# Q & A: what is singularity

Q:
Can you explain (in simple version please) what singularity is?
- Batuhan (age 17)
Turkey
A:

Mathematically, a singularity is an undefined point (or infinity). For example, a function 1/x is not well defined at x = 0. (it "blows up" to infinity) In this case, x=0 is the singularity for this function.

Similary in physics, a singularity usually refers to a point of infinity, and thus a not-well-defined point. In other words, physics breaks down at a singularity (we cannot describe it with our known physical laws - infinite mass or infinite energy is not something we expect from our nature). When we encounter a singularity, it usually means that we need some other ways to view the problem so that we can get rid of the infinity and get a better view of what is going on (and make sure that physics makes sense!). In other words, singularities lead us to a new theory of physics.

For example, when we study the beginning of Big Bang or the inside of a black hole, we use general relativity. However, both cases have a singularity; our universe started from a single "point", and celestial bodies are attracted by a point inside a black hole - both points involve infinity like 1/x as x->0. Since it is about an infinitesimal distance, physicists try to use quantum mechanics to resolve this singularity issue. Unfortunately, this theory of quantum gravity is an ongoing study that we still do not fully understand.

In conclusion, a singularity is a point which gives us infinity, which means that our known physics is no longer a good tool to view the problem and thus we need to seek a new theory.

SHC.

(published on 01/03/2015)