31 ms·

Gravity is the most romantic force in all of nature. The idea that everything in the universe is connected and pulling is mind blowing.

pugio 9y ago
I'm a physics teacher, and we just did Universal Gravitation last week. I whimsically explained it as "the longing of everything for everything". (They liked it, but devolved into a giggle fest about being attracted to each other.) Other easily romantic notions in physics: * we are all born of star stuff * every breath we take has elements of the same breath as every human who ever lived (excluding some currently living ones, due to diffusion rates, but eventually...) * (The current grav force between my partner and me is 1.9159965e-15 N)
- pm 9y ago
  That's a great lyric - I will have to put it into a song. Credit goes to pugio.
- TheSpiceIsLife 9y ago
  > every breath we take has elements of the same breath as every human who ever lived (excluding some currently living ones, due to diffusion rates, but eventually...) Is it conceivable that some of the oxygen and nitrogen, etc, in the atmosphere today wasn’t present in the atmosphere, say, 40,000 years ago due to it being bound up in minerals or biological matter?
mrybczyn 9y ago
Well.... I'm pretty sure the field interpretation of EM also applies across the universe. So you could, on a dark night, with the electrons in the atoms of your body, feel the movement of electrons in a star, millions of light years away in space and time...
- ISL 9y ago
  That interpretation is entirely valid, but the fact that objects can be electrically neutral mitigates the magnitude of that effect substantially.
  - goldenkey 9y ago
    Neutral is a tricky thing. Composite particles aren't truly neutral..just like gravity isn't really from point sources but can be considered as such. https://en.wikipedia.org/wiki/Truly_neutral_particle https://en.wikipedia.org/wiki/Truly_neutral_particle
- tzs 9y ago
  Yeah, but the electrons in the star are pushing on your electrons, not pulling. I think bluetwo called gravity romantic because it is bringing together, not driving apart.
  - deleted 9y ago
    [deleted]
  - strainer 9y ago
    I hesitate to say this because I dont entirely grasp it at the moment but I think when electrons are travelling parallel to each other they can stop repelling... their repulsive force is overtly effected by their relative movement, as well as their position and charge - due to how charges in motion modify and follow the magnetic field.
    - tzs 9y ago
      I believe that if we were just dealing with electrons, the repulsion from the electric field would be much much stronger than the attraction from the magnetic field. We only see a net attraction between current carrying parallel wires because the wires contain both electrons and protons in almost perfect balance, so that the electron/electron repulsions and proton/proton repulsions between the wires are almost perfectly canceled by the electron/proton attractions between the wires, leaving no net electrical attraction or repulsion. That lets the weak magnetic attractions (or repulsions, depending on the directions of the currents) dominate.
oh_sigh 9y ago
I know gravity has a speed limit, but does it have a upper distance limit or lower magnitude limit? As in, are we really feeling gravitational effects of mass that is 14 light years away, even if they are insignificantly tiny and we probably can't measure it, or is there a point where a force is so miniscule that the universe truncates the force to 0?
- portofcall 9y ago
  No, but neither does the EM force, it all just asymptotically approaches zero. Don’t let that fool you though, in that it really approaches zero to a high degree.
- andrepd 9y ago
  As far as we can tell no. Of course, what we know with certainty is bounded by a nonzero experimental resolution.
- spacehome 9y ago
  Something is happening to hold galaxies and galaxy clusters together.
- Treblemaker 9y ago
  If one arbitrarily defines "zero force" as less than the force sufficient to accelerate one proton at one planck length per age-of-universe^2, I come up with a distance of 10^12 meters between two protons (+/- an order of magnitude). However, (and if I didn't screw up the math) since gravity scales linearly with mass, and the size of the visible universe is about 10^27 meters, then anything with mass greater than 10^15 protons -- or about the mass of a human cell -- has a "non zero" gravitational effect on you.
  - crististm 9y ago
    Didn't check the math but I enjoyed your "zero force" definition!
  - Treblemaker 9y ago
    Ah, one little slip of the pen and everything changes. It's more like 3.6 * 10^16 meters.

pugio 9y ago

I'm a physics teacher, and we just did Universal Gravitation last week. I whimsically explained it as "the longing of everything for everything". (They liked it, but devolved into a giggle fest about being attracted to each other.) Other easily romantic notions in physics: * we are all born of star stuff * every breath we take has elements of the same breath as every human who ever lived (excluding some currently living ones, due to diffusion rates, but eventually...) * (The current grav force between my partner and me is 1.9159965e-15 N)

pm 9y ago
That's a great lyric - I will have to put it into a song. Credit goes to pugio.
TheSpiceIsLife 9y ago
> every breath we take has elements of the same breath as every human who ever lived (excluding some currently living ones, due to diffusion rates, but eventually...) Is it conceivable that some of the oxygen and nitrogen, etc, in the atmosphere today wasn’t present in the atmosphere, say, 40,000 years ago due to it being bound up in minerals or biological matter?

mrybczyn 9y ago

Well.... I'm pretty sure the field interpretation of EM also applies across the universe. So you could, on a dark night, with the electrons in the atoms of your body, feel the movement of electrons in a star, millions of light years away in space and time...

ISL 9y ago
That interpretation is entirely valid, but the fact that objects can be electrically neutral mitigates the magnitude of that effect substantially.
- goldenkey 9y ago
  Neutral is a tricky thing. Composite particles aren't truly neutral..just like gravity isn't really from point sources but can be considered as such. https://en.wikipedia.org/wiki/Truly_neutral_particle https://en.wikipedia.org/wiki/Truly_neutral_particle
tzs 9y ago
Yeah, but the electrons in the star are pushing on your electrons, not pulling. I think bluetwo called gravity romantic because it is bringing together, not driving apart.
- deleted 9y ago
  [deleted]
- strainer 9y ago
  I hesitate to say this because I dont entirely grasp it at the moment but I think when electrons are travelling parallel to each other they can stop repelling... their repulsive force is overtly effected by their relative movement, as well as their position and charge - due to how charges in motion modify and follow the magnetic field.
  - tzs 9y ago
    I believe that if we were just dealing with electrons, the repulsion from the electric field would be much much stronger than the attraction from the magnetic field. We only see a net attraction between current carrying parallel wires because the wires contain both electrons and protons in almost perfect balance, so that the electron/electron repulsions and proton/proton repulsions between the wires are almost perfectly canceled by the electron/proton attractions between the wires, leaving no net electrical attraction or repulsion. That lets the weak magnetic attractions (or repulsions, depending on the directions of the currents) dominate.

oh_sigh 9y ago

I know gravity has a speed limit, but does it have a upper distance limit or lower magnitude limit? As in, are we really feeling gravitational effects of mass that is 14 light years away, even if they are insignificantly tiny and we probably can't measure it, or is there a point where a force is so miniscule that the universe truncates the force to 0?

portofcall 9y ago
No, but neither does the EM force, it all just asymptotically approaches zero. Don’t let that fool you though, in that it really approaches zero to a high degree.
andrepd 9y ago
As far as we can tell no. Of course, what we know with certainty is bounded by a nonzero experimental resolution.
spacehome 9y ago
Something is happening to hold galaxies and galaxy clusters together.
Treblemaker 9y ago
If one arbitrarily defines "zero force" as less than the force sufficient to accelerate one proton at one planck length per age-of-universe^2, I come up with a distance of 10^12 meters between two protons (+/- an order of magnitude). However, (and if I didn't screw up the math) since gravity scales linearly with mass, and the size of the visible universe is about 10^27 meters, then anything with mass greater than 10^15 protons -- or about the mass of a human cell -- has a "non zero" gravitational effect on you.
- crististm 9y ago
  Didn't check the math but I enjoyed your "zero force" definition!
- Treblemaker 9y ago
  Ah, one little slip of the pen and everything changes. It's more like 3.6 * 10^16 meters.