This is my semi-educated guess as to what's going on here. Beware that semi-educated guesses are sometimes worse than uneducated ones, since they are more plausible and not necessarily more correct.
The Alcubierre warp drive requires both positive and negative curvatures. Positive curvatures are "easy" to make, since mass and energy bend space positively. Negative curvatures are typically said to require negative energy to produce, but the full story is thankfully more complex.
The universe, despite being filled with mass and energy, is roughly flat. That means that the natural bending of spacetime, without any stuff inside it, has to be negative - otherwise all the mass would make it extra positive. If you believe the consequence of vacuum energy in QED, that the fields filling the universe are VERY heavy, even when no particles are around, then you must believe the natural curvature to be very negative indeed.
So, it stands to reason, if you want to bend the universe backwards, take the weights off of it - really off of it, in this case using metal plates to forbid certain vacuum fluctuations, and let it unbend itself.
> Beware that semi-educated guesses are sometimes worse than uneducated
> ones, since they are more plausible and not necessarily more correct.
This is one of the most insightful comments I've read on the internet ever.
This is why we shouldn't take medical advice from people who have read a few Wikipedia articles. This is why years of experience in e.g. software are necessary to even begin to understand how deeply hidden security issues can be. This is why self-driving cars still elude us, but will be so much safer than human drivers when they finally do arrive.
I was thinking the opposite point: sometimes the experienced doctor or researcher made a mistake, and the guy who posted something on Reddit is correct. Usually not, but sometimes.
Generally speaking, you should trust someone whose professional or experienced more than some random stranger. Especially if it's not one person but a large group of experienced professionals (most of the controversial "anti-science" issues today).
But it's actually important to "do your own research", and not just listen to authority. Provided you actually know how, i.e. you can find accurate sources and distinguish fact from fiction. Because even the most qualified, unbiased, genius authority are occasionally wrong. The big issue today is that a lot of people don't know how to research and distinguish lies, but (although it's probably impossible for most) finding a way to teach someone how to find the truth, will always be more effective having some authority tell them the truth.
Key example: doctors often miss symptoms and diagnoses that a patient can discover on their own. It's not that the doctor is stupid or unqualified, in fact they have way more medical knowledge than you. But the doctor only has a series of questions and maybe a few tests to make a diagnosis, whereas you have the full experience of symptoms and an internal understanding of your "normal". IMO people actually should "play Internet doctor" and research their symptoms, not to reach any 100% conclusions, but to suggest diagnoses and tests to their real doctor.
> IMO people actually should "play Internet doctor" and research their symptoms, not to reach any 100% conclusions, but to suggest diagnoses and tests to their real doctor.
I agree, and do this. But I never tell the doctor "I suspect that I have X", rather I tell the doctor "I've observed J, K, and L under Foo conditions" and let the doctor decide where to go from there. In short time we can learn to give the doctors better information, but we cannot replace their breadth of knowledge.
Yeah sometimes people say "doctor I have X, I'm trying to get diagnosed with X". You're biasing the doctor to give you a diagnosis so you don't drop them, and you're biasing the doctor to ignore your symptoms because you're just saying them to get the diagnosis and maybe you just want to get certain medication.
Even if you don't outright say it, you should never convince yourself you have a diagnosis. The human body is extremely complex and some particularly weird issues need patient research, doctor's research, and experimentation to solve.
I recently had an appointment with specialist for my son. My son has ADHD but was never diagnosed within Kaiser and so Kaiser won't prescribe medication.
The appointment started with, "My son has ADHD, was first diagnosed at 7 by _____, here are volumes of paperwork demonstrating that he had this diagnosis, has continued to have symptoms, and documenting what we have done for him. He wants to go back on medicine despite the side effects from last time. Here is more documentation that he continues to have symptoms."
There really ARE times when you're coming with enough background that the diagnosis is never in doubt.
For a less recent but more trivial example, I once showed up to the doctor and said, "I broke this bone in my hand while playing volleyball, what should I do about it?" Again, the diagnosis was never in doubt.
If you manage to hit the exact diagnostic questions they were trained for, that's the same, actually worse, than saying you have X, because you'll make them think they had the idea that you have X, when in reality you saw the list of symptoms, thought "I guess I have those," and then repeated them to the poor unsuspecting doctor.
>This is why we shouldn't take medical advice from people who have read a few Wikipedia articles.
>sometimes the experienced doctor or researcher made a mistake, and the guy who posted something on Reddit is correct
Both of those points are true, and we can reconcile them thusly:
Broadly, the doctor is the fully educated, while the layman-interested-in-subject is making semi-educated guesses. However this relationship inverts on narrow subjects, like a particular rare disease: the doctor ends up making a semi-educated guess (based on his general medical education), whereas a layman with intense interest in this particular rare disease can easily be the fully educated one - again, on this particular narrow subject.
> I was thinking the opposite point: sometimes the experienced doctor or researcher made a mistake, and the guy who posted something on Reddit is correct. Usually not, but sometimes.
If a researcher made a mistake and if 50 people on reddit said 50 different things, at random, one might be correct by chance.
Being correct once means nothing unless you are correct most of the times, but by then you are the researcher in the scenario above.
>Generally speaking, you should trust someone whose professional or experienced more than some random stranger. Especially if it's not one person but a large group of experienced professionals
Except if the large group is mostly a handful of experts with non-scientific private interests (say, to publish papers, to get grants, paid by companies with a product to sell), plus a large mass of professionals who seldom/never question the information they receive and just follow everything they read from their research and protocol-setting breathen.
When non-reproducible papers with BS mistakes get top citation counts and are held as gospel without any researcher/peer reviewer bothering verify them for decades, does anyone really think the average "professional doctor" really questions what they're told to follow?
> But it's actually important to "do your own research", and not just listen to authority. Provided you actually know how, i.e. you can find accurate sources and distinguish fact from fiction.
And to know if you’re only seeing narrative-approved sources, when contra-narrative sources have been suppressed.
Lots of folks got fooled by Iraq WMD because you couldn’t say anything to the contrary without being fired. Other examples, some more recent, are available.
> IMO people actually should "play Internet doctor" and research their symptoms
You should probably not play internet doctor if you’re a hypochondriac or prone to anxiety. The least probable cause of almost any symptoms is cancer or another deadly condition and you can probably find a gruesome description of someone’s experience online somewhere. If your nervous system can’t grasp that, stay away from googling your symptoms!
> IMO people actually should "play Internet doctor" and research their symptoms, not to reach any 100% conclusions, but to suggest diagnoses and tests to their real doctor.
I do this regularly, and having a hard sciences background it's usually an educated and well-thought research. Unfortunately some doctor can get quite upset if you dare to suggest a diagnosis, especially if it's an evidently correct one they didn't think about. You really have to be very careful, allude to things, stress key symptoms and try to make them reach the same conclusion without explicitly telling them how to do their job.
> some doctor can get quite upset if you dare to suggest a diagnosis
A well known idiom is that when the client says he has a problem, he's right. When the client tells you what the cause is, he's wrong.
Don't tell the doctor your diagnosis. You didn't go through a decade of medical training. Tell the doctor what you've observed, let him conclude the diagnosis.
> When the client tells you what the cause is, he's wrong.
using a software analogy, I've seen plenty of bug reports where the reporter did some research on his own that turned out to be determinant in the issue resolution. You have training, inside knowledge of the system that's failing, but you see plenty of issues everyday, cannot dedicate to each one the time they would deserve. The reporter instead is motivated to reach a solution and has plenty of time to research it properly. Discarding a potentially fundamental input just because it comes from someone supposedly untrained would be a shame.
Indeed. My hypothyroidism was ultimately diagnosed by my mother's work colleague who recognized the (frankly quite textbook) symptoms because her dog had it.
Doctors are like everyone else: 90% of them are kinda shit at their job.
> This is one of the most insightful comments I've read on the internet ever.
On the other hand, if I’m in the market for a guess, I’ll probably go for the educated guess rather than the uneducated one, because even though I recognize it’s not necessarily more correct, it probably is less wrong.
Sometimes it's better to know you don't know than to think you know. If it's midnight and you're standing at the edge of a cliff you're better off thinking that you have no idea what's ahead of you than if you listen to a guy with "better than average night vision" telling you that there's a sidewalk ahead.
If you are, as you say, "in the market for a guess" that would imply that you are actively looking at different guesses and comparing the credentials of the guessers. Then you would _probably_ be right to choose eg. the guess from the virologist over the proctologist or the mechanic when you need a guess on how the Covid situation will unfold. But the issue might be that an "educated guess" in itself could be worse because you wouldn't base any major decisions on a mechanic that present an "uneducated guess" that "the virus will die down in a month" but if you have a crackpot chiropractor presenting themselves as a "certified doctor with an expertise in everything concerning the body" that says the same thing, you might be worse off in saying that this "educated guess" is worth basing your travel plans on.
Medical advice on the internet can be n=1, but read enough to get to n=100+, while still limited, can be quite valuable. I can't ask 100 doctors what’s wrong with me, but I can ask my question to hundreds in an online forum. They might lead me astray, but so can a single doctor’s misdiagnosis. A doctor can prescribe treatment that helps or harms, but I can ask a forum of people, with the same problem I have, if I should take his advice. I can't, however, ask 100 of his colleagues or peers if I should trust his advice, and that's why we end up with so many charlatans in medicine. But he's a doctor. Of course you can trust him! I don't know about the rest of you, but I've found a fair number of doctors to be mostly useless.
>This is why self-driving cars still elude us, but will be so much safer than human drivers when they finally do arrive.
Isn't that just a by definition thing?
My Tesla can already drive itself, I don't trust it and I don't think it's safe. When I get one that I trust and is safe then it will be safer than me, and by extension other humans.
The problem is that the current generation of algorithms are brittle.
The way I state the above point is: "The smartest people in the room are the most skilled at convincing people (including themselves) of a narrative that sounds logical but is wrong".
I am afraid many times when talking about educated guesses we mean schooled
guesses. The problem is that, more than once, we learn per Mark Twain's
famous quote ...that schooling has a way of interfering with education...:-)
Specially for subtle but critical concepts:
"Researchers misunderstand confidence intervals and standard error bars"
As a trained physicist, I think you are getting this relatively right. Some of the issues at play are simply unknown according to the current state of theoretical physics.
Our Quantum Field Theories naively predict an infinite energy density all throughout space time. A naive guess at regularizing this leads to absurd predictions 120 orders of magnitude off [1]. So there has to be something else happening here. One of the things that supersymmetry brings to the table is that it makes this energy density exactly zero (but then it get's complicated because you need to break super symmetry...).
The thing is though, without gravity the absolute energy density of a quantum field is just some unobservable number. But how to reconcile gravity and quantum field theory is an unsolved problem to begin with, so it's completely unclear what that naive infinite number actually means. We are working without a firm theoretical (or empirical for that matter) foundation here.
However, the Casimir effect is remarkable exactly because it appears that the local energy density between two conducting plates is lower than in the ambient space. This is an energy difference that can and has been measured [2].
It is entirely plausible that it interacts with gravity in the right way to cause an effective negative energy density. This has been speculated by serious physicists for a long time. However: The Casimir effect is exceptionally weak. Space time is exceptionally hard to bend. So the idea of an actual warp bubble from Casimir effect geometry seems extremely far fetched[3] right now.
How stiff is space time? LIGO the gravitational wave observatory, measures changes to a 4000m distance that are smaller than an atomic nucleus, at its full design it will detect changes that are many time smaller than a proton. This is a feat of experiment that is the more astonishing the more you know. If you had told me you want to build something like this I would have assumed that it's likely impossible. Now, the first signal that could be detected by LIGO was a black hole merger that radiated away the energy equivalent of three solar masses. The peak power output of this event was larger than the combined energy output of all visible stars in the observable universe.
How small is the Casimir effect? Micro Newtons/m force gradients for micro meter distances [4]. Again we are talking about an effect so subtle that it's only been measured reliably in recent decades.
So these are the orders of magnitudes involved: White et.al. claim they can use an effect so small as to be barely perceptible, to manipulate space time in such a way to create interesting effects, when it takes the energy output of the entire universe to generate a ripple in space time strong enough to be detectable (a few galaxies over) by the most sensitive instrument ever devised. So I am sceptical.
[3] My physicist intuition says: Far fetched but not impossible. One of the heuristics for looking at this result though is this: The lead author is Harold White, one of the people who really pushed the EMDrive. The EMDrive is not far fetched but simply impossible (to a physicist the EMDrive is in exactly the same category as perpetuum mobiles). Worse, the original EMDrive paper by Harold White, despite supposedly showing evidence overthrowing three centuries of established physics, did not attempt to get published in a physics journal (which would have required extraordinary proof for such an extraordinary claim). Finally it involved some theoretical speculation that were just abject nonsense. These things mean I will not spend serious time on understanding and analyzing the details of this latest work.
I'll just put my back-of-the envelope calculation here to insert some optimism. While the energy emitted is immense, since the event was so far away (1.6e9 lt-yr), then if we plug in the solid angle subtended by the detector (~4000m4000m) I'm only seeing about ~2 kJ of energy passing through LIGO.
Caveats:
I assume the gravitational wave pattern is spherical; probably wrong but I'm not sure what the radiation pattern looks like for these event and in where we lay in relation to it.
Seems like White should get a little more credit; he's going well outside established science, and accepting a much higher risk of failure than most are comfortable with. Seems like he's throwing ideas at the wall in the hopes that maybe something sticks. More of us should do that, or at least, support those of us willing to see if something did stick.
The tone of this paper seemed less like an academic assertion of an effect, and more like "hey, found something cool, someone should look into this, I gotta get back to what I was doing."
I'm also not going to blame the guy for being interested in space-age propulsion systems.
If he was doing what you're saying that would do him credit. But I see it more as indulging in wishful thinking and gaming the funding system by promising vaguely plausible nonsense and avoiding the tough questions that would come with seriously engaging with the physics community.
A lot of the writing falls woefully short of being a serious effort at science. It's more "wouldn't it be cool if" science fiction.
The entire "attempt" to link the EMDrive to Bohmian quantum mechanics is just a grand amalgamation of conceptual confusion.
I read the new paper and I'm familiar reading physics articles. It strikes me almost as GPT-3 generated in places.. It certainly would not be accepted in its current form by any peer review process in a high impact journal. I'm sure the intent and ambition is absolutely sincere and there is serious research here but it's presented in a very unclear way IMHO. I think the paper could be rewritten to be more focused..
What the heck are peer review scores? And why would you expect it to be correlated with citation count? High quality research isn't the same thing as highly citable research. Peer review is supposed to check plausibility and maintain minimum quality standards. Peer review isn't a sign that something is good. But if something can not even get peer review it's a sure sign that it's pretty bad.
I know that video. This is also different from pure peer review because it involves an editorial decision/recommendation. I am sure >95% of the papers rejected from NeuralIPS will pass peer review elsewhere.
So this isn't about getting published in peer reviewed venues, this is about getting published in a particular, selective, high visibility venue.
So as far as I can see none of this has any bearing on anything you replied to.
They can and do, and are an important part of intermolecular interactions (van der Waal's forces have a substantial Casimir effect component).
Matter just ordinarily isn't structured to produce a strong version of an interesting effect - which when you get down to it is essentially what all human technology is based on.
It's quite possible there are some weird molecular structures (if this paper is correct) which could also induce natural warp-field structures out of their crystal lattice.
Going down this route, it strikes me as more feasible to find lattice effects or nano-scale effects facilitating cold fusion than warp fields. After all fusion itself is at least provably existing, just difficult to arrange.
While I understand your reservations, I think you are really underselling the power of Ansatz.
Ansatz reduce the search space of possible solutions because it adds various constraints that makes it possible to get to solutions much faster.
For example, without these constrained searches we will never have developed any analytical solutions to differential equations that are pervasive across science, engineering, finance among others.
"Negative curvature" isn't quite the right term. (For one thing, curvature in 4-dimensional spacetime cannot be described by a single number.) The Alcubierre drive requires "exotic matter", i.e., matter that violates the weak energy condition. One way of phrasing that condition is that the matter will have negative average energy density as measured by certain observers.
> Which kind negative curvature does the drive need?
The issue with your reasoning is not what kind of curvature the drive needs, but the idea that there is a "natural" bending of spacetime at all. There is no such thing.
The biggest issue - based on your explanation - seems to be the need for negative energy...
I might have a non-educated theory that could explain negative energy; could you tell me if this is potentially correct or am I completely wrong here?
Disclaimer: I haven't read the article (it doesn't load), and I am (probably) lacking even the basics of the required knowledge.
Let's assume the law of energy conservation applies to the universe: if you assume the total energy in the universe is constant, the negative energy is a relative imbalance instead of an absolute one, caused by the universe expanding at a different speed relative to the "things" it contains.
As the universe is "expanding" constantly, the "energy amount per expanding area" gets "less dense", so the "things" that are not "expanding" at the same speed get "more dense" in comparison. This imbalance creates different types of energy perturbation. From the point of view of the things that do not expand as fast, the energy levels relative to yours seem to evolve in a "negative way".
It's like looking at a stationary train from a train that is moving: from the point of view of the moving train, the train standing still seems to go backwards.
Does this make any sense at all, or am I completely missing the mark here?
Updated: reworded some things and provided extra context.
Energy conservation follows from Noether's theorem and time translational symmetry. This doesn't hold in general for an arbitrary space-time. In fact, it holds for a very specific subset (static spacetimes) of which our universe is not one of them.
As another complete layman just pooling my intuition:
Relatively more or less dense "things" (to each other) will always generate positive curvature of spacetime. What you want is relatively less dense area than vacuum in another region of space, since vacuum is (for now) what we constitute as (somewhat) flat.
That's what Casimir effect tries to accomplish: define a small enough region of spacetime where some larger quantum fluctuations don't have enough space to happen, thus lowering its energy below vacuum.
Since the idea is to define small enough space-like interval in spacetime to curb some energies off, could defining small enough time-like interval help the same purpose, multiplying the former?
Thanks, this makes a bit more sense to me now, but let's figure out if I understood it correctly:
The Casimir effect is about creating a spacetime "corset" so to speak, that is so tight that even the regular quantum fluctuations don't have "enough room to pass", so they "almost freeze", and when they "come out on the other end", they could for example break or delay entanglement?
On the other hand I think your assumption about the time aspect might be correct as we are talking about spacetime after all. The biggest issue might be that measuring time deltas might be harder than space deltas?
I don't think the Casimir effect is utilizing some medium flowing between the plates. Its not about a quantum fluctuation freezing as it passes trough the passage between the plates. Its rather that the quantum fluctuation comes into existence and disappears at random point in a vacuum, how often depends on the energy of the vacuum. When you put two plates really close together, there is not enough space for the quantum fluctuation to materialize, as it's wavelength is bigger than the gap. That way you limit the amount of those fluctuations materializing between the plates, and because there's less of them, there should be less energy than in unobstructed space, even vacuum. Thus negative energy, because its less than the 0 we assume for vacuum.
Regarding working with time-interval, it might as well just be the opposite: minimize space-interval and maximize time-interval for maximum effect. It's just wild guesses at my side. But minimizing time-interval should be trivially doable by just slinging the plates past each other at high speed.
LOL, looks like one gets seriously downvoted for mental freewheeling on HN... I did not see that coming, especially since I added a disclaimer.
Anyway, thanks for taking the time to try to explain this to a total layman, but I'll defer engaging into subject matters that I never heard about before; lesson learned...
The Alcubierre warp drive requires both positive and negative curvatures. Positive curvatures are "easy" to make, since mass and energy bend space positively. Negative curvatures are typically said to require negative energy to produce, but the full story is thankfully more complex.
The universe, despite being filled with mass and energy, is roughly flat. That means that the natural bending of spacetime, without any stuff inside it, has to be negative - otherwise all the mass would make it extra positive. If you believe the consequence of vacuum energy in QED, that the fields filling the universe are VERY heavy, even when no particles are around, then you must believe the natural curvature to be very negative indeed.
So, it stands to reason, if you want to bend the universe backwards, take the weights off of it - really off of it, in this case using metal plates to forbid certain vacuum fluctuations, and let it unbend itself.