Saturday, February 27, 2021

Schrödinger’s Cat – Still Not Dead

[This is a transcript of the video embedded below.]

The internet, as we all know, was invented so we can spend our days watching cat videos, which is why this video is about the most famous of all science cats, Schrödinger’s cat. It is really both dead and alive? If so, what does that mean? And what has recent research to say about it? That’s what we’ll talk about today.

Quantum mechanics has struck physicists as weird ever since its discovery, more than a century ago. One especially peculiar aspect of quantum mechanics is that it forces you to accept the existence of superpositions. That are systems which can be in two states at the same time, until you make a measurement, which suddenly “collapses” the superposition into one definite measurement outcome.

The system here could be a single particle, like a photon, but it could also be a big object made of many particles. The thing is that in quantum mechanics, if two states exist separately, like an object being here and being there, then the superposition – that is the same object both here and there – must also exist. We know this experimentally, and I explained the mathematics behind this in an earlier video.

Now, you may think that being in a quantum superposition is something that only tiny particles can do. But these superpositions for large objects can’t be easily ignored, because you can take the tiny ones and amplify them to macroscopic size.

This amplification is what Erwin Schrödinger wanted to illustrate with a hypothetical experiment he came up with in 1935. In this experiment, a cat is in a box, together with a vial of poison, a trigger mechanism, and a radioactive atom. The nucleus of the atom has a fifty percent chance of decaying in a certain amount of time. If it decays, the trigger breaks the vial of poison, which kills the cat.

But the decay follows the laws of quantum physics. Before you measure it, the nucleus is both decayed and not decayed, and so, it seems that before one opens the box, the cat is both dead and alive. Or is it?

Well, depends on your interpretation of quantum mechanics, that is, what you think the mathematics means. In the most widely taught interpretation, the Copenhagen interpretation, the question what state the cat is in before you measure it is just meaningless. You’re not supposed to ask. The same is the case in all interpretations according to which quantum mechanics is a theory about the knowledge we have about a system, and not about the system itself.

In the many-worlds interpretation, in contrast, each possible measurement outcome happens in a separate universe. So, there’s a universe where the cat lives and one where the cat dies. When someone opens the box, that decides which universe they’re in. But for what observations are concerned, the result is exactly the same as in the Copenhagen interpretation.

Pilot wave-theory, which we talked about earlier, says that the cat is really always in only one state, you just don’t know which one it is until you look. The same is the case for spontaneous collapse models. In these models, the collapse of the wave-function is not merely an update when you open the box, but it’s a physical process.

It’s no secret that I myself am signed up to superdeterminism, which means that the measurement outcome is partly determined by the measurement settings. In this case, the cat may start out in a superposition, but by the time you measure it, it has reached the state which you actually observe. So, there is no sudden collapse in superdeterminism, it’s a smooth, deterministic, and local process.

Now, one cannot experimentally tell apart interpretations of mathematics, but collapse models, superdeterminism, and, under certain circumstances, pilot wave theory, make different predictions than Copenhagen or many worlds. So, clearly, one wants to do the experiment!

But. As you have undoubtedly noticed, cats are usually either dead or alive, not both. The reason is that even tiny interactions with a quantum system have the same effect as a measurement, and large objects, like cats, just constantly interact with something, like air or the cosmic background radiation. And that’s already sufficient to destroy a quantum superposition of a cat so quickly we’d never observe it. But physicists are trying to push the experimental boundary for bringing large objects into quantum states.

For example, in 2013, a team of physicists from the University of Calgary in Canada amplified a quantum superposition of a single photon. They first fired the photon at a partially silvered mirror, called a beam splitter, so that it became a superposition of two states: it passed through the mirror and also reflected back off it. Then they used one part of this superposition to trigger a laser pulse, which contains a whole lot of photons. Finally, they showed that the pulse was still in a superposition with the single photon. In another 2019 experiment, they amplified both parts of this superposition, and again they found that the quantum effects survived, for up to about 100 million photons.

Now, a group of 100 million photons not a cat, but it is bigger than your standard quantum particle. So, some headlines referred to this as the “Schrödinger's kitten” experiment.

But just in case you think a laser pulse is a poor approximation for a cat, how about this. In 2017, scientists at the University of Sheffield put bacteria in a cavity between two mirrors and they bounced light between the mirrors. The bacteria absorbed, emitted, and re-absorbed the light multiple times. The researchers could demonstrate that this way, some of the bacterias’ molecules became entangled with the cavity, so that is a special case of a quantum superposition.

However, a paper published the following year by scientists at Oxford University argued that the observations on the bacteria could also be explained without quantum effects. Now, this doesn’t mean that this is the correct explanation. Indeed, it doesn’t make much sense because we already know that molecules have quantum effects and they couple to light in certain quantum ways. However, this criticism demonstrates that it can be difficult to prove that something you observe is really a quantum effect, and the bacteria experiment isn’t quite there yet.

Let us then talk about a variant of Schrödinger’s cat that Eugene Wigner came up with in the nineteen-sixties. Imagine that this guy Wigner is outside the laboratory in which his friend just opens the box with the cat. In this case, not only would the cat be both dead and alive before the friend observes it, the friend would also both see a dead cat and see a live cat, until Wigner opens the door to the room where the experiment took place.

This sounds both completely nuts as well as an unnecessary complication, but bear with me for a moment, because this is a really important twist on Schrödinger’s cat experiment. Because if you think that the first measurement, so the friend observing the cat, actually resulted in a definite outcome, just that the friend outside the lab doesn’t know it, then, as long as the door is closed, you effectively have a deterministic hidden variable model for the second measurement. The result is clear already, you just don’t know what it is. But we know that deterministic hidden variable models cannot produce the results of quantum mechanics, unless they are also superdeterministic.

Now, again, of course, you can’t actually do the experiment with cats and friends and so on because their quantum effects would get destroyed too quickly to observe anything. But recently a team at Griffith University in Brisbane, Australia, created a version of this experiment with several devices that measure, or observe, pairs of photons. As anticipated, the measurement result agrees with the predictions of quantum mechanics.

What this means is that one of the following three assumptions must be wrong:

1. No Superdeterminism.
2. Measurements have definite outcomes.
3. No spooky action at a distance.

The absence of superdeterminism is sometimes called “Free choice” or “Free will”, but really it has nothing to do with free will. Needless to say, I think what’s wrong is rejecting superdeterminism. But I am afraid most physicists presently would rather throw out objective reality. Which one are you willing to give up? Let me know in the comments.

As of now, scientists remain hard at work trying to unravel the mysteries of Schrödinger's cat. For example, a promising line of investigation that’s still in its infancy is to measure the heat of a large system to determine whether quantum superpositions can influence its behavior. You find references to that as well as to the other papers that I mentioned in the info below the video. Schrödinger, by the way, didn’t have a cat, but a dog. His name was Burschie.

Wednesday, February 24, 2021

What's up with the Ozone Layer?

[This is a transcript of the video embedded below.]

Without the ozone layer, life, as we know it, would not exist. Scientists therefore closely monitor how the ozone layer is doing. In the past years, two new developments have attracted their attention and concern. What have they found and what does it mean? That’s what we’ll talk about today.

First things first, ozone is a molecule made of three oxygen atoms. It’s unstable, and on the surface of Earth it decays quickly, on the average within a day or so. For this reason, there’s very little ozone around us, and that’s good, because breathing in ozone is really unhealthy even in small doses.

But ozone is produced when sunlight hits the upper atmosphere, and accumulates far up there in a region called the “stratosphere”. This “ozone layer” then absorbs much of the sun’s ultraviolet light. The protection we get from the ozone layer is super-important, because the energy of ultraviolet light is high enough to break molecular bonds. Ultra-violet light, therefore, can damage cells or their genetic code. This means, with exposure to ultraviolet light, the risk of cancer and other mutations increases significantly. I have explained radiation risk in more detail in an earlier video, so check this out for more.

You have probably all heard of the ozone “hole” that was first discovered in the 1980s. This ozone hole is still with us today. It was caused by human emissions of ozone-depleting substances, notably chlorofluorocarbons – CFCs for short – that were used, among other things, in refrigerators and spray cans. CFCs have since been banned, but it will take at least several more decades for the ozone layer to completely recover. With that background knowledge, let’s now look at the two new developments.

What’s new?

The first news is that last year we have seen a large and pronounced ozone hole over the North Pole, in addition to the “usual” one over the South Pole. This has happened before, but it’s still an unusual event. That’s because the creation of an ozone hole is driven by supercooled droplets of water and nitric acid which are present in polar stratospheric clouds, so clouds that you find on the poles in the stratosphere. But these clouds can only form if it’s cold enough, and I mean really cold, below about −108 °F or −78 °C. Therefore, the major reason that ozone holes form more readily over the South pole than over the North Pole is quite simply that the South Pole is, on average, colder.

Why is the South Pole colder? Loosely speaking it’s because there are fewer high mountains in the Southern hemisphere than in the Northern hemisphere. And because of this, wind circulations around the South Pole tend to be more stable; they can lock in air, which then cools over the dark polar winter months. Air over the North Pole, in contrast, mixes more efficiently with warmer air from the mid latitudes.

On occasion, however, cold air gets locked in over the North Pole as well, which creates conditions similar to those at the South Pole. This is what happened in the Spring of 2020. For five weeks in March and early April, the North Pole saw the biggest arctic ozone hole on record, surrounded by a stable wind circulation called a polar vortex.

Now, we have all witnessed in the past decade that climate change alters wind patterns in the Northern Hemisphere, which gives rise to longer heat waves in the summer. This brings up the question whether climate change was one of the factors contributing to the northern ozone hole and whether we, therefore, must expect it to become a recurring event.

This question was studied in a recent paper by Martin Dameris and coauthors, for the full reference, please check the info below the video. Their conclusion is that, so far, observations of the northern ozone hole are consistent with it just being a coincidence. However, if coincidences pile upon coincidences, they make a trend. And so, researchers are now waiting to see whether the hole will return in the Spring of 2021 or in the coming years.

The second new development is that the ozone layer over the equator isn’t recovering as quickly as scientists expected. Indeed, above the equator, the amount of ozone in the lower parts of the stratosphere seems to be declining, though that trend is, for now, offset by the recovery of ozone in the upper parts of the stratosphere, which proceeds as anticipated.

The scientists who work on this previously considered various possible reasons, from data problems to illegal emissions of ozone-depleting substances. But the data have held up, and while we now know illegal emissions are indeed happening, these do not suffice to explain the observations.

Instead, further analysis indicates that the depletion of ozone in the lower stratosphere over the equator seems to be driven, again, by wind patterns. Earth’s ozone is itself created by sunlight, which is why most of it forms over the equator where sunlight is the most intensive. The ozone is then transported from the equatorial regions towards the poles by a wind cycle – called the “Brewer-Dobson circulation” – in which air rises over the equator and comes down again in mid to high latitude. With global warming, that circulation may become more intense, so that more ozone is redistributed from the equator to higher latitudes.

Again, though, the strength of this circulation also changes just by random chance. It’s therefore presently unclear whether the observations merely show a temporary fluctuation or are indicative of a trend. However, a recent analysis of different climate-chemistry models by Simone Dietmüller et al shows that human-caused carbon dioxide emissions contribute to the trend of less ozone over the equator and more ozone in the mid-latitudes, and the trend is therefore likely to continue. I have to warn you though that this paper has not yet passed peer review.

Before we talk about what this all means, I want to thank my tier four supporters on Patreon. Your help is greatly appreciated. And you, too, can help us produce videos by supporting us on Patreon. Now let’s talk about what these news from the ozone layer mean.

You may say, ah, so what. Tell the people in the tropics to put on more sun-lotion and those in Europe to take more vitamin D. This is a science channel, and I’ll not tell anyone what they should or shouldn’t worry about, that’s your personal business. But to help you gauge the present situation, let me tell you an interesting bit of history.

The Montreal protocol from 1987, which regulates the phasing out of ozone depleting substances, was passed quickly after the discovery of the first ozone hole. It is often praised as a milestone of environmental protection, the prime example that everyone points to for how to do it right. But I think the Montreal Protocol teaches us a very different lesson.

That’s because scientists knew already in the 1970s, long before the first ozone hole was discovered, that chlorofluorocarbons would deplete the ozone layer. But they thought the effect would be slow and global. When the ozone hole over the South Pole was discovered by the British Antarctic Survey in 1985, that came as a complete surprise.

Indeed, fun fact, it later turned out that American satellites had measured the ozone hole years before the British Survey did, but since the data were so far off the expected value, they were automatically overwritten by software.

The issue was that at the time the effects of polar stratospheric clouds on the ozone layer were poorly understood, and the real situation turned out to be far worse than scientists thought.

So, for me, the lesson from the Montreal Protocol is that we’d be fools to think that we now have all pieces in place to understand our planet’s climate system. We know we’re pushing the planet into regimes that scientists poorly understand and chances are that this will bring more unpleasant surprises.

So what do those changes in the ozone layer mean? They mean we have to pay close attention to what’s happening.

Saturday, February 20, 2021

The Science of Making Rain

[This is a transcript of the video embedded below]

Wouldn’t it be great if we could control the weather? I am sure people have thought about this ever since there’ve been people having thoughts. But what are scientists thinking about this today? In this video we’ll look at the best understood case of weather control, that’s making rain by seeding clouds. How is cloud seeding supposed to work? Does it work? And if it works, is it a good idea? That’s what we’ll talk about today.

First things first, what is cloud seeding? Cloud seeding is a method for increasing precipitation, which is a fancy word for water that falls off the sky in any form: rain, snow, hail and so on. One seeds a cloud by spraying small particles into it, which encourages the cloud to shed precipitation. At least that’s the idea. Cloud seeding does not actually create new clouds. It’s just a method to get water out of already existing clouds. So you can’t use it to turn a desert into a forest – the water needs to be in the air already.

Cloud seeding was discovered, as so many things, accidentally. In nineteen-fourty-six a man named Vincent Schaefer was studying clouds in a box in his laboratory, but it was too warm for his experiment to work. So he put dry ice into his cloud box, that’s carbon dioxide frozen at about minus eighty degrees Celsius. He then observed that small grains of dry ice would rapidly grow to the size of snowflakes.

Schaefer realized this happened because the water in the clouds was supercooled, that means below freezing point, but still liquid. This is an energetically unstable state. If one introduces tiny amounts of crystals into a supercooled cloud, the water droplets will attach to the crystals immediately and freeze, so the crystals grow quickly until they are heavy enough to fall down. Schaefer saw this happening when sprinkles of solid dry ice fell into his box. He had seeded the first cloud. In the following years he’d go on to test various methods of cloud seeding.

Today scientists distinguish two different ways of seeding clouds, either by growing ice crystals, as Schaefer did, that’s called Glaciogenic seeding. Or by growing water droplets, which is called hygroscopic seeding.

How does it work?

The method that Schaefer used is today more specifically called the “Glaciogenic static mode”, static because it doesn’t rely on circulation within the cloud. There’s also a Glaciogenic dynamic mode which works somewhat differently.

In the dynamic mode, one exploits that the conversion of the supercoooled water into ice releases heat, and that heat creates an updraft. This allows the seeds to reach more water droplets, so the cloud grows, and eventually more snow falls. One of the substances commonly used for this is silver iodide, though there are a number of different organic and inorganic substances that have proved to work.

For hygroscopic seeding one uses particles that can absorb water that serve as condensation seeds to turn water vapor into large drops that become rain. The substances used for this are typically some type of salt.

How do you do it?

Seeding clouds in a box in the laboratory is one thing, seeding a real cloud another thing entirely. To seed a real cloud, one either uses airplanes that spray the seeding particles directly into the cloud, or targets the cloud with a rocket which gives off the particles, or one uses a ground-based generator that releases the particles slowly mixed with hot air, that rises up into the atmosphere. They do this for example in Colorado, and other winter tourism areas, and claim that it can lead to several inches more snow.

But does it work?

It’s difficult to test if cloud seeding actually works. The issue is, as I said, seeding doesn’t actually create clouds, it just encourages clouds to release snow or rain at a particular time and place. But how do you know if it wouldn’t have rained anyway?

After Schaefer’s original work in the nineteen-fifties, the United States launched a research program on cloud seeding, and so did several other countries including the UK, Canada, India, and Australia. But evidence that cloud seeding works didn’t come by for a long time, and so, in the late nineteen-eighties, funding into this research area drastically declined. That didn’t deter people from trying to seed clouds though. Despite the absence of evidence quite a few winter sport areas used cloud seeding in an attempt to increase snow fall.

But beginning around the turn of the millennium, interest in cloud seeding was revived by several well-funded studies in the United States, Australia, Japan, and China, for just to name a few. Quite possibly this interest was driven by the increasing risk of drought due to climate change. And today, scientists have much better technology to figure out whether cloud seeding works, and so, the new studies could finally deliver evidence that it does work.

Some of the most convincing studies used radar measurements to detect ice crystals in clouds after a plane went through and distributed the seeds. This was done for example in a 2011 study in Australia and also in a 2018 study in the northern part of the United States.

These radar measurements are a direct signature of seeding, glaciogenic seeding in this case. The researchers can tell that the ice crystals are caused by the seeding because the crystals that appear in the radar signal replicate the trajectory of the seeding plane, downwind.

From the radar measurements they can also tell that the concentration of ice crystals is two to three orders of magnitude larger than those in neighboring, not-seeded areas. And, they know that the newly formed ice-crystals grow, because the amount of radar signal that’s reflected depends on the size of the particle.

This and similar studies also contained several cross checks. For example, they seeded some areas of the clouds with particles that are known to grow ice crystals and others with particles that aren’t expected to do that. And they detected ice formation only for the particles that act as seeds. They also checked that the resulting snowfall is really the one that came from the seeding. One can do this by analyzing the snow for traces of the substance used for seeding.

Besides this, there are also about a dozen studies that evaluated statistically if there changes in precipitation from the glaciogenic static seeding. These come from research programs in the United States, Australia, and Japan. To get statistics, they monitor the unseeded areas surrounding the seeded region as an estimation of the natural precipitation. It’s not a perfect method of course, but done often enough and for long enough periods, it gives a reasonable assessment for the increase of precipitation due to seeding.

These studies typically found an increase in precipitation around 15% and estimated the probability that this increase happened just coincidentally with 5%.

So, at least for the seeding of ice crystals, there is now pretty solid evidence that it works better than a rain dance. For the other types of seeding it’s still unclear whether it’s efficient.

Please check the information below the video for references to the papers.

The world’s biggest weather modification program is China’s. The Chinese government employs an estimated 35,000 people to this end already, and in December 2020 they announced they’ll increase investments into their weather modification program five-fold.

Now, as we have seen, cloud seeding isn’t terribly efficient and for it to work, the clouds have to be already there in the first place. Nevertheless, there’s an obvious worry here. If some countries can go and make clouds rain off over their territory, that might leave less water for neighboring countries.

And the bad news is, there aren’t currently any international laws regulating this. Most countries have regulations for what you are allowed to spray into the air or how much, but cloud seeding is mostly legal. There is an international convention, the Environmental Modification Convention, that seventy-eight states have signed, which prohibits “the military and hostile use of environmental modification techniques.” But this can’t in any clear way be applied to cloud seeding.

I think that now that we know cloud seeding does work, we should think about how to regulate it, before someone actually gets good at it. Controlling the weather is an ancient dream, but, thanks to Vincent Schaefer, maybe it won’t remain a dream forever. When he died in 1993, his obituary in the New York Times said “He was hailed as the first person to actually do something about the weather and not just talk about it”.

Tuesday, February 16, 2021

Saturday, February 13, 2021

The Simulation Hypothesis is Pseudoscience

[This is a transcript of the video embedded below.]

I quite like the idea that we live in a computer simulation. It gives me hope that things will be better on the next level. Unfortunately, the idea is unscientific. But why do some people believe in the simulation hypothesis? And just exactly what’s the problem with it? That’s what we’ll talk about today.

According to the simulation hypothesis, everything we experience was coded by an intelligent being, and we are part of that computer code. That we live in some kind of computation in and by itself is not unscientific. For all we currently know, the laws of nature are mathematical, so you could say the universe is really just computing those laws. You may find this terminology a little weird, and I would agree, but it’s not controversial. The controversial bit about the simulation hypothesis is that it assumes there is another level of reality where someone or some thing controls what we believe are the laws of nature, or even interferes with those laws.

The belief in an omniscient being that can interfere with the laws of nature, but for some reason remains hidden from us, is a common element of monotheistic religions. But those who believe in the simulation hypothesis argue they arrived at their belief by reason. The philosopher Nick Boström, for example, claims it’s likely that we live in a computer simulation based on an argument that, in a nutshell, goes like this. If there are a) many civilizations, and these civilizations b) build computers that run simulations of conscious beings, then c) there are many more simulated conscious beings than real ones, so you are likely to live in a simulation.

Elon Musk is among those who have bought into it. He too has said “it’s most likely we’re in a simulation.” And even Neil DeGrasse Tyson gave the simulation hypothesis “better than 50-50 odds” of being correct.

Maybe you’re now rolling your eyes because, come on, let the nerds have some fun, right? And, sure, some part of this conversation is just intellectual entertainment. But I don’t think popularizing the simulation hypothesis is entirely innocent fun. It’s mixing science with religion, which is generally a bad idea, and, really, I think we have better things to worry about than that someone might pull the plug on us. I dare you!

But before I explain why the simulation hypothesis is not a scientific argument, I have a general comment about the difference between religion and science. Take an example from Christian faith, like Jesus healing the blind and lame. It’s a religious story, but not because it’s impossible to heal blind and lame people. One day we might well be able to do that. It’s a religious story because it doesn’t explain how the healing supposedly happens. The whole point is that the believers take it on faith. In science, in contrast, we require explanations for how something works.

Let us then have a look at Boström’s argument. Here it is again. If there are many civilizations that run many simulations of conscious beings, then you are likely to be simulated.

First of all, it could be that one or both of the premises is wrong. Maybe there aren’t any other civilizations, or they aren’t interested in simulations. That wouldn’t make the argument wrong of course, it would just mean that the conclusion can’t be draw. But I will leave aside the possibility that one of the premises is wrong because really I don’t think we have good evidence for one side or the other.

The point I have seen people criticize most frequently about Boström’s argument is that he just assumes it is possible to simulate human-like consciousness. We don’t actually know that this is possible. However, in this case it would require explanation to assume that it is not possible. That’s because, for all we currently know, consciousness is simply a property of certain systems that process large amounts of information. It doesn’t really matter exactly what physical basis this information processing is based on. Could be neurons or could be transistors, or it could be transistors believing they are neurons. So, I don’t think simulating consciousness is the problematic part.

The problematic part of Boström’s argument is that he assumes it is possible to reproduce all our observations using not the natural laws that physicists have confirmed to extremely high precision, but using a different, underlying algorithm, which the programmer is running. I don’t think that’s what Bostrom meant to do, but it’s what he did. He implicitly claimed that it’s easy to reproduce the foundations of physics with something else.

But nobody presently knows how to reproduce General Relativity and the Standard Model of particle physics from a computer algorithm running on some sort of machine. You can approximate the laws that we know with a computer simulation – we do this all the time – but if that was how nature actually worked, we could see the difference. Indeed, physicists have looked for signs that natural laws really proceed step by step, like in a computer code, but their search has come up empty handed. It’s possible to tell the difference because attempts to algorithmically reproduce natural laws are usually incompatible with the symmetries of Einstein’s theories of special and general relativity. I’ll leave you a reference in the info below the video. The bottomline is, it’s not easy to outdo Einstein.

It also doesn’t help by the way if you assume that the simulation would run on a quantum computer. Quantum computers, as I have explained earlier, are special purpose machines. Nobody currently knows how to put General Relativity on a quantum computer.

A second issue with Boström’s argument is that, for it to work, a civilization needs to be able to simulate a lot of conscious beings, and these conscious beings will themselves try to simulate conscious beings, and so on. This means you have to compress the information that we think the universe contains. Bostrom therefore has to assume that it’s somehow possible to not care much about the details in some parts of the world where no one is currently looking, and just fill them in in case someone looks.

Again though, he doesn’t explain how this is supposed to work. What kind of computer code can actually do that? What algorithm can identify conscious subsystems and their intention and then quickly fill in the required information without ever producing an observable inconsistency. That’s a much more difficult issue than Bostrom seems to appreciate. You cannot in general just throw away physical processes on short distances and still get the long distances right.

Climate models are an excellent example. We don’t currently have the computational capacity to resolve distances below something like 10 kilometers or so. But you can’t just throw away all the physics below this scale. This is a non-linear system, so the information from the short scales propagates up into large scales. If you can’t compute the short-distance physics, you have to suitably replace it with something. Getting this right even approximately is a big headache. And the only reason climate scientists do get it approximately right is that they have observations which they can use to check whether their approximations work. If you only have a simulation, like the programmer in the simulation hypothesis, you can’t do that.

And that’s my issue with the simulation hypothesis. Those who believe it make, maybe unknowingly, really big assumptions about what natural laws can be reproduced with computer simulations, and they don’t explain how this is supposed to work. But finding alternative explanations that match all our observations to high precision is really difficult. The simulation hypothesis, therefore, just isn’t a serious scientific argument. This doesn’t mean it’s wrong, but it means you’d have to believe it because you have faith, not because you have logic on your side.

Saturday, February 06, 2021

Don't Fall for Quantum Hype

[This is a transcript of the video embedded below.]

Quantum technology is presently amazingly popular. The United States and the United Kingdom have made it a „national initiative”, the European Union has a quantum technology “flagship.” India has a “national mission”, and China has announced they’ll put quantum technology into their next 5 year plan. What is “quantum technology” and what impact will it have on our lives? That’s what we will talk about today.

The quantum initiatives differ somewhat from nation to nation, but they usually contain research programs on four key topics that I will go through in this video. That’s: quantum computing, the quantum internet, quantum metrology, and quantum simulations.

We’ll start with quantum computing.

Quantum computing is one of the most interesting developments in the foundations of physics right now. I have talked about quantum computing in more detail in an earlier video, so check this out for more. In brief, quantum computers can speed up certain types of calculations dramatically. A quantum computer can do this because it does not work with “bits” that have values of either 0 or 1, but with quantum bits – “qbits” for short – that can be entangled, and can take on any value in between 0 and 1.

It’s not an accident that I say “between” instead of “both”, I think this describes the mathematics more accurately. Either way, of course, these are just attempts to put equations into words and the words will in the best case give you a rough idea of what’s really going on. But the bottom line is that you can process much more information with qbits than with normal bits. The consequence is that quantum computers can do certain calculations much faster than conventional computers. This speed-up only works for certain types of calculations though. So, quantum computers are special purpose machines.

The theory behind quantum computing is well understood and uncontroversial. Quantum computers already exist and so far they work as predicted. The problem with quantum computers is that for them to become commercially useful, you need to be able to bring a large number of qbits into controllable quantum states, and that’s really, really difficult.

Estimates say, the number we need to reach is roughly a million, details depend on the quality of qbits and the problem you are trying to solve. The status of research is presently at about 50 qbits. Yes, that’s a good start, but it’s a long way to go to a million and there’s no reason to expect anything resembling Moore’s will help us here, because we’re already working on the limit.

So, the major question for quantum computing is not “does it work”. We know it works. The question is “Will it scale”?

To me the situation for quantum computing today looks similar to the situation for nuclear fusion 50 years ago. 50 years ago, physicists understood how nuclear fusion works just fine, and they had experimentally checked that their theories were correct. The problem was “just” to make the technology large and still efficient enough to actually be useful. And, as you all know, that’s still the problem today.

Now, I am positive that we will eventually use both nuclear fusion and quantum computing in everyday life. But keep in mind that technology enthusiasts tend to be overly optimistic in their predictions for how long it will take for technology to become useful.

The Quantum Internet

The quantum internet refers to information transmitted with quantum effects. This means most importantly, the quantum internet uses quantum cryptography as a security protocol. Quantum cryptography is a method to make information transfer secure by exploiting the fact that in quantum mechanics, a measurement irreversibly changes the state of a quantum particle. This means if you encode a message suitably with quantum particles, you can tell whether it has been intercepted by a hacker, because the hacker’s measurement would change the behavior of the particles. That doesn’t prevent hacking, but it means you’d know when it happens.

I made an entire video about how quantum cryptography works, so check this out if you want to know more. Today I just want to draw your attention to two pointes that the headlines tend to get wrong.

First, you cannot transfer information faster than the speed of light with the quantum internet or with any other quantum effect. That quantum mechanics respects the speed of light limit is super-basic knowledge that you’d think every science writer knows about. Unfortunately, this is not the case. You see this over and over again in the headlines, that the quantum internet can supposedly beat the speed of light limit. It cannot. That’s just wrong.

And no, this does not depend on your interpretation of quantum mechanics, it’s wrong either way you look at it. No, this is not what Einstein meant with “spooky action at a distance”. It’s really just wrong. Quantum mechanics does not allow you to send information faster than the speed of light.

This isn’t the major issue I have with the coverage of the quantum internet though, because that’s obviously wrong and really what do you expect from the Daily Mail. No, the major issue I have is that almost all of the of the articles mislead the audience about the relevance of the quantum internet.

It’s not explicitly lying, but it’s lying by omission. Here is a recent example from Don Lincoln who does exactly this, and pretty much every article you’ll read about the quantum internet goes somewhat like this.

First, they will tell you that quantum computers, if they reach a sufficiently large number of qbits, can break the security protocols that are currently being used on the internet quickly, which is a huge problem for national security and privacy. Second, they will tell you that the quantum internet is safe from hacking by quantum computers.

Now, these two statements separately are entirely correct. But there’s an important piece of information missing between them, which is that we have security protocols that do not require quantum technology but are safe from quantum computers nevertheless. They are just presently not in use. These security protocols that, for all we currently know, cannot be broken even by quantum computers are, somewhat confusingly, called “post-quantum cryptography” or, in somewhat better terminology, quantum-safe cryptography.

This means that we do not need the quantum internet to be safe from quantum computers. We merely need to update the current security protocols, and this update is already under way. For some reason the people who work on quantum things don’t like draw attention to that.

Quantum metrology

Quantum metrology is a collection of techniques to improve measurements by help of quantum effects. The word “metrology” means that this research is about measurement; it’s got nothing to do with meteorology, different thing entirely. Quantum metrology has recently seen quite a few research developments that I expect to become useful soon in areas like medicine or material science. That’s because one of the major benefits of quantum measurements is that they can make do with very few particles, and that means minimal damage to the sample.

Personally I think quantum metrology is the most promising part of the quantum technology package and the one that we’re most likely to encounter in new applications soon.

I made a video especially about quantum metrology earlier, so check this out for more detail.

Quantum Simulations

Quantum simulations are a scientifically extremely interesting development that I think has been somewhat underappreciated. In a quantum simulation you try to understand a complicated system whose properties you cannot calculate, by reproducing its behavior as good as you can with a different quantum system that you can control better, so you can learn more about it.

This is actually something I have worked on myself for some years, in particular the possibility that you can simulate black holes with superfluids. I will tell you more about this some other time, for today let me just say that I think this is a rather dramatic shift in the foundations of physics because it allows you to take out mathematics as the middleman. Instead of modeling a system with mathematics, either with a pen on paper or with computer code, you model it directly with another system without having to write down equations in one form or another.

Now, quantum simulations are really cool from the perspective of basic research, because they allow you to learn a great deal. You can for example simulate particles similar to the Higgs or certain types of neutrinos, and learn something about their behavior, which you couldn’t do in any other way.

However, quantum simulations are unlikely to have technological impact any time soon, and, what’s worse, they have been oversold by some people in the community. Especially all the talk about simulating wormholes is nonsense. These simulated “wormholes” have nothing in common with actual wormholes that, in case you missed it, we have good reason to think do not exist in the first place. I am highlighting the wormhole myth because to my shock I saw it appear in a white house report. So, quantum simulations are cool for the most part, but if someone starts babbling about wormholes, that is not serious science.

I hope this quick summary helps you make sense of all the quantum stuff in the headlines.