Gravity

[ragor]

Maybe you can answer these questions... or maybe not.<br /><br />A recent article in the Discover magazine stirred my interest when they proclaimed that more planets existed out of Pluto's orbit, nearly twice as far.. Although I don't know the specifics since this was communicated to me.<br /><br />Suppose hypothetically an object of enormous mass exists at point a. At point b, which is a considerable distance from "a", just exists space. Now supposed an object of slightly smaller mass than the object at point a suddenly exists at point b. How long does it take for the object at point b to feel a gravitational pull from the object at point a? Or is it instantaneous?<br /><br />If gravity is not limited by time why is it hindered by space? Or maybe I'm confused?<br /><br />And how much space is needed between objects for them to exist as a single object exerting a single field of gravity?<br /><br />This question came to mind when I thought that these far out planets were not rotating around the sun but instead the solar system as a whole.

 

[Saiph]

you're basically asking about the speed of gravity. How fast does a change in the gravitational field communicate itself to other bodies.<br /><br />Observed answer: Really fast, not actually sucessfully measured.<br /><br />Theoretical answer: The same as the speed of light.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>And how much space is needed between objects for them to exist as a single object exerting a single field of gravity? <p><hr /></p></p></blockquote><br /><br />Well...the distance between the two objects needs to be much, much smaller than the distance to the "observing" object. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[detriech69]

While I believe Pluto should forever remain a "planet", objects farther out from the Sun should probably be considered as Kuiper belt asteroids or objects no matter how big they are discovered to be. But as for the speed of Gravity, it is probably similar to light speed which varies depending on the medium it must propagate through, wether it is near vacuum or through dense dust clouds. Relying on a "constant" which isn't really constant, is better I suppose than trying to guage the many variations a stream of photons must experience traveling millions or even thousands of light years. But realizing this, most physicists would say the variations are negligible. The absolute fastest light can travel is the Constant they use in all calculations. I wonder just how much undiscovered gas and dust is clouding up their math when they figure how much the expansion of the Universe is accelerating?! But really, I don't mean to dilute anyone's trust in Science. It IS the best method we currently have to attempt to understand our place in this enormous cosmos we find ourselves in. My only point is, new discoveries are always being made that force us to re-evaluate previous theories and even re-examine the accepted physics they are based upon.<br />But, again, without being able to detect gravity waves, if they even exist, the speed of gravity is just a guesstimate on anyone's part, even Steven Hawking's.<br />These thoughts are only my opinions and everyone is entitled to their own. Keep looking up!!

 

[para3]

I<b>'m curious about something that makes sense to me. Would there be a universe if the force of gravity wasn't present? </b> <div class="Discussion_UserSignature"> <p><strong><font size="3" color="#99cc00">.....Shuttle me up before I get tooooooooo old and feeble.....</font></strong></p><p><strong></strong></p><p><strong><font size="4" color="#ff6600">---Happiness is winning a huge lottery--- </font></strong></p> </div>

 

[kmarinas86]

If there was no gravity there would be no gravitational orbits. The whole universe would be much like the emptyness between the galaxies, with a very homogeneous distribution of matter. Heat death would occur soon as the time need to cool would be much shorter since nothing is heating up to begin with. The absence of gravity means the absence of friction due to gravity. The only remaining friction would be due to electromagnetic, strong, and weak interaction, and those forces are neutralized beyond short distances so no large structures would form. In fact, since there would be no stars, there would be no heavy elements either, therefore planets would not be able to form.

 

[SpeedFreek]

It is theorised that, soon after the initial singularity, the young universe was full of superheated "quagma" (quark-gluon plasma). Supposedly, if this plasma had been uniform in nature, there would have been no concentrations of mass. Quantam fluctuations during the initial inflation caused there to be a slight non-uniformity of the plasma and due to gravity, the slightly denser areas attracted material from the less dense areas. (The non-uniformity of the plasma was required for the "big bang" model to work, and was seen recently in the slight differences in the cosmic background radiation).<br /><br />Without gravity, however "lumpy" the early quagma was, there would have been no method for anything to form into stars. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[search]

The Special Theory of Relativity describes the events which take place in a universe with no gravity...

 

[ehcuob]

Does a person weigh more lets say a mile below sea level because warp space time or is it unmeasurable?

 

[vogon13]

Theoretically less, and not due warped space time, but simply that a mile worth of mass above you pulls upward and cancels out a tiny bit of gravity coming up from below.<br /><br />(overlooking relativistic effects because they are tiny in this example, it is late, and I am tired)<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[bbk1]

Interesting.... I thought you would weigh more as you near the center of Earth where the gravity is at its greatest magnitude.

 

[Mee_n_Mac]

If you model the Earth as being the same density independant of what direction you go from the center then you weigh nothing at the center of the Earth. The gravitational force of any matter to your right is exactly cancelled by the force of matter that's equidistant to you left. You're being pulled to the right with exactly the same strength as you're being pulled to the left so there is no net force. Same for forces due to matter above and below you and in general any direction. All the forces cancel at the center so your weight is zero. There was (probably still is but I haven't found it) a nice diagram illustrating this on the WWW. The pressure however is immense, I wouldn't advise a trip there just to loose weight. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>

 

[abhinavkumar_iitr05]

A person weigh less when he is near the center, if only his own mass is considered not the pressure force due to the see water.Its simple because gravity varies inversely with square of the distance from the center but mass of a spherical object varies directly to the cube of the distance from the center.<br />

 

[doubletruncation]

All the above explanations are quite excellent. I would only add a cute fact - since, as mentioned above, the internal mass scales as the radius cubed whereas the gravitional force due to a point mass scales as 1/radius^2, the net gravitational force that you experience is directly proportional to your distance from the center (until you pass above the surface, in which case the mass inside the sphere below your feet stays the same as you move up, so the net gravitational force drops as 1/r^2). The force being directly proportional to the distance is just like what happens for a spring. So if you where to somehow drill a tunnel through the center of the Earth to the other side (and keep it from collapsing) and jumped in your motion would be analogous to that of a stretched slinky. The force would be greatest at the surface and fall to zero as you past through the center, so you'd accelarate the most at the surface and your acceleration would be zero at the center (but your speed would be largest there). You would continue all the way to the other side of the Earth, but decelerating the whole way so that just as you made it to the other side your speed would reach zero and you'd fall back down. Assuming no friction (you somehow evacuate the air out of the tunnel) this periodic motion would continue indefinitely, with you falling from one side of the Earth to the other - it'd actually only take you about 2 and a half minutes to fall from one side to the other and back.<br /> <div class="Discussion_UserSignature"> </div>

 

[falsify]

i was just thinking of a movie i watched when i was younger and there were sort of a motorcycle moving in the air!!<br />i know it's unreal but what if we did find the secret of gravity? would we be able to invent such things as vehicles floating around />?

 

[kelvin_zero]

I would lay odds against antigravity discoveries, but there might be other ways to get your floating motorbikes. For starters, helicopters and hot air balloons do a fair imitation of levitating, we just dont consider it as such for asthetic reasons. Helecopters make lots of noise and wind and need a fair bit of power, and balloons get pushed around by winds too easily. Solve any of these problems and you have something that looks like levitation.<br /><br />One idea I like for example is a membrane that lets air through it one way only.. so it only maintains air pressure on one side. This violates that rule about entropy but perhaps if it took some power it could be a more efficient and totally soundless helicopter while violating no laws. You could wear it like a parachute with a small power supply and trigger it on the ground to pull you into the sky. Since the chute is made from some sort of miracle nanotube fibre it would probably be pretty much invisible but for a shimmer.<br /><br />Or what about fusion power and some sort of sound damping technology. Then you could have a hovering craft that stayed perpetually aloft and made very little noise, perhaps some magnetic way of pushing the air so it is not hot.<br /><br />Another rather wacky approach could be paramagnetism to push on the air around you over a large area. lowering the air pressure around you slightly could give you lift the same way a hot air balloon does but would be invisible and insubstantial and not blown around by the wind.<br />

 

[mrcurious]

Post deleted by MrCurious

 

[MeteorWayne]

If an apple falls from a tree above you, does it not hit you in the head?<br />Granted that is macroscopic, but it shows the rules work pretty well.<br />At the microscopic level, AFAIK, all experiments have verified the common understanding of gravity.<br />Can you provide some evidence that disagrees with this so we can discuss it? <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[mrcurious]

So that's evidence of gravity on a microscopic level? <br />I was thinking that since we didn't have;<br /><br />1)We don't have a theory for quantum gravity that can provide us testable evidence. <br /><br />2) We haven't found a particle to mediate this force. <br /><br />3) We're just now starting to create experiments to show that gravity.<br /><br /><br />[url=http://www.weburbia.com/pg/qugrav.htm]http://www.weburbia.com/pg/qugrav.htm<br />http://www.physorg.com/news76605596.html<br />

 

[cazuke]

Hi Guys<br /><br />I was watching a program about the universe and there they said that the universe is expanding in all directions. (so nothing new there! ) Everything is moving away from everything else (unlike a bomb explosion where everything is moving away from the centre)<br /><br />Anyway... first I thought "Isn't that ironic? We say there gravity everywhere and all matter pulls all other matter towards itself but despite that everything is moving away from one another" I.e two contradictory forces.<br /><br />Then I got an idea. Is it possible to view gravity not as a pull force but maybe as the lack of a push force? I've been thinking about this for a while but now I think maybe the two are even linked. I.e, the same force that pushes everything from another results in the planet 'pulling' me closer.<br /><br />So may theory goes something like this:There's only this one force that pushes everything in all directions. But if one mass is in a the 'shadow' of another mass, that results in a relative pull between the two. <br /><br />Does this make any sense?

 

[alokmohan]

The expanding universe is like a ballon expanding.All points receding from each other.

 

[weeman]

<font color="yellow"> We say there gravity everywhere and all matter pulls all other matter towards itself but despite that everything is moving away from one another" I.e two contradictory forces. </font><br /><br />The expansion of space only takes over when there is an absence of gravity. Gravity overpowers the expansion in several situations. Which is why we even have stars, planets, solar systems, and galaxies in the first place. <br /><br />Cosmic expansion is only overcome on much smaller scales (like our solar system). The space between Earth and the Sun does not expand because the presence of gravity is powerful enough to prevent expansion.<br /><br />However, on larger scales, say several billion lightyears, gravity is far too weak and far too scarce to overpower the expansion. This is why we see expansion on a scale of billions of lightyears, yet the Milky Way and Andromeda galaxies are rocketing towards each other. <br /><br />They are not two contradictory forces. <br /><br /><font color="yellow"> But if one mass is in a the 'shadow' of another mass, that results in a relative pull between the two. </font><br /><br />That just sounds to me like the general definition of gravity that has been around for decades. <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[cazuke]

I get what you're saying weeman. But I think you misunderstood my 'shadow' sentence.<br /><br />In one dimention I mean something like this:<br />----O--o----<br />Where O is my sun and o is my planet. Because they 'shield' eachother from the pushes from all directions, they seem to pull at one another. But o is not moving away from O because O is in the way of all the pushes that would have pushed o away from it. <br /><br />What do you think?<br />

 

[weeman]

I apologize, I am having a tough time understanding your theory! We need to get some other brains in on this topic from the rest of the discussion board <img src="/images/icons/rolleyes.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[schmack]

Hi cazuke, <br /><br />welcome to SDC!<br /><br />This is an interesting question, and i'm not sure i can explain it as well as some others, but i think what weeman is trying to say is simply this. Gravity and the "expanding universe force" (EUF?) are two very different forces because, as you stated, <font color="yellow"> But if one mass is in a the 'shadow' of another mass, that results in a relative pull between the two. </font>gravity works on a MUCH smaller scale than EUF. i'm guessing its almost like quantum physics on the next scale up rather than down. ie: the forces just don't seem to be related so simply. <br /><br />Though as i have stated before, IMO physics will become an elementary science before we are finished exploring this galaxy or universe.<br /> <div class="Discussion_UserSignature"> <p><font size="4" color="#ff0000"><font size="2">Assumption is the mother of all stuff ups</font> </font></p><p><font size="4" color="#ff0000">Gimme some Schmack Schmack!</font></p> </div>

 

[themage]

The idea that you propose is very interesting and simple. But remember that not only do you need to apply this to large celestial bodies; you would also need to apply it to everything else. Can you incorporate into your theory what GR and Newtonian theory already accurately predicts?