Naked Science Forum

General Science => General Science => Topic started by: JeanCunniff on 06/07/2017 11:43:55

Title: What are the basics of string theory?
Post by: JeanCunniff on 06/07/2017 11:43:55
Hi! I understand that such complicated things can't be described in a couple of words, but I shouldn't write a term paper about it, so can someone tell me the very basics of this theory? Thanks!
Title: Re: What are the basics of string theory?
Post by: evan_au on 08/07/2017 00:33:46
The idea is that the elementary particles (https://en.wikipedia.org/wiki/Elementary_particle) we know (eg electron, muons, quark, etc) or consider likely (eg graviton) are not truly fundamental, but are vibrations on a tiny string. To produce the variety of particles we see, these strings must vibrate in more than 3 dimensions.

An equivalent of the graviton falls easily out of string theory, and agrees perfectly with Einstein's General Relativity.

Unfortunately, theoreticians have not (yet) managed to produce anything similar to electrons or quarks.

You could start here: https://en.wikipedia.org/wiki/String_theory
Title: Re: What are the basics of string theory?
Post by: jeffreyH on 08/07/2017 11:23:00
If particles are vibrating strings then are anti-particles vibrating out if phase so as to cancel with them? Alternatively they partly cancel, resulting in the vibrations of the decay products. Partial cancelation would explain the asymmetry between matter and anti-matter since the big bang.
Title: Re: What are the basics of string theory?
Post by: puppypower on 08/07/2017 12:45:37
If particles are vibrating strings then are anti-particles vibrating out if phase so as to cancel with them? Alternatively they partly cancel, resulting in the vibrations of the decay products. Partial cancelation would explain the asymmetry between matter and anti-matter since the big bang.

One of the problems with wave and string theories is connected to the destructive interference of vibration/waves. Destructive interference is when two waves, that are out of phase by 180 degrees, interact and cancel. For all practical purposes, there is now nothing left, thereby causing an energy balance problem.

Particle matter cannot interact this way since matter cannot occupy the same space, as can waves. If matter tried to occupy the same space it needs to change, allowing the energy to stay in play. Since string theory has not been able to produce elections and quarks suggests that these two things are better described as particles.

As far a matter and antimatter, another way to interpret the asymmetry of the universe is the assumption that matter is more stable than anti-matter under extreme conditions. This means that matter and anti-matter are not exactly equal and opposite under all conditions.

For example, in beta plus (β+) decay, a proton is converted to a neutron and the process creates a positron and an electron neutrino. This is an example of matter giving off anti-matter, which at one time was part of matter. This suggests that matter, under certain conditions can absorb antimatter and convert it to matter without both having to annihilate.

Beta plus decay usually occurs with larger atoms than hydrogen. Early in the universe, there was mostly hydrogen and some helium. So one may ask where is the large atom sponge for anti-matter, like positrons, before large atoms were formed?

Once answer has to due with hydrogen under extreme density; primordial atom. Consider a neutron star. This is proton deficient and therefore should have the capacity to absorb positrons to form proton matter. The absorption would mean the neutron density would fluff out. Sufficient anti-matter absorption would reverse the neutron density; boom!
Title: Re: What are the basics of string theory?
Post by: dutch on 08/07/2017 14:34:46
Particle matter cannot interact this way since matter cannot occupy the same space, as can waves.

I don't think this is right. Fermions have anti-symmetric wavefunctions that can overlap provided the particles are in different quantum states. For example electrons pair up inside orbitals because there are two options spin up and spin down. Because the states differ they can overlap.

Identical particles are described by the below under exchange:

ψ = ψa(1) ψb(2) ψa(2) ψb(1)

More on identical particles here: https://en.wikipedia.org/wiki/Identical_particles

Fermions use the negative sign and thus cancel if they completely overlap and therefore their wavefunctions can't overlap (Pauli Exclusion Principle). The probability of the particles being somewhere can't disappear. Even if they could the state has a zero probability of getting observed. There is actually a fictitious force-like effect one can work out in Qauntum Mechanics that seems to "push" fermions apart and bosons together (LASERS use this natural tendency of bosons to overlap to create a coherent beam; there simply is a higher probability for bosons to overlap and a lower probability for fermions to overlap).

Fermions overlapping below (probability is 0):

ψ = ψa(1) ψa(2) - ψa(2) ψa(1) = 0

Bosons use the plus sign therefore they can overlap.

ψ = ψa(1) ψa(2) + ψa(2) ψa(1) = 2 ψa(2) ψa(1)

One of the problems with wave and string theories is connected to the destructive interference of vibration/waves. Destructive interference is when two waves, that are out of phase by 180 degrees, interact and cancel. For all practical purposes, there is now nothing left, thereby causing an energy balance problem.

If this a quantum system it isn't true. A quantum system takes the sum of all possible waves. String Theory does incorporate all quantum mechanics now. If quantum mechanics has the Pauli Exclusion Principle then so does String Theory:

Quote
Bosonic string theory was eventually superseded by theories called superstring theories. These theories describe both bosons and fermions, and they incorporate a theoretical idea called supersymmetry. This is a mathematical relation that exists in certain physical theories between the bosons and fermions. In theories with supersymmetry, each boson has a counterpart which is a fermion, and vice versa.

https://en.wikipedia.org/wiki/String_theory

String Theory hasn't fully described quarks yet but they're still working on it.
Title: Re: What are the basics of string theory?
Post by: jeffreyH on 08/07/2017 14:40:01
In beta plus decay the positron would annihilate with a partner electron since the neutron doesn't require it to balance charge so this makes perfect sense.