Great read! One fascinating to me is how the article frames the field as progressing once again now that researchers are getting over the quasi particle model.
Reminds me of the elephant and rope adage: young elephants are trained with small chains, which as they mature they outsized and could easily break but don't.
Though to give credit to researchers, those new experiments of "listening" for electron perturbations seem amazing. That's just a brilliant idea. Theorists often like to pretend they're better than the experimentalists, but without proper data the theorists get stuck in dead ends. ;)
IANAP, but I thought that quantum field theory (which isn't incredibly controversial) already treats particles as merely emergent convenient ways to describe common excitations of the fields. I'm surprised it isn't mentioned here at all.
> A regular particle isn't really emergent, it corresponds 1:1 to the excitation of the field
Maybe 'emergent' was the wrong word here. I meant that particles are convenient ways of describing behavior of the fields in many (but not all) cases, with the fields themselves considered to be the (more) fundamental description of reality.
I would assume that's mostly a function of this being for a general audience. Yes, you absolutely can talk about quasiparticles using techniques adapted from QFT. I don't know if Landau originally conceived of it that way, but there were definitely a bunch of Soviet physicists shortly after him who did.
QFT is perfect for a single particle, but it gets harder to describe the behavior of particles en masse. It's super hard to find simplifications that reveal emergent behavior.
So superconductivity is a laminar flow of electron goop?
Ok, it's different in that liquid flows through pipes and electrons flow through crystal lattices or whatever, so electrons go between and around the material while liquid is bounded by it.
It makes me speculate that electron flow through a metal is sort of like liquid flowing through a compressible boundary tube, whereas flow through a non-metal has rigid walls. Non-metals reject the electrons, metals allow them to play Spiderman and hitch a temporary ride (if you'll forgive the overly particle-centric analogy.)
If resistivity is determined by the equivalent of turbulence, though, I've no idea what the graph against temperature should be. Do electrons travel faster when there's less resistance?
Turbulence on a small scale acts like increased viscosity on a large scale, because they're both forms of momentum diffusion. However, current doesn't have any momentum diffusion terms, the momentum is lost to the conductor.
Progress is seeing the cloud from the particles I reckon. I am excited to see practical uses of measuring entanglement to push forward materials research. I’m curious about what other materials have linear changes related to temperature or other inputs, seems uncommon.
The article says that resisivity in normal metals follows a quadratic curve, but the article also says that it follows an exponential curve. Does anyone know which it right?
From the other responses, it sounds like "none of the above". It's more like a "polynomial curve" that is only sometimes quadratic. Is "polynomial curve" a thing? "Power curve" / "power function"?
Typically, the behavior of any given metal is a mix of mechanisms so the measured behavior is fit to a curve where you fit n. So for metals the exponent is typically a decimal between 2 and 5.
But the specific word they were looking for is "quintic". (And the corresponding word for 4th-degree, in case anyone is curious, is "quartic"; one sometimes sees "biquadratic", which unfortunately is also sometimes used to describe a particular subset of quartics.)
Oh right, silly me. Wow, my own vocabulary deserted me there, huh?
Yeah I think generally "sextic" is the highest you see before people stop doing that, and that one's somewhat uncommon I'd say. ("Quintic" is actually fairly common, contrary to what I said earlier, oops.) The fact that seventh-degree would be "septic" might be one reason stop with the words at that point!
No. Exponential growth or decay is much faster than quadratic growth or decay. You may be mixing up exponential functions, of the form x maps to ab^x, with power functions, of the form x maps to ax^b. These are very different!
Annoyingly, people often use "exponential" colloquially to mean anything faster than linear, but in fact lots of things are faster than linear.
so electrons are just like photons being a wave/particle?
The article seems to suggest in strange metals
their particle properties are absent and only 'electron field' gradients move,
like if electrons exhanged their 'charge'.
Electrons are not just like photons. It's tempting to say that, but there are some significant differences that can lead you in error if you think in this picture.
First of all, if you think of a photon as some small ball, not that's not what it is. Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
Unlike photons, electrons have a position operator, so in principle you can measure and say where one electron is. The same is impossible for photons. Also electrons have a mass, but photon are massless. This means you can have motionless electrons, but this is impossible for photons: they always move at the speed of light. Electrons have a non-relativistic classical limit, while photon do not.
W. E. Lamb used to say that people should be required a license for the use of the word "photon", because it can be very misleading.
Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Since it lives and dies in the same instant, it can't have a position—because the moment it exists and the moment it doesn't is exactly the same time.
It takes time—even for light—to get from point A to point B. However, the measurement of any positions—relative to the photon itself—will always be the same. It's related to that property of quantum physics that allows two particles to exists in two different places at the same time.
> > > Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
> Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Would an appropriate analogy be a "glider" from Conway's Game of Life? "Lives and dies in the same instant" isn't exactly the same, but I'm thinking of how no parts of the glider move while the glider as a whole "moves" across the board.
Not just like photons. For one thing, they can travel slower than light. But many experiments on photons can also be done on electrons, such as diffraction. You can perform a double-slit experiment with electrons. Also, they're fermions, but photons are bosons.
Great read! One fascinating to me is how the article frames the field as progressing once again now that researchers are getting over the quasi particle model.
Reminds me of the elephant and rope adage: young elephants are trained with small chains, which as they mature they outsized and could easily break but don't.
Though to give credit to researchers, those new experiments of "listening" for electron perturbations seem amazing. That's just a brilliant idea. Theorists often like to pretend they're better than the experimentalists, but without proper data the theorists get stuck in dead ends. ;)
IANAP, but I thought that quantum field theory (which isn't incredibly controversial) already treats particles as merely emergent convenient ways to describe common excitations of the fields. I'm surprised it isn't mentioned here at all.
A regular particle isn't really emergent, it corresponds 1:1 to the excitation of the field
Quasiparticles arise out of a collection of particles, that's why they're emergent
> A regular particle isn't really emergent, it corresponds 1:1 to the excitation of the field
Maybe 'emergent' was the wrong word here. I meant that particles are convenient ways of describing behavior of the fields in many (but not all) cases, with the fields themselves considered to be the (more) fundamental description of reality.
Eh, in the wave-particle duality wars you may have been swayed a bit too strongly into the wave camp.
Quantization exists and isn't just a convenience.
What? QFT doesn't preclude quantization at all. You're attacking a weird straw man here.
And wave particle duality isn't some kind of scientific debate with camps on both sides.
I would assume that's mostly a function of this being for a general audience. Yes, you absolutely can talk about quasiparticles using techniques adapted from QFT. I don't know if Landau originally conceived of it that way, but there were definitely a bunch of Soviet physicists shortly after him who did.
QFT is perfect for a single particle, but it gets harder to describe the behavior of particles en masse. It's super hard to find simplifications that reveal emergent behavior.
So superconductivity is a laminar flow of electron goop?
Ok, it's different in that liquid flows through pipes and electrons flow through crystal lattices or whatever, so electrons go between and around the material while liquid is bounded by it.
It makes me speculate that electron flow through a metal is sort of like liquid flowing through a compressible boundary tube, whereas flow through a non-metal has rigid walls. Non-metals reject the electrons, metals allow them to play Spiderman and hitch a temporary ride (if you'll forgive the overly particle-centric analogy.)
If resistivity is determined by the equivalent of turbulence, though, I've no idea what the graph against temperature should be. Do electrons travel faster when there's less resistance?
Turbulence on a small scale acts like increased viscosity on a large scale, because they're both forms of momentum diffusion. However, current doesn't have any momentum diffusion terms, the momentum is lost to the conductor.
Progress is seeing the cloud from the particles I reckon. I am excited to see practical uses of measuring entanglement to push forward materials research. I’m curious about what other materials have linear changes related to temperature or other inputs, seems uncommon.
The article says that resisivity in normal metals follows a quadratic curve, but the article also says that it follows an exponential curve. Does anyone know which it right?
Ouch, not a good look for a technical article.
From the other responses, it sounds like "none of the above". It's more like a "polynomial curve" that is only sometimes quadratic. Is "polynomial curve" a thing? "Power curve" / "power function"?
If I'm reading Wikipedia correctly, the formula is quadratic for some metals, and cubic or quintuplic(?) for others: https://en.wikipedia.org/wiki/Electrical_resistivity_and_con...
Typically, the behavior of any given metal is a mix of mechanisms so the measured behavior is fit to a curve where you fit n. So for metals the exponent is typically a decimal between 2 and 5.
Thanks, I appreciate the explanation. :)
You would normally just say "5th degree" or "5th power".
But the specific word they were looking for is "quintic". (And the corresponding word for 4th-degree, in case anyone is curious, is "quartic"; one sometimes sees "biquadratic", which unfortunately is also sometimes used to describe a particular subset of quartics.)
Oh right, silly me. Wow, my own vocabulary deserted me there, huh?
Yeah I think generally "sextic" is the highest you see before people stop doing that, and that one's somewhat uncommon I'd say. ("Quintic" is actually fairly common, contrary to what I said earlier, oops.) The fact that seventh-degree would be "septic" might be one reason stop with the words at that point!
afaiu quadratic is a subtype of exponential, so they are not mutually exlusive
No. Exponential growth or decay is much faster than quadratic growth or decay. You may be mixing up exponential functions, of the form x maps to ab^x, with power functions, of the form x maps to ax^b. These are very different!
Annoyingly, people often use "exponential" colloquially to mean anything faster than linear, but in fact lots of things are faster than linear.
so electrons are just like photons being a wave/particle? The article seems to suggest in strange metals their particle properties are absent and only 'electron field' gradients move, like if electrons exhanged their 'charge'.
Electrons are not just like photons. It's tempting to say that, but there are some significant differences that can lead you in error if you think in this picture.
First of all, if you think of a photon as some small ball, not that's not what it is. Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
Unlike photons, electrons have a position operator, so in principle you can measure and say where one electron is. The same is impossible for photons. Also electrons have a mass, but photon are massless. This means you can have motionless electrons, but this is impossible for photons: they always move at the speed of light. Electrons have a non-relativistic classical limit, while photon do not.
W. E. Lamb used to say that people should be required a license for the use of the word "photon", because it can be very misleading.
Why don't photons have a position operator?
Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Since it lives and dies in the same instant, it can't have a position—because the moment it exists and the moment it doesn't is exactly the same time.
It takes time—even for light—to get from point A to point B. However, the measurement of any positions—relative to the photon itself—will always be the same. It's related to that property of quantum physics that allows two particles to exists in two different places at the same time.
> > > Mathematically a photon is defined as a state of the EM field (which has been quantised into a set of harmonic oscillators called "normal modes") in which there is exactly one quantum of excitation of a specific normal mode (with given wavevector and frequency). Depending on which kind of modes you consider, a photon could be a gaussian beam, or even a plane wave, so not something localised like you would say of a particle.
> Think of it like this: From the perspective of the photon, it lives and dies in the same instant. Even if it traveled across the entire universe.
Would an appropriate analogy be a "glider" from Conway's Game of Life? "Lives and dies in the same instant" isn't exactly the same, but I'm thinking of how no parts of the glider move while the glider as a whole "moves" across the board.
It’s really not accurate to say that a photon has no position at all. How would a photodiode work? You have to be careful with this stuff. https://physics.stackexchange.com/questions/492711/whats-the...
Not just like photons. For one thing, they can travel slower than light. But many experiments on photons can also be done on electrons, such as diffraction. You can perform a double-slit experiment with electrons. Also, they're fermions, but photons are bosons.
All matter is wavelike. Even some molecules comprised of multiple particles have been empirically proven to exhibit wavelike behavior.
https://en.wikipedia.org/wiki/Matter_wave
Yeah, electrons are waves and experience quantum tunneling which we see in high density electronics and specifically apply in flash memories.
Yeah, everything is just like photons, everything is a wave/particle
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