# Tag Archives: physics

What happens when you drop a Slinky? Specifically, what happens if you let it dangle down motionless, then let go of the top end? It falls, right? And maybe bounces around a bit as it does so?

Here’s a slow-motion video. I came across it the other week. Unless you’ve either seen it before or carefully worked out the physics, I think you’ll be quite startled.

It looks utterly impossible. Most of the Slinky apparently levitates, remaining almost completely stationary for most of the time, while the top part falls. YouTube being YouTube, last time I looked some of the comments were from people refusing point-blank to believe the explanation in the video. I’m not sure what they wanted the explanation to be—maybe some kind of impossible magic more in keeping with the impossible-looking behaviour? I don’t know.

The video talks in terms of information about what’s happened at the top of the Slinky taking time to get to the bottom. Although that’s accurate, I found a different way of looking at it more helpful. I need to explain a bit of very basic mechanics, though. Just one of Newton’s Laws of Motion.

Before Newton, a popular idea was that in order for something to move, you had to apply a force to it. Give it a push or a pull. This seems reasonable from everyday experience: something resting on the table will stay there until some force makes it move, and to drag a heavy object across the floor you have to keep on pulling all the time it’s moving.

That’s not actually the case, though. Everyday heavy objects need a force to keep them moving because there’s another force, friction, resisting the movement. What forces do is to accelerate objects: that is, to change their velocity. Start something moving in empty space and it’ll just keep on moving in a straight line unless you apply some force to change the motion. How much force? Newton’s Second Law answers that: force equals mass times acceleration. That is, to accelerate something weighing 2 kg by as much as something weighing 1 kg, you need to push twice as hard.

“Yes but what about gravity?” I hear you saying (whether you are or not). “That’s there all the time, and I can feel it pulling me down into my chair, but I’m not accelerating at all. I’m just sitting here. I’m not moving and I’m not starting to move either. And all the things on the table are just sitting there too.”

The answer, of course, is that there are two forces acting on you: gravity pulling you down, and the chair pushing you up. They cancel out so you don’t accelerate.

“Yes but why do they cancel out? Why is the force from the chair just the right size?” That bothered me when I first learnt basic mechanics. One answer is simply to cite Newton’s Third Law: “To every action there is an equal and opposite reaction”. The chair obeys this and reacts to gravity pulling you down onto it by pushing up against you. The Third Law says the forces are equal and so they are. But that doesn’t seem much like an answer. It amounts to “The forces balance simply because they do, and we’ve got a name for it: Newton’s Third Law of Motion.”

OK then: what would happen if the chair didn’t push quite hard enough? It wouldn’t quite cancel out the gravitational force on you, so you’d accelerate downwards. Into the chair. Squashing the upholstery and thereby making it push a bit harder, so you accelerated less . . . you’d overshoot a bit and bounce up again . . . and after a few bounces you’d end up stationary, at exactly the right point for the two forces to cancel out. The forces have to be equal because if they weren’t, they’d adjust your position until they were.

If you put a mug of tea on the table, the same explanation applies, but on a smaller scale. The outer electrons of the atoms of the two objects are repelling each other. Push them closer together and they repel more. Instead of macroscopic bouncy upholstery we’ve got a microscopic bouncy electric field. The mug rests in just the right place for  the repulsion to cancel out the gravity trying to pull it through the table.

The key thing is: stationary objects around us stay stationary because the net force acting on them is zero. They accelerate when the forces are out of balance.

How does all this relate to the Slinky? And why, when you let go of the top, doesn’t the force holding it up disappear so gravity wins and it accelerates downwards? Why does it “levitate” so counterintuitively? Surely it’s disobeying everything I just described?

Consider just one small piece of the Slinky. Imagine holding it in your hand, gently pulling one turn of it away from the next. To stretch it further, you have to pull a little harder. A given amount of stretch requires a precise strength of pull; a given strength of pull produces a precise amount of stretch.

Now consider the dangling, stationary Slinky. Think about just one turn of the spring. It has three forces acting on it:

• The turn above is pulling upwards on it. How hard depends solely on how far apart the two turns are.
• The turn below is pulling downwards on it. Again, how hard depends just on how far apart the two turns are.  (They’ll have stretched just enough to support the part dangling below.)
• Its own weight is also pulling downwards.

Before the Slinky is dropped, the three forces are in balance, so the turn we’re looking at remains stationary. It has to; moving would require accelerating. That would require at least one of the forces to change, so they didn’t balance any more. They won’t change unless one of these changes:

• The weight of this turn of the Slinky—which is constant.
• The distance between this turn and the one above. This requires the turn above to move (this one won’t until the forces change).
• The distance between this turn and the one below–i.e. the turn below must move.

In other words, the only way for a turn within the Slinky to start moving is for an adjacent one to move first.

The top turn is supported not by another turn above, but by an upward force from your fingers. When you let go of the Slinky, you simply remove this force. Now the only forces acting on the top turn are its own weight and the pull of the turn below. So it accelerates downwards, becoming the first one to move. This moves it closer to the turn below. The reduced stretch means the two turns don’t pull on each other quite so hard, so the one below no longer has quite enough upwards pull on it to keep it stationary, and it too starts accelerating.

But further down the Slinky, where nothing has moved yet, the turns are spaced  just as before. Since the pull between them depends only on their spacing, it is unchanged. Neither has the pull of gravity changed. So the forces remain in exactly the same balance, happily continuing to cancel each other out. There’s nothing to start those turns moving; they have to remain stationary.

You know from playing with such things that if you waggle one end of a Slinky or similar, a wave of movement travels along it. The same happens here: it takes time for the pulling together of adjacent turns to travel down the Slinky. And since none of the turns can start falling until the wave reaches them, they remain suspended in that impossible-looking way.

Yes but—it still seems wrong. What’s holding the bottom part up now you’ve let go? How can it hang there with nothing to hang from?!

Imagine doing pull-ups: you pull yourself up towards the bar by pulling down on it. Similarly, as the bottom part of the Slinky hangs down from the top part, it supports itself by pulling down on the top part. Once you let go, it continues doing exactly the same thing. It’s still hanging from it. The only difference is that the downward which previously went into resisting the upward pull from your hand now goes into making the top section fall faster than it would under gravity alone. It’s being forcibly accelerated downwards,  and the reaction to that accelerating force is what supports the stationary section.

The Slinky is simply behaving the way it has to.

And yet, it still looks impossible. And it took more words to explain than I expected.

## Boatswains and silicon

What do particle physics and breast implants have in common?

BBC mispronunciation, that’s what! I’m not sure whether this is a worrying trend or just a worrying longstanding tradition, but lately I’ve noticed what at least seems like an increased carelessness on the radio about the pronunciation of slightly difficult words. In some cases this is merely a bit irritating—as with the routine pronunciation of Angela Merkel as Anjullah Murkle, which probably just means the speaker is unfamiliar with how to say German words—but in other cases it’s downright misleading. Two of the latter variety have been in the news a lot over the last few days; meaning that the misinformation has been reinforced over and over again in various news bulletins.

Interestingly they both involve the same syllable, -on, in entirely different contexts. In one case it’s mispronounced; in the other it’s said instead of the correct syllable. Specifically:

### Bosons are not boatswains

If newsreaders on Radio 4 are to be believed, physicists (sorry, generic scientists) working at the Large Hadron Collider are close to confirming the existence of something called “the Higgs Bosun”. Bosun is one of those words whose spelling used to be littered with apostrophes representing omitted letters. It is now spelt either bo’sun, bosun or boatswain. (Boatswain is the original form, and the other two are derived from it, presumably because its pronunciation is so different from its spelling.) The vowels rhyme with those in open.

I’ve never been quite sure what a boatswain was, other than that it was some role on a boat. So I looked it up. According to the OED:

boatswain (also bo’sun or bosun) n. a ship’s officer in charge of equipment and the crew.

So they run the LHC like a ship and they’ve spent all this time wondering whether the the bosun exists or not, but now they’ve finally half-glimpsed him? He must spend a lot of time working from home, then . . . Or is the Higgs a ship and he’s in charge of its equipment? Ah, that must be it. He’s not the Higgs Bosun but the Higgs’ Bosun. Bosun of the Higgs. Arrrrrr.

But of course what they really mean is the Higgs Boson. The OED defines a boson as

boson n. Physics a subatomic particle, such as a photon, which has zero or integral spin.

Ah, that’s it. The entry also includes a reminder that such particles are named after the  Indian physicist S N Bose.

The s  of boson is pronounced like a z, and unsurprisingly the word rhymes with ones such as photon, proton and Vogon. The -on is pronounced like the word on.

Its mispronunciaton as bosun puzzles me. Surely even newsreaders have heard of electrons, protons, neutrons, photons . . . ? OK so they may not have heard of fermions, leptons, nucleons, mesons, kaons, pions, gluons, gravitons, positrons or (a favourite from when I studied electronics) phonons, but the basic principle is clear enough: huge numbers of particles have names ending in -on, and in every case it’s pronounced the same way. Why would it suddenly change just because of a superficial resemblance to the term for a ship’s officer?

### Silicone is not silicon

The other piece of news lately has been about women’s breasts. Specifically, ones containing what the newsreaders and even some of their expert interviewees have been calling “silicon implants”. There have been concerns that some of these may have been made using “inferior quality silicon”.

Rather than go to the OED, I’ll give you my own definition of silicon, focusing on its most relevant features. I had rather a lot to do with silicon when I was studying electronic engineering. It is

silicon n. A very hard, brittle, rigid, reflective material whose appearance is between that of glass and a metal such as steel. It has a crystal structure similar to that of diamond and is used in electronics for its semiconductor properties. Silicon is the chemical element Si, occurring naturally in the mineral quartz (silicon dioxide).

Probably your best bet if you want to see a piece of silicon is to have a look at a solar panel, which is likely to be made out of it. A piece of silicon crystal basically looks like a piece of metal made out of glass, insofar as that’s a possible appearance for anything to have.

Whenever I hear the phrase silicon implants I immediately expect to hear something about electronic devices (“silicon chips”, “microchips”) being embedded in people’s bodies—maybe for purposes like allowing nerve impulses to control prosthetic limbs, or to let artificial retinas send signals to the optic nerve to help blind people see.

You seriously don’t want to be making breasts out of silicon.  Or at least not if you want them to be anything like real ones. If your thing is razor-sharp nipples which cut through anything they touch, or built-in body armour, then maybe. But stainless steel would be cheaper.

What they mean, of course, is silicone. This doesn’t just refer to one material, but to a whole range of them including oils, substitute rubber, and squishy plastics. There’s a Wikipedia article about silicones here. The -one is pronounced exactly the same way as it is in traffic cone, telephone, semitone and the like.

The key difference between silicones and ordinary plastics is that whereas those are based on long chains of carbon atoms, silicones instead use long chains of silicon atoms alternating with oxygen atoms. So the best way to think of them is as plastics, oils, greases etc based on silicon instead of carbon.

But emphatically don’t think of silicones as silicon: calling the material breast implants are made from “silicon” is as ridiculous as calling alcohol or rubber “diamond”. Even if you’re the Higgs‘ Boatswain. And definitely if you’re a BBC newsreader.

## Books I ought to finish reading

Just for fun, here’s a list of them. As it happens, they’re also books I want to finish reading but keep forgetting to, or doing something else instead. In no partcular order (actually, the order in the pile):

#### Books to finish

• Miles Kington, How Shall I Tell The Dog?
• Oliver Sacks, Musicophilia: tales of music and the brain
• Stephen Fry, The Book of General Ignorance
• Stephen Fry, The Book of Animal Ignorance
• Steven Mithen, The Singing Neanderthals: the origins of music, language, mind and body
• Robin Dunbar, The Trouble with Science
• Seth Lloyd, Programming the Universe: a quantum computer scientist takes on the cosmos
• John D Barrow, Impossibility: the limits of science and the science of limits
• Rodney Huddleston, English Grammar: an outline
• Barry Green, The Inner Game of Music
• Andrew George (trans.), The Epic of Gilgamesh
• Eknath Eswaran (trans.), The Upanishads
• Stephen Fry, Stephen Fry’s Incomplete and Utter History of Music
• Roger McGough, Collected Poems

Some of those are books I’ve started, some I’m half way through, some I’ve nearly finished . . . and maybe some aren’t exactly for finishing, since really they’re for dipping into.

Actually, one of the most interesting of those is also one of the most demanding to read: the grammar book. It’s not, as you might imagine, a guide on how to write; it’s a very concentrated analysis of how English grammar works, and I see that on the next page I have a section which starts

Constructions involving a non-finite as complement of the predicator exhibit a great deal of diversity and complexity; they present formidable problems for the analyst—and it is not surprising that widely varying accounts are to be found in the literature. One problem is this. The prototypical complement is an NP, which is why we speak of the occurrence of non-finites in complement function as involving nominalisation.

All of which does in fact make sense, but it’s not the kind of material that effortlessly goes into the brain, especially if it’s a few months since you were last reading the book and need to remind yourself what a predicator is and what is or isn’t being nominalised, i.e. being treated like a noun. Let’s just say that once we start looking at how English grammar actually works, it makes languages like German with nice, rigid, clearly-defined rules start to look a lot more straightforward than English.

Maybe I’ll focus instead on the Miles Kington book, which has stuff like this coming up (see, I can’t help reading ahead):

Dear Gill,

People are making a lot of money out of self-help books these days, and I would like you to be one of those people.

By helping to promote my new self-help book.

Did you notice in my first letter that I referred to the jumble of self-pitying thoughts I first had when I was diagnosed with cancer?

My immediate response was to be apologetic for this stance, because we are always taught not to be sorry for ourselves, as if there were something dreadfully feeble about it. There are no nice words in English at all for ‘self-pity’. There are lots of disapproving ones. Whingeing, sulking, moping, etc., etc.

(Personally, I think we are entitled to indulge in a little self-pity when we are told we have cancer, as long as we disguise it as something else. Shock, a nervous breakdown, long sobbing fits. Something like that.)

But self-pity is so common that it earns no respect at all, only disapproval, as in phrases like: ‘Sitting around all day feeling sorry for herself,’ or ‘You’d think he was the only one who had ever had leukaemia.’ Which quickly leads to phrases like: ‘Why doesn’t she just pull herself together?’ and ‘Cheer up dear—it’s only bi-polar disorder!’

My brilliant idea would be to turn it all round and treat self-pity as a potentially positive force.

This certainly seems to be a brilliant book, from the 40% or so that I’ve read in its intended order. Miles Kington wrote it in the last months of his life, when he knew that he did in fact have cancer and might well die from it. It takes the form of supposed letters to his literary agent about ideas for books he might write about the situation, but is really a humorous but heartfelt look at attitudes encountered and so on. Very entertaining, but also thought-provoking.

But that’s just one list of books. Here’s another:

#### Books to start

The main reason I haven’t started the books in this list is that I don’t have them. They’ve been recommended, or mentioned, by other people:

• [I don’t know the author], The Universe is a Green Dragon
• Peter Bernstein, Against the Gods: the remarkable story of risk
• Daniel M Wegner, The Illusion of Conscious Will

Now that’s a much shorter list, but I’ve a nasty feeling that’s simply because of having forgotten to make a note of them all . . . Oh dear. I wonder what’s missing . . .

## The bizarre similarity between money and quantum physics

I don’t know about you, but I’ve always found money very puzzling for various reasons. Especially when it comes to what the banks do with it. I’ve never been quite convinced that money actually exists: it’s a number that we do things with. If you pay me for something, your number goes down and my number goes up. If my number goes down to zero and my bank won’t let it keep going then I’m in big trouble, because people won’t hand things over to me in shops and so on. To do that, they want me to make their number go up.

And I’ve never really understood how “the money supply” can be increased. Coins and notes can be printed, sure, but whose are they and how do they get into circulation without somebody in effect “stealing” them? Is it actually valid to create it out of nowhere? All very strange.

The subject came up again when my friend PamBG, who once worked in finance and is now a Methodist minister, wrote a puzzled post about “quantitative easing”.

She didn’t get the answer to her question, some discussion ensued about the nature of money, the value of a company’s stocks, and the like. (The more I think about these things, the more convinced I become that money is really just a mental trick.)

As it happens, I had to study quite a lot of quantum physics at university, for my electronics degree. (This isn’t surprising, since quantum physics is the physics of the extremely small, electrons are extremely small, and electronics is based on their behaviour.) And in studying that, I had the same sense of things only just existing, or not quite existing. (I mean, an electron exists but doesn’t properly know where it is or how fast it’s going, or if it knows one it doesn’t know the other; that’s roughly what the Uncertainty Principle says.) It seemed very much like a game played with certain rules and numbers. A game which happened to predict very well what measurement you’d get if you did a particular experiment, but a game nevertheless, which simply dealt with the numbers and rules and was silent about the actual nature of the physical objects playing the game. All it said was that they obeyed the rules. (Scientifically, all that can be studied is the rules and numbers, since they can be observed; all we can say about any underlying reality is that if there is one, it’s one which fits them.)

And it also so happens that I find the ideas of quantum physics easier to “grasp” [1] than the ideas of finance, so the analogy that follows was a bit of a breakthrough for me. Here are some shortened extracts from the later part of the conversation:

Pam:

In some senses ‘money doesn’t really exist’ – which was people’s complaint when the West went off the gold standard in the 1970s. (Previously, all money printed had to have a certain value with respect to an ounce of gold.)

And markets are driven by psychology. Fear and greed. A very simple explanation: financial instruments are priced according what people will think that they will be worth in the future. So, if a particular company is expected to grow by 5% per annum over the next two years, and its assets are now £100, its stock price would be £110.25. (This is hugely simplistic for illustrative purposes.)

The problem, of course, is that you have to guess how much everything is going to grow [. . .]

Tim:

[. . .] I heard on a radio programme that the first time there was a real banking crisis after the Bank of England formed, people were very unhappy about paper money, complaining that it wasn’t actually money.

It’s interesting: atheists accuse us of basing our lives on something that doesn’t exist, namely God, but arguably modern society runs on something that doesn’t exist, namelly money! (I’m only half joking.)

ISTM you’re saying that the value of a piece of paper simply exists in the mind of the buyer and seller.

Pam:

Yes, I think it probably is. It’s a corollary of ‘something is only worth what a buyer is willing to pay for it’ [. . .]

Tim:

Bizarrely, there’s a parallel with quantum physics, too [. . .]

In quantum physics—the physics of the ultra-small—a quantity generally exists in an “indeterminate” state until it is measured. The act of measurement forces it to stop being indeterminate and have a definite value.

Similarly it seems to me that a house, say, doesn’t have a definite value until you measure the price by letting somebody pay for it.

So in a way, the financial value of something is always in the future and hovering on the brink of existence.

Hmmm…

Pam:

Tim – Not only does that seem quite correct to me with respect to money and financial markets, but you’ve just helped me to better understand that principle in quantum physics.

And maybe that’s why money is so confusing. In quantum physics, you mostly don’t know things like the position or momentum of a particle; you only know the probability of it being within a particular range. And, according to the most widely accepted interpretation, the particle doesn’t “know” either. It really doesn’t have a precise position or momentum until it’s “observed” in some way.

Similarly with money: your house doesn’t have a precise value except at the moment of sale. All it has is a particular probability of lying in a particular price range. And the same is true of the the things in which your money in the bank is invested.

And it seems to me that this might be why the economy gives us so much grief: we’re dealing with things which have at best a shadowy existence, but much of the time we treat them like the most concrete reality there is.

Thoughts?

#### Note

[1] I think it was either Heisenberg or Schrödinger who said that if you weren’t confused by quantum mechanics you hadn’t understood it; hence “grasp” in quotes. Back

## Sanity and the Large Hadron Collider

Sorry this is a bit long–I’m trying to cram quite a lot of science into a rather small space–but not at anything like the speed of light 😉
Wednesday was the “start-up” of the Large Hadron Collider at CERN. As I’m sure you all know…

#### Encouraging the insanity

What should have been an exciting day was marred for me by all the persistent “end-of-the-world” hype in the media and on the Internet. There was a news report of a teenage girl in India who believed the stories enough to kill herself: she thought that when it was switched on, the Earth would be swallowed up by a black hole. It makes me angry that there’s so much misinformation around, both about what is/was being done and about the “likely” effects.

It makes me particularly angry to hear that small children, who one would hope would be getting excited about science in the same way that we as children got excited about space when we saw the moon landings, have instead been going around terrified of the end of the world.

Now, not everyone understands particle physics. But surely simple explanations are possible which address people’s fears. And one would hope that the media would search these out and pass them on.

OK, maybe that was a reckless statement, because I now have to try to write a simple explanation myself. And I’m not a particle physicist, just someone who did a physics-related subject at university. But here goes. [Edit: someone has now helpfully pointed out that as a blogger, I am one of the media. Hmmm…]

#### What are they doing?

Eventually (but not on Wednesday): trying to bash protons together at very high speeds, i.e. with a lot of energy. A proton is the heavy bit in the middle of a hydrogen atom. If you do this hard enough, the actual energy of the collision is converted into extra particles. One hope of the experiment is that these will include the famous Higgs Boson which everyone wants to find. Being a particularly heavy particle if it exists, it needs a lot of energy to make it, which means incredibly high speeds.

Wednesday: simply tests to check that a beam of protons, going at speeds that have been in use for years–not at the colossal speeds hoped for in future–could make it all the way round the 27-km circuit in a clockwise direction. Then a similar test to see if another beam could get round in the anticlockwise direction. No ultra-high energies. Not even two beams colliding with each other. Lots of very relieved engineers who’d spent years of their lives working on the project finally getting some indication that the machine might work. Bottles of champagne.

Given that what happened on Wednesday wasn’t even really new, it’s hard to see why so many people thought it was going to end the world. Unless maybe THE MEDIA didn’t bother to find out the facts properly and report them responsibly… Perish the thought.

#### Is it going to destroy the world, then?

We’ve heard a lot about various speculative ways for this to happen. Sadly we’ve heard a lot less about why nobody in the physics community thinks they’re the least bit likely. I suppose “nothing will happen” and “science fiction is fiction” aren’t really news. They’re not even particularly exciting. So they don’t get reported. I also suspect that to the physicists, who are intimately familiar with the science, the idea seems so fatuous that it barely seems to need explaining. Would you expect someone to come and ask you to explain why sailing over the horizon won’t make you drop off the edge of the world? No, because you’d have to change your whole view of the world you deal with every day.

CERN has produced a quite informative Safety page. What follows is a summary of that, with some additions from other sources. The CERN page also includes links to various safety reports and relevant scientific publications.

#### The experiment has happened already

In fact, it happens all the time. I’m talking about cosmic rays.

These are particles from space which routinely hit the earth, some at extremely high energies–considerably higher than the LHC is aiming for. So, in fact, the LHC experiment (and more energetic ones) is effectively happening in the Earth and its atmosphere every day. But at random and mostly without any fancy detectors to observe it. The LHC safety page points out that the Earth has already been hit by the cosmic-ray equivalent of about a million LHC experiments. Oddly, it still hasn’t been destroyed.

Is it really like cosmic rays, though? After all, cosmic rays don’t arrive all bunched together in a very thin beam. Might this make a difference? After all, we’ve got lots of collisions happening close together… Well I asked someone at the LHC about this and it turns out that the collisions are still WAY too far apart to have any effect whatever. So yes, it’s like cosmic rays.

#### Ways the world won’t end

Black holes: Could the LHC produce an earth-swallowing black hole? Well…

• Standard theory says it can’t produce black holes at all. But if that’s wrong, then
• the theories that think it can all say that the black holes would disappear in a tiny instant and have no chance to start growing.
• a black hole that could grow and swallow its surroundings would need to start off as heavy as Mount Everest anyway. (Imagine trying to stuff a whole mountain into the machine and accelerate it to almost the speed of light…)
• If the LHC could swallow up the earth in a black hole, then so could the cosmic rays which keep hitting us. Not only haven’t they succeeded, but there’s no sign that its happened anywhere else in the universe either.

Vacuum bubbles: As I understand it, these are part of a speculative theory where regions of the universe could “flip” into a different state, where matter would have different properties and we could not exist.

• If the LHC could cause this, then high-energy cosmic rays would already have done it. The LHC is quite weedy in comparison
• and actually there’s no evidence of ANYTHING having caused it anywhere in the observed universe.

Strangelets: the idea here is that the LHC produces a tiny lump of an exotic kind of matter, which then converts ordinary matter to strange matter when it comes in contact with it.

• This is the opposite of what strange matter would be expected to do. If it can exist, it’s expected to convert itself immediately to ordinary matter.
• The “possibility” was however explored before the start-up in 2000 of another machine, the Relativistic Heavy Ion Collider or RHIC, which was far more likely than the LHC to produce strangelets. Eight years on, it still hasn’t managed to produce any.
• The particles to make strangelets can only stick together if they’re travelling slowly enough; the LHC simply bashes things together too fast. If the RHIC couldn’t do it, the RHC hasn’t a chance.

Magnetic monopoles: These are hypothetical particles a bit like magnets with only one end. (I have trouble imagining them!). Some theories think they could do nasty things to the protons in ordinary matter. However,

• the theories that say they can do this also say they’re too heavy for the LHC to produce.
• if the LHC could make them, then the cosmic rays that hit us are already making them, and have been for billions of years, with no ill effect.

So they’re either impossible for the LHC to make, or safe and here already.