Does Anti-Gravity Explain Dark Energy?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]


One of the lesser known facts about me is that I’m one of the few world experts on anti-gravity. That’s because 20 years ago I was convinced that repulsive gravity could explain some of the puzzling observations astrophysicists have made which they normally attribute to dark matter and dark energy. In today’s video I’ll tell you why that didn’t work, what I learned from that, and also why anti-matter doesn’t fall up.

Newton’s law of gravity says that the gravitational force between two masses is the product of the masses, divided by the square of the distance between them. And then there’s a constant that tells you how strong the force is. For the electric force between two charges, we have Coulomb’s law, that says the force is the product of the charges, divided by the square of the distance between them. And again there’s a constant that tells you how strong the force is.

These two force laws look pretty much the same. But the electric force can be both repulsive and attractive, depending on whether you have two negative or two positive charges, or a positive and a negative one. The gravitational force, on the other hand, is always attractive because we don’t have any negative masses. But why not?

Well, we’ve never seen anything fall up, right? Then again, if there was any anti-gravitating matter, it would be repelled by our planet. So maybe it’s not so surprising that we don’t see any anti-gravitating matter here. But it could be out there somewhere. Why aren’t physicists looking for it?

One argument that you may have heard physicists bring up is that negative masses can’t exist because that would make the vacuum decay. That’s because, if negative masses exist, then so do negative energies. Because, E equals m c squared and so on. Yes, that guy again.

And if we had negative energies, then you could create pairs of particles with negative and positive energy from nothing and particle pairs would spontaneously pop up all around us. A theory with negative masses would therefore predict that the universe doesn’t exist, which is in conflict with evidence. I’ve heard that argument many times. Unfortunately it doesn’t work.

This argument doesn’t work because it confuses to different types of mass. If you remember, Einstein’s theory of general relativity is based on the Equivalence Principle, that’s the idea that gravitational mass equals inertial mass. The gravitational mass is the mass that appears in the law of gravity. The inertial mass is the mass that resists acceleration. But if we had anti-gravitating matter, only its gravitational mass would be negative. The inertial mass always remains positive. And since the energy-equivalent of inertial mass is as usual conserved, you can’t make gravitating and anti-gravitating particles out of nothing.

Some physicists may argue that you can’t make anti-gravity compatible with general relativity because particles in Einstein’s theory will always obey the equivalence principle. But this is wrong. Of course you can’t do it in general relativity as it is. But I wrote a paper many years ago in which I show how general relativity can be extended to include anti-gravitating matter, so that the equivalence principle only holds up to a sign. That means, gravitational mass is either plus or minus inertial mass. So, in theory that’s possible. The real problem is, well, we don’t see any anti-gravitating matter.

Is it maybe that anti-matter anti-gravitates. Anti-matter is made of anti-particles. Anti-particles are particles which have the opposite electric charge to normal particles. The anti-particle of an electron, for example, is the same as the electron just with a positive electric charge. It’s called the positron. We don’t normally see anti-particles around us because they annihilate when they come in contact with normal matter. Then they disappear and leave behind a flash of light or, in other words, a bunch of photons. And it’s difficult to avoid contact with normal matter on a planet made of normal matter. This is why we observe anti-matter only in cosmic radiation or if it’s created in particle colliders.

But if there is so little anti-matter around us and it lasts only for such short amounts of time, how do we know it falls down and not up? We know this because both matter and anti-matter particles hold together the quarks that make up neutrons and protons.

Inside a neutron and proton there aren’t just three quarks. There’s really a soup of particles that holds the quarks together, and some of the particles in the soup are anti-particles. Why don’t those anti-particles annihilate? They do. They are created and annihilate all the time. We therefore call them “virtual particles.” But they still make a substantial contribution to the gravitational mass of neutrons and protons. That means, crazy as it sounds, the masses of anti-particles make a contribution to the total mass of everything around us. So, if anti-matter had a negative gravitational mass, the equivalence principle would be violated. It isn’t. This is why we know anti-matter doesn’t anti-gravitate.

But that’s just theory, you may say. Maybe it’s possible to find another theory in which anti-particles only anti-gravitate sometimes, so that the masses of neutrons and protons aren’t affected. I don’t know any way to do this consistently, but even so, three experiments at CERN are measuring the gravitational behavior of anti-matter.

Those experiments have been running for several years but so far the results are not very restrictive. The ALPHA experiment has ruled out that anti-particles have anti-gravitating masses, but only if the absolute value of the mass is much larger than the mass of the corresponding normal particle. This means so far they ruled out something one wouldn’t expect in the first place. However, give it a few more years and they’ll get there. I don’t expect surprises from this experiment. That’s not to say that I think it shouldn’t be done. Just that I think the theoretical arguments for why anti-matter can’t anti-gravitate are solid.

Okay, so anti-matter almost certainly doesn’t anti-gravitate. But maybe there’s another type of matter out there, something new entirely, and that anti-gravitates. If that was the case, how would it behave? For example, if anti-gravitating matter repels normal matter, then does it also repel among itself, like electrons repel among themselves? Or does it attract its own type?

This question, interestingly enough, is pretty easy to answer with a little maths. Forces are mediated by fields and those fields have a spin which is a positive integer, so, 0, 1, 2, etc.

For gravity, the gravitational mass plays the role of a charge. And the force between two charges is always proportional to the product of those charges times minus one to the power of the spin.

For a spin zero field, the force is attractive between like charges. But electromagnetism is mediated by a spin-1 field, that’s electromagnetic radiation or photons if you quantize it. And this is why, for electromagnetism, the force between like charges is repulsive but unlike charges attract. Gravity is mediated by a spin-2 field, that’s gravitational radiation or gravitons if you quantize it. And so for gravity it’s just the other way round again. Like charges attract and unlike charges repel. Keep in mind that for gravity the charge is the gravitational mass.

This means, if there is anti-gravitating matter it would be repelled by the stuff we are made of, but clump among itself. Indeed, it could form planets and galaxies just like ours. The only way we would know about it, is its gravitational effect. That sound kind of like, dark matter and dark energy, right?

Indeed, that’s why I thought it would be interesting. Because I had this idea that anti-gravitating matter could surround normal galaxies and push in on them. Which would create an additional force that looks much like dark matter. Normally the excess force we observe is believed to be caused by more positive mass inside and around the galaxies. But aren’t those situations very similar? More positive mass inside, or negative mass outside pushing in? And if you remember, the important thing about dark energy is that it has negative pressure. Certainly if you have negative energy you can also get negative pressure somehow.

So using anti-gravitating matter to explain dark matter and dark energy sounds good at first sight. But at second sight neither of those ideas work. The idea that galaxies would be surrounded by anti-gravitating matter doesn’t work because such an arrangement would be dramatically unstable. Remember the anti-gravitating stuff wants to clump just like normal matter. It wouldn’t enclose galaxies of normal matter, it would just form its own galaxies. So getting anti-gravity to explain dark matter doesn’t work even for galaxies, and that’s leaving aside all the other evidence for dark matter.

And dark energy? Well, the reason that dark energy makes the expansion of the universe speed up is actually NOT that it has negative pressure. It’s that the ratio of the energy density over the pressure is negative. And for anti-gravitating matter, they both turn negative so that the ratio is the same. Contrary to what you expect, that does not speed up the expansion of the universe.

Another way to see this is by noting that anti-gravitating matter is still matter and behaves like matter. Dark energy on the contrary does not behave like matter, regardless of what type of matter. This is why I get a little annoyed when people claim that dark energy is kind of like anti-gravity. It isn’t.

So in the end I developed this beautiful theory with a new symmetry between gravity and anti-gravity. And it turned out to be entirely useless. What did I learn from this? Well, that I wasted a considerable amount of my time on this was one of the reasons I began thinking about more promising ways to develop new theories. Clearly just guessing something because it’s pretty is not a good strategy. In the end, I wrote an entire book about this. Today I try to listen to my own advice, at least some of time. I don’t always listen to myself, but sometimes it’s worth the effort.

The 3 Best Explanations for the Havana Syndrome

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]


In late 2016, United States diplomats working in Cuba began reporting health problems: persistent headaches, vertigo, blurred vision. They were dizzy. They heard sounds coming from nowhere. The affected diplomats were questioned and examined by doctors but the symptoms didn’t fit any known disease. They called it the “Havana Symptom”.

More cases were later reported from China and Russia, Germany and Austria, even from near the White House. A CIA agent in Moscow was allegedly so badly affected that he had to retire. And just a few weeks ago another case made headlines: a CIA officer fell ill during a visit to India. What explanations have doctors put forward for those incidents? What could the Havana Syndrome be? That’s what we’ll talk about today.

Before we talk about sounds from nowhere, I want to briefly thank our supporters on Patreon. Your support makes it so much easier to keep this channel going. Special thanks to our biggest supporters in tier four. We couldn’t do it without you. And too you can help us. Go check out our Patreon page, or support us right here on YouTube by clicking on the “join” button just below this video. Now let’s look at the Havana Syndrome.

The “Havana” Syndrome got its name from the place where it was first reported in 2016. But since then it has appeared in many other countries. For this reason, a spokesperson from the US State Department told Newsweek “We refer to these incidents as “unexplained health incidents” or “UHIs.””

A common report among the affected people is that they hear recurring sounds but can’t identify a source. The Associated Press obtained a recording of what is allegedly one of those mysterious sounds. It was recorded in a private home of a diplomat in Cuba. Here is how that sounds.

Hmm. But not all the affected people in Cuba heard sounds, and it’s not clear that those who *did heard exactly the same thing. Doctors have focused on three different explanations (a) mass hysteria (b) microwaves and (c) ultrasound. We’ll go through these one by one.

(a) mass hysteria

Are those people just imagining they’ve been targeted by some secret weapon and are making themselves ill by worrying about their health? Are they maybe just stressed or bored? Well, in Cuba, the affected diplomats were examined by a military doctor who found most of the patients had suffered inner-ear damage, apparently from an external force. The problem is though that the patients’ health records from before the incident are spotty, so it’s difficult to pinpoint when that damage happened, if it happened.

In the United States, the affected government personnel were also thoroughly examined. Unfortunately, a 2018 paper about their symptoms was widely discredited, but in 2019 a group of neurologists published another paper in the Journal of the American Medical Association and they did find quite compelling evidence for neurological problems among the affected people.

They compared 40 members of the US government who had reported suffering from the Havana Syndrome with 48 control patients with similar demographics, so similar age, gender and educational attainment. They scanned all these people’s brains using magnetic resonance imaging and found the following:

First, no significant difference between groups in the brain gray matter, and no significant difference in the so-called executive control subnetwork, that’s the part of the brain involved in thinking and planning.

But, they did find significant between-group differences for the brain white matter that contains the connective tissue between the neurons. The patients’ volume of white matter was on the average twenty-seven cubic centimeters smaller. That means they’ve lost about five percent of the entire white matter.

This finding that has a p-value of below 0.001. As a reminder, the p-value tells you how statistically significant a finding is. The smaller, the more significant. The typical threshold is 0.05, so this finding meets the criterion of statistical significance.

They also found that patients had a significantly lower mean diffusivity in the connection between two hemispheres of the brain. Just exactly what consequences this has is somewhat unclear, but this difference too has a p-value of below 0.001.

Then there’s a significantly lower mean functional connectivity in the auditory subnetwork that you need for hearing and orientation with a p-value of about 0.003, and a lowered mean functional connectivity in the part of the brain necessary for spatial orientation, with a p-value of 0.002

The lead author of the paper, told the New York Times that this means a wholly psychogenic or psychosomatic cause is very unlikely. In other words, they probably didn’t imagine it.

Case settled? Of course not. A caveat of this study is that the patients had done exercises to improve their physical and cognitive health already before the examination, so the differences to the control group may have been affected by that. However, seeing those p-values I am willing to believe that something strange is going on.

There are other reasons to think that purely psychosomatic reasons don’t explain what’s happened. For example, the first cases in Cuba were treated confidentially and didn’t appear in the news until six months later. And yet there were several different people suddenly seeing doctors for similar symptoms at almost the same time. Those symptoms came on rather suddenly and were reportedly accompanied by strange sounds. The affected people described those sounds as sharp, disorienting, or oddly focused.

Let’s then talk about the second explanation, microwaves.

Microwave troubles in embassies aren’t entirely new. During the cold war, the US embassy in Moscow was permanently radiated by microwaves, presumably by the Soviets. No one knows exactly why, but the speculation is that it was for surveillance or counter-surveillance and not designed to cause health damage.

But in the 1970s the US ambassador to the Soviet Union, Walter Stoessel, fell dramatically ill, besides nausea and anemia, one of his symptoms was that his eyes were bleeding. Ugh.

In a now declassified nineteen seventy-five phone call, Henry Kissinger linked Stoessel’s illness to microwaves, admitting “we are trying to keep the thing quiet.” Stoessel died of leukemia at the age of sixty-six, about ten years after he first fell ill.

So, microwaves have been the main suspect because they have history. Could they maybe have caused those mysterious sounds? But how could that possibly be? Microwaves are electromagnetic waves, not sound waves. Certainly our ears don’t detect microwaves.

Well, actually. Let me introduce you to Allan Frey. Frey was an American neuroscientist. In 1960, a radar technician told Frey he could hear microwave pulses. This didn’t make any sense to Frey but he tried it himself and heard it too! He then did a series of experiments in which he exposed people to pulses of microwave radiation at low power, well within the safe regime. He found that not only did they generally hear the pulses, much weirder: deaf people could hear them too. It’s a real thing and is now called the “Frey effect.”

Frey explained that this works as follows. First, the electromagnetic energy from the radiation is absorbed by neural tissue near the surface of the skull. This creates tiny periodic temperature changes. It’s only about five millionths of a degree Celsius but these temperature changes further cause a periodic thermal expansion and contraction of the tissues. And this oscillating tissue creates a pressure wave that propagates and excites the cochlea in the inner ear. This is why we interpret it as a sound.

The frequency of the induced sound, interestingly enough, does not depend on the frequency of the microwaves. It’s a kind of resonance effect and the frequency you hear depends on the acoustic properties of brain tissue and… the size of your head. So, could microwaves lead to mystery sounds? Totally.

Microwave pulses have also been tested as weapons by various nations and are known to cause a variety of symptoms like headaches, dizziness, or nausea. There is also the work of professor James Lin an American electrical engineer who subjected himself to microwaves in his laboratory during the 1970’s. He has written a book on the subject of auditory effects of microwaves and continues publishing papers on the subject. His descriptions match the ones of the people affected by the Havana syndrome quite well.

The authors of the most in detail paper on the cases in Havana also concluded that microwaves were the most likely explanation. And more anecdotally, there’s the report of Beatrice Golomb, a professor at the University of California, San Diego.

Golomb has long researched the health effects of microwaves and offered help to the diplomats affected in China. She claims that family members of personnel tried to measure if there were microwaves by using commercially available equipment. She told the BBC: “The needle went off the top of the available readings.” Then again one person’s story about how someone else tried to measure something isn’t exactly the most reliable evidence.

Still, microwaves seem plausible. A recent piece in the New York Times claimed that microwave weapons are too large to target people in secret. However, several experts have argued that it’s full well possible to put such a weapon into a van and this way bring it into the vicinity of an embassy. Of course this makes you wonder why the heck someone would want to expose diplomats around the world to microwaves with no particular purpose or outcome.

Let’s then talk about option (c) Ultrasound.

Depending on the intensity, exposure to sound, even if we can’t hear it, can cause temporary discomfort, nausea, or even permanent damage of the eardrum. In some countries, for example the United States and Germany, the police sometimes use sonic weapons to disperse crowds. But last year, the US Academy of Doctors of Audiology released a statement warning that these devices sometimes cause permanent loss of hearing, problems with orientation and balance, tinnitus, and injury to the ear. That doesn’t sound so different from the symptoms of the Havana syndrome.

The advantage of this hypothesis is that there’s a possible answer to the “why” question. In 2018, researchers from the University of Michigan proposed the effects could have been caused by improperly placed Cuban spy gear. If two or more surveillance devices that use ultrasound are placed too closely together, they can interfere and create an audible sound. Then again, if you want to explain all the reported cases that way, you’d need a lot of incompetent spies.

So, well. Let’s hear that recording from the associated press again. Hmm. What does it sound like to you? When Fernando Montealegre heard the sound it reminded him of the crickets he collected as a child. Montealegre is a professor of sensory biology at the University of Lincoln in the UK. Together with a colleague, he searched a database of insect sounds to see if any matched the tape. The researchers found that the recording from Cuba matches perfectly to the call of the Indies short-tailed cricket.

As you see, this is a really difficult story and no one presently has a good explanation for what has happened. Most importantly I think we must keep in mind that there could actually be a number of different reasons for why those people fell ill. While it seems unlikely that the first cases in Cuba spread by mass hysteria, the cases in China only began after those in Cuba had made headlines, so that’s an entirely different situation.

There are also of course a lot of conspiracy theories ranking around the Havana syndrome. Is it a coincidence that the cases in Cuba began right after Trump’s election? It is a coincidence that Fidel Castro died around the same time? Is it a coincidence that only a few weeks later Russia and Cuba signed a defense cooperation agreement? I don’t have any insights into this, but let me know what you think in the comments.

Why can elementary particles decay?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]


Physicists have so far discovered twenty-five elementary particles that, for all we currently know, aren’t made up of anything else. Most of those particles are unstable, and they’ll decay to lighter particles within fractions of a second. But how can it possibly be that a particle which decays is elementary. If it decays doesn’t this mean it was made up of something else? And why do particles decay in the first place? At the end of this video, you’ll know the answers.

The standard model of particle physics contains 25 particles. But the matter around us is almost entirely made up of only half of them. First, there’s the electron. Then there are the constituents of atomic nuclei, the neutrons and protons, which are made of different combination of up and down quarks. That’s 3. And those particles are held together by photons and the 8 gluons of the strong nuclear force. So that’s twelve.

What’s with the other particles? Let’s take for example the tau. The tau is very similar to the electron, except it’s heavier by about a factor 4000. It’s unstable and has a lifetime of only three times ten to the minus thirteen seconds. It then decays, for example into an electron, a tau-neutrino and an electron anti-neutrino. So is the tau maybe just made up of those three particles. And when it decays they just fly apart?

But no, the tau isn’t made up of anything, at least not according to all the observations that we currently have. There are several reasons physicists know this.

First, if the tau was made up of those other particles, you’d have to find a way to hold them together. This would require a new force. But we have no evidence for such a force. For more about this, check out my video about fifth forces.

Second, even if you’d come up with a new force, that wouldn’t help you because the tau can decay in many different ways. Instead of decaying into an electron, a tau-neutrino and an electron anti-neutrino, it could for example decay into a muon, a tau-neutrino and a muon anti-neutrino. Or it could decay into a tau-neutrino and a pion. The pion is made up of two quarks. Or it could decay into a tau-neutrino and a rho. The rho is also made up of two quarks, but different ones than the pion. And there are many other possible decay channels for the tau.

So if you’d want the tau to be made up of the particles it decays into, at the very least there’d have to be different tau particles, depending on what they’re made up of. But we know that that this can’t be. The taus are exactly identical. We know this because if they weren’t, they’d themselves be produced in larger numbers in particle collisions than we observe. The idea that there are different versions of taus is therefore just incompatible with observation.

This, by the way, is also why elementary particles can’t be conscious. It’s because we know they do not have internal states. Elementary particles are called elementary because they are simple. The only way you can assign any additional property to them, call that property “consciousness” or whatever you like, is to make that property entirely featureless and unobservable. This is why panpsychism which assigns consciousness to everything, including elementary particles, is either bluntly wrong – that’s if the consciousness of elementary particles is actually observable, because, well, we don’t observe it – or entirely useless – because if that thing you call consciousness isn’t observable it doesn’t explain anything.

But back to the question why elementary particles can decay. A decay is really just a type of interaction. This also means that all these decays in principle can happen in different orders. Let’s stick with the tau because you’ve already made friends with it. That the tau can decay into the two neutrinos and an electron just means that those four particles interact. They actually interact through another particle, with is one of the vector bosons of the weak interaction. But this isn’t so important. Important is that this interaction could happen in other orders. If an electron with high enough energy runs into a tau neutrino, that could for example produce a tau and an electron neutrino. In that case what would you think any of those particles are “made of”? This idea just doesn’t make any sense if you look at all the processes that we know of that taus are involved in.

Everything that I just told you about the tau works similarly for all of the other unstable particles in the standard model. So the brief answer to the question why elementary particles can decay is that decay doesn’t mean the decay products must’ve been in the original particle. A decay’s just a particular type of interaction. And we’ve no observations that’d indicate elementary particles are made up of something else; they have no substructure. That’s why we call them elementary.

But this brings up another question, why do those particles decay to begin with? I often come across the explanation that they do this to reach the state of lowest energy because the decay products are lighter than the original. But that doesn’t make any sense because energy is conserved in the decay. Indeed, the reason those particles decay has nothing to do with energy, it has all to do with entropy.

Heavy particles decay simply because they can and because that’s likely to happen. As Einstein told us, mass is a type of energy. Yes, that guy again. So a heavy particle can decay into several lighter particles because it has enough energy. And the rest of the energy that doesn’t go into the masses of the new particles goes into the kinetic energy of the new particles. But for the opposite process to happen, those light particles would have to meet in the right spot with a sufficiently high energy. This is possible, but it’s very unlikely to happen coincidentally. It would be a spontaneous increase of order, so it would be an entropy decrease. That’s why we don’t normally see it happening, just like we don’t normally see eggs unbreak. To sum it up: Decay is likely. Undecay unlikely.

It is worth emphasizing though that the reverse of all those particle-decay processes indeed exists and it can happen in principle. Mathematically, you can reverse all those processes, which means the laws of nature are time-reversible. Like a movie, you can run them forwards and backwards. It’s just that some of those processes are very unlikely to occur in the word we actually inhabit, which is why we experience our life with a clear forward direction of time that points towards more wrinkles.

New book now available for pre-order

In the past years I have worked on a new book, which is now available for pre-order here (paid link). My editors decided on the title "Existential Physics: A Scientist's Guide to Life's Biggest Questions" which, I agree, is more descriptive than my original title "More Than This". My title was trying to express that physics is about more than just balls rolling down inclined planes and particles bumping into each other. It's a way to make sense of life.

In "Existential Physics" each chapter is the answer to a question. I have also integrated interviews with Tim Palmer, David Deutsch, Roger Penrose, and Zeeya Merali, so you don't only get to hear my opinion. I'll show you a table of contents when the page proofs are in. I want to remind you that comments have moved over to my Patreon page.

How bad is plastic?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]


Plastic is everywhere, and we have all heard it’s bad for the environment because it takes a long time to biodegrade. But is this actually true? If I look at our outside furniture, that seems to biodegrade beautifully. How much should we really worry about all that plastic? Did you know that most bioplastics aren’t biodegradable? And will we end up driving cars made of soybeans? That’s what we will talk about today.

Pens, bags, cups, trays, toys, shoe soles and wrappers for everything – it’s all plastic. Those contact lenses that I’m wearing? Yeah, that’s plastic too.

The first plastic was invented in nine-teen-0-seven by the chemist Leo Baekeland. Today we use dozens of different plastics. They’re synthetic materials, molecules that just didn’t exist before humans began producing them. Plastics usually have names starting with “poly” like polyethylene, polypropylene, or polyvinyl chloride. The poly is sometimes hidden in abbreviations like PVC or PET.

You probably know the prefix “poly” from “polymer”. It means “many” and tells you that the molecules in plastic are long, repetitive chains. These long chains are the reason why plastics can be easily molded. And because plastics can be quickly mass-produced in custom shapes, they’ve become hugely popular. Today, more than twenty thousand plastic bottles are produced – each second. That’s almost two billion a day! Chewing gum by the way also contains plastic.

Those long molecular chains are also the reason why plastic is so durable, because bacteria that evolved to break down organic materials can’t digest plastic. So how long does plastic last? Well, we can do our own research, so let’s ask Google. Actually we don’t even have to do that ourselves, because just a year ago, a group of American scientists searched for public information on plastic lifetime and wrote a report for the NAS about it.

For some cases, like Styrofoam, they found lifetimes varying from one year to one thousand years to forever. For fishing lines, all thirty-seven websites they found said it lasts six-hundred years, probably because they all copied from each other. If those websites list a source at all, it’s usually a website of some governmental or educational institution. The most often named one is NOAA, the National Oceanic and Atmospheric Administration in the United States. When the researchers contacted NOAA they learned that the numbers on their website are estimates and not based on peer-reviewed science.

Fact is, no one has any good idea how long plastics last in the environment. The studies which have been done, often don’t list crucial information such as exposure to sunlight, temperature, or size and shape of the sample, so it’s unclear what those numbers mean in real life. Scientists don’t even have an agreed-upon standard for what “degradation of plastic” is.

If anything, then recent peer-reviewed literature suggests that plastic in the environment may degrade faster than previously recognized, not because of microbes but because of sunlight. For example, a paper published by a group from Massachusetts found that polystyrene, one of the world’s most ubiquitous plastics, may degrade in a couple of centuries when exposed to sunlight, rather than thousands of years as previously thought. That plastic isn’t as durable as once believed is also rapidly becoming a problem for museums who see artworks of the last century crumbling away.

But why do we worry about the longevity of plastic to begin with? Plastics are made from natural gas or oil, which is why burning them is an excellent source of energy, but has the same problem as burning oil and gas – it releases carbon dioxide which has recently become somewhat unpopular. Plastic can in principle be recycled by shredding and re-molding it, but if you mix different types of plastics the quality degrades rapidly, and in practice the different types are hard to separate.

And so, a lot of plastic trash ends up in landfills or in places where it doesn’t belong, makes its way into rivers and, eventually, into the sea. According to a study by the Ellen Macarthur Foundation, there are more than one-hundred fifty million tons plastic trash in the oceans already, and we add about 10 million tons each year. Most of that plastic sinks to the ground, but more than 250000 tons keep floating on the surface.

The result is that a lot of wildlife, birds and fish in particular, gets trapped in plastic trash or swallows it. According to a 2015 estimate from researchers in Australia and the UK, over ninety percent of seabirds now have plastic in their guts. That’s bad. Swallowing plastic cannot only physically block parts of the digestive system, a lot of plastics also contain chemicals to keep them soft and stable. Many of those chemicals are toxic and they’ll leak into the animals.

Okay you may say who cares about seabirds and fish. But the thing is, once you have a substance in the food chain, it’ll spread through the entire ecosystem. As it spreads, the plastic gets broken down into smaller and smaller pieces, eventually down to below micrometer size. Those are the so-called microplastics. From animals, they make their way into supermarkets, and from there back into the canalization and on into other parts of the environment from where they return to us, and so on. Several independent studies have shown that most of us now quite literally shit plastic.

What are the consequences? No one really knows.

We do know that microplastics are fertile ground for pathogenic bacteria, which isn’t exactly what you want to eat. But of course other microparticles, for example those stemming from leaves or rocks, have that problem too, and we probably eat some of those as well. Indeed, in 2019 a group of Chinese researchers studied bacteria on different microparticles, and they found that the amount of bacteria on microplastics was less than that on micoparticles from leaves. That’s because leaves are organic and deteriorate faster, which provides more nutrients for the bacteria. It’s presently unclear whether eating microplastics is a health hazard.

But some of those microplastics are so small they circulate in the air together with other dust and we regularly breathe them in. Studies have found that at least in cell-cultures, those particles are small enough to make it into the lymphatic and circulatory system. But how much this happens in real life and to what extent this may lead to health problems hasn’t been sorted out. Though we know from several occupational studies that workers processing plastic fibers, who probably breathe in microplastics quite regularly, are more likely to have respiratory problems than the general population. The problems include a reduced lung capacity and coughing. The data for lung cancer induced by breathing microplastics is inconclusive.

Basically we’ve introduced an entirely new substance into the environment and are now finding out what consequences this has.

That problem isn’t new. As Jordi Busque has pointed out, planet Earth had this problem before, namely, when all that coal formed which we’re now digging back up. This happened during a period called the carboniferous which lasted from three-hundred sixty to sixty million years ago. It began when natural selection “invented” for the first time wood trunks with bark, which requires a molecule called lignin. But, no bug, bacteria, or fungus around at that time knew how to digest lignin. So, when trees died, their trunks just piled up in the forests and, over millions of years, they were covered by sediments and turned into coal. The carboniferous ended when evolution created fungi that were able to eat and biodegrade lignin.

Now, the carboniferous lasted 300 million years but maybe we can speed up evolution a bit by growing bacteria that can digest plastics. Why not? There’s nothing particularly special about plastics that would make this impossible.

Indeed, there are already bacteria which have learned to digest plastic. In twenty-sixteen a group of Japanese scientists published a paper in Science magazine, in which they reported the discovery of a bacterium that degrades PET, which is the material most plastic bottles are made of. They found it while they were analyzing sediment samples from nearby a plastic recycling facility. They also identified the enzyme that enables the bacteria to digest plastic and called it PETase.

The researchers found that thanks to PETase, the bacterium converts PET into two environmentally benign components. Moreover 75 percent of the resulting products are further transformed into organic matter by other microorganisms. That, plus carbon-dioxide. As I said in my earlier video about carbon capture, plastics are basically carbon storage, so maybe we should actually be glad that they don’t biodegrade?

But in 2018, a British team accidentally modified PETase making it twenty percent faster at degrading PET, and by 2020 scientists from the University of Portsmouth had found a way to speed up the PET digestion by a factor of six. Just this year, researchers from Germany, France and Ireland used another enzyme which found in a compost pile to degrade PET.

And the French startup Carbios has developed another bacterium that can almost completely digest old plastic bottles in just a few hours. They are building a demonstration factory that will use the enzymes to takes plastic polymers apart into monomers, which can then be polymerized again to make new bottles. The company says it will open a full-scale factory in twenty-twenty-four with a goal of producing the ingredients for forty thousand tons of recycled plastic each year.

The problem with this idea is that the PET used in bottles is highly crystalline and very resistant to enzyme degradation. So if you want the enzymes to do their work, you first have to melt the plastic and extrude it. That requires a lot of energy. For this reason, bacterial PET digestion doesn’t currently make a lot of sense neither economically nor ecologically. But it demonstrates that it’s a real possibility that plastics will just become biodegradable because bacteria evolve to degrade them, naturally or by design.

What’s with bioplastics? Unfortunately, bioplastics look mostly like hype to me.

Bioplastics are plastics produced from biomass. This isn’t a new idea. For example, celluloid, the material of old films, was made from cellulose, an organic material. And in nineteen 41 Ford built a plastic car made from soybeans. Yes, soybeans. Today we have bags made from potatoes or corn. That certainly sounds very bio, but unfortunately, according to a review by scientists from Georgia Southern University that came out just in April, about half of bioplastics are not biodegradable.

How can it possibly be that potato and corn isn’t biodegradable? Well, the potato or corn is biodegradable. But, to make the bioplastics, one uses the potatoes or the corn to produce bioethanol and from the bioethanol you produce plastic in pretty much the same way you always do. The result is that the so-called bioplastics are chemically pretty much the same as normal plastics.

So about half of bioplastics aren’t biodegradable. And most of the ones that are, biodegrade only in certain conditions. This means they have to be sent to industrial compost facilities that have the right conditions of temperature and pressure. If you just trash them they will end up in landfill or migrate into the sea like any other plastic. A paper by researchers from Michigan State University found no difference in degradation when they compared normal plastics with these supposedly biodegradable ones.

So the word “bioplastic” is very misleading. But there are some biodegradable bioplastics. For example Mexican scientists have produced a plastic out of certain types of cacti. It naturally degrades in a matter of months. Unfortunately, there just aren’t enough of those cacti to replace plastic that way.

More promising are PHAs, that are a family of molecules that evolved for certain biological functions and that can be used to produce plastics that actually do biodegrade. Several companies are working on this, for example Anoxkaldnes, Micromidas, and Mango Materials. Mango Materials. Seriously?

Researchers from the University of Queensland in Australia have estimated that a bottle of PHA in the ocean would degrade in one and a half to three and a half years, and a thin film would need 1 to 2 months. Sounds good! But at present PHA is difficult to produce and therefore 2 to 4 times more expensive than normal plastic. And let’s not forget that the faster a material biodegrades the faster it returns its carbon dioxide into the atmosphere. So what you think is “green” might not be what I think is “green”.

Isn’t there something else we can do with all that plastic trash? Yes, for example make steel. If you remember, steel is made from iron and carbon. The carbon usually comes from coal. But you can instead use old plastic, remember the stuff’s made of oil. In a paper that appeared in Nature Catalysis last year, a group of researchers from the UK explained how that could work. Use microwaves to convert the plastic into hydrogen and carbon. Use the hydrogen to convert iron oxides into iron, and then combine it with the carbon to get steel.

Personally I’d prefer steel from plastic over cars of non-biodegradable so-called bioplastics, but maybe that’s just me. Let me know in the comments what you think, I’m curious. Don’t forget to like this video and subscribe if you haven’t already, that’s the easiest way to support us. See you next week.