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Would it help if we thhrew out the concept of a 'force' in this context, and said that there are four fundamental interactions ? We don't know the exact nature of these nteactions, but we have various ways of modelling them. None of the models tell us what they are, but they make good predictions where they are applicable.

True, but it's not unreasonable to ask. How unsatisfactory would it be to a end a discussion about whether, or at what age, abortion should be legal, or the legal status of various drugs with 'whatever a court says'. AGI is irrelevant to this particular discussion. DABUS is far from AGI yet its legal personhood is still being discussed, and apparently granted, in some courts. With the development of narrow AI like AlphaFold, which vastly improves previous attempts to model protein folding with implications in drug discovery, these legal discussions will likely (and rightly in my opinion) become more frequent regardless of AGI development. Given the glacial speed of politics and law, starting the discussion before it becomes a pressing matter seems prudent. Regarding AGI, that blog was a bit vague. Here, about 350 ML researchers were surveyed regarding the estimated timeline of human level machine intelligence development. Granted, it might be something like fusion power (another 20 years right?), but it's the most thorough guess i've seen kicking around. I found it incredibly hard to find out anything about the actual architecture of this model. This is the closest i could find - short on detail. I very much doubt it's anywhere near GPT-3, AlphaFold or Tesla's self-driving architecture. Sounds more like a gimmick to start a discussion.

What is gravity? As @MigL and @beecee said, ultimately we don't know. You can model it as force at a distance, à la Newton, but that doesn't work for rapidly changing or relatively strong (stellar) fields. There comes general relativity to the rescue. You can model it as geometry of space-time, but that leads to a couple of problems: 1) Horizons are entropic (they hide information) 2) Gravity is non-renormalisable at arbitrarily strong fields (ultraviolet limit, high-energy collisions), because it's dimensionally bad-behaved. Problem 1) is both conceptual: What is this geometry with an entropy/temperature; what are the hidden degrees of freedom? And it is also wanting in mathematical/logical consistency: Since Hawking we know that black holes must evaporate if gravity is a quantum field, so microscopic information disappears ==> Distinctions between trajectories disappear ==> Predictability vanishes at too fundamental a level. Black holes are so interesting because they are quantum objects and they are general-relativistic objects; so many people hope they will show us eventually what's wrong with the present picture. A very interesting change in the mind frame of physicists took place in the 20th Century: Renormalisation. What is renormalisation? In very general terms, it's the realisation that physical problems look one way or another depending on the scale and the range of phenomena at which you wish to describe things. Consider a wooden stick. What is it? Newtonian mechanics considers it as a rigid body, which is described by 6 real variables --typically the position of its centre of mass and three orientation angles. But what if you want to consider situations like shooting at it, deforming it, breaking it into pieces? (higher energies, changes at small spatial scale). Then your parametrisation is no longer useful, and you need to take into account interatomic interactions. The motto for this loss of innocence is: My parametrisation of the physical system is not the physical system; it's just my parametrisation of the physical system.

This question is for the physicists mainly, I suppose, though there may also be a philosophical element to it. (Mods may wish to relocate the thread as appropriate). I ask as an interested layman. We're routinely told--by scientists--that there are four fundamental forces of nature, one of which is gravity. This is so commonly heard that I assume quotations are unnecessary. Gravity construed as a force seems entirely unproblematic under the erstwhile Newtonian paradigm. But times have moved on . . . Much of the lay reading I've done in this area seems to suggest that general relativity--if read literally--treats gravity not as a force at all; rather, it is to be identified with the curvature/geometry of spacetime. Here are a few examples: - Einstein, "The Meaning of Relativity" - Jeffrey Crelinsten, "Einstein's Jury", p88 - John B. Kogut, "Special Relativity, Electrodynamics, and General Relativity", p198 Would it be accurate to say that contemporary physicists continue to speak of gravity as if it were a force, even though (assuming Einstein got it right) it is not . . . perhaps out of deference to their scientific forebears, or to engender a sense of continuity? Anyway, the question in short: Is gravity a force or not? (In layperson's terms, insofar as possible) Interested to hear any comments. Thanks!

So I have been reading a book about relativity by Paul Davies ("About Time"). In this book he mentions that in order to fully understand the physical (or chemical) properties of heavy atoms such as gold and uranium, one has to take into account that electrons move at relativistic speeds around the nucleus. Additionally he mentions synchroton radiation (which might be not entirely related to my question). My question is that I was under the impression electrons do not actually move around the nucleus at all, but just 'are' at specific locations around a nucleus, based on the probability cloud of electrons in that specific shell. This does not really fit (for me) with what is said about electrons moving at relativistic speeds, as in that view there is no motion at all? He mentions as well that synchroton radiation is at higher frequencies than would be expected from the speed at which electrons orbit the machinery, because they are moving at relativistic speeds and thus the radiation pattern is at a much higher frequency. I am not sure if synchroton electrons also follow the quantum mechanical probability clouds, and thus not sure if this might not be related to my initial question. Could some helpful members show me which assumptions are wrong or provide me with a better way of thinking about these things. I do realise that this also might be a case of where quantum mechanics and relativity don't merge yet, but I don't wanna come to that conclusion yet as it is much more likely I just don't understand the concepts well enough. Kind regards, Dagl

Well, as a wise man once said, "For every complex issue there's a simple answer . . . and it's almost certainly false". Clearly, as other posters (e.g. Studiot) have pointed out, my expecting a simple answer to a deceptively simple, but apparently complex, question was a little overly sanguine. Thanks to all who have contributed. Just a few (no doubt incompetent) thoughts for now: Supposing Jones were asked "What is an aye-aye?" and he responds . . . "The aye-aye is a long-fingered lemur, native to Madagascar with rodent-like teeth that perpetually grow and a special thin middle finger. It is the world's largest nocturnal primate." No doubt there are many things Jones does not know about aye-ayes, indeed, doubtless there are many things about aye-ayes unknown to anyone. Nonetheless, is it not reasonable to say that Jones has answered the question, that Jones knows what an aye-aye is? Even supposing he is quite wrong, he has still given an answer to the question; he has attempted to answer the question. Now, certain posters (e.g. Swansont) have expressed the opinion that science cannot answer the question "What is gravity - really?" on the grounds that it's metaphysical. First of all, how metaphysics is to be demarcated from physics, or simply science in general, remains obscure, assuming it can be done at all. Perhaps the most celebrated attempt to do so was from the logical positivists armed with their 'verifiability criterion of meaning' (that which cannot be verified constitutes metaphysics and is literally meaningless). The project failed for reasons that needn't be rehearsed here. But let's suppose, for the sake of argument, it is a metaphysical question. Why should that preclude science (à la Jones), whether right or wrong, from providing an answer to the question? The existence and nature of atoms, say, might well have been regarded as a metaphysical question once. Science now tells us a great deal about atoms, even if not all their properties are known, à la Jones once again with his incomplete knowledge of aye-ayes. It seems to me that the Newtonian realist (not necessarily the great man himself) of yesteryear who pronounced that "Gravity is an attractive force which acts instantaneously over any distance . . . etc., etc." is answering the question "What is gravity?" even if her answer is no longer widely accepted nowadays. Similarly, the GR realist of today who asserts "Gravity is the curvature of spacetime. It increases around massive bodies . . . etc., etc." is answering the question "What is gravity?" Finally, I think we must recognize that scientists are a heterogeneous bunch; they do not all speak with one voice. Of course there are scientists of a more antirealist (positivist, instrumentalist, empiricist, William Tell, whateverist) persuasion who echo sentiments expressed by certain contributors here to the effect that science is not in the business of telling us what gravity is, science just constructs models which more or less save the phenomena, just shut up and calculate, etc., etc. Not all scientists feel this way. Many--those of a more realist bent--feel it is the business of science to answer such questions; it is the business of science to provide us with a complete and faithful representation of reality. (cf. "One can’t affirm that GR is reality, only that it models observed behavior very well." - Swansont) I leave you with the arch-realist himself . . . -- Albert Einstein, "Reply to Criticisms"

I'm assuming flat spacetime (no mass, SR only), and inertial motion unless specified. Generally yes. Also "when are you talking about?" matters and is more complicated than a Newtonian description. The positions of things on a map are coordinates within a coordinate system, and those are different for different observers. You could have a map where the Milky Way is at a fixed location and Andromeda is moving, or one where Andromeda is fixed and the Milky Way is moving. Those correspond to the coordinate systems of 2 observers at rest in the respective galaxies. Yes, the distance to the star is different in the different frames of reference. There are invariant measures of distance, eg. the "proper length" of a 1 m stick at rest is always 1 m and everyone will agree on that, even if the stick is moving relative to some observer and is length-contracted ie. has a coordinate length less than a meter in that observer's coordinates. We can say that. We can measure the distances to both galaxies using one frame of reference (eg. the one in which we're at rest), and you can measure the motion of objects using the coordinates of that frame. Consider the map analogy. The spatial coordinates can be represented by a grid drawn on the map. The same grid coordinates can be shown by putting a lattice of rulers throughout space. In our own frame of reference, our rulers are not moving and so they don't length-contract. An object light years away can wobble at speeds near c, but yet stay near one place in the grid of rulers. Meanwhile, that distant wobbling object is moving relative to our lattice of rulers, and our rulers do length-contract, in its frame of reference. For simplicity consider two different inertial frames of reference F1 and F2 that the wobbling object switches between. Each of those frames has its own set of rulers making up a lattice throughout space, each at rest and not length-contracted in its own rest frame. Say I'm at 1 LY from Earth, as measured by Earth, and I'm wobbling relative to Earth. I stay near the 1 LY mark on Earth's set of rulers, but those rulers are contracted by different amounts in F1 vs F2. For example, in F1 Earth might be 0.8 LY away from me and the 1 LY mark, and only 0.6 LY away in F2's frame. The reason that the distance as measured by Earth isn't changing much, and the distance measured by me is changing drastically, is that I'm switching between different frames of reference. The distance between Earth and the 1 LY mark, which has a proper distance of 1 LY, is length-contracted by different amounts to different observers, depending on their relative speed.

No, I made no mention of speed. There are relativistic corrections to the energy. Synchrotrons are classical and you can talk about the speed of the electrons. No, but you don’t know the speed. The explanations talking about this are making an invalid connection, using a classical equation/concept where it’s not valid https://en.wikipedia.org/wiki/Klein–Gordon_equation#Derivation

Reading online seems like chosen to harmonize for safety purposes and that those particular colors were selected due to color blindness concerns. Could still do it of course. Think UK plugs are already unique with the fuses so may not be that big a deal in terms of cost/Market size.

I think you are conflating mask use in a controlled manner (e.g. hospital, labs) where folks are trained and follow protocol for mas use. Unfortunately that is not the case with the broader population and it has been shown how masks of different materials have different levels of theoretical protection. That being said wearing any mask is better than not wearing. To look at the effectiveness of masks to prevent infected persons to infect others is based on simple maths. In a situation where an unmasked person is present the room can fill up with infectious particles, if even one badly masked or unmasked person comes in (or takes their mask off) there is a high risk of infection. If conversely the infected wears a mask (source control as described in the link you provided) the risk for the badly or unmasked person drops. In a controlled situation you can ensure that everyone wears PPE properly. In a public space situation, you generally cannot control that and it really just takes a few minutes in any space to identify a few who do not wear masks properly (if at all, given lifting of masking mandates).

Must you resort to arguing against strawmen? Zapatos obviously suggested nothing of the sort. It's a shame you feel the need to move the goalposts so completely in order to defend your stance.

First, welcome @Davy_Jones, who I know as another contributor of my now-defunct sciencechatforum. While I agree that the whole question of what forces and fields really are crosses into the land of metaphysics, I am also one who wonders at how tenuous our grasp of what gravity is. If we're allowed to free-fall in a gravitational field, then we don't experience a force. We only experience a force when we land on something and our body's atom's outer electrons experience electrostatic forces from, say, a chair's outer electrons. Without that repulsive force, we would just continue our freefall through the chair, the floor, the earth's crust and so on along a space-time geodesic. (and be in pretty bad shape, no doubt?) So, is gravity then construed there as a pseudoforce? Were we only following a line of curved space until a real electrostatic force made itself known to us? It's in such perspectives that gravitons seem especially incoherent as anything but a math toy. John Wheeler always comes to mind... "Spacetime tells matter how to move; matter tells spacetime how to curve." From a meta perspective, it's awfully hard to say what this "telling" process is.

I believe the crux of any disagreement we may have here resides in the fact that you're thinking of computers in the 1970s, and I'm saying we've come a very long way in the 50 years since then such that these simplistic assertions are no longer quite as valid as you propose. Rather like humans is the core of my counter-proposal. We're simply running similar programs on wet computers. In short, I am suggesting you're making a distinction without a difference. If a corporation can be human in our laws, then likely so too can AIs. There's precedent here. I refer you here to please go review the insular cortex, the anterior cingulate cortex, and the medial prefrontal cortex. You're welcome. How else would you describe the way action potentials are triggered across the nervous system only after sufficient build-up of potassium and sodium ions? Once enough of those elements have come together in the plasma membrane within the hillock, a threshold is crossed and the axon depolarizes. I readily acknowledge there are many crucial differences between our minds and digital computers, but the lack of bit flipping and registration of electrical signals is not IMO one of them. I suggested that we're just flipping sodium and potassium channels on a biological substrate. That has been very well understood and well evidenced for several decades now. Will you kindly please clarify which specific part of this you believe has "no evidence" and which is "just not true?" Of all the claims I made, this one is perhaps the best supported, yet this is the one you've chosen to cast aside with the brush of a hand as blanketly untrue, and that rather confuses me. I welcome clarification of your dismissal. Here I'm going to go so far as to say you're arguing against a strawman. I don't believe it's intentional, but I do believe your comments suggest a deep ignorance of the last several decades of research into neurobiology and function, or at the very least an overconfidence in your own seemingly limited understanding of this space. Here yet again, I must dismiss this as quite obviously untrue to the point of being a strawman... it doesn't even raise to status of hyperbole. It's just false. It's fine for you to hold this opinion, but I believe your opinion is not representative of reality on this particular point. Agreed. Thanks for the cordial exchange and intelligent discussion thus far. It's always appreciated. Let's also remind ourselves to be cognizant of the OPs intention for this thread and hopefully we don't hijack it with this interesting aside.

This is a very interesting question and much like you Davy-Jones the nature of what gravity is, rather than how it is modelled, is one that I often ponder. Interestingly in QM gravity is modelled as a force; "In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity" So which is it, the curvature of space time or the exchange of particles between masses, or a field in which mass interacts?

Wave functions of stationary states work pretty much as the density/current of a stationary fluid. Consider the flow lines of a fluid in a stationary flow state. At every point in the fluid, the velocity field is well defined, has a direction and a speed, even though nothing seems to be moving on the whole. More mathematically: If your stationary state is represented by wave function \( \psi_{n,l,m,s}\left(\boldsymbol{x},t\right)=e^{-iE_{n,l,m,s}t/\hbar}\Psi_{n,l,m,s}\left(\boldsymbol{x}\right) \), your 'cloud' of probability would be independent of the time-varying phase factor: \[ \varrho\left(\boldsymbol{x}\right)=\left|\Psi_{n,l,m,s}\left(\boldsymbol{x}\right)\right|^{2} \] The whole situation would be static, and yet, it would have an associated velocity field, which mathematically is given by the Fourier transform of the amplitude, \[ \hat{\psi}_{n,l,m,s}\left(\boldsymbol{p},t\right)=\frac{1}{\left(2\pi\hbar\right)^{3/2}}\int d^{3}xe^{i\boldsymbol{p}\cdot\boldsymbol{x}/\hbar}e^{-iE_{n,l,m,s}t/\hbar}\Psi_{n,l,m,s}\left(\boldsymbol{x}\right)=e^{-iE_{n,l,m,s}t/\hbar}\hat{\Psi}_{n,l,m,s}\left(\boldsymbol{p}\right) \] So the distribution in momenta doesn't depend on time either: \[ \varrho\left(\boldsymbol{p}\right)=\left|\hat{\Psi}_{n,l,m,s}\left(\boldsymbol{p}\right)\right|^{2} \] This is only valid for stationary states. I hope that answers your question. It's good to see you around.

What is gravity, really ? Short answer; we don't know. We know how it behaves in most circumstances ( not hi energy/small separations ), and our most accurate model, Einstein's GR, is a field'model where geometry is the 'field'. in general, all of the effects that you have termed 'forces', where "material points move under the influence of forces acting between them" have been given the field model treatment, such that we have field theories for Electrodynamics ( QED ) and the color interaction ( QCD ). It is more the case, that our description of the effect's behaviour, can be modelled in different ways, sometimes with equivalent accuracy,sometimes nearly equivalent accuracy, as in Newtonian vs GR.

Maybe for you…

Second that. Wow. Instrumental breaks were outstanding. Though maybe bring the piano break up a little in the mix -- didn't need quite so much rhythm section right there. And agree with @swansont the Dead cover of Good Lovin really thrives with their unique sound. You people are going to have me in a tie-dye and ponytail, if this keeps up.

Internal. You’d still have a self-identity even if you’d never met another being in your entire life. Also, you don’t know what other people think of you. You only have your own filtered version of what you think they think about you. Keep in mind self identities evolve. How we see ourselves changes with experience and we have incredible power to author who we wish to be… at least to ourselves.

Everyone makes mistakes. You were honest enough to admit it. That makes you one of the good guys.

I'm not sure I understand what you are getting at here. Surely solenoids are beyond grade 10 ? Yes as the length of wire making the solenoid increases so will the resistance (I think that is grade 10) but the resistance of winding wire in any coil is generally insignificant compared to the magnetic effect causing an opposition to change of current, which is called reactance. I don't think reactance comes into it until later grades, but I will explain if you wish. Swansont mentioned that each turn or loop of the coil adds to this effect so the number of coils is significant. This is rather like (but not exactly the same as) the force that can be generated by a pressure depends upon the area the pressure acts over. The larger the area the greater the force a given pressure will generate. You have probably done something like this in mechanics with say the principle of the hydraulic lift

I think I speak for most everyone here when I say that intellectual honesty is high up there; above erudition or any similar razzle-dazzle. +1.

The voltage generated is proportional to the number of turns. Every loop counts toward the area that is experiencing the changing magnetic field. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html The reason for more turns depends on the application. The voltage might be the important factor. You might be using the solenoid to create a magnetic field by supplying it with current, and a longer solenoid has a more uniform field inside of it. You could be current-limited but not voltage-limited, and want a stronger field.

Holy crap! That is the best thing I've seen posted in this thread in a long time! Thanks for sharing!!!!

There is no threshold.

When you have two opposing forces clearly the stronger one will 'win', regardless of how the forces are generated. The Magdeburg Hemispheres is a famous experiment to demonstrate this. https://en.wikipedia.org/wiki/Magdeburg_hemispheres Clearly the atmouspheric pressure force will win until Guerike harnesses enough horses. Then the horses will win. Similarly a given gravitational force can be stronger than, weaker than or even equal to a given electromagnetic force.

I'm not much of a Philosopher, but this is a Science Forum, and I do know some Quantum Mechanics ... Quantum Mechanics, which does describe all of existence, says wave functions are 'unsubstantiated' and 'remain imaginings' until observations/interactions collapse the wave function to become 'actual' and 'observable'. By your definition, that makes much of the universe unsubstantiated, and simply, imagined, yet it has an effect on us. That seems very different to Studiot's unsustantiated, future grandkids, which have no effect on him till realized. You may want to re-think your definitions.

But requiring everyone in a venue to wear a mask protects everyone, including me. By wearing it in public, I'm not just protecting myself and possibly others, I'm also encouraging the practice of safety in general. People are more likely to comply if they see others doing it.

Can you provide a more specific reference than “some people”? Pretty much all matter (in the form of hydrogen and some helium) was formed early in the Big Bang. That is the “one source” and why matter is evenly distributed throughout the universe

Unfortunately, it’s likely not far from now…. I read an article by IPCC that by 2040, there will be a disaster. With the extreme droughts, wildfires, floods and hurricanes that’s occurring more nowadays. To avoid that, scientists stated that we have to reduce global carbon emissions by 40 percent by 2030.

GR tells us that when a sufficiently large enough star uses its available fuel, it will go S/Nova and the remnant turn into a BH...GR tells us that this happens because once the Schwarzchild radius is reach [equal to the EH] further collapse is compulsory, at least up to the quantum level where GR fails us. Also the BB is the evolution of space/time/universe from t+10-43 seconds. Anything before that, or anything at and beyond the quantum/Planck level of a BH, can only ever be speculated on. Some of that speculative talk revolves around our BB being the arse end of a BH in another universe, and BH's in our spacetime, leading to ERB's/wormholes and other universes. Wormholes while predicted in the maths of GR have never been realized, and WH's [white holes] are as far as I know, also in the same boat, with even less speculations about their possibilities. Here is an interesting rundown here...... http://curious.astro.cornell.edu/physics/89-the-universe/black-holes-and-quasars/theoretical-questions/425-what-is-a-white-hole-advanced

So neurobiology occurs without a brain? Without a functioning brain? Sure, stand without a functioning brain, see how long that lasts. Name one thing that is self-creating, ie created itself.

He stated something that is factually not true, reflexes do not happen without a functioning brain. I pointed out the fact that functioning brains are needed for any action to occur. In my mind, all your examples refer to a dead frog having electrodes attached to it to make it move without a functioning brain, without a thought behind that functioning brain. You are going to have to give me better examples than that. Perhaps actions, standing, breathing, etc.,are the something coming from nothing completely detached from all reason, all causation. That’s your goalpost just so you understand. Ideas aren’t needed for intelligence and intelligence isn't needed for a complex system, nor is intelligence needed for interacting complex systems...unthinkable. lol

Intelligence has always existed, eternal, imagining, creating, but limited and imperfect. My logic is simple, based on observations completely void of logical fallacies, paradoxes, and impossible theories never to be resolved. I am not a member of any religion, but I can accept how I live on this smaller Earth scale then turn and apply it to the largest scale possible, Existence.

Let’s agree to disagree. People stand brainless, thoughtless, without any consciousness at all. You win. Makes perfect sense. Science is wrong however you argue on behalf of science, your prerogative. Science has never been wrong before, right? Time waster for me since it lacks the basic logic that equals existence. Causation. Without the idea of an eyelid, an eye, a puff of smoke, without those ideas, non-existence would be the actual rather than its antithesis existence. Everything is an idea, came from an idea, formed by intelligence, not necessarily any religious intelligence, simply intelligence...an intelligent energy which is one of a kind, eternal, imperfect, limited, etc. My philosophy is based off of observed reality, not all those never to be proven scientific theories which are pure numeric speculations not based on a limited nature(natural laws), not based on causation(but rather “magic”), not accounting for imperfections in any provable way(chaos is fantasy). What is imperfect order? Our 4-D dimension. Imperfect but all is ordered. Not incomprehensible.