Scientists create matter from pure light, proving the Breit-Wheeler effect | Hacker News Reader

Scientists create matter from pure light, proving the Breit-Wheeler effect

bnl.gov

399 pointswas_a_dev204 comments

It looks like one of the authors is on HN with us. Can you offer any insight into the cause of the confusing language in the "Science News" piece? It reads like it was written by a bot not a human.

In the sentence "With the theory physicists Gregory Breit and John Wheeler were able to prove that when two high-energy photons collide, a positron and an electron arise, i.e. matter is formed" shouldn't the word be "predict" not "prove"?

A more flagrant example of a strange word choice for a human science writer to make is "A direct conversion would require a laser that emits gamma-ray photons in a highly concentrated steel." Shouldn't the word "steel" instead be "beam"? This seems like the sort of thing an uncomprehending bot might do, conflate those two words.

Are my the nits I've picked, above, unfounded? Does the author of the original paper have any information which might suggest that an actual human wrote the "Science News" piece?

If not I would suggest that we've got a bot on the loose! Eeek!

Further, I think I'm seeing rather a lot of "content" floating around recently which smacks of machine origins.

Also, to Daniel... Great paper. Amazing stuff!

Author here, thanks! I am not familiar with this website (science-news.co) so I cannot comment on the quality of the writing (or human origin). I agree with you that "prove" should be "predict" - they did not prove anything except that from a theory standpoint, this process can happen in quantum mechanics.

The sentence about lasers is also strange, I have no idea what is meant there. My only guess is that it might be trying to describe some laser experiment that uses lasers to "heat" a hohlraum to produce a field of photons. Then some other high energy photon beam is used to collide with the photons inside the hohlraum.

edit: Original article from DOE press release is here with a bit more info: https://www.bnl.gov/newsroom/news.php?a=119023

Ok, we've changed the URL to that from https://science-news.co/scientists-create-matter-from-pure-l.... Thanks!

Dang, the old URL is the Google translation of a German-language magazine article (not attributed, so it's functionally plagiarism):

https://www.forschung-und-wissen.de/nachrichten/physik/mater...

You've previously asked for examples [0] of this type of fraud on HN: so this is one example! Credit to 'smurpy' in this thread, who noticed the 'bot'-like writing style.

[0] https://news.ycombinator.com/item?id=27295943

Thank you! I have banned the site.

Automated synonym replacement is the current cutting edge in plagiarism, or more generously, avoiding automated plagiarism detection. There was recently a large scandal in which some large number of scientific papers were traced to a ghostwriting house via their automated synonyms.

So my guess would be that the science news "author" is rewording things to avoid stepping on another author's copyright.

> So my guess would be that the science news "author" is rewording things to avoid stepping on another author's copyright.

And doing it badly...

How can two photons collide? Aren't photons force carriers/bosons?

Yes, photons are bosons / force carriers, but they interact with charged particles, and in this case produce e+ e- pairs via this Feynman diagram [1]. By rotating the diagram in spacetime, you get different known interactions: pair production (this topic), pair annihilation (same diagram running the other way in time), and, if memory serves, Compton scattering.

[1] https://en.wikipedia.org/wiki/Two-photon_physics#/media/File...

So, can photons interact and produce matter without particles to interact with?

One of the consequences of E=MC^2 is that there is a strong implication that energy can be converted directly into energy and vice versa.

Photons, although mass-less, have energy and can therefore be converted into matter under some circumstances.

I think you mean "directly into matter".

Yes. Thank you!

Apparently my well intentioned ramblings can be directly converted into brain farts.

I’ve always understood photons as being “stuff” in it’s all energy no mass state.

What is “stuff” as all matter no energy?

Probably any matter at absolute 0 would qualify? I think otherwise all mass has some excess of energy in it, I could be wrong.

Alternatively, possibly dark matter would qualify, although I am not sure either as we haven't even proven that it exists.

Wait, no, I was wrong. Matter and Energy are the same thing. Only nothing has no energy or matter.

"Rotate the diagram in spacetime" would make for some top-tier technobabble (not expressing doubt that it is a real thing, just wow, it sounds so cool).

Well, "rotating the diagram in spacetime" is also exactly what you do when you move your hands while holding the printout of a diagram...

(In this case though it's about rotating what's shown in the diagram, that is the interactions pictured, not the diagram itself :-))

This is as deliciously anti-climactic as finding out what "non-Euclidean space" means after hearing it a lot in Cthulu-like horror settings

Ok, so high enough energy photons fluctuating to other particle/antiparticles and then being able to interact with other high enough photons is an explanation I'm willing to settle for, because I thought that multiple bosons can occupy the same space, thus they were not able to interact with each other, by the "boson" definition.

It's still blows my mind that a photon could do that -- turn into a particle-antiparticle pair, the pair then quickly gets annihilated and turns back into the same photon and continues in the exact same direction and form the initial photon was travelling.

But if this process is real, does it mean that high energy photons travel slower than low energy photons?

Because low energy photons could not transform into particles that have mass, while higher energy photons could and thus spend just a liiiiiiitle bit more time as massive particles that can't travel at the speed of light.

Although in propositional logic we can say:

x ⊢ y

which means "x proves y".

It's Google's machine translation of a German-language article,

https://www.forschung-und-wissen.de/nachrichten/physik/mater...

Good shout! The German article definitely misspells Strahl (beam) as Stahl (steel), which makes no sense in context.

I was surprised because I thought the Breit-Wheeler Effect has been demonstrated already. It just looks like what they mean here is single photon (or really, two photon), not the so-called strong field Breit-Wheeler that was demonstrated at SLAC and with powerful lasers for decades now.

One of the authors here. You are correct, the famous SLAC result already demonstrated that light can be converted into matter, but they needed several photons >4, average of about 6 - that is the so called non-linear Breit-Wheeler (BW) process. This result is the original linear BW process where only 2 photons collide. The main difference is that for the linear BW you need much higher energy photons. Also, in this experiment we are able to measure the wavefunction of the two-photon system, which proves other aspects of the original predictions by Breit & Wheeler and others.

I was always curious before I heard of this today what would happen if you concentrated more and more light into a ultra fine point. It makes sense that at some point particles would begin to emerge as photons appear to have various electromagnetic properties and also carry a small amount of kinetic force (solar sail principle)

I have had this mental question about 'what time is it when photons collide'. Given that a photon could have been travelling for a million years colliding with one that has only been travelling for a microsecond, and from the photon perspective there is no passage of time and no distance.

I then kept reading things that tell me photons don't interact, which saddened me because I like the question. This now appears to not be the case, is there a specific condition under which photons can interact like this?

In classical electromagnetism photons (light) do not interact, period. But in quantum mechanics the photons can briefly fluctuate into electron + positron pairs which allow them to interact with each other. But the probability for interacting is very small AND you need enough energy to make the electron positron pair (for the Breit-Wheeler process), so it is very rare in practice.

I am not sure about the "time" the photons collide, but the interesting thing is that the Breit-Wheeler process is what determines the opacity of the universe - since high energy photons traveling through the universe can hit low energy photons from the cosmic microwave background and convert (disappearing) into an electron positron pair.

This is a good example of one of the errors that I often see in what is otherwise the best scientific writing, which is either forgetting to specify what a certain model says, or simply straight up forgetting/confusing that a certain model isn't reality.

Maxwell's equations say that light doesn't interact. Maxwell's equations are known to be wrong in that way. They're still a very good simplifying case that you can do very well with using, by all means, just like Newtonian physics in the right conditions, but they aren't the way reality works. Maxwell's equations also have no place to put a gravity term, yet gravity clearly affects light.

The one I probably see the most often is articles about black holes confidently speaking about "what goes on below the event horizon" from an Einstein relativity point of view, which is where you get all the singularities and ring singularities that lead to different universes somehow, etc, again either forgetting to point out or simply forgetting entirely that those are the specific predictions of Einstein relativity, which is known to be inadequate to describe the inside of a black hole. It is certainly fair to discuss that theory's predictions, and whatever really is happening in there, relativity will certain shine some sort of light on it, but it is a mistake to present it simply as "what happens on the inside". The model is known to be broken here.

I am working out how to phrase this in a way that makes sense to the HN crowd because this tends to ruffle feathers when I say it, but this is all what should be well-known stuff. It's not like I'm "denying science" when I say this; quite the contrary! It's "denying science" when you insist the known-by-science-to-be-broken models are in fact not broken where the science is pretty clear that they are.

>Maxwell's equations also have no place to put a gravity term, yet gravity clearly affects light.

The place to put the "gravity term" is in the coordinate system that Maxwell's equations take place in, and the definition of the derivative which is implicitly brought in via the curls, divergences, etc. That's general relativity, and Maxwell's equations are already fully compatible with it.

>[this tends to ruffle feathers when I say it] ... It's "denying science" when you insist the known-by-science-to-be-broken models are in fact not broken where the science is pretty clear that they are.

People are probably taking issue with your use of the words "broken" and "wrong," because you're describing a car that says 90mph on the dealership's sticker but can't go 900mph as "broken," or a one pound lump of beef as "wrong," because although the butcher said it weighed a pound, and you were charged for a pound, it'd be nice if it were two.

Yes, if you add relativity to Maxwell's equations, you get relativistic Maxwell's equations. Ultimately not particularly relevant here anyhow since it's QM describing what's going on here, not relativity.

I don't deal in automotive metaphors because they rarely enlighten, so I'll just stick with, yes, they are broken in those places, and are not suitable for unqualified claims about the nature of reality. This isn't about what would be nice if it were true or slight exaggerations, it's about the models being broken by being applied outside of their domain in an unqualified manner. That's exactly not how they are wrong. They are wrong in a much stronger manner.

And what's more, their strong brokenness is scientific consensus, not some sort of whacky theory. Whack theorization is what you're doing when you take these models, apply them in a domain they are known to be broken in, then claim this is the absolute truth about what is going on.

> relativity to Maxwell's equations, you get relativistic Maxwell's equations

Maxwell's equations imply (special) relativity, so there's nothing to be added. Maxwell's equations imply the speed of light is the same in all reference frames, which is all you need to derive special relativity.

That is why people of the time were trying to understand how this can ben so, why the did things like Michaelson-Morely to look for invariance/ether, and why so many of the terms used in relativity predate relativity, since they were invented to handle that Maxwell's Equations had this invariance.

Basically, Maxwell's equations, as written were relativistically invariant, thus compatible.

Special relativity is (partially) predicted by Maxwell's equations, and they are fully compatible. They are instead incompatible with classical mechanics.

GP claimed that Maxwell's equations are missing a term for gravity/mass, which would be the domain of General Relativity. This is more complicated, as it's true that they didn't predict gravitational lensing. But, they are still compatible with GR, as GR modifies the coordinate system, and Maxwell's equation in the GR curved space-time coordinate system do predict gravitational lensing.

GP also pointed out that Maxwell's equations are not compatible at all with QM, as they incorrectly predict that photons can't interact. Here there is no way to save them - Maxwell's equations are just an approximation, and the actual laws governing the behavior of light are substantially different, only reducing to ME in certain approximations (just like classical mechanics is not compatible with either QM or SR/GR, except as an approximation of either of the two others).

> or simply straight up forgetting/confusing > that a certain model isn't reality.

That's partly to do with the way that high school science is taught. If we made the context clear at all times then people would have a better grounding.

I find your comment confusing. What exactly is the "good example" you're referring to? The person you are replying to appears to have done exactly what you are saying to do, by my reading, so I'm wondering what you're referring to.

'The map is not the territory' is the phrasing I've heard: https://en.m.wikipedia.org/wiki/Map%E2%80%93territory_relati...

Wait. I did a physics undergrad but I never asked myself this question. How is it possible that the EM fields from photos can't interact with each other? Doubly funny, I did my undergrad research for the PHENIX experiment.

Fields are abstractions that ease the calculation of the forces on charges caused by the positions and motions of other charges. The charges interact, but the fields don’t; there is nothing “there” to interact. (This is classical EM.)

If you are in a room with two charges, the electrostatic field at any point is the addition of the fields from each charge. There is no extra interaction term.

Phillips gave you a good answer, but another good answer is that Maxwell's equations are linear; forbidding any interaction between solutions f and g because if L is a linear operator, L[f+g] must = L[f] + L[g].

Oooo. Wow. This is a great answer, thanks for explaining it that way.

Where do they teach physics like this? Anywhere?

I feel like this would be mentioned in a typical undergraduate wave mechanics course taught in a typical American university, but I have not been to enough undergraduate wave mechanics courses in enough American universities to know, really.

This is what we are taught in high school / college as the super-position principle

Photons are EM fields -- self-propagating ones, like a glider in the Game of Life. The electric field changes, creating a magnetic field, but the magnetic field changes, creating an electric field. Use sines for the functions and you can see how the function just keeps re-appearing.

Now, combine that with the superposition principle ... photons pass through one another under most circumstances because of this (unlike gliders).

Stupid question I’m sure, but do our estimates for the total amount of matter in the universe account for this effect? Could this effect end up being the source of dark matter? Or is too infrequent to generate enough matter to explain the discrepancy?

Not a stupid question. However, I think that this process (whether it is included in calculations or not) shouldn't contribute to the dark matter issue. Electrons and positrons are "normal" matter and if they are anywhere near e.g. a star, they will contribute to the plasma around the star and therefore be visible. Also, even if it were not visible, my intuition is that the process is too rare to produce enough mass to account for the dark matter

If by "this effect" you mean particles fluctuating so that every field has at least some role to play in every interaction, it also applies to empty space, which has a nonzero energy density due to its own fluctuations. In fact, empty space has an enormous energy density due to this stuff. It is so enormous that it's implausible, and that's considered to be one of the major unsolved problems in physics.

If by "this effect" you mean radiation occasionally interacting to produce particles, that actually doesn't change the amount of gravity in the universe when it happens, because energy is what gravitates and it's conserved in particle interactions.

https://en.wikipedia.org/wiki/Cosmological_constant_problem

Best estimates are that photons only make up about 0.005% of the energy density of the universe. There's just not enough of them.

Thank you! I was curious about exactly this. But now I have a new question. If a photon is sufficiently energetic to be capable of briefly fluctuating into an electron-positron pair, does that imply that it would, over a long distance, be slower than c, since the e-p pair can't travel at c for the brief moment it exists?

The structure of the photon (here meaning the fact that it can fluctuate into an electron positron pair) is what leads to the speed of light being c and not something even larger. So your intuition is somewhat correct, except that the effect is "already taken into account" when we first learned what the speed of light was. Also, a photon can do this fluctuating even if it doesnt have a lot of energy, since the electron positron pair can be virtual - i.e. they have almost no mass and live only for an instant before annihilating back into a photon

Hmm... is the right mental model then that the photon has a speed higher than C in its photon state but on average it's C due to the fluctuation into an electron/positron pair? I would imagine that's the wrong model because there's contradictions that arise (e.g. the speed of light would vary with the energy of the photons so that those not fluctuating would have a higher speed but that's not the case AFAIK). Is this just "quantum mechanical weirdness" or do we have an "intuitive" explanation for how the speed of light and this fluctuation interplay?

I don't think this is right at all. C is a universal constant, and it is not in fact known for sure whether light travels at c or just below (whether photons have a mass). However, individual photons in certain conditions can absolutely move at speeds lower than c. If photons of different energy move at different speeds, this would be detectable by firing the photons at the same far-away mirror, and measuring how much time it takes for each photon to return (on average).

That's really interesting. What's this effect called? I'd love to learn more about it. This topic fascinates me to no end!

Rest mass is conserved. So the "system" of the photons has to have sufficient rest mass to support the particle production. Rest mass depends on the energy of the individual photons, and the angle they are colliding with (head on is best, nearly parallell photons grazing is worst).

Photons are not generally thought to have a rest mass, unless something has changed in the last 25 years or so. The conversion of energy into 2x electron masses (positron + electron). So the photon pair needs at least 2 x 911 MeV of energy. This would be around 1.82 GeV of photon energy. To give a sense of the frequency of this, a 911 MeV photon (colliding with another of the same energy) would have a frequency of 911 x 10^6 ev/(4.14 x 10^-15 ev/Hz) or 2.2 x 10^23 Hz, with a wavelength of 1.4 x 10^-15 m. That is, very hard gamma.

But the photons really shouldn't have rest mass.

If you have two photons, then neither of them will have rest mass. But the system of both of them does. This happens because |p_system| < |p_1| + |p_2|.

https://en.wikipedia.org/wiki/Energy–momentum_relation

I'd suggest looking at the Invariant mass page. What you are talking about isn't rest mass of a photon, rather the center of mass invariant mass[1]. This arises from the equivalence principle, the relation between mass and energy, not because a photon (a massless particle) has a rest mass (it doesn't).

It might be a pedantic argument on my part, but still, it is worth being clear on this point.

[1] https://en.wikipedia.org/wiki/Invariant_mass#Collider_experi...

(Center of mass) invariant mass is synonymous with rest mass.

Is it? It sounds like you are explicitly disagreeing with hpcjoe's position, but just a bare "no, I'm right" isn't informative. Can you give some reason or argument that supports your position over hpcjoe's?

> In physics, the energy–momentum relation, or relativistic dispersion relation, is the relativistic equation relating total energy (which is also called relativistic energy) to invariant mass (which is also called rest mass) and momentum. It is the extension of mass–energy equivalence for bodies or systems with non-zero momentum

Those are the first few sentences in the article I already posted.

> The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object or system of objects that is independent of the overall motion of the system. More precisely, it is a characteristic of the system's total energy and momentum that is the same in all frames of reference related by Lorentz transformations.[1] If a center-of-momentum frame exists for the system, then the invariant mass of a system is equal to its total mass in that "rest frame".

Those are the first few sentences in the article he already posted.

In the last sentence of the article he posted, it's unclear to me how that applies to a system with two photons in it. If I have two photons heading off in opposite directions, I'm in the center-of-momentum frame for that system. Then the invariant mass is equal to the system's "total mass" in that frame. For two photons, is that 0, or E/mc^2?

I know what your position is. I'm just not sure that the quote from his article supports your position.

I will grant you that if you take the energy-momentum equation and apply it to such a system as a whole, and plug in the total energy (non-zero) and the total momentum (zero), then out comes a non-zero mass. I just am unclear on whether that's a valid thing to do. (I also don't know that it's not valid.) Can you make a convincing case that it's reasonable to apply that equation in that way?

Well there are a couple of things to address here. The first is that the invariant mass is invariant - it's the same in any reference frame. So the invariant mass of a system will either equal the sum of the masses of the particles or it won't, irrespective of frame. And equality will only hold if there is no internal movement.

> Can you make a convincing case that it's reasonable to apply that equation in that way?

Even hpcjoe did not object to that, only to the name "rest mass" for the result. We saw that the number you get out was useful upthread, because it allowed predicting if pair production can occur or not.

Rest mass is not conserved. Total energy is conserved, which includes both rest mass and momentum (E^2=m^2+p^2). Photons have momentum but no rest mass; ordinary matter has rest mass but (usually) little momentum.

Photon - photon scattering in vacuum is a known process, they can interact through virtual particles. The problem is that the probability of such an event is very low and requires very high photon energies.

"From the photon perspective there is no passage of time" What exactly happens when light travels through denser medium? Speed is less than c, so does that mean it experiences time?

https://en.wikipedia.org/wiki/Ewald–Oseen_extinction_theorem

It bounces around, thus not travelling in a straight line, thus covering more distance whilst still moving at c.

My understanding, which could be wrong, is that it doesn't 'bounce around' as much as it is absorbed and re-emitted. This process isn't instantaneous and accounts for the net propagation delay through the medium.

Sort of. Refraction it better looked at from a wave perspective than a particle one, IMO. The wavefront expands at the speed of light, but the wave bounces off of the medium it's traveling through and self interacts in a way that means that the highest probability area moves slower than C despite the edge of the wavefront still moving at C. That smearing is also why the wavelength changes upon refraction. (And obviously leaving concepts like time dilation off the table for simplicity's sake).

Both ideas are incorrect. Bouncing around would be random and the outgoing light would be scattered (as in matte reflections) in all directions. Absorbtion simply destroys the original light. If photons are mostly absorbed, we call that “a wall” or ”a fog”, not “a transparent medium”, which to be transparent shouldn’t have electrons whose energy level differences correspond to a photon’s wave length. The transparency and slowdown effect is a complex interaction between fields in the medium, which I honestly don’t have enough courage to retell.

https://youtube.com/watch?v=CiHN0ZWE5bk

That would imply light getting scattered willy-nilly as it crosses any medium, which it isn't in case of transparent media...

There's no perfectly transparent media other than pure vacuum.

> Speed is less than c, so does that mean it experiences time?

There is no absolute clock in the world; we can only know about what happened where and when by looking.

A way to understand this (and special relativity) is from an information-theoretic perspective, and to think of c as the “Mach number” of free space, nothing more and nothing less.

So imagine that you couldn’t see but could only know about what happened where and when by hearing. All those phenomena (foreshortening, frequency shift, apparent time dilation) would be exhibited though the speed of information travel would be much lower. You have probably experienced the equivalent of blue shift/red shift yourself by listening to a high speed vehicle.

Change the medium from ordinary air to something with a different density and all these phenomena will be detectable, even though the speed of sound will be different.

There are two pictures that you could take of the situation. Classically, where the medium is smooth continuous stuff with a permeability and a permittivity, there are no photons, only waves. Quantum mechanically, where the medium is made up of lots of little particles, there are photons indeed, but no smooth medium, and no region where the speed is less than C (because there is no "region," only lots of separate particles). So there's one picture missing "photons," and the other missing "speed less than c," so you can't capture "photons in a region where the speed is less than c," in a single image.

I guess if you wanted to pose that question in a framework where a medium where the speed was less than c, and photons, could exist simultaneously, you would want an effective field theory (maybe). But you will have to get someone else who knows more than me to explain that. :-)

Don't feel sad. If you look at a set of all ever existing humans, the number that ever interact is incredibly small.

Even if in the same vicinity, and time, eg same apartment building, subway, street, driving down the road, there is often zero interaction.

Really, humans interact very rarely too. Yet, humans do interact, in meaningful ways. Thus, it is likely the same for photons.

This theory also explains why, with the rarity of human interaction, I am unmarried. In fact, it probably explains it on multiple levels.

Fun question: if photons do not experience time as they travel at the speed of light, do we know that photons are stable? Maybe they would decay if they were subject to time. Or maybe the concept is meaningless as they are massless.

This induces some severe Star Trek replicator fantasies. Though I assume the result of this compares to having a cup of earl like opening a lego drawer vs. a visit to Legoland

I've been thinking about it a lot, and I feel that the road to Star Trek replicator is not through matter synthesis. Instead, a better way - perhaps the only way - is through some sort of universal feedstock (or few of those) and a library of carefully designed chemical processes (possibly involving nanoengineering).

It seems nice at first - the idea of turning raw energy into things. But the amount of energy required is just ludicrous, going through antimatter intermediary is extremely dangerous, and... there's really no point. It isn't buying you anything.

If you tried to store the amount of energy needed to replicate a kilogram of stuff in some advanced batteries, you'd quickly discover that those batteries now weigh a kilogram more. E=mc^2 works both ways - storing energy adds mass. So, unless you can literally fly through a star and suck it dry as you replicate your tea, replicators won't be reducing weight of a starship. It turns out, matter itself is the ultimate energy storage device.

And then, turning energy into matter just gives you elementary particles. You need more work to assemble that into useful stuff. This is nuclear work, and then chemical work. So why not just ditch the matter/antimatter intermediary, and start from some feedstock that already has the necessary elements, and is optimized to be easy to react into the stuff you want (and then to be recycled from that stuff)?

I think this is right. And this, plus unlimited power (coming soon) gives you the route to the Roddenberry economy where everyone works to improve themselves and society and there is no money.

Think about it. If you put dirt in the replicator and you get a Rolex or a hamburger or a garment, you don't need money for anything: everyone is equal and they can go off and study or work on whatever they want. Wealth is a false proxy for social status anyway.

Real Estate! That'll be the only valuable thing in such an economy.

we'll all have a pocket universe to design as we wish :D

That's something that always bugged me. Why does Picard get to have an entire, private vineyard to himself?

Maybe when beaming down to earth they really beam down into a holodeck (or the Matrix).

Primogeniture, apparently. Great thread athttps://mobile.twitter.com/sarahtaber_bww/status/12002306275...

That's a great (and long) thread. Reminds me of a pet theory I have: that the post-scarcity utopia of the Federation is based on expansionism, and not sustainable.

They've managed to turn Earth into a paradise and give (mostly) everyone great life quality, but they did this by doubling down on exponential growth, which manifests in the constant need to get more and more planets to join the Federation.

You can see the expansionist vibes all over the show, and they've even been hinted at by various aliens in DS9 (although without any mention of economic implications).

I really think this is right, it would be nice to have a Star Trek like sci fi series that actually tried to tackle the issues. As a series it's been a source of inspiration for decades. It's a shame modern Star Trek is just generic sci-fi drama.

That thread points out some interesting observations about typical Star Trek inconsistencies (another one would be to think about why someone should move to a colony in the first place or rather about why not everyone can simply travel between planets as they like). But the objection against desalination is pointless. We can manage that problem already today (e.g., by drying up the brine or by pumping it into old oil wells). There is absolutely no reason to assume water would be scarce in the 24th century of TNG.

They might have some sort of immigration quotas for the Earth, and if the population is approximately what it is now, then there's going to be a lot of open space, farmland, and wilderness still. That's assuming you have cities with a lot of people packed close together, and rural areas with sparse population. That seems much better than the alternative of turning the entire land-surface of the Earth into a uniform-density suburb.

There's plentiful space all over the universe if you're a multiplanetary species.

There's a pretty big difference between being able to colonize the universe and being able to colonize planets near to you. As an example, the Federation wasn't even able to map out a single galaxy nevermind colonize it.

> you don't need money for anything

Except for intellectual property, and possibly information in general. Which probably means that protecting it would become even more of a focus than it is now.

Yup. The current intellectual property regime pretty much shuts down any dream of replicator-driven utopia, even if a 24th century starship suddenly showed up in orbit and beamed down working replicators along with full specs.

It's not really a theoretical consideration - as we get better at turning information into matter, intellectual property laws literally centralize the means of production away from the people!

When replicator will be ready to use, you will be able to replicate iphone XXX freely, because copyright for iphone XXX will expire at that time.

Unless the legislators go the Disney route and effectively extend copyright and patents indefinitely.

If that happened, people would just break intellectual property laws left and right until they became unenforceable.

I'm not sure I follow. Private property exists right now to enable the accumulation of wealth. In a post-scarcity economy, what is the value of wealth accumulation?

Power and status. People want something to bargain with, to show off, and to control other people. If money is not an option, information will do (and possibly cryptocurrency, which in some way is both).

Sorry, still struggling to understand here. Today power and status is derived from scarcity. What is an example of power or status not derived from scarcity?

Energy is not free. Humans can always find something desirable/influential that requires more energy than is cheaply available.

Ex.: the Star Trek replicator requires staggering amount of energy. Owning one, and affording the fuel, would provide power and status. Were energy cheap enough to give everybody one would enable something next level scarce and desirable/influential.

That's disappointing. I was more interested in deducing the implications of power assuming scarcity was eliminated.

I appreciate the interest, but see it as pure fantasy. Essence of supply is energy, and we can ALWAYS use however much energy we can get our hands on. Think of the casual interplanetary/interstellar travel depicted in sci-fi: huge energy use for petty purposes. Think of the huge energy use of median western lifestyle, relative to historical norm sustenance living.

Hate to pop the bubble. You are promoting me to further analyze/quantify modern vs sustenance living, in terms of sheer energy consumption.

“Post-scarcity” is a myth. There will always be some limited-supply thing humans will value.

Consider how utterly dissatisfied people are with abundant cheap food, clothing, water, fuel, housing, etc. today vs not all that long ago, having integrated new norms into mundane sustenance making abundance seem unattainable. An hour’s minimum wage today buys medieval luxury but for regulations demanding even better.

It's more complicated than that. People are dissatisfied with abundance today because they're being made dissatisfied, in several ways:

- Creating fake dissatisfaction is literally the cornerstone of sales and marketing. To get someone to buy stuff where they otherwise wouldn't, you have to create in them the state of being dissatisfied with what they already have (e.g. make them desire something else, or make them afraid of something). I'm not sure we can blame regular folks for being whiny if the richest industry on the planet is making them whiny on purpose.

- Value engineering means things that were good and cheap, like food and clothing, keep getting worse over time, as companies keep trying to squeeze extra margins. Besides competitive pressure, this is also driven by inflation. Overall result: things that were good before are barely usable today, despite being abundant.

- Related, some people recognize this abundance is being turned into a play to chain and exploit people. The more things are becoming services instead of products, the more people become dependent on providers. It's becoming clearly visible in developed countries: to make use of abundance, you need to keep running the rat race to exhaustion. We're reaching a ridiculous point that, in order to have the good fruits of our civilization, you have to be busy working so hard you that don't have time to enjoy them.

- We're barely few generations into a subset of population having some sort of decent life. Call it being biased by time and place of birth, but frankly, I consider the average quality of life before late 20th century West to be tragic and unacceptable, and current one to be barely scratching the surface of how people should live.

I see no reason to assume that people wouldn't stop consuming obsessively in a post-scarcity economy, if said economy would be able to guarantee actual high-quality goods to meet everyone's needs, without bullshit strings attached (no "X as a Service"!), and without marketers constantly trying to ruin everyone's mood.

We're already there, nearly. Calories are incredibly cheap and a modest dwelling can be produced very inexpensively as well. Humans will find scarcities to focus on, or barring that, make them. (Housing cartels come to mind).

Access to healthcare remains genuinely scarce, admittedly, and Baumol's cost disease is a real problem when you need to buy someone else's time.

What do you mean you don’t need money? How will you pay for services where people must spend their time to serve you? Any time you start tracking who owes something to someone you have the beginnings of currency. The post-scarcity economy being free of money never really made sense.

If everyone's needs and even all non-extravagant desires can be met for free (or "too cheap to meter" free; this is the "post-scarcity" part), then the need for accurate tracking of value flow vanishes. Everything else can be mostly handled on a pay-it-forward basis, perhaps with a bit of "reputation economy" sprinkled in, and the remaining exceptions don't warrant a society-wide currency.

I would expect the remaining exceptions to be enraging examples of unfairness to any post-scarcity society, and for civilization to really test the boundaries of "too cheap to meter".

Perhaps, but then I would expect people in a post-scarcity society to be fine with the idea that life is not fair - that it's not possible for everyone to have equal access to everything at the same time. I'd expect them to not care that much, having a comfortable life all needs taken care of.

I'd also expect post-scarcity people to not even stress the "too cheap to meter" boundaries that hard - when comparing with people of today, it's worth remembering that most consumption of non-essentials is driven by artificial needs created by advertising, and advertising is predicated on scarcity. Post-scarcity people wouldn't be brainwashed to consume so much.

> Perhaps, but then I would expect people in a post-scarcity society to be fine with the idea that life is not fair - that it's not possible for everyone to have equal access to everything at the same time.

Are you kidding??? Life today is better than it has been at any time in history with more opportunities and luxuries more accessible than ever and people still complain.

> Life today is better than it has been at any time in history with more opportunities and luxuries more accessible than ever and people still complain.

I think the complaints can be divided into two parts:

- Complaining about how their life is still full of pain and problems;

- Complaining about how the world sucks, is unjust, discriminating, etc.

Humans have infinite capacity for that second type of complaints, but I posit that the first type should go away once life gets good enough.

And note that even for most Westerners, "with more opportunities and luxuries more accessible than ever", the life isn't good because they don't get to make much use of those opportunities and luxuries. They spend almost all their life working in bad physical or mental (or both) conditions, having little time to enjoy those luxuries and opportunities, because they need to keep making money to pay for access. Rents, mortgages and everything-as-a-service are mostly cancelling out the quality-of-life increase from better products and healthcare.

I dream of a post scarcity world. Live long and prosper as they say.

> Wealth is a false proxy for social status anyway

Wealth is just the current proxy. I suspect you'll never be able to fully eliminate a social hierarchy. Many animals compete physically, humans compete socially, and without money we'll find new ways to socially standout. The game just changes, it's not going to go away.

Maybe nobody has to starve, work, or even die from anything besides a freak accident ever again, but not all the 100 billion humans who want to can possibly live in Neo-Manhattan (at least until the Mega Dome is finished in 50 years, but then not everyone can live on the Upper Rim). Not everybody can meet the coolest celebrity in the metaverse, or all have the same clever instagram handle. Not everyone can control who is allowed to visit and build on holy sites or nature preserves.

I think people can always invent or discover new things that are functionally finite, and their claims on these kinds of things and the way they decide to distribute it can always theoretically be quantized into something we can understand as currency or wealth. Even if it's not done explicitly, it will simply be done in something like an extremely advanced algorithm or even an opaque shadow economy of networks of favors and patronages.

It's true that some things are naturally scarce (like land, or celebrity exposure, or attention), and that people can make things scarce on purpose. It probably isn't possible to work around this - but this doesn't mean we couldn't have a post-scarcity society in spite of it.

The way I see it, if "nobody has to starve, work, or even die from anything besides a freak accident ever again", if everyone has free access to as much varied, healthy and tasty food as they want, if they can pursue almost arbitrary hobby[0], or do interesting and challenging service adjacent to their interests - then the bits that remain fundamentally scarce (like land or attention) won't be enough to justify having a money-based economy, and without it, people will lose the reason for creating artificial scarcity. Some people may end up trading IOUs over trivialities like clever Instagram handle - something that, on a global scale, nobody cares about. But there would be no need to e.g. DRM movies or games anymore - the producers aren't getting paid for it, they do it for fun/reputation/self-actualization - so what's the point of making infinitely-copyable good artificially scarce?

Post-scarcity doesn't have to be absolute for it to be a money-less utopia - it's enough to make enough goods too cheap to meter that money becomes irrelevant for everyday life of average citizen.

[0] - There will always be limits to what individuals can do - post-scarcity is a practical concept, not an absolute one. Even Star Trek societies wouldn't be able to afford people having a hobby of "detonating warp cores to use the gamma ray flash for interplanetary Morse code".

Energy does have one big advantage over matter: you can send it at the speed of light.

The implications of this in a world with both mass->energy and energy->mass conversion are left as an exercise for the reader.

Unless, of course, you take speed out of the equation by folding space to transport things.

Sounds a lot like the CHON (Carbon, Hydrogen, Oxygen, Nitrogen) food I've read about in some science fiction novels I've read.

It would make sense that if you could "print" food from CHON then to restock during your inter-galactic travels you'd just need to find some nice asteroids with the requisite materials.

I'm thinking higher level than that, for practical reasons.

Assembling complex things - particularly biologics - from raw atoms is a painful, slow, and energy-intensive work. The growth rates of various organisms on Earth give you a ballpark of how fast you can get with this. I for one would love replicators to work faster if possible :).

I feel a better idea would be to make universal feedstock (or family of those) out of complex molecules - perhaps proteins, or protein-like nanostrutures. Molecules selected for having energy advantage in bulk reactions and precision nanowork required to assemble the most common things people replicate.

CHON food would not really work because it doesn't have any sodium or chloride, and who wants to live without salt? (But more seriously, we need our mineral nutrients to survive.)

Well, then just add an S and a Cl in there.

>> ... because it doesn't have any sodium or chloride ...

> Well, then just add an S and a Cl in there.

If we're talking sodium, wouldn't "S" instead be "Na"? Though I'm guessing sulfur has some importance as well.

But Star Trek replicators don't work through matter synthesis, they work through matter transformation. It's a variant of transporter technology; a source fuel is deconstructed and then reconstructed in the desired configuration.

I know. Or at least that's how I interpreted various remarks during the show.

Direct matter synthesis doesn't make sense in this context, but I've seen a lot of people on the Internet assume this is what happens. The way they talk about it on the show could lead you to either theory, for both replicators and transporters.

But to the extent we're discussing it as technology we could potentially have, and/or may want to make happen, I feel it's worth pointing out that transforming feedstock is a better design, doesn't require mastery of bulk antimatter processing, and is perhaps closer to possibility than one would otherwise assume.

Hell, I'd go as far as saying that there are problems with reasonable "attacks"[0] on the road to a replicator - engineering, chemical and biotech problems we could be working on right now.

-- [0] - In the Hamming sense, see https://www.cs.virginia.edu/~robins/YouAndYourResearch.html.

Like 3D printing.

Of course I don't think your statement's motive is to understand how we replicate the exact process of what is in Star Trek in the real world. More of a functional equivalent. However, because I have the poster, if you look at plans of the Enterprise, it contains a large volume that is reserved for "bulk matter". I believe it's this, along with some transporter technology enables the replicator to create a variety of combinations of chemicals and materials.

Oh, nice! I never saw that in any of the supplemental materials I stumbled upon. Which Enterprise is on the poster? Do you have a link handy?

Poop, gentlemen. The bulk matter is poop.

And red shirt corpses

dougmwne's right. Though I can't find my poster online (for the life of me), the technical manual is pretty clear:

[...]The various waste sludges recovered from the water recycling processes are a valuable resource. The organic waste processing system subjects the sludge to a series of sterilizing heat and radiation treatments. The waste is then electrolytically reprocessed into an organic particulate suspension that serves as the raw material for the food synthesizer systems. Remaining byproducts are conveyed to the solid waste processing system for matter replication recycling. [...] Material that cannot be directly recycled by mechanical or chemical means is stored for matter synthesis recycling. This is accomplished by molecular matrix replicators that actually dematerialize the waste materials and rematerialize them in the form of desired objects or materials stored in computer memory. While this process provides an enormous variety of useful items, it is very energy intensive and many everyday consumables (such as water and clothing) are recycled by less energy intensive mechanical or chemical means. Certain types of consumables (such as foodstuffs) are routinely recycled using matter replication because this results in a considerable savings of stored raw material (See: 13.5).

From tngtm section 12.5: https://xaeyr.typepad.com/files/franchise-star-trek-tng-tech...

Spoiler for S3 of Star Trek: Discovery - https://www.youtube.com/watch?v=GIIYb04HGbQ

That's basically the idea in The Diamond Age by Neil Stephenson. It's years since I read it but it's set in a world of nanoengineering where whatever you need can be created out of common feedstock.

I've never read it. Thanks, I'm fast-tracking it to the top of my "to-read" pile!

Unfortunately the energy requirements of those replicators would be ludicrous… like 10x the yield of the Tsar Bomba (largest H-bomb in history) to make a cup of tea. Replicator malfunction would be an extinction level event.

Just do E=mc^2 on the mass of your cup of tea.

More like 1/10th the Tsar Bomba. 1KG = 9e16J, where the bomba was ~209 PJ or 2e17J and a cup of tea is only like 0.2kg so 2e16J.

So only merely wiping a city off the map, nothing as dramatic as an extinction level event, then? ;)

Twice that. One cup antimatter, one cup ambient matter.

I would prefer a cup of dark matter please.

Joseph Mallozzi has you covered, then

Not everything that produces mater also produces antimatter otherwise the universe would be a 50:50 mix of each. Why Baryon asymmetry exists is unknown, but as long as we’re talking magic tech we might as well make it efficient.

> Not everything that produces mater also produces antimatter otherwise the universe would be a 50:50 mix of each.

That's not known. It's also possible that the initial stuff of the universe, before inflation happened, had more particles than antiparticles. Since we have no physics for what happened before inflation started, this wouldn't break any theory at all. It's a bit unsatisfactory as theories go, but it is absolutely compatible with all physical observations so far.

That’s just a turtles argument, whatever happened before the Big Bang now has the asymmetry.

Well, technically whatever happened between the big bang and inflation. But, while unsatisfactory, this is not an invalid argument. It is very plausible that it is impossible to replicate the conditions of the big bang, or anything close to them, so it is plausible we will never be able to scientifically describe that process.

As such, it is possible that the processes of the Big Bang (or whatever came before) somehow created more matter than anti-matter, but all of the physics that comes after is symmetrical with respect to charge. So, we have no reason to expect that we'll ever find a theory explaining why there is more matter than antimatter, just like we don't have any reason to expect to ever find a theory that explains why there are two kinds of electrical charge and not 5. So, it's not a promising avenue for research, and not a promising assumption.

In contrast, there are reasons to expect we will some day find a theory of quantum gravity, since we know for sure matter does interact gravitationally and QM doesn't account for that.

Before or after the Big Bang you still get some process. The ability to replicate it is of course in question, but we are already talking about a device we have no idea how to build so that doesn’t change anything.

As to impossibilities, we already figured out how to break conservation of energy due to the expansion of the universe. Arguing about what is in isn’t possible for some process we don’t know about seems silly.

I said nothing about impossible. I was discussing whether 'we will discover some process in the universe as it is that favors matter over anti-matter' is a useful working hypothesis, and my claim is that it is not.

Of course, it is possible that one exists, just like expansion of space (which probably does exist, though apparently there are starting to be reasons to doubt that [0]) turns out to be a way to break conservation of energy or the speed of light.

[0] http://backreaction.blogspot.com/2021/09/new-evidence-agains...

Whoa... so that means the Tsar Bomba actually converted many kilograms of mass into energy? Holy crap.

Ahh... the YOLO days of nuclear physics...

Star Trek will use existing matter to replicate stuff(but maybe not all the time) , otherwise it would cost a lot of energy.

You forget about one smaaaal issue: disposal of created antimatter. Also why bother creating matter from energy when even today we are able to create stockpiles of raw elements (although quite inefficiently and with almost no control over isotopic composition). Assuming that waste will be converted back to those elements, you don't need those stockpiles be too big and energy consumption will be modest when compared to creation of matter directly from energy.

What about using the antimatter as engine fuel?

Much like how we can turn lead into gold but don't, this process isn't remotely cost-effective. There's plenty matter lying around that you can have for probably 20 orders of magnitude cheaper.

At the risk of sounding like an idiot, why doesn't this happen when you point two flashlights at each other? Or point a flashlight at the sun? Or when light from one star reaches another? Etc etc.

does your flashlight emit gamma rays

It's funny that you ask, but I have this flashlight that I found in my weird neighbor's garage/machine shop...

Is your weird neighbor's surname, Smith, by any chance?

I also mentioned stars, but thanks.

You need to have enough energy (aka. mass, physicist will use the two interchangably) to pay for whatever particle you want.

An electron weighs about 10^-30 kg, or about half a megaelectronvolt, but because of cosmic balance you'll want to make a positron at the same time. So your total bill will be about 1 MeV. Visible light photons have about 1 eV of energy, if you want a photon with an MeV then you're past even hard x-rays and into gamma rays. This process is the same as matter-antimatter annihilation, except backwards.

A proper explanation would take several years.

By the way, you can use more than one photon at a time, but to my knowledge nobody has managed to fuse the million flashlight photons you'd need to do pair-production.

Fascinating.

Could two cooperating civilizations a and b use this effect to create matter (perhaps even something self-replicating?) at a 3rd location in space?

    incoming ascii art

      (a)---(c)
             |
             |
             |
            (b)

It is very unlikely that teleportation could ever be achieved by generating matter from light.

There are 2 problems.

First is that the energy required for generating a human-sized body is huge, several hundreds times greater than that of a nuclear bomb with the same amount of active material.

Second is that even if you would be able to do that, you would make 2 bodies, one of matter and the other of antimatter and you would not be able to dispose of the antimatter one except by causing an explosion equivalent with hundreds or thousands of nuclear bombs.

In general, for now it appears to be completely impossible to do teleportation towards an arbitrary place.

At most, it could be imagined a method that would work between 2 large installations existing at the end points, where the destination could manufacture a replica of what was sent from local materials (e.g. by placing one atom after another until an exact replica is made; extremely unlikely, but not completely impossible).

Wouldn’t the no cloning theorem make an exact replica impossible?

The "no cloning theorem" refers to replicating the same quantum state.

It does not apply to making a replica of a body that is composed by the same kinds of atoms linked in the same way between themselves, which can be considered as identical with the original for any practical purposes.

In a very rudimentary form, such technology exists today, it is possible to remove one atom at a time from a certain position of a body and identify it with a mass spectrometer and it is possible to grow a structure a few atoms at a time.

It is likely that the precision of such techniques could be improved well enough to be able to replicate some extremely small microscopic objects.

The most difficult limitation to overcome is the speed of the process.

To be able to make some human-sized object atom-by-atom and molecule-by-molecule in a reasonable time would require a many orders-of-magnitude higher speed than possible with the current technologies.

> First is that the energy required for generating a human-sized body is huge, several hundreds times greater than that of a nuclear bomb

I thought this was a bit short, I'm pretty sure it's closer to:

1 gram = 90000000000000 joules

1 average us man = ~89000 grams

Google tells me 1 Hiroshima bomb = 63000000000000 joules

So the average us man should be ~127,142 Hiroshima bombs, or ~110,000 Hiroshima bombs for the average us woman.

I have said that a factor of hundreds applies for the same weight of active material.

Most nuclear bombs have just a few kilograms of active material, much less than a human.

Also the number that I have given was for ideal conversion and for a fusion bomb, which is more efficient per weight.

The fission bombs, like that from Hiroshima, are limited by the excess energy of uranium or plutonium, which is only about 0.13% of mass compared to iron.

Because we cannot actually split plutonium into iron but into nuclei with higher energy, the available energy from fission is slightly less than 0.1% of mass.

Taken into account that only a fraction of the active material is consumed, let's say 10% and that the active material of a bomb is ten times lighter than a human, then an annihilated human mass would be equivalent to 100 thousand fission bombs, so your numbers match this.

For a fusion bomb, the efficiency is much higher, about 0.5% of mass becomes energy and also the mass of active material can be much higher, so an equivalence with less than one thousand nuclear bombs is possible.

In any case I have given just the most optimistic limit, i.e. a few hundreds nuclear bombs of maximum energy, with smaller bombs, of course you need more.

This amount of energy is required to CREATE mass from scratch. IMHO, it's much easier to use transmutation of atoms to print an object layer by layer instead.

Teleportation has that issue of "the reprinted is not the original" - ironically, turning someone into light and then re-assembling them into matter seems closer to "true sci-fi" teleportation. Of course, it still wouldn't be the same person since you essentially converted all the constituents, kind of like melting down a sword and reforging.

Given that we don't know how sentience works, I like to think that you could achieve true teleportation if it turns out that the "you" are not the connections of your brain, but something else that exists in a fourth dimension.

I have seen a few science fiction stories where everyone is happily running teleporters until someone accidentally turns off or breaks the part of the machine that annihilates the guy standing on the sending terminal.

The idea would be to build a nanoassembler that can receive instructions via light.

Imagine engineering teams from different civilizations trying to collaborate to the precision of a few atoms :) That's a sci-fi I'd watch.

Publication link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...

Free link:

https://arxiv.org/abs/1910.12400

So, a question: traditional objections to galactic travel (e.g. 1G accel) is the requirement for huge amounts of propulsion mass. Even with a method of perfect E=mc^2 of some special fuel matter, you still need a whole load of propulsion mass to chuck in the opposite direction, which in turn requires more energy to accelerate.

the question is, could we get around that by converting from mass-less forms of energy, and generating mass on-the-fly, skipping the need to accelerate tons of acceleration mass; or is there some restriction that would disallow this?

If I fire 2 photons at each other on a ship travelling at 0.5c, and this creates 2 particles e+ and e-; would the particles also be travelling at 0.5c along with the ship; would their velocity/momentum be in random directions etc?

Better article: https://www.bnl.gov/newsroom/news.php?a=119023

Curious, can this process be reversed? Also, is momentum conserved, then if it is wouldn't the positron and electron be ejecting at the speed of light (and wouldn't that violate the principle that matter cannot reach the speed of light)? If not what is slowing them down / where is the energy going? Could this be theoretically a way to power something? Either by the ricochet of the particles off something, or by using them to energize something?

All quantum-mechanical processes can be reversed. In fact, this process is actually a lot more common in the other direction; a positron and an electron making a pair of photons is matter-antimatter annihilation and it happens all the time. This is because a couple photons are thermodynamically preferred over an electron-positron pair at room temperature. It's kind of like how allotropes of solids will form and reform as you change the heat and pressure.

Momentum is mass times velocity. Momentum is conserved, but you're going from (probably) mass-less photons moving at c to mass-ive electrons/positrons moving at <c.

when you say mass times velocity, I take it you mean relativistic mass? I assume you know all the following, and I'm just saying it to explain my reasoning for the above / to elaborate for other readers. One can certainly pick a frame of reference such that the total momentum of the electron and positron afterwards is non-zero, and therefore the total momentum of the photons beforehand (in that reference frame) will also be non-zero , despite photons having (or, believed to have, but I believe it also) 0 rest mass.

We have matter at home.

> A direct conversion would require a laser that emits gamma-ray photons in a highly concentrated steel. However, research has not yet been able to develop such a laser.

What does "highly concentrated steel" mean here?

All my Googling is getting hits for the metal, but I feel like something else is meant here.

This domain was never submitted to HN before, so I suspect this is some other article which was put through the so-called "synonymizer" software.

Here is an article from Brookhaven Lab website: https://www.bnl.gov/newsroom/news.php?a=119023

> This domain was never submitted to HN before, so I suspect this is some other article which was put through the so-called "synonymizer" software.

If that's true the domain should be banned. There's no point in reading things that garbled plagiarizations.

Can someone ELI5 the relationship between electrons and photons? So far we have:

* Electrons emit photons when going from a high energy state to a low energy state (but remain electrons)

* Two photons colliding produce an electron-positron pair (always exactly one?)

There's no ELI5 answer. You can look at some Standard Model charts. In principle, any particles in the SM can interact or decompose into any other particle, as long as mass-energy, spin, charge, color charge etc are conserved. The probability of many of these interactions may be minuscule.

Curious if the reverse is true ... also is momentum conserved in this, then wouldn't the positron electron pair be shooting off at the speed of light, and if not where is the extra energy going? Or have I missed something?

So, after all, it seems science fiction writers are prophets in disguise.

List of Star Trek inventions that came true: https://qz.com/766831/star-trek-real-life-technology/

Although, from "light into electron and positron" to "Tea, Earl Grey, Hot" there is a long way to go.

You can't give credit to Star Trek because I am pretty sure this possibility was understood before Gene got to it. ;)

True, Star Trek initial release was October 14, 1986 while theory was there from 1934. Thanks for correction.

Now the real question is, when can I order my replicator and dilithium crystals to power it?

> they collided gold nuclei accelerated to 99.99 percent of the speed of light.

How did they achieve that?

Sentence before:

> Relativistic Heavy Ion Collider

https://en.wikipedia.org/wiki/Relativistic_Heavy_Ion_Collide...

As a Saivite, this perfectly aligns with both my religious and scientific understanding of the universe.

Matter from pure light huh, today's job market is getting competitive for sure.

Except electrons aren't matter.

I am positive that electrons are matter. Never heard your claim before.

You are positive you were told that electrons are matter maybe. This is the standard (see: current) model, in QFT electrons are not particles, so are not leptons, so are not matter.

Is the mass measurement of electrons an abberation then in the QFT interpretation of the empirical data? Or is it that energy can have mass prior to being converted under some conditions?

> Is the mass measurement of electrons an abberation then in the QFT interpretation of the empirical data.

I'm not sure this is resolved. see: https://en.wikipedia.org/wiki/Quantum_electrodynamics#Conclu...

> Or is it that energy can have mass prior to being converted under some conditions?

Using https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalenc... you can (theoretically) convert between energy and mass, and then measure everything as https://en.wikipedia.org/wiki/Electronvolt. I have yet to see anything create protons from energy, so I am hesitant to do this.

> I have yet to see anything create protons from energy, so I am hesitant to do this.

Won't a proton/antiproton annihilation also create two photons? If so, wouldn't that also work in reverse?

> Won't a proton/antiproton annihilation also create two photons?

I expect it would make a lot more than just two photons. See: https://en.wikipedia.org/wiki/Annihilation#Proton%E2%80%93an...

> If so, wouldn't that also work in reverse?

It would have to be demonstrated.

Thanks, I didn't know proton/antiproton annihilation is so complex. But it makes sense.

How do you think we got matter from the big bang?

I don't pay much attention to big bang things, as far as I'm concerned it's as unprovable as an infinite universe theory. I'm not sure we can ever know either way.

Wikipedia says "Even restricting the discussion to physics, scientists do not have a unique definition of what matter is." (in the sense of contrasting with antimatter), and then later says "In a wider sense, one can use the word matter simply to refer to fermions.". (Presumably this means, fermions and things comprised of fermions. One would not say that Helium-4 is not matter just because it is a boson (and is comprised of an even number of fermions).)

Electrons are fermions.

I am therefore comfortable saying that electrons are matter.

I don't know why you say that electrons are "not particles" in QFT. Sure, there's an electron field, and electrons are just, like, excitations in that field. There's also a quark field. What of it? If you are saying "because everything is fields, there are therefore no particles, and therefore no matter", you are using the word "matter" in a silly way.

Also, isn't a "particle" just a representation of a compact Lie group? What's the problem?

(edit : though, I admit that I'd be a little hesitant about calling a massless fermion "matter". But, seeing as there are no known massless fermions, meh.)

This gives me a negative feeling.

"The electron is a subatomic particle, (denoted by the symbol e− or β− ), whose electric charge is negative one elementary charge.[9] Electrons belong to the first generation of the lepton particle family,[10] and are generally thought to be elementary particles because they have no known components or substructure.[1] The electron has a mass that is approximately 1/1836 that of the proton."

https://en.m.wikipedia.org/wiki/Electron

Electrons are Fermions, and therefore matter. That's in contrast to Bosons, which are "energy" (more precisely force carriers).

Matter (aether) is constant, it cannot be created or destroyed. Mass is created in places where matter's (aether's) density gets slightly higher or lower than its baseline density. Photons don't exist. You're welcome.

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