Tag Archives: relativity

Fun with Misunderstandings

Perimeter had its last Public Lecture of the season this week, with Mario Livio giving some highlights from his book Brilliant Blunders. The lecture should be accessible online, either here or on Perimeter’s YouTube page.

These lectures tend to attract a crowd of curious science-fans. To give them something to do while they’re waiting, a few local researchers walk around with T-shirts that say “Ask me, I’m a scientist!” Sometimes we get questions about the upcoming lecture, but more often people just ask us what they’re curious about.

Long-time readers will know that I find this one of the most fun parts of the job. In particular, there’s a unique challenge in figuring out just why someone asked a question. Often, there’s a hidden misunderstanding they haven’t recognized.

The fun thing about these misunderstandings is that they usually make sense, provided you’re working from the person in question’s sources. They heard a bit of this and a bit of that, and they come to the most reasonable conclusion they can given what’s available. For those of us who have heard a more complete story, this often leads to misunderstandings we would never have thought of, but that in retrospect are completely understandable.

One of the simpler ones I ran into was someone who was confused by people claiming that we were running out of water. How could there be a water shortage, he asked, if the Earth is basically a closed system? Where could the water go?

The answer is that when people are talking about a water shortage, they’re not talking about water itself running out. Rather, they’re talking about a lack of safe drinking water. Maybe the water is polluted, or stuck in the ocean without expensive desalinization. This seems like the sort of thing that would be extremely obvious, but if you just hear people complaining that water is running out without the right context then you might just not end up hearing that part of the story.

A more involved question had to do with time dilation in general relativity. The guy had heard that atomic clocks run faster if you’re higher up, and that this was because time itself runs faster in lower gravity.

Given that, he asked, what happens if someone travels to an area of low gravity and then comes back? If more time has passed for them, then they’d be in the future, so wouldn’t they be at the “wrong time” compared to other people? Would they even be able to interact with them?

This guy’s misunderstanding came from hearing what happens, but not why. While he got that time passes faster in lower gravity, he was still thinking of time as universal: there is some past, and some future, and if time passes faster for one person and slower for another that just means that one person is “skipping ahead” into the other person’s future.

What he was missing was the explanation that time dilation comes from space and time bending. Rather than “skipping ahead”, a person for whom time passes faster just experiences more time getting to the same place, because they’re traveling on a curved path through space-time.

As usual, this is easier to visualize in space than in time. I ended up drawing a picture like this:

IMG_20160602_101423

Imagine person A and person B live on a circle. If person B stays the same distance from the center while person A goes out further, they can both travel the same angle around the circle and end up in the same place, but A will have traveled further, even ignoring the trips up and down.

What’s completely intuitive in space ends up quite a bit harder to visualize in time. But if you at least know what you’re trying to think about, that there’s bending involved, then it’s easier to avoid this guy’s kind of misunderstanding. Run into the wrong account, though, and even if it’s perfectly correct (this guy had heard some of Hawking’s popularization work on the subject), if it’s not emphasizing the right aspects you can come away with the wrong impression.

Misunderstandings are interesting because they reveal how people learn. They’re windows into different thought processes, into what happens when you only have partial evidence. And because of that, they’re one of the most fascinating parts of science popularization.

The Three Things Everyone Gets Wrong about the Big Bang

Ah, the Big Bang, our most science-y of creation myths. Everyone knows the story of how the universe and all its physical laws emerged from nothing in a massive explosion, growing from a singularity to the size of a breadbox until, over billions of years, it became the size it is today.

A hot dense state, if you know what I mean.

…actually, almost nothing in that paragraph is true. There are a lot of myths about the Big Bang, born from physicists giving sloppy explanations. Here are three things most people get wrong about the Big Bang:

1. A Massive Explosion:

When you picture the big bang, don’t you imagine that something went, well, bang?

In movies and TV shows, a time traveler visiting the big bang sees only an empty void. Suddenly, an explosion lights up the darkness, shooting out stars and galaxies until it has created the entire universe.

Astute readers might find this suspicious: if the entire universe was created by the big bang, then where does the “darkness” come from? What does the universe explode into?

The problem here is that, despite the name, the big bang was not actually an explosion.

In picturing the universe as an explosion, you’re imagining the universe as having finite size. But it’s quite likely that the universe is infinite. Even if it is finite, it’s finite like the surface of the Earth: as Columbus (and others) experienced, you can’t get to the “edge” of the Earth no matter how far you go: eventually, you’ll just end up where you started. If the universe is truly finite, the same is true of it.

Rather than an explosion in one place, the big bang was an explosion everywhere at once. Every point in space was “exploding” at the same time. Each point was moving farther apart from every other point, and the whole universe was, as the song goes, hot and dense.

So what do physicists mean when they say that the universe at some specific time was the size of a breadbox, or a grapefruit?

It’s just sloppy language. When these physicists say “the universe”, what they mean is just the part of the universe we can see today, the Hubble Volume. It is that (enormously vast) space that, once upon a time, was merely the size of a grapefruit. But it was still adjacent to infinitely many other grapefruits of space, each one also experiencing the big bang.

2. It began with a Singularity:

This one isn’t so much definitely wrong as probably wrong.

If the universe obeys Einstein’s Theory of General Relativity perfectly, then we can make an educated guess about how it began. By tracking back the expansion of the universe to its earliest stages, we can infer that the universe was once as small as it can get: a single, zero-dimensional point, or a singularity. The laws of general relativity work the same backwards and forwards in time, so just as we could see a star collapsing and know that it is destined to form a black hole, we can see the universe’s expansion and know that if we traced it back it must have come from a single point.

This is all well and good, but there’s a problem with how it begins: “If the universe obeys Einstein’s Theory of General Relativity perfectly”.

In this situation, general relativity predicts an infinitely small, infinitely dense point. As I’ve talked about before, in physics an infinite result is almost never correct. When we encounter infinity, almost always it means we’re ignoring something about the nature of the universe.

In this case, we’re ignoring Quantum Mechanics. Quantum Mechanics naturally makes physics somewhat “fuzzy”: the Uncertainty Principle means that a quantum state can never be exactly in one specific place.

Combining quantum mechanics and general relativity is famously tricky, and the difficulty boils down to getting rid of pesky infinite results. However, several approaches exist to solving this problem, the most prominent of them being String Theory.

If you ask someone to list string theory’s successes, one thing you’ll always hear mentioned is string theory’s ability to understand black holes. In general relativity, black holes are singularities: infinitely small, and infinitely dense. In string theory, black holes are made up of combinations of fundamental objects: strings and membranes, curled up tight, but crucially not infinitely small. String theory smooths out singularities and tamps down infinities, and the same story applies to the infinity of the big bang.

String theory isn’t alone in this, though. Less popular approaches to quantum gravity, like Loop Quantum Gravity, also tend to “fuzz” out singularities. Whichever approach you favor, it’s pretty clear at this point that the big bang didn’t really begin with a true singularity, just a very compressed universe.

3. It created the laws of physics:

Physicists will occasionally say that the big bang determined the laws of physics. Fans of Anthropic Reasoning in particular will talk about different big bangs in different places in a vast multi-verse, each producing different physical laws.

I’ve met several people who were very confused by this. If the big bang created the laws of physics, then what laws governed the big bang? Don’t you need physics to get a big bang in the first place?

The problem here is that “laws of physics” doesn’t have a precise definition. Physicists use it to mean different things.

In one (important) sense, each fundamental particle is its own law of physics. Each one represents something that is true across all of space and time, a fact about the universe that we can test and confirm.

However, these aren’t the most fundamental laws possible. In string theory, the particles that exist in our four dimensions (three space dimensions, and one of time) change depending on how six “extra” dimensions are curled up. Even in ordinary particle physics, the value of the Higgs field determines the mass of the particles in our universe, including things that might feel “fundamental” like the difference between electromagnetism and the weak nuclear force. If the Higgs field had a different value (as it may have early in the life of the universe), these laws of physics would have been different. These sorts of laws can be truly said to have been created by the big bang.

The real fundamental laws, though, don’t change. Relativity is here to stay, no matter what particles exist in the universe. So is quantum mechanics. The big bang didn’t create those laws, it was a natural consequence of them. Rather than springing physics into existence from nothing, the big bang came out of the most fundamental laws of physics, then proceeded to fix the more contingent ones.

In fact, the big bang might not have even been the beginning of time! As I mentioned earlier in this article, most approaches to quantum gravity make singularities “fuzzy”. One thing these “fuzzy” singularities can do is “bounce”, going from a collapsing universe to an expanding universe. In Cyclic Models of the universe, the big bang was just the latest in a cycle of collapses and expansions, extending back into the distant past. Other approaches, like Eternal Inflation, instead think of the big bang as just a local event: our part of the universe happened to be dense enough to form a big bang, while other regions were expanding even more rapidly.

So if you picture the big bang, don’t just imagine an explosion. Imagine the entire universe expanding at once, changing and settling and cooling until it became the universe as we know it today, starting from a world of tangled strings or possibly an entirely different previous universe.

Sounds a bit more interesting to visit in your TARDIS, no?

What Can Replace Space-Time?

Nima Arkani-Hamed is famous for believing that space-time is doomed, that as physicists we will have to abandon the concepts of space and time if we want to find the ultimate theory of the universe. He’s joked that this is what motivates him to get up in the morning. He tends to bring it up often in talks, both for physicists and for the general public.

The latter especially tend to be baffled by this idea. I’ve heard a lot of questions like “if space-time is doomed, what could replace it?”

In the past, Nima and I both tended to answer this question with a shrug. (Though a more elaborate shrug in his case.) This is the honest answer: we don’t know what replaces space-time, we’re still looking for a good solution. Nima’s Amplituhedron may eventually provide an answer, but it’s still not clear what that answer will look like. I’ve recently realized, though, that this way of responding to the question misses its real thrust.

When people ask me “what could replace space-time?” they’re not asking “what will replace space-time?” Rather, they’re asking “what could possibly replace space-time?” It’s not that they want to know the answer before we’ve found it, it’s that they don’t understand how any reasonable answer could possibly exist.

I don’t think this concern has been addressed much by physicists, and it’s a pity, because it’s not very hard to answer. You don’t even need advanced physics. All you need is some fairly old philosophy. Specifically we’ll use concepts from metaphysics, the branch of philosophy that deals with categories of being.

Think about your day yesterday. Maybe you had breakfast at home, drove to work, had a meeting, then went home and watched TV.

Each of those steps can be thought of as an event. Each event is something that happened that we want to pay attention to. You having breakfast was an event, as was you arriving at work.

These events are connected by relations. Here, each relation specifies the connection between two events. There might be a relation of cause-and-effect, for example, between you arriving at work late and meeting with your boss later in the day.

Space and time, then, can be seen as additional types of relations. Your breakfast is related to you arriving at work: it is before it in time, and some distance from it in space. Before and after, distant in one direction or another, these are all relations between the two events.

Using these relations, we can infer other relations between the events. For example, if we know the distance relating your breakfast and arriving at work, we can make a decent guess at another relation, the difference in amount of gas in your car.

This way of viewing the world, events connected by relations, is already quite common in physics. With Einstein’s theory of relativity, it’s hard to say exactly when or where an event happened, but the overall relationship between two events (distance in space and time taken together) can be thought of much more precisely. As I’ve mentioned before, the curved space-time necessary for Einstein’s theory of gravity can be thought of equally well as a change in the way you measure distances between two points.

So if space and time are relations between events, what would it mean for space-time to be doomed?

The key thing to realize here is that space and time are very specific relations between events, with very specific properties. Some of those properties are what cause problems for quantum gravity, problems which prompt people to suggest that space-time is doomed.

One of those properties is the fact that, when you multiply two distances together, it doesn’t matter which order you do it in. This probably sounds obvious, because you’re used to multiplying normal numbers, for which this is always true anyway. But even slightly more complicated mathematical objects, like matrices, don’t always obey this rule. If distances were this sort of mathematical object, then multiplying them in different orders could give slightly different results. If the difference were small enough, we wouldn’t be able to tell that it was happening in everyday life: distance would have given way to some more complicated concept, but it would still act like distance for us.

That specific idea isn’t generally suggested as a solution to the problems of space and time, but it’s a useful toy model that physicists have used to solve other problems.

It’s the general principle I want to get across: if you want to replace space and time, you need a relation between events. That relation should behave like space and time on the scales we’re used to, but it can be different on very small scales (Big Bang, inside of Black Holes) and on very large scales (long-term fate of the universe).

Space-time is doomed, and we don’t know yet what’s going to replace it. But whatever it is, whatever form it takes, we do know one thing: it’s going to be a relation between events.

Made of Energy, or Made of Nonsense?

I did a few small modifications to the blog settings this week. Comments now support Markdown, reply-chains in the comments can go longer, and there are a few more sharing buttons on the posts. I’m gearing up to do a more major revamp of the blog in July for when the name changes over from 4 gravitons and a grad student to just 4 gravitons.

io9 did an article recently on scientific ideas that scientists wish the public would stop misusing. They’ve got a lot of good ones (Proof, Quantum, Organic), but they somehow managed to miss one of the big ones: Energy. Matt Strassler has a nice, precise article on this particular misconception, but nonetheless I think it’s high time I wrote my own.

There’s a whole host of misconceptions regarding energy. Some of them are simple misuses of language, like zero-calorie energy drinks:

Zero Purpose

Energy can be measured in several different units. You can use Joules, or electron-Volts, or dynes…or calories. Calories are a measure of energy, so zero calories quite literally means zero energy.

Now, that’s not to say the makers of zero calorie energy drinks are lying. They’re just using a different meaning of energy from the scientific one. Their drinks give you vim and vigor, the get-up-and-go required to make money playing computer games. For most of the public, that “get-up-and-go” is called energy, even if scientifically it’s not.

That’s not really a misconception, more of an amusing use of language. This next one though really makes my blood boil.

Raise your hand if you’ve seen a Sci-Fi movie or TV show where some creature is described as being made of “pure energy”. Whether they’re peaceful, ultra-advanced ascended beings, or genocidal maniacs from another dimension, the concept of creatures made of “pure energy” shows up again and again and again.

You can’t fight the Drej, they’re pure bullshit!

Even if you aren’t the type to take Sci-Fi technobabble seriously, you’ve probably heard that matter and antimatter annihilate to form energy, or that photons are made out of energy. These sound more reasonable, but they rest on the same fundamental misconception:

Nothing is “made out of energy”.

Rather,

Energy is a property that things have.

Energy isn’t a substance, it isn’t a fluid, it isn’t some kind of nebulous stuff you can make into an indestructible alien body. Things have energy, but nothing is energy.

What about light, then? And what happens when antimatter collides with matter?

Light, just like anything else, has energy. The difference between light and most other things is that light also does not have mass.

In everyday life, we like to think of mass as some sort of basic “stuff”. If things are “made out of mass” or “made out of matter”, and something like light doesn’t have mass, then it must be made out of some other “stuff”, right?

The thing is, mass isn’t really “stuff” any more than energy is. Just like energy, mass is a property that things have. In fact, as I’ve talked about some before, mass is really just a type of energy. Specifically, mass is the energy something has when left alone and at rest. That’s the meaning of Einstein’s famous equation, E equals m c squared: it tells you how to take a known mass and calculate the rest energy that it implies.

Lots of hype for a unit conversion formula, huh?

In the case of light, all of its energy can be thought of in terms of its (light-speed) motion, so it has no mass. That might tempt you to think of it as being “made of energy”, but really, you and light are not so different.

You are made of atoms, and atoms are made of protons, neutrons, and electrons. Let’s consider a proton. A proton’s mass, expressed in the esoteric units physicists favor, is 938 Mega-electron-Volts. That’s how much energy a proton has alone and and rest. A proton is made of three quarks, so you’d think that they would contribute most of its mass. In reality, though, the quarks in protons have masses of only a few Mega-electron-Volts. Most of a proton’s mass doesn’t come from the mass of the quarks.

Quarks interact with each other via the strong nuclear force, the strongest fundamental force in existence. That interaction has a lot of energy, and when viewed from a distance that energy contributes almost all of the proton’s mass. So if light is “made of energy”, so are you.

So why do people say that matter and anti-matter annihilate to make energy?

A matter particle and its anti-matter partner are opposite in a lot of ways. In particular, they have opposite charges: not just electric charge, but other types of charge too.

Charge must be conserved, so if a particle collides with its anti-particle the result has a total charge of zero, as the opposite charges of the two cancel each other out. Light has zero charge, so it’s one of the most common results of a matter-antimatter collision. When people say that matter and antimatter produce “pure energy”, they really just mean that they produce light.

So next time someone says something is “made of energy”, be wary. Chances are, they aren’t talking about something fully scientific.

Editors, Please Stop Misquoting Hawking

If you’ve been following science news recently, you’ve probably heard the apparently alarming news that Steven Hawking has turned his back on black holes, or that black holes can actually be escaped, or…how about I just show you some headlines:

FoxHawking

NatureHawking

YahooHawking

Now, Hawking didn’t actually say that black holes don’t exist, but while there are a few good pieces on the topic, in many cases the real message has gotten lost in the noise.

From Hawking’s paper:

ActualPaperHawking

What Hawking is proposing is that the “event horizon” around a black hole, rather than being an absolute permanent boundary from which nothing can escape, is a more temporary “apparent” horizon, the properties of which he goes on to describe in detail.

Why is he proposing this? It all has to do with the debate over black hole firewalls.

Starting with a paper by Polchinski and colleagues a year and a half ago, the black hole firewall paradox centers on contradictory predictions from general relativity and quantum mechanics. General relativity predicts that an astronaut falling past a black hole’s event horizon will notice nothing particularly odd about the surrounding space, but that once past the event horizon none of the “information” that specifies the astronaut’s properties can escape to the outside world. Quantum mechanics on the other hand predicts that information cannot be truly lost. The combination appears to suggest something radical, a “firewall” of high energy radiation around the event horizon carrying information from everything that fell into the black hole in the past, so powerful that it would burn our hypothetical astronaut to a crisp.

Since then, a wide variety of people have made one proposal or another, either attempting to avoid the seemingly preposterous firewall or to justify and further explain it. The reason the debate is so popular is because it touches on some of the fundamental principles of quantum mechanics.

Now, as I have pointed out before, I’m not a good person to ask about the fundamental principles of quantum mechanics. (Incidentally, I’d love it if some of the more quantum information or general relativity-focused bloggers would take a more substantial crack at this! Carroll, Preskill, anyone?) What I can talk about, though, is hype.

All of the headlines I listed take Hawking’s quote out of context, but not all of the articles do. The problem isn’t so much the journalists, as the editors.

One of an editor’s responsibilities is to take articles and give them titles that draw in readers. The editor wants a title that will get people excited, make them curious, and most importantly, get them to click. While a journalist won’t have any particular incentive to improve ad revenue, the same cannot be said for an editor. Thus, editors will often rephrase the title of an article in a way that makes the whole story seem more shocking.

Now that, in itself, isn’t a problem. I’ve used titles like that myself. The problem comes when the title isn’t just shocking, but misleading.

When I call astrophysics “impossible”, nobody is going to think I mean it literally. The title is petulant and ridiculous enough that no-one would take it at face value, but still odd enough to make people curious. By contrast, when you say that Hawking has “changed his mind” about black holes or said that “black holes do not exist”, there are people who will take that at face value as supporting their existing beliefs, as the Borowitz Report humorously points out. These people will go off thinking that Hawking really has given up on black holes. If the title confirms their beliefs enough, people might not even bother to read the article. Thus, by using an actively misleading title, you may actually be decreasing clicks!

It’s not that hard to write a title that’s both enough of a hook to draw people in and won’t mislead. Editors of the world, you’re well-trained writers, certainly much better than me. I’m sure you can manage it.

There really is some interesting news here, if people had bothered to look into it. The firewall debate has been going on for a year and a half, and while Hawking isn’t the universal genius the media occasionally depicts he’s still the world’s foremost expert on the quantum properties of black holes. Why did he take so long to weigh in? Is what he’s proposing even particularly new? I seem to remember people discussing eliminating the horizon in one way or another (even “naked” singularities) much earlier in the firewall debate…what makes Hawking’s proposal novel and different?

This is the sort of thing you can use to draw in interest, editors of the world. Don’t just write titles that cause ignorant people to roll their eyes and move on, instead, get people curious about what’s really going on in science! More ad revenue for you, more science awareness for us, sounds like a win-win!

What’s A Graviton? Or: How I Learned to Stop Worrying and Love Quantum Gravity

I’m four gravitons and a grad student. And despite this, I haven’t bothered to explain what a graviton is. It’s time to change that.

Let’s start like we often do, with a quick answer that will take some unpacking:

Gravitons are the force-carrying bosons of gravity.

I mentioned force-carrying bosons briefly here. Basically, a force can either be thought of as a field, or as particles called bosons that carry the effect of that field. Thinking about the force in terms of particles helps, because it allows you to visualize Feynman diagrams. While most forces come from Yang-Mills fields with spin 1, gravity has spin 2.

Now you may well ask, how exactly does this relate to the idea that gravity, unlike other forces, is a result of bending space and time?

First, let’s talk about what it means for space itself to be bent. If space is bent, distances are different than they otherwise would be.

Suppose we’ve got some coordinates: x and y. How do we find a distance? We use the Pythagorean Theorem:

d^2=x^2+y^2

Where d is the full distance. If space is bent, the formula changes:

d^2=g_{x}x^2+g_{y}y^2

Here g_{x} and g_{y} come from gravity. Normally, they would depend on x and y, modifying the formula and thus “bending” space.

Let’s suppose instead of measuring a distance, we want to measure the momentum of some other particle, which we call \phi because physicists are overly enamored of Greek letters. If p_{x,\phi} is its momentum (physicists also really love subscripts), then its total momentum can be calculated using the Pythagorean Theorem as well:

p_\phi^2= p_{x,\phi}^2+ p_{y,\phi}^2

Or with gravity:

p_\phi^2= g_{x}p_{x,\phi}^2+ g_{y} p_{y,\phi}^2

At the moment, this looks just like the distance formula with a bunch of extra stuff in it. Interpreted another way, though, it becomes instructions for the interactions of the graviton. If g_{x} and g_{y} represent the graviton, then this formula says that one graviton can interact with two \phi particles, like so:

graviton

Saying that gravitons can interact with \phi particles ends up meaning the same thing as saying that gravity changes the way we measure the \phi particle’s total momentum. This is one of the more important things to understand about quantum gravity: the idea that when people talk about exotic things like “gravitons”, they’re really talking about the same theory that Einstein proposed in 1916. There’s nothing scary about describing gravity in terms of particles just like the other forces. The scary bit comes later, as a result of the particular way that quantum calculations with gravity end up. But that’s a tale for another day.

What are colliders for, anyway?

Above is a thoroughly famous photo from ATLAS, one of six different particle detectors that sit around the ring of the Large Hadron Collider (or LHC for short). Forming a 26 kilometer ring spanning a chunk of southern France and Switzerland, the LHC is the biggest experiment of its kind, with the machine alone costing around 4 billion dollars.

But what is “its kind”? And why does it need to be so huge?

Aesthetics, clearly.

Explaining what a particle collider like the LHC does is actually fairly simple, if you’re prepared for some rather extreme mental images: using incredibly strong magnetic fields, the LHC accelerates protons until they’re moving at 99.9999991% of the speed of light, then lets them smash into each other in the middle of sophisticated detectors designed to observe and track everything that comes out of the collision.

That’s all well and awesome, but why do the protons need to be moving so fast? Are they really really hard to crack open, or something?

This gets at a common misunderstanding of particle physics, which I’d like to correct here.

When most people imagine what a particle collider does, they picture it smashing particles together like hollow shells, revealing the smaller particles trapped inside. You may have even heard particle colliders referred to as “atom smashers”, and if you’re used to hearing about scientists “splitting the atom”, this all makes sense: with lots of energy, atoms can be broken apart into protons and neutrons, which is what they are made of. Protons are made of quarks, and quarks were discovered using particle colliders, so the story seems to check out, right?

The thing is, lots of things have been discovered using particle colliders that definitely aren’t part of protons and neutrons. Relatives of the electron like muons and tau particles, new varieties of neutrinos, heavier quarks…pretty much the only particles that are part of protons or neutrons are the three lightest quarks (and that’s leaving aside the fact that what is or is not “part of” a proton is a complicated question in its own right).

So where do the extra particles come from? How do you crash two protons together and get something out that wasn’t in either of them?

You…throw Einstein at them?

E equals m c squared. This equation, famous to the point of cliché, is often misinterpreted. One useful way to think about it is that it describes mass as a type of energy, and clarifies how to convert between units of mass and units of energy. Then E in the equation is merely the contribution to the energy of a particle from its mass, while the full energy also includes kinetic energy, the energy of motion.

Energy is conserved, that is, cannot be created or destroyed. Mass, on the other hand, being merely one type of energy, is not necessarily conserved. The reason why mass seems to be conserved in day to day life is because it takes a huge amount of energy to make any appreciable mass: the c in m c squared is the speed of light, after all. That’s why if you’ve got a radioactive atom it will decay into lighter elements, never heavier ones.

However, this changes with enough kinetic energy. If you get something like a proton accelerated to up near the speed of light, its kinetic energy will be comparable to (or even much higher than) its mass. With that much “spare” energy, energy can transform from one form into another: from kinetic energy into mass!

Of course, it’s not quite that simple. Energy isn’t the only thing that’s conserved: so is charge, and not just electric charge, but other sorts of charge too, like the colors of quarks.  All in all, the sorts of particles that are allowed to be created are governed by the ways particles can interact. So you need not just one high energy particle, but two high energy particles interacting in order to discover new particles.

And that, in essence, is what a particle collider is all about. By sending two particles hurtling towards each other at almost the speed of light you are allowing two high energy particles to interact. The bigger the machine, the faster those particles can go, and thus the more kinetic energy is free to transform into mass. Thus the more powerful you make your particle collider, the more likely you are to see rare, highly massive particles that if left alone in nature would transform unseen into less massive particles in order to release their copious energy. By producing these massive particles inside a particle collider we can make sure they are created inside of sophisticated particle detectors, letting us observe what they turn into with precision and extrapolate what the original particles were. That’s how we found the Higgs, and it’s how we’re trying to find superpartners. It’s one of the only ways we have to answer questions about the fundamental rules that govern the universe.