# String theory & interactions

Discussion in 'General Science & Technology' started by Crisp, Aug 10, 2000.

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1. ### CrispGone 4everRegistered Senior Member

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1,339
Hi people,

I've been doing some thinking on the basics of string theory (found some documents on the web describing them) and one question just popped into my mind: How do strings interact ?

Perhaps the texts I read didn't go into enough detail, but I've understood that two strings can collide, form a new string, split again, ... and give rise to all sorts of phenomena. Now what I didn't read and couldn't immediatelly find is what causes this merging of strings.

Do they just happen to meet eachother and merge or are they drawn together by some sort of "force" ?

I can imagine that there are a lot of strings just floating around everywhere, and that when two strings merge they cause effects like gravity (this would be the "they just happen to meet eachother" explanation). Some strings give rise to matter, others just sit around and do nothing, but all string-interactions explain all attraction/repulsion phenoma in matter.

Or is it the other way around (the mysterious "force"): ALL strings give rise to matter and interaction-like particles (gravitons, photons, dunno-what-ons), but those strings are somehow drawn together and can collide/merge/split ? This would mean that string-interactions are not explained by strings.

I just hope someone can make sense of this posting

Bye!

Crisp

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"The best thing you can become in life is yourself" -- M. Eyskens.

[This message has been edited by Crisp (edited August 09, 2000).]

3. ### PlatoRegistered Senior Member

Messages:
366
Hello Crisp,

enjoying the vacation ?

I don't know that much about stings but I do know a lot about gauge theory in general and since string theory is a gauge theory I might shed some light on your problem.

You see you are turning the reasoning upside down, there are no forces between the strings, the strings ARE the forces.

Everything is a string according to string theory but all these strings have different properties when they have different vibration frequencies. I don't have the faintest idea how this works but I thing this is what the theory says.
This would mean that some string vibrating in one way are fermions, others vibrating in an other way are bosons.
When two fermions with some kind of charge of one force or an other meat, they exchange bosons. These bosons are created and annihilated almost at the same instant and are therefor said to be virtual in nature.
In string theory these are all strings but of different kinds of vibrations.
So this is how stings interact, they spontaneously respond to one another according to their properties.

I hope I didn't confuse you more now ?

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I err, therefore I exist !

5. ### CrispGone 4everRegistered Senior Member

Messages:
1,339
Hi there Plato,

Surely enjoying the vacation. Bored to death and my order of "Quantum Mechanics" (the two-volume set ofcourse) from Claude Tannoudji just wont arrive

.

Yes, this was already what I thought (and hoped for the sake of string theory) it was.

Aha, now this poses a rather annoying problem: how does one fermion string know another is there ? You might say, because of interacting bosons, but how does a string know it should "exchange" bosons ?

They can't possibly be "transmitting" (e.g. sending them bosons out) all the time since a boson itself is also a string which can also interact with other strings (so that boson would also have to send out bosons... you get the idea).

Anyway, more generally speaking: in string theory the string is the fundamental building block of everything. This means ofcourse that there cannot be something even more fundamental than a string (unless you accept string theory to be wrong or incomplete). If you start looking at interactions of strings, then you cannot say that they just happen to respond to eachother - this would be complete chaos. So if strings interact (e.g. in some way exchange information to let eachother know of their presence) then this must also be done by the mean of strings, the fundamental building block.

Now to get to the point: how can something that is localized into space (string is about 10^(-33) m in size if I remember correctly) interact with another string, also localized into space, when there is only those two strings ?

This is generally speaking ofcourse. Examples of interaction could be:
• Fermion-Fermion string interaction: As you said, Plato, those two strings exchange bosons, which are another form of strings. But then again, how does a Fermion transmit a boson ? Next interaction type:
• Fermion-Boson string interaction: The more interesting case: this interaction involves a Fermion string "requesting" a boson string to somehow go to the second Fermion string to interact with.
• Boson-Boson String interaction: Don't know if this is possible (I don't see a reason why it shouldn't), but this is definitly the most problematic case to handle because of bosons also interact through "bosons of bosons" (in contrast to "bosons of fermions" in the two cases above) then you get an endless loop of bosons of bosons of bosons interacting...

Bye!

Crisp

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"The best thing you can become in life is yourself" -- M. Eyskens.

[This message has been edited by Crisp (edited August 10, 2000).]