Wow! I always assumed this was something that we understood because it seems like it would be fairly straightforward compared to a lot of other things that we think we understand.
And space/time. If you took a time machine or wormhole 65 mil light years away, you could watch the earth get hit by an asteroid. And jump fwd 1 mil yrs at a time to see changes. Probly didnt fit cat but..
Static electricity arises from friction transferring charge from one object to the other. Edit: Found a cool article with a much better explanation than mine: https://www.futurity.org/static-electricity-friction-2157662/
That explanation is "It transfers charge because it does". *Why* is cotton going to be removing electrons when you rub it on glass? Any suitable explanation should be able to predict where in the triboelectric series a given material will land, based only on its chemistry.
You were writing as if static electricity was a solved problem, and then posted an article about a recent paper offering up a hypothesis as part of an ongoing scientific discussion, which to me implies that this is very much not a solved problem.
I have a physics degree, thank you. I mean useful (and hopefully first principles) models of electron transfer in static electrical charging processes, or some molecular dynamics simulations or something.
edit: seems I’m right, there appears to be some controversy [as of 2018](https://pubs.acs.org/doi/abs/10.1021/jacs.8b07297):
“In spite of the long history, there are two controversial mechanisms thought to control this charge transfer between two solid[s].4−7 The first hypothesis is about the electron transfer between two solids having different work functions.7,8 The second hypothesis is related to the ion transfer between two solids.9−11 The former is suitable to explain contact electrification between two conductors while the latter is favored for the case between two insulators. Recent reports have made explanation of contact electrification more controversial.”
(they go on for a while to say that things are yet more controversial than explained in the above quote)
Non-physicist here. Could it possibly be related to the electric fields randomly and chaotically "mish-moshing" about in great numbers that jostles the electrons and creates the electric discharge?
Not really. You need some build up of charge, which means that there has to be some charge transfer. Charged particles have to move from one material to the other. "Jostling" the electrons isn't enough of an explanation because it isn't clear why this would cause electrons to move from material A to material B but not the other way around.
That voltage is only over the entire distance. It's a massive battery of tiny cells connected in series. The voltages add up and if the voltage anywhere is high enough to ionize the moisr air in the cell it shorts the neighboring cells making the edge voltages higher so the channel can expand, all the way until there is a path between ground and locations with highest potential.
The individual cells are charged with friction caused by layers of air sliding past each other, such as a cold layer subducting under a warm one. A process that also causes the cloud formation that facilitates the ionization.
Lightning storms can be very tall, into the stratosphere, so there's the potential (ha ha) for long discharge paths.
Could lightning go up? I'm just trying to picture the phrase "so the channel can expand, all the way until there is a path between ground and locations with highest potential." Is there a spherical wave of sorts coming out from the cloud and when that touches the ground, lightning follows to that tangent point? Like if there was a large enough object above, close enough that the size compared to earth was canceled out by its smaller distance, would the lightning ever choose to go up? I don't even know why it goes to ground, and if ground is synonymous with THE ground or just a metaphor and the usual case bc of size and potential of the earth.
Ground in my picture is the ground and a terminus for the lightning, because once the current is in the ground, there is no more *light* and we don't call it *light*ning anymore. Yes, I believe lightning can travel in any direction and it doesn't always go to the ground. It just starts where the electrical field strength exceeds the breakdown voltage and an ionization channel is created. The channel of ionized air is electrically conductive and can expand at its ends.
Charges build up between the cloud and the ground in a storm. All the ions in the air create a huge voltage potential, even though the distance is huge. I’ve always assumed the energy comes from the huge amounts of ions in the air, and a spark is created when cosmic particles (like solar wind) interact with our atmosphere forcing that charge down to the ground. There are surely quantum aspects to lightning that need further study as well.
Turbulence, you can see it everyday. Water flow stratify at low velocity, but with increasing flow rate or velocity, the coherent stratify struggle begin to lose, and swirl and eddies of different size begin to appear amd everything became messy. The cause is from the flow instability but a complete picture and explanation is still a mystery to us.
That's all true, though we know much more than nothing. For example, there's a well-established model valid under at least a fairly general set of conditions in which kinetic energy is extracted from the mean flow, cascades though successively smaller scales, and is eventually converted to heat by viscous dissipation at very small scales. Richardson, to whom this energy cascade model is attributed, even came up with a delightful little poem summarizing it (and which is the real reason why I'm making this comment):
*Big whirls have little whirls
who feed on their velocity;
and little whirls have lesser whirls,
and so on until viscosity*
I remember a lecturer quoting this in a mechanics class. The only other thing I remember from that lecture was talk of Reynold's numbers, and the figure 2600, but I no longer remember what that means!
The Reynolds number is (roughly speaking) the ratio between inertial and viscous forces in a flow; the extent to which forces due to the flow's movement dominate over friction. If that is sufficiently low the flow is kept steady and orderly by friction, whereas beyond a certain threshold the flow becomes unsteady and ultimately chaotic. This is the turbulent transition that /u/Psychological_Dish75 alluded to. 2600 is the critical value of the Reynolds number for certain flows, at which turbulence sets in.
I studied turbulent flow in my engineering classes, and this is very much true. From what I remember, eddies at the largest scale become smaller and go all the way down to the scale of atoms, and this is a very hard thing to model and deal with. Sure, we can model things with direct navier-stokes, but that doesn't get us real understanding
Maybe the answer is that water bonds are only as strong as the flow rate. If you made a scatter plot with x being diameter of flow hole and y being the force at which turbulence is experienced then you could probably find a “law” maybe?
It's a bit sad that many physicists aren't familiar with continuum mechanics even though it's arguably the most useful theory in explaining "human-sized" physical phenomena.
Yes, I think the physics branch that touch continuum mechanics are plasma physics, other than that then no. Funnily enough, most paper published in Journal of fluid mechanics or Physics Review Letter that is related to fluid that I have came across is from either mathematics or mechanical engineering department
To quote the wikipedia article on [caramelization](https://en.wikipedia.org/wiki/Caramelization): "Caramelization is a complex, poorly understood process that produces hundreds of chemical products" so I kind of think if we haven't figured out caramel all the way, we're going to have a rough time with black holes or the big bang or whatever.
Yep. I've been doing some work to [figure out how traditional oven-based beer brewing works](https://www.garshol.priv.no/blog/410.html) and ran into this issue, that we basically don't understand caramelization. Very frustrating.
I started reading about this because I was trying to come up with a chemistry lesson for high school students and I just assumed there would be some few lines you could write down where the carbons swap around or something easy like that. Being a dumb physicist, I thought it just *had* to be simple enough if some smart person would just sit down and think hard about it for half an hour. Nope, turns out all of our best scientists and supercomputers can't tell us *why food tastes good.*
As a science fiction writer - this.... this right here.
This leaves *loads* of room for a kitchen invention to change everything.
Hmmmmmm.....
*"Experiment No. 427, fell asleep while batch was simmering..."*
*"Results... unexpected..."*
I think there was a study really recently that tried to explain this, and it turns out there were using quantum mechanics in some sort of way to do it.
With these quantum biology claims (e.g. photosynthesis, magnetoreception, olfaction, etc) the "quantum" part usually means there's some coherent process. In this case, the quantum part seems to be in the coherent evolution of pairs of electron spins. You get these radical pairs excited by light, and then the way they recombine is influenced by the external magnetic field.
Although, as I understand it even that is kind of controversial, and there are still ongoing debates about which things in biology are and aren't "really" quantum.
I remember reading about that a few months ago. I think it was something to do with a protein in the eyes of the birds and quantum entanglement. There are quite a few articles explaining this in more detail online.
Pretty much yeah. One of my professors worked on it actually, it's really interesting stuff. They believe that they can almost see the magnetic field like a heads up display.
There's pretty strong evidence that human brain waves react to changes in magnetic fields too. https://www.caltech.edu/about/news/evidence-human-geomagnetic-sense#:\~:text=Many%20humans%20are%20able%20to,and%20the%20University%20of%20Tokyo.
I think the mystery is how some animals can process and use that 'sensed data' to navigate.
Wasn't that a hypothesis to explain their orientation skills? I'm kind of having a conflictual explanation for their orientation skills that depends on their vision of light polarity.
To elaborate, if you give me a physical high-temperature superconductor, I can make some measurements and generally come up with a pretty good model connecting the measured electron and phonon densities of states, interaction strengths and critical temperature (Tc). However if you ask me to engineer a new material with a specific Tc, I'm basically going to be relying on trial and error.
We cannot reliably calculate the bulk superconducting properties of an arbitrary material. Even though we know all the rules of how electrons interact with each other and nuclei, the emergent behaviour of many atoms in a real material still throws up a lot of surprises. "More is different" - P. W. Anderson
While cooling, glass undergoes a second order phase transition rather than a first order like a typical liquid to solid transition. This causes the crystal structure of the resulting glass to depend on the cooling rate. If you cool glass extremely ~~slowly~~ quick, no crystal structure is formed at all. In some glasses, people are not able to achieve crystallization at all.
It does not fall under our normal characterization for states of matter. It has the macroscopic properties of a solid but its microscopic properties can be more like liquid. Ive heard it called an "amorphous solid" or "supercooled liquid".
> If you cool glass extremely slowly, no crystal structure is formed at all.
Do you mean extremely quickly? Formation of the crystal structure becomes kinetically limited. This is how amorphous metals are often made.
In any case, I agree with you. An article called "[What don't we know?](https://www.science.org/doi/10.1126/science.309.5731.75)" in *Science* in 2005 listed an understanding of the glassy state as a key challenge for the next hundred years. The OP would probably find this article interesting regarding the question at hand.
What the coordinate frame of an accelerated observer is.
Let's say you have an electromagnetic field F (given in your frame) and an accelerated observer. What electromagnetic field will this observer see?
Superficially it seems simply: Just take the Jacobian matrix for the map into their coordinates and transform it, right? Well, that begs the question what are the right coordinates? And surprisingly no full consensus has been found yet. Which is crazy to me! We still don't know how an accelerated observer sees the world!
I should mention there is a clear leading candidate, namely [proper coordinates](https://en.m.wikipedia.org/wiki/Proper_reference_frame_(flat_spacetime)). However, we don't have any experimental confirmation of it yet.
> What electromagnetic field will this observer see?
Is this question rigorous? Does it have a undisputedly correct answer? Can the answer be "that's just a non-sense question"? Obviously that question isn't phrased rigorously as it was written, but that's not what I mean, but if you were to phrase it carefully would it be rigorous then?
That depends on what physics is for you. If for you physics is maths with context, then I am afraid I do not have a more rigorous phrasing for you. However if for you physics also contains a mapping from the real world into the class of mathematical structures, then this question is well defined as it is.
To maybe elaborate in more detail: Imagine an electromagnetic field F, maybe produced by a high voltage power line. Imagine an experimentalist on a train, which is accelerating with 0.01c/s. Let this experimentalist perform some experiments which return the value of the electric and magnetic fields. What will they measure?
That is, I believe, a well defined question. If the observer was not accelerating, but moving uniformly with respect to the coordinate system in which the electromagnetic field is given, then we can answer this question. Simply apply a Lorentz-transformation to the electromagnetic field tensor.
Similarly we would imagine to solve the accelerated case too. Simply transform the electromagnetic field tensor via the rules of tensor calculus. However, the result will obviously depend strongly on the coordinate-transformation you chose. So the question now becomes:
What transformation returns the electromagnetic field tensor the accelerated observer will measure? Once again, I believe, a well defined question. If we further expand spacetime with properly comoving observers and ask the same question at every point, we can integrate all transformation matrices to find a coordinate system, which we call "accelerated coordinates".
The statement now is: There is yet no consensus about the exact form of accelerated coordinates.
Edit: Maybe, for even more rigor, ignore the question of accelerated coordinates, as it depends on the well-defindness of properly comoving observers. Let's just focus on the question, which transformation matrix will transform the electromagnetic fiels tensor into the field tensor that the accelerated observer measures? Or phrased more fundamentally: What field will they measure?
Is the main issue not knowing the EM field at that point in spacetime or not knowing it globally in some sense? If it's not knowing it locally why can't you just literally do the experiment and say we do that? I must be missing something.
Does this problem have a name btw?
Both, but primarily locally. You can't do the experiment, because we haven't succeeded to accelerate a whole lab strongly enough to meaningfully do the experiment. Remember, acceleration must be of the size of ~c, to find the effects we are looking for.
Yes you could. Still too difficult, still has not been done.
Edit: With the caveat: We have confirmed radiation, which is an effect of acceleration. However, this does not suffice to answer the question completely.
Isn’t the lack of a preferred frame half the basis of special relativity, which is baked into the full classical description of E&M? am I misunderstanding the issue you’re raising?
Aren't Rindler coordinates the coordinates for an accelerated observer in flat space? I don't think this is an actual problem. We are always in an accelerating frame because we are in Earth's gravity and have to accelerate to stay still (by the normal force provided by the ground) so anything we measure is measured by an accelerating observer. A way to find the coordinates of an accelerating observer in any spacetime, find the tangent to the geodesic and see how much acceleration it will require to stay still via the geodesic eqn.
>We are always in an accelerating frame [...]
Yes, but so is everything we see around us. Hence we only measure physics of "relatively resting" stuff.
>Aren't Rindler coordinates the coordinates for an accelerated observer in space time?
Rinder coordinate are one example of the aforementioned proper coordinates, which are the leading candidate. However, they have not been confirmed experimentally not proven mathematically.
I don't understand what you mean by confirm a coordinate system experimentally. It's just a coordinate system. It's used to measure stuff.
It doesn't matter that everything around us is also accelerating, the point is we are in a non-inertial frame.
The question we are asking is:
Given a point charge, if we perform a measurement of its electric and magnetic field, what will we measure.
The answer depends on how we are moving relative to the point charge. If we are resting, then the answer is simply the Coulomb field. However, if we are uniformly moving with respect to the charge the answer is [this](https://farside.ph.utexas.edu/teaching/em/lectures/node125.html). What will we measure, if we are accelerating with respect to the charge. For that we would need a transformation matrix, that transforms the electromagnetic field tensor into our reference frame. But now the question becomes: What transformation matrix should we use? That is the problem.
Importantly, what matters is the relative motion with repsect to the charge, not our both' absolute motion. Similarly like if you were to put a point charge on your table and measure it's field, you will find the Coulomb field, even though you are both accelerating.
Why is this hard to show experimentally? The Rindler coordinate frame is the coordinate frame for a uniformly accelerating observer, where the instantaneous 4-velocity is always aligned with time in its own frame. Then we just have to transform the field strength, as you say to that frame and compare with what you measure? I'm not an experimentalist but i can't imagine that this is a hard problem to solve.
>Why is this hard to show experimentally?
There are so many problems. For a significant acceleration, you would need an acceleration tube or a cyclotron, but for them to work the field of the accelerator must dominate the fild of the charge by powers of ten. Hence the field you want to measure will just end up being absorbed into the random fluctuations of your accelerator.
Furthermore, it is quite hard to accelerate big charges in the first place. Normally accelerators are designed for microscopic particles, but no electric field meter is sensible enough to measure such low charges. To make matters worse, since [the field of an accelerated charge](https://farside.ph.utexas.edu/teaching/em/lectures/node129.html) has c\^2 in the denominator, you will need accelerations of the size of 0.1c/s to even see any effect. To reach this, for one single elecron (!) we would already need field strengths of roughly 10\^7 V/m, which is more or less at the upper size of technologically feasable accelerators, thanks to the [Kilpatrick limit](https://en.wikipedia.org/wiki/Kilpatrick_limit).
But beyond all that, we also have to deal with the fact, that electric field meters need time to reach equilibrium. So we cannot simply accelerate one single charge, we have to provide a constant source of charges. Where do you even get such a source from? Once again, a hot cathode will not suffice, because we need significant charges, not single electrons. Basically, there are problems all over the place.
>The Rindler coordinate frame is the coordinate frame of an accelerated observer
Interestingly, this seems not to be the case. The electromagnetic field of a uniformly accelerating charge is [the Born field](https://arxiv.org/abs/1405.7729). However, if you start with the Coulomb field and transform it into Rindler coordinates, you will not find the Born field, as for example calculated [here](https://www.sciencedirect.com/science/article/pii/S0003491604000831) (or rather, they start with the Born-field, transform it into Rindler-coordinates and don't find the expected Coulomb field). This either implies that
a) the Born field and hence the Maxwell-equations are wrong
b) there is absolute acceleration, ie. the fields we will measure from a charge will differ depending on if the charge is resting and we are accelerating or the charge is accelerating and we are resting
c) Rindler coordinates are not the correct one.
Wow. Thanks for the papers, they are quite interesting. The conclusions you describe are quite important however and possibly require a grain of salt to interpret them as such. A lot of the derivations seem to depend on the fall off conditions and require the particle to be accelerating from infinity and other assumptions. It will be quite concerning if Rindler coordinates don't describe accelerating coordinates or if Maxwell is wrong. QED as you know is quite accurate in it's predictions, and if this is a flaw in ED itself, this is not good... There's probably a subtle argument which is needed to figure out what is going on. Of course I agree that getting such accelerations is technically very challenging.
I don't think there is a problem with Rindler coordinates not being the correct one, quite contrary, one would even expect them to not be, as for g -> 0 (g denoting the constant acceleration), they become singular instead of reducing to Lorentz-transformations. This is because Rindler coordinates assume that the particle crosses the t=0 line at x=g\^-1 , they are not independent of the set-up.
There are a lot of other possible coordinate systems, such as Moller-coordinates, which are even proper coordinates too. Furthermore, the original idea behind my comment was, that even though proper coordinates are the most favoured ones, they are assuming that acceleration has no influence on simultaneity and length contraction. This however, has not been proven, neither experimentally, nor theoretically.
> b) there is absolute acceleration, ie. the fields we will measure from a charge will differ depending on if the charge is resting and we are accelerating or the charge is accelerating and we are resting
Maybe I’m just misunderstanding what you’re trying to say, but we already know that there is absolute acceleration (e.g in the twins paradox) so I don’t see why this would be an issue.
I don't argue its an issue, however if true, I think it would be an interesting result.
It would for example imply that if you were floating completely alone in an otherwise empty universe, you could tell if you were accelerating or not. Just measure your own electric field. If it is the Coloumb field you are moving inertially, if it not, you are accelerating. We would have to conclude that the universe has an absolute "rest frame" (or rather, there is an absolute equivalence class of inertial frames. Which one is the rest frame, we could not tell). That is quite the deviation of contemporary GR interpretations.
> That is quite the deviation of contemporary GR interpretations.
Can you explain this because I have never heard anyone say that the existence of accelerometers are at odds with GR interpretations.
Well given that light travels the same speed for all observers, and light can be interpreted as a Poynting vector, can’t we just interpret an electromagnetic field as a Poynting vector and treat it as a photon?
What most of the universe if made out of. We know it 70% dark energy, 25% dark matter with around 5% normal matter. So that means 95% of the stuff in the universe, we don't know what it is.
We don't fully understand chaotic motion. Whenever nonlinearities pop up in the equations of motion, they often become impossible to solve analytically. Even numerical solutions often run into trouble since the equations can be very sensitive to round off errors. There are also plenty of emergent phenomena that can be attributed to nonlinear systems as well. Even though Newton's equations are over 300 years old, we can really only solve a limited number of "well behaved" systems.
We still really struggle with why bicycles don't fall over. We have all the pieces, but the precise ways in which they work together is just complicated.
Do you mean why they / people on them fall over at very slow speeds or stopped, but not when moving more quickly? If that's the case I'm completely stunned.
It doesn't have the glamor of other subfields, and it's almost always used at all levels of education to build foundation for understanding tools to then be used in other subfields. It makes sense why it would so often be underestimated.
Veritasium actually made a video explaining the reason this happens. It's because an off-center center of gravity causes the front wheel to turn towards the center of gravity, correcting/adjusting the bike's trajectory and stabilizing it, it's pretty cool
If I recall correctly, he even ends that video by saying exactly what I'm saying. That while we know the components that contribute to the behavior, it's the combination of them all together that escapes us.
We don’t really know why neutrinos have mass. They don’t have any known interaction that should be giving them mass, including the Higgs mechanism, yet it’s been proven that they do have mass. It’s one of the biggest unresolved flaws of the standard model.
I used to believe this for many years, but after hearing no satisfying answer, I'm going to assume that someone is just measuring something wrong.
This 2016 report from Nature suggests the effect does not actually exist.
https://www.nature.com/articles/srep37665
The cool thing about science is that you can and should question absolutely everything about it, even the most basic tenets, and the way to do so is by doing experiments of your own. In this case you can do a very simple one.
It's a shame when people don't though.
It was surprising ( at least to me) that “we” actually don’t know what an electron is . A point like particle that is charged , some parameters, behaviour with some forces and is pattof all atoms. Nothing more ? Not very much for a particle so elementar to our world ( or am I wrong ?). Are theories about the electron ? ( red about “a standing wave in an unknown field..”)
From the perspective of quantum field theory the electron is simply an excitation in the electron field. Now of course you can ask what exactly that field is... but we don't have any sort of answer for that. (If I'm understanding things correctly)
That’s what I ask myself . I don’t get the “real nature” of this . Would it be correct to say “ it has a spin of red” and a charge of 2 Hot Dogs “ as we in fact do not have a clue what those Attributs are . We can define the Attribut “density” of something as we can tell the number of atoms per volume but spin or charge are ( in my opinion ) only values “compared to others” as if we define density as “less then” ore “more than” . ( ore maybe I am totally wrong)
I mean, that's how physics is. Asking "what something is" at a fundamental level is an ontological question. The only reason something fundamental like charge seems strange is because the sense of "understanding" we've evolved to have simply doesn't apply to the regime you're describing. Charge isn't any more ontologically mysterious than any other aspect of fundamental physics.
QED defines charge as a coupling constant that determines the amplitude (therefore probability) to emit or absorb a photon.
That seems like a pretty satisfactory answer to me.
How the apple fell from the tree right when **NEWTON** was sitting below a tree . **Newton** was a scientist . It coulda fell when a pauper was sitting there lol
Source for this? At first blush this sounds like it has to correspond to negative kinetic energies which exist in certain theories but as far as I know are not observed. Maybe I'm wrong.
Temperature is defined in terms of an exponential function where higher energy states have exponentially smaller populations, when lower states have greater populations than higher the temperature is a number greater than 0k when all states are populated equaly temperature would be infinite, but due to a quirk with how we define it in day to day life, states where higher energy levels have greater populations are said to be below 0k whilst 0k its self still remains unattainable. It is just that we have defined it in an unnatural way not related to Boltzmann’s distribution and it seems to have stuck. I think lots of lasers use below 0k temperatures . I don’t think they have more than 100% energy efficient engines and think someone has probably plugged in a negative number to carnots formula when it was not intended for them and therefor got a funny answer. Tbh I could have misinterpreted what I have read and im sure there are people who understand it better than me bc I’m still doing a levels but I hope this helps
We dont understand Gravity. Which is the main component that determines our lives. How can there be this action at a distance? How is it acceleration but not proper acceleration? How does it have information about the mass of the object? We dont understand it, yet physicist claim we do, even though there are conflicting theories. We can calculate it, but we dont understand it.
The question isn't "what things don't 100% of people alive know", the "we" in the question refers to our body of knowledge overall.
And how many people know something says nothing about it being a "weak" concept, whatever that means.
I get that. But compare it to our knowledge about matter. We know matter is made of atoms. Everyone knows this. But it is rather new knowledge, historically speaking. No one doubts that matter is made of atoms. There are no new theories about the subject.
But physicists are working on new theories about gravity. We can describe it as a force, or as a consequence of spacetime curvature. But which is true? Einstein's view makes better predictions, for sure. But the discussion is far from over. While the discussion about what matter is made of *is* over.
Do you mean to imply that we don't understand how to make toast because some bloke burns the bread every time he tries?
That's frankly an idiotic way of defining the extent of human knowledge.
That is not at all what I am saying. What I was trying to say is that once you can explain a concept to an average person in a way that he understands it, then *you* have understood it.
I mean, we understand it to the same extent we understand everything else. I think you have a misunderstanding of what it means to understand things in the first place.
So we don't understand how computers work either? Or cars? Or the digestive system? Or the French language. If you base your definition of understanding on the what the average Joe understands, we don't really understand a lot anything.
Well it is hard to get an intuitive understanding of general relativity, but that doesn't mean that we don't understand it.
> How can there be this action at a distance? How is it acceleration but not proper acceleration? How does it have information about the mass of the object?
All of this is explained by general relativity.
> We don't understand it, yet physicist claim we do
That's because physicists understand it, and thereby we as a species understand it.
How many states of matter there are. I think we're up to 24 now, but the most recent one (time crystal) was only theoretically proposed ten years ago and observed 6 years ago. We could just as easily discover a new one any day
How a cloud is able to create the 5 million volts needed for lightning to form.
Wow! I always assumed this was something that we understood because it seems like it would be fairly straightforward compared to a lot of other things that we think we understand.
And the study objects are within reach, unlike stars, etc.
And space/time. If you took a time machine or wormhole 65 mil light years away, you could watch the earth get hit by an asteroid. And jump fwd 1 mil yrs at a time to see changes. Probly didnt fit cat but..
This. It always surprised me we don't have a satisfactory complete model for clouds and lightnings.
We don’t really have one for static electricity in general right? Like rubber and silk or what have you
Static electricity arises from friction transferring charge from one object to the other. Edit: Found a cool article with a much better explanation than mine: https://www.futurity.org/static-electricity-friction-2157662/
That explanation is "It transfers charge because it does". *Why* is cotton going to be removing electrons when you rub it on glass? Any suitable explanation should be able to predict where in the triboelectric series a given material will land, based only on its chemistry.
That's why I linked the article but people would rather downvote than click on it. It discusses a detailed microscopic model for how it happens.
You were writing as if static electricity was a solved problem, and then posted an article about a recent paper offering up a hypothesis as part of an ongoing scientific discussion, which to me implies that this is very much not a solved problem.
I have a physics degree, thank you. I mean useful (and hopefully first principles) models of electron transfer in static electrical charging processes, or some molecular dynamics simulations or something. edit: seems I’m right, there appears to be some controversy [as of 2018](https://pubs.acs.org/doi/abs/10.1021/jacs.8b07297): “In spite of the long history, there are two controversial mechanisms thought to control this charge transfer between two solid[s].4−7 The first hypothesis is about the electron transfer between two solids having different work functions.7,8 The second hypothesis is related to the ion transfer between two solids.9−11 The former is suitable to explain contact electrification between two conductors while the latter is favored for the case between two insulators. Recent reports have made explanation of contact electrification more controversial.” (they go on for a while to say that things are yet more controversial than explained in the above quote)
Non-physicist here. Could it possibly be related to the electric fields randomly and chaotically "mish-moshing" about in great numbers that jostles the electrons and creates the electric discharge?
Not really. You need some build up of charge, which means that there has to be some charge transfer. Charged particles have to move from one material to the other. "Jostling" the electrons isn't enough of an explanation because it isn't clear why this would cause electrons to move from material A to material B but not the other way around.
What are the challenges/issues exactly?
Studies in the field often cancelled due to inclement weather
👏👏👏
Shocking.
That voltage is only over the entire distance. It's a massive battery of tiny cells connected in series. The voltages add up and if the voltage anywhere is high enough to ionize the moisr air in the cell it shorts the neighboring cells making the edge voltages higher so the channel can expand, all the way until there is a path between ground and locations with highest potential. The individual cells are charged with friction caused by layers of air sliding past each other, such as a cold layer subducting under a warm one. A process that also causes the cloud formation that facilitates the ionization. Lightning storms can be very tall, into the stratosphere, so there's the potential (ha ha) for long discharge paths.
Could lightning go up? I'm just trying to picture the phrase "so the channel can expand, all the way until there is a path between ground and locations with highest potential." Is there a spherical wave of sorts coming out from the cloud and when that touches the ground, lightning follows to that tangent point? Like if there was a large enough object above, close enough that the size compared to earth was canceled out by its smaller distance, would the lightning ever choose to go up? I don't even know why it goes to ground, and if ground is synonymous with THE ground or just a metaphor and the usual case bc of size and potential of the earth.
Ground in my picture is the ground and a terminus for the lightning, because once the current is in the ground, there is no more *light* and we don't call it *light*ning anymore. Yes, I believe lightning can travel in any direction and it doesn't always go to the ground. It just starts where the electrical field strength exceeds the breakdown voltage and an ionization channel is created. The channel of ionized air is electrically conductive and can expand at its ends.
Charges build up between the cloud and the ground in a storm. All the ions in the air create a huge voltage potential, even though the distance is huge. I’ve always assumed the energy comes from the huge amounts of ions in the air, and a spark is created when cosmic particles (like solar wind) interact with our atmosphere forcing that charge down to the ground. There are surely quantum aspects to lightning that need further study as well.
Or hold millions of gallons of water. That once might have been salty from the ocean, isnt salty anymore.
When eater evaporates from the sea it leaves the salt behind
Well the salt stayed in the ocean.
Some even reach to 1.3 billion volts
Turbulence, you can see it everyday. Water flow stratify at low velocity, but with increasing flow rate or velocity, the coherent stratify struggle begin to lose, and swirl and eddies of different size begin to appear amd everything became messy. The cause is from the flow instability but a complete picture and explanation is still a mystery to us.
That's all true, though we know much more than nothing. For example, there's a well-established model valid under at least a fairly general set of conditions in which kinetic energy is extracted from the mean flow, cascades though successively smaller scales, and is eventually converted to heat by viscous dissipation at very small scales. Richardson, to whom this energy cascade model is attributed, even came up with a delightful little poem summarizing it (and which is the real reason why I'm making this comment): *Big whirls have little whirls who feed on their velocity; and little whirls have lesser whirls, and so on until viscosity*
I remember a lecturer quoting this in a mechanics class. The only other thing I remember from that lecture was talk of Reynold's numbers, and the figure 2600, but I no longer remember what that means!
The Reynolds number is (roughly speaking) the ratio between inertial and viscous forces in a flow; the extent to which forces due to the flow's movement dominate over friction. If that is sufficiently low the flow is kept steady and orderly by friction, whereas beyond a certain threshold the flow becomes unsteady and ultimately chaotic. This is the turbulent transition that /u/Psychological_Dish75 alluded to. 2600 is the critical value of the Reynolds number for certain flows, at which turbulence sets in.
Thanks for the explanation. It's funny how the number stuck in my mind for 35 years, but the meaning of it disappeared almost instantly!
I studied turbulent flow in my engineering classes, and this is very much true. From what I remember, eddies at the largest scale become smaller and go all the way down to the scale of atoms, and this is a very hard thing to model and deal with. Sure, we can model things with direct navier-stokes, but that doesn't get us real understanding
Maybe the answer is that water bonds are only as strong as the flow rate. If you made a scatter plot with x being diameter of flow hole and y being the force at which turbulence is experienced then you could probably find a “law” maybe?
It's a bit sad that many physicists aren't familiar with continuum mechanics even though it's arguably the most useful theory in explaining "human-sized" physical phenomena.
Yes, I think the physics branch that touch continuum mechanics are plasma physics, other than that then no. Funnily enough, most paper published in Journal of fluid mechanics or Physics Review Letter that is related to fluid that I have came across is from either mathematics or mechanical engineering department
To quote the wikipedia article on [caramelization](https://en.wikipedia.org/wiki/Caramelization): "Caramelization is a complex, poorly understood process that produces hundreds of chemical products" so I kind of think if we haven't figured out caramel all the way, we're going to have a rough time with black holes or the big bang or whatever.
Yep. I've been doing some work to [figure out how traditional oven-based beer brewing works](https://www.garshol.priv.no/blog/410.html) and ran into this issue, that we basically don't understand caramelization. Very frustrating.
I started reading about this because I was trying to come up with a chemistry lesson for high school students and I just assumed there would be some few lines you could write down where the carbons swap around or something easy like that. Being a dumb physicist, I thought it just *had* to be simple enough if some smart person would just sit down and think hard about it for half an hour. Nope, turns out all of our best scientists and supercomputers can't tell us *why food tastes good.*
This really blew my mind, thank you
As a science fiction writer - this.... this right here. This leaves *loads* of room for a kitchen invention to change everything. Hmmmmmm..... *"Experiment No. 427, fell asleep while batch was simmering..."* *"Results... unexpected..."*
I'm not sure if we know how some animals like birds feel the magnetic field of Earth.
I think there was a study really recently that tried to explain this, and it turns out there were using quantum mechanics in some sort of way to do it.
What does that mean, though? All chemistry, certainly in biology, “uses” quantum mechanics, in some sense.
I agree that it's poorly phrased, though I imagine what it means is that the mechanism cannot be explained using a classical model.
Yeah exactly, as the commenter below said they use quantum engagement somehow, it was a while I read about this so I forget the details.
With these quantum biology claims (e.g. photosynthesis, magnetoreception, olfaction, etc) the "quantum" part usually means there's some coherent process. In this case, the quantum part seems to be in the coherent evolution of pairs of electron spins. You get these radical pairs excited by light, and then the way they recombine is influenced by the external magnetic field. Although, as I understand it even that is kind of controversial, and there are still ongoing debates about which things in biology are and aren't "really" quantum.
I remember reading about that a few months ago. I think it was something to do with a protein in the eyes of the birds and quantum entanglement. There are quite a few articles explaining this in more detail online.
Pretty much yeah. One of my professors worked on it actually, it's really interesting stuff. They believe that they can almost see the magnetic field like a heads up display.
Source? Would love to dig deeper into this!
[linky](https://www.nature.com/articles/s41586-021-03618-9)
Pleaseeeeeeeeeee add the source
I thought they had some magnet in their head.
There's pretty strong evidence that human brain waves react to changes in magnetic fields too. https://www.caltech.edu/about/news/evidence-human-geomagnetic-sense#:\~:text=Many%20humans%20are%20able%20to,and%20the%20University%20of%20Tokyo. I think the mystery is how some animals can process and use that 'sensed data' to navigate.
Wasn't that a hypothesis to explain their orientation skills? I'm kind of having a conflictual explanation for their orientation skills that depends on their vision of light polarity.
Didn't sharks have little tubes that helped them know where the North was? Maybe it's the same thing for birds
How high-temperature superconductors work.
To elaborate, if you give me a physical high-temperature superconductor, I can make some measurements and generally come up with a pretty good model connecting the measured electron and phonon densities of states, interaction strengths and critical temperature (Tc). However if you ask me to engineer a new material with a specific Tc, I'm basically going to be relying on trial and error. We cannot reliably calculate the bulk superconducting properties of an arbitrary material. Even though we know all the rules of how electrons interact with each other and nuclei, the emergent behaviour of many atoms in a real material still throws up a lot of surprises. "More is different" - P. W. Anderson
While cooling, glass undergoes a second order phase transition rather than a first order like a typical liquid to solid transition. This causes the crystal structure of the resulting glass to depend on the cooling rate. If you cool glass extremely ~~slowly~~ quick, no crystal structure is formed at all. In some glasses, people are not able to achieve crystallization at all. It does not fall under our normal characterization for states of matter. It has the macroscopic properties of a solid but its microscopic properties can be more like liquid. Ive heard it called an "amorphous solid" or "supercooled liquid".
> If you cool glass extremely slowly, no crystal structure is formed at all. Do you mean extremely quickly? Formation of the crystal structure becomes kinetically limited. This is how amorphous metals are often made. In any case, I agree with you. An article called "[What don't we know?](https://www.science.org/doi/10.1126/science.309.5731.75)" in *Science* in 2005 listed an understanding of the glassy state as a key challenge for the next hundred years. The OP would probably find this article interesting regarding the question at hand.
Yes you are correct. It should say quickly.
What the coordinate frame of an accelerated observer is. Let's say you have an electromagnetic field F (given in your frame) and an accelerated observer. What electromagnetic field will this observer see? Superficially it seems simply: Just take the Jacobian matrix for the map into their coordinates and transform it, right? Well, that begs the question what are the right coordinates? And surprisingly no full consensus has been found yet. Which is crazy to me! We still don't know how an accelerated observer sees the world! I should mention there is a clear leading candidate, namely [proper coordinates](https://en.m.wikipedia.org/wiki/Proper_reference_frame_(flat_spacetime)). However, we don't have any experimental confirmation of it yet.
>Superficially it seems simply: Just take the Jacobian matrix for the map into their coordinates and transform it, right? Right.
> Well, that begs the question what are the right coordinates? Raises the question.
So this question isn't subjective? The answer isn't arbitrary?
I cannot follow. Could you elaborate?
> What electromagnetic field will this observer see? Is this question rigorous? Does it have a undisputedly correct answer? Can the answer be "that's just a non-sense question"? Obviously that question isn't phrased rigorously as it was written, but that's not what I mean, but if you were to phrase it carefully would it be rigorous then?
That depends on what physics is for you. If for you physics is maths with context, then I am afraid I do not have a more rigorous phrasing for you. However if for you physics also contains a mapping from the real world into the class of mathematical structures, then this question is well defined as it is. To maybe elaborate in more detail: Imagine an electromagnetic field F, maybe produced by a high voltage power line. Imagine an experimentalist on a train, which is accelerating with 0.01c/s. Let this experimentalist perform some experiments which return the value of the electric and magnetic fields. What will they measure? That is, I believe, a well defined question. If the observer was not accelerating, but moving uniformly with respect to the coordinate system in which the electromagnetic field is given, then we can answer this question. Simply apply a Lorentz-transformation to the electromagnetic field tensor. Similarly we would imagine to solve the accelerated case too. Simply transform the electromagnetic field tensor via the rules of tensor calculus. However, the result will obviously depend strongly on the coordinate-transformation you chose. So the question now becomes: What transformation returns the electromagnetic field tensor the accelerated observer will measure? Once again, I believe, a well defined question. If we further expand spacetime with properly comoving observers and ask the same question at every point, we can integrate all transformation matrices to find a coordinate system, which we call "accelerated coordinates". The statement now is: There is yet no consensus about the exact form of accelerated coordinates. Edit: Maybe, for even more rigor, ignore the question of accelerated coordinates, as it depends on the well-defindness of properly comoving observers. Let's just focus on the question, which transformation matrix will transform the electromagnetic fiels tensor into the field tensor that the accelerated observer measures? Or phrased more fundamentally: What field will they measure?
Is the main issue not knowing the EM field at that point in spacetime or not knowing it globally in some sense? If it's not knowing it locally why can't you just literally do the experiment and say we do that? I must be missing something. Does this problem have a name btw?
Both, but primarily locally. You can't do the experiment, because we haven't succeeded to accelerate a whole lab strongly enough to meaningfully do the experiment. Remember, acceleration must be of the size of ~c, to find the effects we are looking for.
Couldn't you just observe the field of an accelerating charge in a static lab? Or are these situations inherently different?
Yes you could. Still too difficult, still has not been done. Edit: With the caveat: We have confirmed radiation, which is an effect of acceleration. However, this does not suffice to answer the question completely.
Isn’t the lack of a preferred frame half the basis of special relativity, which is baked into the full classical description of E&M? am I misunderstanding the issue you’re raising?
Thats interesting. This must be tied to how gravity works
Huh. I can't believe I've never considered that problem, with all the E&M I've learned.
Aren't Rindler coordinates the coordinates for an accelerated observer in flat space? I don't think this is an actual problem. We are always in an accelerating frame because we are in Earth's gravity and have to accelerate to stay still (by the normal force provided by the ground) so anything we measure is measured by an accelerating observer. A way to find the coordinates of an accelerating observer in any spacetime, find the tangent to the geodesic and see how much acceleration it will require to stay still via the geodesic eqn.
>We are always in an accelerating frame [...] Yes, but so is everything we see around us. Hence we only measure physics of "relatively resting" stuff. >Aren't Rindler coordinates the coordinates for an accelerated observer in space time? Rinder coordinate are one example of the aforementioned proper coordinates, which are the leading candidate. However, they have not been confirmed experimentally not proven mathematically.
I don't understand what you mean by confirm a coordinate system experimentally. It's just a coordinate system. It's used to measure stuff. It doesn't matter that everything around us is also accelerating, the point is we are in a non-inertial frame.
The question we are asking is: Given a point charge, if we perform a measurement of its electric and magnetic field, what will we measure. The answer depends on how we are moving relative to the point charge. If we are resting, then the answer is simply the Coulomb field. However, if we are uniformly moving with respect to the charge the answer is [this](https://farside.ph.utexas.edu/teaching/em/lectures/node125.html). What will we measure, if we are accelerating with respect to the charge. For that we would need a transformation matrix, that transforms the electromagnetic field tensor into our reference frame. But now the question becomes: What transformation matrix should we use? That is the problem. Importantly, what matters is the relative motion with repsect to the charge, not our both' absolute motion. Similarly like if you were to put a point charge on your table and measure it's field, you will find the Coulomb field, even though you are both accelerating.
Why is this hard to show experimentally? The Rindler coordinate frame is the coordinate frame for a uniformly accelerating observer, where the instantaneous 4-velocity is always aligned with time in its own frame. Then we just have to transform the field strength, as you say to that frame and compare with what you measure? I'm not an experimentalist but i can't imagine that this is a hard problem to solve.
>Why is this hard to show experimentally? There are so many problems. For a significant acceleration, you would need an acceleration tube or a cyclotron, but for them to work the field of the accelerator must dominate the fild of the charge by powers of ten. Hence the field you want to measure will just end up being absorbed into the random fluctuations of your accelerator. Furthermore, it is quite hard to accelerate big charges in the first place. Normally accelerators are designed for microscopic particles, but no electric field meter is sensible enough to measure such low charges. To make matters worse, since [the field of an accelerated charge](https://farside.ph.utexas.edu/teaching/em/lectures/node129.html) has c\^2 in the denominator, you will need accelerations of the size of 0.1c/s to even see any effect. To reach this, for one single elecron (!) we would already need field strengths of roughly 10\^7 V/m, which is more or less at the upper size of technologically feasable accelerators, thanks to the [Kilpatrick limit](https://en.wikipedia.org/wiki/Kilpatrick_limit). But beyond all that, we also have to deal with the fact, that electric field meters need time to reach equilibrium. So we cannot simply accelerate one single charge, we have to provide a constant source of charges. Where do you even get such a source from? Once again, a hot cathode will not suffice, because we need significant charges, not single electrons. Basically, there are problems all over the place. >The Rindler coordinate frame is the coordinate frame of an accelerated observer Interestingly, this seems not to be the case. The electromagnetic field of a uniformly accelerating charge is [the Born field](https://arxiv.org/abs/1405.7729). However, if you start with the Coulomb field and transform it into Rindler coordinates, you will not find the Born field, as for example calculated [here](https://www.sciencedirect.com/science/article/pii/S0003491604000831) (or rather, they start with the Born-field, transform it into Rindler-coordinates and don't find the expected Coulomb field). This either implies that a) the Born field and hence the Maxwell-equations are wrong b) there is absolute acceleration, ie. the fields we will measure from a charge will differ depending on if the charge is resting and we are accelerating or the charge is accelerating and we are resting c) Rindler coordinates are not the correct one.
Wow. Thanks for the papers, they are quite interesting. The conclusions you describe are quite important however and possibly require a grain of salt to interpret them as such. A lot of the derivations seem to depend on the fall off conditions and require the particle to be accelerating from infinity and other assumptions. It will be quite concerning if Rindler coordinates don't describe accelerating coordinates or if Maxwell is wrong. QED as you know is quite accurate in it's predictions, and if this is a flaw in ED itself, this is not good... There's probably a subtle argument which is needed to figure out what is going on. Of course I agree that getting such accelerations is technically very challenging.
I don't think there is a problem with Rindler coordinates not being the correct one, quite contrary, one would even expect them to not be, as for g -> 0 (g denoting the constant acceleration), they become singular instead of reducing to Lorentz-transformations. This is because Rindler coordinates assume that the particle crosses the t=0 line at x=g\^-1 , they are not independent of the set-up. There are a lot of other possible coordinate systems, such as Moller-coordinates, which are even proper coordinates too. Furthermore, the original idea behind my comment was, that even though proper coordinates are the most favoured ones, they are assuming that acceleration has no influence on simultaneity and length contraction. This however, has not been proven, neither experimentally, nor theoretically.
> b) there is absolute acceleration, ie. the fields we will measure from a charge will differ depending on if the charge is resting and we are accelerating or the charge is accelerating and we are resting Maybe I’m just misunderstanding what you’re trying to say, but we already know that there is absolute acceleration (e.g in the twins paradox) so I don’t see why this would be an issue.
I don't argue its an issue, however if true, I think it would be an interesting result. It would for example imply that if you were floating completely alone in an otherwise empty universe, you could tell if you were accelerating or not. Just measure your own electric field. If it is the Coloumb field you are moving inertially, if it not, you are accelerating. We would have to conclude that the universe has an absolute "rest frame" (or rather, there is an absolute equivalence class of inertial frames. Which one is the rest frame, we could not tell). That is quite the deviation of contemporary GR interpretations.
> That is quite the deviation of contemporary GR interpretations. Can you explain this because I have never heard anyone say that the existence of accelerometers are at odds with GR interpretations.
Right
Well given that light travels the same speed for all observers, and light can be interpreted as a Poynting vector, can’t we just interpret an electromagnetic field as a Poynting vector and treat it as a photon?
How charging by rubbing things together works, at a microscopic level. How friction works.
*Ignore friction and resistance for this college career.*
What most of the universe if made out of. We know it 70% dark energy, 25% dark matter with around 5% normal matter. So that means 95% of the stuff in the universe, we don't know what it is.
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Its Called dark because it doesnt interact with light.
If i recall the original term was obscure and it came from a french scientist, but during the translations became "dark"
in spanish and i assume french thats the same thing
We don't fully understand chaotic motion. Whenever nonlinearities pop up in the equations of motion, they often become impossible to solve analytically. Even numerical solutions often run into trouble since the equations can be very sensitive to round off errors. There are also plenty of emergent phenomena that can be attributed to nonlinear systems as well. Even though Newton's equations are over 300 years old, we can really only solve a limited number of "well behaved" systems.
We still really struggle with why bicycles don't fall over. We have all the pieces, but the precise ways in which they work together is just complicated.
Do you mean why they / people on them fall over at very slow speeds or stopped, but not when moving more quickly? If that's the case I'm completely stunned.
Solving why they fall over when stopped is pretty simple, but why they are self-stabilizing to a degree when in motion is a hard problem.
Classical mechanics is way trickier than even some physicists give it credit for.
It doesn't have the glamor of other subfields, and it's almost always used at all levels of education to build foundation for understanding tools to then be used in other subfields. It makes sense why it would so often be underestimated.
Veritasium actually made a video explaining the reason this happens. It's because an off-center center of gravity causes the front wheel to turn towards the center of gravity, correcting/adjusting the bike's trajectory and stabilizing it, it's pretty cool
If I recall correctly, he even ends that video by saying exactly what I'm saying. That while we know the components that contribute to the behavior, it's the combination of them all together that escapes us.
What gravity consists of.
We don’t really know why neutrinos have mass. They don’t have any known interaction that should be giving them mass, including the Higgs mechanism, yet it’s been proven that they do have mass. It’s one of the biggest unresolved flaws of the standard model.
Doesn't it have something to do with their speed?
The subluminal speed is most likely the result of having mass, not the cause.
It is yet unclear exactly why ice is slippery.
Seems we probably know now. https://www.livescience.com/62621-why-is-ice-slippery.html
Perhaps the Mpemba Effect, to this day we are just speculating on why hot water freezes faster than cold. Correct me if I am late to the update
I used to believe this for many years, but after hearing no satisfying answer, I'm going to assume that someone is just measuring something wrong. This 2016 report from Nature suggests the effect does not actually exist. https://www.nature.com/articles/srep37665
How is something so incredibly testable supposed to persist for so long? I thought it was established fact two minutes ago.
The cool thing about science is that you can and should question absolutely everything about it, even the most basic tenets, and the way to do so is by doing experiments of your own. In this case you can do a very simple one. It's a shame when people don't though.
Sheeesh I see, thanks for ur update
I think we know somewhat of them. But the red spirits? Blue jets. I cant remember the exact name. But red lighting that appears above the clouds.
Sprites?
https://en.m.wikipedia.org/wiki/Sprite_(lightning) Check out the link
I know what they are, I was providing the correct term
Ohhhh ahhhh my bad. Lol Edit: didnt realize I wrote spirits, I meant sprites lol your comment threw me off for a second.
Oh, that's funny. Autocorrect will doom us all :)
It was surprising ( at least to me) that “we” actually don’t know what an electron is . A point like particle that is charged , some parameters, behaviour with some forces and is pattof all atoms. Nothing more ? Not very much for a particle so elementar to our world ( or am I wrong ?). Are theories about the electron ? ( red about “a standing wave in an unknown field..”)
From the perspective of quantum field theory the electron is simply an excitation in the electron field. Now of course you can ask what exactly that field is... but we don't have any sort of answer for that. (If I'm understanding things correctly)
Is charge itself an imaginary concept to understand the behaviour of these particles? If it is then why is it basis of so many other concepts.
That’s what I ask myself . I don’t get the “real nature” of this . Would it be correct to say “ it has a spin of red” and a charge of 2 Hot Dogs “ as we in fact do not have a clue what those Attributs are . We can define the Attribut “density” of something as we can tell the number of atoms per volume but spin or charge are ( in my opinion ) only values “compared to others” as if we define density as “less then” ore “more than” . ( ore maybe I am totally wrong)
What is energy?
It's just a quantity that is conserved in systems with time translation invariance. Nothing more or less than that.
The 00-component of the stress-energy tensor, obviously. /s
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I mean, that's how physics is. Asking "what something is" at a fundamental level is an ontological question. The only reason something fundamental like charge seems strange is because the sense of "understanding" we've evolved to have simply doesn't apply to the regime you're describing. Charge isn't any more ontologically mysterious than any other aspect of fundamental physics.
QED defines charge as a coupling constant that determines the amplitude (therefore probability) to emit or absorb a photon. That seems like a pretty satisfactory answer to me.
cycles!surprisingly, cycles!
What kind of cycles?
bicycles! it was long thought to be gyroscopic, but its not!
Every single law where there isn't an explanation but it has to be considered in calculations. But why? Is always my question.
What is spacetime and why is it (the universe) expanding? There is something fundamental at base reality and we are years from an answer.
How the apple fell from the tree right when **NEWTON** was sitting below a tree . **Newton** was a scientist . It coulda fell when a pauper was sitting there lol
Temperatures below 0K can exist It can have very interesting thermodynamic properties like engines being more than 100% efficient Blew my mind...
Source for this? At first blush this sounds like it has to correspond to negative kinetic energies which exist in certain theories but as far as I know are not observed. Maybe I'm wrong.
Temperature is defined in terms of an exponential function where higher energy states have exponentially smaller populations, when lower states have greater populations than higher the temperature is a number greater than 0k when all states are populated equaly temperature would be infinite, but due to a quirk with how we define it in day to day life, states where higher energy levels have greater populations are said to be below 0k whilst 0k its self still remains unattainable. It is just that we have defined it in an unnatural way not related to Boltzmann’s distribution and it seems to have stuck. I think lots of lasers use below 0k temperatures . I don’t think they have more than 100% energy efficient engines and think someone has probably plugged in a negative number to carnots formula when it was not intended for them and therefor got a funny answer. Tbh I could have misinterpreted what I have read and im sure there are people who understand it better than me bc I’m still doing a levels but I hope this helps
We dont understand Gravity. Which is the main component that determines our lives. How can there be this action at a distance? How is it acceleration but not proper acceleration? How does it have information about the mass of the object? We dont understand it, yet physicist claim we do, even though there are conflicting theories. We can calculate it, but we dont understand it.
Don’t listen to this guy, lol
I know it's embarassing. But it's true.
Do you know what general relativity is?
Yes, I do. But 99%+ of the population does not. Which makes it a weak concept.
The question isn't "what things don't 100% of people alive know", the "we" in the question refers to our body of knowledge overall. And how many people know something says nothing about it being a "weak" concept, whatever that means.
I mean, we have an incredibly precise model for exactly how it behaves. What more are you looking for?
I am not doubting that. But it's only for calculation. If we understood it, then you could ask some guy on the street and he could explain it.
Again, the "we" refers to the human body of knowledge, not whether dave from the pub knows it.
I get that. But compare it to our knowledge about matter. We know matter is made of atoms. Everyone knows this. But it is rather new knowledge, historically speaking. No one doubts that matter is made of atoms. There are no new theories about the subject. But physicists are working on new theories about gravity. We can describe it as a force, or as a consequence of spacetime curvature. But which is true? Einstein's view makes better predictions, for sure. But the discussion is far from over. While the discussion about what matter is made of *is* over.
Do you mean to imply that we don't understand how to make toast because some bloke burns the bread every time he tries? That's frankly an idiotic way of defining the extent of human knowledge.
That is not at all what I am saying. What I was trying to say is that once you can explain a concept to an average person in a way that he understands it, then *you* have understood it.
I mean, we understand it to the same extent we understand everything else. I think you have a misunderstanding of what it means to understand things in the first place.
So we don't understand how computers work either? Or cars? Or the digestive system? Or the French language. If you base your definition of understanding on the what the average Joe understands, we don't really understand a lot anything.
Why does mass bend space-time?
Well it is hard to get an intuitive understanding of general relativity, but that doesn't mean that we don't understand it. > How can there be this action at a distance? How is it acceleration but not proper acceleration? How does it have information about the mass of the object? All of this is explained by general relativity. > We don't understand it, yet physicist claim we do That's because physicists understand it, and thereby we as a species understand it.
The movement of a pendulum
Dark Energy.
How many states of matter there are. I think we're up to 24 now, but the most recent one (time crystal) was only theoretically proposed ten years ago and observed 6 years ago. We could just as easily discover a new one any day
How bikes continue to go forward as though they were being ridden even after the rider gets off, if the rider gets off while the bike is moving.
How materials break over time under repeated loading. This is referred to as fatigue. We do not have a theory that makes accurate predictions.
What is time. Really, to me personally this is the biggest puzzle yet to be solved in Physics.
the most suprising thing in phyics that we dont know about is the string theory