Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 03/12/2005 04:34:27
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It occurred to me a while ago that all the forces of which we are aware are forces of attraction - weak, strong, electro-magnetic, gravity (yes, I'm aware that like poles of a magnet repel each other, but magnetism is basically an attraction). Is there any theory as to why this is? Or are there forces of repulsion of which I am not aware?
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The reason you see it that way is not because the forces are all attractive it is because only the attractive parts of the forces produce associations that last and can be more easily observed. Of all the fundamental forces all have repulsive components as well as attractive ones. For example like electrical charges repel each other and as you mentioned like poles repel each other. The only force for which no repulsive element is known is gravitation, however there are several important repulsive effects in cosmology that have to be fully accounted for: firstly the existence of a "big bang" itself, then the possibility of an inflationary period to explain the extreme homogeneity of the initial expansion, the continued expansion of the universe and finally the current "dark energy" observations of an increasing rate of expansion in more recent times. It is hoped that a truly quantum theory of gravitation and space-time will include some of these and explain the dark matter.
Learn, create, test and tell
evolution rules in all things
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But, as you mentioned, it is only like that repels like - magnetic poles, positive or negative charges etc. Inflation theory is simply that - a theory; & there are ways other than by repulsion forces that it could have occurred.
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...the extreme homogeneity of the initial expansion
That is far from certain. Among the theories I've come across is 1 that speculates that areas of low homogeneity may have acted as seeds for galaxies. Another that "cracks" in the fabric of the very early universe may have split it into separate regions which may have evolved differently from each other. Nor do graphical representations of CBR demonstrate homogeneity.
From what I can gather, theories that involve homogeneity are no more authoritative than heterogeneous ones.
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i agree we are dealing with a very speculative area and what matters is whether the theoreticiand and observers like the ideas and can find enough evidence to support them. There are fashions in Physics as there are fadhions in clothing.
Learn, create, test and tell
evolution rules in all things
God says so!
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There are fashions in Physics as there are fadhions in clothing.
Very true. Does Louis Viton have any theories on cosmology that are worth discussing here? [:D]
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Originally posted by DoctorBeaver
It occurred to me a while ago that all the forces of which we are aware are forces of attraction - weak, strong, electro-magnetic, gravity (yes, I'm aware that like poles of a magnet repel each other, but magnetism is basically an attraction). Is there any theory as to why this is? Or are there forces of repulsion of which I am not aware?
Is not the distinction between attraction and repulsion merely one of relative perception.
Gravity is seen as a a force of attraction, insofar as matter attracts matter; but could we not equally view it as a force of repulsion, insofar as matter is repelled by empty space?
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Gravity is seen as a a force of attraction, insofar as matter attracts matter; but could we not equally view it as a force of repulsion, insofar as matter is repelled by empty space?
We could; but isn't that just playing with words? Also, could orbits be explained by that viewpoint? It is the attractive force of gravity that causes 1 object to orbit another. I don't see how that could be explained by it being a repulsion to empty space.
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Originally posted by DoctorBeaver
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Gravity is seen as a a force of attraction, insofar as matter attracts matter; but could we not equally view it as a force of repulsion, insofar as matter is repelled by empty space?
We could; but isn't that just playing with words? Also, could orbits be explained by that viewpoint? It is the attractive force of gravity that causes 1 object to orbit another. I don't see how that could be explained by it being a repulsion to empty space.
I agree that it is playing with words, but then ideas and language are closely intertwined, and the use of language (including the language of mathematics) is the only way we have to express and manipulate ideas.
The difference in emphasis between viewing gravity as an aspect of matter, or of an aspect of empty space, is to ask whether in looking for the causes of gravity, one should look to the attributes of matter, or the attributes of space. In fact, as I understand it, relativity (as distinct from the Newtonian view of gravity) actually does emphasise the attributes of empty space, and regards matter itself as simply an attribute of space.
The description of one object orbiting another is equally described by both models. An orbit is described by a balance of the outward centrifugal force of the revolution of a satellite counterbalanced by some force that prevents the satellite flying off at a tangent. Whether one regards that force to be the pull of the object around which the satellite is orbiting, or regards it as the push of the empty space beyond the orbit, is an arbitrary distinction.
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Originally posted by another_someone
An orbit is described by a balance of the outward centrifugal force of the revolution of a satellite counterbalanced by some force that prevents the satellite flying off at a tangent. Whether one regards that force to be the pull of the object around which the satellite is orbiting, or regards it as the push of the empty space beyond the orbit, is an arbitrary distinction.
Interesting take - that sort of fits in with the rubber sheet model, the satellite is travelling in a straight line but space is curved by the massive object it is orbiting such that it travels "straight" around the centre of gravity.
Actually, using that model, couldn't you equally argue that no force is acting on satellite, it is travelling in a straight line with unchanged velocity, and that gravity only acts on space - not matter! [:)]
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Originally posted by Simmer
Interesting take - that sort of fits in with the rubber sheet model, the satellite is travelling in a straight line but space is curved by the massive object it is orbiting such that it travels "straight" around the centre of gravity.
Actually, using that model, couldn't you equally argue that no force is acting on satellite, it is travelling in a straight line with unchanged velocity, and that gravity only acts on space - not matter! [:)]
Or, if you want to get even more esoteric:
http://en.wikipedia.org/wiki/Stochastic_electrodynamics
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Inertia
Inertia is predicted by stochastic electrodynamics as an electomagnetic drag force on accelerating particles, produced by the zero-point field.
Gravity
Gravity is predicted by stochastic electrodynamics as an electomagnetic induced dipole shielding effect similar in nature to the Van der Waals force.
The commonality of mechanisms of inertia and gravity provides an elegant explanation for the equality of gravitational and inertial mass, which is assumed but not derived in general relativity. This also allows the Planck constant to be correctly calculated from the gravitational constant, or vice versa.
And if you can understand that, you are a better man than I [:)]
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Interesting take - that sort of fits in with the rubber sheet model, the satellite is travelling in a straight line but space is curved by the massive object it is orbiting such that it travels "straight" around the centre of gravity.
I think that view re-inforces gravity being a function of matter not empty space. If you remove the sphere, the sheet will be flat. It is the sphere that causes the warping.
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Originally posted by DoctorBeaver
I think that view re-inforces gravity being a function of matter not empty space. If you remove the sphere, the sheet will be flat. It is the sphere that causes the warping.
Not that gravity is a function of matter, but that gravity is an interaction between matter and space.
Put another way, if you had an even distribution of matter, in the absence of empty space, there would not be any perceivable gravitational force. It is the two together which provide the conditions for gravity to be a perceptible force. Whether you attribute this to a property of matter, a property of empty space, or a shared property between them, is an arbitrary distinction.
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Put another way, if you had an even distribution of matter, in the absence of empty space, there would not be any perceivable gravitational force.
But that doesn't necessarily mean that gravity wouldn't exist, just that there would be no way of measuring it.
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Originally posted by DoctorBeaver
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Put another way, if you had an even distribution of matter, in the absence of empty space, there would not be any perceivable gravitational force.
But that doesn't necessarily mean that gravity wouldn't exist, just that there would be no way of measuring it.
That is why I used the term 'perceivable gravitational force'.
One may always argue that forces exist that one cannot perceive, but these must be regarded as as mere fictional constructs of whatever model we use, for all that we can say to actually exist is that which we perceive to exist.