That approach has never really done it for me, because what makes it seem impressive is that the magnet is so much smaller than the planet. If you made the planet more dense, it would be smaller, making the comparison less impressive. Squeeze the planet all the way down to a black hole, and it would be about the size of the magnet.
I think it works better to think of it in terms of the minimum force you can get. Imagine two test masses a fixed distance apart. The minimum non-zero electromagnetic force you can get between those two test masses is the force you get if each test mass has a charge equal to that of an electron.
I'm not sure what the lowest mass particle is that you could reasonably hold near a test point, but since you can reasonably confine an electron to a small region the gravitational force between two electrons is an upper bound on the minimum gravitational force, and that is a ridiculous number of orders of magnitude lower than the minimum electromagnetic force.
The ratio of the electric force to the gravitational force for two protons is a good way to get a numerical feel, but the intuitive "aha!" is what the demos are trying to help with.
There's a similar demo for showing the strength of atmospheric pressure. You can boil a little water in a soda can, and quickly invert it into a little bowl of water. The water vapor inside quickly condenses causing a startling implosion of the can. It gives an intuitive feel for what 1 atm actually is.
You think of astronauts going to where they have to counteract that pressure, and what would happen on failure, and you think "holy shit." Then you think of James Cameron going to where the pressure is 1000 times as great, and what would happen on failure, and you think "holy fucking shit!!"
> Then you think of James Cameron going to where the pressure is 1000 times as great, and what would happen on failure, and you think "holy fucking shit!!"
Indeed, see Byford Dolphin diving bell accident (very NSFW/NSFL):
You need to squeeze the earth to a much smaller size than that of a fridge magnet to make it into a blackhole and even then you'll get a blackhole with a pull of 1g which would be like a cute puppy.
That's a confusing way to look at things. Lets make the two scenarios more similar.
Say "earth" is a sphere with radius 1 meter and you're 1 meter away. And that puny magnet defeats its gravitational pull in the same way it defeats earth. How heavy would our sphere have to be in order to have the same pull as earth if it has a radius of 1 meter and our magnet is 1 meter away?
If you remember Newton's law of gravitation the force an object will feel looks like: F=Gm/r^2. G is small, 10^-11 Nm^2/kg^2, m is the mass of earth 10^24 kg, r is normally 10^6 m (the radius of the earth). Plug in these numbers you get 10 m/s^2. The real answer is closer to 9.8, but we're looking for the order of magnitude here. We're still remarkably close for how much rounding we did.
How lets say that we're now 1 meter away. How heavy would the mass have to be to still pull with 10m/s^2, which we know our magnet can defeat. (10^6)^2 ~> 10^12 so we have to be 10^24/10^12 ~> 10^12 kg.
So to defeat a tiny magnet 1 meter away you need 10^12kg. Lets pretend our mass is a cube whose volume is 1m^3. That's 10^12kg/m^3. The center of the sun has a density of 10^5kg/m^3. This is 10^7 times denser! We're lucky that our sphere is far too light by many orders of magnitude to collapse into a black hole (maybe not so lucky because it's going to explode immediately!) but it's even denser than a white dwarf. This is on the order of the mass of Mt. Everest (this is a very rough and unprincipled comparison and when you unpack it can mean many different things, but it's something easy to visualize).
So you can see. Gravity is indeed insanely weak. A magnet can defeat Mt. Everest.
That the comment as a whole is confusing doesn't matter.
The point is that you should use something human-scale to show off the strength of gravity.
So if you want a fridge-sized block that can hold things with gravity like a normal fridge holds a magnet, how heavy does it have to be? As heavy as an entire mountain.
The magnet is also incredibly weak compared to what it could be. As it happens, the most recent "What If" from xkcd describes the difference in a more equal manner: http://what-if.xkcd.com/140/
One difference between gravity and electromagnetism is that there are positive and negative charges in electromagnetism, that tend to cancel each other out over large distances.
I don't think this is the thing that the theoreticians are looking for (no Nobel Prize for me), but it is a unique feature of gravity that gravity has only one polarity. And I don't remember how this goes with the strong and weak forces.
The inflation models of the universe actually depend on repulsive gravitational force, but it requires a very specific set of circumstances for it to happen.
IIRC a MIT professor says something similar. After rubbing a glass rod and lifting a piece of paper he asked is it a small or big force ? and then proceed to explain that the rod pulls more than a whole planet.
Conceptually and per unit measurement the force of gravity is many orders of magnitude weaker than the force of electromagnetism. No argument there.
But that's just not the way the force of gravity is thought about by humans, because the gravitational effect is so small as to be undetectable between human-scaled bodies. So we attribute gravity to more massive things, and consider it only en masse, never divisibly.
To the extent that the gravitational force of the earth has measurable effects on more things than the electromagnetic force of the refrigerator magnet, it is more...spread out. More distributed. More diffused.
It follows the same inverse square law as everything else, but it does a lot more of it, over human-scaled distances.
And this is how high school physics teachers can be counterintuitively correct, but I think the takeaway is more about how hopeless humans are at conceptualizing very large numbers than about physics.
So if people are bad at it, then why make it worse by using an incorrect word?
Also the magnetic force in a physical object does not follow inverse square, it's more like inverse of the 5th root (because there are no magnetic monopoles the two fields cancel out very quickly at distance).
So if anything the magnetic force is more diffuse than gravity since it fades out so quickly.
So if anything the magnetic force is less diffuse than gravity since it's concentrated right near the object.
The fact that both of those sentences are correct tells you quite definitively that diffuse is very very much an incorrect word.
Well, I'd argue that sentence one is incorrect. Things that fade out quickly are less diffuse, though more fully diffused when measured at the same distance.
Gravitational force is both much weaker and (for that of large bodies) diffused over a much greater area than electromagnetic force (of very small bodies). These are the circumstances of the example comparison.
"More diffuse" vs. "more greatly diffused" appears to be our disconnect here. Something which is "more diffuse" is expected to be less measurable at a single point, all other variables controlled. This is true of gravity but not for the reasons implied.
Nevertheless, if the total gravitational force of the relevant object from the example (earth) was concentrated into the same area as the total EM force of the magnet, we would have a black hole in our kitchen. Fortunately, that gravitational force is diffused over much a larger area.
Things which are more diffuse are necessarily diffused over a larger area. Not all things which are diffused over a larger area are necessarily more diffuse.
I see the hangup, and I appreciate your objection.
Edit: and thank you for the EM force inverse power law correction. I was using distant memories of the math for EM radiation, which is obviously different. But if those numbers are right, it supports the argument that gravitational force is less concentrated...and therefore more diffuse, does it not?
> Gravitational force is both much weaker and (for that of large bodies) diffused over a much greater area than electromagnetic force (of very small bodies).
No, that is simply not true. Not at all. You keep saying this, and it keeps being not true.
I don't really know how else to say it to you. You have a mistake in your intuition.
> Nevertheless, if the total gravitational force of the relevant object from the example (earth) was concentrated into the same area as the total EM force of the magnet, we would have a black hole in our kitchen.
No! That is not true. If you turned the earth into a black hole, and placed that black hole in the center of where the earth used to be, you would notice NOTHING whatsoever in your kitchen. NOTHING. You could not tell the difference.
> Things which are more diffuse are necessarily diffused over a larger area.
And gravity is NOT diffused over a larger area than electric charge.
If you had enough electric charge to pull on you (assuming you were of opposite charge, at the same ratio as your mass vs earth mass) placed in the center of the earth it would act IDENTICALLY to gravity. And that charge would be very small, much much smaller than gravity, because gravity is WEAKER than the electric force. NOT because it is more diffuse.
> Edit: and thank you for the EM force inverse power law correction. I was using distant memories of the math for EM radiation, which is obviously different.
Not EM force. Magnets with two poles. EM force is the regular inverse square.
> But if those numbers are right, it supports the argument that gravitational force is less concentrated...and therefore more diffuse, does it not?
No it does not. It just means you have two opposite magnets that cancel each other out at a distance. If it were electric charge, which is a monopole, it would not happen.
I'm really struggling to understand how you're not following my meaning here. I will take just one point, because it's probably adequate to cover the entire disconnect.
I wrote:
> Gravitational force is both much weaker and (for that of large bodies) diffused over a much greater area than electromagnetic force (of very small bodies).
I mean:
- *the* gravitational force is much weaker than
*the* electromagnetic force
- large bodies (earth sized) have more *gross*
gravitational force than refrigerator magnets
have *gross* EM force.
- the gravitational force of an earth sized body
extends, in the realm of practicality, much
farther than the EM force of a refrigerator
magnet. In fact both extend into infinity, but
that's only interesting in the theoretical sense.
Are any of those statements incorrect? If so, you're right and my intuition and everything else is wrong. If not, then I think we're talking past each other, and I apologize for the confusion.
> If so, you're right and my intuition and everything else is wrong.
The reason you think this way is because magnets fall off by the power of 5 (approximately, it's not a specific number, but depends on the geometry of the magnet), because of the two poles.
If on the other hand you played around with charged objects (which are monopoles like gravity) your intuition would work better for this. But unlike magnets highly charged objects are not commonly found around the house.
----------
Also the second one is debatable - the acceleration of one magnet to another is higher that the acceleration of an object falling on earth.
Even a lightly charged object can accelerate another object at greater than what the earth can manage.
The reason I use acceleration to measure gross force is because gravity (and charge) depend on the product of the two objects and distance - the only single number you can assign a single object is acceleration and even that depends on distance.
I still think I am not explaining myself clearly enough.
When I say gross force, I mean the sum total of all relevant force exerted by the object. So the gross gravitational force of the earth is strong enough to hold the moon in orbit, but clearly the magnet has no such ...strength.
Now obviously (I shouldn't use that word!) in the case of massive bodies like earths and moons, there's a more complex interaction going on than a one-sided force. But there's a total magnitude of force that just doesn't exist in the magnet.
A lit match burns paper more readily than the sun, but clearly the sun distributes a larger amount of gross energy over a wider area than does a match.
> Even a lightly charged object can accelerate another object at greater than what the earth can manage
Ack. Considering acceleration without mass is no way to properly reason about force! Surely I remember that much, at least.
Regardless, I will desist and defer. Though I do wish I felt that I now understood something more clearly than I did before. :(
> When I say gross force, I mean the sum total of all relevant force exerted by the object.
There is no such concept. Really. I promise you, there is no such concept! The amount of force it exerts simply depends on who is close to it, rather than any property of the Earth. Like, if the moon was not there would you say the total of all relevant force is lower? But nothing changed on the Earth. So this concept does not apply to the Earth, rather it applies to the specific situation.
I do get what you are trying to say, but it's just not correct. The force depends on the specific setup of where the bodies are, not an intrinsic property of Gravity, or the Earth.
> So the gross gravitational force of the earth is strong enough to hold the moon in orbit, but clearly the magnet has no such ...strength.
Only because it is small, it would not take much charge to hold the moon. I did the math for you - it would take about 3 tons worth of electrons to hold the moon. That's it - about 1 car worth. (If you could somehow keep all those electrons in one place, which you can't.) Walk outside and look at a car - if it was replaced with equivalent mass of electrons it would be enough to hold the moon (if the moon had some extra protons on it). I mean you can push a car, that's how little mass it is, yet it's enough to hold something as heavy as the moon.
Another way to look at it is if you took 1 electron away from every grain of sand sized piece of the earth - just one single electron, the resulting charge would be enough to hold the moon. (And give one extra electron to every grain of sand sized piece of the moon.) Charging a grain of sand with one extra electron is nothing, it's a minuscule amount, it's too low to even measure.
> Ack. Considering acceleration without mass is no way to properly reason about force!
The nice thing about gravity is that it's invariant to mass since the force goes up right along with the mass. If you scale the charge of the object together with the mass then the acceleration of a charged object will also be invariant to mass.
i.e. if you made the magnet bigger (heavier) it would also be more magnetic, so the acceleration would stay the same (more or less).
> Regardless, I will desist and defer.
It's OK, I don't mind the conversation.
> Though I do wish I felt that I now understood something more clearly than I did before. :(
Remember that we started with you saying gravity is diffuse and electromagnetism is concentrated. All I did is try to show you that that is not a good way to look at it.
Your efforts are appreciated, and I'm sure you're correct in all you say, but I can't escape the feeling that we're talking about different things.
I readily concede that "diffuse" has ambiguous meaning and therefore a poor choice, however.
Beyond that, I don't think what I'm saying is any more complicated or controversial than the example of the match and the sun.
My attempts to clarify have revealed further gaps in my precision of phrasing, but your explanations haven't identified any specific points of confusion for me. I'm sure that says more about my comprehension than about your explanations.
We're now in open battle with HN's anti-dialogue margin creep -- and we know who wins that battle, every time -- so I'll take my distant memories of undergrad mechanics and E&M, mark the page dirty, invalidate the cache, etc.
Thanks again for your efforts, they're not as wasted as they appear.
if a tiny piece of metal is on an orbit with an equal distance between earth and a tiny fridge magnet will the tiny fridge magnet really affect that metal more than the earth does?
If I hold a tiny magnet 5 feet above the piece of metal, and the earth is 5 feet below the piece of metal. in which direction will the piece of metal move. In other words while I don't think my examples are any great ones, I don't think the example you're quoting really makes much sense either.
On Preview: I see there's an explanation for why being far away from the magnet makes the magnet have less effect than being far away from a gravitational object https://news.ycombinator.com/item?id=10727977
Most likey, it would be able to do this. If you can place the fridge on a surface parallel to the ground, it should stay there (depends on the fridge magnet, but you get the gist)
That is correct, but only because of the particular position of the fridge magnet. The firction force from the magnet on the surface < magnetic pull(not always true, depends on the type of material the firdge and magnet is made of, but very likely true). Thus, if you put the magnet suspended on a horizontal surface, the magnetic force WOULD be the one holding it up.
It might sound silly, but isn't it like asking why blue is blue?
If Gravity is a fundamental force, isn't it like a mathematical axiom? We can't really prove or explain it, it's just the basis for all the other rules.
Electricity and magnetism used to be considered separate phenomena, but then they were found to be two aspects of a single electromagnetic force.
Electromagnetism and the weak force used to be considered separate phenomena, but then they were found to be two aspects of a single electroweak force.
Progress can't be made if we just accept everything as-is and don't investigate more deeply.
Agreed, and the interesting fundamental thing we discover this year sometimes has practical applications 30 years down the line.
The semi-conductor wouldn't have existed except for such fundamental work in prior decades.
I dislike the "well, that's just the way it is" response to our not understanding something (as do fortunately the smarter people than me scientists!).
I think what grandparent means is that the question in the title is odd, I thought the same thing, maybe the article explains it bit bit otherwise this seems based on a perception and thus noto really more interesting than, say, why is 3 larger than 2.
The question is valid, but it is phrased the way a two-year-old would ask it. Better phrasing would be: is there some reason to gravity being so weak compared to the other forces?
It turns out if you start with "sky is blue", and keep looking up answers to all the ensuing "but why?" questions, soon you will learn a lot about (in no particular order): Rayleigh scattering, tri- and tetra-chromatism, phenomenology of perception, blindsight, electromagnetic radiation, black body radiation, nuclear fusion, etc. etc, the rabbit hole goes deep. Sometimes stupid questions have really profound and unobvious answers.
It's suboptimal that you get down votes for asking an honest question hoping to understand better. I think replies to your question will give a fair number of people a better understanding of the issues.
It is not silly. The only reason life exists is because gravity is so weak. So it is better if we are able to know more about it.
My favorite pet theory - was watching some of the superstructures of the universe - and was thinking how much the light matter represents the protein structure of a foam or a gel. The question is what is the filling since there is the vast bulk of the space in the universe.
"Blue" is just a name for a particular range of wavelengths of light. Those are "blue" by definition. The "why" is because we declared it so.
The gravitational constant is not set by definition. The reason for its value, and the reason why this value is such that the force is so weak, is not known.
It could just be arbitrary, but nobody knows. And even if it is arbitrary, it's a completely different arbitrary from how "blue" is arbitrary.
It's not that it's a problem but it's "The Greatest Unsolved Problem" in the article words or an interesting one at any rate. We understand why the sky is blue - diffraction of the shorter wavelengths. If that was unsolved it would be a cool unsolved problem too.
A related issue is "If electricity and magnetism are so strong, why do we feel the effects of gravity more?"
To see why this is the case, let's look at magnetism first. Every magnet is composed of a north pole and a south pole. If you split a magnet in two, you get two magnets, each with a north pole and a south pole. You never get a magnet with more "north" charges than "south".
This means that the "north" and "south" portions of the field right are always next to each other. Which also means that when you go very far from a magnet, the net effect of the magnet is zero. Because the two fields cancel each other out.
So we should expect that magnetism doesn't have many practical impacts on our daily life. If you're close to a magnet, you might feel it. But if you're far away, you won't be able to feel a magnetic field.
Electricity is a bit different. The positive and negative charges can be separated from one another, unlike magnetism.
This means that when electrical charges are separated, there is a force pulling them together for differing charges, or separating them for similar charges. The net effect over time is that most objects should be electrically neutral. Because the charges will naturally come together.
So we should expect that electricity has an impact on our daily life. We should be able to tell when the charges are separated. This occurs only for a short time, until the charges move and cancel each other out.
Gravity is different again. There is no "positive" and "negative" charges with gravity. It's all positive.
This means that when two gravitational bodies are separated, there will be a force pulling them together. The net effect is that all objects with "gravitational charge" will tend to clump together.
So we should expect that gravity has a huge impact on our lives. We should always be able to tell that gravity exists.
Note that these conclusions are independent of the relative strengths of the forces. Magnetism and electricity will generally have net zero impact. Gravity will have net positive impact.
If gravity was strong, like the other forces, then gravitational objects would group together. A lot. Which means that the universe would end up as one big clump of matter.
It's only because gravity is weak that we have gravitational objects which are separate from each other for any extended period of time.
I'm not sure why physicists think gravity is a force and Pauling exclusion principle isn't.
Gravity is fake "inertial" force caused by shape of the space time. Why do they insist that it should have gravitons when everything so far show it doesn't fit quantum field models?
>I'm not sure why physicists think gravity is a force and Pauling exclusion principle isn't.
>Gravity is fake "inertial" force caused by shape of the space time.
Because all forces are like that? Electromagnetism is just a force created by the shape of the electromagnetic gauge field.
In mathematical terms: it is the curvature of the gauge connection. In exactly the same way that gravity is a force created by the curvature of the metric connection.
Space-time is the environment that matter moves through. Curvatures in spacetime affects how matter moves.
What is the electromagnetic gauge field? Why does it only affect charged particles? Why does it affect particles differently depending on the type of charge they hold (positive/negative)?
It doesn't seem to be the same thing as spacetime.
Given the nature of this subject not all your questions have definitive answers, but I'll try to give it my best shot. You should probably consider these answers a subjective interpretation, rather than objective facts.
The most consistent interpretation of QFT I've seen so far views gauge fields as principal bundles. This implies that matter not only propagate through space-time but also through the gauge field, and the way it is 'changed' as it passes through the gauge field is related to the charge.
Now technically the electromagnetic gauge field (and others) also affects uncharged particles, mainly because it couples to gravity, but perhaps also in more subtle ways (think of the way light can be affected by simply passing through a piece of matter).
Admittedly there are quite a few differences (since the metric has a somewhat special position) but there are also quite a few similarities. Unfortunately nobody has yet found a (testable) theory that either unifies the forces or can treat the separately. I'm placing my bets on the 'unification' side though.
> It is not a force, since at the particle level forces have carriers that are exchanged between particles so that momentum and energy change.
In other words, we couldn't fit it to model of quantum fields and carriers and it fits perfectly other model where it's not a force.
Gravity could be described with same exact words.
Although I agree that exclusion principle superficially looks much less like a force than gravity does.
Still, gravity is exactly same as forces that come from choosing accelerating frame of reference ... are there plans to look for carriers of those forces as well? Or should we expect gravitons popping up once we accelerate that don't exist for stationary observer?
Gravitons are usually formulated by perturbing the metric around the flat Minkowski metric, but you can do perturbation theory around any metric, include those that describe accelerating frames.
So, you might actually get gravitons in an accelerated frame. What you call background metric and what you call gravitons can get mixed together. However, because gravity is formulated in a generally covariant (ie. invariant under diffeomorphisms) the physical predictions must nevertheless agree when formulated in a frame-independent manner, much as they must in special relativity.
Maybe the best example of quantum effects being different for accelerating and stationary observers is the Unruh Effect ( https://en.wikipedia.org/wiki/Unruh_effect ). If an observer accelerates relative to a 0-temperature vacuum, they will see a blackbody background with T ~ a.
It is not true that it does not fit quantum field models. Plenty of meaningful results have been derived from effective QFT (Hawking radiation for instance). The model does break at a certain scale, but that is true for models without gravity too.
>> Plenty of meaningful results have been derived from effective QFT (Hawking radiation for instance).
> You mean unobservable (yet?) predictions?
Unruh effect is observed in accelerators (it warms up the particles in the acceleration rings). Admittedly it has to do more with the principle of equivalence than directly with gravity, but it would be hard to find a physicist that has an issue with this.
>> The model does break at a certain scale, but that is true for models without gravity too.
> That's kind of deal breaker when it comes to gravity.
What do you mean? All our models break at certain energy scales and of course it is a deal breaker for all of them, no matter if we are talking about the Standart Model or an Effective QFT with gravity. Yes, we do not know what happens when curvatures reach the plank scale, but there are plenty of other things that we do not know even if we do not include gravity.
>>> The model does break at a certain scale, but that is true for models without gravity too.
>> That's kind of deal breaker when it comes to gravity.
> What do you mean? All our models break at certain energy scales ...
I thought that by scale you meant size not energy and that theory breaks at larger distances (larger than typical distance for observable quantum effects). You can see how could I see this as a deal breaker for gravity that only over large distances is strong enough to be measurable).
Being so weak is not the only disturbing attribute of gravity.
It's also being the only far-reaching attracting force.
Far reaching, not connected to mechanical forces is only explainable with the wave model, not the mechanical counterpart, and attractive is only similar to electro-magnetism, with a completely different explanation.
That's what made Newton think of being a supernatural force created by god to hold all the planets and the universe together.
And that's what made Heisenberg say: "Are you silly? An attracting force having the mechanical interpretation, the Higgs boson, which jumps on each other nucleons back to create an attraction?"
That cannot be it.
But physics doesn't answer this kind of question. We don't know why magnetism, for example, works the way it does - we just measure it's effects and model it with mathematics.
OTOH I think it's interesting to imagine universes with stronger or weaker gravity, and to realize that in most of them it's hard to imagine life being possible at all. (Life would not arise without gravity (since you need to smush matter together to get life) but it also wouldn't arise with super strong gravity (since life needs to be able to move around).)
> science will never progress unless we try, and that’s what these ideas and searches are: our attempt to move our knowledge of the Universe forward. And as always, as the LHC’s Run II has already begun, I can’t wait to see what — beyond the already-discovered Higgs boson — just might turn up!
If they want data from colliders, I would say it's a problem for experimental physics, or physics in general.
I like to think of Gravity as a result of mass deforming space in the same way a brown turd deforms toilet water as it spins inevitably toward the outlet during flushing. Standing atop the turd you are affixed to its mass, but the entire system is affixed to the spinning, evacuating forces of the great flush. The Bono/Kurick South Park episode was instrumental in this theory's formulation.
"Gravity is so weak that force of a tiny fridge magnet is able to counter gravity pull of the whole planet".