# Is empty space made of 1-dimensional strings?

Discussion in 'Pseudoscience Archive' started by John J. Bannan, Jul 24, 2008.

1. ### blobranaRegistered Senior Member

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OK, i understand what you are saying.
So you`re saying that strings are the fundamental object, and the ends wave about in n dimensions, creating Dn-branes.
(where as i assumed the strings themselves were products of branes, with branes manifesting in different dimensions and being the fundamental objects).

Yes, that way seems easier to understand.

3. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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No, he doesn't. He ACTAUALLY says "Notice that the way they vibrate is affected by the geometry of the extra dimensions..."

By "Extra dimensional objects" you mean "higher dimensional space-time", just as I said a few posts ago.

5. ### John J. BannanRegistered Senior Member

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Did you notice the visual aid he uses, where the backdrop for the string is the higher dimensional object. The visual aid makes it appear as though the string resides on the geometry of the higher dimensional object. Now, take a look at that visual aid again, and tell me how I am wrong.

7. ### AlphaNumericFully ionizedRegistered Senior Member

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The 'backdrop' is a Calabi Yau manifold, which properties I can go into painful algebraic details of if you want. The CY is the space within which the string moves (as well as the usual space-time we see). The string is 1 dimensional, moving in 10 dimensions, 1 time, 3 big spacial dimensions and the 6 in the Calabi Yau. The string is not part of the Calabi Yau 'edge on' any more than an electron is time 'edge on'.

I'll point out that Ben and I research this stuff for a living. We've written papers on it (not together). See these introductory lecture notes where it talks about the world line a particle sweeps out and a worldsheet a string sweeps out. It's a 1d object which moves through time.

The formula I gave for the string's position and motion has 2 coordinates, $\tau$ is proper time and $\sigma$ is a measure of the position along the length of the string. That's all you need.

And as I explained a few posts up, there's a difference between the fundamental string and branes. The strings define the branes.

8. ### fadingCaptainare you a robot?Valued Senior Member

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John,
What you are calling an object is a visualization of tiny curled up dimensions of space. It is just a visualization. Just like the lines and loops shown earlier.

So, the string vibrates in these dimensions, where the geometry of these dimensions gives the string its vibrational frequency.

9. ### John J. BannanRegistered Senior Member

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So, is the visualization given by Brian Greene incorrect, or not? Also, is the 1-dimensional string in contact with the CY in order for the geometry of the CY to affect its vibration?

10. ### John J. BannanRegistered Senior Member

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So, how is that different than saying the 1-dimensional string is the contact of the CY in our universe?

11. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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It's not incorrect, but it IS just a cartoon. It's meant to give laypeople some idea about what's going on, not a mathematically rigorous framework for calculating things. To think that you can understand what's really happening in string theory from a 20 minute seminar (even if it IS Brian Greene) is pretty ridiculous.

12. ### John J. BannanRegistered Senior Member

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So, is the 1-dimensional string in contact with the CY in order for the geometry of the CY to affect its vibration?

13. ### CannonRegistered Senior Member

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if you have points a through z and you move point a, thus point b moves too and c shall follow ever so slightly. Basis on string states that all matter is interconnected, but if we are talking about a 1 dimentional plane, than there is matter super existing over each other and that there is what you could call a ever expanding picometer of mass. but even then, a 1 dimentional plane of existance is like a drawing a piece of paper, horizons may still exists and that even the paper may be curved.

14. ### fadingCaptainare you a robot?Valued Senior Member

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The CY manifold is made up of the extra dimensions. That is all it is - an intermingling of these dimensions. The strings exist in these dimensions. Just as we exist in the dimensions we are familiar with. You shouldn't take the animation so seriously. There aren't little balls as depicted existing with empty space around them. It is just a representation.

15. ### John J. BannanRegistered Senior Member

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So, is the 1-dimensional string in contact with the CY in order for the geometry of the CY to affect its vibration?

16. ### fadingCaptainare you a robot?Valued Senior Member

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The string EXISTS in the dimension that is a part of the CY. I wouldn't say "in contact" - I am not "in contact" with up/down, left/right, or front/back. I exist in these dimensions just like the string.

17. ### CannonRegistered Senior Member

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For starters, where does earth sit on the 1d plane? Where does our solar system sit on the 1d plane? This plane therefore can only be forward and back, or up and down. Not up and left, for that is x and y, that is 2d which is an exostension of the 3d realm. Now as said so where do we sit? The string must start with a numarical value, so what one is it, and what one are we? the numarics of this matter so that when numaric one is moved it changed from one to another number suplimenting that number, but with the expansion of space the numbers go on forever do they not? Lastly, space is either expanding by volume expanding ever so slowly, or by radius. Space does no expand by accumulative radius as you are trying to say.

18. ### AlphaNumericFully ionizedRegistered Senior Member

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You didn't even try to understand what I said, did you?

The string is no more 'in contact with the CY' then you are in contact with time. It is 'in it'.

Just like a the Earth's motion is affected by the gravitationl field of the Sun and in turn affects the field itself, strings exist in the CY space but also affect it, inline with general relativity.

There is a VAST amount of subtly you are not getting here. People like Ben and I have been studying physics for years, including string theory full time for a number of years (2 in my case, I think it's the same for Ben) and w have barely begun to grasp it. The behaviour of the curled up dimensions in string theory is the topic of research in string theory. I work on it, Ben works on it, Witten and Greene work on it.

19. ### John J. BannanRegistered Senior Member

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Fine. If the string exists inside the CY space, and the CY space is curled up, this explains why the 1-dimensional string is so small. Correct? So, the string's size has an intimate connection with the size of the CY space. Now, where does the string come from? Is it pinched off Brane? And if so, how is a Brane different than dimensional space?

Last edited: Jul 26, 2008
20. ### AlphaNumericFully ionizedRegistered Senior Member

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The string's size defines the CY's size, not vice versa.
Considering I said there's a difference between a fundamental string and a string-brane, what do you think?
That's like saying "How is a sheet of paper different from space?". A brane is an object in space.

21. ### John J. BannanRegistered Senior Member

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How does a string control the size of the CY? Isn't that like saying the size of matter controls the size of empty space?
What is the difference between a fundamental string and a string-brane?
So, I take it that a string is made of Brane, but empty space is not made of Brane?

22. ### AlphaNumericFully ionizedRegistered Senior Member

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General relativity says matter and energy curve space-time.
No.

23. ### John J. BannanRegistered Senior Member

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Ed Witten said, "NOVA:If these extra dimensions exist, does string theory offer any explanation of why there are apparently three space dimensions larger than the rest?

Witten: That's a big problem that has to be explained. As of now, string theorists have no explanation of why there are three large dimensions as well as time, and the other dimensions are microscopic. Proposals about that have been all over the map." http://www.pbs.org/wgbh/nova/elegant/view-witten.html
Now, if you are correct that the size of the string determines the size of the CY, then you would have an explanation for why the CY is so small, i.e. because the string is so small. Now, are you contradicting Ed Witten, or has Ed Witten since changed his mind?

But, Ed Witten also proposed that the Big Bang could have created a string so large, that we could see it with a telescope.
Ed Witten said, "But it's conceivable that the big bang could have produced a string so large that it would be present in today's universe and visible in telescopes, perhaps discoverable by the satellites that are now mapping out the microwave sky. If that were discovered, it would be a dramatic confirmation of the existence of strings."
So, then Ed Witten is saying that strings don't have to be small. And therefore, according to what you said, CY's don't have to be small. Do you agree with this?