Time, Light, Instatinious

[richard quest]

My question.

If you had a solid metal rod that went from the east coast to the west coast of the USA and you moved it one inch at the east coast would it move one inch at the west coast instantaniously or would it move at the speed of light / time later?

 

I beleave it would move at a difference time equil to the speed of light.

 

I realise there are flaws in this hypothetical example such as phsycal compression and inertia but I am disreguarding these in hopes to grasp a little better the concept of light and time.

 

Any coments?

 

Please excuse my spelling that is a art that I have never grasped.

 

samson

[Klaynos]

The movement moves down the rod as a wave, each atom when it moves effects the atoms around it.

 

This propagates at the speed of sound for the material.

[swansont]

The compression in a material limits the speed to much less than c. One of the implications of relativity is that there is no such thing as an infinitely rigid material. At the very least, the molecular forces within the material, being electromagnetic in nature, are limited to travelling at c.

[someguy]

what about gravity? if a gravity well somehow affected me light years away, and suddenly the source vanished when would i notice? light years later? or if you don't like vanishing, what it moved away at some speed would there be a lag? or would i experience the change of gravity as though it were the object right close to me. I know such a gravity well would be hard to find and moving it even harder but you know what i'm saying? just for the sake of argument. how fast does gravity move? it seems to me like it is fixed with the source and no matter the radius it moves instantly with the source as though it were the source. so then if you could manipulate gravity somehow with massive amounts of energy you could send some weird morse code message faster than light. (destroying the universe in the process i guess though, even if the pulses were hyper short)

[theCPE]

Well it all depends on whom you believe.

 

If you listen to Newton gravity is instantaneous.

 

If you listen to Einstein its propogations are limited by the speed of light.

 

Relativity has proven time and time again to be more accurate than Newtonian models however the "speed" of gravity has thus far never actually been measured experimentally that I know of.

 

Of course causing matter to vanish is the biggest problem with your idea:)

[insane_alien]

well, the speed of gravity has been measured just not with any great accuracy because it is so weak. we got upper and lower speed limits though which would indicate that it is definitely NOT instantaneous

[swansont]

the "speed" of gravity has thus far never actually been measured experimentally that I know of.

 

The orbital decay of binary pulsar PSR1913+16 has been measured to be consistent with the speed of gravity being c

 

Fomalont and Kopeikin measured it by measuring starlight deviate around Jupiter.

[theCPE]

Yep, looks like it has been measured and 5 years ago too!

 

http://www.nrao.edu/pr/2003/gravity/

[Sisyphus]

I wonder what the most rigid material is. As in, the compressive wave in that scenario would move fastest going through what? Would anything have a significant fraction of C? No readily available materials, obviously, but what about, like, a neutron star? Do we know enough about neutron stars to even begin to calculate an answer?

[someguy]

I'm not really sure.. but i would think it would be the most dense material. so a bar of mercury at 0 kelvin would probably be up there.

[insane_alien]

1/ mercury isn't as dense as osmium/iridium

2/ nothing can be at 0 K

3/ neutron stars are on a whole new level of denseness.

[someguy]

oops i thought the question meant what sort of element would work best, i must have skipped the star part. i never meant mercury would be the best because it was most dense i just meant that it would be a good one, amongst the best, because there are probably some elements i was not familiar with that are denser. so then a bar of osmium/iridium at n kelvin when n->0. but if we're gonna go into the realm of gravitationally squished celestial bodies then the big bang would be the best, the entire universe conglomerated together, i don't think you could find anything denser than that.

[Farsight]

Pity that density was zero, but nevermind.

 

Here's something on the speed of sound in steel (and other stuff) samson. It would take about a quarter of an hour for the west coast to notice anything.

 

http://library.thinkquest.org/19537/Physics4.html