41–50 of 90 posts
This is really interesting. Perhaps there is also a chance that electromagnetic fields are indeed entirely responsible for gravity, in some complicated yet unknown manner.
Can anyone with with real knowledge of gravity comment on whether these two intuitions are correct?
What I've always found wild about gravity and photons is that gravity produces the same proportionate effect, i.e., acceleration, on them as it does normal matter and the only reason the sun and planets don't render light nearly unusable for sensing by utterly distorting the light's path is that it travels so quickly it doesn't spend any significant amount of time in a gravity well. I don't think I'll ever fully wrap…
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"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 le…
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 wi…
If you think electrons and positrons have a gravitational influence, then it seems to me you should also think photons do. Otherwise, if an electron and positron annihilate, producing photons, there will be a discontinuous drop in the gravitational field, which doesn't seem right somehow. Furthermore, if you put all this in a black box, the gravitational influence of the box will change because of what's happening wi…
Having said that, your intuition that photons should have gravitational influence makes sense, since according to special relativity, mass and energy are equivalent. Since total energy (mass + energy) is conserved, the gravitational influence of the photon should equal that of the electron-positron pair (assuming they are all located at the same position). I think the article is agreeing with this point of view.
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I don't think you are correct: you can view the extra degrees of freedom as just a symmetry
It is usually called a gauge symmetry but it is kind of a misnomer and should better be called a gauge redundancy. It is artifical and only due to the mathematical formalism we are using. As an analogy, probably not a really good one, is that you could decide to describe temperatures with a complex number and just say temperature is invariant under translation along the imaginary axis. Sure, the symmetry is in your m…
If you think electrons and positrons have a gravitational influence, then it seems to me you should also think photons do. Otherwise, if an electron and positron annihilate, producing photons, there will be a discontinuous drop in the gravitational field, which doesn't seem right somehow. Furthermore, if you put all this in a black box, the gravitational influence of the box will change because of what's happening wi…
I don't have real knowledge of gravity, but I can speculate a bit. First, I don't think the blackbox argument necessarily makes sense. If the black box contains a massive point particle, and this particle moves from the left side of the box to the right, then the gravitational properties certainly change. For example, if there is a particle on top of the box, it will initially be pulled to the left, and subsequently…
But on further thought, I wouldn't be surprised if some changes in the internals of the box could produce gravitational waves, so maybe my intuition for this is wrong. Although if I further clarify that the box isn't supposed to be emitting energy (which will obviously reduce its gravitational influence as it loses energy), then maybe the intuition is correct after all...
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> 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.
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…
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.
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It is usually called a gauge symmetry but it is kind of a misnomer and should better be called a gauge redundancy. It is artifical and only due to the mathematical formalism we are using. As an analogy, probably not a really good one, is that you could decide to describe temperatures with a complex number and just say temperature is invariant under translation along the imaginary axis. Sure, the symmetry is in your m…
That would not work in the same way as a typical gauge theory though - typically the symmetry of a gauge is for shifts of the entire system along the gauge - changes along the gauge locally do have physical meaning. For example, in an electrical diagram you can arbitrarily shift every voltage in the system by a billion Volts (ground rail is 1b Volts, 5V rail is 1b+5V, etc) and the system will behave identically. The…