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angry

Mass and gravity :=)

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Heh, okay this is a question i've been carrying around for a while. It's probably dead-stupid. And well, I could probably find out the answer on my own, however it could take anywhere from 1 day to a lifetime. So I'll ask instead. My question is. Can you actually prove that mass creates gravity? And that gravity didn't exist before the mass ever got there? An idea would be that universe is a bathtub, the water in the bathtub is space, and a rubber duck floating in the water is mass. Then when you pull the plug, causing a "gravity hole", will cause the water to flow out, until the duck covers the hole. Heh, like I said it's dead stoopid, but i think it's a nice idea :)

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No experimental data exists that indicates that mass and gravity are in any way decoupled. There are some new experiements going on right now that are testing the laws of gravity at extreme close ranges, like a few millimeters, but so far every experiment ever does matches the theory well within experimental error bounds.

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In theoretical space, where there exists no mass(1), a mass(2) arriving at the location would be attracted to no other mass(1 or anything else). Meaning, without a mass, there is nothing to be attracted to. Rather than proving mass creates --> gravity, I proved (kind of) that without mass, gravity cannot exist(therefore, can't be created).

('cuse the grammar).

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In General Relativity, gravity is a manifestation of the curvature of space-time. The space-time curves one way in the presence of mass (actually something more complex, momentum-energy). Space-time that is not in the presence of mass but is in the immediate presence of curved space-time, curves in a different manner. G.R. has been tested to very high precision, and agrees with observations made. If the sun was to suddenly disapper, the Earth would still remain in its current orbit as if the sun was still there for about the following 8 minutes until the gravity wave passed us by.

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According to Einstein, and it makes sense: gravity is the acceleration of one electrodynamic body toward another.

So without two bodies, there is no gravitation (yes, I just cut out about 90% of the explanation).

For instance, can you gravitate toward a cookie if it's not there? No. Oppositely, if there is no cookie, then it cannot gravitate you toward it. Either way, it boils down to the fact that there is no co-gravitation.

If you find this answer unsatisfactory, ask yourself this: Is there anywhere in the universe where mass doesn't exist?

Better yet, is there anywhere in/on the cookie where the cookie doesn't exist?

Best yet, what would you consider massive? Does the space between the molecules inside of the cookie count as massless? What about the Dirac Sea? Does it apply to these spaces? Is there a Cookie Sea?

If you had the grand opportunity to step outside of the universe and check this out for yourself, you've already run into a big problem: You are as much of the universe as anything else is, so in essence, the universe would "follow" you, maintaining the fact that you are still part of the universe.

So really, can there be gravitation without mass? Nope, there's nothing without mass. Not cookies, not Einstein, not you.

If you want to throw Einstein out the window and go with Newton's half-correct approach: Without mass, there is nothing to be forced, so how could a force exist when there is nothing to force? It can't, because it serves no purpose, because it acts not in a forceful way.

The question then is: Can gravity act in a non-forceful way? Can mass act in a forceful way?

Here we end up back with Einstein: The accumulation of mass in an area is due to gravity. The accumulation of gravitation in an area is due to mass. Sounds to me like they're interconnected beyond separation, because really, they are the same thing. Like electricity and magnetism: The only difference between them is the spelling of the word.

[Edited by - taby on October 2, 2006 11:03:12 PM]

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Quote:
Original post by Sneftel
Quote:
Original post by angry
until the duck covers the hole

what



LMAO... at that part of the reply.
I see what your saying and its interesting.

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Think about this, my favorite way of explaining mass and gravity relation, though it does make me think of it's flaws, as it tends to be a 2D example that's wrong in 3D but none-the-less.

Say the Universe (or Space) was represented by a large cloth that was stretched out. Now on this cloth are a bunch of moarbles, of different sizes. Each of these marbles causes the cloth to stretch and create a small divet in it. When two marbles come close enough, if one weights enough it could stretch the cloth creating a sort of hole, and when that other marbles gets close enough, it falls into the hole with the bigger marble. Wich would be the effect of gravity pulling objects near to it.

With this example the same bit of physics that applys to gravity apply here, the heavier and bigger the object the bigger the hole, the greater the effect of gravity. Say you rolled a bowlling ball across the cloth, it would emit it's gravity in the form of the hole, pulling in anything around it.

Well that's the way I think about it.

Deeper thoughts... everything is built up of Atoms, and the theory of atoms, is they love to fill in missing electrons by stealling them from other atoms, causeing the two to come together formming one and a little bit of spare energy that's shot back out. On a large scale, the surface of a massive object could be one large scale chemical reaction pulling atoms together, destroying them with the released energy and pulling more in to replace them, on a continuos cycle.


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Original post by angry
An idea would be that universe is a bathtub, the water in the bathtub is space, and a rubber duck floating in the water is mass. Then when you pull the plug, causing a "gravity hole", will cause the water to flow out, until the duck covers the hole.

So... The water is space, and the water drains out the plug-hole, which means the amount of space in the universe is dissapearing through a "gravity hole"?

Can I ask the question, is it possible for space (which is pretty much nothing) to be sucked into a hole?
If the hole in nothing-space sucks up nothing-stuff made of nothingness, then it must be even more nothing than nothingness. So if space = 0, and space-gravity-hole = 0, then 0 < 0! Cool...

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Original post by taby

If you had the grand opportunity to step outside of the universe and check this out for yourself, you've already run into a big problem: You are as much of the universe as anything else is, so in essence, the universe would "follow" you, maintaining the fact that you are still part of the universe.

So really, can there be gravitation without mass? Nope, there's nothing without mass. Not cookies, not Einstein, not you.


That explains it well.

Mastaba; although the Earth would continue orbit until the gravity wave (made up of gravitrons, correct if wrong) passes by, your reply deals with motion after decrease of gravity. What if there was no gravity to begin with? An earth not in motion can be affected by the sun only if the sun & earth exist (mass).

This is the micro explanation (most common). There might be a sub-micro (dealing with smaller than planet, mass), but people also explain this in a macro explanation, such as the quote above dealing with inner/outer-universe examples.

Where are you? Inside the universe or outside?

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Original post by D Shankar
Mastaba; although the Earth would continue orbit until the gravity wave (made up of gravitrons, correct if wrong) passes by, your reply deals with motion after decrease of gravity. What if there was no gravity to begin with? An earth not in motion can be affected by the sun only if the sun & earth exist (mass).

This is the micro explanation (most common). There might be a sub-micro (dealing with smaller than planet, mass), but people also explain this in a macro explanation, such as the quote above dealing with inner/outer-universe examples.

Where are you? Inside the universe or outside?


I refuse to address the metaphysical nature of the question. What matters is not what happens when there is no mass period, but what happens in our Universe (the only one that matters!), and in our Universe there is mass, and there is an observer of said mass.

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Nice lots of answers =) Oh and I never thought about the "When the sun explodes" gravity goes away.. or does it? :P

Quote:

Can I ask the question, is it possible for space (which is pretty much nothing) to be sucked into a hole?
If the hole in nothing-space sucks up nothing-stuff made of nothingness, then it must be even more nothing than nothingness. So if space = 0, and space-gravity-hole = 0, then 0 < 0! Cool...

If space was nothing you wouldn't be able to travel through it. Also space wouldn't be able to bend if it was nothing. So space is something.
And the hole in the bathtub might not be a hole that goes to any place in particular, but might just be an inverted bump which pulls/draws the water and the duck to it for some reason.

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Original post by angry
Nice lots of answers =) Oh and I never thought about the "When the sun explodes" gravity goes away.. or does it? :P

"Suddenly disappear" was the actual phrase, an event that would be significantly different from "explode"; the former is just a hypothetical, but not physically possible event (or so I speculate). Though I suppose the end result would be the same either way: We would die.

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To answer your question, there is evidence that mass bends space-time (gravity is the noticible effect of this bending) from tests of light being bent as it passes close to stars. A quick and well illustrated read is Stephen Hawkings "Universe in a Nutshell."

cheers,

Bob

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You might educate yourself a little in current research about gravity, and about all constrains that are known. Gravity has NO aberration (proven by moon eclipse), thus the most simple explanation would be effect of central star disappearing would be immediately noticed. (even before light would disappear from the sky)

You are also talking about particles that highly likely doesn't exist. The hint could be distance at what gravity interacts.

Of course considering photons are momentum carriers, the gravitational lensing effects would work. On the other hand not all people believe that photons are massless.

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Original post by Raghar
You might educate yourself a little in current research about gravity, and about all constrains that are known. Gravity has NO aberration (proven by moon eclipse), thus the most simple explanation would be effect of central star disappearing would be immediately noticed. (even before light would disappear from the sky)

You are also talking about particles that highly likely doesn't exist. The hint could be distance at what gravity interacts.

Of course considering photons are momentum carriers, the gravitational lensing effects would work. On the other hand not all people believe that photons are massless.


ESA.int : Relativity and the 1919 eclipse
Space.com article: Einstein's Warped View of Space Confirmed

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Two links the second talks about effects that could be viewed as a spin affecting momentum carriers. The first talked about an old irrelevant experiment.

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Original post by Raghar
Two links the second talks about effects that could be viewed as a spin affecting momentum carriers. The first talked about an old irrelevant experiment.


Care to explain yourself? Why is 1919 eclipse irrelevant? It's been verified during subsequent eclipses.

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It was important not for only one theory, this behavior is actually expected by more different theories.

It actually didn't verify anything, it's just a gravitational lensing, they didn't know its unimportance however, so for them an experiment proving the light might be affected by gravity was an important experiment anyway.

I consider more important that research about passive mass, and other types of masses.

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Original post by Raghar
I consider more important that research about passive mass, and other types of masses.


There is absolutely no observation to date that indicates an inequality between passive mass and active mass. Sure, there are mathematical hypotheses that outline the consequences of such an inequality, but those are absolutely useless without any verified, repeatable observations that show they are unequal. Indeed, there have been repeated observations looking for such an inequality, and they never find it, and instead set a maximum difference which is remarkably small, and getting smaller with each experiment.

Regarding other types of mass, I find it reckless to assume such things are even meaningful when present theory fully fits observations without such complexities added to the mix.

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