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String theorists squeeze 9 dimensions into 3

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A simulation of the early universe using string theory may explain why space has three observable spatial dimensions instead of nine.

The leading mathematical explanation of physics goes beyond modern particle theory by positing tiny bits of vibrating string as the fundamental basis of matter and forces. String theory also requires that the universe have six or more spatial dimensions in addition to the ones observed in everyday life. Explaining how those extra dimensions are hidden is a central challenge for string theorists.

“This new paper demonstrates, for the first time, that our 3-D space appears naturally … from the 9-D space that string theory originally has,” says Jun Nishimura of the High Energy Accelerator Research Organization in Tsukuba, Japan. He and his colleagues will publish their findings in an upcoming issue of Physical Review Letters.

arrow3.gifView: Nine into three

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Interesting post, encouraged.

In the simulation, the universe starts off as a tiny blob of strings that is symmetric in nine different dimensions. As the strings interact, a random energy fluctuation — provided by the quantum laws that govern these small scales — breaks the symmetry. Three dimensions balloon outward, leaving the other six stunted at a billionth of a trillionth of a trillionth of a centimeter, far too small to be detected.

I suppose the mathematics describes how only the three dimensions balloon out. I wonder what is the connection between a string and a quark, for instance? What physical process enables a string to create a quark? This I don't understand.

Also, what is the relationship between quantum mechanics and string theory? Do strings create the laws that govern behavior of particles on the quantum scale? If so, do events on the quantum scale effect the behavior of strings?

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I really think a quantum computer is going to be needed to prove string theory.

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Interesting post, encouraged.

I suppose the mathematics describes how only the three dimensions balloon out. I wonder what is the connection between a string and a quark, for instance? What physical process enables a string to create a quark? This I don't understand.

Also, what is the relationship between quantum mechanics and string theory? Do strings create the laws that govern behavior of particles on the quantum scale? If so, do events on the quantum scale effect the behavior of strings?

I think the gist of string theory is that quarks are strings that are vibrating in a particular manner. Different modes of vibration would produce different types of quarks. I think electrons are also a different vibration of the same fermion string that a quark is made of.

In my understanding, this is why string theory needs so many ``extra'' dimensions. In 3+1 space-time there simply isn't enough ``room'' for a single object to be the basis for all fermions: A 1D object in 3+1 space time has only 2 transverse directions available for vibrations. In 9+ dimensions there would be 8+ transverse directions, sufficient for a single type of object (i.e. a string) to account for all the different manifestations of fermions (electrons, up quarks, muons, etc.).

One of the reasons why many scientists dislike string theory (including myself) is that it seems to be just trading a Universe with a simple geometry (3+1 space-time) and a complex set of particles (3 families of leptons and quarks) for a complicated geometry (9+1 space-time) and a simple set of particles (strings).

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I really think a quantum computer is going to be needed to prove string theory.

Its going to take something really special if that is no further than they could get with a cray super.

One of the reasons why many scientists dislike string theory (including myself) is that it seems to be just trading a Universe with a simple geometry (3+1 space-time) and a complex set of particles (3 families of leptons and quarks) for a complicated geometry (9+1 space-time) and a simple set of particles (strings).

That is very thought provoking. From there I can a draw a continuum between those extreems and make the statement that is so often true, "I wonder if the truth isn't somewhere between?"

Would that be 6+1 space-time and 2 families of leptons and quarks... Oh my...

I just finished watching Lawrence Krauss lecture on "Nothing". It seems they are mentioning a nothing that really consists of something. I will have to absorb that for a while.

His point that we are uniquely placed in a time in which we can see and theorize cosmology and the major thropic theory makes one wonder if this is a nice little dog and pony show someone is putting on for our benefit! LOL

Edited by encouraged

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I think the gist of string theory is that quarks are strings that are vibrating in a particular manner.

As the size of strings are supposed to be about the Planck length, and quarks are around 16 magnitudes larger, and the two are quite different in their properties, how does this come about? Well, they may have the same properties, but they're different entities, aren't they? Maybe you know what I mean.

As you say, string theory just seems to switch one complication for a different complication. Sometimes I yearn for a return to the Newtonian mechanical universe. Those were the days.

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As you say, string theory just seems to switch one complication for a different complication. Sometimes I yearn for a return to the Newtonian mechanical universe. Those were the days.

Yeah! and even I can understand that! LOL

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As the size of strings are supposed to be about the Planck length, and quarks are around 16 magnitudes larger, and the two are quite different in their properties, how does this come about? Well, they may have the same properties, but they're different entities, aren't they? Maybe you know what I mean.

I dunno about that, I mean the mass of a free up or down quark is less than 10 few MeV, but the mass of a proton or neutron (3 quarks) is about 1 GeV. Obviously the self-energy of binding the quarks to a nucleus has some effect on the mass.

I suspect a similar thing happens with strings, the tension in a free string causes it to shrink to the Heisenberg limit, but in bound ``quark state'' strings could have a larger size since they aren't free.

An electron would also be a string, how big is an electron? A somewhat dated study puts it at under 10-22 m, possibly with better equipment one could resolve an electron down to a Planck length...

I think the bonus of adding constrained dimensions in string theory is that these constrained dimensions can only support limited vibrational modes, so who is to say that the string vibration in dimension x manifests as charge in our normal (unconstrained) 3+1 space-time, and that the vibration in dimension y manifests as spin?

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Thanks for the explanation, sepulchrave. Can't elementary particles also be described as excitations of their respective fields? Not being knowledgeable enough of string theory, I'm wondering how the four fields are understood in string theory.

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You guys sure do enrich my experience on this site! Thanks

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Thanks for the explanation, sepulchrave. Can't elementary particles also be described as excitations of their respective fields? Not being knowledgeable enough of string theory, I'm wondering how the four fields are understood in string theory.

Yes, currently elementary particles are described by Quantum Field Theory as fundamental excitations of a field (the Dirac field for electrons, quarks, etc., the electromagnetic field for photons, etc.).

As I understand it, String Theory basically just postulates that field excitations are finite 1D (line-like) rather than 0D (point-like). The extra degrees of freedom provided by a 1D quanta allow one to reduce the number of fields required to explain all the particles, and more importantly, because each string-string interaction has a finite size, provide a spin-2, mass-0 field excitation that behaves sensibly. (We know from General Relativity that gravity behaves like a spin-2 mass-0 particle, but existing quantum field theory cannot provide such an excitation.)

This site shows the Lagrangian action for a pure bosonic field in String Theory (``X'' is the field), Quantum Field Theory uses the same Lagrangian action formulation: see the wiki on Quantum Electrodynamics for the Lagrangian for an electron (the ``psi'' field) interacting with a photon (the ``F'' field).

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Perhaps string theory is interesting because it gives theoretical physicists something to do.

Is the construction of the universe really this complicated? Present string theory seems complicated to me. I guess we have to understand and work through these complications to get to a simple explanation. An equation from which can be derived the properties and behaviors of the fundamental forces, particles and dimensions. The fundamental origin that determines how the universe behaves in macro- and micro scales, and perhaps what the universe actually is.

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Yeah! That is why I took a go at the model I suggested. To simplify things.

It seems to me that explaining our universe as two disassociated constituents, one already in existence and the other a product of the Big Bang, might provide some answers to why gravity is such a difficult part of our attempt to come up with one explanation for everything. Combining both in some homogenized way due to the various aspects of the the Big Bang.

If some of what we see is the way gravity behaves when another membrane is really close, or... whatever other gravity explanation..., then why can't gravity become a weak effect locally by the disassociation in the gap idea, and yet still be effective in the accumulative whole beyond the gap.

Well, anyway, If our universe were to have "assimilated"/absorbed another universe, then the combined physical laws from both might very well be as peculiar a thing as we presently observe. The stronger universe's physical properties being the 3 + 1 (dominate) and the weaker universe being something like 6 + 0 or 6 + 1 (recessive).

Wouldn't that be simpler and allow people like me to understand it. Perhaps not?

I understand the notion of Plank units being contiguous without a start and end. But it seems to me that they could be as easily non-contiguous and in random small multiples. Perhaps that would help with the new discovery of gravity being variant and increasing from one side to the other in a span of space. The gaps being more frequent because of single unit gaps on one end of the span and less frequent because of random numbers of multiple units being contiguous at the other end of the span.

Oh, well...

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