View Full Version : Gravity?
icvotria
Apr25-05, 07:59 PM
What actually is gravity? I understand it in terms of what it does but I don't know the whys or hows at all.
Join the club, no one knows for sure but I think special relativity was aimed at this question.
Well, no body exactly knows what gravity is, but we at least know that it causes rupture in time space and that mass travels the shortest way possible. There is allot we don't know about. It seems that dark matter plays a crucial role in the phenomenon of gravity. But we don't even know if dark matter has the same dimensional mass as real mass.
neurocomp2003
Apr25-05, 09:20 PM
gravity only exists in mathematical physics modelling world...because its near impossible yet to study the flow of massive multi-particle systems...try programming the effect tracing out all the particles in the system. However gravity is nice cuz it describes the system in 1 numerical value, just like time.
Truth is a tremendous thing ;)
James R
Apr25-05, 10:21 PM
The Newtonian view of gravity:
Gravity is one of four fundamental forces in our universe. It is an attractive force which acts between every pair of objects with mass.
Einstein's view of gravity:
Gravity is an apparent attraction between masses which is due to the fact that masses curve the space and time around them in such a way that nearby objects look as if they are attracted.
Why does gravity exist?
Nobody knows. It is just one of the four basic interactions between things in our universe, the other three being electromagnetism, the strong nuclear force and the weak interaction.
Why is gravity the way it is?
Nobody knows. Why does an electron have the precise mass it has, rather than some other value? Nobody knows.
KingNothing
Apr25-05, 11:45 PM
At this point in time it's all just philosophy.
Einstein's view of gravity:
Gravity is an apparent attraction between masses which is due to the fact that masses curve the space and time around them in such a way that nearby objects look as if they are attracted.
Wait, APPEAR to be attracted? Like, theyre not really moving, they just look it? That doesnt sound right to me.
James R
Apr26-05, 01:42 AM
They move relative to one another, but there is no attractive force involved in the general relativistic picture. If masses move towards each other, it is because spacetime curves in such a way that they naturally do that. Technically, all objects move along geodesics in spacetime, in the absence of forces (and remember, in this picture gravity is not a force).
Ok, thats pretty different from what you said. I interpreted it as they arent really moving at all, and that it was just an illusion due to gravity working in a number of dimensions higher than what we see.
Thats really cool.
icvotria
Apr26-05, 03:43 PM
Let me check I've got this right; gravity is just a description of the effects of mass curving spacetime, it's not a force at all, and the real question is why/how does mass curve spacetime? Which is something I'm going to have to wait a very long time to have the answer to.
neurocomp2003
Apr26-05, 06:38 PM
Learn some 3D graphics Programming and then learn some advanced level physics then in 20-30 years time perhaps we will have the computational power to implement what you seek =]
icvotria
Apr26-05, 08:31 PM
Alas, I'm terminally lacking in both patience and intelligence. Tis a shame, I would love to solve gravity :)
James R
Apr26-05, 08:32 PM
Yes, that's right icvotria. And NOBODY knows right now why mass/energy curves spacetime. It just does! We know a whole lot about exactly how it does it, though.
<<<GUILLE>>>
Apr27-05, 01:14 AM
we still don't know the very background reason for gravity. or for many other things, specially in physics.....
At this point in time it's all just philosophy.As is all of physics (in this sense*) :smile:
Perhaps 'just' is just too strong though ... after all, using the GR concept - plus the math, of course - you can *send spaceprobes across the solar system, *find your position on the Earth's surface with great accuracy, *'account for' (a.k.a. 'explain') the changes in the radio signals received from distant pulsars such as PSR 1913+16, etc.
*what is an 'electron', a 'quark', a 'superconductor', 'charge', ...
Starship
Apr27-05, 04:23 AM
General relativity does not tell us what mass-energy & spacetime are, therefore it can't be a correct theory of the physical universe. We don't know why stuff has mass therefore i think it's correct to assume that gravity is a quantum dynamical effect.
The Higgs bosons should give particles their mass:
\mathcal{L}_S = \frac{1}{4} h \upsilon^{4} + \mathcal{L}_H + \mathcal{L}_{HG^2},
\mathcal{L}_H = \frac{1}{2} \partial_{\mu}H \partial^{\mu} H - {1 \over 2} M_{H}^{2} H^{2} - \frac{M_H^2}{2 \upsilon} H^{3} - \frac{M_H^2}{8 \upsilon^2} H^4,
M_H = \sqrt{-2\mu^2} = \sqrt{2h} \upsilon .
General relativity does not tell us what mass-energy & spacetime are, therefore it can't be a correct theory of the physical universe. I agree that it can't possibly be a comprehensive theory ... but that's because it is inconsistent with QM, in certain domains (or rather, the two are mutually inconsistent).
Looking at the Standard Model (particle physics), how well are concepts such as 'isospin', 'charge', 'particle', and 'colour' spelled out? I mean, what 'are' these, in the physical universe?
Starship
Apr27-05, 08:47 AM
I agree that it can't possibly be a comprehensive theory ... but that's because it is inconsistent with QM, in certain domains (or rather, the two are mutually inconsistent).
Looking at the Standard Model (particle physics), how well are concepts such as 'isospin', 'charge', 'particle', and 'colour' spelled out? I mean, what 'are' these, in the physical universe?
The standard model is equally unsatisfactory, therefore quantum gravity is highly speculative.
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