Gravity and Time

[castelle]

This is my first time posting a question, so be gentle. I have a fairly simple question about the force of gravity. What is the threshold at which an object will start to exert gravity or does every thing with mass create gravity, just not enough to notice? Also, is there a threshold at which speed start to affect time, or does all speed affect time, just not enough to notice? ex. At what speed does time start to slow, according to the theory of relativity?

 

[kyle_baron]

<i><br />Also, is there a threshold at which speed start to affect time, or does all speed affect time, just not enough to notice?</i><br /><br />Yes, any speed (movement) will slow time down. And your right most of it isn't noticeable.<br /><i><br /> At what speed does time start to slow, according to the theory of relativity?</i><br /><br />Time stops at the speed of light. Time slows down with any movement. Not to confuse you, but ANY MOVEMENT thru space/time (all 4 dimensions at once) is at the speed of light. This is according to Special Relativity. From The Elegant Universe p.50 "...all objects at rest relative to us, move thru time, they age at exactly the same rate. If an object does move thru space, this means that some it's motion thru time must be diverted." This is how space-time works, according to Special Relativity. Your question on gravity, I'll leave to someone else here at SDC, because I'm not sure. <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[search]

Gravity is the force of attraction between massive particles. So you've got mass you've got gravity. Threshold is to have mass.<br /><br />As for speed and time its more complicated. There are two theories of relativity (both from Einstein): <br />Special Relativity and <br />General Relativity.<br /><br />The phenomena you are refering between speed and time is called Time dilatation but it varies from one theory to another (they are both correct just see the phenomena from a different perspective).<br /><br />Your Trip to Paris...<br />In Special Relativity you and your best buddy run to catch the bus to Trocadero but without accelerating (uniform speed), your best buddy will see your clock going slower. The funny thing is that you will see his clock running slower also. This is because time does not change for the reference point.<br /><br />In General Relativity during that trip that you and your best buddy did to Paris you went up the Eiffel tower but your best buddy (which is afraid of heights) decided to stay on the ground. This time you look down and see that your buddys clock is running slower and in fact he agrees with you.<br /><br />"In special relativity, the time dilation effect is reciprocal: as observed from the point of view of any two clocks which are in motion with respect to each other, it will be the other party's clocks that is time dilated. (This presumes that the relative motion of both parties is uniform; that is, they do not accelerate with respect to one another during the course of the observations.)"<br /><br />"In contrast, gravitational time dilation (as treated in General Relativity) is not reciprocal: an observer at the top of a tower will observe that clocks at ground level tick slower, and observers on the ground will agree. Thus gravitational time dilation is agreed upon by all stationary observers, independent of their altitude."

 

[derekmcd]

There is no actual threshold for gravity. Try not to think of gravity as an actual physical force. General relativity describes it as more of a 'well' in space creating curvature. Anything with mass creates this well. Even subatomic particles have gravitational fields. However, with gravity being the weakest of the 4 forces, experimentation and observation at such small scales remains so difficult that gravity isn't even part of the Standard Model of particles.<br /><br />A better question might be at what particle sizes or scales can gravity be observed or at what combination of lengths and scales do Einstein and Newton's laws no longer have relavance. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>