News from the LHC

[Elder Iptuous]

so, if gravity has a speed, then wouldn't a mass oscillating in space (as in translation) set up a gravitational wave?  why does the mass itself have to change rather than just the distance?

P3nT: wouldn't it seem stranger if it was instantaneous?  a 'spooky action at a distance'?

[P3nT4gR4m]

so, if gravity has a speed, then wouldn't a mass oscillating in space (as in translation) set up a gravitational wave?  why does the mass itself have to change rather than just the distance?

P3nT: wouldn't it seem stranger if it was instantaneous?  a 'spooky action at a distance'?

I'm seeing a tin can, deforming as you kick it. It deforms at the speed the boot is moving. Would seem stranger if it had it's own speed of deformation, independent of the velocity of the boot. Surely gravity should work at whatever speed the mass is moving at? Gravity is a shape, affecting the motion of things. Shapes neither have nor require speed, that's the job of the moving things.

I'm not seing a spooky action, I'm seeing a deformation

[Golden Applesauce]

so, if gravity has a speed, then wouldn't a mass oscillating in space (as in translation) set up a gravitational wave?  why does the mass itself have to change rather than just the distance?

P3nT: wouldn't it seem stranger if it was instantaneous?  a 'spooky action at a distance'?

I'm seeing a tin can, deforming as you kick it. It deforms at the speed the boot is moving. Would seem stranger if it had it's own speed of deformation, independent of the velocity of the boot. Surely gravity should work at whatever speed the mass is moving at? Gravity is a shape, affecting the motion of things. Shapes neither have nor require speed, that's the job of the moving things.

I'm not seing a spooky action, I'm seeing a deformation

The can does have its own speed of deformation, actually - the speed of sound (or any other physical wave) in tin.  The speed of sound in metal is really fast relative to how a boot moves (and at small distances might be more determined by other physical properties, including boot velocity) so it's not something you can observe by eye, but it's there.

In general, the speed of a wave is determined only by the matter it's travelling through, and nothing else. It doesn't matter if you yell louder or sing at a higher / lower pitch, the speed of sound is determined only by the properties of the air (temperature, humidity, density). It's easier to observe directly in water waves - go to a swimming pool and start punching water in the middle. How hard you hit the water affects the amplitude and wavelengths of the resulting water wave, but outside of the initial splash zone (think the area immediately around the boot) the crests will travel at the same velocity.

[Elder Iptuous]

gravity is a field, right?
so the change in the field would propagate out with some speed, no?
so i guess it's not really the 'speed of gravity', but the speed of a gravitational wave.  like the speed of light is the speed that EM waves propagate.

[Golden Applesauce]

For gravity specifically - imagine that you're on a space ship and a pirate three light-minutes away has fired a cannonball at you. It will take three minutes for the muzzle flash to reach you. If you could detect a change in gravity (from the cannonball getting closer) instantaneously, then you'd be able to detect that you were being fired upon three whole minutes before the light from the shot reached you - which would mean information was moving faster than the speed of light. If the pirate also had gravity sensors, you could set up FTL communication between the two of you by shooting cannonballs at each other! That opens up all kinds of causality paradoxes with relativity, so theoretical physicists are pretty sure that gravity travels at most as fast as light in a vacuum, possibly less (which is the scenario were you see muzzle flash -> detect gravity waves -> get hit by a cannonball.)

gravity is a field, right?
so the change in the field would propagate out with some speed, no?
so i guess it's not really the 'speed of gravity', but the speed of a gravitational wave.  like the speed of light is the speed that EM waves propagate.

Exactly.

[Kai]

Supernovae might generate gravity waves. Though, who wants to be close enough to a supernova to find out.

Minor planets moving to proximity with each other may generate small gravity waves. That's a far more feasible thing, but they would have to be moving very quickly towards each other.

[P3nT4gR4m]

  So gravity is a wave? WTF? Waves make things bob up and down, they do not suck things toward the source of the wave.

[LMNO]

Any macro-world metaphor you create is false.  The quantum world does not behave intuitively.

[Elder Iptuous]

So gravity is a wave? WTF? Waves make things bob up and down, they do not suck things toward the source of the wave.

a water wave will make things bob up and down orthogonally to the direction of the wave.
and a transverse EM wave will do the same with a charged object.
but, a longitudinal EM wave will certainly suck a charged object back and forth.
and a sound wave will vibrate things back and forth.
a wave is anything that follows a wave equation, which has various forms

[P3nT4gR4m]

Any macro-world metaphor you create is false.  The quantum world does not behave intuitively.

Got ya. Didn't realise we weren't talking about macro scale. Was Kai's supernova thing that threw me.

[Faust]

So gravity is a wave? WTF? Waves make things bob up and down, they do not suck things toward the source of the wave.

Yes they do. Look at lines of magnetic flux for the magnetic effect.

[P3nT4gR4m]

So gravity is a wave? WTF? Waves make things bob up and down, they do not suck things toward the source of the wave.

Yes they do. Look at lines of magnetic flux for the magnetic effect.

Are you talking about when you put a magnet under a bunch of iron filings? If so then I didn't realise that was a wave that made that happen. Is it a static wave of some kind or is that how iron filings look when there's a moving wave going through them?

[Faust]

So gravity is a wave? WTF? Waves make things bob up and down, they do not suck things toward the source of the wave.

Yes they do. Look at lines of magnetic flux for the magnetic effect.

Are you talking about when you put a magnet under a bunch of iron filings? If so then I didn't realise that was a wave that made that happen. Is it a static wave of some kind or is that how iron filings look when there's a moving wave going through them?

I'm not sure what you mean? Magnets are a little different from the electromagnetic effect which is a waves but I imagine its the same for the ferrormagnetic effect just from a different cause.

[P3nT4gR4m]

Yeah, I'm kinda lost now I'll just duck out this thread before I pollute it any more with dumbass questions

[Faust]

Yeah, I'm kinda lost now I'll just duck out this thread before I pollute it any more with dumbass questions

No man don't say that, I'm not great at explaining it. They are both waves. Magnets have that attractive force because of alignment of electrons in the material, the electromagnetic radiation is a little different but both operate as a wave.