from the order-a-billion-pendulums-from-Amazon! dept.
A Billion Tiny Pendulums Could Detect the Universe's Missing Mass:
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have proposed a novel method for finding dark matter, the cosmos's mystery material that has eluded detection for decades. Dark matter makes up about 27% of the universe; ordinary matter, such as the stuff that builds stars and planets, accounts for just 5% of the cosmos. (A mysterious entity called dark energy, accounts for the other 68%.)
According to cosmologists, all the visible material in the universe is merely floating in a vast sea of dark matter — particles that are invisible but nonetheless have mass and exert a gravitational force. Dark matter's gravity would provide the missing glue that keeps galaxies from falling apart and account for how matter clumped together to form the universe's rich galactic tapestry.
The proposed experiment, in which a billion millimeter-sized pendulums would act as dark matter sensors, would be the first to hunt for dark matter solely through its gravitational interaction with visible matter. The experiment would be one of the few to search for dark matter particles with a mass as great as that of a grain of salt, a scale rarely explored and never studied by sensors capable of recording tiny gravitational forces.
[...] "Our proposal relies purely on the gravitational coupling, the only coupling we know for sure that exists between dark matter and ordinary luminous matter," said study co-author Daniel Carney, a theoretical physicist jointly affiliated with NIST, the Joint Quantum Institute (JQI) and the Joint Center for Quantum Information and Computer Science (QuICS) at the University of Maryland in College Park, and the Fermi National Accelerator Laboratory.
[...] Because the only unknown in the experiment is the mass of the dark matter particle, not how it couples to ordinary matter, "if someone builds the experiment we suggest, they either find dark matter or rule out all dark matter candidates over a wide range of possible masses," said Carney. The experiment would be sensitive to particles ranging from about 1/5,000 of a milligram to a few milligrams. That mass scale is particularly interesting because it covers the so-called Planck mass, a quantity of mass determined solely by three fundamental constants of nature and equivalent to about 1/5,000 of a gram.
Journal Reference:
Daniel Carney, Sohitri Ghosh, Gordan Krnjaic, et al. Proposal for gravitational direct detection of dark matter [open], Physical Review D (DOI: 10.1103/PhysRevD.102.072003)
(Score: 1, Funny) by Anonymous Coward on Wednesday October 21 2020, @10:25PM (3 children)
Call it "TikTok"
(Score: 0) by Anonymous Coward on Wednesday October 21 2020, @10:40PM
And have it spy on the universe? [youtube.com]
(Score: 1, Interesting) by Anonymous Coward on Wednesday October 21 2020, @11:49PM (1 child)
Are they literally pendulums, or can they be very sensitive accelerometers (of some other technology)?
c.1970 I had a tour of the MIT Instrumentation Labs (later Draper Labs) including the accelerometer cal room. They built the dead reckoning inertial nav that got Apollo to the Moon and back. Anyway, one way they calibrated a sensitive accelerometer was to fix it to something stable, sensitive axis horizontal (so it doesn't measure acceleration from Earth gravity), and then move a ~300 pound iron wrecking ball toward and away (total of about 30 feet), on a track. I forget the number, but I think that analog accelerometer could measure the position of the ball to an inch or better.
(Score: 2, Interesting) by Billy the Mountain on Thursday October 22 2020, @04:31AM
I think you are on the right track but I don't think a MEMS accelerometer would quite do it but I think a similar MEMS device consisting of a spiral structure with a mass at the end and using standard electronic movement detection that MEMS sensors typically use to sense movement would work.
What is nice about MEMS is it's relatively easy to make an array of sensors in one go.
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(Score: -1, Offtopic) by Anonymous Coward on Wednesday October 21 2020, @10:59PM
You're an idiot. These people want to be like me, not like you.
(Score: 0, Touché) by Azuma Hazuki 2.0 on Thursday October 22 2020, @02:24AM
Do not worry for I am here to listen to your troubles. What is troubling you my child?
(Score: 1, Interesting) by Anonymous Coward on Thursday October 22 2020, @12:03AM (21 children)
I don't understand the search for, 'dark matter,' and, 'dark energy.' We now have confirmed for some time now that black holes are the driving force behind every single galaxy in the universe. Galaxies are HUGE. Isn't a blackhole a massive enough object to make up for any perceived, 'missing matter,' or, 'dark energy.' Whatever is missing after that, could surely just be non-luminous matter floating here or there between or inside the galaxies?
(Score: 4, Informative) by Immerman on Thursday October 22 2020, @01:14AM (20 children)
There is still some chance, but we have ruled out most of the range of possible black hole masses as dark matter candidates.
To explain the galactic rotation curves under accepted theory, there must be a _lot_ of invisible mass in the outer reaches of the galaxy. If that "dark matter" were made of black holes, we would expect to see regular gravitational lensing events when looking at nearby galaxies whenever a black hole passed (almost) between them and us. The bigger the average size of black holes, the more dramatic and less frequent those events would be. Current observations have ruled out most of the potential size spectrum, and most of what's left is too small to have formed through any known mechanism. Primordial black holes formed during the first instants of the universe are still a possibility, but at present there is no evidence that such things exist.
(Score: 2) by deimtee on Thursday October 22 2020, @02:46AM (4 children)
I may be mis-remembering here, but I thought the only remaining black hole candidate masses for dark mattter were in the 50 - 70 solar mass range. Considered unlikely because they are too small to be formed like galactic centers, but too big to have formed from star collapse.
Coincidentally, LIGO is picking up many more mergers of that size than was expected.
No problem is insoluble, but at Ksp = 2.943×10−25 Mercury Sulphide comes close.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @03:23AM (2 children)
Black holes supposedly have gravity so strong light can't escape, but then they shoot massive beams of light and matter out of the north and south poles. Doesnt make any sense.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @03:53AM (1 child)
Hint: the light and matter is near the black hole, not in it.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @04:43AM
https://en.m.wikipedia.org/wiki/Blazar [wikipedia.org]
(Score: 2) by Immerman on Thursday October 22 2020, @01:27PM
Actually, I think you're right - there's still room at both extremes, beyond what we would expect to form "normally" - either too large to explain, or too small to form through stellar collapse. I believe there's also a narrow band in the middle somewhere that hasn't yet been ruled out, but it's getting so narrow that it seems increasingly improbable that such a huge population of black holes would "just happen" to have ended up almost the same size.
(Score: 2) by RS3 on Thursday October 22 2020, @02:46AM (14 children)
Not sure if you're a physicist but you sound like you know much more than my barely amateur knowledge.
Anyway, could it be possible that black holes actually contain far more mass than is understood; that like light being unable to escape, gravity only ekes out, like Hawking radiation?
(Score: 3, Informative) by Immerman on Thursday October 22 2020, @02:24PM (13 children)
Not really.
The amount of mas determines the size of the gravity well, and it's evidence of the the gravity wells that we're observing.
For example, Sagittarius A* is believed to be the supermassive black hole at the center of our galaxy ( https://en.wikipedia.org/wiki/Sagittarius_A* [wikipedia.org] ), and we've determined it's mass is (4.154±0.014) million solar masses. We've nailed down that mass so precisely by tracking the movement of the stars that are orbiting it at close range - mostly a few dozen to a few hundred AU at closest approach, and moving at several percent the speed of light. If the black hole were more massive, the stars would orbit faster, since orbital speed is 100% determined by the mass of the thing they're orbitting.
Most black holes don't have such obvious orbital companions, but like any massive object they still produce a gravitational lens ( https://en.wikipedia.org/wiki/Gravitational_lens [wikipedia.org] ), which becomes obvious whenever they pass between us and a distant star (or galaxy) - and the size and strength of that lens is determined purely by the mass of the black hole
And finally there's the gravitational wave observatories ( https://en.wikipedia.org/wiki/Gravitational_wave [wikipedia.org] ), which can detect the massive release of energy that comes from the death-spiral of two black holes spiraling in and merging. As they spiral in faster and faster the frequency of the gravitational waves rapidly climbs, until they touch and merge and stop radiating, resulting in a "chirp" whose maximum frequency is determined by the masses of the black holes involved. If we assume that there's no as-yet unknown mechanism that increases or decreases the probability of mergers of certain sizes, the size of those mergers we detect should be fairly representative of the size distribution of all black holes, as well as giving some hint as to how many black holes are actually out there, since mergers are pretty improbable: It's really unlikely for two stellar masses to end up orbitting each other in the first place unless they formed that way, any sort of gravitational capture requires the assistance of one or more additional stellar masses that can absorb the momentum lost during the capture. And that assistance has to happen within a very narrow time window, since otherwise the original two bodies will simply slingshot past one another in a single pass, never to pass again.
As I recall (dimly, so don't quote me), gravitational wave observations so far suggest that there's actually a lot more black holes out there than we expected, and an unexpected number are within the size range that we haven't yet ruled out as candidates for dark matter - so they're definitely still in the running. But there are so many untested assumptions guiding our expectations that we can't really say anything more conclusive.
(Score: 2) by RS3 on Thursday October 22 2020, @02:46PM (12 children)
Thank you, that's awesome info. I kind of get all of that, but it's based on the concept that mass and gravitational attraction are Newtonian.
I'm suggesting that maybe our methods of measuring (estimating) mass are incorrect, because "gravity waves" (for example) don't escape the black hole as much as they would if they were not being held back - by the unimaginable forces in the black hole.
IE: some gravity waves escape so we see the motion of other objects, including photons (lensing), and think we can calculate the mass in the black hole, but we're wrong.
(Score: 2) by Immerman on Thursday October 22 2020, @03:49PM (11 children)
I think there's a bit of confusion - gravitational waves don't transmit gravity, not like elecromagnetic waves transmit light, radio, and other forms of electromagnetic radiation. A better comparison would be that gravity is more like a (monopole) electric charge - no waves involved, it simply sits there pulling all other charges towards it*. Start accelerating an electric charge, and it will radiate away kinetic energy in the form of electromagnetic radiation (a.k.a. Bremsstrahlung radiation). Similarly, start accelerating a mass, and it will begin radiating away some of it's kinetic energy as gravitational waves - which is what causes black to spiral inwards and once they get close to each other. Planets, etc. also radiate away kinetic energy as gravitational waves, but since the acceleration (and their gravity) is so low, the energy radiated away is too tiny be be measured and there's no appreciable spiraling.
(* well, according to GR gravity isn't actually a force, but rather a curvature in the shape of spacetime itself, which causes objects on a straight-line path to appear to curve around it. Much as a straight line drawn on the surface of a sphere will loop back on itself to form a circle like the equator. So the analogy is flawed if you dig too deeply, but I think it does a good job of clarifying the distinction between "charge" and "waves")
Perhaps most importantly to this conversation - since the lens is caused directly by the gravitational spacetime distortion, anything that somehow caused mass to be "undercounted" would have exactly the same effect on the black holes gravitational effect on galaxies.
Gravitational waves don't have to escape a black hole - in fact NOTHING escapes a black hole (even Hawking radiation forms just outside the event horizon). But so long as you're outside the event horizon, a black hole acts exactly like any other mass of the same magnitude. There's even some alternative theories to GR that would prevent black holes from forming at all, with gravitational pull instead plateauing at an intensity slightly less than required to form an event horizon - but even those would have an almost identical gravitational lensing effect, because virtually the entire lens exists far outside the event horizon.
Also, gravitational waves have nothing to do with lensing (well, I suppose they'd create some minor distortion in the lens, but that's it). Substantial gravitational waves only get created where you have two massive objects orbitting each other, which causes the shape of the spacetime curvature to swirl around in alignment with them. Lensing is instead caused by the gravitational "charge" directly, every massive object creates a gravitational lens - it's just light being bent by gravity. We can see the lensing from our own sun, which causes stars to appear to move slightly as they pass behind it. Black holes just show the effect much more dramatically because they are basically invisible so they're easy to see past, and since lensing gets stronger the closer you get to the center of mass, and with a star, the star itself gets in the way, while a black hole is so tiny that you can see almost past its center and the lensing becomes much more intense.
As an example - if our sun magically turned into a black hole tomorrow, nothing would change in the orbits of the planets, or in the weak, low-frequency gravitational waves the planets produce as they orbit. However, instead of the sun being about 1.4 million km across, the black hole would be only 6km across - completely invisible from Earth except with our most powerful telescopes. That would mean we would see MUCH more powerful lensing of the stars passing behind it, since light could pass 233,000x closer to its center, and thus be distorted by gravity 54 million times stronger than at the sun's surface. But importantly, so long as you stay outside the sun's old radius there would be absolutely no difference in the gravitational effects, lensing included.
Also, a bit of an aside - gravity waves are also a thing, but they're completely unrelated to gravitational waves. Gravity waves are things like waves in the ocean, where the "springiness" that lets the waves exist is caused by gravity. Confusing name, but they were named long before anyone had even considered the possibility that gravitational waves could exist.
(Score: 2) by RS3 on Thursday October 22 2020, @05:57PM (10 children)
Thanks, I appreciate all you've written.
Let's get rid of "gravity waves" and just say- maybe something happening inside of a black hole is so powerful and so beyond what we imagine that the FORCE of gravity (mass to mass attraction) is altered.
In other words, and again you have to think far outside of the box (as many have over the years) of whatever we think we know so far.
We measure the mass of the black hole based on the force it exerts on other objects. But what if that very force is altered by something (that's beyond our imagination, let alone our current understanding) inside of the black hole. If that's true, our assumptions about the mass of a black hole would be incorrect.
Here's a simple example (ONLY an analogy) - an 80 lb bag of concrete that has a powerful magnet inside, and another magnet in the ground is in repulsion such that the bag seems very light at first.
(Score: 2) by Immerman on Thursday October 22 2020, @06:30PM (8 children)
Gravitational waves - as I said gravity waves are something *completely* different. You'll just confuse things if you try to use them interchangeably. Gravity waves are waves in materials pulled towards equilibrium by gravity, gravitational waves are fluctuations in the geometry of space itself, which make the distances between fixed points grow and shrink as they pass despite everything remaining motionless.
So you're saying, maybe we magically turn our sun into a black hole, and it suddenly starts acting like it's only half the mass or something? All the planets fly out onto larger orbits, and the gravitational lensing isn't nearly as intense as we'd expect?
The thing is, if the force of gravity is somehow altered like that - then it doesn't actually change anything. If black holes are dark matter, then you need X amount of combined force leaving the black holes to hold the galaxy together - and that exact same force is what causes the lensing. Basically, lensing is a way to indirectly see the shape and size of the gravitational field itself, not the amount of mass creating it.
Or to correct it a bit, since under GR gravity isn't a force - the mass of a black hole curves space around it. If space isn't actually curved as much as it should be (too little or too much) based on how much mass is in the black hole... it doesn't matter. All we care about is how much space is curved by the mass. Is it curved enough to contribute the required amount to hold the galaxy together? Then it will also be curved enough to bend light passing nearby by X amount. Both effects take place so far away from the black hole itself that any weirdness near or inside the event horizon just doesn't matter much.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @08:26PM (7 children)
If you turned the Sun into a black hole, by the time it collapses to a singularity in the center it would be about 1054 times as massive due to the added gravitational potential energy. E =MC2 after all.
Fortunately, the event horizon shields us from that ridiculously monstrous mass and we only "see" the gravitational attraction from the original mass, otherwise we would be accelerating towards the nearest black hole at several thousand gees.
It also leads to lots of "wow man, maybe there's like, you know, a whole new universe in there" speculation by stoned hippie physics students. The mass is certainly enough.
(Score: 2) by Immerman on Thursday October 22 2020, @09:15PM (6 children)
I think you swapped a minus sign somewhere. The closer two masses get together, the *less* gravitational potential energy they have. You put more potential energy into a weight by raising it, not lowering it. Which is why, by convention, all gravitational potential energy is negative. It's taken that two masses have zero potential energy at infinite distance: infinite distance is the only common reference point that applies to all things, and they're so far away they can't influence each other, so it doesn't make sense to say they have any potential energy at all. Then, as they get closer the potential energy between them is reduced - just as lowering a weight will reduce the potential energy it has stored. The closer they get, the lower the amount of energy between them, and since they started at zero that extra energy is negative. Which gives rise to the serious speculation that there may be no net energy in the universe - all the mass-energy from matter and radiation is perfectly canceled by its negative gravitational potential energy, and thus stoned hippie physics students can speculate that the universe was in fact created from nothing. Without violating conservation of mass-energy because there's *still* nothing, once you sum everything together. It's just nothing that's been broken apart so we can see the details and it looks like something.
Back to your original claim...
There is energy stored in the gravitational field of course - but general relativity states that such energy does NOT produce a gravitational field of its own, unlike all other forms of energy. Einstein felt that doing otherwise would amount to double-counting the original mass. There is however an alternative version of GR (unfortunately I can't remember the name) that was developed some years ago that *does* count gravitational field energy the same as all other forms of energy - and one of the big consequences is that black holes can't exist at all. The gravitational field energy from the surrounding gravity well pulls back on the central mass, creating a bowl-shaped gravitational "plateau" at the center where gravity (almost) stops increasing, rather than asymptotically approaching an infinite singularity. Even if you piled in infinite mass, the equations say gravity will never get strong enough to prevent light from escaping, so you can't create a black hole. Gravitational pressure could still get far too high for Pauli exclusion pressure to keep a neutron star from collapsing, and who knows what sort of weird degenerate matter state might exist beyond that, but whatever it might be it wouldn't have to deal with a singularity or event horizon, so it could all just swirl around as some sort of weird degenerate matter soup, bouncing off the walls of its gravitational prison.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @09:48PM (5 children)
The less potential energy, yes. How much energy could be liberated by dropping a 1kg mass down an infinite gravitational well? That energy has to go somewhere, and it manifests as the mass of the singularity. It's just that the effects of that mass cannot influence anything outside the event horizon.
(Score: 2) by Immerman on Thursday October 22 2020, @11:40PM (4 children)
> How much energy could be liberated by dropping a 1kg mass down an infinite gravitational well?
Exactly zero, energy can be neither created nor destroyed.
Lowering a weight does not change the energy of the system at all - you release kinetic energy (or some other form of work), but that energy *exactly equals* the loss in potential energy. Drop a mass down an infinite gravitational well, and its kinetic energy will increase at exactly the same rate its potential energy decreases. The amount of total mechanical energy wlll never change by the slightest iota, and thus neither will its mass.
(Score: 0) by Anonymous Coward on Friday October 23 2020, @12:39AM (3 children)
Yes, the net is zero. You actually mentioned the effect in one of your other posts when you speculated that the Universe net energy was zero. Yet there are lumps of mass all over the place. This is the same thing on a much more condensed and exaggerated scale.
(Score: 2) by Immerman on Friday October 23 2020, @01:38AM (2 children)
>This is the same thing on a much more condensed and exaggerated scale.
No, it's really not. Drop a brick into a black hole and that brick will have some innate mechanical energy E_total = E_kinetic + E_potential.
That total may be zero, or it may not be, but you cannot separate those energies from the brick, they're both innate to every particle within it, and and their totals will never change unless you transfer energy from some outside system. Do something clever to pull energy from the black hole, and you could increase the energy of the brick, but only by exactly the a same amount as you decrease the energy of the black hole. The black hole + brick would then be the closed system, and its total energy (and thus mass) would then be what remains constant.
Heck, even if you get into chemical energy, antimatter annihilation, etc, it remains the same. If you were in a perfectly mirrored sphere, an idealized closed system, and had a lump of matter and a lump of antimatter with you, then you could annihilate those lumps to create high energy radiation, use that radiation to boil water, then that steam to turn an engine, then use the engine to wind a giant clockwork battery... the total energy within that sphere would still remain the same throughout, and thus its total mass would never fluctuate.
Conservation of energy is one of the most fundamental laws of physics, and the basis of one of the most basic tools of physical analysis: draw an imaginary bubble around anything, anywhere, no matter how big or small, and the amount of energy inside will only ever change by the amount of energy that passes through the skin.
(Score: 0) by Anonymous Coward on Friday October 23 2020, @08:31AM (1 child)
Different AC. Thanks and mad respect.
I think the original confusion of OP was that there might be some unknowable feature of black hole that will account for dark matter and energy.
Will it be right to say, then, that the original problem is not at all about black holes but what is actually keeping the universe so "hot", so to say? What is making it expand at the rate it is? That is dark energy, right?
So the original problem is that of missing energy. The idea that black holes have that is not in any way a better answer than calling it dark energy, or to say that god made it so.
Is my understanding right?
(Score: 2) by Immerman on Friday October 23 2020, @07:52PM
You're welcome.
Dark energy is getting into a whole different topic, and is really only relevant across the vast distances between galaxies, so I'll leave that alone for now. Except to say that dark energy makes dark matter look positively mundane in comparison, since it seems to be stretching the fabric of space relatively uniformly everywhere in the universe, and more seems to be created to fill the new space it creates so that the density never changes. Seemingly severely breaking conservation of energy.
The original problem of this conversation is that galaxies are spinning much too fast. Given the mass we can see, and the speed at which they're spinning, they should be ripping themselves apart. The measured speed of stars far from the galactic core is 2-3x faster than what we would expect from the mass we can see. And even more strangely, orbital speed actually keeps increasing the further you get from the core, rather than slowing down as we'd expect. There's a lovely graph showing the discrepancy here: https://en.wikipedia.org/wiki/Galaxy_rotation_curve [wikipedia.org]
The implication being that either there must be a LOT more mass that we can't see in the outer reaches of the galaxy, or gravity behaves strangely at very long distances, or perhaps Newtons law of motion (F=ma) isn't accurate at very low accelerations.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @08:23PM
The simple answer is that it doesn't matter for dark matter purposes. Whether or not black holes have a different mass from what they appear to have doesn't change what its apparent mass is based on how it interacts with the rest of universe. To push the analogy, when our calculations say that the universe appears like it is missing 20 lbs bags of concrete in particular spots based on how they interact with the universe, it doesn't matter if it is an actual 20 lbs bag of concrete or an 80 lbs bag with a 60 lbs magnet pushing it up. Either way, the interaction based on apparent weight is the same.
(Score: 3, Touché) by Anonymous Coward on Thursday October 22 2020, @12:05AM (10 children)
is how many $billions can be successfully spent on a "search" for a figment of wild imagination.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @12:50AM (9 children)
Dark matter could be global warming causing covid particles?
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @12:52AM (8 children)
Covids don't come in particles, they are clusters of dark molecules.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @01:08PM (7 children)
the gravity formula is so beautiful (and easy when considering approximation to general relativity, e.g. newton) that we want to keep it.
so the theory is correct but nature is wrong hence "dark X" and "billions of neutrinos falling thru your head per second".
also days are 24 hours long and a year has 365 days and witches don't float ^_^
(Score: 2) by Immerman on Thursday October 22 2020, @02:42PM (6 children)
The real problem is we don't have any strong evidence to support any alternative theory of gravity. GR is extremely well tested, and in every situation where we can independently verify the starting conditions it produces perfect predictions to within the limits of measurement.
It's quite possible it breaks down at galactic scales and larger, and there are dozens of competing theories that could explain galactic rotation curves without resorting to dark matter, as I recall some even manage to explain away dark energy as well. The problem is none of them are as well-developed as GR, and none have made any testable predictions that would give them some validity since they only diverge from GR at galactic scales.
One alternative to DM that I like, and that may be testable, isn't an alternative to gravity at all, but instead to Newtonian mechanics (F=ma) - quantized inertia. It offers an explanation for why inertia exists (the first I've ever heard), and predicts that acceleration can only occur in discretely quantized increments, which would become apparent at extremely low accelerations such as in the galactic arms.
(Score: 2) by PiMuNu on Thursday October 22 2020, @06:49PM (1 child)
> It offers an explanation for why inertia exists
What does this mean?
I can understand asking something like "Why do different particles have different inertial masses" or "Why are most particles' inertial mass non-zero". Another nice question is "why is inertial mass the same as gravitational mass".
I thought Higgs Boson coupling makes a mass term in standard model lagrangian
https://en.wikipedia.org/wiki/Mathematical_formulation_of_the_Standard_Model#The_Higgs_mechanism [wikipedia.org]
which maybe answers partially some of these questions, but perhaps this is not the question you meant to ask.
(Score: 2) by Immerman on Thursday October 22 2020, @08:36PM
A little off-topic, but as I understand it, the Higgs field only gives fundamental particles their mass, while most of the mass of something relatively big and complicated like a single atom comes from the binding energies of the quarks within the nucleons, with a bit more coming from the binding energies between nucleons into an atomic nucleus. I want to say that initial "Higgs mass" of the quarks is only a few percent of the total.
As for why inertia exists - that's one of the Big Questions in physics - right up there with why gravity exists. GR explains how mass bends spacetime to create gravity (aka the shape spacetime will take in the presence of mass), but we have no explanation for *why* spacetime bends in response to mass at all, rather than just staying flat.
Similarly, we know how inertia behaves, F=ma, but not *why* it behaves that way. Why does mass resist acceleration at all? QI proposes an explanation related to the Casimir effect, which causes two slightly separated plates to be pushed together because there's a greater density of virtual particles popping in and out of existence outside them than there is between them, since the only particles that can exist between them are those with wavelengths smaller than the separation between plates.
What QI does (as I understand it) is apply the same concept to the concept of Rindler horizons, a sort of event horizon that forms behind accelerating objects (and whose existence and has apparently been confirmed):
In front of an object ("in front" being the direction in which it's accelerating) we get the full range of virtual particles with wavelengths between zero and the distance to the edge of the visible universe, all pushing it backwards. And so long as the object is moving at constant speed you also get the same number of virtual particles behind it, and the effects of the two cancel out. An object in motion will remain in motion unless acted on by a net external force.
But, if you accelerate the object then you create a Rindler horizon behind it, which gets closer the faster you're accelerating. QI proposes that the horizon will prevent the formation of virtual particles larger than the space between the accelerating object and the horizon, greatly reducing the number of virtual particles pushing it forward. The net effect being that you have a larger "virtual particle pressure" pushing against the direction of acceleration than with it, creating a force that resists the acceleration, limiting it to a finite rate.
Of course, that's what's happening from the perspective of the accelerating object - a stationary observer won't see the Rindler Horizon and will instead see some other combination of effects that has the same net result. Just as an accelerating object will see a different ambient temperature of space than a stationary one, for somewhat related reasons. Relativistic physics is weird and I don't claim to really understand it, but I guess the temperature difference thing at least has has been experimentally confirmed. The QI stuff, not so much.
(Score: 0) by Anonymous Coward on Thursday October 22 2020, @08:52PM (3 children)
QI is not the only explanation of why inertia exists. It also has its own problems, including its primary proponent tending to use it to explain every anomaly he can find. Some of which have been found to have other explanations.
(Score: 2) by Immerman on Thursday October 22 2020, @09:47PM
Care to name a few? I'd be very interested to explore - like I said, QI is the only (plausible) explanation that I've heard, but I have no attachment to it, and am always curious to explore plausible alternatives.
I don't know that I'd count the inventor's... enthusiasm against a theory - theoretical physicists tend to be odd ducks even by physicist standards, and those swimming against the tide tend to be odder still. I think its a case of "give a man a hammer and all problems look like nails", plus perhaps a little persecution complex and desperation for supporting evidence mixed in for flavor for those bucking the tide. In the end though, science cares about the results, not the personalities (though the personalities can dramatically affect the speed of progress)
What caught my eye is that unlike most MOND theories (which I think QI would fall under, at least in the context of dark matter alternatives) there don't seem to be any constants to fiddle with to make things fit properly. Rindler horizons are already well defined, as is the magnitude of the Casimir effect based on the amount of regional restriction applied. If the calculations really do show a decent fit to observed rotation curves without any constant-tweaking then that would seem to be a substantial point in its favor.
(Score: 2) by deimtee on Thursday October 22 2020, @09:58PM (1 child)
As far as using to explain every anomaly he can find, if it is correct, then it would appear in every relevant explanation. It would be far more of an argument against it if it was only invoked occasionally. It may be vanishingly small and unnecessary in some calculations, but it should never be necessary to exclude it.
No problem is insoluble, but at Ksp = 2.943×10−25 Mercury Sulphide comes close.
(Score: 2) by Immerman on Friday October 23 2020, @01:11AM
Like I said, it seems irrelevant to me how wildly overenthusiastic the inventor has become in misapplying their theory. What matters is,
1 Does it make predictions that agree with observed data?
2 Does it mis-predict other observations explained by current theory?
3 Can we make an experiment to test it? Or at least provide corroborating evidence?
Dark matter actually fares badly on all of those, despite decades of attempting to detect different possible candidates. (in fact, 1 and 2 almost don't apply, since dark matter distributions have to be reverse engineered to fit the data, and you could do that for virtually any anomaly you could imagine). I don't know that QI is actually any better, but I'm glad to see more professionals getting interested in exploring possible alternatives - it's very possible we've been looking in the completely wrong direction for over a century, since Lord Kelvin made the first crude measurements of the Milky Way's rotational speed and concluded that "many of our stars, perhaps a great majority of them, may be dark bodies" in 1884 (https://en.wikipedia.org/wiki/Dark_matter#Early_history) 136 years of looking, and while we've discovered neutron stars and black holes, we're still searching in vain for most of that "missing mass".
I don't think we should give up on searching for dark matter, altogether, or the extra dimensions needed for superstrings, but I would like to see them become much less prominent contenders. They've consumed an astronomical number of man hours and every test has come back negative, but not conclusively so. There's still lots more possibilities to explore, but we've confirmed than none of the potential low-hanging fruit exists, and there's a very real possibility that even if both theories are true we might never be possible to confirm them. It's always possible there's a big breakthrough waiting just around the bend, but useful research appears to be at a dead end. Long past time to step back and start taking alternatives more seriously - understanding full well that they probably won't initially explain anything nearly as well as the current theories which have been refined by millions of man-hours.