Why are there so many sub-atomic particles (e.g. quarks, mesons etc) being found all the time?! Doesn't it seem science is getting more complicated instead of reducing the complexity we find in nature? Is there some other theory being looked at which might eliminate the need for such particles?
Finally, does anyone believe that all these particles are made of the same stuff (condensed energy) and may just have varying properties like charge, spin etc.?

I believe string theory says that there really are no particles... just vibrations of string that are like 10^-39 cm long and have no width. Not 100% sure.. someone confirm me on this.

That is right John. I thought physics was supposed to be a simple framework for nature! It seems to me that the more we investigate the more questions we find and then the more theories we have to devise to explain them. When is this going to stop? Probably when they find the missing link between gravity and the other fundamental forces, and even then there is going to be a lot to explain.

I will have to read up on string theory as it sounds very interesting. Is this theory taken very seriously today? How likely is it that it might replace our present theories on subatomic particles???

Well for the time being, there isn't the slightest piece of experimental evidence for string theory. It is taken serious by physicists working in quantum gravity, but I don't know how anyone could answer the question of "how likely" it is to be correct, given an absence of testible predictions made by the theory.

The solution of reducing the zoo of particles into mere vibrations of strings is elegant, but keep in mind that string theory creates additional arbitrary features in nature. For one, the theory requires a 10 - 11 dimensional universe, and does not actually provide an explantion for the nature of spacetime itself.

The great beauty of string theory is that it is really geometry...
It seems as if it is the only theory that can bring relativity and quantum mechanics together. The lie algebras that under-lie Maxwell's theory and strong and weak interactions can be explained by symmetry breaking; the reason that strings are so successful is because it has so many symmetries that can absorb all the infinities, anomalies and inconsistancies...

And we hopefully won`t have to add in any arbitrary values , because there would only be one answer...

The strings actually create space and time, they don`t exist <b>in</b> space-time...
The lowest vibrations would be the particles we see around us. Gravity for example comes naturally out of the symmetry. The way that the 6 dimensions folded would some how explain why we have 3 families of particles(electron, mu-electron,tauelectronetc...), they would correspond to the `holes` in the topology... ;)

Originally posted by blobrana
The strings actually create space and time, they don`t exist <b>in</b> space-time...

Actually, this a current problem with string theory. The strings are dependent on a pre-existing background of spacetime to move about in. So in it's current state, string theory is background dependent and cannot be a complete description of quantum gravity. Ideally, physicists would like to have a superstring theory that is background free, and can build up spacetime as mere gemetric relations between strings.

But this background free theory has yet to be formed.

Hum,
Sorry, i don`t know what you mean. I haven`t heard of this particular `background free` question.
I hope they don`t mean the `background` to be a sort of Aether?
Or is it just a term for the configurations of a Calabi-Yau manifold of six dimensions and our Minkowski manifold of four dimensions?
(Which leads to the awkward question of <i>what</i> is a dimension)....
BTW. The dual symmetry to a ten dimensional Heterotic string theory is the <b>Eleven</b> dimensional M-theory (involving membranes).

As far i was aware the strings vibrate in these `dimensions`; they create the `quanta` of space and time, as well as all the bosons & fermions.
We know that space and time must be composed of descrete quanta;
because of the uncertainty principle, where the values of space and time are smeared together.
<b>delta x delta p < h </b> (position and velocity smearing) less than Planck`s constant.
<b>delta E delta t < h </b> (momentum and time smearing) less than Planck`s constant.
(h= 6.63 x 10^-34 joule seconds.)
And that the spin of a particle is quantizised and measured in units of planck`s constant devided by 2pi. (eg. 1/2 X h/2pi.) which implies a greater `freedom` for particles than what <b>we</b> are aware of.

It seems strange to introduce another term into the <i>simple</i> `string` theory. What would this `background` be
made from?
The theory, i last remembered, had two five dimentional membranes colliding to form the E(8) 10 dimensional Heterotic Superstring theory that contains only closed strings, that breaks into the E(6) GUT type theory...This breaks down to SU(3) X SU(2) X U(1)...

It maybe that the <i>theory</i> itself may be wrong, perhaps the universe <b> has</b> only 4 dimensions with 6 `internal` structures to describe the forces and particles. (<i>there are problems with this though</i>)

Perhaps if we figure how the Higgs particle breaks the Yang-Mills field symmetry,
we can perhaps get a better understanding on how it all fits together...



-------------------------------------------------
Off note, just checked the `4th Dimension Question`bit... ;)

Originally posted by blobrana
Hum,
Sorry, i don`t know what you mean. I haven`t heard of this particular `background free` question.
I hope they don`t mean the `background` to be a sort of Aether?
Or is it just a term for the configurations of a Calabi-Yau manifold of six dimensions and our Minkowski manifold of four dimensions?
(Which leads to the awkward question of <i>what</i> is a dimension)....


The standard model of particle physics, which excludes gravity, is formulated on a background of space and time. The is backdrop is the flat spacetime of SR, and is much like the absolute silent stage of Netwon's space. Quantum fields are of course distrbuted throughout continuously throughout spacetime, and this spacetime is assumed to be a fixed background metric. It makes sense that any quantum theory of spacetime itself, would not be dependent on any additional background. String theory can unify QM with GR, but it requires this additional flat background spacetime to do so. The goal of many string theorists is to formulate the theory in a way that eliminates this presky background.

We know that space and time must be composed of descrete quanta;
because of the uncertainty principle, where the values of space and time are smeared together.

Discrete quanta does not necessarily mean discrete space.

It seems strange to introduce another term into the <i>simple</i> `string` theory. What would this `background` be
made from?
The theory, i last remembered, had two five dimentional membranes colliding to form the E(8) 10 dimensional Heterotic Superstring theory that contains only closed strings, that breaks into the E(6) GUT type theory...This breaks down to SU(3) X SU(2) X U(1)...

I don't think the colliding branes are required in M theory, and certainly aren't in the individual string theories. At any rate, this background I mentioned is part of SST, though I'm not sure how M theory has been able to alter the picture.

Actually string theory makes one prediction: the cosmological constant, which it predicts to be 55 orders of magnitude larger than the observed value, making it about as inaccurate as seriously researched theories get. I found this article, and it makes some interesting points:

http://www.americanscientist.org/template/AssetDetail/assetid/18638

Re: GT_Phys

Hum, the cosmological constant should be at least around 55 orders
of magnitude larger than the observed value?
i`m not sure about this, anybody know about this?...
As for the "two fundamental problems" outlined in your link, it seems no stranger to me than suggesting that the universe expanded exponentially (say 10<sup>50</sup>) during the big-bang,
or saying that a 1/2 spin particle has to turn 720 degrees to return back to the original position ; or blaming lack of mathematical tools to understand the `inconsistencies` as a detraction to string theory..

Re: Beercules
Hehe, Er, i still don`t get the problem, background or no-background...?
I take it that having a background reference helps remove some sort of new mathematical inconsistency in some way?

The uncertainty principle (and light speed) does lend itself to me <B>assuming</b>
that that the particles that exist in this space-time exhibit a `quanta` nature...
(The underlying dimensions themselves are continuous),
<i>for example virtual particles can have discrete energies thus they can only exist in certain (discrete?) time periods</i>, from the equation <b>delta E delta t is less or equal to h</b>.
So, perhaps my assumption (a la, standard quantum theory) that the underlying space/time is quantized is <b>wrong</b>.
I must add that i tend to think that the uncertainty principle is actually a `real` physical constraint and not just a artifact created by our lack of our measuring skills.
My <b>assumption</b>, also, that space and time can be `smeared` together,
implying somehow that they are interchangeable, Er, a bit like mass and energy (sort of;)
, maybe actually wrong...<b>Doh!</b>...
Now i have to reconsider (or dismiss) Hawking`s description of the big-bang, and re-evaluate how that effects the Feynman- Wheeler theory of time...
However...(Typing as i think,,,)
The string theory's, i thought (<i>be they right or wrong</i>), have always said that space (and i wrongly assumed ALSO time) are composed from a mesh of (closed?) strings.
They of course exist/vibrate in continuous SPATIAL dimensions...
And the bonus, for me, was that it got rid of the question `what the background was composed of`; (<i>Is space/time, something` in between the VOID and matter</i>?),
and simplified <b>everything</b> to different modes of vibrations on a single string...
For example, a particle when it moves, is taken to be just a traveling wave, jumping from string to string; so a string(s) can be a bit of space/time one moment and a particle the next...

But i admit that it does sound non-sensible to talk of a `particle` transforming into a time quanta...
i now see that the string is bit of `space` that can also vibrate in a time dimension.

String theory is really the only game in town, for the present time.
And i now think that simply it states the two properties:
1) A vibration, <i>on a string</i>, is a particle/force
2) A string is a space quanta

But, i would speculate that ultimately perhaps even strings can be `created` from purely the geometrical interaction of dimensions (spatial and temporial)...

But now that you mention it, I can however see a few questions and flaws raised with my assumptions, or lack of information...
If a time/space `particle` (for argument sake) were indeed a closed string then vibrations can trans-cross the string diameter (10^-33) cm in no less than 10^-43 seconds,
(<b>1. </b>Why not instantaneously because it is a time `quanta`?),

We assume that this speed would be no grater than 3 X 10<SUP>10</SUP>cm/sec...
And given the <i>estimated</i> figures, for the sizes (10^-32-10^-33)
of a string, we can put a rough guess on how fast `information` can travel <b>between</b> strings; the speed of light is conveyed across 10⁴² strings per second...
(hum, did i work that out correctly?)
<b>2.</b> So, is the maximum speed of the vibrations <b>on</b> a string, <i>or the interaction
between strings</i>, the limiting value for the speed of light?
<b>3. </b>Is this speed limited if a string exists in a `background`?
<b>4.</b> Can there be a speed limit if it can vibrate in a time dimension?
And if there is a maximum value (light speed) to how fast a string can vibrate
(Assuming that there can be an infinite amount of harmonies/frequency's that lead to an unlimited number of particles types that could be created, and assuming that the particles are different vibration modes),
<b>4.</b> can we work out the tension/tensile strength (<i>ZeroPointEnergy?
Is this the 55 orders of magnitude bigger cosmological constant?</i>) of the
string?
<b>5.</b> would a string moving/vibrating at the speed of light be affected by
a sort of time-dilation, (like time seems to freezes for a photon)

hUM...i can smell mistakes here...

So to conclude, on what i have learned today in class, is that space is not
the equivalent to time...
;)