In light of the recent failure of the Jupiter/Galaxy experiment to measure the speed of gravity, how do you think man will eventually measure this speed? Will we have to wait until the sun explodes?

I think it's jsut a case of improving technology and the right oppurtunity.

Even if the sun explodes, how do you propose we measure the speed of gravity?

Well if I devised an experiment that could undisputably measure garvity I wouldn't be sitting infront of my computer posting on this message board right now!

If we are thrown out of orbit 8 minutes before it explodes we will know Einstein was wrong? If we see it explode he was right.

when the sun explodes? is that a joke? when the sun explodes, we re all dead. there will be no more experiments.

yes, i am aware of that lethe. this is hypothetical, or can you not think outside of your textbook?

Originally posted by yayacatfight
yes, i am aware of that lethe. this is hypothetical, or can you not think outside of your textbook?

that s right, i cannot think outside my textbook. in fact, i m just a parrot, all i can do is regurgitate factoids that i ve picked up from various websites. i m incapable of actually thinking.

ok, lethe. here is your chance. give us one original thought. go ahead, hit us with it. go out on a limb, and put something down in writing that makes us think, but god forbid, might be ridiculed.

i didn't think so.

As you probably know, large gravityWAVE detectors are now being build at several continents on earth. While they will probably reveal the amplitude and frequency of gravity waves and through triangulation measurement with detectors elsewhere tell something about the location of the source producing the waves (collapsing star for example) I don't know they can be directly used to measure the universal speed of gravity.

HOWEVER if we think triangulation really BIG we could setup a gravitywave detector on the moon and compare the arrivaltimes of incoming grqvitywaves with detectors on earth and hence calculate the speed of gravity caused by the delay?????

Maybe the distance between the detectors in america and australie would be even big enough to calculate something usefull?

Aussie GRAV detector (http://www.gravity.pd.uwa.edu.au/#OVERVIEW)

thanks. i like that idea. if we had a similar detector on the moon, would there be enough of a delay between the moon and earth from some kind of a disturbance to measure the speed. it seems relatively easy. maybe even on mars?

what exactly do these gravitywave detectors detect?

It would be even easier.

If you detect some gravitational radiation one day, examine the source optically. If it's some kind of neutron-star merger, for example, you should be able to measure its light curve and so on.

You should be able to tell that the gravitational radiation arrived at nearly the same time as the first emergent light, implying that the gravitational radiation propagates with nearly the same speed as light.

When you're talking about, say, a 15-minute difference in arrival times of gravitational and electromagnetic radiation from an object 1000 light-years away, you could conclude that gravity propagates at c within 28 parts in a billion.

Such experiments are (nearly) within the grasp of our current technology -- hopefully we'll start catching some gravitational radiation soon.

- Warren

Originally posted by yayacatfight
ok, lethe. here is your chance. give us one original thought. go ahead, hit us with it. go out on a limb, and put something down in writing that makes us think, but god forbid, might be ridiculed.

i didn't think so.

what is this? you are challenging my ability to have original thought?

compared to you, i am unoriginal because you think that if the sun blew up, gravity would cease existing?

you re an asshole. i m really starting to hate this place.

Originally posted by lethe
what is this? you are challenging my ability to have original thought?

compared to you, i am unoriginal because you think that if the sun blew up, gravity would cease existing?

you re an asshole. i m really starting to hate this place.
Bravo! Bravo!

psst... come to physicsforums.

- Warren

easy, lethe. are you really taking kid challenges seriously?... met that crackpot and had a bad time.?..;)

Originally posted by everneo
easy, lethe. are you really taking kid challenges seriously?... met that crackpot and had a bad time.?..;)

ugh. next time i ll just keep my mouth shut, and let the crackpots wallow in their own ignorance.

my bad.

lethe: your head is so far up einstein's asshole that if something new came along you would refute it simply on principle. go back and read what i wrote, for anyone to take what i wrote about the sun exploding literally has some limits to their imagination. all i am saying is try to think outside your textbook world once and a while.

Wow, it sure does stink up here inside Einstein's asshole. I wonder how many of us can fit up here?

Echo......... echo........

- Warren

or:

Jeez, and all this time I thought I was in his NOSE... :(

- Warren

or:

Q: How are opinions like assholes?

A: Because everyone has one, but Einstein's has more followers.

- Warren

Here's my theory on crackpots.

If you disagree with their theory, you have got your head up Einstein's arse. That would mean that Einstein loved it up the arse, because there would have to be a couple of hundred thousand heads up there.

Textbooks are a conspiracy against the truth, unless you are a crackpot who writes a book, then it is the bible (any difference between the former and the latter).

Crackpots suck.

I want to propose another "thought" experiment that is based on the assumption that the universe doesn't exist. If the universe did not exist, would dog's still chase cats?

Originally posted by yayacatfight
lethe: your head is so far up einstein's asshole that if something new came along you would refute it simply on principle. go back and read what i wrote, for anyone to take what i wrote about the sun exploding literally has some limits to their imagination. all i am saying is try to think outside your textbook world once and a while.

you don t know shit about shit. you don t know anything about my "textbook world", my "original thoughts", my views on einstein s theories.

also, you don t know shit about how gravity works, about how light works, about how stars work, about how physics works.

let s keep it that way, asshole.

well you got me, i don't know as much about gravity, light, or physics as you do. not even close. that is why i came to this site. i was hoping to learn something. instead i got sarcasm, condescending remarks, and called a crackpot when i don't even have a theory. here, at this site, to question einstein's theory is sacreligious and falls on deaf ears. i was taught that no question is stupid. i was only questioning the theory to learn more about it.


also, you don t know shit about how gravity works, about how light works, about how stars work, about how physics works.

let s keep it that way, asshole.

that pretty much sums up my experience here.

We know that radiation travels at the speed of light but we don’t know the speed of gravity.

OK, so the Sun explodes.

If gravity is instantaneous the earth would leave its orbit but we won’t know (if still alive) what caused the orbital loss because the Sun will appear normal – radiation from the Sun’s explosion will not reach earth for at least 8 minutes. When it does it will hit the earth at the speed of light and probably fry everybody. We wouldn’t have time to realize if Einstein was right or not. We’d be dead.

But if Einstein was right, the orbital loss effects and the radiation will hit earth at the same time but we still won’t have time to flinch. We’d be dead.

Either way, if we don’t know the speed of gravity before the sun explodes, we probably never will.

Q,

we probably never will.


I actually think we will very soon.

Originally posted by yayacatfight
instead i got sarcasm, condescending remarks, and called a crackpot when i don't even have a theory. here, at this site, to question einstein's theory is sacreligious and falls on deaf ears. i was taught that no question is stupid.

i never called you a crackpot, and i never called your question stupid. i didn t even give you any sarcastic replies until you made disparaging remarks about my ability to think.

however, i did call you an asshole. asshole.

Originally posted by yayacatfight
well you got me, i don't know as much about gravity, light, or physics as you do. not even close. that is why i came to this site. i was hoping to learn something.

fine. instead of showing interest in learning or going through earlier threads where these things already discussed you started advicing one of the senior and may be the most knowledgable mathamatical physicist here to come out of text books.

instead i got sarcasm, condescending remarks, and called a crackpot when i don't even have a theory.

No one called you a crackpot. had you thought yourself for a moment what lethe said you would have realised even your hypothetical answer turned out to be silly or funny. see [Q]'s explanation.
Its you got first offended for no reason... may be because you are new to this forum.

here, at this site, to question einstein's theory is sacreligious and falls on deaf ears. i was taught that no question is stupid. i was only questioning the theory to learn more about it.
question about anything and everything. not an issue. commenting on capabilities of a trained physicist is surely not a way to learn and its in a way arrogant. obviously you don't know about lethe as well as the subject in question.

that pretty much sums up my experience here.
we too had bad experience from this. lets move on.

Originally posted by everneo

we too had bad experience from this. lets move on.

everneo-

thanks for sticking up for me. i appreciate it. perhaps i overreacted, i ve been getting pissy lately.

yeah.

lethe,

hey... and what happened at the meet with 'vortices' crackpot.. you promised to let us know..

everneo,

lethe,

hey... and what happened at the meet with 'vortices' crackpot.. you promised to let us know..



Maybe you found the cause of lethe saying "I've been pretty pissy lately":D

i got defensive because i like to think abstractly. i am aware of the consequences if the sun explodes, but that doesn't mean there is no value in discussing the subject.

lethe: sorry

i admit, my questions are silly and ridiculous, but i appreciate the comments from people that are smarter than me on the subject.

back to the experiment - if i started my stopwatch at the exact moment we flew out of orbit and the explosion hit slightly after the 504 seconds it takes light to travel here, then wouldn't i have proven that gravity is faster than light?

(yes i know i will be fried when the explosion hits, let's pretend the watch is made of indestructible alien metal and it is found and reads 505 seconds)

yayacatfight,

yes i know i will be fried when the explosion hits, let's pretend the watch is made of indestructible alien metal and it is found and reads 505 seconds)


Just make sure you have your inscription of the stop watch or you'll never get credit for the proof.:D

Originally posted by yayacatfight
i got defensive because i like to think abstractly. i am aware of the consequences if the sun explodes, but that doesn't mean there is no value in discussing the subject.

lethe: sorry

i admit, my questions are silly and ridiculous, but i appreciate the comments from people that are smarter than me on the subject.

back to the experiment - if i started my stopwatch at the exact moment we flew out of orbit and the explosion hit slightly after the 504 seconds it takes light to travel here, then wouldn't i have proven that gravity is faster than light?

(yes i know i will be fried when the explosion hits, let's pretend the watch is made of indestructible alien metal and it is found and reads 505 seconds)

just because the sun novas, does not mean it s gravity disappears. we will stay in orbit until we get fried. the sun still has mass, even if it is exploding.

Let's try to do a more "realistic" thought experiment shall we. I don't have one at this particular instant, but I am sure there is a better one.

The fact is yayacatfight, theory predicts that gravity propogates at a speed c. Experiment is yet to verify or deny this claim. A suggested upper limit to this speed is, as follows from Einsteins theory of relativity and lorentz invariance. There is however counter evidence that suggests that it is much faster than this. Until experiment comes up with a number, we will not know.

And to quash all rumours, to my knowledge know one is currently trying to find a value for the propogation velocity of gravity, they are simply trying to detect changes in the local gravitational field around some location due to the oscillation of say, 2 neutron stars about some centre.

And gravitational waves are not gravitons.

yep. damn. i hadn't thought about that.

HOWEVER if we think triangulation really BIG we could setup a gravitywave detector on the moon and compare the arrivaltimes of incoming grqvitywaves with detectors on earth and hence calculate the speed of gravity caused by the delay?????

What does everyone think about Vortexx's comments? This seems feasible no?

Triangulation. Where's the third detector placed. If there is no third detector, we will not be able to locate the source of the gravitational waves.

Mars. I think there are launches on June 5th and 25th.

June 5th is tomorrow. We better hurry.

HAHAHAHAHA........

Do you realise the size of the equipment being used to detect gravitational waves?

yes i do, it was another attempt at humor. i guess i need to start using the smiley faces.

Originally posted by yayacatfight


back to the experiment - if i started my stopwatch at the exact moment we flew out of orbit and the explosion hit slightly after the 504 seconds it takes light to travel here, then wouldn't i have proven that gravity is faster than light?



As already pointed out, the sun will retain its mass even after its exploded. But let's, just for the sake of argument, assume that instead of exploding, the sun just instantaneously vanishes.

Your experiment has a second problem: How do you determine the exact instant we flew out of orbit? We won't feel any change, The Earth is already following a free-fall trajectory, and would just follow a new one.
The actually change in the Earth's trajectory will be very small at first. In fact, during the 8 min it takes for us it see the sum vanish, the Earth will have drifted less than 1 km out of orbit. Too small a change to really notice.

I think the earth travels through space at 30km/sec. Assuming the speed of gravity was instantaneous we would be around 15,000 km out of original orbit when we saw the sun vanish. I think this assumption also would mean we would feel the change in direction. (Tether model of the earth to sun relationship)

Relativity would say that because gravity travels at the speed of light then it would vanish at the exact instant we see the sun vanish. The fabric of spacetime would not react instantly to the vanishing of the sun but at c. (Would it oscillate and settle at flatness or would it slowly move to flat?)

Or maybe a combination of the two would happen...the fabric of spacetime immediately snaps back to flatness and in that case I think you are right we would feel nothing.

i think a more realistic experiment would be like this

2 people are tugging on opposite sides of a rope ( a VERY long one, mind you) with syncronized clocks beside them, and when one lets go the other one records the time when he falls backwards or whatever. It does little to measure the actual speed of gravity but might give an idea as to whether it is instantaneous or not.:cool:

interesting.

let's say the rope was a light year long. would he fall instantly or in one year?

This has to do with the speed of propogation of electromagnetic forces, since the rope is held together by chemical bonds which are electromagnetic in nature. Thus the change in tension of the rope will propogate at a maximum velocity of c.

i see. back to the three gravitational wave detectors. one on earth, moon and mars. assuming in 100 years we can build massive ones in each place. will this be enough to triangulate the speed of gravity?

Sure, except that to do this you would need syncronized clocks because signals takes minutes to reach mars, etc,etc. But I havent yet thought of a way that u can place synchronized clocks on earth, moon, & mars, yet, because any signal can only travel at the speed of light!! :confused:

never mind there is a way actually
just send a signal from earth to mars at say 4:00 earth time, telling martians to set their clock to 4:15 or whatever length of time it takes for signals to pass...yes it would work:)

Originally posted by yayacatfight
I think the earth travels through space at 30km/sec. Assuming the speed of gravity was instantaneous we would be around 15,000 km out of original orbit when we saw the sun vanish. I think this assumption also would mean we would feel the change in direction. (Tether model of the earth to sun relationship)



Yes we travel at 30 km per sec, in circle with a radius of 149,600,000 km. So while traveling in orbit we trace a shallow arc of 14400 km in length. After the we lost the sun's gravity, we would move at 30km/sec in a straight line at a tangent to this arc and after 8 min would have again traveled 14400 km. The distance between these two end points (Earth's position if it had stayed in orbit, and Earth's position traveling in a straight line) will be less than 1km.


It doesn't matter how far out of position we moved however, we still wouldn't feel the moment of release. Again, the Earth is in free fall as it orbits, and would be in free fall afterwards. It is simular to this example, There is a man in a falling elevator, as he falls, he feels weightless in the elevator. If the Earth were to suddenly disappear from beneath him, the elevator would quit accelerating and would just travel at a constant speed. The Man in the elevator would feel nothing, as he would still feel weightless. There is no transition in forces for him to feel.

It doesn't matter how far out of position we moved however, we still wouldn't feel the moment of release.
Very true...we basically live in earth's inetria and gravitaional field only...we dont feel the suns gravity anyway. So even though earth is travveling around the sun at 30km/sec , and the solar system as a whole travels around our galaxy, the universe meanwhile is rapidly expanding so galaxies are moving farher and farhter apart...i dont know what inetria field to use!!!:confused:

If you want to learn about current gravitational wave research, Caltech and the Jet Propulsion Laboratory are doing some of the most advanced research (with some support from MIT). Here's the link to a web-based course in Gravitational Waves at Caltech. There are pdf's of the class notes and video files of the lectures. These lectures are quite advanced -- I've only seen the first two so far, but just watching the first one should give you ideas about where the current experiments are going.

Gravitational Waves
A Web-Based Course
Organized and Designed by Kip S. Thorne, Mihai Bondarescu and Yanbei Chen

http://elmer.tapir.caltech.edu/ph237/

thanks everybody! i'll be a few days digesting all of this.

Originally posted by yayacatfight
ok, lethe. here is your chance. give us one original thought. go ahead, hit us with it. go out on a limb, and put something down in writing that makes us think, but god forbid, might be ridiculed.

i didn't think so.

One original thought? I believe lethe is doing something called a "thesis" -- i'm sure there's at least one original thought involved. ;)