4 ms·

Pardon the stupid question but since most experiments and observations are done on earth, how do scientists know that fundamental forces like electromagnetism a

by _8j50 3y ago

Pardon the stupid question but since most experiments and observations are done on earth, how do scientists know that fundamental forces like electromagnetism and the strong force are not being influenced by gravity? What if chemical/atomic bonds and molecular structures don't form the same way or require more/less energy depending on gravitational influence? As a layman, I would think that gravity pulls down sub-atomic particles, wouldn't that slow them down compared to say outside the heliosphere and oort cloud? Would electrons spin faster if they are located at an inter-galactic void? More insane is the measurement of 'c', is all using electromagnetism, but if that in itself is being slowed down by gravity, well I can't even begin to comprehend the implications.

antognini 3y ago
If the electromagnetic force changed in some way depending on the gravitational influence then atoms would produce different spectral lines. However, we can observe the spectral lines produced by atoms and molecules in the interstellar medium where the net gravitational force is much weaker. There is no difference between these lines and what we observe in the lab. (Except for certain expected effects from the reduced pressure like reduced Doppler broadening and the appearance of "forbidden" lines.)
- _8j50 3y ago
  But if the atoms produced different spectral lines, wouldn't observers on earth just end up wrongly believing they are seeing a different type of an element? For example you might think a star is made up of hydrogen when it is made up of helium? I have no knowledge of how spectal lines work so pardon my ignorance once more, but is it possible for gravity or other forces to produce spectral lights of similar elements than the original one or is it a very unique fingerprint not similar to close by elements? Also, if gravity can bend light (blackholes), how come it cannot attenuate it? Light is on the EM spectrum and the speed of light is different in different mediums so I am presuming it is similar to how electrons attenuate on copper wire.
  - rnhmjoj 3y ago
    > wouldn't observers on earth just end up wrongly believing they are seeing a different type of an element? It would be very very very unlikely. The spectrum of an ionized atom is not just a single line that you could easily mistake for another: there is a sequence of lines for each electronic level. There's also a lot more structure when you have molecules: in this case you also have lines associated to changes in the rotational and vibrational state of the molecule, and these also combine with electronic transitions to produce even more lines with characteristic spacings. For example, the simplest molecule, H2, has such a rich spectrum some people spent decades in the 50s to fully characterize it. > is it possible for gravity or other forces to produce spectral lights of similar elements than the original one or is it a very unique fingerprint not similar to close by elements? Yes, there's the gravitational redshift: it affects light emitted near a massive object such a black hole and it has been observed. The effect is very small, but I guess it could potentially shift the frequency of a line of element X to near the nominal frequency of a line of element Y. However, the redshift applies to all lines, so it's very easy to recognize you're looking at a shifted spectrum if you see more that a single line. > Also, if gravity can bend light (blackholes), how come it cannot attenuate it? To attenuate light you necessarily need some kind of dissipative process, so light has to be at least partially absorbed by something and its energy converted to something else. In a vacuum this is really not possible. Maybe with the inclusion of some very high energy process like γγ → e⁺e⁻ or the gravitational equivalent of pair production, but these are really way out of the energy ranges of molecular and atomic spectra.
pdonis 3y ago
First, we have extensive observational data from elsewhere in the universe that tells us that the fundamental interactions work the same everywhere. For example, we see light coming from regions that have very different gravity, but it still behaves the same. Second, on the scale of atoms, or even on the scale of ordinary macroscopic objects, gravity is so extremely weak that its effects on things like chemical bonds or the structure of nuclei, atoms, and molecules is negligible. If you have a very massive object like a star (or a white dwarf or neutron star), then of course you have different states of matter possible (degenerate matter in stellar cores, white dwarfs, and neutron stars), but even those states of matter still have all the fundamental interactions working the same way. The different states of matter are due to the extreme density and pressure, not due to any change in the fundamental interactions. Third, what we usually call "the speed of light in vacuum" is actually a property of spacetime, not specifically of light. So the idea of this speed being "slowed down by gravity" is based on a confusion. That property of spacetime (a better name for it would be local Lorentz invariance) is the same everywhere no matter how weak or strong gravity is.
- rkagerer 3y ago
  Isn't gravity a property of spacetime? (curvature)
  - petschge 3y ago
    You can describe it that way. But different parts of spacetime can have different curvature, so you get different impact of gravity. No matter how you describe it, gravity is different on Earth, Moon or in deep space and your theory has to model that no matter if it uses forces, curvature of spacetime or something else.
  - pdonis 3y ago
    More precisely, tidal gravity is spacetime curvature. What most people think of as "gravity"--for example, feeling weight when you are standing on the surface of the Earth--is actually non-gravitational forces, such as the Earth's surface pushing up on you, that are keeping you from freely falling. If you are in free fall, the "force of gravity" as people normally think of it disappears. (This was the key insight that started Einstein on the path to General Relativity.) What is left over is tidal gravity--freely falling objects converging or diverging because of the geometry of spacetime.
simne 3y ago
> most experiments and observations are done on earth Yes, but all astronomy built on same foundations. For example just cup of years, exists literally observation of Black hole, but few decades before their behavior observed only by indirect measurements, which are absolutely confirmed theory. Also last years launched few large scale experiments with satellites, and few others planned. For example, LISA Pathfinder was launched to orbit 500000km..800000km, which is not much for astronomic scales, but definitely is not on Earth surface (Moon is less then half million kilometers from Earth) :) https://en.wikipedia.org/wiki/LISA_Pathfinder https://en.wikipedia.org/wiki/LISA_Pathfinder First very far automatic chemical lab, probably was Mariner series on Mars. Later was Galileo, Cassini–Huygens (list included on bottom of page). https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens https://en.wikipedia.org/wiki/Vega_program https://en.wikipedia.org/wiki/Vega_program Must admit, I cannot remember any space mission, with rich chemical lab , considered to work at open space (Vega has chemical lab on descent craft, Halley comet part was just radar/imaging). But chemical rocket engines work same, and all known electronics also work same as on Earth surface. I'm few decades waiting for any evidence of chemical reactions depending on gravitational influence, but nothing happen.

by _8j50 3y ago

antognini 3y ago

If the electromagnetic force changed in some way depending on the gravitational influence then atoms would produce different spectral lines. However, we can observe the spectral lines produced by atoms and molecules in the interstellar medium where the net gravitational force is much weaker. There is no difference between these lines and what we observe in the lab. (Except for certain expected effects from the reduced pressure like reduced Doppler broadening and the appearance of "forbidden" lines.)

_8j50 3y ago
But if the atoms produced different spectral lines, wouldn't observers on earth just end up wrongly believing they are seeing a different type of an element? For example you might think a star is made up of hydrogen when it is made up of helium? I have no knowledge of how spectal lines work so pardon my ignorance once more, but is it possible for gravity or other forces to produce spectral lights of similar elements than the original one or is it a very unique fingerprint not similar to close by elements? Also, if gravity can bend light (blackholes), how come it cannot attenuate it? Light is on the EM spectrum and the speed of light is different in different mediums so I am presuming it is similar to how electrons attenuate on copper wire.
- rnhmjoj 3y ago
  > wouldn't observers on earth just end up wrongly believing they are seeing a different type of an element? It would be very very very unlikely. The spectrum of an ionized atom is not just a single line that you could easily mistake for another: there is a sequence of lines for each electronic level. There's also a lot more structure when you have molecules: in this case you also have lines associated to changes in the rotational and vibrational state of the molecule, and these also combine with electronic transitions to produce even more lines with characteristic spacings. For example, the simplest molecule, H2, has such a rich spectrum some people spent decades in the 50s to fully characterize it. > is it possible for gravity or other forces to produce spectral lights of similar elements than the original one or is it a very unique fingerprint not similar to close by elements? Yes, there's the gravitational redshift: it affects light emitted near a massive object such a black hole and it has been observed. The effect is very small, but I guess it could potentially shift the frequency of a line of element X to near the nominal frequency of a line of element Y. However, the redshift applies to all lines, so it's very easy to recognize you're looking at a shifted spectrum if you see more that a single line. > Also, if gravity can bend light (blackholes), how come it cannot attenuate it? To attenuate light you necessarily need some kind of dissipative process, so light has to be at least partially absorbed by something and its energy converted to something else. In a vacuum this is really not possible. Maybe with the inclusion of some very high energy process like γγ → e⁺e⁻ or the gravitational equivalent of pair production, but these are really way out of the energy ranges of molecular and atomic spectra.

pdonis 3y ago

First, we have extensive observational data from elsewhere in the universe that tells us that the fundamental interactions work the same everywhere. For example, we see light coming from regions that have very different gravity, but it still behaves the same. Second, on the scale of atoms, or even on the scale of ordinary macroscopic objects, gravity is so extremely weak that its effects on things like chemical bonds or the structure of nuclei, atoms, and molecules is negligible. If you have a very massive object like a star (or a white dwarf or neutron star), then of course you have different states of matter possible (degenerate matter in stellar cores, white dwarfs, and neutron stars), but even those states of matter still have all the fundamental interactions working the same way. The different states of matter are due to the extreme density and pressure, not due to any change in the fundamental interactions. Third, what we usually call "the speed of light in vacuum" is actually a property of spacetime, not specifically of light. So the idea of this speed being "slowed down by gravity" is based on a confusion. That property of spacetime (a better name for it would be local Lorentz invariance) is the same everywhere no matter how weak or strong gravity is.

rkagerer 3y ago
Isn't gravity a property of spacetime? (curvature)
- petschge 3y ago
  You can describe it that way. But different parts of spacetime can have different curvature, so you get different impact of gravity. No matter how you describe it, gravity is different on Earth, Moon or in deep space and your theory has to model that no matter if it uses forces, curvature of spacetime or something else.
- pdonis 3y ago
  More precisely, tidal gravity is spacetime curvature. What most people think of as "gravity"--for example, feeling weight when you are standing on the surface of the Earth--is actually non-gravitational forces, such as the Earth's surface pushing up on you, that are keeping you from freely falling. If you are in free fall, the "force of gravity" as people normally think of it disappears. (This was the key insight that started Einstein on the path to General Relativity.) What is left over is tidal gravity--freely falling objects converging or diverging because of the geometry of spacetime.

simne 3y ago

> most experiments and observations are done on earth Yes, but all astronomy built on same foundations. For example just cup of years, exists literally observation of Black hole, but few decades before their behavior observed only by indirect measurements, which are absolutely confirmed theory. Also last years launched few large scale experiments with satellites, and few others planned. For example, LISA Pathfinder was launched to orbit 500000km..800000km, which is not much for astronomic scales, but definitely is not on Earth surface (Moon is less then half million kilometers from Earth) :) https://en.wikipedia.org/wiki/LISA_Pathfinder https://en.wikipedia.org/wiki/LISA_Pathfinder First very far automatic chemical lab, probably was Mariner series on Mars. Later was Galileo, Cassini–Huygens (list included on bottom of page). https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens https://en.wikipedia.org/wiki/Vega_program https://en.wikipedia.org/wiki/Vega_program Must admit, I cannot remember any space mission, with rich chemical lab , considered to work at open space (Vega has chemical lab on descent craft, Halley comet part was just radar/imaging). But chemical rocket engines work same, and all known electronics also work same as on Earth surface. I'm few decades waiting for any evidence of chemical reactions depending on gravitational influence, but nothing happen.