3 ms·

Disclaimer: Zero formal background in Physics, but I want to learn. It has always felt like gravity is the result of some other "thing" going on. There are two

by bArray 6y ago

Disclaimer: Zero formal background in Physics, but I want to learn. It has always felt like gravity is the result of some other "thing" going on. There are two reasons for why I believe this: 1. Gravitational waves are weird, the idea that the resulting force of gravity can travel away from where it was created. I can't think of any other examples where something similar happens with another force without something "carrying" it. 2. At lot of the issues we have with our current models come from gravity. If it be on the quantum or Universe scale, our picture of what we believe gravity to be seems to be limited to our localized experience of it. I sometimes try to run through a thought experiment where I try to imagine how gravity, space and time may behave at the very edge of the Universe, because things there surely must seem weird. If space and time cannot be created or destroyed, what is being "traded" to expand the Universe? An alternate idea I've had is that the Universe is not expanding outwards, but expanding inwards, where galaxies roughly stay where there are and the properties of space-time between them changes. We always imagine the Universe in the three dimensional space we experience it in when thinking about gravity, but the quantum scale seems to suggest there must exist other spatial dimensions. Just some brain farts anyway, any reading material people can point me towards I would be highly appreciative :)

macspoofing 6y ago
>Gravitational waves are weird Are they though? I know there is a lot of math behind how exactly gravitational waves behave making specific predictions that stem from GR, but even in the Newtonian sense, something like gravitational waves would necessarily exist. That is, even under Newtonian laws, if a body emits a force like gravity which drops in strength with distance, and if that body moves back and forth in relation to you, you would necessarily experience waves of force.
- codethief 6y ago
  > That is, even under Newtonian laws, if a body emits a force like gravity which drops in strength with distance, and if that body moves back and forth in relation to you, you would necessarily experience waves of force. Not if you take the term "wave" literally. Any action in Newtonian gravity is assumed to occur instantaneously, so while an observer far away from that body would certainly see the gravitational pull varying in time, this would not be the same as a wave traveling through space.
Ono-Sendai 6y ago
Gravitational waves (radiation) are not that weird. They're kind of like electromagnetic waves. If you accelerate an electric charge it will radiate. Likewise a mass should radiate gravitational waves. Two objects gravitationally orbiting each other will spiral into each other due to the loss of energy to grav radiation. This is due to the finite speed of light. Basically each object 'sees' the other object slightly behind due to light propagation.
ajross 6y ago
> It has always felt like gravity is the result of some other "thing" going on. That's basically the way General Relativity works. Gravity is the curvature of spacetime, which is a function of the local energy density at all points. It isn't something that happens, it's just a shape. The things that "happen" because of gravity are just a side effect of the fact that lines aren't "straight" in the sense our intuition demands.
walleeee 6y ago
> If space and time cannot be created or destroyed, what is being "traded" to expand the Universe? I'm no physicist, but my understanding of the general consensus is that nothing is being "traded" because the universe is not expanding "into" some other space. Space(time) itself is expanding.

by bArray 6y ago

macspoofing 6y ago

>Gravitational waves are weird Are they though? I know there is a lot of math behind how exactly gravitational waves behave making specific predictions that stem from GR, but even in the Newtonian sense, something like gravitational waves would necessarily exist. That is, even under Newtonian laws, if a body emits a force like gravity which drops in strength with distance, and if that body moves back and forth in relation to you, you would necessarily experience waves of force.

codethief 6y ago
> That is, even under Newtonian laws, if a body emits a force like gravity which drops in strength with distance, and if that body moves back and forth in relation to you, you would necessarily experience waves of force. Not if you take the term "wave" literally. Any action in Newtonian gravity is assumed to occur instantaneously, so while an observer far away from that body would certainly see the gravitational pull varying in time, this would not be the same as a wave traveling through space.

Ono-Sendai 6y ago

Gravitational waves (radiation) are not that weird. They're kind of like electromagnetic waves. If you accelerate an electric charge it will radiate. Likewise a mass should radiate gravitational waves. Two objects gravitationally orbiting each other will spiral into each other due to the loss of energy to grav radiation. This is due to the finite speed of light. Basically each object 'sees' the other object slightly behind due to light propagation.

ajross 6y ago

> It has always felt like gravity is the result of some other "thing" going on. That's basically the way General Relativity works. Gravity is the curvature of spacetime, which is a function of the local energy density at all points. It isn't something that happens, it's just a shape. The things that "happen" because of gravity are just a side effect of the fact that lines aren't "straight" in the sense our intuition demands.

walleeee 6y ago

> If space and time cannot be created or destroyed, what is being "traded" to expand the Universe? I'm no physicist, but my understanding of the general consensus is that nothing is being "traded" because the universe is not expanding "into" some other space. Space(time) itself is expanding.