perfectly obey the predictions of a classical theory that had been developed centuries before it was known that galaxies existed; before their scale, composition and distance from us were understood, and before it was known that we were inside one. I thought — and still think — that the universe is probably full of undiscovered phenomena, and that the discrepancy would gradually go away as more was learnt about the types of matter already known to physics; how much of it exists, how it behaves on large scales and how it is distributed.

I think I felt that the most likely explanation for the observations was what are now referred to as MACHOs (Massive Compact Halo Objects); massive but dark objects, like black holes, dust clouds etc., and I presumed there must be a lot more of them than thought. The assumption that the anomaly must be due entirely to a new form of matter seemed to me like jumping to conclusions; an unjustified leap.

One thing that began to change my mind was learning more about particle physics. I found it interesting that certain well-understood forms of matter were known to be oblivious to some of the fundamental forces of nature. Hundreds of billions of neutrinos pass through our bodies every second almost completely without trace because they do not feel either the electromagnetic force or the strong nuclear force. I did know about neutrinos when I first formed my views about dark matter, but I initially didn't connect the two.

As I thought more about the ability of some kinds of matter to ignore certain forces, I wondered whether there might be as-yet undiscovered forms of matter even more reluctant to interact than neutrinos are (neutrinos do at least interact via the weak nuclear force, hence how they have been detected). Given that neutrinos don't feel the electromagnetic interaction that dominates our visible world, perhaps there could be undiscovered forces that the matter we are made of is insensitive to as well. This led me to wonder whether there might be a whole zoo of 'shy' particles, perhaps similar to the normal luminous matter we are familiar with, but with their own complex interactions, structures and forces; existing around us, in the same spacetime we inhabit, but unseen. The idea of mutually invisible and non-interacting worlds existing side-by-side was fascinating to me; this is usually the province of speculative fiction, but perhaps there was some analogue to it in the real universe.

I found that this 'dark sector' physics was an active area of research for credible scientists. My understanding is that the latest work tends to indicate that this kind of self-interacting matter can't be the dominant component of dark matter, but the possibility of a role for unseen structure like this remains open, and the idea was so interesting to me that it prompted me to reconsider my views about dark matter.

I knew that before its detection was first confirmed, antimatter had been hypothesised to exist based on consideration of mathematical symmetries in physics. Working through the consequences of the symmetries of nature turned out to be a very productive method for discovering new particles, and the approach culminated in the theory of supersymmetry. In the early to mid 2000s, supersymmetry was well-established among leading particle physicists, and was regarded as the likey future of the field (along with the Higgs boson, it was a central motivation for the construction of the Large Hadron Collider). Supersymmetry predicted that many more particles and forces should exist than predicted by the standard model of paticle physics, and at some point I learned that it was a feature of supersymmetric models that the lightest particle they predict has the properties needed to explain the abundance of dark matter in the universe. This is known as the 'WIMP Miracle' (WIMP standing for Weakly Interacting Massive Particle). That the leading particle physics theory of the time was predicting the existence of a particle that just happened to have the properties needed to explain the observations that had first led dark matter to be postulated struck me as unlikely to be a coincidence.

I understand that supersymmetry has since fallen out of favour to some extent, partly because of disappointment that the LHC hasn't yet found the evidence for it that the particle physics community was hoping for, but I think it would be fair to say that it remains the most credible framework for future research at the moment.

At around the time I first learned of the WIMP Miracle I was also coming to understand more about cosmological inflation. In addition to its predictions being borne-out by measurements of the cosmic microwave background radiation (the Boomerang and WMAP experiments had recently pubished their results), inflation had several other properties that appealed to me, and the theory also happened to predict a mass-energy density for the universe that corresponded very well with the observationally derived abundance of dark matter.

Since then, more recent work to map the distribution of mass in the universe using gravitational lensing; computer simulations that strongly suggest dark matter is required to explain the observed large-scale structure formation in the universe; and more detailed studies of supposed astrophysical evidence like the Bullet Cluster, have all tended to reinforce the conclusion for me that dark matter probably does exist and is an as-yet undetected particle or class of particles.

I'm still a bit heterodox in my view about it though in that I hold out the hope for a significant role for self-interacting dark matter and dark sector forces, because I still think that's potentially the most interesting thing about it.

Thanks for this; reading your explanation reminds me of the objections I had too.

The author of the article apparently shares your view about dark matter — could you explain what you find objectionable about it?

It seems to me that there is a class of concepts in theoretical physics that some people take an almost instinctive dislike to: dark matter, string theory, eternal inflation and the many worlds interpretation of quantum mechanics are prominent ones. I get the impression that there is a correlation; a person who is sceptical about dark matter seems to be much more likely to be sceptical about certain other ideas too, and to have a more favourable view of alternatives like Modified Newtonian Dynamics and Bohmian Mechanics.

It's as though there is a sort of partisanship in opinion about theoretical physics: just as it is often possible to tell what somebody's view is likely to be about a whole slew of political issues if you know their opinion about one or two controversial topics, the same seems to apply to a large extent in theoretical physics too.

I'm fascinated by this because in the early to mid 2000s I would have counted myself as both a dark matter and many worlds sceptic, but I take the opposite view of both now, and I find it difficult to put myself back into my old frame of mind.

My sense is that the divide is somehow related to different attitudes to falsifiability, abstractness and explanatory parsimony.

I often find I've already read the article before I see it linked on HN, and its appearance on HN confirms that like-minded people also found it interesting, which is nice.

There are usually about 1-3 articles on the first page that I've read before seeing them on HN.

> Unfortunately each day I click 3x more links on HN than I have time to read through, so I don't always end up reading the article (which ends up in an ever-growing to-read list)

I can sympathise with this.

This might explain why the disappearance was a surprise to me. I never paid much attention to the Subreddit, other than checking to see why there had been an unannounced absence of new episodes for several months.

I remember that both the hosts encouraged audience engagement in different ways — several episodes featured long discussions about topics on the Subreddit, and they solicited audience participation in various projects.

Thanks for mentioning PeerTube — I've been keeping an eye on it for a while now. It has some of the features I noted, including one I didn't but should have; it's open source.

I think PeerTube or systems like it have a lot promise — particularly if more estblished channels on YouTube, and other media producers, were to start to promote them as alternative methods for accessing their output.

I think I agree that uploaders face more of a threat from censorious activists reviewing their old material than they do from retroactive deletion prompted by YouTube policy changes, but surely self-hosting would provide some protection, assuming the audience would be willing and able to transition to a different source?

It seems to me that hosting and payment processing companies ultimately present the greater service denial risk for uploaders with an established audience, though YouTube can definitely hamper new viewer discovery, and there is more competition (and therefore more alternatives) in hosting and payments.

This is my view too. I'm hopeful that eventually some combination of technologies that already exist (peer-to-peer sharing, tor, blockchain, homomorphic encryption, maybe even wireless mesh networking) will evolve into a decentralised hosting and delivery system that everyone will use.

I'm woefully uninformed to speculate about how feasible this might be though, so it remains just a hope for me.

I share the scepticism about the ability of startups to disrupt away the network effects that underlie these quasi-monopolies, but it does seem to me as though decentralisation is the logical and desirable end-point.

How and when that point could be reached though, I couldn't say.

I've watched both Grey's and Haran's videos since their early years on YouTube, and I'd be curious to know what the story is behind the disappearance of their podcast. It seemed like an odd development to me in view of how engaged they both appeared to be with their audience.

I know that Haran eventually posted a brief comment on Reddit acknowledging the hiatus, but it struck me as a strangely subdued way to announce the end of a regular series that had been very successful for several years.

The original article being discussed in this thread is about a doctor who believed that a form of 'body-switching' should be possible for humans, albeit in a relatively crude surgically-mediated fashion.

With the benefit of current scientific knowledge, most people who think carefully about personhood identify the brain as the seat of consciousness, and will tend to assume that any procedure that leaves the brain intact will leave the person intact too. If a brain (or a head in this case) can receive a 'body transplant' though, some will find it natural to wonder whether other radical interventions in the nervous system are possible; for instance whether subdivisions of the brain can be successfully transplanted, and what the effects of that might be.

That kind of speculation in turn prompts questions about the consequences that physical changes in the brain might have for conceptions of personal identity. Thought experiments about teleportation — in which all the physical matter of a brain is replaced while preserving its structure and function — offer a template for thinking about these questions by allowing their scientific and ethical consequences to be examined in the most extreme cases. The most extreme cases may or may not be realisable, but legitimate conclusions can nevertheless be arrived at by thinking about them.

Many of the most influential thought experiments in science were never conceived with the belief that they could be carried out in reality; that is often why they were thought experiments rather than laboratory exercises. The purpose of thought experiments is typically to help extend the theoretical investigation of scientific and philosophical ideas into realms beyond the reach of current empirical methods. They are a tool for considering interesting questions where attempts to test them cannot be made; sometimes this helps to inform practical experimental work, and sometimes the thought experiment itself is sufficient to reach reliable conclusions, if the reasoning is rigorous, and the underlying theory is demonstrably valid in enough areas where verification is possible for its extension to be trusted.

You might be on to something there: https://youtu.be/AtKnsxlUWr8?t=44

In the philosophy of personal identity, teleportation is an intellectual contrivance only intended to help clarify thinking about personal identity. Another version of the same concept is the 'Swampman' thought experiment [1], which is also obviously not intended to be taken seriously as a scientific possibility. Most thought experiments in the philosophy of mind and personal identity have this character, e.g. Mary's Room [2], the China Brain [3], Philosophical Zombies [4], the Chinese Room [5] etc.

Thought experiments are often not intended to be carried out empirically (Schrodinger did not poison cats, Maxwell could not summon demons, Einstein did not throw people off buildings or construct clocks made of light, and so on), but they are nevertheless useful tools that can lead to insights about the real world, or serve as inspiration for actual experiments (Bell tests [6] are perhaps a good example of this, as they derive directly from Ian Bell's careful consideration of a famous thought experiment of Einstein, Podolsky and Rosen [7]).

Quantum teleportation is also of course a real phenomenon [8], and it does have some of the same properties as the imaginary teleportation device that Parfit and other philosophers consider in their work, albeit that it has only been demonstrated at the atomic scale for now.

[1] https://en.wikipedia.org/wiki/Swampman

[2] https://en.wikipedia.org/wiki/Knowledge_argument

[3] https://en.wikipedia.org/wiki/China_brain

[4] https://en.wikipedia.org/wiki/Philosophical_zombie

[5] https://en.wikipedia.org/wiki/Chinese_room

[6] https://en.wikipedia.org/wiki/Bell_test

[7] https://en.wikipedia.org/wiki/Einstein_Podolsky_Rosen_Parado...

[8] https://en.wikipedia.org/wiki/Quantum_teleportation

There is a long tradition in academic philosophy of using this model of teleportation as a device for investigating questions of personal identity. Derek Parfit's 'Reasons and Persons' is probably the best-known treatment [1].

I think there are good reasons to believe this is not generally how the writers of Star Trek thought the transporters in their stories were supposed to work, but they weren't always perfectly consistent on the subject.

[1] https://en.wikipedia.org/wiki/Reasons_and_persons#Personal_i...

Perhaps the results of hand transplantation procedures, which have already been carried out successfully [1], could provide some insight into this question.

The functionality that hand transplant recipients obtain from the transplant apparently varies, but the results can be quite impressive. The Wikipedia article notes one recipient was able to use his transplanted hand to drink from a bottle of water a week after the procedure, and tie shoelaces after a few months.

If brains can successfully adapt to controlling a transplanted hand, under the right circumstances perhaps they can also adapt to multiple transplanted limbs, or a whole body.

[1] https://en.wikipedia.org/wiki/Hand_transplant#Long-term_func...

Here's a link to the video of an interview with Steve Furber [1], who worked on the chip's development, discussing this.

[1] https://youtu.be/1jOJl8gRPyQ?t=508

That was exactly my thought on reading that part of the article: that the author was describing Pagerank, but substituting Pagerank's design objective of algorithmically outsourcing quality judgments to the global community of website publishers with the programmer's prejudices instead.

I hope the project of improving on DuckDuckGo is successful though, and some of the other proposals in the article sound promising to me.

In the future I would like to see an open source search engine 'paid for' using some combination of homomorphic encryption, blockchain and Tor-style technologies to trade bandwidth and processing power with its userbase in exchange for search results and other services, but I don't have the expertise to assess how feasible that might be.

I have noticed the same problem with DuckDuckGo searches recently.

I hope that a verbatim search function will be restored in the future; I think it's an essential basic tool for a search engine, and without it the user can be left with the impression that the engine either doesn't understand what it is being asked to do, or that it is wilfully disregarding instructions because it thinks — often wrongly — that it has a better idea of what the user is searching for than the user does.

I can't see why Newton would lie to his friends and relations about something like this, but in the absence of a time machine and a brain scanner your interpretation is as valid as any other.

In any case, regardless of whether Newton's recollection of his own experiences was mistaken or confected, this is not a myth in the normal sense of being the product of invention or misconstrual by others long after the event.

This is only partly a myth; there are contemporary accounts from Newton's acquaintances noting how he described being inspired by observing the fall of an apple from a tree. It was the fact that an apple falls from a tree specifically in the direction of the Earth's centre that was said to have piqued his curiosity.

The apple falling on his head seems to have been a later embellishment.

The weight of a sample of matter depends on its total mass energy, and heat contributes to that total. If matter is cooled, it will weigh less, and vice-versa; if it is heated it will weigh more.

At the kinds of temperatures that normally exist on Earth, the thermal contribution to the total mass energy of a sample of matter is trivial, but in extremely hot conditions, like the first fractions of a second after the big bang, the situation is reversed.

>It seems that the energy is being stored somewhere, and that matter itself allows us to tap into that, but is not the place where it is stored. Is there anything I can read to better understand what we know about this?

Here are some quick recommendations for views on potential and gravitational energy:

This [1] is a short video from a presentation given by Alan Guth — an early proponent of inflationary cosmology — in which he outlines a thought experiment designed to illustrate how gravitational fields are associated with negative energy. This thought experiment is a standard feature of Guth's introductory talks on inflation; recordings of his academically-oriented talks with more rigorous treatments of the subject are available on YouTube.

The logic of the thought experiment that Guth describes in the presentation is not controversial among physicists, but there are different perspectives on how to describe it. Guth's former MIT colleague, Sean Carroll, prefers to avoid descriptions involving negative energy and says instead that energy is not conserved in General Relativity. He explains his perspective here [2].

The cosmologists Luke Barnes and Geraint Lewis discuss different perspectives on fields and energy conservation in this video [3].

In this video [4], the theoretical physicist Sabine Hossenfelder briefly discusses the physical reality of potentials in the context of the Aharonov-Bohm effect.

If you have several hours, Sean Carroll has a video series about the Biggest Ideas in the Universe [5]. I haven't been through the playlist yet myself, but I imagine he might go into some detail on the questions you raise, particularly in his discussion of Conservation (1), Force, Energy and Action (3), Spacetime (6) and Fields (9). The Q&A videos following each instalment might also be useful, because his audience frequently asks questions like yours.

[1] https://www.youtube.com/watch?v=15IGPyRHOaY

[2] http://www.preposterousuniverse.com/blog/2010/02/22/energy-i...

[3] https://youtu.be/bcE5RQ7A7Ys?t=423

[4] https://youtu.be/0GCHzbmMZf0?t=144

[5] https://www.youtube.com/playlist?list=PLrxfgDEc2NxZJcWcrxH3j...

The Chief Scientific Advisor to the British Government, Patrick Vallance (who is a clinical pharmacologist, and formerly president of research and development at GlaxoSmithKline, a pharmaceutical multinational), said this in a Government press conference on 17 April:

'The vaccine could come from anywhere. We've got a domestic vaccine discovery programme in the UK which is being supported, absolutely, as fast as we can go, but the vaccine can come from anywhere. GSK and Sanofi have announced they're doing a vaccine together, which is fantastic news. Most of the big companies are doing vaccines. This is going to come from somewhere, we just need to back lots of horses at the moment, and to make sure we're in a great position to access a vaccine when it occurs. And that's why organisations like CEPI are so important as well; to make sure that the world sees this as a way to get a vaccine, and we all need to be part of the same approach to trying to get as many vaccines as we can. And we may need more than one vaccine.'

Link to the press conference: https://youtu.be/jWOCpmjdHiw?t=1430

Some other comments have referred to the Gates Foundation's contribution to developing vaccines; the foundation's involvement in establishing CEPI (the Coalition for Epidemic Preparedness Innovations), which Vallance referred to, is a significant part of this.