So, in string theory, is there such a thing as matter?

[Wrinkliez]

This might be a noob question, so excuse me if I'm beating a dead horse. I'm trying to wrap my head around string theory. If it is how the universe operates, is there such a thing as matter? It seems that everything at its most basic form is just energy.

Is this true? Or am I missing a piece of this puzzle?

Thanks guys.

 

[Naty1]

You could say that as a start, but things seem more complex so far. I'd rather note that some forms of energy manifest as matter and other vibrational patterns manifest as energy...says quarks vs photons...which is more "basic" or what is "real" has many forms of interpretation and a number have been discussed here in other threads. I do not believe we yet have an experimental test to detect one versus the other.

You can perhaps offset your interpretation by noting that big bang interpretations require some exotic matter to start things off...not a desirable situation in my opinion, but it's there nevertheless. Strand theory, which is just recently discussed, might offer a "neater" view of things...but all these require some experimental confirmation.

An analogy might be that atoms were once thought "indivisible"; then protons, neutrons and electrons when they were discovered; then quarks were found as constitutents of protons and neutrons, and so forth..often Maybe strings are common to all...so we often make progress piecemeal getting new glimpses as we go.

 

[arivero]

You could say that as a start, but things seem more complex so far. I'd rather note that some forms of energy manifest as matter and other vibrational patterns manifest as energy...says quarks vs photons...

Quarks are Fermions, Photons are bosons. In low energy, not supersymmetric world, probably this is the best way to identify "matter": the elementary fermions of the theory. It has sense from the point of view of classical interpretation, matter "atoms" as a thing occupying some place with exclusivity, while wave "idols" do not claim such exclusivity (The name "idols" appears in Lucretius "De Rerum Nature" to refer to this property). In field theory, we recognize the difference because fermions have a plank constant factor, so that when h goes to zero a fermion field has not existence, while a boson field can stay and appear classically: electromagnetism, for an example (An ancient thinker could have thought that there is some relationship between "idols" and "vacuum" or "extension" in the sense that they can add to fill it. Remember that such thinker would consider "vacuum" as a "no-thing" in duality with the "thing" that atoms are, so the whole scheme becomes more complex).

Problem is, other people calls "matter" to anything with mass, so to anything with energy, both bosons and fermions. It has sense from the point of view of general relativity, where matter is anything you couple via the stress-energy tensor.

Personally I adhere to your view, but it is better to clarify the context. Still, the question about string theory has an affirmative answer in both cases: there are fermions, and there is a stress-energy tensor.

Note also that most of the mass of Nature comes from an elementary boson field with happens to be confined in two non elementary fermions: protons and neutrons, holding the energy of QCD colour force. So if we keep with the first interpretation, the mass of the universe is only "matter" of the "effective theory" of nuclear forces and particles, but not of the "elementary theory" of quarks and colour.