Gravity?

[Waldo]

Is there a maximum distance that gravity could be detected? Assuming any instruments could be used? (invented or not) And would there be a minimum force that gravity could cause? or is there no minimum
Any help would be great.

[ecoli]

well, assuming two bodies have mass, and a theoretical instrument could be used, they could be an infinately far apart, couldn't they.

[Waldo]

Alright, makes sense. how bout i reword my question.

Assuming General Relativity is correct, and the force of gravity is caused by a deformation in space-time, is there a minimum amount of deformation in space-time possible? Is there a minimum detectable force of gravity?

[danny8522003]

Where m > 0.

[RyanJ]

well, assuming two bodies have mass, and a theoretical instrument could be used, they could be an infinately far apart, couldn't they.

I agree, we have a problem though - the speed of gravity. Gravity can only propogate at the speed of light so it could not be detected if we moved to a location to where the gravity had not yet reached.

Considering theoretically gravitational waves could be detected from the merging of two black holes for example I totaly agree with ecoli :)

PART 2

I suppose it depends, is there a plank weight? There are fundamental limits for the the depths to which we can measure space its self before the undulations become too bad.

We should be able to measure the smallest component of the universe given powerfull enough eqiptment (whichwe currently are no-where near having) :)


Cheers,

Ryan Jones

[5614]

Theoretically there is no "minimum detectable force of gravity".

However in reality there is no equipment that would be sensitive enough.

The limiting factor is the technology (ie. measuring equipment) and not the physics.

[RyanJ]

Theoretically there is no "minimum detectable force of gravity".

However in reality there is no equipment that would be sensitive enough.

The limiting factor is the technology (ie. measuring equipment) and not the physics.

Oh.. gravity decreased with distance, so even if something like the strings from string theory made gravity (Not detectable) then one that spread out it would get harder and harder...

Since we have not yet found those gravity waves I would preume we are quite a long way from detecting these :)

Cheers,

Ryan Jones

[aj47]

So gravity is a continous force, not quantized like E.M?

[5614]

Why do you say that?

There is a well respected theory that gravity can be quantised (into gravitons) but there is no experimental proof because (quite on topic) gravity cannot and has never been observed on an atomic scale. Scientists have tried to observe gravity on an atomic scale but have never succeeded. This is a problem when trying to quantise gravity.

EM forces are quantised, sure, but it still goes on forever. The inverse square law applies to both the EM forces and gravity. Quantising something doesn't limit the distance it can travel.

[JustStuit]

Eventually, wouldn't the mass of the measuring instrument create more (however little) gravity than the object, creating a limit at which the source couldn't be measured?

[insane_alien]

Eventually, wouldn't the mass of the measuring instrument create more (however little) gravity than the object, creating a limit at which the source couldn't be measured?

could be factored out assuming you know the exact shape of the gravitaional field of the measuring device. and the observer of course.

[ydoaPs]

Is there a maximum distance that gravity could be detected? Assuming any instruments could be used? (invented or not) And would there be a minimum force that gravity could cause? or is there no minimum
Any help would be great.
you don't have to go far for gravity to become weak. it is proportional to r^-2
F_g=G\frac{m_1m_2}{r^2}
so, if we increase our distance infinitely, \lim_{r{\to}\infty}{F_g}=0.

now, we don't even have to go that far for it to be weak. just pick some random values for m1 and m2. then let r be 10, then 100, then 1000, then 10000, etc. now, if we have the sensitivity of a measuring device, it's mass, and the mass of the object whos gravity we are trying to measure, we can approxamate how far we would have to be from it to not detect it's gravity.

[5614]

Whilst this \lim_{r{\to}\infty}{F_g}=0 is correct may I point out that it is a limit. It shows that as the distance gets nearer to infinity the force of gravity (F_g) tends to 0... it never actually reaches 0.

[ydoaPs]

thanx for pointing out the typo. it is fixed now.

yes, it tends to it, but it is infinitely close to it at infinity. can you actually get infinately far away from it? no. the whole idea of introducing the limit was to show that it does get smaller as you get farther.

[5614]

Agreed, but if people misinterpret the limit then the answer to the original question "Is there a maximum distance that gravity could be detected?" could be answered incorrectly.

At an infinite distance the answer is infinitely close to zero, but mathematically it is not actually zero.

[ydoaPs]

not necesarily. you would need to make a graph. most of the time, \lim{x{\to}a}f(x)=f(a). that is one of the things needed for a function to be continuous over an interval. if f(a) exists and \lim_{x{\to}a}f(x)=f(a) over a certain interval, then the function is continuous over said interval.

[5614]

You say "not necesarily" and then seem to agree with me.

What do you mean "if f(a) exists"? Do you mean it is a real number or a non-zero value?

If you drew a graph of F_g vs r^2 then F_g = 0 would be an asymptote, ie. it is never actually reached. This is my point.

[ydoaPs]

You say "not necesarily" and then seem to agree with me.

What do you mean "if f(a) exists"? Do you mean it is a real number or a non-zero value?

If you drew a graph of F_g vs r^2 then F_g = 0 would be an asymptote, ie. it is never actually reached. This is my point.I was too lazy to even draw it out. You seemed to say that a limit is never the same as the actual value at that point. I'm sorry. Yea, it would be an assymptope.

[anglepose]

Any way it would be seriusly hard to tell what object the gravity came from with the amount of matter in between you and the object at suck large diffrences.

[Sashatheman]

can i ask a question while we are talking about gravity.

If gravitrons are discovered. How does more mass mean more gravity? wouldnt gravitrons just be separate particles that are flying around in space? or are they somewhere in the atom.

[Klaynos]

Gravitons (if they exist) act as communication particles they pass between massive objects to "tell" each other they exist. They are virtual particles like virtual photons when we talk about EM force... So they both fly around space and are inside atoms (sub atomic particles do feel gravity it's just very weak).

[Sashatheman]

Gravitons (if they exist) act as communication particles they pass between massive objects to "tell" each other they exist. They are virtual particles like virtual photons when we talk about EM force... So they both fly around space and are inside atoms (sub atomic particles do feel gravity it's just very weak).


thanks man .

so gravitron particles act the same way as those gluons with quarks. they interact between two bodies

[Klaynos]

thanks man .

so gravitron particles act the same way as those gluons with quarks. they interact between two bodies


Yep, they're both exchange particles...

[dkv]

Is there a maximum distance that gravity could be detected?
REP: Yes it can be detected.... and is always detected. But yes there is nothing called as Gravity and what exists is Gravitation.
A Gravitational theory may produce short distance repulsive forces.
BUt only after we include Anti-Gravitational Field.It comes with Einstein's theory.
Long Distance Repulsion is also not ruled out.
===============================================
Assuming any instruments could be used? (invented or not) And would there be a minimum force that gravity could cause? or is there no minimum
Any help would be great.
REP: Yes there is always a minimum. No Field theory can not be comunicated.

[Sashatheman]

i heard a theory that states, that gravitrons may be such a weak force, because they can travel into parallel universes. It was a documentary about the string theory , and they used slices of bread to represent each universe, which cannot interact with each other, but it was proposed that gravity can travel from slice to slice ei through different universes.

anyway whos heard this and want to explain it in more detail.


i got this from a docu called "elegant universe"

[5614]

I once read that a theory explaining why gravity was so weak was because it had to spread across all 4 of the dimensions in the universe.

(sub atomic particles do feel gravity it's just very weak)Just a point: Graivty has never been observed on an atomic (or subatomic scale). That is gravity is so weak at that scale it is totaly undetectable with modern equipment. This is part of the problem of observing the graviton.