osmie: (Default)
The other really neat scientific oddity I've run across lately is strangelets.

Before I go further, let me wonder aloud how I could possibly have made it all the way through a physics degree in the early 1990s without ever hearing about these particular beasties. There; it is wondered. I don't know the answer.

To understand strangelets, you need a basic grasp of quarks. Now, there are six types of quark in the standard model, which have been given six perfectly arbitrary names that all begin with a different letter: Up, Down, Charm, Strange, Top and Bottom. Up and Down are the only quarks which show up in ordinary matter; the rest are too heavy, and tend to decay into Up and Down quarks if you take the ridiculously high pressure off for even an instant.

Quarks like to bind together in groups: no one has ever seen a quark on its own, and there probably hasn't been such a beast since the early days of the Big Bang. When two quarks get together, they're called a "pion." When three quarks get together, they're called either a "proton" or a "neutron." Four quarks split up into two pions; five split into a pion and a proton-or-neutron; and so on. 274 quarks split up into two pions and one really enormous group of 270 quarks. If 130 of those quarks happen to be Up quarks and 140 are Down quarks -- which is actually quite likely, since no other combination of 270 quarks is stable -- then you've got a Zirconium nucleus.

It's those groups of three quarks which are most relevant to today's rant.

The next thing to know about quarks is that they all carry electric charge. An Up quark has a charge of +2, while a Down quark has a charge of -1 -- the units aren't important. So if you imagine every possible combination of three Up & Down quarks, here are the results:

  • (Up Up Up) ... charge of 2+2+2=6 ... breaks apart instantly from the electromagnetic repulsion
  • (Up Up Down) ... charge of 2+2-1=3 ... this is called a "proton"
  • (Up Down Down) ... charge of 2-1-1=0 ... this is called a "neutron"
  • (Down Down Down) ... charge of -1-1-1=-3 ... breaks apart instantly from the electromagnetic repulsion


So if every observable group of three quarks has a charge of either +3 or 0, it's easy to see why last century's scientists thought the 3 was a fundamental unit, and called it 1. You'd have made the same mistake too.

One final fact about quarks is that they're a type of particle called "fermions." This means, basically, that only a finite number of them can dance on the head of a pin. If you tell a room full of fermions to go stand in a corner, only one or two of them will actually be able to touch the corner without another fermion getting in the way. Within an atomic nucleus, no two fermions can occupy exactly the same energy state, just as within a rock concert, no two fans can occupy exactly the same position in the mosh pit.

The third-lightest quark is the Strange quark, which (like the Down quark) also has a charge of -1. So theoretically you could grab a mix of (Up Up Strange) quarks, and it would look just like an (Up Up Down) mix, only heavier. (And stranger, obviously.) The reason this doesn't happen is because the lowest energy level for a Strange quark is much more energetic than the lowest energy level for a Down quark. Think of it as a fan who never stops moshing. If there aren't enough fans bouncing Up and Down below it, it will fall hard to the floor, mutter, "Screw this," and walk away.

The heaviest isotope of matter which is even close to stable is Mendelevium-258, with 101 protons and 157 neutrons ... that is, with 359 Up quarks and 415 Down quarks. And that's just not enough to support a Strange quark in the mix. However, there are much larger collections of quarks in the universe: in a neutron star, the entire mass of a star rather larger than the Sun has been compressed into a rapidly spinning object roughly the size of the Fraser Valley. And it's all made of neutrons, from side to side.

With millions upon billions of quarks dancing about in a single Live Earth-sized nucleus, there is plenty of room for moshers. It seems extremely likely that under the huge gravitational pressures of a neutron star nucleus, some of the outermost Down quarks would leap up into the excited state of Strangeness, in order to mosh closer to the centre of the star. This would mean that neutron stars are even denser than neutronium: they are made of something called "strange matter."

Where the notion of strange matter becomes purely speculative is the question of what happens when you take away that gravitational pressure. How big does a crowd of Up and Down quarks have to be before it can sustain Strange quarks within its mix, even within a vacuum?

No one's quite sure of this answer. What is certain is that unlike normal nucleic matter, which becomes less stable the larger it gets, strange matter becomes more stable at large sizes. The larger a clump of strange matter, or "strangelet," grows, the stabler and stranger it gets. Should it happen to strike a clump of nucleic matter, it will act rather like a katamari, converting some of the Down quarks in the nucleic matter to Strange quarks as it rolls.

Fortunately for the continued existence of the universe, the nuclei have to come into direct contact for this to be an issue. A clump of 50,000,000 Up quarks, 50,000,000 Down quarks, and 49,999,997 Strange quarks will have a net charge of +3, the same as a single proton -- and it will promptly attract an electron to shield it from all the other atoms in the cosmos. (And it would act just like any other hydrogen atom, chemically speaking, except that it would be about 50,000,000 times heavier.) You can't put your hand through solid matter because the electron shells in your fingers won't pass through the electron shells in your computer desk: the nuclei stay well separated. If it were easy to force them to bounce into each other, we'd have fusion power by now.

So the second piece of radical speculation is, what if you had a clump of 50,000,000 Up quarks, 50,000,000 Down quarks, and 50,000,003 Strange quarks? Suddenly it would have a charge of -3, and free-floating protons would race rapidly towards it -- only to find themselves converted into undifferentiated strange matter. Above a critical size, a negatively charged strangelet would just chow down on any ordinary matter it encountered.

Current theory says that if strangelets exist at all, they would have to be positively charged. There's an asymptotic limit of 1 Up quark to 1 Down quark to 1 Strange quark, which in turn corresponds to a charge of 0. And this agrees with the common-sense observation that nothing has eaten the universe yet, or at least not this part of it. But what if current theory is wrong (cue ominous music)?

Current theory also makes no useful predictions about the size of the smallest stable strangelet. Maybe it's infinite in size; maybe there is no stable minimum without external pressure. Or maybe the limit is actually quite small, say 99 quarks. The only real requirement is that for small strangelets, there have to be about as many Strange quarks as Down quarks, or the strangelet will break down ... which explains why we never see zirconium nuclei spontaneously strangeifying. The odds of one Down quark overcoming its anxiety and starting to mosh are already pretty low, and the speed with which everyone mocks it until it reverts to a plain ordinary Down quark again is very, very fast; the odds of 70 of them deciding to start moshing, all at once, before the laughter starts, are infinitesimal.
osmie: (Default)
The other really neat scientific oddity I've run across lately is strangelets.

Before I go further, let me wonder aloud how I could possibly have made it all the way through a physics degree in the early 1990s without ever hearing about these particular beasties. There; it is wondered. I don't know the answer.

To understand strangelets, you need a basic grasp of quarks. Now, there are six types of quark in the standard model, which have been given six perfectly arbitrary names that all begin with a different letter: Up, Down, Charm, Strange, Top and Bottom. Up and Down are the only quarks which show up in ordinary matter; the rest are too heavy, and tend to decay into Up and Down quarks if you take the ridiculously high pressure off for even an instant.

Quarks like to bind together in groups: no one has ever seen a quark on its own, and there probably hasn't been such a beast since the early days of the Big Bang. When two quarks get together, they're called a "pion." When three quarks get together, they're called either a "proton" or a "neutron." Four quarks split up into two pions; five split into a pion and a proton-or-neutron; and so on. 274 quarks split up into two pions and one really enormous group of 270 quarks. If 130 of those quarks happen to be Up quarks and 140 are Down quarks -- which is actually quite likely, since no other combination of 270 quarks is stable -- then you've got a Zirconium nucleus.

It's those groups of three quarks which are most relevant to today's rant.

The next thing to know about quarks is that they all carry electric charge. An Up quark has a charge of +2, while a Down quark has a charge of -1 -- the units aren't important. So if you imagine every possible combination of three Up & Down quarks, here are the results:

  • (Up Up Up) ... charge of 2+2+2=6 ... breaks apart instantly from the electromagnetic repulsion
  • (Up Up Down) ... charge of 2+2-1=3 ... this is called a "proton"
  • (Up Down Down) ... charge of 2-1-1=0 ... this is called a "neutron"
  • (Down Down Down) ... charge of -1-1-1=-3 ... breaks apart instantly from the electromagnetic repulsion


So if every observable group of three quarks has a charge of either +3 or 0, it's easy to see why last century's scientists thought the 3 was a fundamental unit, and called it 1. You'd have made the same mistake too.

One final fact about quarks is that they're a type of particle called "fermions." This means, basically, that only a finite number of them can dance on the head of a pin. If you tell a room full of fermions to go stand in a corner, only one or two of them will actually be able to touch the corner without another fermion getting in the way. Within an atomic nucleus, no two fermions can occupy exactly the same energy state, just as within a rock concert, no two fans can occupy exactly the same position in the mosh pit.

The third-lightest quark is the Strange quark, which (like the Down quark) also has a charge of -1. So theoretically you could grab a mix of (Up Up Strange) quarks, and it would look just like an (Up Up Down) mix, only heavier. (And stranger, obviously.) The reason this doesn't happen is because the lowest energy level for a Strange quark is much more energetic than the lowest energy level for a Down quark. Think of it as a fan who never stops moshing. If there aren't enough fans bouncing Up and Down below it, it will fall hard to the floor, mutter, "Screw this," and walk away.

The heaviest isotope of matter which is even close to stable is Mendelevium-258, with 101 protons and 157 neutrons ... that is, with 359 Up quarks and 415 Down quarks. And that's just not enough to support a Strange quark in the mix. However, there are much larger collections of quarks in the universe: in a neutron star, the entire mass of a star rather larger than the Sun has been compressed into a rapidly spinning object roughly the size of the Fraser Valley. And it's all made of neutrons, from side to side.

With millions upon billions of quarks dancing about in a single Live Earth-sized nucleus, there is plenty of room for moshers. It seems extremely likely that under the huge gravitational pressures of a neutron star nucleus, some of the outermost Down quarks would leap up into the excited state of Strangeness, in order to mosh closer to the centre of the star. This would mean that neutron stars are even denser than neutronium: they are made of something called "strange matter."

Where the notion of strange matter becomes purely speculative is the question of what happens when you take away that gravitational pressure. How big does a crowd of Up and Down quarks have to be before it can sustain Strange quarks within its mix, even within a vacuum?

No one's quite sure of this answer. What is certain is that unlike normal nucleic matter, which becomes less stable the larger it gets, strange matter becomes more stable at large sizes. The larger a clump of strange matter, or "strangelet," grows, the stabler and stranger it gets. Should it happen to strike a clump of nucleic matter, it will act rather like a katamari, converting some of the Down quarks in the nucleic matter to Strange quarks as it rolls.

Fortunately for the continued existence of the universe, the nuclei have to come into direct contact for this to be an issue. A clump of 50,000,000 Up quarks, 50,000,000 Down quarks, and 49,999,997 Strange quarks will have a net charge of +3, the same as a single proton -- and it will promptly attract an electron to shield it from all the other atoms in the cosmos. (And it would act just like any other hydrogen atom, chemically speaking, except that it would be about 50,000,000 times heavier.) You can't put your hand through solid matter because the electron shells in your fingers won't pass through the electron shells in your computer desk: the nuclei stay well separated. If it were easy to force them to bounce into each other, we'd have fusion power by now.

So the second piece of radical speculation is, what if you had a clump of 50,000,000 Up quarks, 50,000,000 Down quarks, and 50,000,003 Strange quarks? Suddenly it would have a charge of -3, and free-floating protons would race rapidly towards it -- only to find themselves converted into undifferentiated strange matter. Above a critical size, a negatively charged strangelet would just chow down on any ordinary matter it encountered.

Current theory says that if strangelets exist at all, they would have to be positively charged. There's an asymptotic limit of 1 Up quark to 1 Down quark to 1 Strange quark, which in turn corresponds to a charge of 0. And this agrees with the common-sense observation that nothing has eaten the universe yet, or at least not this part of it. But what if current theory is wrong (cue ominous music)?

Current theory also makes no useful predictions about the size of the smallest stable strangelet. Maybe it's infinite in size; maybe there is no stable minimum without external pressure. Or maybe the limit is actually quite small, say 99 quarks. The only real requirement is that for small strangelets, there have to be about as many Strange quarks as Down quarks, or the strangelet will break down ... which explains why we never see zirconium nuclei spontaneously strangeifying. The odds of one Down quark overcoming its anxiety and starting to mosh are already pretty low, and the speed with which everyone mocks it until it reverts to a plain ordinary Down quark again is very, very fast; the odds of 70 of them deciding to start moshing, all at once, before the laughter starts, are infinitesimal.

Profile

osmie: (Default)
Osmium Penguin

April 2016

S M T W T F S
     12
345678 9
10 111213141516
171819202122 23
2425262728 2930

Syndicate

RSS Atom

Most Popular Tags

Style Credit

Expand Cut Tags

No cut tags