Couple of quick points:

Electrons may be 'fundamental. but protons are composed of three quarks, and a neutron is equivalent to a proton plus an electron.

Current theory envisages force being conveyed, somehow, by other particles moving between the particles that 'feel' the force.

Photons convey electromagnetic forces, and the hypothetical 'graviton' carries gravity.

Along similar lines, 'mass' is somehow due to the way basic particles interact with something called the Higgs Boson, the most important target of the LHC experiments.

I don't quite follow how these particle interaction lead to field forces and mass, but it seems to work for physicists.

As to matter and energy, I will need more time to sort out my own thoughts...

As a partial response (it's almost dinner time) to your question as to string theory's conception of mass, a string vibrates at a particular resonant energy through an extra-dimensional geometry that confines its vibration such that "physical properties" like mass may be defined. While the extra dimensions are obviously outside the realm of the physically observable, their effect on vibrational patterns nonetheless dictates the properties of the open or closed loop's perception as a fundamental particle.

OK, thanks, that was pretty much how I interpreted it.

And Bob, just think about how much sleep you could get if you didn't hang around this forum... I haven't been around long but I've already spent a few nights up later than I should have  

This is not 100% physics-perfect, but it's a pretty good intuitive explanation. It's how I generally think of particle physics, based on an advanced undergrad course plus keeping up with the science mags like Scientific American etc.

Energy is primary. That's what the universe began with. That's what all the conservation laws work with.

Energy comes in particle/waves. If you think of them as particles, you'll screw up. If you think of them as waves, you'll screw up. When I visualize them, I imagine a kind of standing wave, which can translate through space while maintaining itself in a sort of stable standing wave formation. The standing wave moves around in a particle-like fashion, but it's always a wave regardless. The standing wave is measuring probabilities, so the higher the wave, the greater the probability you'll 'find' the particle/wave at that location. There is no fixed limit to these particle/waves. This means that they pretty much stretch on forever, it's just that the probability for most waves gets really low beyond a certain distance from the centre that it's basically zero, but still not exactly zero. This is why these particle/waves appear to be 'point' particles, but they are really not point particles, they always have some extension in space. There are no true point particles in modern physics, although you might hear people talking that way as a kind of short-hand to avoid dealing with the quantum/wave nature of things.

As for mass, the way I think of it is like this: Primary energy always moves at the speed of light (which is really the 'speed of information' or the 'speed of interaction', since it limits more than just light). Thus, energy particles by default move at the speed of light. It's only when they take on mass that they 'slow' down to sub-light speeds. So, you can think of mass as a kind of state switch: If mass is off, speed is c; if mass is on, speed is sub-c. The connection between mass and velocity is not something they teach you in highschool, but if you ponder for a second you'll see that it's plainly written in E = mc^2.

Another interesting thing about mass is its connection to time, and this is another interesting twist. Massless energy, traveling at speed c, does not experience time. It is 'frozen' in its state until it interacts with another particle, at which time it might change state. But massive particles (matter) experiences time according to relativity in proportion to how 'slow' it is going compared to c (the proportion is not simple, but calculated according to the Lorenz transformations). The faster the particle moves, the less time it experiences. The interesting twist is that if you calculate the combined 'speed' at which the particle is traveling through space and through time, as if time were a forth dimension of space, then you'll find that the combined speed is always c^2 (or c if you take a final square root). So, when a particle is not moving (in its inertial reference frame) it is 'moving through time' at speed c, and when a particle is moving through space at speed c, it is not moving through time at all. So, this interesting twist is that all particles move through *spacetime* at a 'speed' of c, if you consider c to be a spacetime velocity and not just a space velocity.

So mass has this interesting connection to velocity and time. It's a special case of primal energy where the 'velocity' shifts into the time dimension, slowing the particle from its default spatial velocity of c. When this shift happens, mass is required to become non-zero in order to balance everything out.

In regards to forces/interactions: Different particle/waves (both energy and mass) have different physical properties, and so some are able to interact with some physical forces, and others are able to interact with other physical forces. For example, neutrinos tend not to interact with the electromagnetic force, which is why they pass right through most matter so easily. Light, on the other hand, is pretty much defined as a carrier and interactor of electromagnetic force, and so will interact with normal matter, depending on the wavelength of light and the energy states of the electrons in its path.

All matter/energy interacts with gravity, as far as we know. Dark matter is interesting because it's matter (sub-c energy) but it doesn't interact with the electromagnetic force (or any other force, I think, except gravity), which all of our 'everyday' matter does. We humans are fundamentally electromagnetic phenomena. DNA, proteins, water, cells, neurons, brains, consciousness are all governed by electromagnetic interactions. We live in the electromagnetic portion of the universe. Of course, below the level of molecules, we are also nuclear phenomena, interacting with the strong and weak nuclear forces. But dark matter only interacts with gravity. There could be dark matter flying through you right now, and you'd never know because it would only interact with you gravitationally, and I guess it's not as dense as something like the Earth, so the interaction is too weak to feel at this small scale.

I'm pretty sure that's fallacious. If the particle is moving as sub-c, it has mass (as far as I know, there may be some esoteric exceptions to this rule). Quarks, for instance, have mass.

I'm not as strong on string theory, I only read enough to get the gist of it. I'm pretty sure that string vibration is somewhat analogous to the 'standing wave' idea I was describing earlier. The vibration probably confers the physical properties of the particle.

But I sense a confusion in your question which I'm more confident to answer: Mass is not a property that is continuous from X down to zero. It's more like a switch, as I tried to explain earlier. You either have mass or you don't. Similarly, you're either moving at c or you're not. A particle is either a massless particle, and it moves at c, or it has mass and does not move at c (again, there may be esoteric exceptions, but for a simple intuitive idea, this will serve you well).

So, a continuous change to string vibration won't slowly turn on mass, it would have to be a fundamental change in the string, from one kind of 'standing wave' to a different kind. This is how mass particle/waves can transform into energy particle/waves, again, according to E = mc^2. Usually you don't get full conversion from mass to energy. I think most, if not all, transformations are from one mass particle/wave to another mass particle/wave plus some energy, or one m p/w to two m p/ws plus some energy, or what have you. What I gather is happening here is that one string with a particular 'standing wave' pattern snips off another smaller string with a different pattern. But I think the mass/velocity relationship is the most important thing to remember when thinking about this. Either the new string is massless and moves at c, or has mass and moves at sub-c.

person on the thread whose brain exploded at the end of this paragraph.

Check out these videos for how you might visualize standing waves:

http://www.youtube.com/watch?v=GtiSCBXbHAg

http://www.youtube.com/watch?v=tI6S5CS-6JI

http://www.youtube.com/watch?v=t0FsSYLH_SY

Now imagine these standing waves have no limit but just diminish in amplitude really quickly from the centre so that they seem mostly like a 'point' in space. But it's not really a point, because the wave itself takes up space. Something like this:

----------------~~mWm~~--------------------

At a small scale, it's clearly a wave, but at a bigger scale it appears to be a 'point' particle. Here's a wave/particle in motion in 1D:

t1: ---~~mWm~~---------------------------------

t2: ------------------~~mWm~~------------------

t3: ---------------------------------~~mWm~~---

Extend this metaphor into three dimensions, and you have a wave/particle.

I used 'slow' with quotes to indicate it's a loose metaphor. You have to think in terms of interactions to understand physics. Two things with particular states interact and out come two different things with different states. The energy doesn't literally slow, what happens is that an interaction occurs such that one of the resulting things coming out of the interaction is energy with a particular state wherein that energy has two measurable properties: Non-zero mass, and sub-c speed. These properties are linked, as I described earlier, meaning if you have one, you have the other, which is what I meant by it being like a 'switch'.

Below the level of interaction, no, it is not understood. That's why they are called fundamental forces. Actually, they are really called fundamental interactions, which is why I said you have to think in terms of interactions.

Sometimes, due to quantum nature, an 'interaction' can occur without an obvious outside 'cause'. These can be called quantum fluctuations. A particle/wave can suddenly decompose into some other particle/wave(s). This is related to what I said earlier about the 'standing waves' being measures of probability. There is a fundamental limit to predictability of interactions. They are statistical and probabilistic at the quantum level. If you think about particle/waves as standing probability waves, it helps visualization.

So, I don't know the exact process by which the initial energy of the universe became partially matter, but the explanation will be in terms of fundamental interactions at a probabilistic quantum level. Some energy 'interacted' with itself splitting into gazillions of particle/waves, and some of those interacted in such a way as to take on the linked properties of non-zero mass and sub-c speed. That's essentially how energy gave rise to matter. The more complex details I leave to the experts. I'm satisfied with my intuitive understanding, and if I need to look up the facts, I'll be able to understand them.

Matter is energy which has mass at a sub-c velocity. Mass is the property associated with gravity. It is relativistic, being based on a 'rest mass' which is measured as if the object were not moving (inertial reference frame). Thus while light and other energy is massless while moving at c, it still has a 'rest mass' equal to its energy divided by c^2 which is how Einstein predicted that it would bend in the presence of a strong gravitational field. So, no, mass and matter not synonymous.

I have read all the posts on this thread, and my eyes are now crossed with x's  over both.

But, I've given this ALOT of thought over the past 15 years or so. And, feel free to laugh if you want, but

here is my take on it.

I tried to imagine the 'singularity' that is claimed by many experts which was the precursor of the big bang(rapid expanse) from which all matter came into existence. It was difficult for me until I realized that since matter and energy are interchangable via E=mc^2  , a limitless amount of energy can exist in a zero volume amount of space. as without mass no space is needed, energy doesn't occupy space, mass does. Without mass that interacts, no motion occurs, without motion, no time is needed as time is a measure of the motion of mass. This making any sense to anyone?

I think that all mass that we can perceive and all that we can't could easily have been an unbelievably large amount of energy that was at an unbelievably huge temperature occupying no space and without time until it 'condensed' and dropped to a temperature that allowed matter to form rapidly at first and slowing exponentially over time.

I also think that is why time dilation exists for objects in motion and accerleration. We know time dilation exists, but I can't find a single reason as to what the actual cause is.

Stay with me here,  If an object travels from point A to point B, it experiences less time than if it had remaind stationary. Suppose the object undergoes much the same effect that an electron does when raised to a higher energy level. From one quantum state to the next higher quantum state without ever being between those states.

Suppose the traveling object experiences a matter to energy to matter..etc  existence during the acceleration(energy input) and doesn't experience 'time' while it is in an energy state. That would explain the time loss of the object in question.

Any thoughts?  Anyone?