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Science

A Gas Made From Light Becomes Easier To Compress as You Squash It (newscientist.com) 62

Posted by msmash from the closer-look dept.
Particles of light called photons can be trapped inside mirrors to form a gas with unusual properties, New Scientist reports. From the report: A gas made of particles of light, or photons, becomes easier to compress the more you squash it. This strange property could prove useful in making highly sensitive sensors. While gases are normally made from atoms or molecules, it is possible to create a gas of photons by trapping them with lasers. But a gas made this way doesn't have a uniform density -- researchers say it isn't homogeneous, or pure -- making it difficult to study properly. Now Julian Schmitt at the University of Bonn, Germany, and his colleagues have made a homogeneous photon gas for the first time by trapping photons between two nanoscale mirrors. They then moved one of the mirrors to measure the compressibility of the photon gas and derive basic properties about it. "We can consider the system to be like an air pump, but it's not filled with air, it's filled with light," says Schmitt. "We compress it and look at how it responds. In this way, we can learn about very fundamental properties." Journal reference: Science, DOI: 10.1126/science.abm2543.
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A Gas Made From Light Becomes Easier To Compress as You Squash It More

A Gas Made From Light Becomes Easier To Compress as You Squash It

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  • I can't make it out from the article.
  • If this is truly what it appears, it will lead to a major advance in physics. Noble Prize time.

    • If this is truly what it appears, it will lead to a major advance in physics.

      Really why? It's behaving consistently with the predictions of quantum mechanics. It's certainly a neat experiment and may lead to some useful sensor devices but it is hardly a major advance in our understanding of physics, just a very clever application of the physics we already know.

      • Yeah.. but there has not been anything new in that sense since the standard model. At some point. I mean, a lot of prizes have gotten awarded for obtaining experimental confirmation of existing theories.

        • Yeah.. but there has not been anything new in that sense since the standard model.

          Except for neutrino oscillation.

        • Yeah.. but there has not been anything new in that sense since the standard model.

          That's not true - literally (neutrino oscillations) and in that new physics does not have to be beyond the Standard Model. Superconductivity is an example of something that was a new phenomenon that was unexpected but ultimately explainable by applications of the physics we knew in ways we had not thought of. This advanced our understanding of condensed matter physics but did not require beyond the Standard Model physics. Creating a Bose-Einstein Condensate, a new state of matter, and studying its properti

  • Boyle's law says a gas has uniform distribution throughout a closed container. Is it really a gas, or actually something else that kind of acts like one, and kind of doesn't? I looked up the physics definition and got back "a substance possessing perfect molecular mobility and the property of indefinite expansion, as opposed to a solid or liquid." But this "gas" not only doesn't have molecules, it doesn't have atoms. I don't know if the word molecular is literal in this definition or used in the sense of th

    • It's not a gas. It's a bunch of photons bouncing back and forth between two mirrors. As the mirrors get closer, the photons exert less pressure on the mirrors.

      If it were a gas, I would want to solidify it, taste it, and eat it.

      • It certainly doesn't make sense to me that it would be a gas without atoms to have nuclei, which are AFAIK responsible for most of the behavior of a gas.

        • Oh. Wait until you learn about entropy in information theory. You should get used to that, scientists do that all the time, especially physicists.

    • Oh, now that I've re-read it again, I see they are stating that it's normally neither uniform nor homogeneous. However, the summary only explicitly says it's the latter...

    • Re: (Score:2)

      by ceoyoyo ( 59147 )

      I think the modern formal definition of a gas has something to do with exerting isotropic pressure in the absence of outside forces and regardless of density. A bunch of photons do that, probably better than any gas consisting of atoms or molecules.

      It's pretty easy to find uncontroversial exceptions to most other definitions. The noble gasses are rarely or never found as molecules. Boyle's law is for ideal gasses, which don't actually exist, and no actual gas, including technically a photon gas, uniformly f

      • I imagine, particularly when you're dealing with elementary particles like photons, that even if the absence of gravity, quantum effects, particularly as the particles increase in density, will start to demonstrate behaviors that would defy Boyle's law. I guess to some extent if it walks like a duck and quacks like a duck, you call it a duck, it's just the when we talk about gas even in most physics contexts, we're talking about a kind of atomic and/or molecular behavior.

        • Re: (Score:2)

          by ceoyoyo ( 59147 )

          Inter-particle interactions make "real" gasses depart from the ideal gas law. From one of the the OPs definitions, ideal gasses have particles that have "perfect molecular mobility" but atomic and molecular gases always have inter-particle forces that distort that. The ideal gas law also assumes only elastic scattering, but matter particles can all interact inelastically.

          So in at least some ways, a photon gas would be closer to an ideal gas than matter particle gasses.

          • but atomic and molecular gases always have inter-particle forces that distort that.

            A significant component of the non-ideality of real gases is that the ideal gas model assumes the particles have zero volume (not "a very small volume"), but in real gases the particles have a volume. Consequently the volume through which the other particles can pass is not the container volume, but the container volume minus the molecule's volume.

            The effect is most pronounced at low temperatures and high pressures, as the

            • Re: (Score:2)

              by ceoyoyo ( 59147 )

              The article is pretty crappy, but taking a look at the abstract of the actual paper it sounds like what they've actually done is characterized the transition of a photon gas to a Bose-Einstein condensate. Presumably the gas itself behaves like an ideal gas down to the phase transition, then it sounds like it becomes a very good BEC. That's not surprising, since photons are fundamental bosons while the non-bosonic properties of the constituents of composite bosons presumably start becoming important when you

    • Re: (Score:2)

      by msauve ( 701917 )
      >Is it really a gas

      No. Plasma is closer to correct, but that's not right either.

      • >Is it really a gas

        No. Plasma is closer to correct, but that's not right either.

        It's not closer to correct. Plasmas have components which are charged (responding to electromagnetic fields, for example; in Standard Model theory, the communicator of the force is the photon); photons do not. These are fundamental and important distinctions.

        Gases have no defined shapes or volume in the absence of external forces, they exert pressures, their components transfer momenta upon collisions or ad/absorption, and so forth. Photons do exactly the same. So do people contained within a room.
        Plasmas m

        • Re: (Score:2)

          by msauve ( 701917 )
          I submit that gases are atomic (or molecular), and the constituents can carry a charge (e.g. ionic or Van Der Waals forces). Plasmas are subatomic, and carry a charge. Photons are subatomic, but carry no charge. As I said, I believe it is _closer_ to correct, but still not right. You're redefining things and trying to pound a square peg into a round hole. Photons are not a gas.

          • I submit that gases are atomic (or molecular)

            Now who's redefining things?

            I do notice that you're writing as though someone is claiming a SINGLE photon is a gas. No one has, so that's not a useful route for you.

            Since Boltzmann and Gibbs, and /certainly/ since Planck---since before the term "photon" was used in this context---physicists have been thoroughly comfortable speaking of collections of photons as gases. Entropy, pressure, chemical potential, et alia: ALL the statistical mechanical and classical thermodynamical quantities translate over just fi

            • Re: (Score:2)

              by msauve ( 701917 )
              Congrats. I was confident that if you pounded hard enough, that peg would go into that hole. You did it.

          • Re: (Score:2)

            by ceoyoyo ( 59147 )

            Any inter-particle forces in a gas (yes, they exist in real gasses) cause them to depart from the ideal gas law. Photons don't have these (well, much, they do a tiny little bit) so they are *closer* to being ideal gasses than those messy atoms and molecules.

            Plasmas have constituents that have strong inter-particle forces. Because of that they behave very differently than gasses, ideal or otherwise.

            • Exactly. And of course there have to be coupling forces between the photons (as you say, a "tiny, little bit") in order for them to thermalize in the first place.

          • The word gas is overloaded. See https://en.wikipedia.org/wiki/... [wikipedia.org], https://en.wikipedia.org/wiki/... [wikipedia.org], https://en.wikipedia.org/wiki/... [wikipedia.org]

    • Re: (Score:2)

      by quenda ( 644621 )

      Boyle's law says a gas has uniform distribution throughout a closed container. Is it really a gas, or actually something else that kind of acts like one

      I think the term you are looking for is "perfect gas". Boyle's law describes an ideal "perfect gas". Real gases are more varied, and approximate this behaviour within certain limits.

    • Re: (Score:2)

      by necro81 ( 917438 )
      Gasses (the kind you and I commonly interact with) have the properties they do because the individual particles can interact: have inelastic collisions between each other and the walls of whatever container, transfer momentum, and by doing so achieve a more or less predictable set of average properties in equilibrium (average particle velocity, pressure for a given temperature, etc.). The Ideal Gas Law can be derived from first principles using statistical mechanics.

      Photons don't really interact with ea

  • Gas is a state of *MATTER*. Photons can be often modeled of as particles, but they are not *actually* particles, much less matter.

    The elements are, by definition, the lowest building blocks of matter. Photons are not made of elements so they are not matter. They are something else (in this case, radiation).

    • Re: (Score:2)

      by bws111 ( 1216812 )

      It is a photon gas https://en.wikipedia.org/wiki/... [wikipedia.org]

    • Photons have zero mass, so yes, they're not like matter in that respect, and yet they do behave like other particles in that they interact with gravity (well, properly, they follow spatial curvature) and electromagnetism. But the chemical elements themselves are the products of more basic kinds of matter, and once you get down to the basic constituents of baryonic matter, at least, are quarks, with gluons mediating the strong interaction. Let's just say that neutrons and protons are, at least so far as we k

      • Re: (Score:2)

        by mark-t ( 151149 )

        "Behave like" does not mean that it is.

        Matter is ultimately composed of fermions. Photons are bosons.

        It's as much of a misnomer to call a phenomenon entirely composed of light a "gas" as it would be to say that the asteroid Ceres is a planet.

        • Again, it comes down to a "walk like a duck, talk like a duck". Is it a gas in the strictest sense, no, but it's clear that under certain conditions, the mechanical effect of radiation pressure and the exchange of momentum behaves a lot like a gas. It seems the most reasonable term. It's like a quark-gluon plasma (at one period in the universe the dominant form of matter). A plasma is usually described as a state of matter dominated by atomic nuclei (ions) and electrons, and that is the normal description o

    • Photons are not made of elements so they are not matter.

      Careful. Neutrons and electrons are also not made of elements.

    • Photons can be often modeled of as particles, but they are not *actually* particles, much less matter.

      That's simply not true. Photons are just as much particles as e.g. electrons. Both are quantum excitations of a fundamental (as far as we know) field in nature. The differences between them are that an electron is an excitation of a fermion field and a photon is an excitation of a vector field. This is why macroscopically photons give us a force (EM force) and electrons make up matter. Having (or not) mass not relevant. The Z-boson has a huge mass and yet even it were stable would not make up matter becaus

      • Additional information: Ideal gasses, Fermi gasses, and Bose gasses each have wildly different properties.

        https://en.wikipedia.org/wiki/... [wikipedia.org]
        https://en.wikipedia.org/wiki/... [wikipedia.org]
        https://en.wikipedia.org/wiki/... [wikipedia.org]

      • Re: (Score:2)

        by mark-t ( 151149 )

        Quarks and leptons are the lowest building blocks of ordinary matter but 80% of the matter in the universe is made up of something that has nothing to do with elements whatsoever since it is Dark Matter.

        Quarks and leptons are the building blocks of atoms. You cannot create any quantity of matter out of them except insomuch as they can be combined to create discrete atoms, which themselves are the "atomic" building blocks of matter. For what it's worth, it's my understanding that the general consensus is th

        • Quarks and leptons are the building blocks of atoms. You cannot create any quantity of matter out of them except insomuch as they can be combined to create discrete atoms, which themselves are the "atomic" building blocks of matter.

          ,,,and so following your chain of logic backwards matter is made of atoms which are made of quarks and leptons therefore matter is made of quarks and leptons QED.

          For what it's worth, it's my understanding that the general consensus is that dark matter isn't really matter either

          Your understanding is wrong. Dark Matter is considered matter because it has a gravitational field like the more regular form of matter. It certainly has different properties and behaviour to baryonic matter but it is most definitely matter.

          why call it a "gas" in the first place?

          A gas consists of a collection of particles moving in random motion. If you change the particles then the

  • Predicted in the John Wood Campbell novella Solarite, gathered in book form with other related stories as The Black Star Passes.
  • Those mirrors have mass, which means they have gravity, and the closer you move them the more they pull on each other.. Probably not significant here but well, ya' never know.

    Another useless baseless theory is that the reflected (refracted?) photons need to speed back up and don't have as much distance to do this as the distance between mirrors decreases.

    -crowd sourcing with mirrors
  • !RemindMe 10Years

  • I know (Score:3)

    by nospam007 ( 722110 ) * on Monday March 28, 2022 @04:01PM (#62397891)

    "Particles of light called photons can be trapped inside mirrors "

    I use a photon catcher everyday, it's called a camera and I compress them into JPGs.

  • If you just put light in a reflective bag, when you compress it the pressure will go up - the number of photons remains the same, but the moving walls will blue-shift them, increasing their momentum and energy and applying more pressure. This isn't completely made up, in some particle accelerators, the pressure from the radio frequency photons in the cavity is significant, and its is also a large effect for LIGO.

    This is something different where the density of photons allows them to condense into som
  • Or maybe it's a liquid? https://english.bouletcorp.com/2015/01/16/heavy-light/ [bouletcorp.com]
  • ...Greta Thunberg making bold statements about greenhouse effects triggered by photon gas.

  • Eh, how can you have a gas when you have no partial pressure? Photons being bosons cannot exert pressure on each other, an essential feature of a gas I thought.

  • Gas is made from fermions. Photons are bosons.

  • Well done "msmash" for including a link to the original paper. So few editors (and submitters!) bother. Even good quality science journalism (and NS was relatively good, before the Daily Flail brought it, and I stopped reading it) frequently introduces errors, omissions and misunderstandings which were dealt with in the paper, but deemed too complicated for the readership. (NS's example is one of selecting your readership ; when the title changes to "New Tits and Scientist Will Lower House Prices", we'll kn
  • Couldn't access article so couldn't see if it answers my questions:

    Photons have no mass and the term "gas" is used for a state of matter. What does it mean to make a "gas" out of photons? If you can make a gas out of photons, can you make a liquid or a solid?

    Also, photons don't exhibit any of the typical nuclear forces that atoms do and have no charge so what does it mean to "compress" them? What force(s) are resisting such compression?

    Is it perhaps better to say that scientists have just achieved
  • If it "becomes easier to compress", then it's not a "gas". Ideal Gas Law, anyone? Perhaps it's got some vaguely gas-like properties. Sounds like they've stretched (whatever) it (is) pretty thin.

  • Of course, it's compressible, a photon is a Boson. Bosons, unlike other particles many Bosons can occupy the same state (position is a state). So, it should be infinitely compressible. Photon pressure is not the same as a gas under pressure.

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