Is empty space made of 1-dimensional strings?

The string could be likened to the edge of a sheet of paper.
But all that matters, for your original question, is that empty space and matter are made of the same thing - strings.

 

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Wouldn't it be more correct to say that empty space is made of higher dimensional objects on which our universe or brane intersects creating these 1-dimensional strings we experience in our universe as matter?

 

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Who said anything about branes?

 

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No.

 

Isn't a 1-dimensional string just the curvature of a higher dimensional object which appears in our universe? Have you seen this video by Brian Greene? http://www.ted.com/index.php/talks/brian_greene_on_string_theory.html

 

Are you asking about strings or about branes, because there's a difference.

If you're talking about space-time curvature, you're talking about gravity. If you're talking about gravity, you're talking about closed strings, always. (AN can correct me, but I think this is right.) If you're talking about closed strings, you don't need branes at all.

So gravity is just a specific excitation of closed strings.

 

Yeah.
A closed string is not anchored to a D-branes and can float about the bulk. However, IMHO, the strings themselves are the ends of branes.

 

I don't see this. Is there a reason to think this?

The brane tension is usually too big for the brane to have an ``end''. It has to always be wrapped on something, I thought.

 

Yeah
the string/1-dimensional brane has to be anchored to a D-brane, or onto itself.

(Depending on which theory/version your looking at, i guess)

 

But, is a 1-dimensional string the curvature of a higher dimensional object that appears in our universe, or not?

 

Sure if you're talking about open strings.

But I don't see hwo to go from there to "A string is an edge of an object".

 

No.

Who said this?

 

Brian Greene. See http://www.ted.com/index.php/talks/b...ng_theory.html

 

Link broken.

I could be wrong, but if "higher dimensional object" means "four dimensional space-time", then I change my answer.

 

No, he didn't. Strings are fundamentally one dimensional objects, there's nothing like what you're describing to them.

Open strings have their ends stuck to branes (it's the definition of a brane) and the branes can be any number of dimensions, from 0 to 9. There are some instances where a multidimensional brane, say a D7 brane in AdS/CFT, extends through all of our space-time AND 3 other directions and so we see 4 dimensions of what is actually a 7 dimensional thing, but strings are strings are strings. The 1d strings as 1d. They then go on to define other objects but they are always one dimensional themselves.

 

Sry, for the confusion.
The `object` is a brane; strings are not separate entities from branes, they are the same - in this case a 1 dimensional brane. And a two dimensional brane is just a membrane.

@AlphaNumeric
You agree?

 

The link works in Post #25. Try it there.

 

No, 1d branes and fundamental strings are different.

Strings, fundamental strings, have a set length, \(\sqrt{\alpha '}\). If they are closed then they don't have end points. If they are open then obviously they do have end points. The dynamics of the end points define regions of space-time of particular dimension, if the string end points can move in d dimensional regions, then you have a d-brane. The size of the d-brane depends on the dynamics of the fundamental strings, in the case of a 0-brane (ie the string's end cannot move at all) then the brane is obviously just a point. In the case of 1-branes they can be anything from loops to infinite length lines. Hence the distinction between a d-string (ie a 1-brane) and an f-string, a fundamental string.

But it doesn't stop there. IIB string theory possesses a kind of duality (string theory is PACKED with dualities! As my 'custom title' mentions) which allows you to turn d-strings to f-strings and vice versa. So under a redefining of your fields and coordinates etc you find you don't have a hard and fast definition of what an f-string is and what a d-string is.

It's discussed in Volume II of Polchinski if I remember correctly. I wrote about it for my 4th year essay, though compared to my understanding now I didn't have a ****ing clue what was going on back then...

 

Look at 15:30 on the link to Brian Greene. He said that strings reflect the geometry of the higher dimensional objects. The visualization he presents clearly shows a string vibrating in accordance with the geometry of the higher dimensional objects. Now, how is this not the intersection of our universe with the geometry of the higher dimensional object, where that intersection takes the form of a string?

 

The way I understood it is that the way strings vibrate is dependent on the folding of the dimensions. Hmm I see now that you actually meant that, although I don't know why you call them objects..
The way I see it the dimensions define the properties of matter (vibrations of the strings) by their folding, the strings are just the "building materials".
So space (dimensions) is not the same thing as strings.