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String theory facts for kids

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Open and closed strings
The fundamental objects of string theory are open and closed strings.

String theory is a theoretical framework in which the dot-like particles of particle physics are replaced by one-dimensional objects called strings.

Physics has two basic scientific laws: quantum physics and general relativity.

Quantum physics revolves around things that are very small, like electrons and atoms. General relativity is about the universe as a whole and how everything works together.

The theory of quantum gravity could be a way to bring together quantum physics and general relativity, and string theory (or it's sometimes called the Theory of Everything) may be the way the way to make that happen.

Neutron quark structure
A picture of a neutron. The 'u' stands for an up quark, and the 'd' stands for a down quark. A neutron is made of three quarks, and is a baryon (a type of hadron). The colors represent the colour strong force in quantum theory.

To understand string theory you need to know where the scientists think the strings are.

If you cut a table in half, and then cut it into small pieces, then grind it up finely enough, you will be able to see tiny particles of the table under a microscope.

Things get much much smaller inside those particles. First there's molecules, then you'll get to the atoms, then you get to the electrons in the atoms that are spinning around the nucleus, which also has protons and neutrons...and inside them, there's even smaller particles, called quarks!

String theory is the idea that inside these tiny tiny dot like particles, there are little vibrating strings of energy.

Imagine a guitar string vibrating, that is similar to what the scientists think the strings are doing, except they aren't making musical notes when they vibrate. If the string vibrates at a certain frequency, it could create a quark, if it vibrates slightly differently on another frequency it could create an electron or a photon.

String theory tries to tie together the four forces in the universe, electromagnetic force, the strong nuclear force, the weak nuclear force, and gravity. Scientists theorize that the strings from these 4 different forces interact with each other.

D3-brane et D2-brane
Open strings attached to a pair of D-branes

Scientists over the years have also discovered that the theory needs objects other than just strings. Imagine a big sheet with strings attached to the ends. Scientists call these sheets branes.

String theory only makes sense if our world is made up of more than just 3 dimensions. Our 3 dimensionalal world has a front and back, a left and right and an up and down. Scientists say we may live on a 3 dimensional sheet or brane and it might be possible that there are other dimensions that are a attached to that brane that we can't see.

One of the main concepts of string theory is supersymmetry. According to string theory every particle in the universe can be divided into two groups, a boson (which is a force particle like a photon) or a fermion (which is a matter particle like an electron).

In string theory supersymmetry means that if you have a boson, there has to be fermion partner for it somewhere in the universe, and the same for a ferimon, there has to be boson particle partner.

Scientists are still trying to find out whether string theory will solve how quantum physics and gravity fit together.

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