I often read sci-fi and find that writers tend to use physics phenomenon or theories which to the general public are quite obscure and mysterious. They often use them incorrectly or completely violate the rules they're supposed to be using. I thought I would provide a thread that gives some incite into how we determined what the rules are and what some of the actual strange behavior is. The universe is weird, but it's not as mysterious as most people think it is. I'd also like to invite questions or requests for more detail on whatever aspect of physics you wish. As a computer scientist, my expertise is obviously in the quantum mechanics, but I've kept myself in circles of physicists from varying disciplines and read the literature often. Classical Physics Natural Philosophy (Birth of man - 1728) Man has always tried to figure out the universe. Ironically, religion was the first science. They used it to describe the seasons, life, flood... It worked and was consistent with everything that they knew. A long slow trickle of knowledge began when we started writing with people like Imhotep and Archimedes making the first ideas of how things worked, they discovered the five basic machines, but not much else happened until mathematics really took off. Motion, Gravity, and Electromagnetism (1728 - 1915) The modern scientific age can be credited to many people, but since I'm only doing a quick overview, I'll start with Isaac Newton. In 1728 he published what is probably the most important book of all time: Philosophiae Naturalis Principia Mathematica. In it, he described the laws of physics of the day with exact mathematics and unified the falling of objects on Earth to the motions of the heavens. He also codified something that'd been known for a bit longer: relativity. According to Newton (building on Galileo,) all reference frames are equally valid and motions add (if you are moving at x speed towards an objects traveling towards you at y speed, the relative speed to you is x + y.) So gravity was figured out and electromagnetism was next. Lots of people helped with current, Ohms, charge, and it was known that alternating electricity created magnetism. Maxwell discovered and mathematically formulated the opposite. So a disturbance in the electric field created one in the magnetic field, which disturbed the electric field, which disturbed the magnetic field... and he calculated a value for the propagation of the electromagnetic wave (which is light.) Maxwell noticed the problem right away: he'd formulated a velocity that did not depend on the motion of the observer. Newton says velocities must add together, but here was this weird equation where the measured speed must always be the same, regardless of your own motion. Something was rotten in physics. Modern Physics Einstein (1915 - now) Einstein solved this. If everything is relative to your motion, yet somehow this velocity is constant, what's different? Velocity is relative to distance and time, so those must be what's changing, they're stretching This solved the relativity problem, but he wasn't done yet because it didn't work for accelerating objects. Newton's laws of gravity were dependent only on the distance between two objects and their mass, not their motion relative to each other. He didn't need it, his gravity force worked instantly across the universe, so whole new equations had to be worked out to allow the speed of gravity to be equal to light, that took a long time but something incredible happened: gravity fell away, the force completely vanished from the equations, it's just another acceleration. Gravity is an illusion based on curved spacetime. The planets actually travel in straight lines in 4D that look like curves in 3D. Like how if you look at a flat map, the shortest distance between London and NYC looks like its straight across the Atlantic, but in actuality, the straightest path curves up near Greenland. He realize that the speed of light was the translation ratio between motion through space and motion through time. Quantum Mechanics (1905 - now) Around the same time, electromagnetism was also starting to cause more problems. They started to realize that when they hit black bodies with different intensities of light, electrons would pop off. They knew it was because the light was exciting the electrons because the light carried energy. They assumed that as they increased the energy, more would pop off, but it didn't happen. Intensity seemed to have nothing to do with it, only the frequency of the light itself. Planck and Einstein finally figured out that it was because light, and electrons had wave and particle properties. Where waves can have any amount of energy, quantum waves had specific values. This is why electrons would only pop off it specific photons hit them and would ignore others regardless of intensity. It solved the problem of the electrons but opened a whole mess hat took 50 years to figure out as the standard model of Quantum physics. They realized that there were no forces and particles, it was all the same thing and forces acted by matter exchanging other particles. As they kept querying though, things got weirder and weird as things like particles appearing in multiple places at the same time or particles that were connected mathematically, but not in space. Eventually a probability based model of the universe came out of the math and has worked ever since. Particles don't seem to even exist until they interact with another particle, weird, I know, but it's happening. Behaviors are usually described by something called Feynman diagrams which help us visualize. Here we have a possible interaction of two electrons (arrows coming from the bottom) repelling each other by exchanging a photon (wave line.) QM takes all possible interactions like this one and averages them to determine the actual predicted outcome. This encompasses all known forces except for gravity. GR and QM don't play nice - What's next? So we have two models of the universe right now: general relativity and quantum mechanics. They've got some problems which sci-fi writers can capitalize on. First off, they don't use the same kind of math. QM is probabilistic and discreet. Everything has exact, integer values, but has no exact position or state. In GR, everything is smooth, fractions are no problem and everything is fully deterministic. Secondly, they describe different things. Quantum mechanics tells us what happens to particles as they move through space and time. GR describes the spacetime itself. There are other problems like the fact that they have cosmological constants than are orders of magnitude off from both each other and the observed value, but those are the big ones. Third, they describe spacetime differently: GR says it's smooth and can be divided forever, QM says that once you zoom to the tiniest scales, spacetime is chaotic and full of random fluctuations: There are two major competitors to fix the incompatibilities: String (or M) Theory and Loop Quantum Gravity. String Theory (1960s - now) String theory came out of the standard model research. It was original used to describe the nuclear forces, but it failed. They kept up with the math and realized that not only was a gravity particle possible, it was required. Instead of imagining particles like points when they interact and possibility space when not, they picture them as strings vibrating in higher dimensions. QM has the biggest problem with describing the points where particles interact, the points disappear when working with strings because the strings themselves have width so there are no zeros in the math. Those Feynman diagrams with points and lines become more like a bunch of tubes. On the right is a string theory version of the two electrons repelling via a photon (the left side is the original QM version.) Because the diagrams themselves are 3D, you can then "time slice" it however you want to account for relativity. That's a problem still. It unifies gravity and relativity with everything else, but then it leaves space and time as a background player where stuff happens. Loop Quantum Gravity (1990s - now) Loop Quantum Gravity went way outside the box, instead of trying to figure out how to get gravity to fit with the standard model, they decided to figure out how to quantize relativity and describe both whats happening in space and time with spacetime itself. They created a framework in which the interaction of gravity was a property of the spacetime of a specific area. The point interactions of the other models are replaced by regions of spacetime with specific spins and structures. This unifies everything together, stuff doesn't happen in space and time, space and time are woven into what's happening. Once they figured out quantized gravity, the rest of the standard model was formulated by imagining particles as twists or kinks in the spacetime: LQG and string theory's dirty little secret Interesting tidbit that is often overlooked though: neither LQG nor string theory have mathematically described our universe. They are frameworks. Think of simple video game physics in an old 2D scroller. Able to go side to side, jump and have gravity pull you down, bump into objects and have a force between them. That's a framework. Using different parameters you can create any universe from Marios, to Sonics, to Contra, but only one configuration describes each. No one has found a configuration of string theory that actually describes the forces and interactions how we see them, only that it can describe forces and interactions. Likewise, no one has formulated LQG to actually match general relativity, only that GR is within it's range. Usefulness and limits for fiction So here are some common sci-fi tropes and how they match up with different sets of physical laws. Most are expressly forbidden, and usually when I write sci-fi I determine not what's possible given the stringent laws of physics but what's the most minimal thing I'd have to alter in order for my story to work. Time travel - GR, string theory, would make this impossible within two causally connected parts of the universe. In QM, it's possible to formulate interactions so that there appears to be a backwards in time communication, but it's a mathematical illusion, causality is always preserved. In LQG, time gets fuzzy at small scale and at ever smaller scales goes away completely, so it's not a valid question, but in the macro world, it's not possible. Wormholes - GR allows wormholes, but only if they've existed since the beginning of the universe. They can exist, but can to be created or destroyed, spacetime can not tear. String theory and LQG has the theoretical ability to tear spacetime, but the rips appear out of the quantum fuzziness, they aren't manipulable. Warp travel - GR allows it. You can quite easily describe a valid bubble that shoots around the universe unbounded by the speed of causality as long as you are moving forwards in time. It requires an imaginary energy density however, which doesn't seem to have a way to be physically described. Tachyons - GR, LQG, and string theory all forbid it. QM actually requires it, the now-famous Higgs field is actually tachyonic, because it has imaginary mass values. However, no information travels faster than causality and disturbances in the field instantly decay. Subspace communication - All theories forbid it. Lots of people think quantum entanglement will work, but it won't. Entangled particles must be left alone or else their entanglement disappears, so you can't bring them with you anywhere. Negative mass - GR and string theory allow it, but it's not special. It won't move faster than light, and won't respond to forces backwards. In fact, it shouldn't respond to any forces we're aware of at all except gravity. Negative is not the same as imaginary in mathematics. (and imaginary isn't as not-real as it sounds.) QM would not allow it because we understand what makes mass mass. You can't negatively interact with the Higgs field, you either do or do not, it's not like charge that can be positive or negative or energy density, which can be positive or negative. Backwards arrow of time - Since our consciousness only works in one direction, we could never perceive it but GR and string theory allow time to work in either direction and the arrow of time is though to emerge from something else (entropy.) In QM, it's not possible, interactions are one way and destroy information. In LQG, time is an emergent property so the question is nonsensical. Shadow universes - There is no reason to exclude the possibility that there are things we simply don't interact with. Dark matter is one of them (though it is not complex like matter.) If gravity is a boson, then there is no reason that there could be an infinite number more fields with various other things in them, however, if gravity is part of spacetime, everything would be required to interact with it and we'd be able to detect it. Antimatter - It's not sci-fi, this is real and we can make it. It was actually predicted by the laws of QM before it was discovered, and new we understand it very well. it's exactly the same as matter but with opposite charge. It falls in gravity attracts everything else just like matter. We can contain it in magnetic bottles. Mini black hole drives - Very real, tiny black holes put of incredible amounts of energy, but they can not be held in place in any way or subject to any movement. They're also ticking time bombs, if an anti-matter/matter engine fails, just stop feeding it and everything will be fine, if a black hole engine fails, it'll melt down and blow up. A micro black hole will not grow though by pulling everything around it in, it'll simply explode due to Hawking radiation which is a QM affect. Strangelet - often used as a weapon in sci-fi, it's very real. A strange quark is a special type of quark that's more stable than regular quarks and will convert any other quark it touches. All matter is made of quarks at their nuclei, so a single strange quark dropped on a planet, could completely destroy it. It fits with the math of QM, but we've never seen such a thing. Antigravity - GR allows it, it actually requires it. Gravity simply causes space to curve inwards, anything that pushes it outwards (like dark energy) is a form of antigravity. Neutronium - the strongest material in the universe. It's real, but it's only stable under incredible gravitational fields. Neutron stars are these objects, they're gravity is so crazy that atomic nucleii crunch together and form neutrons with then push together until degeneracy pressure stops them. You can't harvest it because once you remove it from the gravitational field, it's no longer stable and will decay. Force fields / light sabres - sort of? You can trap a plasma inside of a magnetic bubble, but they will have energy limitations and radiate massive amounts of heat. You can contain the plasma, but not the heat. Invisibility - Yes, we're already working on that. There are plenty of ways to bend light around an object. Remote sensors - No. QM forbids it, in order to get information about anything, you must interact with it, that requires locality. Teleportation - No, all theories would forbid any type of macro teleportation. You may hear that QM allows particles to teleport. In lay terms, they do, in mathematical terms, they don't. The movement is hidden in the math, but it's there and it's not mysterious. EmDrive - You've probably seen this come out of NASA. Yes, it's real, it does work, and nobody understands why. The most likely explanation is that it's pushing against the quantum foam, there are several other prototypes that do the same thing. I mentioned earlier how GR and QM predict different levels of quantum foam energy. It's very small for GR's, but when calculated with QM it's something like 10^120 times larger, so if that's right empty space still has an insane amount of energy in it. Conclusion / Q&A If you would like a deeper explanation of any of the concepts that I described here or physics in general, please go ahead and ask them here. I only ask that you keep it relevant to science fiction. I could talk for hours about n-branes, but they have no relevance to our universe. If I don't know the answer to something, I probably know someone who does. If you want to see how some of the math works, lemme know what you want to see and what you're level of understand of math is and I'll try to explain it in those terms. If you have a sci-fi cliche that you'd like to know why it would be or would not be possible, list those too.
Oh, I guess I mentioned it in passing where I mentioned particles connected mathematically but not in space. Entanglement is a weird thing that pops out of the type of math QM uses. It still mystifies physicists and even has string theorists scratching their heads (they have some out there ideas but no proof.). To understand it you have to think of the particles as waves and understand that these things don't travel from here to there by visiting every place in between, they exist in all their possible states at once (called superposition, remember that for later) and only chose one during an interaction. Still with me? Okay so imagine a quantum system (a wave packet) that splits in half and travel in opposite directions. You have the state of the wave when it was one and you can get it to two in your imagination right? So maybe from there you can see a problem already: they had no exact position in the in between and that's where the split takes place. If you can't know how the split, you can't know their end state until you measure one of them. Which means it's not defined and exists in that superposition. That means the measurement of one instantly determine the state of the other, violating Einsteins concept that information can't travel faster than causality. He called it spooky action at a distance and it's still pretty spooky. He assumed it was just an artifact in the math and proposed an experiment to prove it was impossible. In the 80s they did the experiment and proved its completely real.
uh huh...the "possible" states...and it "chose" one, extrapolated as we can "theoretically assume" they are manifested in all possible states...looking at them causes them to choose a state, but that's a principal I'm certain will be visited....oh, you did. The meaning of causal seems to be rather fluid. Upshot: I guess this guy from Krypton flying around stopping bullets with his chest is out of the question, then.
@newjerseyrunner "They realized that there were no forces and particles, it was all the same thing and forces acted by matter exchanging other particles" What do you mean by this (bold) exactly? Or rather I think you ought to clarify so that people don't get confused.
Most of what you have under the heading, "Usefulness and limits for fiction" should read, so far as we know at this juncture in human history, "Wishful Thinking & Junk Science". There is no real evidence supporting Wormholes, String Theory may well be nonsense, we have no idea what Dark Matter/Energy is or can quantify how it interacts with gravity. There is some reason to believe in the Multiverse Theory, but it's as likely no two universes operate under the same physical laws, so it's all for not... and Quantum Mechanics has become something of a magical spell we cast at everything we can't explain. We will never colonize a world outside our solar system, and no amount of dreamy science fiction, or misspent tax dollars going to NASA will change that. This is better reading on how plausible SF really is, from Charles Stross (SF Writer). You won't find any fantasy science in this article, High Frontier Redux... http://www.antipope.org/charlie/blog-static/2007/06/the_high_frontier_redux.html
Wait, some of what you said are the type of misconceptions I'd like to clear up. QM is not as mysterious as people think. It's not intuitive, but it's the best understood and well tested theory we have, even of the weird phenomenon. It explains why DNA has the shape it does, why gold has its color and almost every other observed phenomenon, all in an equation that fits on one line. Most of the weird stuff wasn't discovered and then worked in, it fell out of the math and was thought to be not real but turned out to be proven experimentally by experiments like the quantum eraser experiment. We have no idea about the underlying stuff that causes this behavior, but we certainly have the math that describes it. That's nothing new, newton didn't say how gravity worked, he just gave it a formula. We know how dark matter interacts with gravity actually. Gravity doesn't care what kind of matter, mass, energy you are, it all gets treated the same way. There is actually space for dark matter built into the standard model. You know how electric charge can be positive or negative so you can have regular and antimatter? That's not the only field that can flip and there is a whole family of heavy theoretical particles in theory. Dark energy is measurable because we can plot the expansion of the universe over time by looking at further and further away standard candles. We can also measure the flatness of the universe and determine how much dark energy there is by solving Einsteins equations of the universe, which was done in the early 2000s. Sure, I'll use electromagnetism as an example. You learned about the electromagnetic field in school and you probably have also heard of a photon right? A photon is a light quanta. (Quanta is a quantum particle, we use it to avoid confusion because this had the wave particle duality.) Now imagine two electrons. Negatively charged. You know from Maxwells equations that they will push each other apart with strength relative to the square of the distance between them (at least st the macro scale.) Both excite the electromagnetic field and of course will interact with each other. But how? Remember that only specific packets of energy amounts are allowed. That packet is a photon of course, the electromagnetic quanta. Refer to the Feynman diagram in my first post where I said it respresented two electrons exchanging a photon. That's the electromagnetic force. It's nice that I happened to use one with math involved. These diagrams aren't just pictures, they actually are a representation of integral equations. Spoiler: Math See by each election there is an e to the power of something? That's the wave form of the electron. You'll see a similar term in the squiggly line, that's the waveform of the photon. Q is charge D is distance This formulation appears to be missing special relativity, but it has been properly taken into account for quantum electrodynamics. In QM you think of all of the possibilities and average then together. The possibilities are they either exchange a photon or they don't and each has a probability. (There are other weird things that can happen, but those get lower and lower in probability.). When you average all of those probabilities up, at the macro scale, they'll converge on Maxwells equations. Pretty neat, huh? So now you know that a force is actually caused by a type of particle being passed between two other types of particles.
Not causality, causality is still preserved. Order doesn't change, just when things happen is fuzzy. That's true in relativity too to an extent, two observers of the same event may not agree on the order of events, but that's because of bending spacetime, not quantum randomness. It's determinism that has to be abandoned. Knowing the state beforehand and the laws of physics does not give you a deterministic later state. Einstein hated the idea. He famously declared that "god does not play dice with the universe." He was convinced that as soon as we had the technology to do experiments to test all the weird predictions, itd have to be thrown out. Then slowly for the past hundred years the results have been coming in. I think it was Feynman who said later "not only does god play dice but sometimes he throws them where they can't be seen." This is one of the experiments that Einstein predicted would not work but did:
I think what you're really describing is a mathematical representation that uses virtual photons- this is different from an actual photon. That's what I meant when I asked for clarification.
Oh, I was trying to keep it in layman's terms and avoid virtual particles for simplicity. A virtual photon is what's actually passed between them, but it's actually not that different than a photon. Remember that a "real" particle is a standing wave in a field. In order to interact between two other particles, it is not necessary to have an actual standing wave, just the wave form. There are circumstances where virtual particles can become real and vise verse, it has to do with how much energy is in the field. Because everything is quantized, whats exchanged is the same regardless of if the particle pops off of the field or not. The easiest way to think about real or virtual particles is with an analogy of water: Here you can see how a "real" particle would form in the quantum fields, but you can also see how information could easily be passed without actually requiring a droplet to pop off. Droplets will "pop" off of a wave in the surface of water if given enough energy, just like a real particle will "pop" off of the 3D fields. This is how the Higgs particle was discovered, but putting energy into the Higgs field and making a wave big enough to sustain itself, but like the water droplet, few particles are actually stable as standing waves.
Go on and call 100 years of quantum mechanics that has been proven time after time a "magical spell we cast at everything we can't explain." You have no validity naming these sciences as such, and your thinking isn't going to spark anything for a debate the way you go on about; you're merely sating my daily wish for humour.
Proven? Quantum? LOL. One thing about this thread is it's getting rather fast and loose with the language. Unified theorists have said, "We've proved the possibility of God." Then, the main of talk about a deity is science has replaced belief in one...you're either "scientific" or "superstitious". I did notice my Superman reference went unnoticed. However, of all the typing done on this thread, Superman has surpassed it as fiction even though we all (secretly) know he's impossible. That's not the point of fiction, to accurately represent "reality". Fiction's purpose is entirely to inaccurately represent reality. I write 300-page lies a LOT! So...I'm supposing what the subject was supposed to be is, when you're creating your lie, and you need some "truthiness" to give it the air of plausibility....or, am I mistaken? Are we pushing a sci fi that is "proved" by math equations that "solve" the problems - or laboratory tried and true - or it's junk? "Urinalysis, Spock?" One of my favorite science fiction problems is, once you have all these vehicles and apparatus and have moved into deep space, how do you account for gravity - or the lack thereof? How can these people just walk around their spaceships without bouncing off the walls? Do all science fiction stories need a boiler-plate paragraph asserting the sort of "artificial gravity" (Guardians of the Galaxy) being employed? (At least Kubrick gave us magnetized boots and a huge centrifuge.) I for one don't really care if the entire physics department at Princeton laughs if I have my space crew jump into their ship and take off! Vroom! Hyperwarp!! Lord knows how boring it'd be watching Superman with them. "Hey! He can't do that! It's physically impossible!!"
Warp Travel involves creating a bubble of space behind you, and a bending of it in front. All the while you don't move but the space moves around you. I have heard the theory is to basically be pulled along by a black hole, the same way that horse pulls a carriage. Granted it would devastate everything in your path, but hey you got their faster. So basically warp drives are bad for the planet you are traveling to, as it would be crushed under the gravitational tides of your black hole bending time and space in front of you. Time travel is possible. Just leave the planet at high velocity (99% LSP), and when you get back on your return it will be the future because of time dilation. While you have aged 20 years, the planet will have aged 20,000. So you can go into time travel, but you can only go forward. Though there is a theory that if you could ride the event horizon in the opposite direction you could travel back in time. But this is just a theory. Also you could travel into a black hole provided it is massive enough that gravitational tide is more spread out compared to smaller black holes. Though it is unknown if you would survive such a journey.
You're sort of being pulled along, but it's more like body surfing a wave. You create a gradient of positively curved spacetime behind u and negative in front of you. Time travel to the future is fine, you're doing it right now. Time dilation affects the rate at which time passes so I guess you could use the twin paradox as a type of forwards time travel. You can't enter a black hole and exit it. You'd survive passing the event horizon of a big one because the tidal effects are small, but the event horizon itself isn't anywhere special, it's just the location in space where the black hole curves space so tightly that there is no our direction. Literally, once past the event horizon, not only can you not get out because the escape velocity is higher than light speed, you can't even point in a direction that leads out, all paths lead straight back towards the singularity. Remember how straight lines in bent 4D can loop back on themselves in 3D. Denegroth, science isn't in the business of proving, only disproving. Quantum mechanics math had some really really strange things fall out of it: entanglement, superposition, spin, strangeness, the Higgs field... each individual component can be proven experimentally and has been. Watch the video on the quantum eraser experiment. Again, there has been 100 years of experiments and the data agrees with predictions to an extremely high degree (way higher than GR.). So far no one has come up with an experiment that disproves the weird crap in the maths. Einstein proposed several of them and even made bets to their outcome, he lost. the existence of the Higgs field was the last major piece to be checked and we got those results a few years ago from LHC. Now there are only standard model extensions like SUSY left to check. I think you may be thinking of the interpretation of QM. That's up in the air and more like philosophy. Do Quinta really exist in all states at once like in the Copenhagen interpretation? No idea, it just works out that the math says so. Are their hidden variables like Bohr thought? Possibly, but any proposal for them have been experimented and rejected. Is there an underlying spacetime structure connecting entangled particles like string theory says? Maybe. Exactly what's going on physically doesn't matter, we only care if the math accurately describes the experiments and they do. Just like Newton: he didn't describe gravity, he only formulated maths to describe its affects. Do you have a specific aspect of QM that you'd like an explanation of? I have access to the academic libraries and can get you some literature on a specific experiment if you wish.
Thank-you. I appreciate your concern. I'm putting a stepson through theoretical physics, he's a graduate student ATM. We have daily discussions. What I'm "thinking of" is as I said; the language use gets fast and loose. This is, after all, a writing forum not a physics forum. My resistance is with how things are being said, not whether what is being discussed exists, or not. I appreciate your offer to explain quantum mechanics, however I don't think that will be necessary. Thanks all the same.
I realized when speaking with someone else today it might actually be easier to describe entanglement with math rather than with analogies. I'll spare you the real math and reduce it to simple algebra. So you know a particle exists in a location and it's probablility. When interacting with something, it has a probability of 100% at a specific location and zero everywhere else, then it smears out again based on schrodingers wave equation. So let's define a wave function with two lobes traveling away from each other as f(x). Now have one side of the wave interact with something, so it's probability drops to zero everywhere except one point. It's new wave function we'll call g(x). That simple act is breaking the entanglement and forcing you to define both particles regardless of how far apart they are. Because once you define g(x), By definition, the other side is f(x) - g(x). That's what I mean when I say that weird things like that simply "pop out" of the math.