If anti-matter would be found to be affected differently by gravity, then that would be a big problem for general relativity wouldn't it? If gravity is warped spacetime geometry, then it has to affect the path of all particles in the same way.
It’s important to note the distinction between being able to model antiparticles as the time-reverses versions of their partners, and then actually “moving backwards through time” as it were. It’s not as though a sample of anti-hydrogen experiences a reverse or cause and effect.
It will! Imagine the ball right before it hits the ground: it will have a large downward velocity. Reverse time and the ball acquires an upwards velocity, that slows as it reaches your hand, exactly as if it's accelerating towards the earth.
If you know some calculus, observe that Newtonian gravity is coupled to acceleration but NOT velocity:
d^2 x / dt^2 = a = g
Now run time backwards: let dt be negative. This doesn't change a, because dt is squared and squaring a negative is still positive. The acceleration is independent of the direction of time.
To show this isn't just mathematical hand-waving: consider a magnetic field. This does couple to velocity. Reverse time, and the magnetic field pushes the other way. Electromagnetism is not time symmetric, it's time ANTI-symmetric. Gravity is different from EM in this respect.
I don't understand the difference with magnetism though. Let's say you have a positively charged item and you're standing on top of a large negatively charged surface. You "drop" the positively charged item. How does its velocity over time differ from the gravity example? And how is it different with time reversed? Seems like it would be the same to me... In forward motion, it would accelerate until it collided with the surface. With time reversed, it would start with a fast velocity and slow down over time.
Edit: I googled this. It sounds like the motion of magnetized bodies is time symmetric, but when the charge of the electric field produced by the motion is taken into account it has to be reversed. Is this correct?
In classical electromagnetism, we separate the electric field E and the magnetic field B.
If we isolate E, we get rest: electrostatics. Charged particles exert an attractive or repelling force in proportion to their charge, just like gravity, except charge instead of mass. So E is time-symmetric. This applies to your example.
Now consider just B. A positively charged particle is moving to the left, through a magnetic field that points inwards. By the right-hand rule, the force on the particle is up. Reverse time: now the particle is moving to the right, so you rotate your hand 180 degrees and the force is downwards. This magnetic field produced an upwards force forwards in time and a downwards force backwards in time: it's antisymmetric.
Put mathematically we have:
F = qv x B
where q is the charge, v is the velocity, B is the field. Reverse time and the velocity gets a minus sign, so F reverses.
Positive charges obey the right hand rule, while negative particles obey the left hand rule. Classical EM doesn't distinguish between these, and we might as well reverse the signs and hands.
QM does so distinguish, for reasons way beyond me.
Seems like a very important/foundational answer to know, though. Do you happen to know of anything I can read about why charged particles behave by that rule?
How does that work in relativity where d = sqrt(x^2 + y^2 + z^2 - ct^2). If it is moving backwards in time, it seems the spacetime interval would point the other direction.
It would also have to be moving faster than c.
I'm basically arguing that anti-matter is anti-mass/anti-energy, which is not true but still fun to think about.
Well intervals by definition don't point anywhere, they're scalars!
Relativity says:
E^2 = m^2 - p^2
If we treat antimatter as normal matter moving backwards in time, with negative energy - then energy reverses sign, so any time we connect back to experiments we get positive energy. Ok, cool.
Even in this view nothing moves faster than c. If we permit faster than c, then either E or M has to become imaginary to get a negative sign after squaring. Imaginary energy is even weirder than negative energy and is well above my pay grade; google "John Baez tachyon" for more.
I'm just thinking through the implications of this... General relativity says that mass and energy are equivalent; an electron produces as much gravitational attraction in another particle as an equivalent amount of energy does. If matter and antimatter gravitationally repulse each other, then an electron and positron in close proximity will produce a near-zero amount of acceleration in a nearby particle, since the attraction and repulsion cancel. However, if they annihilate, producing gamma rays, then the gravitational acceleration experienced by that nearby particle will suddenly increase, since the energy of both particles will occupy the region previously occupied by the matter and antimatter.
Is that correct? That sounds wrong. Why should the net gravitational "charge" of the gamma rays not be negative or zero?
What you're thinking of is negative mass, not Antimatter. Antimatter has positive mass-energy, as far as we know, including empirical measurements. We've already operated Penning traps and stored minuscule amounts of antimatter.
Depends on how exactly different. Repulsion is time reversed attraction so IIRC if antimatter is a time reversed normal matter then it should behave as a negative gravitational mass.
Negative gravitational mass is supposed to attract other negative gravitational mass and repulse positive gravitational mass. In your example time inversion makes both Sun and Earth negative mass so they still attract each other.
If earth is falling towards the sun it is due to higher order effects, like friction or gravitational waves. It's not due to gravity itself, which is time symmetric.
If you reversed the trajectory, the earth would still be falling towards the sun, but reversed orbit. i.e. orbiting counterclockwise instead of clockwise from a fixed observation point.
The current view of antimatter (at least in quantum chromodynamics) is that it is matter moving backwards in time. This is the key thing that allows Feynman diagrams to be used to describe fermion interactions. Is it actually travelling backwards in time? Maybe, maybe not. But if we model it as travelling backwards in time we can make all sorts of accurate predictions.
Is this accepted though? I know it's a possible interpretation, but things get super-weird once you allow regular matter to be moving in alternative time-directions because you wind up at the "nothing is real" problem - a single particle oscillating through spacetime gives rise to all matter everywhere by doing the loop in indefinite cycles.
The argument against this is you should end up with equal amounts of matter and anti-matter if that's the case - though I don't think it excludes the possibility we're just in a universe where the antimatter part of the loop was extremely rarefied.
I'm not really sure what you mean by accepted and interpretation here. Feynman diagrams encode the idea of particles traveling backwards in time very strongly -- it's one of their principle features. Feynman's 1949 paper on "The Theory of Positrons"[1] states as much in the abstract (I would recommend reading at least the abstract -- effectively he succinctly contrasts the new theory with the old one and how the model of positrons being backward-traveling electrons allows you to explain many observed effects).
And given that Feynman diagrams (and many other things based on them like Feynman path integrals, QED, and QCD) are the backbone of quantum theory, I think it's more than a safe bet that this view is widely accepted. One of the many predictions using them is the existence (and method of synthesis) of the Higgs boson.
The reason I said "maybe" is because it's important to have a distinction between models and reality (maybe bringing this up in this discussion was a bad idea). Physics is all about constructing models that approximate reality with strong predictive power, it's not really interested in what reality is but rather how it can be modeled so we can predict it. Obviously, the models have to be true on some level in order to be reliable, but many examples (like fields for instance) are not real objects.
So while saying "the particles are traveling backward in time" (theory == reality) is the most accurate statement you can make with modern physics, I would say "at the very least the particles act like particles that are traveling backwards in time" (theory >= model). Even if newer theories are discovered that invalidate the current theories the latter is still just as true of a statement -- otherwise Feynman's models wouldn't work and we know for a fact that they do.
Does that make more sense?
> a single particle oscillating through spacetime gives rise to all matter everywhere by doing the loop in indefinite cycles
This is the idea of the "one electron universe" (which attempted to explain why all electrons appear to be so identical that we've never detected discrepancies)[2], which was arguably one of the inspirations for Feynman's 1949 paper. To be clear, this is a non-standard interpretation of the implications of Feynman's ideas (though this was actually an idea pitched by John Weller on a phone call to Feynman very late at night). Like most interpretations of quantum mechanics, it doesn't make much of a difference to your life -- at the end of the day the maths is the same either way.
There is an open question about what the source of "the arrow of time"[1] is, which is this apparent weirdness where at very small scales the laws of physics are symmetric in time but at larger scales there appears to be something dictating that they are asymmetric in time. It should be clear that at larger scales, most physical laws are still symmetric in time it's just that we generally see that the results are biased towards one direction (hence the "arrow" of time).
Now, this is a more general and complicated thing than entropy. Entropy is a statistical effect (and has very little to do with cooking eggs -- other than its link to thermodynamics). I can give you a short primer on entropy with an example:
You have 2 balls and push one so that it knocks the other one. Record it, then reverse the footage. In principle neither view of the event is more correct than the other (this is slightly untrue due to friction and the ball would appear to accelerate on the tabletop, but imagine it's a sufficiently frictionless surface for the purpose of this discussion). So motion is symmetric in time, right? As with most things in physics, the correct answer is "yes, but..."
But what happens when we add more balls? Imagine you have 100 lined up in a grid and you knock one -- you end up with a completely jumbled mess. Now reverse the footage, and a jumbled mess becomes 100 perfectly lined up balls. Which is the correct direction of the footage? Obviously there is a difference and you can tell what it is without me needing to explain it -- it's almost impossible that knocking a jumbled mess would just sort it! Why is it so improbable -- after all, isn't the motion just as time-symmetric as in the 2-ball example? Yes, but the problem is the statistics. What is the probability that a given jumbled set of balls will be sorted when you knock them? It's astronomically small.
In thermodynamics, these same statistics are the basis for what we consider entropy (imagine the 100 balls are countless numbers of particles). Effectively the idea is that because there are so many particles of matter involved in gas interactions, that the probability distributions are so skewed that you only ever see one macro-level result (that the ideal gas law is obeyed for instance). So while entropy may look like some fundamental force, it's a statistical effect that effectively guarantees that certain effects will happen.
Entropy is the thermodynamic arrow of time (and was the first thing that spawned the idea of an "arrow of time"), but there are other arrows of time. For instance, the universe is clearly expanding and thus there is a cosmological arrow (if you reversed the motion the CMBR would be different). There is a "weak" quantum arrow of time where some reactions violate CP-symmetry and thus by CPT theorem they must violate T-symmetry (the T in CPT being time).
Nothing you said made any sense. I'm not saying this to be rude.
I recommend (if you're interested) that you really study things more thoroughly, not just skim some material, as you plainly did. That way you avoid mixing up concepts like you are doing right now.
Notice how your comment is content-less and makes no arguments or actual corrections.
Not saying this to be rude, just found your comment rude.
As for what the parent said, it's quite clear. If it doesn't hold up, it's not because of lack of clarity:
"Repulsion is time reversed attraction so IIRC if antimatter is a time reversed normal matter then it should behave as a negative gravitational mass".
I.e. => seeing something being repulsed will be the same as seeing something between attracted played in reverse. (e.g. if we film a falling ball --attracted to Earth by gravity-- and play the video in reverse, it will look the like it's repulsed by the Earth and goes upwards).
Hence, the parent argues, if antimatter is "time reversed normal matter" (something often used as a description of antimatter, at least in layman terms), then it should behave like it is mass with inverse gravitational force.
> seeing something being repulsed will be the same as seeing something between attracted played in reverse. (e.g. if we film a falling ball --attracted to Earth by gravity-- and play the video in reverse, it will look the like it's repulsed by the Earth and goes upwards).
Here lies the problem. If you play the video in reverse, the ball won't look like it's repulsed by the Earth. It will go upwards, yes, but only because of an upwards velocity. It will still look like it's trying to fall back. That is, it will still be accelerating downward.
Acceleration doesn't change under time reversal. It is velocity that switches signs:
> It will go upwards, yes, but only because of an upwards velocity.
In this picture, what imparted the upwards velocity to it, given its starting point on the ground?
>> a falling ball [...] in reverse
> it will still be accelerating downward.
It seems strange to ask this of someone with your choice of username, but for the sake of anyone else who is reading along in this thread :
Which way does a freely-falling accelerometer point? [1]
(Ignoring the atmosphere.)
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(But if we don't ignore the atmosphere, in the limit where a smartwatch inside a dropped wall reaches terminal velocity, which way does the accelerometer point? If the smartwatch can move freely within the ball, where does one expect it at terminal velocity, and where does one expect it far from terminal velocity? cf. "vomit comet" [5]).
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[Now make the ball transparent to a broadcast of the accelerometer's reading. Who is "more right" about the interpretation broadcasted value: you standing below and observing it moving ever faster towards terminal velocity, or a skydiver who manages to tuck into a shape that allows her to remain alongside the ball-and-accelerometer for some time at the start of their descent? What do they make of your on-the-ground accelerometer as they are (a) far from terminal velocity, (b) as aerodynamics separates one from the other?]
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I agree that the value of the accelerometer on the ground with you does not change if we run a film of this experiment backwards; it's the only one that should remain effectively constant throughout.
As we take the anti-falling ball from resting on the ground -- can we agree its accelerometer will be at the ground-facing end of the ball, and that it will have the same reading as your always-on-the-ground accelerometer? -- to a drop balloon hovering kilometres overhead, what do you expect the direction of the accelerometer to be? How does the magnitude evolve, approximately? (In the human-time direction, experimenter lifts the ball off the floor of the gondola of the balloon, carries it to the door, extends her arm, and drops the ball. The ball falls and eventually crashes onto the ground right beside you. Let's pretend we absorb bounces and avoid bursts and breaks of the ball resp. accelerometer inside the ball.)
- --
> It is velocity that switches signs
(with the caveat that we are supposing that we are working with a family of systems of coordinates, and coordinate velocity, and a way for all parties to measure that; or that everything is moving slowly with respect to light and aren't aiming for maximal precision, so don't engage Pound-Rebka and similar results if we want to measure spectroscopically rather than kinematically (or astrometrically, per IAU [2]) [3]. More generally, velocity can get really complicated especially when we are dealing with a system in which matter's coupling to gravitation is what's under study.)
Taking a different view, Baez says, "In general relativity, we cannot even talk about relative velocities, except for two particles at the same point of spacetime -- that is, at the same place at the same instant. The reason is that in general relativity, we take very seriously the notion that a vector is a little arrow sitting at a particular point in spacetime. To compare vectors at different points of spacetime, we must carry one over to the other. The process of carrying a vector along a path without turning or stretching it is called `parallel transport'. When spacetime is curved, the result of parallel transport from one point to another depends on the path taken! In fact, this is the very definition of what it means for spacetime to be curved. Thus it is ambiguous to ask whether two particles have the same velocity vector unless they are at the same point of spacetime."[4] and I find it hard to disagree.
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[1] If you have an iPhone or iPad, I highly recommend https://phyphox.org/ and a case like https://griffintechnology.com/survivor and a visit to a grassy or snowy park where you can give your device a good hard throw (or e.g. climb a tall tree or form a human pyramid and drop it). Don't rely solely on gedanken experiments or search-engine results. Go measure! What a pity Einstein didn't have these tools for his jumping-off-a-roof, and that Newton didn't for his apple tree.
[2] Soffel et al. The IAU 2000 resolutions for astrometry, celestial mechanics and metrology in the relativistic framework: explanatory supplement. Astron. J. 126(2003), 2687–2706 ( https://arxiv.org/abs/astro-ph/0303376 ).
[3] Lindegren, Dravins. The fundamental definition of ‘radial velocity’. Astron. Astrophys. 401(2003), 1185–1202 ( https://arxiv.org/abs/astro-ph/0302522 ).
Science is quite opposite to "believing", but if you "believe" in a theory, then, if you are looking for a word to describe me, this word is "heretic".
However, I see no significant differences in position about QM between me and Mario Bunge, famous scientist. :-/
Bunge seems to be described primarily as a philosopher, but I also see that he recently wrote a notable paper suggesting that the detection of gravitational waves implies the realism of spacetime.
Yes, I'm standing at the same position. But consequences of that are much deeper. If spacetime(this word hurts me) is material, as alternative to empty space AKA void, then we can study it, and make theories about it constituents. We can measure it velocity, we can measure it fiction, we can try to cool it down, we can use it as (very light but abundant) propellant, and so on.
I think, it will be put in it own category, when it properties will be discovered, but it still will be on material side, not a pure energy.
Everything is fiction at hypotheses generation phase. It will be science only when it will be confirmed by an experiment and reproduced by some one else and withstand critics. String theory requires extra-dimensions, which are never seen, while my theories are doesn't, so they are less fictional.
Oh geez. I like your intuition, but it seems it has led you astray. Here, have some reading material to put you on a saner track that I strongly suspect will jive more with your intuition:
Fascinating. I believe that what you are saying makes sense to you, but you need to understand that it sounds something like: "raccoons aren't mammals because purple is wet" to the people you are saying it to.
I can just say that «correspondence rules must be used to translate from math to real physical world» and be done with that, but it's very different kind of game we are playing here. Some people are smart enough to recognize my moves early. It's game about funding, tenures, fame, elitism, influence, power, etc.
As we know, OpenGL is good at predictions. With OpenGL we can predict physical look of an imaginary object with high precision. It's Ok to say that by applying of non-linear transformation to vertex array we can create visual effect of strong gravitational field, as in "Interstellar". It's not Ok to say that this non-linear transformation of vertex array is nature of gravity.
We can use math freely for predictions and to describe laws of nature. But we cannot use math to explain nature.
Whether parent is right about his idea of physics (which I don't know and haven't seen written here), what he says in the above comment boils down to:
"Don't confuse the map with the territory".
His reasoning seems to be:
Math is used as a tool in physics to model reality.
But the mere use of math doesn't make such a model real. It could be still way off.
And his example is:
Similar to how we use math to model physical reality, we also use OpenGL (or 3D graphic APIs in general) to model real world objects (e.g. in movies).
Well, just like OpenGL doesn't correspond to some deeper reality (it's just a tool to make models, which could be totally non realistic), same is the case with math. It's just a tool we use to build physical models, it doesn't automatically lend legitimacy to those models (i.e. it's not like "this physics theory uses math so it must be correct representation of reality').
This is all true but it's not actionable. By that I mean, it's philosophically correct but not practically applicable.
Yes, mathematical theories are merely a model of actual reality. But a model that produces accurate predictions is useful--even if we know it is not a complete model.
Even if we know it's not always accurate, we can model the inaccuracies of the model and constrain how we apply it. NASA knows Newtonian physics is less complete than general relativity, but they still use Newtonian to plot routes through the solar system because it's good enough.
So, sure, mathematical physics is not reality. But unless someone has a better tool than mathematical physics for making predictions, merely pointing out that fact is a pointless. Scientists already know it... that's why they do science!
Telling a scientist "your theory is not complete yet" is like telling a writer "you haven't written the perfect book yet." Yeah--they know.
EDIT to clarify that, while I'm replying to coldtea, my comments are really directed at what v_lisivka is saying in this thread.
v_lisivka, you're not wrong, but you're also not adding anything of substance to the conversation. "Physics is not a complete description of reality" is a critique can be dropped into any discussion of physics, which means it does not add any value to a discussion of a specific topic within physics.
It's like saying "you can't prove the sun will come up tomorrow" when someone is trying to plan a lunch date.
>This is all true but it's not actionable. By that I mean, it's philosophically correct but not practically applicable. Yes, mathematical theories are merely a model of actual reality. But a model that produces accurate predictions is useful--even if we know it is not a complete model.
That's true, but that's not all the above says though.
It also says something else that _is_ actionable: don't just trust (or defend) a physics theory because it says it uses math or because it got its math right.
It could still be not just non corresponding with "real reality", but even get its predictions wrong.
What people trust in or defend wrt/ physics theories isn't really relevant to the science, all it does is setup some social direction -- Which one needs regardless of whether they have a correct theory or not.
You've got to fund somebody. So you fund the people with the math that looks good. Objecting to that is basically asking for unrestrained corruption. Crackpots certainly can't be relied upon to identify themselves.
Forgive me if this sounds presumptuous, but is this experiment literally trying to answer "does antimatter attract normal matter"? To me, this seems like a pretty simple thing to test–why hasn't this been done before?
The strength of the gravity between a proton and an (anti-)proton is 30+ orders of magnitude weaker than electromagnetism. The only reason we are able to notice gravity at all is because the electromagnetic forces between macroscopic amounts of matter (~10^23 protons) cancel out essentially perfectly, leaving only the gravitational force remaining. But the amounts of antimatter we can create and collect is extremely microscopic, so we can't use this canceling trick. Furthermore, we can't keep antimatter from annihilating for long enough to take long detailed measurements.
Antimatter is generated at extremely high (relativistic) speeds and generally has to be slowed down ("cooled") in order to make careful measurements or to even collect multiple particles together. And that can't be done unless you can steer the particle with electromagnetism.
If you just generated individual relativistic anti-neutrons and tried to watch them follow ballistic trajectories in gravity, I suspect they'd just look like perfectly straight lines up to the limits of your detector resolution. Not sure though.
(The only other quasi-stable neutral particles are neutrinos, and those are essentially non-interacting with any detector. They leave relativistically and you'll never see them again.)
Neutrons can be contained in a magnetic bottle, even if they don't last long in isolation. Presumably the same is true for antineutrons, although I don't know how hard it would be to slow them with magnetic fields...
Yea, thanks for mentioning. I believe those bottles only work when the neutrons are already at very slow speeds. They exploit the strong force and the residual electromagnetic "handle" neutrons have by virtue of being built from charged components (quarks), which leave them with a magnetic dipole moment.
what I get from the article is that all 3 experiments are doing something new with antimatter in some way. So I imagine the extend to which we can actually make, handle and measure antimatter to be a very determining factor in what sort of experiments can be done
Place your container in freefall and then watch the antimatter collide with the walls of your (shaped) container due to the attraction between the container and the antimatter?
In that case you'll only have to figure out how to cool the antineutrons down enough to ensure that they aren't colliding with the walls simply due to random thermal motion (remember, neutrons don't stick together on their own, so there's no vibrating bonds to dump potential energy into, all that thermal energy in 1.5kT will basically get dumped into kinetic energy, and they don't have much mass; at room tempature they're whizzing around at about 2 km/s). You'll also run into the issue that regular free neutrons (and also anti-neutrons) are stable for only 15 minutes, after which point they'll decay. Note you'll also need to cool them off in that 15 minutes too (though you might be able to be generate them in a way that they start off cool).
So a fun problem that comes up is how long will it take for the neutrons to collide assuming they're only being accelerated by the mass of the container.
Yes. And it's a difficult question to ask because the effects of gravity on subatomic particles is incredibly hard to measure. Thats why they need to make anti-hydrogen to remove the effects of other forces on the particles because it's electrically neutral. If it touches matter of any kind it will instantly annihilate so you need near perfect vacuums, without electric/magnetic fields.
Lots of stuff you'd think is "pretty simple" is still an area of active experimental research. For example, ongoing experiments to test whether inertial mass is the same as gravitational mass.
The title can be misleading if it is not read literally (or your brain tries to fill in extra information). This is testing the effects of gravity on antimatter, NOT antigravity testing.
So antimatter warps space in opposite way that matter does? Then you’d probably then need a negative-Earth-mass amount to counteract the depth of the earth-mass caused gravity-well we’re in.
The antimatter mass equal to our planet is a lot of antimatter. Rockets, even antimatter powered ones, seem a lot better way out of Earth’s well.
Do you need mass equal to earth, or mass slightly greater than whatever you're launching? (Alternatively, does antimatter experience the opposite force of the same mass of regular matter, or is it something else?)
If antimatter has negative mass in the context of the gravitational equation (F = Gm_1m_2/r^2) then you just need more antimatter than matter (by mass). Of course, that also means general relativity is incomplete.
That's not to say launching/lifting something on an antimatter platform would be practical anyway. There'd be issues around how you keep the platform and payload together, let alone the difficulty of constructing an antimatter platform in the first place...
but wouldn’t the 1.01kg of antimatter have an “inverted gravity well” that propogates in all directions, sitting at the bottom of Earth’s much much larger gravity well?
I mean I’m looking at gravity in that it isn’t like electromagnetism; propagating waves of energy through space. Gravity is the bending of space itself; mass’s impression.
But maybe I’m using the wrong/incomplete model of gravity here
That sounded to me as experiments to influence gravity using antimatter. I figured it was either a long shot or clickbait so went to the comments first, but as someone with little clue of these things (the most I know of physics is the half of A Brief History of Time by Stephen Hawking that I understand, and probably half of that half I already forgot again), it wasn't too far fetched.
A black hole is a creature of pure self-sustaining curvature — the field itself has enough energy in it to maintain the warpage (as the singularity presumably at the core is beyond the event horizon and gravity, like everything else, cannot escape it’s own grip and emanate from the singularity to the event horizon where we observe the effects).
So tossing in antimatter would not do much. It would never cross the horizon in an external observer’s reference frame and thus would never interact with anything and thus would produce no effects.
Besides we know that when matter and antimatter react, they emit energy that has positive sign, not zero... twice the value of any particle’s mass. That in turn implies that matter and antimatter have the same sign of energy despite opposite charge.
Furthermore by coupling attractive matter and repulsive antimatter one could create a perpetually-accelerating device as the repulsive antimatter would try to escape the matter and the matter would chase after it. This obviously is cause for concern (but in general General Relativity does not conserve energy, so it’s not incompatible with the theory per se — just very dubious).
I’m expecting the antimatter to fall downwards just as matter would. But the whole point of science is to check that what you expect conforms to what the universe actually does. So this is definitely not a waste of resources: much the contrary, it’s a vitally important measurement to make.
I don't this is exactly accurate. Hawking radiation for example, causes black holes to evaporate over time. While the radiation that is detected outside the black hole has positive mass/energy the in-falling anti-particles have negative mass/energy which results in the net reduction of the black hole's mass/size. Does it not then make sense that in-falling anti-matter would have an evaporating effect?
The “one of the virtual particles of the pair created in the vicinity of the black hole’s horizon falling in leaving the other one to escape to infinity as radiation whose mass-energy must be subtracted from that of the black hole” view of Hawking radiation is a pedagogical construct thought up by Hawking himself after calculating the effect by other means for the sake of public promulgation. In reality it has to do with the restriction of the resonant modes of quantum fields imposed by having a border (horizon). Case in point: if the full truth were that of infalling versus escaping virtual particles there’d be a definite trajectory associated with the escaping particle that would convey information about where, approximately, the virtual particle/antiparticle pair popped into existence, violating Heisenberg uncertainty. In reality, Hawking radiation has wavelengths comparable to the diameter of the black hole that make it impossible even in theory to resolve where the supposed particle/antiparticle pair “popped” into existence, preserving the uncertainty principle. This is also why radiation becomes more energetic as the hole shrinks in size: that’s because the associated diameter shrinks and allows wavelengths of emitted radiation to contract, packing more energy into those waves. If it really were particle/antiparticle being shorn apart by the hole’s gravitational attraction you’d expect more radiation to be emitted by a big hole (vacuum activity per volume area being constant, and thus a bigger hole would border more unit volumes and allow for greater interaction with the quantum vacuum that would slow down as it shrank).
Hang on, Heisenberg's uncertainty principle doesn't need to be preserved with virtual particle/anti-particle pairs - that's the point of Hawking radiation - the particles are no longer virtual, and so much must acquire a real value of energy from somewhere (and do so from the mass energy of the black-hole).
You're very much trying to draw a line here that QM doesn't support - everything is a particle and a wave at the same time, and the interpretation that one pair of a particle in-falls is at least as valid as the interpretation that it's to do with the exclusion of wavelengths.
EDIT: For example, the proposed argument with bigger black holes falls down by a similar interpretation to the wavelengths - for virtual particle pairs with sufficient initial velocity to escape the gravity of the black hole, the initial location of them by necessity becomes very indeterminate, or their mass very light - in both cases making it progressively less likely with black hole size that one part of the pair appears initially inside the black hole event horizon, or makes the resulting energy of the radiation less and less.
No, it was in his 1975 work [1], which considers a non-interacting quantum field in a Schwarzschild black hole spacetime [2]. The negative energy infallers keep the spacetime static, which is handy for preserving a timelike Killing vector field that is orthogonal to the spacelike hypersurfaces at each Schwarzschild time coordinate. That picture made it straightforward to show the mechanism for evaporation; perturbing the picture does not make Hawking radiation vanish, but does make it much harder to calculate.
> sake of public promulgation
It [1] was a hard academic paper aimed at experts. That should be abundantly clear not far down its first page and certainly by its second.
> restriction of the resonant modes of quantum fields imposed by having a border
It has to do with vacuum states.
> the [bh] shrinks and allows wavelengths of emitted radiation to contract
I think you run into controversy (and indeed a bit of inconsistency in your "true picture" argument) with "emitted". There is a secondary issue surrounding gravitational time dilation, depending on where you think Hawking quanta are found.
> Heisenberg uncertainty
How does that enter into the (non-string) picture except at the latest times when the radius of curvature is on the order of Planck length? I'm genuinely curious to see how you'd use Heisenberg uncertainty except in an argument involving remnants (in which a generalization of HUP could dynamically prevent complete evaporation, with the dynamics becoming important at some small minimum BH mass).
Anyway, I strongly recommend Wald [in [2]] to you.
[2] It's hard to summarize this better than Wald in the Hawking Radiation section of https://dx.doi.org/10.12942%2Flrr-2001-6 notably starting with 'The original derivations [54, 98] made use of notions of "particles propagating into the black hole", ...' and I don't want to plagiarize him.
Hawking radiation is a pure hypothesis based on one particular assumption how thermodynamics and quantum mechanics can be applied to gravity. We have no evidence that it exists. If one follows a different school of thought, then the temperature of the event horizon of the black hole is zero and there is no radiation.
> Does it not then make sense that in-falling anti-matter would have an evaporating effect
Yes, kinda. More precisely, it would depend on how anti-gravitation works exactly, i.e., how anti-matter couples to gravity differently from matter. So even more precisely, "we don't know but can model various remotely plausible ideas with current theory" [a concrete attempt to model below at [1]].
One approach to model anti-matter anti-gravitation is to have a second metric which anti-matter feels but matter doesn't. Bimetric theories have been studied for several decades, and the problem is that one has to hide the effects of the second metric or we get a very different night sky than we observe. So while bimetric theories aren't ruled out, the effect today (as opposed to the very early universe) is extremely small. A tiny present-day effect would be interesting in that it would suggest a possible mechanism for the overwhelming dominance of matter in our part of the universe: a decaying secondary metric could strongly segregate matter from antimatter in the very early universe (preferentially collapsing matter together with other matter, and antimatter together with other antimatter), while not interfering with today's observations of high-redshift galaxies or laboratory experiments to date.
In a bimetric setup, a black hole would source something akin to Schwarzschild for the dominant metric, and something akin to anti-Schwarzschild (for matter) as a secondary metric. We could contrive a secondary metric that causes antimatter produced in the hot accretion disc to receive a dynamical boost that transfers extra energy-momentum into the antimatter and flings it off towards infinity. In that case, anti-matter that anti-gravitates would have an evaporative effect on the black hole.
There is of course no observational evidence favouring a strong secondary metric anywhere in the known universe, and it would be an awesome surprise if forthcoming black hole telescopy found any. Meanwhile people are working on ruling out a weak secondary metric in laboratory settings.
There are other approaches to theoretical modelling of anti-gravitating anti-matter, but they generally need a dynamical suppression of the effect at modern times and large mass scales, for the same reasons. Such approaches typically look really highly contrived on their faces, and of course suffer from lack of evidence, since we don't have a good view (with current technology) of the universe before the cosmic microwave background formed.
We can be pretty sure that anti-matter doesn't anti-gravitate at all from nuclear physics (electron anti-neutrinos in beta decay, and the antiquark halves of mesons) in astrophysical observations (you get a lot of both in supernovae (SN), and anti-gravitation of anti-quarks or anti-neutrinos would lead to a noticeably differently massed SN remnant). Of course we would like to be very sure with many more lines of evidence. :D
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[1] Modelling anti-matter anti-gravitation is not a popular academic area of enquiry, mostly because there's no evidence for it, and there's already lots of model-building in high-energy physics (and string-theoretical gravitation) where one has to "hide" side-effects that aren't seen around here-and-now somewhere in the universe (distant past or future, well outside the Hubble volume, or in extra dimensions) that solve a broader range of problems than introducing anti-matter anti-gravitation.
However, on that front, see Hossenfelder's blog entry http://backreaction.blogspot.com/2017/04/why-doesnt-anti-mat... which refers to her paper https://arxiv.org/abs/gr-qc/0508013 which does not deal with anti-matter as you conceive it in your question, because she proposes duplicating the ENTIRE Standard Model (including its anti-neutrinos, positrons, anti-quarks, etc.) that feels gravity normally with an exactly similar set of quantum fields that is feels gravity as a repulsive force. She then introduces an anti-gravitation which this second set of standard-model-like-fields feels as attractive, while the Standard Model is adapted so that its constituents feels it as repulsive. She likes toying with mathematics, and this is a classic example of building a model and chasing down its consequences just for fun -- she certainly does not propose that this is a plausible model of nature, since it breaks the equivalence principle in a way that conflicts with tests of it.
In her model for technical reasons the anti-gravitating extra set of particles have to be suppressed from Hawking radiation, and therefore are not evaporative of black holes. (They would be repelled from black holes if they were brought from outside a BH towards a BH, though, just as they would be repelled from the Earth if brought near the Earth). She does not elucidate a mechanism for this suppression.
Finally, Hossenfelder's model is single-metric, rather than the sketch of a bimetric approach that I described above. However, it's also closer to the exact wording -- if not the spirit -- of your comment.
> So tossing in antimatter would not do much. It would never cross the horizon in an external observer’s reference frame and thus would never interact with anything and thus would produce no effects.
It would never be directly seen crossing the horizon by the accelerated observers you are thinking about (it just gets redder and dimmer), but it sure crosses the horizon, and this can be seen by those observers indirectly: the mass term of the BH metric describing the exterior spacetime changes, with observables like the Einstein lensing subtending a greater angle and a change in the apparent location of the ISCO.
Consider the act of throwing a smaller black hole of mass M_small into a larger one of mass M_big: General Relativity tells us that within about a light-crossing time of the sum of the diameters of the two BHs there will be a larger BH of M_merged \lt (M_big + M_small) with the missing mass dumped into a large dynamical perturbation of your choice of background metric. (Linearizing this picture is literally how gravitational waves are studied; with the present detections of gravitational waves, we can be pretty confident that neutron stars do in fact cross into the horizons of black holes rather than gathering up as some structure microscopically close to the horizon, and even more clearly not as a long-lived bump near the horizon of a BH where J \gt 0).
There are of course other observers who could outright see the infallers cross the point of no return.
(Power-orbit yourself close to the horizon of an ultramassive black hole where the tidal forces at the horizon are even less than those we experience here on Earth. Poke your little finger through the horizon. By virtue of your orbit it will slice right off, and using a highly sensitive gravimeter you would detect it behind you as you continue on your orbit. If you don't believe in gravimeters that sensitive, feel free to substitute a prominent mountain on a rocky planet for your finger and you, and you could then use existing technology. (Also, you could use a highly elliptical orbit instead of a highly powered circular one) In either case, a distant outside accelerated observer has to contend with the redshift, and so won't directly see what happened, and might not be patient enough for you to communicate your results. Additionally, the "bump" will only survive for a fraction of your orbit around the BH, since the bump is hair that will be balded within about a light-crossing time. The ringdown will propagate as gravitational radiation which will get to distant outside accelerated observer sooner than you, or a message from you, will.)
In that situation wouldn't it be impossible to shove antimatter into a black hole in the first place because the gravity-antigravity force would repel instead of attract?
Long answer: When equal amounts of matter and antimatter collide, they are annihilated. They haven't disappeared or canceled out, they’re converted into pure energy. Both mass and energy are just different aspects of the same thing: you can turn mass into energy, and you can turn energy into mass. Black holes turn everything, both matter and energy, into more black hole.
Be careful, this is not correct and is a common misconception. You cannot turn mass into energy or energy into mass. This would violate not one, but two fundamental laws of physics - conservation of energy and conservation of mass.
A more appropriate way to think about this is simply that all energy has mass, and all mass has energy, and these amounts are related through the famous E=mc2.
Black holes destroy information don't they - they would be neither matter nor antimatter. Nor energy, for that matter. They're just point mass. Which implies that both matter and antimatter would be attracted to the black hole equally, but that kind of breaks the idea that antimatter reverse-curves spacetime, doesn't it?
So anti-black-holes would have to exist in a "antimatter has antigravity" universe, wouldn't it?
Which contradicts the idea of black holes destroying all information.
This is called the black hole information paradox. Today most physicists believe that hawking radiation preserves quantum information. Hawking himself made a bet that it doesn’t, but by 2004 he had become convinced and conceded the bet. But as far as I know this is still an open question - we’ve never detected hawking radiation experimentally.
That anti-gravity matter would need to be traveling faster than light to reach the black hole. It's the reverse problem of getting normal matter out of one.
But, it would mean that if you created a nuclear reactor inside a black hole, you would be able to communicate with the external world. That is problematic enough by itself.
Are we sure they have to pay for it? Edit: It appears that they do, though it was at least in the past based on a reallocation of savings on operational expenses. It seems like they might be filing it under "outreach" which makes sense. I'll authorize it. ;-)
The motivation for CERN to acquire its own generic top level domain was to be able to better support its Web communication strategy. In addition to the traditional CERN domain .cern.ch, that is used for all IT infrastructure and also for internal Web sites, other benefits of owning its own TLD are in the area of conveying:
"As such, a domain that limits CERN to one country doesn’t acknowledge the international, and increasingly global, nature of the organization, nor that its science and values transcend geographical and political boundaries."
CERN has all sorts of stuff going on, I don't know the details but its not just like a normal lab in a single country, there's special tax rules and diplomatic treatment for people who work there etc.
The UN also has funding issues and the cost of changing domains (even to an .int, which is probably more appropriate than an .org, much less acquiring a TLD as well) is probably not going to fly.
The most amazing thing I've ever seen is probably the original manuscript proposed hypertext with the hand scribbled comment at the top "Vague but interesting!"
Perhaps you can consider it as a marketing expense. Think about all of the communications that CERN deals with external parties. It could be that they justified it as a recruiting tool - “You get your very own name.cern webpage” to attract candidates.
Or, they just thought it’s cool :-). Companies spend all kinds of money on things without ROI: fancy decors and furniture, landscaping and fancy buildings.
So these experiments are about to be ready to run just as their feeding accelerators will be shut down for two years? That timing certainly sucks for all the PhD students involved.
To be perfectly clear, is this testing how antimatter and matter interact gravitationally, or is it testing how antimatter and antimatter interact gravitationally?
It's testing how antimatter and matter interact gravitationally.
It isn't possible to test how antimatter and antimatter interact gravitationally, because only single atoms of antimatter can be produced, and single atoms don't exert enough gravitational pull on each other to be measurable.
How do you think UFO's move through earth's atmosphere? They repel matter via real-time manifold dynamics allowing them to move at supersonic speed. I think we already know this.
Some stats and figures in case the original comment gets permanently buried. (-8, +4) leaving me with -4 points. Meaning there are at least 4 intuitive people with open minds and at least 8 hard nosed skeptics. My dad, who mastered in Physics at the University of Odessa being one of them. I've pestered him for years about the sighting and he hates talking about it.
The original comment:
"How do you think UFO's move through earth's atmosphere? They repel matter via real-time manifold dynamics allowing them to move at supersonic speed. I think we already know this."
Hm. I'm a skeptic and I typically hit all the standard checkmarks on dismissing nutjobs. It's almost a mental stamp worn down to the nubs. But this right here reminded me of the time I scratched my head.
Cue the weird release of the NYT pieces on Navy recordings of UFOs released over the past year. Did you happen to see that one? If not, look it up. There were basically two FLIR recordings of something pretty spooky and, wow, it was something else. The videos were followed up by a leaked NIMITZ carrier group report of the incident cataloging and verifying pretty much everything the pilots said in the interview. The pilots were made fun of by their peers. Means of propulsion in the video was nothing like I'd ever seen anywhere before. The Navy basically said "we don't know what this is" and "it demonstrated propulsion capabilities beyond any known means." One of the videos is downright spooky in places.
First thing skeptical me did was check the provenance of the videos themselves. They were directly provided to NYT by a weird organization headed by an ex band member from Blink 182. Nutjobs, check.
Second thing I checked was who the writers of the article were. One was a general assignment reporter (meh, they have to put someone on it and they were all out of stolen tomato plant stories that day), another was a has-been burnout whose name got used to elevate the story, and last author was a person who wrote books on ghosts and spirituality or some such. Cranks, check.
Then WaPo and other orgs released a bunch of regurgitated hashes of the same story. So I sifted through to see if there were any more details. Nope, they were all borrowed from NYT. Nothing original, lazy re-reporting, check.
Then just to be sure the guy was just lazy I reached out to a WaPo reporter. Nothing.
Then two weeks went by.
He got back to me and told me that they got caught with their pants down. They had been working on the story long before NYT published it - in cooperation with the bizarre group with the ex-Blink 182 guy, and WaPo were under the false impression that they had an exclusive story with them. So when NYT's came out, they felt betrayed and buried what work they had and scrambled to get their own GA reporter to finish the deal. Not lazy. They just cut their losses best they could.
Here's the kicker. The guy verified the provenance of the flight cameras. They WERE provided by the Pentagon under a FOIA act request. Despite the fact that NYT's videos were provided by the Blink 182 people, WaPo had an independent copy of it obtained from the military.
The part that made me scratch my head was that it wasn't just an empty boast. I was given a tip on making a very specific FOIA request to the Pentagon. Goes something like "query seeking cockpit videos cleared for release to Luis Elizondo in the Fall of 2017 (Sep-Oct)."
So what of it? Well, our high energy physics people are making discoveries, and while I don't know what to make any of this, for the first time in awhile I'm feeling like we're making some forward progress in science that might make its way to engineering, or our understanding of its limits. Just recently scientists identified 2-3 candidate anomalies as potential new particles (sigh, some reporters kept calling it a ghost particle). Maybe something will come of it, maybe not. But we're trying, and once these are eliminated there will be more observations, more research, more science. We still have a very poor understanding of gravity and how it relates to things we feel we know.
But for once in this horrible climate we find ourselves in, both political and social, I'm feeling optimistic that we're even looking.
For myself. I'm just a software engineer with an armchair understanding of physics. I knew my comment would be controversial, hence the down-votes. But I witnessed this phenomenon with my own eye's looking at constellations at night with my dad and my sister in 1996 or 97 in Orange County, CA. Judging distance, it must have been near the El Toro Marine Base which closed shortly after. I have no idea what I saw, but it was fast, I mean hyper fast. Maybe 5x to 10x faster then a humming bird. It did a figure 8 in the sky, stopped in mid-air, moved left to right and dissipated. The phenomenon lasted maybe 3 minutes and I had to make a decision to either go for the camcorder or stare at the thing.
I'm putting this together now because the most defining characteristic was that this was a white star shaped spec that was very clearly mechanical in nature.
What does this mean? Did it have metal plates and gears on it? Ailerons, flaps, and windows? You cannot identify something as mechanical on the basis of its motion.
>It did a figure 8 in the sky, stopped in mid-air,
You say 'stopped', but things moving far in the distance are insensitive to depth perception. Probably it was moving toward or away from you. Any idea how you would know the difference?
>I have no idea what I saw
Yet here you are saying it must be an antigravity device, and not some ball lightning. A rational conclusion, if ever there was one.
I was hoping someone would comment but it looks like you already dismissed it by down voting so that tells me you aren't really curious about my answer. As such this comment is meant for everyone else who is. But I'll directly answer all your questions.
When I say it was clearly mechanical. I don't mean that it looked mechanical. I said it was clearly mechanical in nature by the way it moved. My brain instantly went there. Maybe it's instinctual.
The object resembled a star or meteor. It was so small that if it was moving forward or backward, I wouldn't know it.
And finally. I think you all have to deduce. Am I trying to justify my original comment on a post that had nothing to do with UFO's with a wacky comment that I saw one in the 90's or did I see this object, saw this post and put it together that way.
Edit: sure, it could have been a supersonic spec of ball lightning. I'll give you that one. Except for the fact, my dad, a witness who actually saw ball lightning in the former Soviet Union said it looked nothing like that. He's sitting next to me and I just asked him about it.
Why would one expect ball lightning to look the same each time?
I shouldn't be asking these questions, you should be. But you'd rather say "oh, we all know these things about fundamental physics because they are necessary to power the alien spaceships I imagine must exist."
That's not a healthy or useful attitude. If it were, you'd have something to show for it.
I'm not sure what you're getting at, but from my understanding ball lightning floats. What I saw wasn't floating. It was moving with force and propulsion. Plus it was a very clear day with no weather disturbance of any kind.
And what I have to show for it is a personal account from myself at 15 and two other members of my family. In retrospect, I went half-way to my parents room to grab the camera but ran back fearing I would miss it entirely. I'm glad, because I'm sure I would have missed it had I looked for the camera. And this phenomenon seems ubiquitous enough that I'm sure there is plenty of footage depicting the exact same thing at least in the private archive. I'm actually pretty disappointed because the footage in the public sphere is much more mild then what I saw. This object wasn't stationary, it was a white ball that moved like a zigzagging rocket; though it didn't look at all like it was out of control. It seemed to move very purposefully.
The standard of "something to show for it" is reproduction, not personal experiences. Society simply doesn't give a shit about anyone's personal experiences unless they can be reproduced and shared. Otherwise, you may as well have dreamed it.
Who's society? Your society? Judging by your activity here, you seem to negiate pretty much everything. Sorry you didn't witness a UFO like I did. It was a pretty cool experience. If I produced a video, you would call it fake. If it was proved real you would call it some new form of ball lightning. If it was proved to be real footage of a UFO, you would cast doubt on that too and tell me not to believe my lying eyes.
BTW, I'd happily take a lie detector test if I was ever presented with one. And don't forget, I'm not the only witness.
Oh and there is that footage from trained fighter pilots. Which gives me all the validation I'll ever need to my own experience prior. I'm happily validated.
Around 27 seconds it starts rotating about one of its axes. Does not follow a fixed wing pattern, and it doesn't show any propulsion emissions on FLIR.
Hm. So again, my whole rant has to do with the fact that the videos (3-4 in total?) have been independently verified to have come from the Pentagon. That part has not, to my knowledge, been debunked as independent sources have FOIA'd copies of it. Heck, you could file a request as a private citizen and obtain the same, and I encourage you to.
So what does this really mean? If you draw it down to either the video being fake or real, I can only see four possibilities and reasons.
1. Fake: this is a product of a Pentagon psyop intended to leak out and cast doubt on our enemies's intelligence, implying that we have access to top secret propulsion technologies beyond their known capabilities.
2. Fake, but conducted by persons unknown and planted inside the Pentagon. It would have taken quite an effort to fabricate because it involved two-three radar tracking stations, an entire naval carrier group, senior pilots, military intelligence, record keeping personnel. Too many of these have issued reports corroborating the observations. Way too many disconnected people to manage for a conspiracy.
3. Real. One of our enemies has access to secret propulsion technologies beyond our capabilities to counter. Enemies, because our own military intelligence was unaware of anything like this and a threat, because it clearly had superior flight characteristics as described by the witnesses.
4. Real. Question is about its origin, however. Terrestrial: are these merely shy biologicals living under the sea we've never cataloged? Extra-terrestrial: automated probes from another place, another time? Other life in the universe?
Only one of these possibilities is bland to a point of ignoring it, that being #1. Rest of the possibilities have profound implications about ourselves, and none so much as #4. It means we're not alone in the universe. So while I agree that a broken clock can tell the right time twice a day, I don't bash what I used to call UFO nutjobs as much anymore.
I don't see why there can't be a fifth possibility.
Real: technology our own military (USA) has had access to for years, and what we see in the video is a test to see how our own pilots would react.
I'm personally leaning in this direction.
But just wanted to say. Reading through the document. The idea that these things cloak themselves when observed is something that I haven't heard and more mind blowing then anything. And the notion that these are technologically advanced beings from our oceans is under scrutinized.
>>At this point, the neutral antiatoms will be released from the trap and allowed to fall from a height of 20 centimetres, during which the researchers will monitor their behaviour.
Assuming it falls, and doesn't tear open the time-space continuum.
