[dschuetz]

"there is gravity in the absence of EM fields" That just cannot be true. EM fields are just about everywhere. They permeate space almost as universally as gravity, but in form of photons (to name higher energy EM fields here) or other low energy waves. Gravity accumulates with great masses, mass is also energy (in rest).

The article explores the idea that pure kinetic energy in form of photons indeed might have at least gravity-like properties.

My presumption is that atoms are somehow made of really high energy EM fields so that they appear to be massive. Consequently, atoms having mass or photons having inertia are responsible for gravitation, and that could mean that EM fields are the cause of gravity entirely. The problem with that presumption is that perhaps there is no way to check.

[zaarn]

Easy way to check, just wave a long piece of iron through the air. If there is truly a massive EM field, it should induce a decent voltage into said iron rod as it moves through the magnetic field lines produced by the "gravity EMism"

Considering noone died from waving iron rods through the air by way of electrocution (other than lightning) I'd say that means gravity is not an EM field.

There is also a different test: EM fields are either positive or negative in charge. If you have three objects, in an EM field they cannot all three attract eachother, one object must be pushed away from one of the other two.

Considering we don't see that behaviour in our solar system, gravity cannot be an EM field.

[100ideas]

I like your elegant thought experiment!

Quarks have -1/3 or +2/3 charge in the standard model and presumably(?) at high enough energies they separate out into a quark-gluon plasma thus exposing the universe to their unholy fractional charges. Above 2 trillion Kelvin according to wikipedia.

[zaarn]

Even with fraction, either you have repulsion or attraction, depending on the sign. -1/3 charge will be repulsed by +1 or +2/3 charge, just at different strengths.

[kgwgk]

> The article explores the idea that pure kinetic energy in form of photons indeed might have at least gravity-like properties.

Saying “explore”, “idea”, “might” makes it sound as if this was not a well-established 100-years-old theory.

> My presumption is that atoms are somehow made of really high energy EM fields so that they appear to be massive.

Somehow... The easiest way to proceed in that program of research may be to rename the standard model as ElectroMagnetism and try to get a unified theory of the strong, weak and the-force-previously-known-as-em forces. Then you unify that with GR and you’re done :-)

[JadeNB]

> The easiest way to proceed in that program of research may be to rename the standard model as ElectroMagnetism and try to get a unified theory of the strong, weak and the-force-previously-known-as-em forces.

Certainly the unification of electromagnetism + the weak force is understood, and there is a theory (or several theories) about electroweak + strong unification: https://en.wikipedia.org/wiki/Grand_Unified_Theory .

[kgwgk]

That links says: “Unsolved problem in physics: Are the three forces of the Standard Model unified at high energies?”

But we may be close, for some values of close :-)

[JadeNB]

> That links says: “Unsolved problem in physics: Are the three forces of the Standard Model unified at high energies?”

Indeed, that's why I said only that there were theories about it.

[kgwgk]

Sure, but the solutions to the solved problems in physics are also called "theories". I'm sure you knew the GUT is not yet done, it was just a clarification.

[JadeNB]

I always appreciate non-shouty clarifications of misunderstandings, combined with charitable interpretations of others' motives and knowledge. Thank you!

[danbruc]

EM fields are just about everywhere.

Fields are mathematical tools, they are not - without wanting to go down the philosophical rabbit hole - real things out there in the universe.

And the thing about everything just being electromagnetic fields is nonsense, physicists understand physics way better than you do. Sorry to sound condescending, but the internet already has enough obviously wrong ideas by random people without a clue what they are talking but.

[cycomanic]

Well by saying that fields are not "real things" you have just started going down the "philosophical rabbit hole". What is a real thing, is the gravitational force that we feel not a real thing, is the energy we feel in an EM wave (e.g. The sun on our skin) not a real thing?

[100ideas]

What, you don’t think the Hylaean Theoric World is realer that reality?

[dschuetz]

Dude, fields are a tool physicists use to describe phenomena. It's okay to say EM fields exist because they interact with everything everywhere and we can actually observe that.

[100ideas]

The universe appears to have expanded or be expanding faster than the speed of light: the diameter of the observable universe is ~42 billion light-years but best estimates of age of universe is ~14 billion years.

So these fields can’t interact with everything everywhere, only the portion of the universe In the field’s lightcone. if the universe keeps this up there’s a chance some day Everything will be so stretched out that the fields will be basically redshifted to null, so not interacting with anything anywhere. That’d be lame.

[danbruc]

[...] the diameter of the observable universe is ~42 billion light-years [...]

That's the radius.

[tsimionescu]

Honest question: aren't radio waves "physical objects" that represent oscillations of an electro-magnetic field, to the best of our current understanding?

[dschuetz]

There is an agreement in physics that low energy EM fields are called waves, such as radio waves, and high energy EM fields are called photons or even particles. In any case they are actually both. If they are physical objects I don't know. I think, I wouldn't go that far.

[tsimionescu]

Sure, they are both, but my point was - if they have wave-like characteristics, they must be a wave of/in something; if we can have experimental evidence that the wave exists, I would consider that experimental evidence that the field the wave is a wave of must also exist, to the same extent.

[100ideas]

Let’s talk virtual particles...

[danbruc]

They are also just in the models and heads of physicists.

[danbruc]

Radio waves are streams of photons, the fields are just a mathematical tool we use to describe this. And there are several of them, the classical electromagnetic field but also an entire set of fields involved in the quantum version.

[tsimionescu]

My understanding was that some kind of wave-particle dualism was well accepted. It's exact physical meaning may not be understood, but isn't there experimental evidence that photons, even individual ones, behave as waves in some circumstances (as does as any other 'particle', in fact)?

I've seen this dualism claimed pretty recently by Leonard Susskind.

[kgwgk]

Other people may say that photons are just mathematical tools that we use to describe fields. :-)

[danbruc]

The fact that gauge fields have redundant degrees of freedom should at least be a strong hint that the fields are not the fundamental description. ;)

[carlob]

I don't think you are correct: you can view the extra degrees of freedom as just a symmetry

[dschuetz]

Oh yes, quantum electromagnetic quantum field. Just add "quantum" and the discussion is over.

[tsimionescu]

> EM fields are just about everywhere. They permeate space almost as universally as gravity

Isn't dark matter most likely some kind of material that has mass, but no EM interaction?

We also know that there are interactions inside atoms (the strong and weak forces) that have no known relation to electro-magnetism, so I'm not sure what you are getting at.

[dschuetz]

As far as I understand, dark matter is an educated guess (which was made upon the discovery that galaxies rotate differently than expected). Something out there must be causing gravity, but we cannot see it, which means that there is no observable EM interaction.

The next guess here is that dark energy has a much much higher rest energy so that no photon in this universe is able to interact with it via EM fields. The search for dark matter was unsuccessful so far, and the LHC is still trying to achieve higher energies to be able to detect dark matter. So, dark matter is just a guess.

The interactions inside atoms seem to have no known relations to EM, because, and this is my guess, there are much higher energies at work than we know. So, if dark matter is hiding behind high energies so that EM interaction seems impossible, why should it be different for EM interactions inside atoms. There still is a slim chance that it might be EM, just at much higher energies.

[danbruc]

The interactions inside atoms seem to have no known relations to EM [...]

The electromagnetic and the weak interaction are known to be different aspects of the unified electroweak interaction. There are several grand unified theories and a few hints that at even higher energies the electroweak and strong interaction also unifiy into the electronuclear interaction. Due to the high energies involved, only indirect experimental evidence seems accessable for the forseeable future but there are various groups looking for hints. I am not aware of any uncontroversial results but there are a few non-reproducable experiments, for example observations of magnetic monopoles, which might be due to experimental error but also due to the rarity of magnetic monopoles.