How "big" would be the smallest possible structure in the universe and what would define such limitation? Is there such a limitation?

Seeing in what manner? We use special machines to view sub atomic

particles now so in reality we cannot "see" them with our naked eyes. Those

particles get smaller and smaller with the advent of more powerful machines

to "see them with.

Define 'structure'.

I'm sure you're well aware of the Planck length. Take it from there, form your own decisions. Check out Loop Quantum Gravity if you're actually interested (and not just being facetious as I suspect).

Gravity gives us a natural minimum length, which is the planck scale.

You may hate string theory, but there's a pretty cute reason why we can never probe past the planck scale. Suppose you want to look at something that is smaller than the planck scale, using strings as your probe. You take strings, and you shoot them at this thing that you want to look at. It turns out that if you want to look at something smaller than the planck length, you need energies greater than the planck energy. But when you put this much enrgy into a string, you only end up stretching it out. So the effective size you are probing is now greater than the planck size.

I thought that was pretty cute when I learned it.

Gravity gives us a natural minimum length, which is the planck scale.

You may hate string theory, but there's a pretty cute reason why we can never probe past the planck scale. Suppose you want to look at something that is smaller than the planck scale, using strings as your probe. You take strings, and you shoot them at this thing that you want to look at. It turns out that if you want to look at something smaller than the planck length, you need energies greater than the planck energy. But when you put this much enrgy into a string, you only end up stretching it out. So the effective size you are probing is now greater than the planck size.

I thought that was pretty cute when I learned it.

Yes, but this only means we cannot know whether there is anything smaller than Planck scale or not..

Edit: Which is pretty much the answer to the thread.. :o

Seeing in what manner? We use special machines to view sub atomic

particles now so in reality we cannot "see" them with our naked eyes. Those

particles get smaller and smaller with the advent of more powerful machines

to "see them with.
I never said anything about our ability to see it. I'm talking about general existance.

Gravity gives us a natural minimum length, which is the planck scale.

You may hate string theory, but there's a pretty cute reason why we can never probe past the planck scale. Suppose you want to look at something that is smaller than the planck scale, using strings as your probe. You take strings, and you shoot them at this thing that you want to look at. It turns out that if you want to look at something smaller than the planck length, you need energies greater than the planck energy. But when you put this much enrgy into a string, you only end up stretching it out. So the effective size you are probing is now greater than the planck size.

I thought that was pretty cute when I learned it.

Yes, but this only means we cannot know whether there is anything smaller than Planck scale or not..

Edit: Which is pretty much the answer to the thread.. :o
Yes, that was what I was looking for. Thanks :)

Actually, Dr Hawking ADMITS, (and this was before my post was deleated) - that even quarks themslelves can be even more fundamental... a sub-subatomic fundamental object.

Actually, Dr Hawking ADMITS, (and this was before my post was deleated) - that even quarks themslelves can be even more fundamental... a sub-subatomic fundamental object.

The theory you refer to is called technicolor. It has died about twenty years ago (I could give you some technical reasons), and people have been trying to fix it up. (I say it died at the risk of offending some friends of mine in Copenhagen at the Bohr Institute!!!) Technicolor theories have been coming back into vogue recently precisely because of string theory, but still most people think they have pretty much died.

Then please... do... explain... because there are still mathematical solutions for the ''soliton'' and other sub-subquantum events?

Old science, isn't old news Ben, just as much as twenty years ago, entanglement was considered a pseudoscience.

Then please... do... explain... because there are still mathematical solutions for the ''soliton'' and other sub-subquantum events?

Well I am not as familiar with the non-perturbative aspects of QCD---i.e. solitons and instantons and such.

I was just making a general statement about composit theories---there are good reasons why they are disfavored compared to things like supersymmetry.

''I was just making a general statement about composit theories''

yet you also said...

''It has died about twenty years ago ''

then...??

''I was just making a general statement about composit theories---there are good reasons why they are disfavored compared to things like supersymmetry.''

and yet you said

''(I could give you some technical reasons), and people have been trying to fix it up. (I say it died at the risk of offending some friends of mine in Copenhagen at the Bohr Institute!!!)''

Please// just explain away. It's obvious that:

1. You think i do not know either enough of the ''non-perturbative aspects of QCD---i.e. solitons and instantons and such'', as you put it

or that

2. You think i wouldn't understand?

I am here to learn as much as to teach. You call yourself a physicist, and yet you won't do the pay the same respect...

Ok, then I will start a new thread.

Thank you sir.

Excellent work.

zephir---

Consider this a warning about posting fringe science in the Physics forum.

...Suppose you want to look at something that is smaller than the planck scale, using strings as your probe. You take strings, and you shoot them at this thing that you want to look at. It turns out that if you want to look at something smaller than the planck length, you need energies greater than the planck energy. But when you put this much enrgy into a string, you only end up stretching it out. So the effective size you are probing is now greater than the planck size.

I think that this is just T-duality at work. But mIght we be able to detect trans-planckian distances (if there are any) by probing with objects other than F-strings, like D0-branes for example?

I think that this is just T-duality at work. But mIght we be able to detect trans-planckian distances (if there are any) by probing with objects other than F-strings, like D0-branes for example?

It's exactly T-duality :) This was the first way I understood it.

I know much less about the Type II string theories (I work pretty exclusively with the heterotic string), but I do know that the D0 brane is a degree of freedom there---perhaps you could probe trans-planckian effects using them, but I do not know.

...you may hate string theory, but there's a pretty cute reason why we can never probe past the Planck scale. Suppose you want to look at something that is smaller than the Planck scale, using strings as your probe.
You probable never heard of preon theory (http://en.wikipedia.org/wiki/Preon), for example and how it can be tested (http://www.nature.com/news/2007/071130/full/news.2007.292.html):cool: WHY did you deleted my post as a "fringe science"? Can you explain it by some rational way?

Do you really believe, the string theory is the center of contemporary physics? Other theories are even presented in Nature (http://www.nature.com) more often.