Physicists Detect Strongest Evidence Yet of Matter Generated By Collisions of Light (sciencealert.com) 103
omfglearntoplay shares a report from ScienceAlert: According to theory, if you smash two photons together hard enough, you can generate matter: an electron-positron pair, the conversion of light to mass as per Einstein's theory of special relativity. It's called the Breit-Wheeler process, first laid out by Gregory Breit and John A. Wheeler in 1934, and we have very good reason to believe it would work. But direct observation of the pure phenomenon involving just two photons has remained elusive, mainly because the photons need to be extremely energetic (i.e. gamma rays) and we don't have the technology yet to build a gamma-ray laser. Now, physicists at Brookhaven National Laboratory say they've found a way around this stumbling block using the facility's Relativistic Heavy Ion Collider (RHIC) -- resulting in a direct observation of the Breit-Wheeler process in action. The research has been published in the journal Physical Review Letters.
Transporter (Score:3, Interesting)
The obvious application for this phenomenon is to build a Star Trek Transporter.
Matter to light. Light back to matter.
Re:Transporter (Score:4, Interesting)
Or perhaps a replicator.
Photons to roast beef, on demand.
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If you think current 3D printing is slow, just wait until the nozzle is one atom wide. Hope you weren't expecting that roast beef to be hot, or even fresh, by the time it finishes. Now you want to bounce light off roast beef, you need the large hardon collider.
Simpson science Re:Transporter (Score:2)
If you think current 3D printing is slow, just wait until the nozzle is one atom wide. Hope you weren't expecting that roast beef to be hot, or even fresh, by the time it finishes. Now you want to bounce light off roast beef, you need the large hardon collider.
Mmmm, haaa-dronszzz
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If you think current 3D printing is slow, just wait until the nozzle is one atom wide.
Guess I better get started on Christmas dinner!
Re:Transporter (Score:5, Insightful)
Better make sure the replicator door is closed if you don't want a house full of gamma rays. And E=mc^2 being what it is, a 200g roast beef will hit you with quite a power bill.
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Better make sure the replicator door is closed if you don't want a house full of gamma rays.
It is awful when your roast beef turns green. Don't eat that. You wouldn't like it when it's angry.
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And E=mc^2 being what it is, a 200g roast beef will hit you with quite a power bill.
What are you talking about? All we need is a ZPM [fandom.com]...
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Or perhaps a replicator.
Photons to roast beef, on demand.
I think you mean Chicken Soup.
And tea, lots of tea.
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Or perhaps a television for dogs to watch.
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Umm, no. Aside from the other myriad issues and laws of physics being broken that the ST transporter involves, this process also generates antimatter which as you can imagine might be a teensy bit of an issue to deal with at the other end.
Re:Transporter (Score:5, Funny)
The matter turns into Earl Grey tea, and the antimatter makes it hot.
Re:Transporter (Score:4, Funny)
Umm, no. Aside from the other myriad issues and laws of physics being broken that the ST transporter involves, this process also generates antimatter which as you can imagine might be a teensy bit of an issue to deal with at the other end.
And the problem with that is? Where do you think you get the antimatter for your attack torpedoes and powering your ship??
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Re: Transporter (Score:2)
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"Pair-production, as it is often called, is always followed up with pair-annihilation."
Unless in the vicinity of a singularity, so no, not always. Just saying.
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It is more likely that the have exess energy to separate than that they pop up with perfect speed and distance to anihilate each other again.
Re: Transporter (Score:2)
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Pair-production, as it is often called, is always followed up with pair-annihilation.
Rubbish. If that were true then the researchers would not have been able to measure the angles of the particles.
Re:Transporter (Score:4, Funny)
So you are saying that a transporter beam using this phenomena will generate an evil twin of the person being transported. Cool.
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But what if I had the goatee first?
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But what if I had the goatee first?
this? [cloudfront.net]
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Then YOU are the evil twin.
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The obvious application of this phenomenon is faster porn feeds.
Re:Transporter (Score:4, Insightful)
Large Hardon Collider.
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What's funny is that the ancient Chinese intuitively understood many of these ideas. Qi for the Chinese could equal either matter or energy. They thought were just different states of Qi. Leibniz also came up with the concept of Monads later that combine the ideas of matter and energy before E=MC^2. Except Leibniz was a huge Chinese philosophy nerd, and would constantly ask the Jesuit to get his hands on whatever Chinese philosophical texts were just translated. Not that Leibniz stole concepts, but you
Re:Transporter (Score:4, Insightful)
What's even funnier is some people think super fuzzy ideas about physical and spiritual worlds somehow map to matter and energy.
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But isn't this how the scientific method works? You have a theory or an idea of how something might work, and therefore create a hypothesis, in which you prove or disprove the hypothesis through experimentation? All ideas are fuzzy until there's rigorous testing/dialectic.
There's nothing funny about coming up with the idea first, before experimenting upon it. It's the start of all of our knowledge. And to a degree it inspired the West to see a connection they might have never saw before.
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And with a little kung-fu you can fly.
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No the obvious application is a Star Trek style holodeck.
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"if you smash two photons together hard enough" (Score:3, Interesting)
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It's worded a bit strangely. They mention later the photons need to be high energy. So it's not just smashing any two photons but rather those which are energetic enough. It makes me wonder better how the energy is conserved by photons with less energy? Does this mean they won't collide and thus pass threw one another at lower energies, or that they produce something smaller than an electron-positron pair.
Re: "if you smash two photons together hard enough (Score:2)
My physics is rusty and was never that great to begin with. But it may just be as simple as needing the right energies to make the math work out. If you combine an electron and positron, it creates a lot of energy, so you get some pretty energetic photons. Conversely, you need to collide some pretty energetic photons to get a positron and electron.
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Yep, a single photon can create the entire universe if it has a short enough wavelength and gets converted to matter.
(about 10^100 Hz if memory serves, Asimov calculated the number in one of his books)
Re: "if you smash two photons together hard enough (Score:5, Insightful)
(about 10^100 Hz if memory serves, Asimov calculated the number in one of his books)
That is a wavelength about 55 orders of magnitude smaller than a Planck length [wikipedia.org].
So it may not be possible, even in theory.
OTOH, Asimov was never wrong about anything.
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OTOH, Asimov was never wrong about anything.
Quite. Calculating the requirement is not the same as saying it's possible to meet the requirement, Friend Elijah.
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Asimog said naming his sci fi artificial brain a "positronic" brain was a mistake, as he really wasn't thinking that positrons are just anti-electrons, which would have the same properties as electricity.
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Jehoshaphat! Stop calling me Elijah! My friends will think I'm more square than you are!
Re: "if you smash two photons together hard enoug (Score:2)
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No, you do not get a 7 MeV photon. When Co-60 decays to Ni-60 you have 2.8 MeV of total energy available. 99.88% of the time it's distributed to 0.3 MeV to be shared between a beta- and a anti-neutrino, a 1.17 MeV photon and a 1.33 MeV photon. For the 0.12% of the time you get 1.48 MeV shared between a beta- and a neutrino and still have the 1.33 MeV photon.
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Correction, its still an anti-neutrino for the 1.48 MeV energy share. No one cares about the neutrino's anyway, lol.
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When cobalt-60 decays you get a resulting 7 MeV (mega electron volt) photon. Think thats energetic enough?
The other commenters debated this, but actually their adjustments make this reaction more likely to work out. The wikipedia article on electron-positron annhilation [wikipedia.org] says if there is no kinetic energy involved, the reaction must create two photons with 0.511 MeV each (somewhere between hard X-rays and gamma rays [wikipedia.org]).
So one 7 MeV electron won't do it. The other commenters [slashdot.org] say it's more likely you'll get a 1.33 MeV photon and a 1.17 MeV photon. That's in the ballpark, but still sounds too high-energy to me -- tho
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You do get it occurring quite a bit. Once you get past about 1.1 MeV pair production is the dominant interaction of gamma rays with matter. There is a decent probability of a photon > 1.02 MeV interacting with a high electric field (like that between an electron cloud and a nucleus) converting it an electron, positron pair. The kinetic energy/momentum is shared with the two particles and through the electric field the nuclei and electrons. Conservation of momentum results in nearly all the energy dumped
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I thought these, and electrons, might be point particles, whatever that means, as they have never seen a collision no matter how hard they are slammed together. Just electrical resistence deflection ala magnets for electrons, never a hard collision.
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Electrons (and photons) are referred to as "point particles", but that is a bit of a misnomer and is intended only to mean that an electron has no internal structure or constituent particles (in contrast to composite particles like protons). The actual physical extent of an electron is not well described as a mathematical point for at least a couple of reasons 1) uncertainty in location of an electron cannot be brought to zero, and 2) the electron will be "surrounded" by virtual photons by which it interact
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It's worded a bit strangely. They mention later the photons need to be high energy. So it's not just smashing any two photons but rather those which are energetic enough. It makes me wonder better how the energy is conserved by photons with less energy? Does this mean they won't collide and thus pass threw one another at lower energies, or that they produce something smaller than an electron-positron pair.
If the E=mc^2 energy needed to make an electron/positron pair is 2x 512keV (mass energy of electrons/positrons), the two photons need at least 1.024MeV between them (n.b. - you also need to conserve momentum before and after, so this is slightly over-simplified). If the two photons have less than this "threshold" energy, then energy is conserved simply by nothing happening: the photons afterwards have the same energy as the photons did to start with, and no matter/antimatter is produced, and they pass thro
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Just be careful here. The E=mc^2 simplification is only for particles at rest and > 99% of the speed of light is about as far away from rest as you can get. The general equation is E^2 = (mc^2)^2 + (pc)^2 where p is the momentum of the item.
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It's not just worded strangely, it's flat wrong. Photons cannot collide because they are bosons. However, photons can interact, which is what they should have said.
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This phrase makes my brain itch, because it suggests we can make photons travel faster than they usually do.
Photons have zero rest mass, so immediately you give any energy to a photon it's travelling at maximum speed. However, they then have mass proportional to their energy.
e=mc^2
=> m = e/c^2
as you push them harder they don't go faster but they do get heavier and thus have more energy, if you do the equation in the other direction. If you could make two 1kg photons smash into each other at the speed of light that would be quite exciting.
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Photons don't have mass.
(If they did then lightspeed drives would be trivial - just mount a big flashlight on the back of your ship)
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You think if you put a black box on a scale the scale is going to care whether some of the energy inside is made up by photons bouncing about internally between mirrors? Oh no , photons don't count , I have to subtract those!
Parent post said 'no rest mass'. You reply 'no mass' and proceed with an argument about rest mass.
Indeed if photons had restmass they couldn't fly at the speed limit. One could ask yes but maybe they have a tiny mass and fly at nearly the speed limit , so fast that it is very hard to sp
Re: "if you smash two photons together hard enough (Score:2)
You means something akin to this?
https://en.m.wikipedia.org/wik... [wikipedia.org]
Photons do have momentum and can be used for propulsion. Solar sails are actually more efficient than riding a flashlight because they reflect the photons, which then impart 2x the photon momentum to the sail.
Re:"if you smash two photons together hard enough" (Score:5, Interesting)
Photons don't have mass.
(If they did then lightspeed drives would be trivial - just mount a big flashlight on the back of your ship)
Photons do have energy and thus, in a sense by definition (e=mc^2) they have mass, though it's really "relativistic mass". Very important to note is that means that they also have "gravitational mass". What they don't have is rest mass (or "invariant mass". A thought experiment is to imagine a box containing a fibre optic ring. Now imagine adding some photons to that ring. According to current theories as validated by experiments to date, adding the photons will increase the gravitational mass of that box.
N.B. I'm not fully disagreeing with you. Some people treat the bare word "mass" as meaning "rest mass". That's just a word definition though. "Relativistic mass" is a completely reasonably understood concept too.
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Some people treat the bare word "mass" as meaning "rest mass". That's just a word definition though. "Relativistic mass" is a completely reasonably understood concept too.
Sure, but photons are never at rest.
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This is my crude understanding. Tell me if I'm heading in the right direction.
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(If they did then lightspeed drives would be trivial - just mount a big flashlight on the back of your ship) ...
It is actually that trivial
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as you push them harder they don't go faster but they do get heavier and thus have more energy
How do you "push them harder"? By what mechanism can we turn a photon of infrared light into higher-energy ultraviolet light?
I understand that high-energy (high frequency) photons are needed for the topic of the article, and that such photons can be created, but I don't see how we can alter the energy of a photon after its creation.
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By what mechanism can we turn a photon of infrared light into higher-energy ultraviolet light?
You could accelerate the emitter to 0.7c.
Re: "if you smash two photons together hard enough (Score:2)
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Are you suggesting that a photon coming from emitter at 0.7c is different to a photon coming from a stationary emitter? In that case, relativity is bunk, we can find out our objective speed relative to the universe by measuring this amazing property.
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Not bunk at all, a photon coming from an emitter moving towards you is blue shifted, away from you red shifted. Energy observed depends on your relative motion
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According to the story, the source of photons is gold atoms stripped of their electrons and accelerated to 0,99995c
Re: "if you smash two photons together hard enough (Score:1)
Re: "if you smash two photons together hard enough (Score:2)
I think it's just poorly worded, but the only classical analogy I can come up with is via momentum. Shorter wavelength = higher momentum = harder "smash".
The sentence implies that they take existing photons and increase their momentum/shorten wavelength to smash harder, but I think they mean just start with shorter wavelengths in the first place. The photons are generated via gold nucleus acceleration to relativistic speeds, so it sounds like maybe they have some control over photon energy/momentum (out of
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How do you "push them harder"? By what mechanism can we turn a photon of infrared light into higher-energy ultraviolet light?
You bounce them off a moving mirror. For any real noticeable effect the mirror has to be moving close to the speed of light.
Imagine, for example, you have two stationary observers, far apart, and put some identical photons in a light clock (bouncing between two mirrors) in a space ship. next to observer 1. Observer 1 measures the energy of the light. Now you accellerate the space ship very close to the speed of light before it meets the second observer who also measures the energy of the light.
At observ
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You can play some tricks.
https://en.wikipedia.org/wiki/... [wikipedia.org]
Frequency doubling crystals are a thing. Doing it with gamma rays might be a neat trick of its own.
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How do you "push them harder"? By what mechanism can we turn a photon of infrared light into higher-energy ultraviolet light? ...
By letting it pass through a gravitational field
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Smashing harder means to apply more force. Force is the derivative of momentum over time. And the momentum of a photon is Planck constant times frequency.
Smashing harder means to apply more momentum, which means to give them a higher frequency and shorter wavelength.
It is actually the same for ordinary matter, if it moves at speeds close to the speed of light.
Ok, there is one issue with this: how do you smash photons? Usually they are generated
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Re: "if you smash two photons together hard enough (Score:1)
Huh (Score:4, Interesting)
I was under the impression that multiple photons can occupy the same point in space and they don't directly interact with each other.
The article (which I skimmed) talks about using virtual photons on the edges of actual atoms, but I'm finding it hard to understand how a collision between just photons would work.
Is it just a case of if you concentrate enough energy in a single spot it makes particles more likely to pop into existence spontaneously?
Virtual Photons have mass? (Score:4, Interesting)
Ticked off by the sentence in the article about photons and vrtual photons differing in mass, and knowing that photons have no mass, I went to https://www.chegg.com/learn/ph... [chegg.com] to read about it.
They clearly state virtual photons have mass.
Can anyone explain to me how is that not a kludge?
Designed to mask our ignorance at what really happens/deficiencies in our model?
And they they state virtual photons can have negative kinetic energy. Oh boy...
I'd really like to read from someone both knowledgeable and didactic about this. Enlighten me, please.
Re:Virtual Photons have mass? (Score:4, Informative)
Can anyone explain to me how is that not a kludge?
You can see the discussion above where we're having different definitions of mass discussed, however what you probably really want to know about is radiation pressure [wikipedia.org] which is an actual experiment you can do and in the solar sail [wikipedia.org] has a real practical applications which have been used to fly spacecraf. This shows that light has momentum and thus "relativistic mass" even though it has no "rest mass". I won't attempt to go further in the hope that someone "both knowledgeable and didactic about this" turns up to help you more.
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Here is a conventional answer and surely correct: Current physics states that photons in motion have mass (don't ask me what a stationary photon is other than an artifact of an incomplete mathematical model of reality). Photons In motion with different energies, i.e. have different mass. e=Mc2 governs this relationship nicely.
The rest of my comment below is my working theory of reality. I'll give you my hypothesis on the four standard forc
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I disagree with saying photons have mass, they don't.
I consider that changing what is called mass, that is 'm', until that point in physics and multiplying it by gamma to call it the new mass ie. 'relativistic mass' a sleight of hand.
"To answer you secondary question: virtual particles are imaginary and therefore can mean whatever you want to balance fanciful equations. I personally am skeptical of anything "virtual" whose only proof of existence is "it makes the math work out". Math is a language and it's
Re: Virtual Photons have mass? (Score:2)
Right before my eyes (Score:2)
Tea, earl gray, hot (Score:2)
Make it so. :-)
Matter is constant, mass gets generated (Score:2)
No such thing as photon "colllisions". (Score:1)
Photons are bosons, and don't obey the Pauli exclusion principle.
What's really happening, is that photons can spontaneously (and usually temporarily) decay into a matter particle and an antimatter particle.
And THOSE can of course collide.
But first of all, that decay is extremely unlikely to happen for both photons at the same point and time, close enough to be able to collide at all.
And second, they of course have to collide correctly too.
And e=mc^2 is why you need a huge amount of energy, to even have enou
Hard enough? (Score:2)
Photons con only go at c speed, neither slower nor faster.
You can only change their energy by working on their frequency.
But you cannot push them harder!
Can Photons Decay? (Score:2)
If a photon has a high enough energy, can it spontaneously decay into matter and ant-matter?
2 photon is what's new (Score:2)